NOAA/WDS Paleoclimatology - King Reef, Great Barrier Reef, Porites spp. trace elements ~4665 yBP and 1989-2006 CE

We present measurements of Sr/Ca, d18O, and spectral luminescence ratios (G/B) from a mid-Holocene Porites sp. microatoll recovered from the nearshore Great Barrier Reef (GBR). These records were used as proxies to reconstruct sea surface temperature (SST), the d18O of surrounding seawater (d18O(sw)), and riverine influence, respectively, and compared with records from a modern Porites sp. microatoll growing in the same environment. Strong riverine influence in the mid-Holocene record is indicated by (1) an increased annual d18O(sw) range in the mid-Holocene record, (2) negative peaks in d18O characteristic of flood events, and (3) a higher G/B luminescence ratio. Seasonal cycles in G/B suggest that humic acid inputs were elevated for a longer portion of the year during the mid-Holocene. The seasonal cycle of d18O(sw) peaked earlier in the year in the mid-Holocene record relative to the modern, while mean d18O(sw) values from the mid-Holocene record were similar to modern values. These records provide an insight into the oceanographic conditions the nearshore GBR experienced during mid-Holocene climatic shifts and are consistent with a strong Australian-Indonesian Summer Monsoon (AISM) system at similar to 4700 cal. yr BP.