Abrupt Color Changes in Isotope Stage 5 in North Atlantic Deep Sea Cores: Implications for Rapid Change of Climate-Driven Events

Summary

Digitized records of optical density in many North Atlantic cores exhibit rapid changes from lighter to darker extremes, typically within less than 200 years, at the 5d/5e, 5b/5c and 4/5 boundaries. In cores from DSDP site 609 the changes from lighter to darker color coincide with increases in relative abundance of N. pachyderma (l. c.), with increases in abundances of lithic grains and with decreases in carbonate content. The rapid changes to dark color, therefore, are climate-driven and correspond to a lowering of sea surface temperatures and to increases in amounts of ice rafted debris relative to biogenic carbonate. At the 5d/5c boundary, δ¹⁸O in N. pachvderma (l.c.) increases abruptly with the change to darker sediment as expected for cooler sea surface temperatures. At the 4/5 boundary, however, δ¹⁸O decreases with the change to darker sediment and cooler sea surface temperatures, suggesting that a layer of fresh surface water was present in the North Atlantic at that time.