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Reconstructing natural modes of Pacific climate variability by geochemical analysis of ocean sediment off Baja California, Mexico


The Pacific Ocean plays a key role in controlling natural periodic changes in regional and global climate. Physical couplings between the oceanic and the atmospheric systems result in variations in local sea surface temperature (SST), coastal marine productivity, and global heat distribution. The El Niño Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO) are two of these forms of physical coupling variability, or modes, that have significant climatic effects on interannual and decadal timescales, respectively. In order to understand how these phenomena have changed over Earth's history, we must supplement and extend the modern record of SST back in time using paleotemperature proxies. In this study, we analyzed organic compounds called alkenones produced by Emiliania huxleyi, a type of marine algae. The ratio of alkenones produced that contain two double bonds to those that contain three double bonds has been shown to correlate linearly with the algal growth temperature. When these algae die, they sink to the bottom and the alkenones are preserved in in the sediment. Using sediment cored off the coast of Baja California, Mexico, an area that has been shown to be strongly influenced by both ENSO and PDO, and we performed chemical analysis by gas chromatography in order to quantify the alkenone ratio and establish an SST record for this region. Additionally, we used the total amount of alkenones as a proxy for regional productivity. Our inferred record is consistent with the historical record for the region and demonstrates the influence ENSO and PDO have on the coastal SST and productivity. These results give us confidence in the use of this method to sample deeper, pushing further back in time beyond the limits of historical data to establish a long-term paleoclimate record for the region, which could elucidate how ENSO and PDO have varied in the past under various global climatic conditions, century to century.


O'Mara, Nicholas, "Reconstructing natural modes of Pacific climate variability by geochemical analysis of ocean sediment off Baja California, Mexico" (2015). Summer Research Symposium. Brown Digital Repository. Brown University Library.



  • Summer Research Symposium

    Each year, Brown University showcases the research of its undergraduates at the Summer Research Symposium. More than half of the student-researchers are UTRA recipients, while others receive funding from a variety of Brown-administered and national programs and fellowships and go …