NOAA/WDS Paleoclimatology - Makassar Strait - Single specimens of P. obliquiloculata d18O and d13C from 704-1851 AD

We present a reconstruction of El Nino Southern Oscillation (ENSO) variability spanning the Medieval Climate Anomaly (MCA, A.D. 800-1300) and the Little Ice Age (LIA, A.D. 1500-1850). Changes in ENSO are estimated by comparing the spread and symmetry of d18O values of individual speciments of the thermocline-dwelling foraminifer Pulleniatina obliquiloculata extracted from discrete time horizons of a sediment core collected in the Sulawesi Sea, at the edge of the western tropical Pacific warm pool. The spread of individual d18O values is interpreted to be a measure of the strength of both phases of ENSO while the symmetry of the d18O distributions is used to evaluate the relative strength/frequency of El Nino and La Nina events. In contrast to previous studies, we use robust and resistant statistics to quantify the spread and symmetry of the d18O distributions; an approach motivated by the relatively small sample size and the presence of outliers. Furthermore, we use a pseudo-proxy to investigate the effects of the different paleo-environmental factors on the statistics of the d18O distributions, which could bias the paleo-ENSO reconstruction. We find no systematic difference in the magnitude/strength of ENSO during the Nothern Hemisphere MCA or LIA. However, our results suggest that ENSO during the MCA was kewed toward stronger/more frequent La Nina than El Nino, an observation consistent with the medieval megadroughts documented from sites in western North America.