RECONSTRUCTION OF MID-LATITUDE SURFACE OCEAN HIGHLY DEPENDENT ON PALEOECOLOGY: ASYNCHRONOUS RESPONSE TO DIFFERENT WARMING EVENTS IN THE KUROSHIO CURRENT EXTENSION DURING THE MPWP

Western boundary currents, like the Kuroshio Current Extension (KCE), are currently warming at a rate 2–3 times faster than other regions in the world ocean. Observational sea surface temperature data from the past century have concluded that the KCE has warmed by approximately 1–2°C. Previous Pliocene studies that have reconstructed the KCE during the mid-Piacenzian Warm Period (mPWP) at a lower resolution determined that the current may have warmed 3–4°C across MIS KM5.

This study uses stable isotopic data from two species of thermocline-dwelling planktic foraminifera, Globoconella inflata and Neogloboquadrina incompta, from Ocean Drilling Program Hole 1207A, northwest Pacific, to characterize the surface ocean behavior within the KCE from 3.5–3.1 Ma. We also investigate how the paleoecology of species that grow during the winter (G. inflata) vs. year-round (N. incompta) affect the interpretations of geochemical records.

Preliminary isotopic data and analyses based on 88 total samples indicate that even though both species are thermocline dwellers, their δ18O and δ13C values differ, namely across MIS KM5. This preliminary data highlights the nonlinear nature in which the KCE responded to warming pulses during the mPWP. Within MIS KM5 warming of the KCE is indicated by a 2.0‰ decrease in the G. inflata δ18O stable isotopic data. However, the N. incompta data remain stable with only about a 0.30‰ increase across MIS KM5. The data also reveal an asynchronous response to MIS K1 and KM5 warming events. During this time, both G. inflata and N. incompta data indicate a slight decrease of values and indicate relative current temperature stability across MIS K1, the second pulse of warming within the mPWP. However, during MIS KM5, the G. inflata record indicates warming, whereas the N. incompta record indicates minor temperature changes. These data indicate that N. incompta and G. inflata records reveal differences in their isotopic signals, and as such care must be taken to address and understand the seasons in which species grow to more precisely reconstruct ancient ocean behavior. In short, paleoecology of organisms has a significant effect on proxy data variability when conducting paleoceanographic studies.