Southern Ocean and atmospheric CO2 in a warm world - unravelling CO2 sinks in the Southern Ocean during the last interglacial climate state (Project acronym: SOCO)
Final Report Abstract
The project SOCO aimed at assessing carbon cycling and ocean circulation changes in the Atlantic, Indian and Pacific sectors of Southern Ocean during the last interglacial climate period, with particular emphasis on its climatic optimum Marine Isotope Stage 5e as it is considered a potential climate analog of future global climate change. The project specifically targeted resolving biological, dynamical and physical control mechanisms of variations in Southern Ocean carbon storage and ocean circulation changes in the Southern Ocean by applying a multi-proxy approach to our study sediment cores. Through reconstructions of deep-ocean oxygenation, carbon storage, export production, bottom water corrosivity, sea ice dynamics and water mass origin, we were able to disclose three key aspects of Southern Ocean dynamics during the last interglacial climate interval: First, the last peak interglacial was characterized by recurrent perturbations in AABW formation that were likely related to warming of CDW by ~2°C above Holocene levels. This in turn might have been caused by ice shelf melting primarily in the Weddell Sea, signifying the impact of destabilizations of the Antarctic ice sheet through Southern Ocean processes on global sea level. Second, ocean circulation dynamics in the Southern Ocean during the last peak interglacial overall significantly differed from the Holocene; specifically, the global deep ocean was filled by more southern-sourced water masses during the last peak interglacial, which also altered the ocean’s capacity to store and release carbon during that time. Lastly, the Southern Ocean is a significant carbon sink as the Earth system transitions into a glacial climate state, yet processes in the Indian and Pacific sectors diverge from those in the Atlantic sector. While dust-driven export production and wind-driven upwelling determine carbon storage in the Atlantic sector, the deep-ocean respired carbon in the Indian and Pacific sectors are primarily influenced by physical and dynamical processes. The project successfully dealt with unexpected scientific surprises (e.g., previous misalignments of core chronologies based on low-resolution data) and setbacks (e.g., contamination issues), primarily by means of adjusting the publication strategy and performing alternative and complementary proxy analyses. The work highlights the importance of Southern Ocean processes in driving CO2,atm changes and Antarctic ice sheet stability during peak climate conditions and interglacial-glacial climate transitions. Yet, it also emphasizes the spatial heterogeneity and temporal differences of carbon cycle variations and ocean circulation changes across the Southern Ocean that was previously underappreciated. Many questions remain to be resolved, such as the character and quantitative impact of latitudinal variations in Southern Ocean– atmosphere gas exchange on CO2,atm levels and other ocean regions, as well as the character and consequences of marine carbon cycling in the Southern Ocean during other warmer-thanpresent day climate intervals such as MIS11 or the mid-Pliocene Warm Period.
Publications
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A 400-kyr record of millennial-scale carbonate preservation events in the deep Cape Basin: Implications for Atlantic Meridional Overturning Circulation dynamics and the global carbon cycle. Paleoceanography and Paleoclimatology 33, 1-21 (2018
Gottschalk, J.; Hodell, D.A.; Skinner, L.C.; Crowhurst, S.J.; Jaccard, S.L.; Charles, C.D.
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Archaeal lipid biomarker constraints on the Paleocene-Eocene carbon isotope excursion. Nature Communications 10:4519 (2019)
Elling, F.J.; Gottschalk, J.; Doeana, K.D.; Kusch, S.; Hurley, S.J.; Pearson, A.
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Mechanisms of millennial-scale atmospheric CO2 change in numerical model simulations. Quaternary Science Reviews 220, 30-75 (2019)
Gottschalk, J., Battaglia, G., Fischer, H., Frölicher, T., Jaccard, S.L., Jeltsch-T., A., Joos, F., Köhler, P., Meissner, K.J., Menviel, L., Nehrbass-Ahles, C., Schmitt, J., Schmittner, A., Skinner, L.C., Stocker, T.
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Old problems and new challenges in understanding past ocean circulation and carbon-cycle changes, Past Global Changes (PAGES) Magazine on Ocean Circulation and Carbon Cycle 27:2, 47 (2019)
Gottschalk, J., Zhang, X., Burke, A. (Eds.)
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Southern Ocean link between changes in atmospheric CO2 levels and northern-hemisphere climate anomalies during the last two glacial periods. Quaternary Science Reviews 230:101667, 1-17 (2020)
Gottschalk, J., Skinner, L.C., Jaccard, S.L., Menviel, L., Nehrbass-Ahles, C., Waelbroeck, C.
