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Air-sea Chemical Fluxes: Impacts on Biogeochemistry and Climate

Ocean-atmosphere flux exchanges of biogeochemically active constituents have significant impacts on global biogeochemistry and climate. Increasing atmospheric deposition of anthropogenically-derived nutrients (e.g., nitrogen, phosphorus, iron) to the ocean influences marine productivity and has associated impacts on oceanic CO2 uptake, and emissions to the atmosphere of climate active species (e.g., nitrous-oxide (N2O), dimethyl-sulfide (DMS), marine organic compounds and halogenated species). Atmospheric inputs of toxic substances (e.g., lead, mercury, cadmium, copper, persistent organic pollutants) into the ocean are also of concern for their impact on ocean ecosystem health. In recent decades the intensive use of plastics has led to significant levels of persistent micro- and nano- plastics being transported into the marine atmosphere and to the ocean, with considerable uncertainty remaining on transport pathways and oceanic impacts. Other influential recent changes include emission reductions for air pollution abatement which have resulted in changes in cloud and aerosol chemical composition, affecting atmospheric acidity, associated chemical processing and impacts via atmospheric deposition on ocean biogeochemistry.
In turn, oceanic emissions of reactive species and greenhouse gases influence atmospheric chemistry and global climate, and induce potentially important chemistry-climate feedbacks. While advances have been made by laboratory, field, and modelling studies over the past decade, we still lack understanding of many of the physical and biogeochemical processes linking atmospheric deposition of chemicals, nutrient availability, marine biological productivity, trace-gas sources and sinks and the biogeochemical cycles governing air-sea fluxes of these climate active species, as well as on the atmosphere-ocean cycle of microplastics and its impact on the environment and climate.
This session will address the above issues on the atmospheric deposition of nutrients and toxic substances to the ocean, the impacts on ocean biogeochemistry, and also the ocean to atmosphere fluxes of climate active species and potential feedbacks to climate. We welcome new findings from measurement programmes (laboratory, in-situ and remote sensing) and atmospheric and oceanic numerical models.
This session is jointly sponsored by GESAMP Working Group 38 on ‘The Atmospheric Input of Chemicals to the Ocean’, the Surface Ocean-Lower Atmosphere Study (SOLAS).

Co-organized by BG4/OS3, co-sponsored by SOLAS and GESAMP WG38
Convener: Parvadha Suntharalingam | Co-conveners: Maria Kanakidou, Robert Duce, Arvind SinghECSECS, Katye AltieriECSECS
| Mon, 23 May, 17:45–18:30 (CEST)
Room F1

Mon, 23 May, 17:00–18:30

Chairpersons: Parvadha Suntharalingam, Maria Kanakidou


Thiago Monteiro et al.

The western Tropical Atlantic Ocean is a biogeochemically complex region due to the structure of the surface current system and the large freshwater input from the Amazon River coupled with the dynamics of precipitation. Such features make it difficult to understand the dynamics of the carbon cycle, leading to contrasting estimates in sea-air CO2 exchanges in this region. Here we demonstrate that these contrasting estimates occur because the western Tropical Atlantic Ocean can be split in three distinct regions regarding the sea-air CO2 exchanges. The region under the North Brazil Current domain, acting as a weak annual CO2 source to the atmosphere, with low interannual variability. The region under the North Equatorial Current influence, acting as an annual CO2 sink zone, with great temporal variability. The third region is under the Amazon River plume influence, and has greater interannual variability of CO2 exchanges, but it always acts as an ocean CO2 net sink. Despite this large spatial variability, the entire region acts as a net annual CO2 sink of –1.6 ± 1.0 mmol m–2 day–1. Importantly, the Amazon River plume waters drive 87% of the CO2 uptake in the western Tropical Atlantic Ocean. In addition, we found a significant increase trend in sea surface CO2 partial pressure in North Brazil Current and North Equatorial Current waters. Such trends are greater than the increase in atmospheric CO2 partial pressure, revealing the sensitivity of carbon dynamics in these regions against a global climate change scenario. Since several studies have put efforts to elucidate the snapshots sea-air CO2 exchanges, we have expanded our knowledge about their spatial and temporal dynamics. Our findings shed a comprehensive light on the risk of extrapolation in estimating sea-air CO2 exchanges from regional snapshots. Hence, in addition to pointing out questions that still need to be answered on the CO2-carbonate system our study may be useful for the sampling design of future studies in this region. This should significantly improve the performance of complex coupled ocean-biogeochemical models to provide more robust information about the natural behaviour and changes that the western Tropical Atlantic Ocean is experiencing.

