H. Bauch

Sea surface temperature variability in the North Atlantic during the last two glacial-interglacial cycles: comparison of faunal, oxygen isotopic, and Mg/Ca-derived records

Climate variability in the northeast Atlantic was investigated on glacial–interglacial and millennial time scales during the last 200u2008000 years, using sea surface temperature (SST) records derived from planktonic foraminiferal diversities and from Mg/Ca measurements on Globigerina bulloides. Paleoceanographical interpretations are supported by species composition analyses, benthic and planktonic isotopic data as well as records of iceberg-rafted debris (IRD). Differences of climate development are recognized for both interglacial and glacial periods. Temperature estimates indicate slightly warmer conditions (up to 2°C) during marine oxygen isotope stage (MIS) 5e than during the Holocene. In contrast to the last glaciation, when the SST minimum coincided with a minimum in solar insolation immediately before Termination I, during the penultimate glaciation a long SST minimum occurred at times of intermediate solar insolation well preceding the onset of Termination II. This discrepancy between two glacial terminations may be explained by an inherently different orbital configuration characteristic for each glacial interval. Despite these differences between the two glacial trends, the superimposed shorter-lived climatic events reveal the same order of principal steps, implying their common causal nature. A direct comparison of faunal SSTs with those retrieved from Mg/Ca analysis shows that Mg/Ca-derived temperatures follow the general glacial–interglacial trend; however, the latter appear to be largely overestimated. Supported by δ18O data in G. bulloides, which show little response to millennial-scale variability, there seems to be a need for species-dependent calibration experiments that also consider the different oceanographic settings this particular species can live in.

Reconstruction of deep-water conditions in the North Atlantic during MIS 9 based on benthic foraminiferal assemblages

Marine isotope stage (MIS) 9 is one of the least investigated Pleistocene interglaciations. The present study describes reconstructions of deep-water conditions during this time interval based on benthic foraminiferal assemblages from sediment core M23414 (Rockall Plateau, North Atlantic). The results of faunal analysis were supported by planktic δ18O, sea surface temperature reconstructions based on planktic foraminiferal assemblages and content of ice rafted debris. Statistical data processing using principal component analysis revealed five climate-related benthic foraminiferal associations that changed in response to alterations of deep-water circulation.