A Coral-based Climate Record from the Western Pacific Warm Pool

The Western Pacific Warm Pool (WPWP) serves as a heat engine for Earth's climate and as a major moisture source for its hydrological cycle. Thermal and hydrologic variations in the WPWP are intimately involved with ENSO variations on the interannual timescale, but the role of these variations on decadal to century timescales remains poorly understood because of the paucity of subannually resolved climate and paleoclimate time series from the WPWP. Coral-based proxy records of thermal and hydrologic variations in the WPWP offer a great opportunity to extend the instrumental record and address the modes and mechanisms of tropical climate variability on decadal to century timescales. Coral-based climate records have been exploited in other regions of the tropical oceans, yet such records are rare from the WPWP. Herein we report the initial results of a stable isotopic and elemental ratio study of a ~1.8 m Porites coral head recovered in ~ 8 m of water from offshore of Rabaul, East New Britain, Papua New Guinea (4°S, 152°E) in September, 1998. Rabaul is a site of active volcanism and has had major eruptive episodes in 1998, 1994, 1943-1937, 1878, 1791 and 1767. Rabaul is located within the 29°C contour of mean annual SST field of the WPWP and seawaters surrounding it experience <1°C seasonal range in SST. In contrast, there is a 1 psu seasonal range in SSS. Average annual rainfall exceeds 2 m per year. X-radiography reveals readily discernable growth bands and we estimate an average extension rate of 10 mm/yr. The coral slab was sampled every 0.625 mm yielding an average sample resolution of 16 samples per year. Coral powder was divided into two samples: one for oxygen and carbon isotopic determinations and one for Sr/Ca ratio determinations. Our initial stable isotope results indicate the existence of a robust annual cycle in addition to large isotopic excursions in 1994, likely the result of the large volcanic event of that year. Stable isotope data acquisition continues and Sr/Ca ratio determinations have just begun. Our goal is to develop a record of the oxygen isotopic and Sr/Ca ratio variations from our coral sample to constrain the history of thermal and hydrologic variations in the WPWP over the past two centuries.