Abstract

Paleoceanographic evidence from midlatitudes bearing on the long-term development of Pacific Ocean surface circulation through the middle and late Pleistocene is scant because of a lack of marine paleorecords exceeding the last four or five glacial cycles. Here we compare benthic and planktonic foraminiferal stable carbon isotope data from a 1-Myr marine record in the southeastern subtropical Pacific with records from the equatorial Pacific and Southern Ocean in order to reconstruct sea surface circulation in this part of the world ocean and its possible link to the El Niño/Southern Oscillation (ENSO). We especially address marine isotope stages (MIS) 13 and 11, when internal climate dynamics are suggested to produce somewhat unusual interglacial periods. Our results show that the Southern Ocean controlled the circulation in the subtropical Pacific throughout the middle and late Pleistocene and that the hitherto existing hypotheses cannot explain the peak δ 13C values in both MIS 13 and 11. We argue that the surface circulation pattern in the southeast Pacific during MIS 13 and 11 should have differed from any other interglacial, and we suggest that the subsequent changes in the latitudinal and meridional heat and moisture transfer contributed to the unusual paleoceanographic settings during these stages. We further hypothesize unusually strong El Niño-like conditions during MIS 13 and 11. This hypothesis, if true, challenges a direct forcing of ENSO by orbital parameters. Copyright 2006 by the American Geophysical Union.