Multi-proxy evidence for the evolution of Indo-Pacific Warm Pool temperature since the Pliocene
Abstract
Variations in the absolute sea surface temperature (SST) and spatial extent of the Indo-Pacific Warm Pool (IPWP), particularly during past warm periods such as the early-to-mid Pliocene, are critically important to our understanding of tropical and global climate change. Some climate modeling studies, when forced with greenhouse gas concentrations above preindustrial values, predict that the IPWP warms, while others demonstrate that the spatial pattern of SST changes; each of these results have different implications for tropical hydroclimate, highlighting the need for validation with paleoceanographic SST data from the early Pliocene, when atmospheric CO2 was ~400 ppm. Past studies using TEX86 show a trend from warmer, in the Pliocene, to cooler values in the Pleistocene, while Mg/Ca of planktonic foraminifera shows no long-term cooling; as such, there is an urgent need for rigorous work to understand potential caveats and biases in all proxies used to reconstruct IPWP SSTs. No available SST proxies should be applied without directly addressing potential limitations. Here, we use new sites (U1488, U1483 and U1482) drilled during IODP Expedition 363 and ODP Site 806 to investigate the validity of Mg/Ca SST reconstructions: B/Ca of benthic foraminifera is used to assess the effects of changing dissolution, clumped-isotopes measured on sample splits provides independent SST estimates to indirectly evaluate the effects of changing Mg/Ca of sea water, and a multi-proxy analyses provides constraints on the possible effects of diagenesis. B/Ca show no long-term trend in dissolution. Clumped-isotopes generally agree with Mg/Ca estimates, even after taking into account possible diagenesis, suggesting that the magnitude of changes in Mg/Ca seawater since the Pliocene are likely to be the very low end of published estimates, and that regional TEX86 records may be biased by subsurface production of GDGTs. Comparing our results to published records in the region confirms the idea of an El Padre mean state in the early Pliocene, with an expanded IPWP and with SSTs that were similar to today. Furthermore, the new Mg/Ca record at U1488 is nearly the same as at 806, solidifying the idea that IPWP SSTs fluctuated by ~1-2˚C since the early Pliocene with a marked step suggesting that Walker Circulation strengthened between 2.0-1.5 Ma.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMPP53A..05R
- Keywords:
-
- 1616 Climate variability;
- GLOBAL CHANGE;
- 1631 Land/atmosphere interactions;
- GLOBAL CHANGE;
- 3022 Marine sediments: processes and transport;
- MARINE GEOLOGY AND GEOPHYSICS;
- 3036 Ocean drilling;
- MARINE GEOLOGY AND GEOPHYSICS