How to cite: Monteiro, T., Batista, M., da Costa Machado, E., Araujo, M., Henley, S., and Kerr, R.: Contrasting sea-air CO2 exchanges in the western Tropical Atlantic Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-417, https://doi.org/10.5194/egusphere-egu22-417, 2022.

Rongxiang Tian and Xiuyi Zhao

Phosphorus is an important nutrient for the growth of marine life in the East China Sea(ECS), where phosphorus is restricted. The external input of phosphorus may cause changes in primary productivity and result in harmful algal blooms. Previous studies emphasized the important contribution of diluted water from the Yangtze River and Kuroshio current. Few researches focus on the sudden and large atmospheric input. Supported by the National Natural Science Foundation of China Open Research Cruise, we collected seawater samples, measured the oxygen isotopes of phosphate and then quantitatively analyze the contribution rate of phosphate from different sources. The results are found that atmospheric input is the main source of phosphorus in the northeast of the East China Sea and the main source of phosphate is from Taiwan Warm Current in the southwest part of the ECS. This finding is helpful for exploring the influencing factors of harmful algal blooms in the ECS and providing some ideas of solution.

How to cite: Tian, R. and Zhao, X.: Contribution of phosphorus transported by atmosphere to the East China Sea in summer, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-925, https://doi.org/10.5194/egusphere-egu22-925, 2022.

Daniela König et al.

Long-range atmospheric transport and deposition of anthropogenically-sourced aerosol iron (Fe) affects surface ocean biogeochemistry far from the emission source. However, it is challenging to establish the integrated impact of anthropogenic aerosol Fe on surface ocean dissolved Fe (dFe) cycling, due to other Fe sources and in situ cycling processes. Previous work has used a distinctively-light Fe isotopic signature (δ56Fe) associated with anthropogenic activity to track the contribution of anthropogenic Fe at the basin scale. However, this requires not only the determination of the δ56Fe endmember of all potential Fe sources, but also the assessment of how upper ocean biogeochemical cycling modulates surface ocean dFe signatures (δ56Fediss). Here we accounted for dust, fire and anthropogenic Fe deposition fields in a global ocean biogeochemical model with an integrated δ56Fecycle to quantify the impact of anthropogenic Fe on surface ocean Fe and δ56Fe, with a focus on the North Pacific. The effect of anthropogenic Fe is spatially distinct and seasonally variable in our model, depending on the biogeochemical state of the upper ocean. In the subtropical regions where Fe is not limiting, anthropogenic Fe input leads to increased dFe levels and, at times, phytoplankton Fe uptake. δ56Fediss declines due to the very light anthropogenic δ56Fe endmember, most prominently in low dFe areas of the subtropical North Pacific gyre. In Fe-limited systems, such as the subpolar gyre, anthropogenic Fe stimulates both primary production and Fe uptake with little change to summertime dFe levels. Moreover, the decrease in δ56Fediss is amplified as extra Fe dampens the impact of the fractionation effects associated with Fe uptake and complexation, whereby the overall δ56Fediss often remains positive. Overall, it is important to account for biological parameters, such as primary productivity or Fe limitation, when assessing the oceanic impact of anthropogenic Fe.

How to cite: König, D., Conway, T., Hamilton, D., and Tagliabue, A.: Surface ocean biogeochemistry regulates the impact of anthropogenic aerosol Fe deposition on iron and iron isotopes in the North Pacific, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1494, https://doi.org/10.5194/egusphere-egu22-1494, 2022.

Weijun Li et al.

Iron (Fe) in aerosol particles is a major external source of micronutrients for marine ecosystems, and poses a potential threat to human health. To understand these impacts of aerosol Fe, it is essential to quantify the sources of dissolved and total Fe. In this study, we applied a receptor modelling for the first time to apportion the sources of dissolved and total Fe in fine particles collected under five different weather conditions in Hangzhou megacity of Eastern China, which is upwind of East Asian outflow. Results showed that Fe solubility (dissolved to total Fe) was the largest in fog days (6.7 ± 3.0%), followed by haze (4.8 ± 1.9%), dust (2.1 ± 0.7%), clear (1.9 ± 1.0%), and rain (0.9 ± 0.5%) days. Positive Matrix Factorisation (PMF) analysis suggested that industrial and traffic emissions were the two dominant sources contributing to the dissolved and total Fe during haze and fog days through the primary emission and atmospheric processing, but natural dust minerals were the dominant source for Fe in dust days. Here the PMF identified additional 15% of dissolved Fe associated with secondary sources during haze and fog days, although it was less than 5% during dust and clear days. Transmission electron microscopy analysis of individual particles showed that approximately 76% and 87% of Fe-containing particles were internally mixed with acidic secondary aerosols in haze and fog days, respectively. Our results indicated that wet surface of aerosol particles promotes heterogeneous reactions between acidic species and anthropogenic Fe aerosol, contributing to higher Fe solubility during fog and haze days.

