Enter Zoom Meeting

OS1.6

EDI
Changes in the Arctic Ocean, sea ice and subarctic seas systems: Observations, Models and Perspectives

The rapid decline of the Arctic sea ice in the last decade is a dramatic indicator of climate change. The Arctic sea ice cover is now thinner, weaker and drifts faster. Freak heatwaves are common. On land, the permafrost is dramatically thawing, glaciers are disappearing, and forest fires are raging. The ocean is also changing: the volume of freshwater stored in the Arctic has increased as have the inputs of coastal runoff from Siberia and Greenland and the exchanges with the Atlantic and Pacific Oceans. As the global surface temperature rises, the Arctic Ocean is speculated to become seasonally ice-free by the mid 21st century, which prompts us to revisit our perceptions of the Arctic system as a whole. What could the Arctic Ocean look like in the future? How are the present changes in the Arctic going to affect and be affected by the lower latitudes? What aspects of the changing Arctic should observational, remote sensing and modelling programmes address in priority?

In this session, we invite contributions from a variety of studies on the recent past, present and future Arctic. We encourage submissions examining interactions between the ocean, atmosphere and sea ice, on emerging mechanisms and feedbacks in the Arctic and on how the Arctic influences the global ocean. Submissions taking a cross-disciplinary, system approach and focussing on emerging cryospheric, oceanic and biogeochemical processes and their links with land are particularly welcome.

The session supports the actions of the United Nations Decade of Ocean Science for Sustainable Development (2021-2030) towards addressing challenges for sustainable development in the Arctic and its diverse regions. We aim to promote discussions on the future plans for Arctic Ocean modelling and measurement strategies, and encourages submissions on the results from IPCC CMIP and the recent observational programs, such as the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC). This session is cosponsored by the CLIVAR /CliC Northern Ocean Regional Panel (NORP) that aims to facilitate progress and identify scientific opportunities in (sub)Arctic ocean-sea-ice-atmosphere research.

Drs Karen Assmann and Wilken-Jon von Appen are the solicited speakers for the session. Karen Assmann will be presenting on physical and ecological implications of Arctic Atlantification. Wilken-Jon von Appen will be talking about eddies in the Arctic Ocean.

Co-organized by AS2/BG4/CL4/CR6, co-sponsored by NORP and C
Convener: Yevgeny Aksenov | Co-conveners: Céline Heuzé, Paul A. Dodd, Krissy Reeve, Yufang Ye
Presentations
| Wed, 25 May, 13:20–18:30 (CEST)
 
Room E2, Thu, 26 May, 08:30–10:00 (CEST)
 
Room E2

Wed, 25 May, 13:20–14:50

Chairpersons: Yevgeny Aksenov, Yufang Ye

13:20–13:25
OS1.6 Changes in the Arctic Ocean, sea ice and subarctic seas systems: Observations, Models and Perspectives Day 1. Session Introduction

13:25–13:35
|
EGU22-6930
|
solicited
|
On-site presentation
Karen M. Assmann et al.

The Atlantic gateway to the Arctic Ocean is influenced by vigorous inflows of Atlantic Water. Particularly since 2000, the high-latitude impacts of these inflows have strengthened due to climate change driving so-called ‘Atlantification’ - a transition of Arctic waters to a state more closely resembling that of the Atlantic. In this review, we discuss the physical and ecological manifestations of Atlantification in a hotspot region of climate change reaching from the southern Barents Sea to the Eurasian Basin. Atlantification is driven by anomalous Atlantic Water inflows and modulated by local processes. These include reduced atmospheric cooling, which amplifies warming in the southern Barents Sea; reduced freshwater input and stronger influence

of ice import in the northern Barents Sea; and enhanced upper ocean mixing and air–ice–ocean coupling in the Eurasian Basin. Ecosystem responses to Atlantification encompass increased production, northward expansion of boreal species (borealization), an increased importance of the pelagic compartment populated by new species, an increasingly connected food web and a gradual reduction of the ice-associated ecosystem compartment.

How to cite: Assmann, K. M., Ingvaldsen, R. B., Primicerio, R., Fossheim, M., Polyakov, I. V., and Dolgov, A. V.: Physical manifestations and ecological implications of Arctic Atlantification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6930, https://doi.org/10.5194/egusphere-egu22-6930, 2022.

13:35–13:40
|
EGU22-5807
|
ECS
|
On-site presentation
Stefanie Rynders and Yevgeny Aksenov

Arctic coastal erosion is an environmental hazard expected to increase under climate change, due to decreasing sea ice protection along with increasing wave heights. In addition to the impact on land, this affects the marine environment, as coastal erosion is a source of organic matter, carbon and nutrients for the coastal waters and shelf seas in the Arctic. Following Barnhart et al., we adapted the White model for iceberg melt to calculate pan-coastal erosion rates. The approach combines ice, ocean and wave model output with permafrost model output and geological characteristics from observations. The calculated erosion rates show large spatial variability, similar to observations, as well as a large seasonal cycle. Additionally, it brings to light the increasing trend between the 1980s and 2010s, with a lengthening of the erosion season, plus inter-annual variability. Using observed nutrient ratios, the erosion rates are converted to biogeochemical sources, which can be used for marine ecosystem models. The approach could be used on-line in earth system models, providing both projections of future erosion rates as well as improved biogeochemistry projections. We acknowledge financial support from Advective Pathways of nutrients and key Ecological substances in the Arctic (APEAR) project (NE/R012865/1, NE/R012865/2, #03V01461), as part of the Changing Arctic Ocean programme, jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF), and from the European Union’s Horizon 2020 research and innovation programme under project COMFORT (grant agreement no. 820989), for which the work reflects only the authors’ view; the European Commission and their executive agency are not responsible for any use that may be made of the information the work contains.

How to cite: Rynders, S. and Aksenov, Y.: A multidecadal model estimate of pan-Arctic coastal erosion rates and associated nutrient fluxes, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5807, https://doi.org/10.5194/egusphere-egu22-5807, 2022.

13:40–13:45
|
EGU22-6421
|
On-site presentation
Torsten Kanzow et al.

In wintertime, the Arctic Ocean mixed layer (ML) regulates the transport of oceanic heat to the sea ice, and transfers both momentum and salt between the ice and the stratified ocean below. Between October, 2019, and May, 2020, we recorded time series of wintertime ML-relevant properties at unprecedented resolution during the MOSAIC expedition. Vertical and horizontal salt and temperature gradients, vertical profiles of horizontal velocity, turbulent dissipation of kinetic energy, growth of both level and lead ice, and ice deformation were obtained from both the Central Observatory and the Distributed Network around it.  

We find that the ML deepened from 20 m at the onset of the MOSAIC drift to 120 m at the end of the winter. The ML salinity showed a decrease between early November 2019 and mid-January 2020 followed by a pronounced increase during February and March 2020 - marking the coldest period of the observations. Applying the equation of salt conservation to the ML as a guiding framework, we combine the abovementioned observations, to intercompare the temporal evolutions of the different processes affecting salinity. Overall, brine rejection associated with thermodynamic ice growth turns out to be the largest salt flux term in the ML salt budget. Thereby the observed amplitudes of upward ocean heat fluxes into the mixed layer are too small for them to have a relevant impact on limiting ice growth. Horizontal salt advection in the ML is the second-most important flux term, actually representing a net sink of salt, thus counteracting brine release. It displays considerably larger temporal variability than brine release, though, due to the variable of ocean currents and horizontal salt gradients. Vertical ocean salt fluxes across the mixed layer base represent the third-most important salt flux term, showing particularly elevated values during storm events, when small-scale turbulence in the ML is triggered by the winds. The results presented will be interpreted in the context of the changes in the regional and temporal ocean, atmosphere and sea ice properties encountered during the MOSAIC drift.

How to cite: Kanzow, T., Rabe, B., Schaffer, J., Kuznetsov, I., Hoppmann, M., Tippenhauer, S., Li, T., Mohrholz, V., Janout, M., von Albedyll, L., Stanton, T., Kaleschke, L., Haas, C., Schulz, K., and Lei, R.: Evolution of the wintertime salt budget of the Arctic Ocean mixed layer observed during MOSAIC, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6421, https://doi.org/10.5194/egusphere-egu22-6421, 2022.

13:45–13:50
|
EGU22-7240
|
ECS
|
|
On-site presentation
Elena Bianco et al.

The Arctic Ocean is transitioning from permanently ice-covered to seasonally ice-free, with thinner and more dynamic sea ice. This strengthens the coupling with the atmosphere and the ocean, which exert a strong influence on sea ice via thermodynamic and dynamic forcing mechanisms. Short-term predictions are met with the challenge of disentangling the preconditioning processes that regulate sea ice variability, as these often trigger a response that is not uniform in time nor in space.  This study assesses the role of ocean heat content (OHC) as a driver of sea ice variability for five different regions of the Arctic Ocean. We choose to focus on a sub-seasonal time frame, with the goal of investigating whether anomalies in ocean heat content offer a source of predictability for sea ice in the following months and whether this coupling varies across different regions and seasons. To account for the different processes that regulate the Arctic Ocean heat budget, we consider ocean heat content in the mixed layer (OHCML) and in the upper 300 m (OHC300), computed from the CMCC Global Ocean Reanalysis C-GLORSv5 for the period 1979-2017. Time-lagged correlations of linearly detrended anomalies suggest a link between heat content and sea ice variability in the following months. This source of predictability is stronger during the melt season and peaks in autumn, with highest correlations in the Kara and Chukchi regions. Consistent with previous studies, a distinctive response is observed for the Barents Sea, where sea ice is more strongly coupled with the ocean during the freezing season.  Our preliminary results support a central role of OHC as a driver of sea ice thermodynamic changes at sub-seasonal scales, a mechanism that is likely to become stronger under ice-depleted conditions.   

How to cite: Bianco, E., Iovino, D., Materia, S., Ruggieri, P., and Masina, S.: Arctic Ocean Heat Content as a Driver of Regional Sea Ice Variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7240, https://doi.org/10.5194/egusphere-egu22-7240, 2022.

13:50–13:55
|
EGU22-7793
|
ECS
|
|
On-site presentation
Wiebke Körtke et al.

