Corals at their latitudinal limits: Laser ablation trace element systematics in Porites from Shirigai Bay, Japan

The rapid analytical technique of laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to measure the trace elements B, Mg, Sr, Ba and U in a high-latitude coral colony (Porites lobata) taken from Shirigai Bay, Japan (32°N). A wide range of sea surface temperatures (SSTs 14.5-28°C) and upwelling events influenced this coral. Cold winter SSTs caused a decrease and/or cessation of skeletal extension. Measurements of U/Ca and Sr/Ca indicate an approximately linear response to SSTs above 18°C and a non-linear response below 18°C. Mg/Ca and B/Ca measurements both showed annual cycles broadly consistent with SST variations, but also exhibited intra-annual fluctuations not associated with temperature, suggesting that the incorporation of Mg and B into the coral skeleton was not simply regulated by temperature. It is shown that Ba/Ca ratios provide a proxy for wind-induced seasonal upwelling. This is inferred from the strong correlations between the strength of zonal winds ~1 month prior to the SST minimum and the Ba/Ca maximum. Secondary upwelling events occurred during the summers of 1982, 1987, 1991 and 1992. These summers were cooler than average and were associated with El Nino Southern Oscillation events.