The ventilation and circulation of the southern Indian Ocean on glacial / interglacial timescales
Final Report Abstract
During this project, we addressed a known-unknown in our paleoceanographicpaleoclimatological understanding of the glacial-interglacial carbon cycle. To do so, we studied the spatio-temporal evolution of water mass residence times in the upwelling cell of the southernmost Indian Ocean. In combination our radiocarbon-based proxy reconstructions (Δ14C) and the transient climate model experiments present an unprecedented insight into the role of the Southern Ocean’s Indian sector and highlight that this region must not be neglected in order to understand the global climate change, past, present and future. In particular our radiocarbon data show that the Indian sector of the Southern Ocean was an integral part of the (now) circumpolar glacial carbon pool that allowed for the drawdown and storage of atmospheric CO2. Our transient modeling experiment showed that an increased density gradient strengthened the oceanic stratification and marked the physical process that explains the ventilation patterns observed by us. Moreover, we were able to show, that the upwelling region in the southern Indian Ocean was an important pathway for stored CO2 from the ocean’s interior to the surface and the atmosphere. At our shallowest core site, two transient pulses of decreasing (decreasing ΔΔ14C) water mass ventilation were observed at the end of the last glacial and during the deglacial. These patterns are also in good agreement to our model experiments. Parallel to dropping ΔΔ14C-values, our model showed two phases of destratification and a breakdown in the density gradient. Both pulses slightly lead the Heinrich Stadial 1 and Younger Dryas increases in atmospheric CO2. We argue that during both times, the weakened stratification allowed for the upwelling of CO2-rich, radiocarbon-depleted circumpolar deep waters and ultimately the release of sequestered CO2. In summary, our results show that the Indian sector of the Southern Ocean was 1) part of the circumpolar glacial carbon pool and, 2) marked an important pathway for CO2 from the ocean to the atmosphere.
Publications
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(2017). A biomarker perspective on dust, productivity, and sea surface temperature of the Pacific sector of the Southern Ocean. Geochimica et Cosmochimica Acta, 204, 120-139
Jaeschke, A., Wengler, M., Hefter, J., Ronge, T. A., Geibert, W., Mollenhauer, G., Gersonde, R., Lamy, F.
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(2017). A Southern Ocean driver of atmospheric CO2 and Antarctic ice sheets. AGU Fall Meeting 2017, New Orleans
Ronge, T. A., Geibert, W., Lippold, J., Lamy, F., Schnetger, B., Tiedemann, R.
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(2017). Circulation patterns of the glacial Southern Ocean. 10th International Carbon Dioxide Conference, Interlaken
Ronge, T. A., Geibert, W., Lippold, J., Lamy, F., Schnetger, B., Tiedemann, R.
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(2018). Climate CO2 and Ice Sheets – A Southern Ocean perspective. 27th International Polar Conference, Rostock
Ronge, T. A., Geibert, W., Lippold, J., Lamy, F., Schnetger, B., Prange, M., Tiedemann, R.
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(2018). The impact of Southern Ocean circulation on the global carbon cycle and Antarctic ice shelf stability. AGU Fall Meeting 2018, Washington DC
Ronge, T. A., Lippold, J., Geibert, W., Lamy, F., Mollenhauer, G., Süfke, F., Tiedemann, R.
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(2018). The ventilation of the Indian Sector of the Southern Ocean. PAGES OC3_IPODS, Cambridge
Ronge, T. A., Prange, M., Mollenhauer, G., Tiedemann, R.