The Arctic is warming stronger and faster than other regions during the climate change. Within this development, the Arctic Ocean’s water masses and ventilation processes are changing as well. Transient anthropogenic tracers can be used to track water masses and to investigate ventilation and mixing processes. For these tracers, e.g. chlorofluorocarbons (CFCs), the atmosphere is the only source to the ocean and they are conservative in the water. In this study, we analyse CFC-12 (CCl2F2) along two transects in the Canadian basin of the central Arctic Ocean covered in different decades (T1: 1994 and 2015, T2: 2005 and 2015), with additional hydrographic data for context. We find differences in both the tracer concentration and the hydrographic properties between the years and transects. Along the first transect (located at ~180°W), the difference in saturation between 2015 and 1994 is largest in the layer of the Atlantic Water at high latitudes (> 82°N). A similar strong increase in CFC-12 saturation is observed along the second transect (located at 150°W). In contrast to the saturation increase in the Atlantic Water layer, we find a decrease close to the surface, which is correlated to oversaturations in 2005 in this region. At the same time, the surface waters were more saline in 2005 indicating a mixing event. Oversaturation is present in all years, except in 1994. Existence of oversaturation can be caused by special events, either inside the ocean (by mixing processes) or at the sea ice-ocean-atmosphere interface (by the occurrence of changes in the sea ice concentration or atmospheric forcing). We compare the tracer results with hydrographic properties, as well as with wind and ice conditions present during the time of measurements, to investigate the causes of the observed changes. Further, the time dependent atmospheric concentrations of CFCs are used to determine the age of water masses. Here, we use the simplest possible approach of age determination to identify the age of the Atlantic Water along the transects, assuming no interaction or exchange with the surrounding water masses after the Atlantic Water left the surface in Fram Strait. Due to the decreasing CFC-12 atmospheric concentration after 2003/04, it is necessary to use sulfur hexafluoride (SF6) as an additional tracer for 2015. Along the first transect, the tracer age of CFC-12 for 1994 is compared to the tracer age of SF6 in 2015. In 2015 the tracer age is much higher in the region south of 80°N compared to 1994, while the ages are quite similar at higher latitudes. The higher age in the southern part of the transect indicates a water mass, that is much older in 2015 than it was in 1994, a sign of a possible circulation change. A similar result is found along the second transect, where the new tracer SF6 is available in both years. Along this transect, the water is also older in 2015 than in 2005.

How to cite: Körtke, W., Walter, M., Huhn, O., and Rhein, M.: Decadal variability in the transient tracer distribution in the upper Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7793, https://doi.org/10.5194/egusphere-egu22-7793, 2022.

13:55–14:00
|
EGU22-8234
|
Virtual presentation
Tristan Cordier et al.

Sea ice has a pivotal role in the regulation of the Arctic climate system, and by extension to the global climate. Our knowledge of its historical variation and extent is limited to the satellite records that only cover the last several decades, which considerably hampers our understanding on how past climate has influenced sea ice extent in the Arctic. Latest modelling efforts indicate that the Arctic may be sea ice free in summer by 2050, making the appreciation of the effects that such major change will have on Arctic ecosystems of paramount importance. Here, we will present the first results of the AGENSI project (www.agensi.eu) aiming at reconstructing the past sea ice evolution with sedimentary ancient DNA. Based on a large collection of surface sediments collected along multiple gradients of sea ice cover in the Arctic, we show that plankton DNA sinking to the seafloor can be used to predict the variation of surface sea ice cover. Further, we will present our current efforts to utilize this dataset to reconstruct the past sea ice variation in Late Quaternary sediment cores.

How to cite: Cordier, T., Grant, D. M., Steinsland, K., Häkli, K., Blindheim, D. I., Weiner, A., Larsen, A., Hestetun, J. T., Ray, J. L., and De Schepper, S.: Towards Late Quaternary sea ice reconstructions in the Arctic with sedimentary ancient DNA. , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8234, https://doi.org/10.5194/egusphere-egu22-8234, 2022.

14:00–14:15
Q&A and Discussion 1 "Pan-Arctic Processes"

14:15–14:20
|
EGU22-9899
|
ECS
|
Highlight
|
On-site presentation
Cécilia Bertosio et al.

The Makarov Basin halocline receives contributions from diverse water masses of Atlantic, Pacific, and East Siberian Sea origin. Changes in surface circulation (e.g., in the Transpolar Drift and Beaufort Gyre) have been documented since the 2000s, while the upper ocean column in the Makarov Basin has received little attention. The evolution of the upper and lower halocline in the Makarov Basin and along the East Siberian Sea slope was examined combining drifting platforms observations, shipborne hydrographic data, and modelled fields from a global operational physical model.

In 2015, the upper halocline in the Makarov Basin was warmer, fresher, and thicker compared to 2008 and 2017, likely resulting from the particularly westward extension of the Beaufort Gyre that year. From 2012-onwards, cold Atlantic-derived lower halocline waters, previously restricted to the Lomonosov Ridge area, progressed eastward along the East Siberian slope, with a sharp shift from 155 to 170°E above the 1000 m isobath in winter 2011-2012, followed by a progressive eastward motion after winter 2015-2016 and reached the western Chukchi Sea in 2017. In parallel, an active mixing between upwelled Atlantic water and shelf water along the slope, formed dense warm water which also supplied the Makarov Basin lower halocline.

The progressive weakening of the halocline, together with shallower Atlantic Waters, is emblematic of a new Arctic Ocean regime that started in the early 2000s in the Eurasian Basin. Our results suggest that this new Arctic regime now may extend toward the Amerasian Basin.



How to cite: Bertosio, C., Provost, C., Athanase, M., Sennéchael, N., Garric, G., Lellouche, J.-M., Kim, J.-H., Cho, K.-H., and Park, T.: Changes in Arctic Halocline Waters along the East Siberian Slope and in the Makarov Basin from 2007 to 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9899, https://doi.org/10.5194/egusphere-egu22-9899, 2022.

14:20–14:25
|
EGU22-11202
|
ECS
|
Virtual presentation
Myriel Vredenborg et al.

The Arctic Ocean is characterized by complex processes coupling the atmosphere, cryosphere, ocean and land and undergoes remarkable environmental changes due to global warming. To better understand this system of unique physical, biogeochemical and ecosystem processes and their recent changes, the year-round ice drift experiment Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) was conducted from autumn 2019 to autumn 2020.

In this study we analyse temperature and salinity measurements of the upper Arctic Ocean taken during MOSAiC with different devices, i.e. on an ice-tethered profiler, a microstructure profiler and water sampler rosettes operated from the ship as well as through an ice hole on the ice floe. Combining all these measurements provides us an exceptional data resolution along the MOSAiC track. Moreover, we compare these observations with a comprehensive dataset of historical hydrographic data from the region.

Along the MOSAiC track we find signatures of a convective lower halocline (Fram Strait branch), as well as advective-convective lower halocline (Barents Sea branch). We see pronounced changes in the salinity and temperature of the lower halocline in comparison to the historical data, in particular, at the beginning of the drift. Furthermore, we show polar mixed-layer and upper halocline conditions in relation to seasonality and local surface conditions. We put the warm Atlantic Water temperature in the context of historical observations and investigate indications for the presence of Pacific Water.

How to cite: Vredenborg, M., Rabe, B., Tippenhauer, S., and Schulz, K. and the Team MOSAiC OCEAN: Upper Arctic Ocean hydrography during the year-round MOSAiC expedition in the context of historical observations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11202, https://doi.org/10.5194/egusphere-egu22-11202, 2022.

14:25–14:30
|
EGU22-11518
|
ECS
|
On-site presentation
Evgenii Salganik et al.

During the melt season, sea ice melts from the surface and bottom. The melt rates substantially vary for sea ice ridges and undeformed first- and second-year ice. Ridges generally melt faster than undeformed ice, while the melt of ridge keels is often accompanied by further summer growth of their consolidated layer. This summer consolidation is related to refreezing of less saline meltwater, originating from snowmelt and ridge keel melt. We examine the spatial variability of ice melt for different types of ice from in situ drilling, coring, and from multibeam sonar scans of remotely operated underwater vehicle (ROV). Seven ROV scans, performed from 24 June 2020 to 28 July 2020 during the Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) expedition were analyzed. The area investigated by the ROV (400 by 200 m) consisted of several ice ridges, surrounded by first- and second-year ice. Seven ice drilling transects were additionally performed to validate ROV measurements. The maximum keel depth of the ridge investigated by ice drilling was 6.5 m. We show a substantial difference in melt rates of first-year ice, second-year ice, and sea ice ridge keels. We also show how ridge keels decay depending on keel depth, width, steepness, and orientation relative to the ice drift direction. These results are important for quantifying ocean heat fluxes for different types of ice during advanced melt, and for estimation of the ridge contribution to the total ice mass and summer meltwater balances of the Arctic Ocean.

How to cite: Salganik, E., Lange, B., Katlein, C., Matero, I., Regnery, J., Sheikin, I., Anhaus, P., Høyland, K., and Granskog, M.: Differential summer melt rates of ridges, first- and second-year ice in the central Arctic Ocean during the MOSAiC expedition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11518, https://doi.org/10.5194/egusphere-egu22-11518, 2022.

14:30–14:35
|
EGU22-13087
|
Virtual presentation
Anna Timofeeva

In September-October 2021 during NABOS-2021 expedition specialized shipborne ice observations were carried following methodological principles developed in AARI. The overall research area for the cruise included Arctic basin area toward north of Laptev and East Siberian seas within 73-82°N 125°E-170°W. Ice conditions were generalized and analyzed along the oceanographic cross-sections in accordance with the ice conditions homogeneousness. Hard ice conditions were unforeseen during the planning period, which made adjustments to the initial expedition plans and several minor northern cross-sections were canceled.

The route fragment with the hardest ice conditions was observed within 78-82°N 160°-172°E. Sea ice concentration was 10 tenths totally, concentration of residual ice varied from 5-7 to 10 tenths directly on the route of the vesse. Prevailing forms of the sea ice were big (500m-2000m) and often vast (2000-10000m) floes with strongly smoothed hummock formations covered with snow 10-15 cm high. The thickness of the residual ice on the route was mainly 50-70 cm (17%), often over 100 cm (6%), in hummocks over 2-3 meters. The water area between the ice fields was captured by young ice, grey and grey-white (3-4 up to 9 tenths).

Several areas were crossed by vessel twice in a time difference of one month. Sea ice formation process during the month long was fixed and analyzed by changes in distribution of ice with different stages of development. In general, 66% of the ship track within the ice during expedition had sea ice concentration of 10 tenths, the residual ice on the route accounted for 26%, young ice was observed for 38%, nilas and new ice 36%.The residual ice thickness varied from 30-50 cm to 160 cm and above, in some cases (hummock formations) over 300 cm. Ice thickness of 30-50 and 50-70 cm accounts for 9% each, thicknesses over 70 cm account for 8% of all thickness ranges observed throughout the entire route of the vessel in the ice.

Key words: shipborne observations, ice conditions of navigation, ice thickness, ice concentration, stage of development of ice.

How to cite: Timofeeva, A.: Navigation in the ice conditions in Arctic basin in September-October 2021 , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13087, https://doi.org/10.5194/egusphere-egu22-13087, 2022.

14:35–14:40
|
EGU22-12793
|
ECS
|
On-site presentation
Seasonal and regional analysis of Arctic sea-ice evolution
(withdrawn)
Markus Ritschel and Dirk Notz

14:40–14:50
Q&A and Discussion 2 "Pan-Arctic Processes"

Wed, 25 May, 15:10–16:40

Chairpersons: Krissy Reeve, Céline Heuzé

15:10–15:15
|
EGU22-60
|
ECS
|
|
Virtual presentation
Aleksandr Konik and Aleksey Zimin

One of the most important phenomena in the Arctic seas, in which all cascades of the scale of variability of oceanological processes are observed, are climatic and seasonal frontal zones. However, despite the climate changes noted by many researchers, so far, the ideas about the long-term dynamics and characteristics of the surface layer in the frontal zones in the Arctic region are fragmentary.

