Controls on Sr/Ca in benthic foraminifera and implications for seawater Sr/Ca during the late Pleistocene

Changes in the Sr to Ca ratio of sea water have important implications for the interpretation of past climate. It has proven difficult to interpret Sr/Ca of foraminiferal calcite as a measure of seawater Sr/Ca or as reflecting the influence of deep water carbonate ion saturation (Delta[CO32-]) on the incorporation of Sr into benthic foraminiferal carbonate. Here, we address this issue by measurements of paired benthic foraminiferal Sr/Ca and B/Ca (a proxy for deep water A[Delta[CO32-]) for core-tops from the global ocean and three down cores at different settings during the Last Glacial-interglacial cycle. These new data suggest a significant control of deep water Delta[CO32-] on benthic foraminiferal Sr/Ca, and that down-core shell Sr/Ca variations can be largely accounted for by past deep water Delta[CO32-] changes. We conclude that seawater Sr/Ca has likely remained near-constant on glacial-interglacial timescales during the late Pleistocene, in agreement with model results. With due caution, benthic Sr/Ca may be used as an auxiliary proxy for deep water Delta[CO32-] if seawater Sr/Ca is constant.</p

Obliquity pacing of the western Pacific IntertropicalConvergence Zone over the past 282,000 years

The Intertropical Convergence Zone (ITCZ) encompasses the heaviest rain belt on the Earth. Few direct long-term records, especially in the Pacific, limit our understanding of long-term natural variability for predicting future ITCZ migration. Here we present a tropical precipitation record from the Southern Hemisphere covering the past 282,000 years, inferred from a marine sedimentary sequence collected off the eastern coast of Papua New Guinea. Unlike the precession paradigm expressed in its East Asian counterpart, our record shows that the western Pacific ITCZ migration was influenced by combined precession and obliquity changes. The obliquity forcing could be primarily delivered by a cross-hemispherical thermal/ pressure contrast, resulting from the asymmetric continental configuration between Asia and Australia in a coupled East Asian–Australian circulation system. Our finding suggests that the obliquity forcing may play a more important role in global hydroclimate cycles than previously thought