21-1 Using Planktic Foraminiferal Paleoecology to Infer the Magnitude of Kuroshio Current Extension Winter Warming across the mid-Piacenzian Warm Period

Session: Insights from Microfossils and Their Modern Analogs: From Traditional to Emerging Approaches

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Today, western boundary currents are warming 2–3 times faster than other regions of the world ocean. As such, it is imperative to quantify how these systems will continue to warm in response to increased anthropogenic warming. The Kuroshio Current Extension (KCE) is a major western boundary current as part of the North Pacific Subtropical Gyre, and is important from a biological, meteorological, and economic standpoint. The long-term behavior of the KCE using observational data is complicated by decadal-scale modulations of the current, but this challenge can be overcome by utilizing the deep-sea sedimentary record. Such records obscure short-term paleoceanographic changes while retaining the longer-term (geologic) footprint of current response to analogue warm periods. This study uses sediments from Ocean Drilling Program Leg 198 Hole 1207A,  located on the northern edge of the KCE, to reconstruct surface ocean temperatures across one such analogue warm period, the mid-Piacenzian Warm Period (mPWP; 3.4–2.9 Ma). Temperature and KCE behavior was reconstructed by creating a stable isotopic time series from two species of thermocline-dwelling planktic foraminifera: Globoconella inflata and Neogloboquadrina incompta. Goals of the study include: 1) investigating the effects of seasonality on recovered geochemical signals; 2) quantifying the degree of intra-sample isotopic variability; and 3) reconstructing thermocline temperatures across the study interval but especially across Marine Isotope Stages (MIS) M2 and the MIS KM5c. Our results indicate: 1) recovered geochemical signals differ due to seasonal preferences of foraminifera, and paleoecology should be considered when reconstructing environmental variables from biotic calcite; 2) the mPWP interval contains the highest intra-sample variability and variance perhaps due to higher sea level and the westerlies located north of the site; and 3) estimated temperatures indicates that the KCE at Hole 1207A warmed by 1.36–1.96°C from MIS M2 to MIS KM5c, a magnitude of warming the KCE has reached over the last century. Our results indicate that further research should be conducted on the KCE and other subtropical western boundary currents across deeper-time analogue warm periods with higher atmospheric carbon dioxide levels that are similar to those levels projected for the coming decades.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-7121

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