High resolution windows into early Holocene climate: Sr/Ca coral records from the Huon Peninsula

High-precision measurements of Sr/Ca ratios are reported for Porites corals from the uplifted Holocene coral terraces at Huon Peninsula, Papua New Guinea. The early Holocene Porites have U-Th mass spectrometric ages of 8920 +/- 60 yr and 7370 +/- 50 yr, and delta(234)U(t) values of 145 +/- 2, similar to modem seawater. The Sr/Ca coral records provide 5-6 year high resolution (near weekly) time windows into early Holocene sea surface temperatures. Seasonal temperature fluctuations are generally in the range of +/- 1 degrees C, with occasional excursions of +/- 2 degrees C, which may indicate the more frequent recurrence of very strong ENSO (El Nino-Southern Oscillation) events. Mean annual Sr/Ca temperatures of 24.2 +/- 1.1 degrees C and 22.9 +/- 0.8 degrees C have been obtained, which are similar to 2-3 degrees C cooler than that exhibited by a modern Porites, These results indicate that, during the early Holocene, the equatorial western Pacific ocean was at least several degrees cooler than present-day temperatures. This is consistent with late glacial coral records from the Caribbean that indicate lower (similar to 6 degrees C) sea surface temperatures for the equatorial oceans. The Huon Peninsula corals also indicate that SSTs were several degrees cooler than those in the Caribbean during the early Holocene. Thus, although the northern hemisphere summer radiation maximum occurred at similar to 10 ka, there appears to have been a significant lag in the response of the equatorial western Pacific ocean to this warming. Cooler early Holocene sea surface temperatures in the western Pacific may have been due to changing patterns of ocean-atmosphere circulation, resulting from the exposure of large areas of continental shelf in the southeast Asia region, a consequence of lower glacial sea levels. It is likely that ocean temperatures in the Huon Peninsula were influenced by the opening at similar to 7 ka of the Torres Strait, that now separates New Guinea from the Australian mainland.