In our work, we considered seasonal and long-term variability of the Polar Frontal Zone (PFZ), the River Plumes Frontal Zone (RPFZ) and the Marginal Ice Zone (MIZ) in the Barents and Kara Seas. The authors evaluated their relationship with eddies structures and atmospheric oscillations. We used satellite data of temperature, salinity and sea level for the period from 2002 to 2020, which we processed using cluster analysis. To isolate the manifestations of eddies structures on the surface, we used radar images of the Envisat ASAR and Sentinel-1A/B. To analyze the relationship between the characteristics of the frontal zones and atmospheric oscillations, we used correlation analysis.

We have shown that the intensity of interannual and seasonal estimates of the SST gradient and the area of the PFZ and RPFZ in the first decade was an order of magnitude higher than in the period from 2011 to 2020. We observe the opposite pattern for the characteristics of the MIZ – in the second decade, the magnitude of the estimates of the SST gradient and area increases. We observe the maximum number of eddies structures in PFZ and RPFZ against the background of a general weakening of the SST gradients. We assume that this is due to the development of intense baroclinic instability in the frontal zones. In our opinion, the intensity of winter meridional transport over Northern Europe affects the growth of summer SST gradients and a decrease in the area of the PFZ and a decrease in SST in the RPFZ. The magnitude of the winter Arctic zonal transfer may increase the characteristics of SST in the RPFZ region. The value of the average seasonal gradient of the SST of the climatic surface PFZ is lower than that of the seasonal RPFZ and MIZ.

The analysis of frontal zone and eddies in this work was supported by RFBR grant 20-35-90053.

How to cite: Konik, A. and Zimin, A.: Seasonal and long-term variability of the characteristics surface frontal zones of the Barents and Kara seas, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-60, https://doi.org/10.5194/egusphere-egu22-60, 2022.

15:15–15:20
|
EGU22-1715
|
On-site presentation
Carlotta Dentico et al.

The interaction between North Atlantic and Arctic Ocean waters plays a key role in climate variability and in
driving the global thermohaline circulation. In the past decades, an increased heat input to the Arctic has
occurred which is considered of high climatic relevance as, e.g., it contributes to enhancing sea ice melting.
In this frame, the progressive northward extension of the Atlantic signal within the Arctic domain known as
Arctic Atlantification is one of the most dramatic environmental local changes of the last decades.
In this study we used in situ data and the Copernicus Marine Environment Monitoring Service (CMEMS)
reanalysis dataset to explore spatial and temporal variability of water masses on different time-scales and
depths in the eastern Fram Strait. In that area, warm and salty Atlantic Water (AW) enters the Arctic Ocean
through the West Spitsbergen Current (WSC). Time series of potential temperature, salinity and potential
density obtained from CMEMS reanalysis in the surface, upper-intermediate and deep layers referring to the
period 1991-2019 have been considered. High-frequency observations gathered from an oceanographic
mooring maintained by the National Institute of Oceanography and Applied Geophysics (OGS) in
collaboration with the Italian National Research Council - Institute of Polar Science (CNR-ISP) have been
used to assess the reliability of CMEMS data in reproducing ocean dynamics in the deep layer (ca 900-1000
m depth) of the SW offshore Svalbard area. The mooring system has been collecting data since June 2014.
In this contribution, we will show how the CMEMS data compared with in situ measurements as far as
seasonal and interannual variations as well as long-term trends are concerned. We will also discuss how
CMEMS reanalyses show differences in resolving ocean dynamics at different depths. Particularly, the severe
limitations in reproducing thermohaline variability at depths greater than 700 m. Finally, we will illustrate how
our results highlight strengths and limitations of CMEMS reanalyses, underscoring the importance of
optimizing measurements in a strategic area for studying climate change impacts in the Arctic and sub-Arctic
regions.

How to cite: Dentico, C., Bensi, M., Kovačević, V., Zanchettin, D., and Rubino, A.: Water masses variability in the eastern Fram Strait explored through oceanographic mooring data and the CMEMS dataset, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1715, https://doi.org/10.5194/egusphere-egu22-1715, 2022.

15:20–15:25
|
EGU22-2426
|
ECS
|
|
Virtual presentation
Bernardo Costa et al.

The average rate of coastal change in the Arctic Ocean is -0.5 m/yr, despite significant local and regional variations, with large areas well above -3 m/yr. Recent data suggest an acceleration of coastal retreat in specific areas due to an increasingly shorter sea ice season, higher storminess, warmer ocean waters and sea-level rise. Moreover, climate warming is inducing the subaerial degradation of permafrost and increasing land to sea sediment transportation. This work consists of the characterization and analysis of the main controlling factors influencing recent coastline change in the Tuktoyaktuk Peninsula, Northwest Territories, Canada. The specific objectives are I. mapping Tuktoyaktuk Peninsula’s coastline at different time-steps using remote sensing imagery, II. quantifying the recent coastal change rates, III., characterizing the coastal morphology, IV. identifying the main controlling factors of the coastal change rates. A very high-resolution Pleiades survey from 2020, aerial photos from 1985 and the ArcticDEM were used. Results have shown an average coastline change rate of -1.06 m/yr between 1985 and 2020. While this number is higher than the Arctic average rate, it neglects to show the significance of extreme cases occurring in specific areas. Tundra cliffs are the main coastal setting, occupying c. 56% of the Tuktoyaktuk Peninsula coast and foreshore beaches represent 51%. The results display an influence of coastal geomorphology on change rates. The coastal retreat was higher in backshore tundra flats (-1.74 m/yr), whereas more aggradation cases exist in barrier beaches and sandspits (-0.81 m/yr). The presence of ice-wedge polygons contributes to increasing cliff retreat. Foreshore assessment may be crucial, as beaches present a hindering impact on coastal retreat (-0.76 m/yr), whereas foreshore tundra flats promote it (-1.74 m/yr). There are 48 areas with retreat rates higher than -4 m/yr, most being submersion cases.

How to cite: Costa, B., Vieira, G., and Whalen, D.: The fast-changing coast of Tuktoyaktuk Peninsula (Beaufort Sea, Canada): geomorphological controls on changes between 1985 and 2020, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2426, https://doi.org/10.5194/egusphere-egu22-2426, 2022.

15:25–15:30
|
EGU22-2717
|
ECS
|
|
Virtual presentation
Zerlina Hofmann et al.

The marginal ice zone in Fram Strait is a highly variable environment, in which dense Atlantic Water and lighter Polar Water meet and create numerous mesoscale and submesoscale fronts. This makes it a model region for researching ocean frontal dynamics in the Arctic, as the interaction between Atlantic Water and the marginal ice zone is becoming increasingly important in an "atlantifying" Arctic Ocean. Here we present the first results of a front study conducted near the ice edge in central Fram Strait, where Atlantic Water subducted below Polar Water. We posit that the frontal dynamics associated with the sea ice edge also apply beyond, both to the open and the ice-covered ocean in the vicinity. They, in turn, can affect the structure of the marginal ice zone. The study comprises a total of 54 high resolution transects, most of which were oriented across the front. They were taken over the course of a week during July 2020 and include current velocity measurements from a vessel-mounted ADCP. Most of the transects also include either temperature and salinity measurements from an underway CTD, or temperature and salinity measurements and various biogeochemical properties from a TRIAXUS towed vehicle. Additionally, 22 CTD stations were conducted, and 31 surface drifters were deployed. This wealth of measurements gives us the opportunity to follow the temporal and spatial development of the density fronts present at the time. We discuss the dynamics of the frontal development, including the associated geostrophic motion, and the induced secondary ageostrophic circulation with subsequent subduction of Atlantic Water and biological material in a highly stratified region. Beneath the stratified upper ocean, subduction is clearly visible in the biogeochemical properties, and water samples indicate a substantial vertical transport of smaller particles. Surface drifters accumulated in locations of subduction, where sea ice, if present, would likely also accumulate. Our study thus demonstrates the importance of frontal dynamics for the vertical transport of water properties and biological material, and the highly variable development of the marginal ice zone in Fram Strait.

How to cite: Hofmann, Z., von Appen, W.-J., Iversen, M., and Hufnagel, L.: Subduction as Observed at a Submesoscale Front in the Marginal Ice Zone in Fram Strait, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2717, https://doi.org/10.5194/egusphere-egu22-2717, 2022.

15:30–15:35
|
EGU22-3069
|
ECS
|
Virtual presentation
Zoé Koenig et al.

The Atlantic Water inflow to the Arctic Ocean is transformed and modified in the ocean areas north of Svalbard, and influences the Arctic Ocean heat and salt budget. As the Atlantic Water layer advances into the Arctic, its core deepens from about 250 m depth around the Yermak Plateau to 350 m in the Laptev Sea, and gets colder and less saline due to mixing with surrounding waters. The complex topography in the region facilitates vertical and horizontal exchanges between the water masses and, together with strong shear and tidal forcing driving increased mixing rates, impacts the heat and salt content of the Atlantic Water layer that will circulate around the Arctic Ocean.

In September 2018, 6 moorings organized in 2 arrays were deployed across the Atlantic Water Boundary current for more than one year (until November 2019), within the framework of the Nansen Legacy project to investigate the seasonal variations of this current and the transformation of the Atlantic Water North of Svalbard. The Atlantic Water inflow exhibits a large seasonal signal, with maxima in core temperature and along-isobath velocities in fall and minima in spring. Volume transport of the Atlantic Water inflow varies from 0.7 Sv in spring to 3 Sv in fall. An empirical orthogonal function analysis of the daily cross-isobath temperature sections reveals that the first mode of variation (explained variance ~80%) is the seasonal cycle with an on/off mode in the temperature core. This first mode of variation is linked to the first mode of variation of the current. The second mode (explained variance ~ 15%) corresponds to a shorter time scale (6-7 days) variability in the onshore/offshore displacement of the temperature core linked to the mesoscale variability. On the shelf, a counter-current flowing westward is observed in spring, which transports colder (~ 1°C) and fresher (~ 34.85 g kg-1) water than Atlantic Water (θ > 2°C and SA > 34.9 g kg-1). This counter-current is driven by Ekman dynamics. At greater depth (~1000 m) on the offshore part of the slope, a bottom-intensified current is detected, partly correlated with the wind stress curl. Heat loss of the Atlantic Water between the two mooring arrays is maximum in winter, estimated to 300-400 W m-2 when the current speed and the heat loss to the atmosphere are the largest.

 

How to cite: Koenig, Z., Kalhagen, K., Kolås, E., Fer, I., Nilsen, F., and Cottier, F.: Atlantic Water properties, transport, and water mass transformation from mooring observations north of Svalbard , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3069, https://doi.org/10.5194/egusphere-egu22-3069, 2022.

