A 170-year Sr/Ca and Ba/Ca coral record from the western Pacific warm pool: 1. What can we learn from an unusual coral record?

A long-lived Porites coral from New Ireland (2.5°S, 150.5°E), Papua New Guinea, has been analyzed for Sr/Ca and Ba/Ca by laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS). The top 50 years of the core are examined here and compared with instrumental sea surface temperatures (SSTs). For the small range of SST in the warm pool, Sr/Ca shows an unusually large response. The best estimate for the slope of a temperature calibration is -0.23 ± 0.03 mmol/mol per°C. This strong slope is partly a result of the high-resolution sampling, but is also due to additional biological mediation of the Sr /Ca ratios, which appears to be associated with seasonal changes of calcification rate, and limits the prediction skills of this proxy thermometer. High-density bands synchronous with high Sr/Ca ratios suggest that calcification may be enhanced by beneficial small amounts of nutrients available during El Niño. Transient Ba enrichment, synchronous with colder than average SST, is also observed during El Niño and attributed to the shoaling of the New Ireland Coastal Undercurrent. The high level of enrichment, in particular during upwelling triggered by westerly wind bursts, suggests an origin from both dissolved seawater and marine biological barium.