NOAA/WDS Paleoclimatology - Double Reef - Stable Isotope Data

We examine the high-resolution (~32 samples/year) carbon and oxygen isotopic composition (d13Ccoral and d18Ocoral) in a coral core (Porites lobata) from Double Reef, Guam over the years 1980-2000. The d13Ccoral shows clear seasonal variations with mean seasonal amplitude of 1.89 per mil, which roughly corresponds with seasonal variations in solar radiation. The seasonal amplitude of d18Ocoral variations are small (0.23-0.57 per mil), but they are significantly correlated with sea surface temperature (SST) and salinity (SSS). The d18Ocoral and SST are more strongly correlated during El Niņo/Southern Oscillation (ENSO) warm phases (r=-0.81, p<0.01) than during non-ENSO phases (r=-0.65, p<0.01) and ENSO cool phases (r=-0.48, p<0.01). These different relationships are due to differences in winter SST and in seawater d18O (d18Osw) during ENSO warm phases (<27 °C and higher values of d18Osw) compared with cool phases (>28 °C and lower values of d18Osw) at Guam. These differences in oceanic parameters result from movements of the Western Pacific Warm Pool (WPWP) during the different phases of ENSO. Anomalies in d18Osw, inferred from the d18Ocoral and instrumental SST, are consistent with SSS anomalies for the years 1980-2000. These d18Osw anomalies may reflect changes in SSS and evaporation-precipitation due to movements of the WPWP. This detailed analysis of a coral from Guam suggests that it may contain an excellent archive of past ENSO events.