15:35–15:40
|
EGU22-6176
|
Virtual presentation
Anna Przyborska et al.

Climate change is affecting all the Svalbard fjords, which are more or less subject to global warming.  In situ observations in the Hornsund fjord indicate that more and more warm Atlantic water is reaching the fjord as well, and this may influence the rate of melting of sea ice and glaciers, which is likely to increase.  

More freshwater enters the fjord in several different ways. Melting glaciers bring freshwater in the form of surface inflows from freshwater sources, in the form of submarine meltwater at the interface between ocean and ice, and in the form of calving icebergs.  Retreating glaciers and melting sea ice allow the warm Atlantic waters to reach increasingly inland fjord basins and more heat stored in the fjords causes increased melting of the inner fjord glaciers.  The increasing amounts of freshwater in the fjord can change the local ecosystem.

Estimates of the heat and the salt fluxes will give a better understanding of how the ocean interacts with the glaciers through submarine melting and vice versa, how glaciers interact with the ocean through freshwater supply.  Budgetary conditions will be calculated from the high resolution model results (HRM) of velocity, temperature and salinity for the interior of the Hornsund fjord.

Calculations were carried out at the Academic Computer Centre in Gdańsk

How to cite: Przyborska, A., Strzelewicz, A., Muzyka, M., and Jakacki, J.: Heat and salt budgets in the Hornsund fjord, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6176, https://doi.org/10.5194/egusphere-egu22-6176, 2022.

15:40–15:55
Q&A and Discussion 1 "Regional Studies"

15:55–16:00
|
EGU22-6934
|
ECS
|
|
On-site presentation
Eivind Hugaas Kolås et al.

The Barents Sea is one of the main pathways by which Atlantic Water (AW) enters the Arctic Ocean and is an important region for key water mass transformation and production. As AW enters the shallow (< 400 m) Barents Sea, it propagates as a topographically steered current along a series of shallow troughs and ridges, while being transformed through atmospheric heat fluxes and exchanges with surrounding water masses. To the north, the warm and salty AW is separated from the cold and fresh Polar Water (PW) by a distinct dynamic thermohaline front (the Barents Sea Polar Front), often less than 15 km in width.

Two cruises were conducted in October 2020 and February 2021 within the Nansen Legacy project, focusing on the AW pathways and ocean mixing processes in the Barents Sea. Here we present data from CTD (Conductivity, Temperature, Depth), ADCP (Acoustic Doppler Current Profiler) and microstructure sensors obtained during seven ship transects and two repeated stations across and on top of a 200 m deep sill (77°18’N, 30°E) at the location of the Polar Front between AW and PW. The ship transects are complemented by five underwater glider missions, two equipped with microstructure sensors. On the sill, we observe warm (>2°C) and salty (>34.8) AW intruding below the colder (<0°C) and fresher (34.4) PW setting up a geostrophic balance where currents exceed 20 cm/s. We observe anomalous warm and cold-water patches on the cold and warm side of the front, respectively, collocated with enhanced turbulence, where dissipation rates range between 10-8 and 10-7 W/kg. In addition, tidal currents on the sill reach 15 cm/s. The variable currents affect the front structure differently in the vertical. While the mid-depth location of the front is shifted by several kilometers, the location of the front near the bottom remains stationary.  The frontal dynamics on the sill result in transformation and mixing of AW, manifested in the troughs north of the sill as modified AW.

How to cite: Hugaas Kolås, E., Baumann, T., Fer, I., and Koenig, Z.: Barents Sea Polar Front dynamics during fall and winter 2020-2021, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6934, https://doi.org/10.5194/egusphere-egu22-6934, 2022.

16:00–16:05
|
EGU22-8055
|
Virtual presentation
Ilker Fer and Algot K. Peterson

One of the major branches of the warm and saline Atlantic Water supply is the current along the west coast of Spitsbergen in Fram Strait. The Yermak Plateau is a topographic obstacle in the path of this current. The diverging isobaths of the Plateau split the current, with an outer branch following the 1000-1500 m isobaths along the rim of the Yermak Plateau (the Yermak branch). Observation based estimates of the volume transport, structure and variability of the Yermak branch are scarce.

Here we present observations from an array of three moorings on the southern flank of the Yermak Plateau, covering the AW boundary current along the slope, between the 800 m to 1600 m isobaths over 40 km distance, from 11 September 2014 to 13 August 2015. The aim is to estimate the volume transport in temperature classes to quantify the contribution of the Yermak branch, to document the observed mesoscale variability, and identify the role of barotropic and baroclinic instabilities on the variability.

All three moorings show depth- and time-averaged currents directed along isobaths, with the middle mooring in the core of the boundary current. Depth-averaged current speeds in the core, averaged over monthly time scale, reach 20 cm s-1 in March. Temperatures are always greater than 0°C in the upper 800 m, or than 2°C in the upper 500 m. Seasonal averaged volume transport estimates of Atlantic Water defined as temperature above 2°C, are maximum in autumn (1.4 ± 0.2 Sv) and decrease to 0.8 ± 0.1 Sv in summer. The annual average AW transport is 1.1 ± 0.2 Sv, below which there is bottom-intensified current, particularly strong in winter, leading to a substantial transport of cold water (<0°C) with an annual average of 1.1 ± 0.2 Sv.

Mesoscale variability and energy conversion rates are estimated using fluctuations of velocity and stratification in the 35 h to 14-days band and averaging over a monthly time scale.  Time-averaged profiles of horizontal kinetic energy (HKE) show a near-surface maximum in the outer and middle (core) moorings decreasing to negligible values below 700 m depth. HKE averaged between 100-500 m depth increases from about 3×10-3 m2 s-2 in fall to (6-9)×10-3 m2 s-2 in winter and early spring.  Temperature and cross-isobath velocity covariances show substantial mid-depth temperature fluxes in winter. Divergence of temperature flux between the core and outer moorings suggests that heat is extracted by eddies. Depth-averaged energy conversion rates show typically small barotropic conversion, not significantly different from zero, and highly variable baroclinic conversion rates with alternating sign at 1-2 month time scales. Observations suggest that the boundary current is characterized by baroclinic instabilities, which particularly dominate in winter months. 

How to cite: Fer, I. and Peterson, A. K.: Atlantic Water boundary current along the southern Yermak Plateau, Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8055, https://doi.org/10.5194/egusphere-egu22-8055, 2022.

16:05–16:10
|
EGU22-10044
|
ECS
|
On-site presentation
Sam Cornish et al.

The Arctic Ocean's Beaufort Gyre is a wind-driven reservoir of relatively fresh seawater, situated beneath time-mean anticyclonic atmospheric circulation, and is covered by mobile pack ice for most of the year. Liquid freshwater accumulation in and expulsion from this gyre is of critical interest to the climate modelling community, due to its potential to affect the Atlantic meridional overturning circulation (AMOC). In this presentation, we investigate the hypothesis that wind-driven sea ice import to/export from the BG region influences the freshwater content of the gyre and its variability. To test this hypothesis, we use the results of a coordinated climate response function (CRF) experiment with four ice-ocean models, in combination with targeted experiments using a regional setup of the MITgcm, in which we apply angular changes to the wind field. Our results show that, via an effect on the net thermodynamic growth rate, anomalies in sea ice import into the BG affect liquid freshwater adjustment. Specifically, increased ice import increases freshwater retention in the gyre, whereas ice export decreases freshwater in the gyre. Our results demonstrate that uncertainty in the cross-isobaric angle of surface winds, and in the dynamic sea ice response to these winds, has important implications for ice thermodynamics and freshwater. This mechanism may explain some of the observed inter-model spread in simulations of Beaufort Gyre freshwater and its adjustment in response to wind forcing.

How to cite: Cornish, S., Muilwijk, M., Scott, J., Marson, J., Myers, P., Zhang, W., Wang, Q., Kostov, Y., and Johnson, H.: Sea ice import affects Beaufort Gyre freshwater adjustment, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10044, https://doi.org/10.5194/egusphere-egu22-10044, 2022.

16:10–16:15
|
EGU22-10191
|
Virtual presentation
Finn Heukamp and Torsten Kanzow

One of the fastest changing environments of the Arctic is the Barents Sea (BS), located north of Norway between Svalbard, Franz Josef Land and Novaya Zemlja. Although covering only about 10% of the Arctic Ocean area, the BS is of Arctic-wide importance,  as the warm water advected from the North Atlantic cause massive heat fluxes in the atmosphere and sea ice melt, ultimately driving major water mass modifications relevant for the Arctic Ocean circulation  downstream.

We focus on the question whether the observed retreat in sea-ice extent in the BS over the past four decades has enhanced the inflow of warm Atlantic water (AW) into the BS via an ocean-sea-ice-atmosphere feedback contributing to Arctic Amplification, as follows. We start by presenting evidence that the retreating winter sea-ice cover of the Barents Sea has been associated with an increase in ocean-to-atmosphere heat flux that can be observed in a strong rise in near surface air temperature - spatially coinciding with the regions of strong sea-ice retreat. Furthermore, the rising air temperature and the associated convective processes in the atmosphere create a local low sea level pressure (SLP) system over the northern BS that results in additional westerly winds in the vicinity of the Barents Sea Opening (BSO), where the warm and saline AW enters the BS. In case these additional winds enhance the AW inflow into the BS a positive feedback is likely as more heat is available for melting further ice, amplifiying the negative SLP anomaly.

In a set of ocean sensitivity experiments using the sea-ice and ocean model FESOM2.1, we investigate the impact of sea ice-related SLP anomalies and their associated anomalous atmospheric circulation patterns on volume transport through the BSO. The simulations rely on a horizontal grid resolution of approx. 4.5 km in the Arctic and Nordic Seas allowing precise modeling of the BS hydrography and circulation. The model is initially driven with a repeated normal year forcing (CORE1) to isolate the impact of the wind anomalies from high frequency atmospheric variability. After a spin-up phase, the model is perturbed by anomalous cyclones over the BS derived from long term SLP differences in reanalysis datasets associated with the observed sea-ice retreat. The results point indeed to a slight increase in net volume transport into the BS across the BSO. This increase, however, is not caused by an increase in the inflow of AW, but rather a decrease of the outflow of modified AW recirculating back towards Fram Strait. In terms of the feedback, our results indicate that the BS AW inflow is not sensitive to cyclonic wind anomalies caused by the sea-ice retreat. The additional volume and heat transport in the modified AW range may not be sufficient to provide enough heat to melt further sea-ice and hence likely does not close the proposed feedback mechanism in the BS.

How to cite: Heukamp, F. and Kanzow, T.: Investigations on the coupling of the Barents Sea sea-ice retreat on the Atlantic Water inflow via an ocean-ice-wind feedback in the context of Arctic Amplification , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10191, https://doi.org/10.5194/egusphere-egu22-10191, 2022.

16:15–16:20
|
EGU22-10689
|
ECS
|
Virtual presentation
Elizabeth Webb et al.

