EGU General Assembly 2007
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  Information - CL1 Organic Carbon-Rich Marine Sediments Past, Present and Future : Oceans and Climate Feedbacks (co-listed in BG & SSP)

Event Information
Sediments rich in organic carbon are uncommon in the modern ocean and have rarely accumulated during the Cenozoic, yet organic-rich sediments were widely deposited during multiple intervals of Mesozoic-Paleozoic time and even earlier in the Proterozoic-Archean.
Earth history has been characterized by a number of relatively short oxygen-depleted or anoxic phases that were intimately linked to volcanic activity, sea-level fluctuation, the opening and closing of oceanic gateways, and orbital forcing. In concert with other, more local mechanisms, they repetitively caused prominent climatic and paleoceanographic perturbations that resulted in short-term and massive fluctuations in hydrologic and nutrient cycles and in ocean chemistry.
Evidence for these past changes is preserved at different time scales and in shallow to deep marine settings across all latitudes. Temporal and spatial differences in organic-carbon-enriched sediments document regional overprinting and amplification or attenuation of global processes. As such, shelf and upper continental margin settings differ systematically from deeper water settings, today and in the geological past. The occurrence of laminated sections in many organic-carbon-rich settings yields annual-scale climate histories. This is particularly valid for the last 10 Myr, yet further back in the geological record similar expressions of climate and sea-level variability are observed, although with less conclusive time control. In particular the Mesozoic experienced a series of short periods of rapid change with massive effects on the environment. Known as Oceanic Anoxic Events (OAEs), these short intervals are directly related to major perturbations in the global carbon cycle, at times even leading to euxinic conditions throughout the water column accompanied by extinction events. This is especially true for the Paleozoic, when the two major crises in the life history occurred. Among possible explanations, a widespread bottom water anoxia has been often advocated.
The significance of the burial of large amounts of organic matter in deep-sea sediments to the global carbon cycle and the nature of the paleoceanographic and paleoclimatic conditions these deposits record remain topics of lively debate. Aim of this session is bringing together scientists studying black shales in all the temporal windows of the geological history, either by studying paleoceanographic and paleoclimatologic proxies or by modeling present and past conditions that can lead to accumulation of organic-rich marine sediments in order to explore the significant biological, geochemical, and physical processes involved in the formation of these peculiar deposits.
Within this broad framework, an integrated geochemical, paleontological, and biological approach on these sediments could provide prominent examples in Earth history to study the mechanisms operating during natural rapid global change either in greenhouse (e.g. the Cretaceous) or icehouse (e.g. Pliocene–Pleistocene) world episodes. Integrated observation of past and current climatological conditions will enhance considerably our global knowledge of basic aspects of the ocean carbon system and associated climate change. This new knowledge will directly impact our ability to make realistic future projections and to assess potential carbon management scenarios, and it will represent a fundamental source of information about future oceanic responses to a warming world.

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