Sea-level and deep water temperature changes derived from benthic foraminifera isotopic records

Abstract

We show that robust regressions can be established between relative sea-level (RSL) data and benthic foraminifera oxygen isotopic ratios from the North Atlantic and Equatorial Pacific Ocean over the last climatic cycle. We then apply these regressions to long benthic isotopic records retrieved at one North Atlantic and one Equatorial Pacific site to build a composite RSL curve, as well as the associated confidence interval, over the last four climatic cycles. Our proposed reconstruction of RSL is in good agreement with the sparse RSL data available prior to the last climatic cycle. We compute bottom water temperature changes at the two sites and at one Southern Indian Ocean site, taking into account potential variations in North Atlantic local deep water δ 18O. Our results indicate that a Last Glacial Maximum (LGM) enrichment of the ocean mean oxygen isotopic ratio of 0.95 ‰ is the lowest value compatible with unfrozen deep waters in the Southern Indian Ocean if local deep water δ 18O did not increase during glacials with respect to present. Such a value of the LGM mean ocean isotopic enrichment would impose a maximum decrease in local bottom water δ 18O at the North Atlantic site of 0.30‰ during glacials.