Multi-Species Temperature and Proxy Reconstructions of the Tropical Pacific Mean State across Marine Isotope Stage 3

Abstract:

The current climatic mean state of the Pacific is characterized by trade wind induced upwelling of cold water in the east and accumulation of warm surface waters in the west, resulting in a strong E-W sea surface temperature (SST) gradient. The initiation and propagation of ENSO events are due to perturbations in this system. Changes in the mean state have the potential to alter ENSO-related processes, feedbacks, and properties. However, it remains unclear how ENSO feedbacks interact as the mean state changes - an increasingly important question as current climate warms, potentially altering the mean state.

Here, we use the abrupt climate warming events of Marine Isotope Stage 3 from 32-64 kyr as a natural experiment for understanding how the tropical Pacific mean state varied across past periods of rapid climate warming. We measured Mg/Ca ratios in the thermocline dwelling planktonic foraminifera N. dutertrei as a proxy for thermocline temperature variability from Eastern Pacific sediment core MV1014-17JC (0°10.8’S, 85°52.0’W). Reconstructing subsurface temperatures removes the seasonal cycle imprint on SSTs, and instead, thermocline temperatures vary with ENSO conditions. Our record reveals that interstadial warming events are characterized by a more El Niño-like mean state, characterized by increased thermocline temperatures up to 6°C. Thermocline warming events are more pronounced from 64-44 kyr when overall global climate was in a warmer state. Moving from 44-32 kyr, our record shows cooler thermocline temperatures, suggesting a shift to a more La Niña-like mean state, as climate began transitioning into the Glacial Maximum.

We also measured Mg/Ca ratios in the surface dwelling planktonic foraminifera G. ruber. Our G. ruber SST record displays the same cooling trend as the N. dutertrei record from 64-32 kyr. SSTs cool 1-1.5°C while thermocline temperatures cool 2.5-3°C. Preliminary comparison with a SST record from the Western Pacific suggests a strengthening of the E-W SST gradient from 44-32 kyr, consistent with our N. dutertrei record revealing a shift to a more La Niña-like mean state. We will also present a record of G. ruber δ¹⁸O_SW variability from the same sediment core, along with a synthesis of available tropical Pacific δ¹⁸O_SW records to examine hydrologic variability across MIS 3.