AN ION PROBE STUDY OF ANNUAL CYCLES OF SR CA AND OTHER TRACE-ELEMENTSIN CORALS/

Corals show great promise for preserving century-long records of ocean chemistry and temperature with weekly time resolution. Allison and Tu dhope (1992) showed that direct microscale analysis of coral skeletons was possible with ion microprobe techniques. We show here that analys is of B, F, Mg, Sr, and Ba (relative to Ca) can be rapidly achieved on Porites skeleton at 50 mu m (sub-weekly) spatial scales with precisio ns of 0.3-3%. The B, F, and Mg concentrations show large well-behaved annual variations of 44-57%, well correlated with Sr/Ca variations of 12%, in the 1967-1969 bands from a live Porites from Two-Mile Reef, So uth Africa. The Sr/Ca ratio correlates well with the delta(18)O record but shows a larger annual temperature amplitude, with additional nume rous sub-weekly temperature spikes. Ba/Ca in recent bands of Porites s hows both a large (factor of 5) annual cycle and a large yearly spike in the late summer; the annual variation is not observed in 30-year-ol d bands, though the annual spikes are still sharp and clear. Barium th us appears to be unstable in Porites during aging and is probably not skeletally-bound. Deep-sea (nonzooxanthellate) corals show uncorrelate d variations of these same trace elements, with amplitudes similar to the Porites. These variations are likely biologically-mediated, as the thermal forcing function in the deep sea is nil. This suggests that t he annual variations seen in Porites may also be driven by vital effec ts and not directly by temperature. Ion microprobe techniques are show n to provide rapid, precise, and high-resolution trace-element records in corals. Full exploitation of trace element paleotemperature method s in corals will require a more sophisticated understanding of how cor als accrete their skeletal components. Ion probe analysis can contribu te significantly to this understanding.