California Margin Sea Surface Temperature (SST) and Paleoproductivity Records at ODP Site 1012

Three to five million years ago, the earth's climate began to transition from relatively warm global temperatures, in which significant ice sheets were limited to the Antarctic, to temperatures cool enough for the intensification and retention of Northern Hemisphere glaciation. This major transition in the earth's climate system is poorly understood despite its integral role in the development of the earth's present state of bi-polar glaciation. We present a high-resolution sea-surface temperature (SST) record from ODP site 1012 off the California Margin that documents the mid/late Pliocene climate shift. Our alkenone derived SST record shows the cooling of surface waters in coastal California between the mid Pliocene and early Pleistocene. Preliminary results suggest that this cooling trend began prior to the onset of Northern Hemisphere glaciation with significant changes in SST variation starting around 3 Ma. Intensification of glacial SSTs by ~7°C occurs 3-2 Ma, with cool water SSTs of ~19°C at 3 Ma to SSTs of ~12°C at 2.1 Ma. This trend ends abruptly 2.1 Ma as glacial temperatures become milder into the early Pleistocene. The end of this cooling of glacial SSTs is coincident with the strengthening of Walker circulation. Our results from ODP 1012 also include measurements of C37 total that indicate an increase in paleoproductivity between 3 and 1.5 Ma. Spectral analysis of both SST and paleoproductivity display presence of the obliquity signal (41kyr) and strong coherency between SST and productivity in the 41kyr frequency.