Stable isotope stratigraphy and amino-acid epimerization for the last 2.4 m.y. at Site 610, Holes 610 and 610A.

Abstract

The record from the late Quaternary (<0.9Ma) shows large amplitudes and high frequencies in oxygen isotopic variation. Prior to 0.9Ma the isotopic variability record is reduced in amplitude compared with the late Quaternary, suggesting lower ice-volume and climatic fluctuations, and higher average eustatic sea level. Left-coiling Neogloboquadrina pachyderma were not found in samples between 1.0-2.2Ma, indicating less influence of polar front migrations in the NE Atlantic. Both polar planktonic faunas and larger isotope fluctuations reappear in the lowermost sample (2.3-2.4Ma), pointing toward a period of larger climatic variability in the late Pliocene than in the early Quaternary. The variation in benthic delta 13C seems to have been constant through the analyzed section, reflecting a stable variability in the production of NADW and possibly in Norwegian-Greenland Sea Overflow. Preliminary analyses of amino-acid epimerization in N. pachyderma (L) indicate a constant rate of epimerization to approx 0.3Ma. Beneath this level the average epimerization rate is much reduced.-from Authors