Glacial-Interglacial Changes in Central Tropical Pacific Sea Surface Temperature

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Paleoclimate data sets can be used to help validate and improve the climate models that are used to predict future change. Of particular use have been data from the Last Glacial Maximum, a time with lowered atmospheric carbon dioxide, reasonably well understood forcing, and potentially broad data coverage. Accurate estimates of sea surface temperature are also essential if data from the geologic record is to be used to constrain equilibrium climate sensitivity -- defined as the global mean temperature response to a doubling of atmospheric carbon dioxide. Studies have shown that the connection between climate sensitivity and Last Glacial Maximum temperature is strongest in the tropics, where greenhouse gas forcing dominates the temperature signal. While Last Glacial Maximum temperature in the Western and Eastern Tropical Pacific is constrained by multiple sea surface temperature proxies, there is little existing data in the Central Tropical Pacific. Past estimates are highly uncertain and suggest little temperature change in this region, a result that is incompatible with reconstructions from climate models forced with Last Glacial Maximum boundary conditions. A series of sediment cores has recently been collected from the Line Islands Ridge in the Central Tropical Pacific, spanning a range of latitude from the equator to 7 degrees North. The PIs propose here to measure Mg/Ca ratios in surface dwelling planktonic foraminifera in order to reconstruct temperature changes over the last glacial cycle. Temperature reconstructions from cores collected over a range of latitude and water depth will help to assess the uncertainty in the new sea surface temperature estimates. Oxygen isotope ratios in surface dwelling planktonic foraminifera from the same set of sediment cores show an increased North-South gradient during glacial times. The PIs will use the Mg/Ca temperature proxy to determine if this corresponds to an increase in the North-South gradient in sea surface temperature. This data will be used to better understand how Tropical Pacific atmospheric and ocean circulation responded to glacial boundary conditions will aid in the understanding of the mechanisms for climate change in the tropics.The research team will make the data available to the climate modeling community, and the age model information and the inferences about the physical circulation generated as part of this project will serve as a useful base for other investigations using this set of sediment cores. Funding also supports education and mentoring of members of groups that are under-represented in science.