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 degrees N). A wide range of sea surface temperature s (SSTs 14.5-28 degrees C) and upwelling events influenced this coral. Cold winter SSTs caused a decrease and/or cessation of skeletal extension. Meas urements of U/Ca and Sr/Ca indicate an approximately linear response to SST s above 18 degrees C and a non-linear response below 18 degrees C. Mg/Ca an d B/Ca measurements both showed annual cycles broadly consistent with SST v ariations, 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 ra tios provide a proxy for wind-induced seasonal upwelling. This is inferred from the strong correlations between the strength of zonal winds similar to 1 month prior to the SST minimum and the Ba/Ca maximum. Secondary upwellin g events occurred during the summers of 1982, 1987, 1991 and 1992. These su mmers were cooler than average and were associated with El Nino Southern Os cillation events. (C) 1999 Elsevier Science B.V. All rights reserved.