A PROXY COMPARISON OF PLIOCENE SEA SURFACE TEMPERATURE IN THE NORTH ATLANTIC

The Pliocene (~3-5 Ma) was the last interval of sustained global warmth in Earth’s history with mean annual temperature ~3° C warmer than modern and atmospheric carbon dioxide concentrations similar to the modern day. As such, the Pliocene can potentially inform our understanding of anthropogenic climate change, because it provides a geologically recent analog to modern climate conditions. Here, we present an orbital scale sea surface temperature (SST) proxy comparison using data from sediment collected at DSDP Site 609 (50ºN, 24ºW, 3884 m water depth) in the North Atlantic Ocean. We generated alkenone-derived SST estimates and compared them with existing Mg/Ca SST estimates that we corrected for dissolution. Preliminary SST estimates derived from alkenones and corrected Mg/Ca data are within error of one another, having similar mean values of 18.1(±1.0ºC, 1 s.d.) for alkenones and 17.7 (±1.4ºC, 1 s.d.) for Mg/Ca based estimates and similar standard deviations of 1.2 (ºC) for alkenones and 1.4 (ºC) for Mg/Ca. However, the structure of the two records is considerably different, resulting in notable differences in the timing of individual glacial-interglacial variations. Despite the difference in structure, spectral analysis reveals that the spectral signatures of these two records are very similar, with dominant 100 kyr power as well as prominent 41 kyr and 23 kyr peaks in both records. These preliminary data suggest that the types of first order climate results (i.e. the mean temperature estimate and the dominant periodicities) that are the focus of most paleoclimate studies on this timescale would be virtually the same regardless of which proxy was used. Studies interested in the onset or termination of individual glacial cycles or the strength of the non-dominant Milankovitch periodicities, however, might obtain different results depending on which proxy was employed.