Surface heat and momentum fluxes between the atmosphere and ocean are mitigated by sea ice cover, resulting in an effective net forcing that can be very different in character from the wind stress alone. The effective stress is often expressed as a weighted sum of air-sea and ice-sea stresses. This is appropriate for levitating ice. Allowing instead for floating ice, one can rewrite the effective forcing in a way that makes no explicit mention of the ice-ocean stress. Instead, the net forcing becomes a linear sum of air-sea and internal ice stresses. These differences are explored in the context of the Beaufort Gyre. Previous studies have introduced the ice-ocean governor as a regulating mechanism for the gyre, and in this limit, the ice-ocean stress is assumed to vanish. For floating ice, the governor limit can be thought of instead as a balance between the wind stress and the internal ice stress. Note that this balance would seem to be unlikely in that the internal stress is associated with small-scale linear kinetic features, which are very different in character from the mesoscale and synoptic features that determine the wind stress. High-resolution ECCO data will be used to examine the instantaneous and time-averaged spatial structure of the various terms that drive the Beaufort Gyre. Future work will also examine the air-sea-ice interface in different wind and ice regimes, as well as the role of eddy fluxes in the gyre dynamics. 

How to cite: Webb, E., Straub, D., Tremblay, B., and Nadeau, L.-P.: Air-Sea, Ice-Sea, and Effective Wind Forcing of the Beaufort Gyre, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10689, https://doi.org/10.5194/egusphere-egu22-10689, 2022.

16:20–16:25
|
EGU22-11472
|
Virtual presentation
Eugenio Ruiz-Castillo et al.

We assessed the spatial and temporal variability of the Arctic Boundary Current (ABC) using a high-resolution array of 7 oceanographic moorings, deployed across the Eurasian continental slope north of Severnaya Zemlya in 2015-2018. In particular, we quantified transports and individual water masses based on temperature and salinity recorders and current profilers. The highest velocities (>0.30 ms-1) of the ABC occurred at the upper continental slope and decreased offshore to below 0.03 ms-1 in the deep basin. The ABC shows strong seasonal variability with velocities two times higher in winter than in summer. Compared to the upstream conditions north of Svalbard, the water mass distribution changed significantly within 20 km from the shelf edge due to mixing with- and intrusion of shelf waters. Further offshore, Atlantic Waters remained largely unmodified. The ABC transported 4.2±0.1 Sv across the region with 63-71% of the volume transport constrained within 30-40 km of the shelf edge. Water mass transport was 0.52±0.13, 0.9±0.27, 0.9±0.33 and 0.9±0.35 Sv for Atlantic Waters (AW), Dense Atlantic Water (DAW), Barents Sea Branch Water (BSBW) and Transformed Atlantic Water (TAW), respectively. A seasonality in TAW and BSBW transport was linked with temperature changes, where maximum transports coincided with minimum temperatures. Our results highlight the importance of the Barents Sea for the ABC along the Siberian slopes, and indicate that a continuing Barents Sea warming would directly translate to reductions in the TAW and BSBW cooling effect and thus lead to warmer oceanic conditions in the ABC pathway. 

How to cite: Ruiz-Castillo, E., Janout, M., Kanzow, T., Hoelmann, J., Schulz, K., and Ivanov, V.: Structure and seasonal variability of the Arctic Boundary Current north of Severnaya Zemlya , EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11472, https://doi.org/10.5194/egusphere-egu22-11472, 2022.

16:25–16:40
Q&A and Discussion 2 "Regional Studies"

Wed, 25 May, 17:00–18:30

Chairpersons: Yufang Ye, Krissy Reeve

17:00–17:05
|
EGU22-571
|
ECS
|
Virtual presentation
Susanna Winkelbauer et al.

This contribution focuses on the Arctic water budget, including its atmospheric, terrestrial, and oceanic components. Oceanic volume fluxes through the main Arctic gateways are calculated, using data from the CMEMS Global Reanalysis Ensemble Product (GREP), and compared to water input to the ocean from atmosphere and land. For this purpose, we use various state-of-the-art reanalyses, including the European Centre for Medium Range Weather Forecast's (ECMWF) latest products ERA5 and ERA5-Land and evaluate them against available satellite (e.g., GRACE) and in-situ river discharge observations.

To obtain a consistent estimate of all physical terms, we combine the most credible estimates of the individual budget terms and perform a variational optimization to obtain closed water budgets on annual and seasonal scales. This up-to-date estimate of the Arctic water cycle is subsequently used to validate historical runs from the Coupled Model Intercomparison Project Phase 6 (CMIP6). Modelled water budget components are analyzed concerning their annual means, seasonal cycles and trends and compared to our observationally constrained data. Results suggest that there remain large uncertainties in the simulation of the Arctic water cycle of the recent decades.

Furthermore, we choose a similar approach to validate the coupled energy budget in CMIP6 models, including oceanic heat transports through the Arctic gateways (where mooring-derived oceanic heat transports are available), atmospheric energy transports and vertical energy fluxes at the surface and top-of-the-atmosphere, as well as Arctic Ocean heat storage.

This assessment helps to understand model biases in typically analyzed quantities such as sea ice extent or volume. It also provides physically based metrics for detecting outliers from the model ensemble which can help to reduce spread in future projections of Arctic change.

How to cite: Winkelbauer, S., Mayer, M., and Haimberger, L.: Validation of the Arctic water and energy cycles in CMIP6 with consistent observation-based estimates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-571, https://doi.org/10.5194/egusphere-egu22-571, 2022.

17:05–17:10
|
EGU22-1414
|
ECS
|
Virtual presentation
Katharina Hartmuth et al.

The Arctic atmosphere is strongly affected by anthropogenic warming leading to long-term trends in surface temperature and sea ice extent. In addition, it exhibits strong variability on time scales from days to seasons. While recent research elucidated processes causing long-term trends as well as synoptic extreme conditions in the Arctic, we investigate unusual atmospheric conditions on the seasonal time scale. We introduce a method to identify extreme seasons – deviating strongly from a running-mean climatology – based on a principal component analysis in the phase space spanned by the seasonal-mean values of surface temperature, precipitation, and the atmospheric components of the surface energy balance. Given the strongly varying surface conditions in the Arctic, this analysis is done separately in Arctic sub-regions that are climatologically characterized by either sea ice, open ocean, or mixed conditions.

Using ERA5 reanalyses for the years 1979-2018, our approach identifies 2-3 extreme seasons for each of winter, spring, summer, and autumn, with strongly differing characteristics and affecting different Arctic sub-regions. Results will be shown for two contrasting extreme winters affecting the Kara and Barents Seas, including their substructure, the role of synoptic-scale weather systems, and potential preconditioning by anomalous sea ice extent and/or sea surface temperature at the beginning of the season.

To statistically quantify and confirm these results, we further apply our method to large ensemble simulations of the CESM climate model, using roughly 1000 years of data in present-day (1990-2000) and end-of-century (2091-2100) climate, respectively. Results show a strong similarity between the characteristics of extreme seasons in ERA5 and CESM for the present-day period. The identified seasons predominantly show the most extreme seasonal-mean anomalies of the applied surface parameters, confirming that our approach captures seasons with extraordinary conditions. Preliminary results will also be shown about our current investigation of possible changes in the characteristics and driving mechanisms of Arctic extreme seasons in the warmer end-of-century climate.

The framework developed in this study and the insight gained from analyzing both, reanalysis and climate model data, will be insightful for better understanding the effects of global warming on Arctic extreme seasons.

How to cite: Hartmuth, K., Boettcher, M., Wernli, H., and Papritz, L.: Identification, characteristics, and dynamics of Arctic extreme seasons in ERA5 and CESM climate simulations, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1414, https://doi.org/10.5194/egusphere-egu22-1414, 2022.

17:10–17:15
|
EGU22-1760
|
ECS
|
On-site presentation
Céline Heuzé et al.

Climate models are our best tools to quantify ongoing changes caused by the climate crisis, but they are not perfect. The Arctic Ocean is particularly challenging to simulate: complex circulation flowing through narrow gateways and around tortuous bathymetry, dense water cascading off the steep shelf break, slow exchanges in canyons, along with known biases in sea ice and neighbouring seas.

We investigate the Arctic Ocean in the historical run of 14 distinct models that participated to the latest Climate Model Intercomparison Project phase 6 (CMIP6) and find large biases in temperature, salinity, density, and depth of critical water masses, both on the shelves and in the deep basins. The biases are consistent throughout the water column and throughout the Arctic, with correlations often exceeding 0.9. However, no significant trend is observed in these biases, suggesting that the deep basins of the Arctic are not correctly ventilated already at the level of the Atlantic Water.

Using the subset of models that submitted the age of water output, we confirm this absence of ventilation by dense water overflows: the overflows occur at too few locations and are diluted at shallow depths.   

Work is ongoing to relate these biases to the relevant processes, the upper water column, and fluxes through the various Arctic Ocean gateways.

How to cite: Heuzé, C., Zanowski, H., Karam, S., and Muilwijk, M.: Large biases in hydrography and circulation of the Arctic Ocean in CMIP6 models, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1760, https://doi.org/10.5194/egusphere-egu22-1760, 2022.

17:15–17:20
|
EGU22-1782
|
On-site presentation
Yevgeny Aksenov et al.

The Arctic Ocean is of central importance for the global climate and ecosystems. It is undergoing rapid climate change, with a dramatic decrease in sea ice cover over recent decades. Surface advective pathways connect the transport of nutrients, freshwater, carbon and contaminants with their sources and sinks. Pathways of drifting material are deformed under velocity strain, due to atmosphere-ocean-ice coupling. Deformation is largest at fine space- and time-scales and is associated with a loss of potential predictability, analogous to weather often becoming unpredictable as synoptic-scale eddies interact and deform. However, neither satellite observations nor climate model projections resolve fine-scale ocean velocity structure. Here, we use a high-resolution ocean model hindcast and coarser satellite-derived ice velocities, to show: that ensemble-mean pathways within the Transpolar Drift during 2004–14 have large interannual variability and that both saddle-like flow structures and the presence of fine-scale velocity gradients are important for basin-wide connectivity and crossing time, pathway bifurcation, and also for predictability and dispersion (the latter are covered in an associated paper [1].

The saddle-points in the flow and their neighbouring streamlines define flow separatrices, which partition the surface Arctic into separate regions of connected transport properties. The separatrix streamlines vary interannually and identify periods when the East Siberian Arctic Shelf, an important source of terragenic minerals, carbon and nutrients, is either connected or disconnected with Fram Strait and the North Atlantic. We explore the implications of this transport connectivity, with our new metric - the Separatrix Curvature Index – which in this context is arguably more informative than either the Arctic Oscillation or Arctic Ocean Oscillation indices.

