Geomagnetic Assisted Stratigraphy and SST Changes in Core MD94-103 (Southern Indian Ocean): Possible Implications for North-South Climatic Relationships Around H4.

The synchronization of Blunier and Brook [2001] indicates that the isotopic events of central Antarctic ice A1 and A2 led by more than 1 kyr the delta18O stadial-interstadial transitions in Greenland records. This time lag may indicate precursor warming of Antarctica, possibly caused by a see-saw mechanism in inter-hemispheric heat transfer by oceanic circulation. However, it has also been recently suggested that A1 and A2 could reflect cooling in surface ocean temperature at the sources of evaporation of the water that precipitates over Antarctica [Mazaud et al., 2000]. In this alternative scenario, cold conditions during the Heinrich events and possibly some other stadials would have characterized the surface waters in the south latitudes. To test this suggestion, a high-resolution record of alkenone-derived SST was obtained in the 30-50 kyr B.P. time interval from a core, MD94-103, located in the Southern Indian Ocean, which is one of the regions fuelling central Antarctic precipitation. A detailed record of the geomagnetic field around the Laschamp geomagnetic event allowed a correlation of core MD94-103 to NAPIS-75, precisely placed on the GISP2 age model [Laj et al., 2000]. SSTs were also estimated from foraminifera and diatom assemblages and compared to the alkenone-derived record. Alkenone-derived SST and diatom assemblages results indicate cooling and low salinity during H4, and possibly during H5. The comparison with the Byrd delta18O record agrees with the idea that temperature at evaporation sites have strongly affected the isotopic signal of the central Antarctic ice during A1. SSTs obtained from foraminifera assemblages depict somewhat different temperature patterns, possibly indicative of water stratification.