Diatom stable isotopes, sea ice presence and sea surface temperature records of the past 640 ka in the Atlantic sector of the Southern Ocean

High-resolution delta(13)C and delta(15)N records of diatom-bound organic matter (delta(13) C-D, delta(15) N-D) from ODP site 1094, South of the Polar Front, are combined with reconstructions of summer sea surface temperature and winter sea-ice to establish changes in surface water characteristics associated with the main climatic events of the past 640 ka. The six glacial-interglacial delta(13) C-D cycles show excellent agreement with SPECMAP delta(18)O and Vostok CO2 content, suggesting that global physical processes rather than local biological factors were the main influences on delta(13)CD. By contrast, there is weak correspondence between the Vostok dust record and the delta(13)C(D) and delta(15)N(D) records. The data do not support the hypothesis that glacial iron fertilization of the Southern Ocean was the main factor lowering atmospheric CO2, if dust accumulation represents iron input. The records indicate that sea ice cover, water column stratification and iron addition from deep water mixing are more likely to explain our observations.