Reassessment of Pliocene Permanent El Niño through new Alkenone based SST Reconstruction in the Pacific Warm Pool

Abstract:

Sea surface temperature estimates from the Pliocene Epoch have been used to draw comparisons between ocean conditions prior to 3 million years ago and today to better understand the effects of elevated atmospheric CO2 on sea surface temperatures and Walker Cell circulation. There is much debate over the existence of permanent El Niño-like conditions in the early Pliocene Epoch due to the use of different sea surface temperature proxies and calibrations, namely the GDGT paleothermometer, TEX86, and the alkenone SST proxy Uk’37. We have recently performed a global calibration of the unsaturation ratio of C38 alkenones (UK38Me) to SST, and extended temperature range of alkenones to 29.5 C. Here we measured the newly established Uk’38ME in sediments from ODP 1143 in the South China Sea to develop a continuous SST record from the Late Miocene to Pleistocene. We established a relationship between C37 total and the Uk’38ME SST - TEX86 SST residuals after the method of the recent work by Lawrence et al. (2020) so that TEX86 could be applied with greater confidence in samples where Uk’38ME reached unity. Our results give a new perspective on the east to west Pacific sea surface temperature gradient, providing important information about sea surface temperature response to elevated CO2 .