How to cite: Li, W., Zhu, Y., and Shi, Z.: Sources and processes of iron aerosols in a upwind megacity of Northern Pacific Ocean, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2714, https://doi.org/10.5194/egusphere-egu22-2714, 2022.

Clarissa Baldo et al.

It is known that mineral dust is the largest source of aerosol iron (Fe) to the offshore global ocean, but acidic processing of coal fly ash (CFA) may result in a disproportionally higher contribution of dissolved Fe to the surface ocean. In this study, we determined the Fe speciation and dissolution kinetics of CFA from Aberthaw (United Kingdom), Krakow (Poland), and Shandong (China) in acidic aqueous solutions which simulate atmospheric acidic processing. The CFA bulk samples were re-suspended in a custom-made chamber to separate the PM10 fraction. The Fe speciation in the PM10 fractions was determined using sequential extraction methods. In the PM10 fractions, 8%-21.5% of the total Fe was as hematite and goethite (dithionite extracted Fe), 2%-6.5 % as amorphous Fe (ascorbate extracted Fe), while magnetite (oxalate extracted Fe) varied from 3%-22%. The remaining 50%-87 % of Fe was associated with aluminosilicates. At high concentrations of ammonium sulphate ((NH4)2SO4) and low pH (2-3) conditions, which are often found in wet aerosols, the Fe solubility of CFA increased up to 7 times. The oxalate effect on the Fe dissolution rates at pH 2 varied considerably, from no impact for Shandong ash to doubled dissolution for Krakow ash. However, high concentrations of (NH4)2SO4 suppressed this enhancement in Fe solubility. The modelled dissolution kinetics suggest that magnetite may also dissolve rapidly under acidic conditions, as the dissolution of highly reactive Fe alone could not explain the high Fe solubility at low pH observed in CFA. Overall, Fe in CFA dissolved up to 7 times faster than in Saharan dust samples at pH 2. These laboratory measurements were used to develop a new scheme for the proton- and oxalate- promoted Fe dissolution of CFA. The new scheme was then implemented into the global atmospheric chemical transport model IMPACT. The revised model showed a better agreement with observations of surface concentration of dissolved Fe in aerosol particles over the Bay of Bengal, due to the rapid Fe release at the initial stage at highly acidic conditions.

How to cite: Baldo, C., Ito, A., Krom, M. D., and Shi, Z.: Atmospheric dissolved iron from coal combustion particles, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4315, https://doi.org/10.5194/egusphere-egu22-4315, 2022.

Maria Kanakidou et al.

Atmospheric Ice nuclei particles regulate in cloud properties such as, cloud lifetime, precipitation rates and cloud’s radiative properties due to their ability to trigger ice heterogenous formation. Particles ejected into the atmosphere during bubble bursting through the sea surface microlayer, which is enriched in organic matter, are considered as the major precursors of INPs over the ocean. In addition, mineral dust particles that are considered as the most important precursor of INP in the mixed-phase cloud regime globally and terrestrial bioaerosols that have been also shown to have INP activity are transported over the ocean and contribute to the INP in the marine environment.

In the present study we present results from the global 3-D chemistry transport model TM4-ECPL that accounts for INPs concentrations from marine organic aerosols, terrestrial bioaerosol and K-rich feldspar and quartz mineral dust particles. The simulated distribution of INP concentrations over the global ocean agrees with currently available ambient measurements. The relative contribution of the various INP precursors in the different compartments of the marine atmosphere is discussed on the basis of simulated 3-dimensional number concentrations of INP, providing insight to the cloud glaciation processes in the marine environment.

Support from PANACEA (MIS 5021516) funded by the Operational Programme "Competitiveness, Entrepreneurship and Innovation" (NSRF 2014-2020) and co-financed by Greece and the European Union (European Regional Development Fund), and the Excellence grant, the U Bremen Excellence Chair and the European Union Horizon 2020 project FORCeS under grant agreement No 821205.

How to cite: Kanakidou, M., Chatziparaschos, M., Daskalakis, N., Myriokefalitakis, S., and Kalivitis, N.: Organic aerosols and dust as contributors to ice nucleating particles formation in the marine atmosphere, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7951, https://doi.org/10.5194/egusphere-egu22-7951, 2022.