Glacial-interglacial sea-surface temperature (SST) variability in the eastern tropical Pacific: spatial patterns from the late Pleistocene to present
Abstract
The equatorial Pacific is an important component of the modern climate system and is critical for understanding climatic and oceanographic changes on glacial-interglacial timescales. While many studies examine the vertical structure of temperature, the spatial variability of SST patterns in the tropical and subtropical Pacific also influence global climate variability. SSTs in the eastern tropical Pacific play a vital role in such climate oscillations as ENSO and the PDO. Iinsight into mechanisms that explain long-term changes in tropical Pacific climate requires and capitalizes on the many realizations of glacial-interglacial cycles preserved in deep-sea sediments. However, most studies are limited to the last 250 ky with the bulk of the research centered on the last glacial maximum. It is now feasible to generate longer records that can resolve many glacial-interglacial cycles. Yet only a handful of geochemical SST records longer than the last few glacial cycles exist for the tropical Pacific. We construct a long geochemical SST record from the Ecuador margin to test various ideas for the causes of tropical climate change (e.g. equatorial ocean currents). In the modern eastern equatorial Pacific, cool nutrient-rich water advects and forms a well-defined cold tongue. Additionally, strong equatorial easterlies drive divergence of surface waters causing cool, deeper water to upwell along the equator and intensify the cold tongue. During periods of strong atmospheric Walker (equatorial Pacific) circulation, the zonal surface temperature gradient is large, supporting a strong equatorial cold tongue. By creating new geochemical records and correlating a number of cores over glacial-interglacial timescales, we evaluate the spatial strength and extent of the equatorial cold tongue for multiple climate cycles through the late Pleistocene and Holocene. To determine past SST we measure the unsaturation index of long-chain lipid ketones (alkenones) found in organic-rich ocean sediments. Alkenones are produced by haptophyte algae, such as the coccolithophorid Emiliani huxleyi and quantified using the lipid unsaturation index (Uk’37). We compare existing Uk’37 records from the center of upwelling (using ODP Site 846) to a new alkenone-based SST record from ODP Site 1239 (120 km from the Ecuador margin) on the northeastern edge of upwelling. This continental margin site constrains the lateral extent of cold, nutrient-rich upwelling in the eastern equatorial Pacific. We develop a clear picture of spatial variability within the equatorial cold tongue on glacial-interglacial scales by comparing this new record to previously analyzed cores (Site 846, southwest of the Galápagos Islands). Specifically, we show the consistent 2°C temperature offset in Site 1239 represents a constant regional temperature gradient to at least MIS 11 (~450 kya).
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP13D1451D
- Keywords:
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- 4954 PALEOCEANOGRAPHY / Sea surface temperature