|Abstracts on Global Climate Change|
Strontium isotope tracing of terrigenous sediment dispersal in the Antarctic Circumpolar Current: Implications for constraining frontal positions
Hemming, SR van de Flierdt, T Goldstein, SL Franzese, AM Roy, M Gastineau, G Landrot, G
GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 8: -
 The vigor of the glacial Antarctic Circumpolar Current (ACC) and the locations of frontal boundaries are important parameters for understanding the role of the Southern Ocean in global climate change. Toward the goal of understanding the locations of currents we present a survey of Sr isotope ratios in terrigenous sediments around the perimeter of Antarctica. The pattern of the variations within the modern ACC is used to suggest that terrigenous sediment from Antarctica is injected into the ACC via the Ross and Weddell gyres in the south. North of the main ACC the Sr isotopes reflect continental contributions from Africa, Australia-New Zealand, and South America. Along a transect northward from the Ross Sea, Sr isotope ratios show a decrease from higher values in the south ( Antarctic provenance) to lower values in the north ( provenance from New Zealand). This otherwise monotonic decrease is interrupted within the ACC by a “zigzag” to lower and then higher values, which accompanies minimum terrigenous flux. This zigzag requires contributions from two additional sediment sources beyond the main Antarctic and New Zealand end-members. The lower Sr isotope ratios are attributable to greater contributions from basaltic sources within the current, a consistent pattern around the ACC. The samples with higher Sr isotope ratios point to an additional contributor, possibly a wind-transported component from Australia. During the LGM there is a systematic geographical variation in the Sr isotope ratios, similar to that of the Holocene. A small offset of the zigzag to the north ( approximately 1 degrees-2 degrees) may indicate a small northward shift of the southern boundary of the ACC. More highly resolved data are required to test whether this northward shift is really significant and whether it applies to other ACC fronts during the LGM.