SPATIAL AND TEMPORAL OCEANOGRAPHIC VARIABILITY OF THE EASTERN EQUATORIAL PACIFIC DURING THE LATE PLEISTOCENE - EVIDENCE FROM RADIOLARIA MICROFOSSILS

Eight 150,000 year long records of sea surface temperatures combined w ith two additional records spanning 400,000 years constrain the spatia l and temporal patterns of oceanographic change in the eastern equator ial Pacific and possible mechanisms of variability in the region. Empi rical orthogonal function analysis shows two important modes of variab ility, one associated with the eastern boundary current and another as sociated with the North Equatorial Countercurrent. The two long time s eries located in the equatorial divergence and within the Peru Current have very different patterns of change. The spectrum for the time ser ies from the Peru Current is dominated by orbital periods of 100, 41, and 23 kyr and is similar in variance distribution and phase to record s from the Southern Ocean. In contrast, the equatorial divergence site has spectral concentrations at the orbital frequencies and also conce ntration of variance at the nonorbital 31,000 year period. The phase a nd amplitude spectra of these two sites support the importance of chan ges in eastern boundary advection and also document a nonlinear respon se of the equatorial Pacific to orbital changes. Finally, these data p rovide a new evaluation of the temperature change in the eastern equat orial Pacific during the last glacial maximum. Cooling in the Peru Cur rent region is predicted to be about 4 degrees C, and cooling in the e quatorial divergence is estimated to be 3 degrees to 5 degrees C. The estimated cooling of the region is of the order of 2 degrees C greater than the cooling predicted by Climate: Long-Range Investigation, Mapp ing, and Prediction (CLIMAP).