Southern Ocean sea-ice extent, productivity and iron flux over the past eight glacial cycles

Abstract

International audienceSea ice and dust flux increased greatly in the Southern Ocean during the last glacial period. Palaeorecords provide contradictory evidence about marine productivity in this region, but beyond one glacial cycle, data were sparse. Here we present continuous chemical proxy data spanning the last eight glacial cycles (740,000 years) from the Dome C Antarctic ice core. These data constrain winter sea-ice extent in the Indian Ocean, Southern Ocean biogenic productivity and Patagonian climatic conditions. We found that maximum sea-ice extent is closely tied to Antarctic temperature on multi-millennial timescales, but less so on shorter timescales. Biological dimethylsulphide emissions south of the polar front seem to have changed little with climate, suggesting that sulphur compounds were not active in climate regulation. We observe large glacial–interglacial contrasts in iron deposition, which we infer reflects strongly changing Patagonian conditions. During glacial terminations, changes in Patagonia apparently preceded sea-ice reduction, indicating that multiple mechanisms may be responsible for different phases of CO2 increase during glacial terminations. We observe no changes in internal climatic feedbacks that could have caused the change in amplitude of Antarctic temperature variations observed 440,000 years ago

Polar stratification: A critical view from the Southern Ocean

“…Because Phaeocystis is a main producer of dimethylsulphide (DMS) atmospheric concentrations of DMS should have increased during the last glacial period. However, recently published analyses on the EPICA Dome C ice core do not show a glacial increase of DMS flux on the Antarctic continent suggesting that the DMS production south of the APF remained fairly constant during the last glacial period (Wolff et al, 2006).…”

Origin and significance of ice‐rafted detritus in the Atlantic sector of the Southern Ocean

“…They noted the similarity between the ash abundance in South Atlantic sediments and ice core records of dust and sodium concentrations. Studies of Antarctic ice cores also suggest that changes in aerosol content may reflect sea-ice extent [Petit et al, 1999;Wolff et al, 2003Wolff et al, , 2006.…”

“…For example, the elements Ca and Na have been used to estimate changes in sea-ice cover from ice cores, as these elements are released by brine rejection during sea-ice formation [Wolff et al, 2003[Wolff et al, , 2006. SSI tephra are also rich in Ca and Na, and weathering of tephra may contribute to these elements found in ice cores as well.…”

PIXE and PIGE techniques for the analysis of Antarctic ice dust and continental sediments

“…Insoluble mineral aerosol (dust) deflated from continental surfaces is an important player in Earth's climate because of its influence on the Earth-atmosphere radiative budget [1]; moreover, records of past dust depositions on the Earth's surface obtained by analysis on insoluble particles trapped in polar ice sheets and temperate glaciers are an important proxy of past continental aridity and atmospheric transport activity [2]. In particular, the identification of the ice core dust source areas is an important tool for the understanding of present day and past pathways of atmospheric transport toward the poles and to infer information on the past environmental conditions of dust source areas.…”