This work resulted from the Advective Pathways of nutrients and key Ecological sub- stances in the Arctic (APEAR) project (NE/R012865/1, NE/R012865/2, #03V01461), part of the Changing Arctic Ocean programme, jointly funded by the UKRI Natural Environment Research Council (NERC) and the German Federal Ministry of Education and Research (BMBF). This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement no. 820989 (project COMFORT). The work reflects only the authors' view; the European Commission and their executive agency are not responsible for any use that may be made of the information the work contains. This work also used the ARCHER UK National Supercomputing Service and JASMIN, the UK collaborative data analysis facility. Satellitebased sea ice tracking was carried out as part of the Russian-German Research Cooperation QUARCCS funded by the German Ministry for Education and Research (BMBF) under grant 03F0777A. This study was carried out as part of the international Multidisciplinary drifting Observatory for the Study of the Arctic Climate (MOSAiC) with the tag MOSAiC20192020 (AWI_PS122_1 and AF-MOSAiC-1_00) and the NERC Project “PRE-MELT” (Grant NE/T000546/1). We also acknowledge funding support received from the NERC National Capability programmes LTS-M ACSIS (North Atlantic climate system integrated study, grant NE/N018044/1) and LTS-S CLASS (Climate–Linked Atlantic Sector Science, grant NE/R015953/1). The authors would like to acknowledge the contribution of Maria Luneva to the discussions about the initial idea of the study and for highlighting the historical importance of observations from the Russian North Pole drifting stations. Sadly, Maria passed away suddenly in 2020 before the draft of the reported paper was written.

[1] Wilson, C., Aksenov, Y., Rynders, S. et al. Significant variability of structure and predictability of Arctic Ocean surface pathways affects basinwide connectivity. Commun. Earth. Environ. 2, 164 (2021). https://doi.org/10.1038/s43247-021-00237-0.

How to cite: Aksenov, Y., Wilson, C., Rynders, S., Kelly, S., Krumpen, T., and Coward, A. C.: Variability of surface transport pathways and how they affect Arctic basin-wide connectivity, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1782, https://doi.org/10.5194/egusphere-egu22-1782, 2022.

17:20–17:25
|
EGU22-3289
|
ECS
|
Virtual presentation
Zhicheng Ge et al.

SODA (Simple Ocean Data Assimilation) is one of the ocean reanalysis data widely used in oceanographic research. The SODA3 dataset provides multiple ocean reanalysis data sets driven by different atmospheric forcing fields. The differences between their arctic sea ice simulations are assessed and compared with observational data from different sources. We find that in the simulation of arctic sea ice concentration, the differences between SODA3 reanalysis data sets driven by different forcing fields are small, showing a low concentration of thick ice and a high concentration of thin ice. In terms of sea ice extent, different forced field model data can well simulate the decline trend of observed data, but the overall arctic sea ice extent is overestimated, which is related to more simulated sea ice in the sea ice margin. In terms of the simulation of arctic sea ice thickness, the results of different forcing fields show that the simulation of arctic sea ice thickness by SODA data set is relatively thin on the whole, especially in the thick ice region. The results of different models differ greatly in the Beaufort Sea, the Fram Strait, and the Central Arctic Sea. The above differences may be related to the differences between the model-driven field and the actual wind field, which leads to the inaccurate simulation of arctic sea ice transport and ultimately to the different thickness distribution simulation. In addition, differences in heat flux may also lead to differences in arctic sea ice between models and observations. In this paper, the differences between the results of arctic sea ice driven by different SODA3 forcing fields are studied, which provides a reference for the use of SODA3 data in the study of arctic sea ice and guidance for the selection of SODA data in the study of sea ice in different arctic seas.

How to cite: Ge, Z., Wang, X., and Wang, X.: Differences in Arctic sea ice simulations from various SODA3 data sets, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3289, https://doi.org/10.5194/egusphere-egu22-3289, 2022.

17:25–17:30
|
EGU22-3595
|
ECS
|
|
On-site presentation
Jakob Dörr et al.

The recent retreat of Arctic sea ice area is overlaid by strong internal variability on all timescales. In winter, the variability is currently dominated by the Barents Sea, where it has been primarily driven by variable ocean heat transport from the Atlantic. As the loss of winter Arctic sea ice is projected to accelerate and the sea ice edge retreats deeper into the Arctic Ocean, other regions will see increased sea-ice variability. The question thus arises how the influence of the ocean heat transport will change. To answer this question, we analyze and contrast the present and future regional impact of ocean heat transport on the winter Arctic sea ice cover using a combination of observations and simulations from several single model large ensembles from CMIP5 and CMIP6. For the recent past we find a strong influence of the heat transport through the Barents Sea and the Bering Strait on the sea ice cover on the Pacific and Atlantic side of the Arctic Ocean, respectively. There is strong model agreement for an expanding influence of ocean heat transport through these two gateways for high and low warming scenarios. This highlights the future importance of the Pacific and Atlantic water inflows.

How to cite: Dörr, J., Årthun, M., and Eldevik, T.: Present and future influence of ocean heat transport on winter Arctic sea-ice variability, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3595, https://doi.org/10.5194/egusphere-egu22-3595, 2022.

17:30–17:45
Q&A and Discussion 1 "Arctic Modelling"

17:45–17:50
|
EGU22-3652
|
ECS
|
On-site presentation
Moritz Zeising et al.

The presence of liquid or ice as cloud phase determines the climate radiative effect of Arctic clouds, and thus, their contribution to surface warming. Biogenic aerosols from phytoplankton production localized in leads or open water were shown to act as cloud condensation nuclei (liquid phase) or ice nuclei (ice phase) in remote regions. As extensive measurements of biogenic aerosol precursors are still scarce, we conduct a modelling study and use acidic polysaccharides (PCHO) and transparent exopolymer particles (TEP) as tracers. In this study, we integrate processes of algal PCHO excretion during phytoplankton growth or under nutrient limitation and processes of TEP formation, aggregation and also remineralization into the ecosystem model REcoM2. The biogeochemical processes are described by two functional phytoplankton and two zooplankton classes, along with sinking detritus and several (in)organic carbon and nutrient classes. REcoM2 is coupled to the finite-volume sea ice ocean circulation model FESOM2 with a high resolution of up to 4.5 km in the Arctic. We will present the first results of simulated TEP distribution and seasonality patterns at pan-Arctic scale over the last decades. We will elucidate drivers of the seasonal cycle and will identify regional hotspots of TEP production and its decay. We will also address possible impacts of global warming and Arctic amplification of the last decades in our evaluation, as we expect a strong effect of global warming on microbial metabolic rates, phytoplankton growth, and composition of phytoplankton functional types. The results will be evaluated by comparison to a set of in-situ measurements (PASCAL, FRAM, MOSAiC). It is further planned that an atmospheric aerosol-climate model will build on the modeled biogenic aerosol precursors as input to quantify the net aerosol radiative effects. This work is part of the DFG TR 172 Arctic Amplification.

How to cite: Zeising, M., Oziel, L., Gürses, Ö., Hauck, J., Heinold, B., Losa, S., Thoms, S., and Bracher, A.: High-resolution modelling of marine biogenic aerosol precursors in the Arctic realm, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3652, https://doi.org/10.5194/egusphere-egu22-3652, 2022.

17:50–17:55
|
EGU22-5299
|
ECS
|
|
Virtual presentation
Morven Muilwijk et al.

The Arctic Ocean is strongly stratified by salinity gradients in the uppermost layers. This stratification is a key attribute of the region as it acts as an effective barrier for the vertical exchanges of Atlantic Water (AW) heat, nutrients, and CO2 between  intermediate depths and the surface of the deep Eurasian and Amerasian Basins (EB and AB). Observations show that from 1970 to 2017, the stratification in the AB has strengthened, whereas, in parts of the EB, the stratification has weakened. The strengthening of the stratification in the AB is linked to a freshening and deepening of the halocline. The weakened stratification in parts of the EB is linked to a shoaling, warming, and lack of freshening of the halocline (Atlantification). Future simulations from a suite of CMIP6 models project that under a strong greenhouse-gas forcing scenario (SSP585), the AB and EB surface freshening and AW warming continues. To meaningfully compare hydrographic changes in the simulations, we present a new indicator of stratification. We find that within the AB, there is agreement among the models that the upper layers will become more stratified in the future. However, within the EB models  diverge regarding future stratification. We discuss and detail some mechanisms responsible for these simulated discrepancies.

 

How to cite: Muilwijk, M., Smedsrud, L. H., Polyakov, I. V., Nummelin, A., Heuzé, C., and Zanowski, H.: Divergence in CMIP6 projections of future Arctic Ocean stratification, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5299, https://doi.org/10.5194/egusphere-egu22-5299, 2022.

17:55–18:00
|
EGU22-5601
|
ECS
|
Virtual presentation
Alice Richards et al.

Atlantic Water is the most significant source of oceanic heat in the Arctic Ocean, isolated from the surface by a strong halocline across much of the region. However, an increase in Atlantic Water temperatures and a decrease in eastern Arctic stratification are thought to have contributed to Arctic sea-ice loss in recent decades. Investigating how Atlantic Water heat is likely to change and affect the upper ocean during the coming decades is therefore an important part of understanding the future Arctic. In this study, data from the Community Earth System Model (CESM) large ensemble are used to investigate forced trends and natural variability in the Atlantic Water layer properties and heat fluxes over the period 1920-2100, under an RCP 8.5 scenario from 2006.

How to cite: Richards, A., Johnson, H., and Lique, C.: Studying Atlantic Water heat in the Arctic Ocean using the CESM Large Ensemble, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5601, https://doi.org/10.5194/egusphere-egu22-5601, 2022.

18:00–18:05
|
EGU22-6572
|
Virtual presentation
Elena Surovyatkina

The unprecedented warming in the Arctic opens broad prospects for connecting the Northern Sea Route (NSR) to the Maritime Silk Road. Such a "docking" will significantly impact the global economy. The main problems of the Northern Sea Route are the harsh environmental conditions of the North and, most importantly, the presence of sea ice. While, on average, the ice-free period lasts from June to November, the dates of start and end of ice season vary from year to year within a month or even more. Such variability is impossible to capture by numerical weather prediction, limiting predictability for five days. Therefore, currently, there is no specific timeframe when the waterway is free of ice.

Here I show that a long-range forecast for the navigation season is possible for specific locations in Bering and Okhotsk Seas. The approach is fundamentally different from the numerical weather and climate models; it is based on statistical physics principles and recently discovered spatial-temporal regularities in the Asian-Pacific monsoon system [1]. The regularities appear in the form of spatially organized critical transitions in the near-surface atmosphere over the see. The specific locations mean critical areas - tipping elements of the spatial-temporal structure of ice formation, which are identified via data analysis. I rely on the distribution of near-surface air temperature and wind data (NCEP/NCAR re-analyses data set) to reveal conditions for ice formation [2]. I show that a transition from open water to ice season begins when the near-surface air temperature crosses a critical threshold, it is a starting point for forecasting the ice season's start date. The approach provides long-term predictions of the ice season's start in critical areas 30 days in advance.

