NOAA/WDS Paleoclimatology - Indo-Pacific Warm Pool Mid-Holocene Coral Sr/Ca SST Reconstructions

STUDY NOTES: Mid-Holocene sea surface temperature reconstructions for the Indo-Pacific Warm Pool region based on fossil coral Sr/Ca ratios. All coral ages are given in years before present (yBP) notation, where present is 1950 AD. Modern coral ages are absolute, based on drilling date and comparison with instrumental records, and are expressed in years before present notation for consistency with the fossil coral data. Fossil coral age determinations were made using calibrated radiocarbon measurements (2s age range) for the Mentawai corals and U/Th measurements for the Muschu/Koil corals (±2s error). 2 standard error on mean Sr/Ca determinations are derived from the average of yearly or composite resolution Sr/Ca measurements, or of the average of triplicate Sr/Ca measurements of bulk coral powders. The mean Sr/Ca values were converted to SST anomalies relative to the mean Sr/Ca value obtained from the modern corals for each locality using a mean Sr/Ca-SST dependence of -0.061 mmol mol-1 °C-1 (Abram et al. 2007, Correge et al. 2006). The error on the reconstructed SST anomaly is a combined error based on the standard error on the mean fossil Sr/Ca determinations and the standard deviation around the reconstruction of modern SST from the modern coral samples at each locality.
ABSTRACT SUPPLIED BY ORIGINATOR: The Indo-Pacific Warm Pool (IPWP) is thought to play a key role in the propagation and amplification of climate changes through its influence on the global distribution of heat and water vapour. However, little is known about past changes in the size and position of the IPWP. In this study, we use a total of 48 modern and fossil coral records from the Mentawai Islands (Sumatra, Indonesia) and Muschu/Koil Islands (Papua New Guinea) to reconstruct oscillations in the extent of the IPWP since the mid-Holocene. We show that reliable estimates of mean sea surface temperature (SST) can be obtained from fossil corals by using low-resolution Sr/Ca analysis of a suite of corals to overcome the large uncertainties associated with mean Sr/Ca-SST estimates from individual coral colonies. The coral records indicate that the southeastern and southwestern margins of the IPWP were cooler than at present between ~5500 and 4300 years BP (~1.2°C ± 0.3°C) and were similarly cool before ~6800 years BP. This mid-Holocene cooling was punctuated by an abrupt, short-lived shift to mean SSTs that were warmer than at present between ~6600 and 6300 years BP (~1.3°C ± 0.3°C), while similarly warm conditions may have also existed after ~4300 years BP. We suggest that mid-Holocene cooling at our study sites was related to contractions of the southeastern and southwestern margins of the IPWP, associated with the more northerly position of the Inter-tropical Convergence Zone (ITCZ) that accompanied mid-Holocene strengthening of the Asian summer monsoon. Conversely, intervals of abrupt warming appear to correspond with widespread episodes of monsoon weakening and accompanying southward migrations of the ITCZ that caused the IPWP to expand beyond our coral sites. Intervals of a strengthened Asian monsoon and cooling in the southwestern IPWP during the mid-Holocene appear to correspond with a more positive Indian Ocean Dipole (IOD)-like mean configuration across the tropical Indian Ocean, suggesting that the Asian monsoon-IOD interaction that exists at interannual time scales also persists over centennial to millennial scales. Associated mean changes in the Pacific ENSO modes may have also occurred during the mid-Holocene. The dynamic and inter-connected behaviour of the IPWP with tropical climate systems during the mid-Holocene highlights the fundamental importance of the warm pool region for understanding climate change throughout the tropics and beyond.