Juan Carlos Herguera, Ph.D.
Center for Scientific Research and Higher Education of Ensenada (CICESE)
Hemispheric links of the southern California Current variability: the past millennium.
Wednesday — October 19, 2011
Pacific Forum — 3:00 p.m.
Instrumental sea surface temperature (SST) variability of the California Current System (CCS) for the last century is thought to be modulated by interannual to interdecadal oscillations superimposed on a background warming trend. However, our understanding of the amplitude of multidecadal SST changes over the last millennium, its persistence through time, and drivers before the instrumental record are still not well characterized. Here we present an absolutely-dated and decadally-resolved planktic foraminiferal Mg/Ca and oxygen isotopic reconstruction of SSTs and mixed layer variability in the southern dynamic boundary of the CCS for the past millennium to explore the links between this eastern boundary current, Northern Hemisphere (NH) temperatures end equatorial ocean dynamics. Summer SST variability is inversely linked with continental NH temperatures on multidecadal timescales and directly linked with the Equatorial Pacific (EP) ocean dynamics until the 19th-20th century, when continental NH temperatures become the dominant driver. This inverse pattern is best explained by the seasonal ocean-land temperature contrast during the spring to early summer warming process that enhances the ocean-continent pressure gradient and drives the persistent alongshore winds, and upwelling processes on multidecadal timescales. However, this pattern seems to reverse during the last third of the 20th century with a trend towards warmer SSTs, probably associated with a cloud cover reduction over the North East Pacific (NEP), that leads to increased SSTs, a weaker subtropical high and a lessening of the trade winds as a positive feedback for further warming in response to increased atmospheric greenhouse gases.
Next: November 19 — Chris Roman, PhD