Furthermore, the transition from water to ice in the Bering and Okhotsk Seas is driven by the Asian-Pacific monsoon air movements. It has the following implications. First, there is a linkage between the onset of ice formation in the northern part of the Bering Sea and the western part of the Sea of Okhotsk. Second, Asian Monsoon, including the Indian monsoon [3], is driven by the same Asian-Pacific system [4]. As a result, the timing of the monsoon is linked with the ice season. These findings show that it is essential to consider these connections to overcome regional forecast limitations. The system approach applied on a continental scale will be relevant for improving the long-term monsoon and ice season forecasts, which we desperately need for climate adaptation.

ES acknowledges the financial support of the EPICC project (18_II_149_Global_A_Risikovorhersage) funded by BMU and the RFBR (No. 20-07-01071).

[1] Stolbova, V., E. Surovyatkina, B. Bookhagen, and J. Kurths (2016): Tipping elements of the Indian monsoon: Prediction of onset and withdrawal. GRL 43, 1–9 [doi:10.1002/2016GL068392]

[2] Surovyatkina, E. and Medvedev, R.: Ice Season forecast under ClimateChange: Tipping element approach, EGU General Assembly 2020, EGU2020-20073, https://doi.org/10.5194/egusphere-egu2020-20073

[3] https://www.pik-potsdam.de/en/output/infodesk/forecasting-indian-monsoon

[4] Surovyatkina, E.: The impact of Arctic warming on the timing of Indian monsoon and ice season in the Sea of Okhotsk, EGU General Assembly 2021, EGU21-13582, https://doi.org/10.5194/egusphere-egu21-13582

How to cite: Surovyatkina, E.: Long-Range Forecast for the Navigation Season: linking the Northern Sea Route and Maritime Silk Road, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6572, https://doi.org/10.5194/egusphere-egu22-6572, 2022.

18:05–18:10
|
EGU22-7237
|
ECS
|
Highlight
|
On-site presentation
Valentin Ludwig and Helge Goessling and the SIDFEx Team

The Sea Ice Drift Forecast Experiment (SIDFEx) database comprises more than 180,000 forecasts for trajectories of single sea-ice buoys in the Arctic and Antarctic, collected since 2017. SIDFEx is a community effort originating from the Year Of Polar Prediction. Forecasts are provided by various forecast centres and collected, and archived by the Alfred Wegener Institute (AWI). AWI provides a dedicated software package and an interactive online platform for analysing the forecasts. Their lead times range from daily to seasonal scales. Among the buoys targeted by SIDFEx are the buoys of the Distributed Network (DN) array which was deployed during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. In this contribution, we show to what extent the deformation (divergence, shear and vorticity) of the DN can be forecasted by the SIDFEx forecasts. We investigate the performance of single models as well as a consensus forecast which merges the single forecasts to a seamless best-guess forecast. 

How to cite: Ludwig, V. and Goessling, H. and the SIDFEx Team: Sea-ice deformation forecasts for the MOSAiC Arctic drift campaign in the SIDFEx database, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7237, https://doi.org/10.5194/egusphere-egu22-7237, 2022.

18:10–18:15
|
EGU22-8941
|
ECS
|
Virtual presentation
Rajan Patel et al.

The North Water Polynya (NOW) in northern Baffin Bay contains nutrient-rich waters which are essential to the biodiversity of the region and the native Inuit people. Over the observational period the size and duration of the NOW in spring has varied considerably, and recent studies suggest the NOW may fail to form in the future. Even small changes to the polynya have the potential to impact local ocean circulation and nutrient cycling. 

To assess the projected changes to the NOW, we look at CMIP5 large ensembles under multiple forcing scenarios. Initial results from CESM1 LE suggest that global temperatures greater than 2.5ºC above pre-industrial levels shift the peak polynya area from June to May. Work is ongoing to assess biogenic and physical impacts of such changes. Implications for climate change are that to avoid large changes to the NOW, warming should be limited.

Additionally, the Polynya area fluctuates with time but decreases as a whole throughout the 21st century.

How to cite: Patel, R., Ugrinow, P., Jahn, A., and Wyburn-Powell, C.: North Water Polynya Sensitivity to Arctic Warming, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8941, https://doi.org/10.5194/egusphere-egu22-8941, 2022.

18:15–18:30
Q&A and Discussion 2 "Arctic Modelling"

Thu, 26 May, 08:30–10:00

Chairpersons: Céline Heuzé, Yevgeny Aksenov

08:30–08:35
OS1.6 Changes in the Arctic Ocean, sea ice and subarctic seas systems: Observations, Models and Perspectives Day 2. Session Introduction, 5 min.

08:35–08:45
|
EGU22-2274
|
solicited
|
Virtual presentation
Wilken-Jon von Appen et al.

Mesoscale eddies are important for many aspects of the dynamics of the Arctic Ocean. These include the maintenance of the halocline and the Atlantic Water boundary current through lateral eddy fluxes, shelf-basin exchanges, transport of biological material and sea ice, and the modification of the sea-ice distribution. Here we review what is known about the mesoscale variability and its impacts in the Arctic Ocean in the context of an Arctic Ocean responding rapidly to climate change. In addition, we present the first quantification of eddy kinetic energy (EKE) from moored observations across the entire Arctic Ocean, which we compare to output from an eddy resolving numerical model. We show that EKE is largest in the northern Nordic Seas/Fram Strait and it is also elevated along the shelfbreak of the Arctic Circumpolar Boundary Current, especially in the Beaufort Sea. In the central basins it is 100-1000 times lower. Except for the region affected by southward sea-ice export south of Fram Strait, EKE is stronger when sea-ice concentration is low compared to dense ice cover. Areas where conditions typical in the Atlantic and Pacific prevail will increase. Hence, we conclude that the future Arctic Ocean will feature more energetic mesoscale variability.

How to cite: von Appen, W.-J., Baumann, T., Janout, M., Koldunov, N., Lenn, Y.-D., Pickart, R., Scott, R., and Wang, Q.: Eddies and the distribution of eddy kinetic energy in the Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2274, https://doi.org/10.5194/egusphere-egu22-2274, 2022.

08:45–08:50
|
EGU22-2125
|
|
Virtual presentation
Wen-Chuan Wu et al.

The dynamics of the Arctic Ocean are changing significantly with increasing global greenhouse gas emissions. Under the current warming scenario, the thinning of sea ice could affect Arctic thermohaline dynamics for the foreseeable future, which would affect the development of the energy cascade. Here, we analyze in situ Lagrangian measurements of the wintertime upper-ocean thermohaline field that were taken during the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition. Horizontal wavenumber spectra of density are examined from 13 approximately 100-km long transects from October 2019 – May 2020 to determine the steepness of spectra for different spatial scales. Unlike the relatively well-defined frequency spectra, horizontal wavenumber spectra yield variable patterns depending on the region of observations. This issue motivates us to investigate the current state of horizontal wavenumber spectra in the multiyear ice zone of the central Arctic. Our preliminary results show that the wavenumber spectra are not consistent in space and time, implying an interplay of stratification, mixed layer depth, and external forcing, such as ice dynamics.

How to cite: Wu, W.-C., Fang, Y.-C., and Rabe, B.: Variability of the Upper Ocean Energy Field in the Amundsen Basin, Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2125, https://doi.org/10.5194/egusphere-egu22-2125, 2022.

08:50–08:55
|
EGU22-3494
|
ECS
|
On-site presentation
Till M. Baumann and Ilker Fer

Mixing along the pathway of Atlantic Water in the Arctic Ocean is crucial for the distribution of heat in the Arctic Ocean. The warm boundary current typically flows along the upper continental slope where energy conversion from tides to turbulence and tidally driven mixing can be important; however, observations -and thus understanding- of these spatiotemporally highly variable processes are limited.

Here we analyze yearlong observations from three moorings (W1, W2 and W3) spanning the continental slope North of Svalbard at 18.5°E over 16 km from 400 m to 1200 m isobaths, deployed between September 2018 and October 2019. Full-depth current records show strong barotropic diurnal (i.e., sub-inertial) tidal currents, dominated by the K1 constituent. These tidal currents are strongest at mooring W2 over the continental slope (~700 m isobath) likely due to topographic trapping far north of their critical latitude (30°N). The diurnal tide undergoes a seasonal cycle with amplitudes reaching minima of ~4 cm/s in March/April and maxima of ~11 cm/s in June/July. Associated with the diurnal tide peak at W2 in summer 2019 is a strong baroclinic semidiurnal signal up to 15 cm/s around 4.5 km further offshore at W3 between 500 m and 1000 m depth. This semidiurnal current signal exhibits a fortnightly modulation and is characterized by upward energy propagation, indicative of generation at the bottom rather than the surface.

We hypothesize that the semidiurnal baroclinic waves are generated by the barotropic diurnal tide about 15 km upstream. There, the slope is oriented approximately normal to the major axis of the tidal current ellipses, maximizing the cross-isobath flow and thus the tidal energy conversion potential. The topographic slope angle approaches criticality for frequencies close to the second harmonic of K1 (2K1, with a semidiurnal period of 11.965 h) around the 620 m isobath and may thus facilitate an efficient generation of second harmonic internal waves. Linear superposition of a 2K1 wave with the rather weak (~5 cm/s) ambient M2 tide would explain the observed fortnightly modulation. The super-inertial wave (w2K1>f) propagates freely and its pathway is presently not known.

Although further research on the generation mechanism is needed, the strong baroclinic semidiurnal currents observed at the continental slope have direct implications for deep mixing. Furthermore, energetic diurnal tidal currents impinging on a steep continental slope are also known to generate non-linear internal lee-waves that can also lead to substantial turbulence and consequent mixing.

How to cite: Baumann, T. M. and Fer, I.: Vigorous Internal Wave Generation at the Continental Slope North of Svalbard, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3494, https://doi.org/10.5194/egusphere-egu22-3494, 2022.

08:55–09:00
|
EGU22-3711
|
Virtual presentation
Igor Kozlov et al.

In this work we investigate the intensity of eddy generation and their properties in the marginal ice zone (MIZ) of Fram Strait and around Svalbard using spaceborne synthetic aperture radar (SAR) data from Envisat ASAR and Sentinel-1 in winter 2007 and 2018. Analysis of 2039 SAR images allowed identifying 4619 eddy signatures in the MIZ. While the overall length and the area of MIZ are different in 2007 and 2018, the number of eddies detected per image per kilometer of MIZ length is similar for both years.
Eddy diameters range from 1 to 68 km with mean values of 6 km and 12 km over shallow and deep water, respectively, suggesting that submesoscale and small mesoscale eddies prevail in the record. At eddy diameter scales of 1-15 km, cyclones strongly dominate over anticyclones. However, in the range of 15-30 km this difference is gradually vanishing, and for diameter values above 30 km anticyclones start to dominate slightly.
Mean eddy size grows with increasing ice concentration in the MIZ, yet most eddies are detected at the ice edge and where the ice concentration is below 20%. The fraction of sea ice trapped in cyclones (53%) is slightly higher than that in anticyclones (48%). The amount of sea ice trapped by a single ‘mean’ eddy is about 40 km2. Here we also attempt to give a first-order estimate of the eddy-induced horizontal sea ice retreat using observed values of eddy radii and amount of sea ice trapped in the eddies, and empirical mean values of ice bottom ablation and ice thickness. The obtained average horizontal ice retreat is about 0.2-0.5 km·d–1 ± 0.02 km·d–1. The spatial patterns of the eddy-induced horizontal sea ice retreat derived from SAR data suggest a pronounced decrease in MIZ area and a shift in the edge location that agrees with the observations.
The analysis of the spatial correlation between eddies, currents and winds shows that the intensity of eddy generation/observations and their detectability in the MIZ, and the width of eddy bands correlate with the intensity of northern and northeasterly winds. In some regions, e.g. along the Greenland Sea shelf break, in Fram Strait and over the Spitsbergen Bank the probability values of eddy occurrence in the MIZ seem to correlate with stronger boundary currents, while north of Svalbard and over Yermak Plateau higher eddy probability values are observed under low/moderate currents and winds.
This study was supported by the Russian Science Foundation grant # 21-17-00278 (analysis of sea ice conditions, ice trapping and melting by eddies) and by the Ministry of Science and Higher Education of the Russian Federation state assignment # 075-00429-21-03 (data acquisition & processing).

