Decadal Variations in Western Pacific Warm Pool Dynamics as Evidenced by Porites Corals from Chuuk Atoll, Federated States of Micronesia
Friday, 19 December 2014
The Western Pacific Warm Pool (WPWP) encompasses some of the warmest sea surface temperatures (SSTs) of the world oceans. This region influences seasonal and decadal variability of the Intertropical Convergence Zone (ITCZ) and climate anomalies such as the El Niño-Southern Oscillation (ENSO). Long-term changes coupled with anomalous events like El Niño can greatly influence the position of the ITCZ and subsequently alter weather patterns on a global scale. WPWP dynamics may have contributed to the slowdown in global warming during the last decade. The processes that control these variations are complex, and gaining insight into these systems on decadal to centennial timescales is necessary to improve climate modeling and future predictions for drought or floods associated with global climate change. Chuuk Atoll (7°N, 152°E), located in the Federated States of Micronesia, is positioned within the WPWP at the northern extent of the mean boreal summer position of the ITCZ, making this location optimal for studying WPWP dynamics and ocean-atmosphere linkages. Two coral cores from the species Porites lobata were collected from the outer-atoll at Fannuk Island and the inner-atoll at Lobata Reef. Using stable isotope (δ18O and δ13C) composition and Sr/Ca trace metal analysis, the sites were identified as distinct hydrologic environments. Low seasonal variability in δ18O and Sr/Ca values at the outer-atoll site indicates a hydrologically-open system that is strongly influenced by the WPWP. At the inner-atoll site, δ18O and Sr/Ca values reflect a small seasonal SST cycle. In this hydrologically-restricted basin, the δ18O record is likely responding to salinity variations influenced by local climatology, specifically anomalously high or low precipitation events associated with ENSO. The average δ18O between 2003-2011 was 0.5‰ lighter at the inner-atoll site. These values can be interpreted as warmer sea surface temperatures and/or lower sea surface salinities, suggesting the inner-atoll coral is more sensitive to seasonal temperature and salinity variations. Comparison of these distinct proxy records could afford some new insights into overall trends and decadal variations in the ocean-atmosphere coupling in the WPWP.