Abstract:
In light of recent predictions for future global climate change, understanding past changes in climate is important because it provides insight into key climate system processes and the mechanisms that drive climatic change. However, our ability to reconstruct past climate conditions relies on paleoclimate proxies, which all have associated uncertainties and limitations. By employing a multi-proxy approach we are able to assess the reliability of individual proxies and provide a more robust characterization of temperature change over time. In this study, we generated orbital-resolution benthic and planktonic stable isotope records and alkenone-derived sea surface temperature (SST) and biological productivity records from 500 ka to the present at Ocean Drilling Program (ODP) Site 662 in the Eastern Equatorial Atlantic (EEA-1 degrees S, 11 degrees W). Our new datasets permit regional inter-proxy comparisons, corroborate observations from existing records, and help refine our understanding of how Equatorial Atlantic climate changed over the past several glacial cycles. Our isotope and alkenone SST records are similar in overall structure, as both display the classic sawtooth pattern representative of late Pleistocene glacial/interglacial cycles. Furthermore, our alkenone SST data are similar in structure with SST proxy data from other EEA sites. The amplitude of glacial/interglacial temperature variations is 3-4 degrees C in our alkenone record, and alkenone and Mg/Ca temperature records from nearby EEA Site GeoB1105 (2 degrees S, 12 degrees W). In contrast, warm faunal SST glacial/interglacial cycles at GeoB1105 are up to 6 degrees C in amplitude while cold faunal SST cycles at the same site are up to 10 degrees C. Overall, our alkenone SST estimates are on average within 1 degrees C of those from Site GeoB1105 alkenones, Mg/Ca, and warm faunal SST estimates, but are on average 5 degrees C warmer than GeoB1105 cold faunal SST estimates. Consistent with other late Pleistocene proxy reconstructions from the EEA, our isotope, alkenone and productivity records contain a persistent precessional signal. We attribute these precession-linked changes to insolation driven variations in atmospheric circulation and trade wind dynamics related to the African monsoon.