How to cite: Kozlov, I., Atadzhanova, O., and Pryakhin, S.: Eddies in the marginal ice zone of Fram Strait and Svalbard from spaceborne SAR observations in winter, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-3711, https://doi.org/10.5194/egusphere-egu22-3711, 2022.

09:00–09:05
|
EGU22-4360
|
ECS
|
On-site presentation
Vasco Müller and Qiang Wang

Mesoscale eddies are believed to play a substantial role for the dynamics of the Arctic Ocean, influencing the interaction of the ocean with the atmosphere and sea-ice as well as the transport and mixing of water masses. Especially their effects on the thermohaline structure and stratification could be crucial for better understanding future changes in the Arctic and the ongoing ‘atlantification’ of the Arctic Ocean water masses. Better understanding of Arctic eddy dynamics also allows the improvement of parametrization of eddy processes in models, which is critical for a realistic representation of the Arctic in climate models and understanding the role of the Arctic Ocean in the global climate. However, simulating Arctic Ocean mesoscale eddies in ocean circulation models presents a great challenge due to their small size at high latitudes and adequately resolving mesoscale processes in the Arctic requires very high resolution, making simulations very computationally expensive.
Here, we use the new unstructured‐mesh Finite volumE Sea ice-Ocean Model (FESOM2) with 1-km horizontal resolution in the Arctic Ocean to evaluate properties of mesoscale eddies. This very high-resolution model setup can be considered eddy resolving in the Arctic Ocean and has recently been used to investigate the distribution of eddy kinetic energy in the Arctic. The analysis here is based on automatically identifying and tracking eddies using a vector geometry-based algorithm and focuses on the model’s representation of eddy properties and dynamics. In-situ observations from the year-long MOSAiC expedition give us the unique possibility to assess the model’s representation of eddy properties against direct observations, both in the Arctic summer and winter seasons.

How to cite: Müller, V. and Wang, Q.: Properties of mesoscale eddies in the Arctic Icean from a very high-resolution model, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4360, https://doi.org/10.5194/egusphere-egu22-4360, 2022.

09:05–09:20
Q&A and Discussion 1 "Eddies and sub-mesoscale processes"

09:20–09:25
|
EGU22-6164
|
On-site presentation
Ivan Kuznetsov et al.

Submesoscale features with profound impact on ocean dynamics and climate-relevant fluxes are frequently observed in the upper ocean including Arctic region. Yet, modelling these features remains a challenge due to the difficulties in the parameterization of submesoscale processes and high resolution required, in particular, in the polar regions. The most effective way to study such phenomena is joint modelling and observational work. Several autonomous observation platforms have been deployed as part of Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) experiment within an approximately 50 km radius around the central observatory. Data from these buoys in combination with data from the central observatory provide a unique opportunity to reconstruct 3D water properties and velocity by constraining a numerical model that resolves the dynamics of the (sub-)mesoscale. It turns out that a minimum root mean square error between results of an optimal interpolation and observations indicates a characteristic length scale of about 7.5 km, corresponding approximately the first-mode barolinic Rossby radius in the area of investigation. However, results of the interpolation are questionable at the sub-mesoscale due to the distribution of the buoy observations in time and horizontal space. In order to describe the in-situ data to achieve a better characterization and understanding of (sub-)mesoscale dynamics we developed and applied a modification of the 3D regional model FESOM-C. The observed temperature and salinity were used to nudge the model to obtain an optimized solution at the resolution of the models. A series of simulations with different horizontal resolutions and model parameters make it possible to analyze the ability of models of this type to reproduce the observed dynamics, to estimate eddy kinetic energy and power spectra, and to compare findings with the observations used to nudge the model. We will show the eddy-induced fluxes and characteristics of eddies along the track of the beginning winter MOSAiC drift.

How to cite: Kuznetsov, I., Rabe, B., Fang, Y.-C., Androsov, A., Zurita, A. Q., Hoppmann, M., Mohrholz, V., Tippenhauer, S., Schulz, K., Fofonova, V., Janout, M., Fer, I., Baumann, T., Liu, H., and Mallet, M. P.: Submesoscale dynamics in the central Arctic Ocean during MOSAiC: optimising the use of observations and high-resolution modelling., EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6164, https://doi.org/10.5194/egusphere-egu22-6164, 2022.

09:25–09:30
|
EGU22-9569
|
ECS
|
On-site presentation
Angelina Cassianides et al.

The paucity of observations over the Arctic Ocean prevents us from fully understanding the interaction between sea ice and mesoscale dynamics. Previous studies on this interplay have documented the interaction between surface eddies and sea ice, omitting the subsurface eddies. This work focuses on the possible role of these subsurface eddies in shaping the sea ice distribution. First, we perform an extensive eddy census over the period 2004-2020 over the Arctic Basin, based on data from Ice Tethered Profilers (ITP) and moorings from the Beaufort Gyre Exploration Project. About 500 subsurface eddies are detected, including both submesoscale (radius between 2-10 km) and mesoscale (up to 80 km) structures. Second, we investigate the dynamical or thermodynamical signature that these eddies may imprint at the surface. On average, these eddies do not cause significant variations in either the temperature of the mixed layer or the melting of sea ice. However, we estimate that subsurface eddies induce a dynamic height anomaly of the order of a few centimetres, leading to a surface vorticity anomaly of O(10^{-5} - 10^{-4}) s^{-1}, suggesting that they may be a significant local forcing for the sea ice momentum balance. Our results suggest that there is no link between the sea ice evolution and the energy level associated with the presence of subsurface eddies. It suggests that once formed, these structures may evolve at depth independently of the presence of sea ice. 

How to cite: Cassianides, A., Lique, C., Treguier, A. M., Meneghello, G., and Demarez, C.: Interplay between subsurface eddies and sea ice over the Arctic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9569, https://doi.org/10.5194/egusphere-egu22-9569, 2022.

09:30–09:35
|
EGU22-9777
|
ECS
|
On-site presentation
Alejandra Quintanilla Zurita et al.

In this work, we will show the main ideas for studying how the (sub-)mesoscale processes impact the flux of nutrients and dissolved inorganic and organic carbon (DIC/DOC) in the upper layers of the central Arctic Ocean. These fluxes are essential since they are one of the primary mechanisms to connect the deeper layers of the ocean with the upper part: nutrients stored deeper can go to the surface mixed-layer and be used for primary production. On the other side, the Arctic Ocean is considered a carbon sink and contributes to the biological pump. For doing this, we are using the high-resolution numerical model FESOM-C to assimilate the hydrographic observations from the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) expedition (2019-2020) to describe the (sub-)mesoscale dynamics (eddies, fronts). We will make use of the OMEGA equation to disentangle the vertical fluxes due to diabatic and adiabatic processes in the model output. Finally, we will analyse those results with in-situ observations of nutrients and DIC/DOC to estimate associated mass fluxes.

How to cite: Quintanilla Zurita, A., Rabe, B., and Kuznetsov, I.: (Sub-)mesoscale Dynamics in the Arctic and its Impact on the Flux of Nutrients and Carbon: a case study from the MOSAiC expedition, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9777, https://doi.org/10.5194/egusphere-egu22-9777, 2022.

09:35–09:40
|
EGU22-13088
Sergey Pryakhin et al.

The early study of eddy properties in the Marginal Ice Zone (MIZ) and of their influence on the ice regime in the Greenland Sea, based on the results of the MIZEX project (Johannessen et al., 1987), revealed that eddies may capture and transport a significant amount of ice, enhancing its ablation. Estimates suggest that eddies may provoke the ice edge retreat as fast as 1–2 km per day during summer. However, up to present, the mesoscale dynamics in polar regions, as well as the effect of eddies on ice edge ablation are poorly understood. This is due to sparse in situ observations and to an insufficient spatial resolution of numerical models, typically not resolving the mesoscale processes due to a relatively small Rossby deformation radius in polar regions.
This study aims to better understand the ways eddies affect the sea ice edge and their relative effect on the MIZ position in the East Greenland Current (75-78°N and 20°W-10°E). Pronounced local water temperature gradients and the importance of thermodynamics ablation in the ice dynamics in the Greenland Sea, derived in previous studies (Selyuzhenok et al., 2020), suggest a possibly strong eddy effect on the MIZ. This effect was noted in several case studies, when eddies were observed to trap and transport a significant amount of ice away from the MIZ (see, for example, von Appen et al., 2018). 
We base our results on the output of the very high-resolution Finite Element Sea ice-Ocean Model (FESOM), tested against the remote sensing observations from ENVISAT. We investigate only the warm period of 2007, when ice is actively melting and during which period a data on eddies, detected in SAR data, is available. Comparison of the location and dynamics of the ice edge in FESOM, AMSR-E-based ice concentration products and ENVISAT ASAR data, as well as of eddy properties in FESOM and in SAR satellite images, suggest that the model is in good agreement with the observations and can be used to study mesoscale dynamics of the MIZ in the region.
The analysis showed that eddies affect the ice edge position through an enhanced horizontal exchange across the MIZ. The sea-ice is trapped by eddies and transported east, in the area of a warmer water, while the warmer water is entrained by eddies and transported west, towards the MIZ. Both effects contribute to the accelerated sea ice melt and destruction. The highest temperature gradients, as well as the largest concentration of eddies in the MIZ were detected in the northern part of the study area, adjacent to the Fram Strait. Here eddies were found to play a particular important role in the MIZ dynamics.
This research was financed by the Russian Science Foundation (RSF) project N 21-17-00278.

How to cite: Pryakhin, S., Bashmachnikov, I., Kozlov, I., and Wekerle, C.: An effect of mesoscale and submesoscale eddies on sea ice processes in the Marginal Ice Zone, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13088, https://doi.org/10.5194/egusphere-egu22-13088, 2022.

09:40–09:55
Q&A and Discussion 2 "Eddies and sub-mesoscale processes"

09:55–10:00
Closing remarks