Increased sensitivity of the Plio-Pleistocene northwest Pacific to obliquity forcing

- High-resolution alkenone-based sea surface temperature estimate from NW Pacific.
- Seasonal, high-latitude context of signal informed by stable isotope records.
- Kuroshio Extension cooled ahead of/during early Pleistocene glacial intervals.
- Cooling apparently seasonal, regional, points to ocean-atmosphere heat transfer.
- North Pacific heat and moisture transfer may have promoted glacier formation.

Insolation-driven changes in poleward heat transport and changes in greenhouse gas concentrations can explain aspects of the rise of obliquity-paced climate variability during the Pliocene-Pleistocene transition. Based on an alkenone-based sea surface temperature (SST) reconstruction of the Kuroshio Current Extension (KCE), we propose here that emergence of this region as the primary locus of ocean-atmosphere heat transfer in the Pacific Ocean promoted Northern Hemisphere Glaciation (NHG). Our record shows that with intensification of NHG at 2.7 Ma, the KCE cooled 2-4 °C during glacial intervals, likely in NH winter/spring. These high-amplitude 41-kyr SST cycles slightly lead δO18 variations, ruling out global ice-volume changes as the primary cause. The lead of SST over δO18 cycles matches the phasing between these two proxies observed in the tropics, supporting changes in CO2 concentrations as a unifying mechanism of ocean surface temperature change. However, the amplitude of the KCE SST cycle is twice that of the tropical records, pointing to an additional, regional process. We infer that cooling of the North Pacific sea surface by the East Asian winter monsoon and associated westerlies intensified during glacial intervals. This transfer of heat and moisture from the ocean to the atmosphere potentially furthered glacial formation by accelerating snow fall in North America. Therefore, these results might also support a role for tropical-extratropical heat balance in enhancing glacial growth via the obliquity pacing.