Long-term stability of the Western Equatorial Pacific warm pool
Abstract
The Western Equatorial Pacific (WEP) warm pool is an important source of heat for the global climate system and small variations in its sea surface temperature (SST) can alter cloud cover and atmospheric circulation with global consequences. Using SST and pCO2 reconstructions of Late Pleistocene glacial cycles, previous studies infer the WEP warm pool responds to pCO2-radiative forcing (Medina-Elizalde and Lea, 2005; Dyez and Ravelo, 2012). However, these SST reconstructions were based on measurements of pooled foraminiferal shells, which do not resolve short-term SST variability. To monitor within population short-term variability, single tests of surface and subsurface dwelling foraminiferal species were analyzed from glacial-interglacial (G-IG) pairs from four intervals since the early Pliocene. Additionally, to investigate long-term changes in the thermocline, which is an important component in tropical dynamics, we generated a low-resolution subsurface temperature record. Over the last four million years, long-term mean SSTs were similar to present day, while the long-term mean subsurface temperatures gradually cooled by ~6°C. We infer the long-term trend in subsurface temperatures to be a shoaling or cooling of the tropical thermocline from the Pliocene to present. Relative to the Holocene, the observed mean G-IG offset in SST and subsurface temperature are ~+0.6 to -2.0°C and ~+0.5 to +5.7°C, respectively. Although the selected intervals show G-IG changes in mean surface and subsurface temperatures, the G-IG temperature distribution of single foramininfera has not changed since the early Pliocene. This implies that while the tropical long-term subsurface mean state (i.e. thermocline structure) and other boundary conditions (e.g. ice, pCO2) have changed over the last four million years, the mechanism and feedbacks responsible for G-IG mean surface and subsurface temperature changes are similar and consistent through time. We infer that on G-IG scales, mean SST and subsurface temperatures have responded largely to pCO2 radiative forcing and related feedbacks since the early Pliocene.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMPP53C2019F
- Keywords:
-
- 4954 PALEOCEANOGRAPHY Sea surface temperature;
- 1050 GEOCHEMISTRY Marine geochemistry;
- 4926 PALEOCEANOGRAPHY Glacial;
- 4936 PALEOCEANOGRAPHY Interglacial