Subpolar Atlantic dynamics drive Arctic climate at the onset of the 20th century.

ABSTRACT. Eight sediment gravity cores, collected from theJoides a nd Drygalski basins, were a nal ysed in order to understa nd late Pleistocene-Holoce ne biogenic flux changes in th e Ross Sea, driven by pa leoenvironm ental changes. Core lithologies and magnetic-susceptibility depth profil es were used for core logging and stratig raphic correlation. Nineteen AMS radiocarbon dates of bulk organic matter were used to se t chronological const raints and ca lculate sediment accumulation rates. These rates, which vary from 1.4-38 cm ka I, were used to obtain the burial fluxes of biogenic components. Th e hig hest fluxes occur in the deepest parts of th e basins (TOC, 0.05-0.2 g cm 2 ka I; biogenic silica, 1.5-5 g cm 2 ka -I), whereas topographic highs show the lowest values (TOC, 0.01 -0.1 gcm 2 ka-I ; biogenic sili ca, 0.1 -1.4 gc m 2 ka-I ). Dra mati c changes in both physical properties a nd Ouxes reco rd the establishment of open m arine-sedimentati on conditions which occurred first in th eJoides basin and then, with a delay of ca. 6000 years, in th e Drygalski basin. Both TOC a nd biogeni c-sili ca fluxes increase through the Holocene, though slightl y differently. The hig h fluxes of both lOBe and biogenic Ba suggest that sediment accumulation at basin sites is strong ly influenced by lateral transport.

This is a pre-publication version. Readers are recommended to consult the full published version for accuracy and citation."Ross Sea. Our study has shown that multi-proxy data derived from laminated sediments can provide hitherto unknown detail regarding past summer sea ice dynamics in coastal Antarctic regions.

The efficiency of deep-ocean CO2 sequestration is regulated by the relative balance between inorganic and organic carbon export respectively acting through the biological carbon pump (BCP) and the carbonate counter pump (CCP). The composition and abundance of calcifying species in the prevailing oceanic plankton community plays a major role in driving the CCP. Here we assess the role of these calcifying organisms in regulating the strength of the CCP in a Southern Ocean region (northern Scotia Sea) known to be a major hotspot for the drawdown of atmospheric CO2. We show that, when shelled pteropods dominate the calcifying community, the total annual reduction of CO2 transferred to the deep ocean doubles (17%) compared to when other plankton calcifiers dominate (3–9%). Furthermore, predation enhances their contribution through the removal of organic soft tissue. Pteropods are threatened in polar regions by ocean warming and acidification. We determine that their potential decline would have major implications to the comparative strengths of the BCP and CCP.