The Southern Ocean, also known as the Antarctic Ocean, is an enormous body of water. It plays an important role in the global carbon cycle and climate change because the ventilation of deep Southern Ocean is tightly linked to glacial-interglacial variations in atmospheric carbon dioxide(CO2). Being the second largest marginal sea of the Southern Ocean and one source of global ocean deep water, the Ross Sea is an ideal area for deep ocean ventilation and paleoceanography studies. In this study, three sedimentary cores BC008(74.13°S, 176.34°W; water depth 1063 m; length 27 cm), BC010(74.10°S, 175.77°W; water depth 2055 m; length 44 cm) and BC006(74.04°S, 175.67°W; water depth 2120 m; length 54 cm) retrieved from the slope and adjacent basin of the Ross Sea. These cores were mainly composed of sandy silt and silty sand and were selected for biogenic silica content and foraminifera isotope ratio analysis. The sedimentary record is dated using accelerator mass spectrometer radiocarbon(AMS14C) methods on acid insoluble organic matter and foraminiferal calcite. The ages of BC008, BC010 and BC006 cores range from 6.0 ka B. P. to 14.8 ka B. P., from 0 to 15.5 ka B. P and from 0 to 22.3 ka B. P, respectively. The biogenic silica contents in the sediment are relatively high during the last deglaciation with the maximum value at about 16 ka B. P. indicate that the upwelling of deep water in the Ross Sea increased during this period and reach the most intense at about 16 ka B. P. The similar pattern on planktonic foraminifera Nps-δ13C changes during the last deglaciation indicate that the upwelling water masses in the Southern Ocean transmit not only dissolved silicate, but also some chemical signals such as carbon isotope to the surface water. In addition, the upward trend of deep water upwelling during the last deglaciation is consistent with the sharp increase of atmospheric CO2 concentration after the last deglaciation, which further verifies the hypothesis of deep water upwelling in the Southern Ocean and its contribution to the increase of atmospheric CO2 concentration. Moreover, the possible triggering mechanisms of deep water upwelling in the Southern Ocean during the last deglaciation are further discussed. The main trigger mechanisms may be the uneven distribution of heat between the north and the south poles, which resulting in changes in the location and intensity of the Southern Hemisphere Westerly Winds belt(SWW) and the strength of Atlantic Meridional Overturning Circulation(AMOC), thus driving the upwelling of deep water in the Southern Ocean. The sediment records of biogenic silica and carbon isotope ratio of planktonic foraminifera in the Ross Sea imply that the second rapid increase in atmospheric CO2(during YD) is driven by processes operating elsewhere in the Southern Ocean, or another region.

Sedimentary records of enhanced deep ventilation during the last deglaciation in the ross sea, Southern Ocean

Rebesco M;
2021

Abstract

The Southern Ocean, also known as the Antarctic Ocean, is an enormous body of water. It plays an important role in the global carbon cycle and climate change because the ventilation of deep Southern Ocean is tightly linked to glacial-interglacial variations in atmospheric carbon dioxide(CO2). Being the second largest marginal sea of the Southern Ocean and one source of global ocean deep water, the Ross Sea is an ideal area for deep ocean ventilation and paleoceanography studies. In this study, three sedimentary cores BC008(74.13°S, 176.34°W; water depth 1063 m; length 27 cm), BC010(74.10°S, 175.77°W; water depth 2055 m; length 44 cm) and BC006(74.04°S, 175.67°W; water depth 2120 m; length 54 cm) retrieved from the slope and adjacent basin of the Ross Sea. These cores were mainly composed of sandy silt and silty sand and were selected for biogenic silica content and foraminifera isotope ratio analysis. The sedimentary record is dated using accelerator mass spectrometer radiocarbon(AMS14C) methods on acid insoluble organic matter and foraminiferal calcite. The ages of BC008, BC010 and BC006 cores range from 6.0 ka B. P. to 14.8 ka B. P., from 0 to 15.5 ka B. P and from 0 to 22.3 ka B. P, respectively. The biogenic silica contents in the sediment are relatively high during the last deglaciation with the maximum value at about 16 ka B. P. indicate that the upwelling of deep water in the Ross Sea increased during this period and reach the most intense at about 16 ka B. P. The similar pattern on planktonic foraminifera Nps-δ13C changes during the last deglaciation indicate that the upwelling water masses in the Southern Ocean transmit not only dissolved silicate, but also some chemical signals such as carbon isotope to the surface water. In addition, the upward trend of deep water upwelling during the last deglaciation is consistent with the sharp increase of atmospheric CO2 concentration after the last deglaciation, which further verifies the hypothesis of deep water upwelling in the Southern Ocean and its contribution to the increase of atmospheric CO2 concentration. Moreover, the possible triggering mechanisms of deep water upwelling in the Southern Ocean during the last deglaciation are further discussed. The main trigger mechanisms may be the uneven distribution of heat between the north and the south poles, which resulting in changes in the location and intensity of the Southern Hemisphere Westerly Winds belt(SWW) and the strength of Atlantic Meridional Overturning Circulation(AMOC), thus driving the upwelling of deep water in the Southern Ocean. The sediment records of biogenic silica and carbon isotope ratio of planktonic foraminifera in the Ross Sea imply that the second rapid increase in atmospheric CO2(during YD) is driven by processes operating elsewhere in the Southern Ocean, or another region.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/20.500.14083/2963
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