Reconstructing ENSO in the Eastern Tropical Pacific from short-lived marine mollusks

The focus of much paleoclimate work on ENSO has been on records spanning multiple decades, such as those derived from corals. Such long records are, however, relatively rare, especially in the Eastern Tropical Pacific. This important limitation for studying past changes in the spatial pattern of ENSO activity can be compensated for by obtaining records from a larger number of shorterlived organisms. In this case, information about past climate is not available as a continuous record, but is compiled to extract climate statistics. Carré et al. (2013) recently presented a technique that responds to the critical need for quantitative estimates of tropical marine interannual variability. This technique uses the shells of marine mollusks that live for 1-4 years, and thus allow us to reconstruct the seasonal range of sea surface temperature (SST). These data can then be compared to coral records and GCM outputs. The technique of using marine mollusk shells shares similarities with the approach of coral studies in that it produces floating windows of climate record at a very high, often monthly, resolution. It also shares similarities with the approach of analyzing many foraminifera shells individually from the same sediment layer (Koutavas et al. 2006; Leduc et al. 2009) in that paleoclimate statistics are estimated from a random sample. Isotopic records in mollusks enable independent reconstructions of the seasonal cycle. This approach is valid for any coastal mollusk species that faithfully records at least one annual SST cycle, and therefore opens up new opportunities for direct, quantitative paleo-ENSO reconstructions in the Eastern Tropical Pacific, using either archeological shell middens or uplifted fossil shell banks from Peru.