Central South Pacific bottom water response to thermohaline circulation crisis during the Middle Pleistocene Transition

Abstract

Mid-Pleistocene Transition (MPT) is still enigmatic in paleoclimatology, and the major disruption of the ocean thermohaline circulation (THC) system, which is known as the THC crisis during the MPT from ∼950 to 860 thousand years ago, is even more puzzling. Hence, benthic foraminifera and Iceberg rafted debris (IRD) of the Central South Pacific (CSP), International Ocean Discovery Program Site U1540 are examined, and compared with existing Nd isotope records (ε_Nd) from the South and North Atlantic, and δ¹³C of South Atlantic and Equatorial Pacific to evaluate the properties and influence of CSP bottom water during THC crisis in comparison to pre and post-THC crisis. Our data suggests variability in CSP bottom water conditions from oxic to suboxic throughout the MPT. During the pre-THC crisis (MIS 38-26), bottom water was suboxic with low bottom water current strength, which continued up to the Marine Isotopic Stage (MIS) 25, except for MIS 31. Evidence of a strong bottom water current with a high oxic species population and low IRD is found at MIS 31. During the THC crisis, between MIS 25 and 23, a sharp decline in the coarse sediment fraction (>63 μm), oxic species and Globocassidulina subglobosa population is observed, which suggests sluggish bottom water at the CSP. However, during MIS 22, bottom water was relatively strong, marked by an increase in G. subglobosa and Nuttallides umbonifera and oxic species abundances. This suggests stronger southern source bottom water, which may reach up to the North Atlantic due to reduced northern sourced bottom water mass and is consistent with the interpretation of observed ɛ_Nd value. After the THC crisis, bottom water became better oxygenated, especially during the interglacials with high bottom water current strength, which continued post-MPT period. Bottom water current strength nearly follows the ACC strength during the MPT except for MIS 22.