Pleistocene δ ¹³ C Variability of North Atlantic Intermediate Water

Abstract

Variations in the stable isotopic composition of benthic foraminifera from Deep‐Sea Drilling Project (DSDP) site 502B in the Caribbean Sea are used to reconstruct Atlantic intermediate water circulation variability over the last 1.2 m.y. Comparison of this record with other North Atlantic benthic isotope records indicates that Atlantic intermediate water circulation was relatively enhanced during glacial maxima when North Atlantic deep water (NADW) production was reduced. However, a simple, compensatory relationship between intermediate and deepwater circulation is not apparent. Geochemical models have shown that such changes in ocean circulation can affect atmospheric CO 2 levels by changing vertical nutrient and alkalinity profiles. The Δδ 13 C difference between Caribbean site 502B and deep equatorial Pacific site 677 is highly coherent and in phase with ice volume. Like the δ 18 O record, there is an increase in amplitude (40%) and a large increase in 100 kyr power after 0.7 Ma. The 1.2‰ Δδ 13 C amplitude scales to 70 ppm V in atmospheric CO 2 using Boyle's (1986) box model result. The implied increase in CO 2 amplitude after 0.7 Ma may suggest a positive feedback role in effecting the higher‐amplitude climatic fluctuations which characterize the last 0.7 m.y.

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