Abrupt Millennial-scale Sea Surface Temperature Changes on the California Margin Through MIS 3 Inferred From Foraminiferal Mg/Ca

High resolution isotopic, faunal and floral records have shown that millennial-scale events are clearly recorded in California margin sediments. However, uncertainties remain in the phasing of these signals relative to global climate change. In particular, recent work based on alkenone unsaturation indices shows a large temperature lead on the terminations, suggesting that temperature changes on the California margin may be dominated by variation in the strength of the California Current. We address this question using planktonic foraminiferal Mg/Ca, a sea surface temperature proxy that is directly comparable with the δ¹⁸O record, yet completely independent. We have extended the G. bulloides Mg/Ca record from ODP Site1017 (Point Conception, California) through Marine Isotopic Stage 3. High productivity and slope location have led to a sedimentation rate of 23 cm/kyr, which is sufficient to resolve millennial-scale events with minimal attenuation. We compare the Mg/Ca record with G. bulloides δ¹⁸O and foraminiferal faunal records. Abrupt millennial-scale temperature events are clearly resolved using Mg/Ca. The Mg/Ca record indicates that the major temperature events, including interstadial warmings, Termination I and the Younger Dryas cooling, were synchronous with δ¹⁸O. Mg/Ca temperatures indicate a glacial-interglacial temperature change of 7°C and full glacial sea surface temperatures of approximately 8 °C. Mg/Ca temperatures also exhibit events, such as the prominent pre-Bolling warming, that are not recorded by δ¹⁸O. Interstadial warmings were as much as 6 °C, and the amplitude of Stage 3 temperature oscillations is, on average, 2 °C larger than those inferred from δ¹⁸O. This work indicates that investigations at high- chronological resolution are necessary to accurately document the timing of paleotemperature changes on the California margin. Recently recovered IMAGES core material will allow us to extend this work to the even higher sedimentation rate Santa Barbara Basin.