Carbon and oxygen isotopic composition of a Guam coral and their relationships to environmental variables in the western Pacific

We examine the high-resolution (∼32 samples/year) carbon and oxygen isotopic composition (δ13Ccoral and δ18Ocoral) in a coral core (Porites lobata) from Double Reef, Guam over the years 1980–2000. The δ13Ccoral shows clear seasonal variations with mean seasonal amplitude of 1.89‰, which roughly corresponds with seasonal variations in solar radiation. The seasonal amplitude of δ18Ocoral variations are small (0.23–0.57‰), but they are significantly correlated with sea surface temperature (SST) and salinity (SSS). The δ18Ocoral and SST are more strongly correlated during El Niño/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 δ18O (δ18Osw) during ENSO warm phases (<27 °C and higher values of δ18Osw) compared with cool phases (>28 °C and lower values of δ18Osw) 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 δ18Osw, inferred from the δ18Ocoral and instrumental SST, are consistent with SSS anomalies for the years 1980–2000. These δ18Osw 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.