2:45 PM - 3:00 PM
[MIS16-04] Reconstruction of Past Hawaiian Sea Surface Temperature (SST) Using Modern Coral Skeletal Sr/Ca ratio: Decadal Response to Trade Winds
Keywords:coral, Hawaii, Sr/Ca ratio, SST, Trade winds
Fast-growing (1cm/year) reef corals provides high-resolution archives of changes in shallow marine environment. Geochemical proxies such as Sr/Ca ratio, have been used in tracking sea surface temperature (SST, ℃) for paleoclimate reconstructions in tropical regions (Beck et al., 1992; Gagan et al., 2000). Hawaiian Islands are located at the central region of North Pacific Ocean where distinct decadal to inter-decadal SST variability with limited influence from the continental/terrestrial factors (Mantua et al., 1997; Di Lorenzo et al., 2008). However, past climate reconstructions using Hawaiian coral skeletons are scarce, as well as only a few numbers of in-situ SST data exist. This study aims to fill the gap of decadal- to centennial-scale SST changes in north-central Pacific using coral geochemical approach.
Modern Porites sp. coral cores sampled at eastern and western side of Oahu Island, were used in this study. X-ray photo of the coral slabs were used to determine maximum growth axis as measurement line. Coral powders were obtained at 0.2mm intervals using a micro drill. Sr/Ca was analyzed using inductively coupled plasma optical emission spectrometer (ICP-OES). Age model for the Sr/Ca profile was made by anchoring the timing of maxima (minima) of Sr/Ca to the minima (maxima) of reference SST. For calibrating Sr/Ca for SST, skeletal Sr/Ca in eastern coral and satellite-based SST time series which was corrected by in-situ SST, were used. Applying the calibration result on Sr/Ca ratio in coral from eastern and western Oahu, long term SST records for each location were reconstructed and compared.
Sr/Ca ratio was highly correlated to reference SST, and the calibration result of coral Sr/Ca-SST from eastern Oahu coral was comparable to the previously reported values from other regions (Gagan, 2000; Swart, 2002; Corrège, 2006). The standard SST error (1σ) was <1°C, suggesting a reliable calibration of the high resolution (bi-weekly) Sr/Ca record. Applying the coral-based thermometry, SST variability was reconstructed from 1920s and 1950s in eastern and western Oahu respectively. Seasonal amplitude was subtracted to the reconstructed SST to show each long-term variability. The eastern and western Oahu SST records did not show covariance. Interestingly, the east-west SST difference during overlapping period showed decadal variability with an amplitude of approximately ±2℃, which could be correlated to northeastern winds intensity (m/s). The windward eastern (leeward western) SST were higher when northeastern winds were stronger (weaker). Based on the previous studies, the prevailing winds around the Hawaiian Islands is trade winds outflow from the northeastern subtropical high pressure (Sanderson et al., 1993; Garza et al., 2012), and the wind stress curl derived by the trade winds drives SST variation in the open ocean around the Hawaiian Islands (Xie et al., 2001). In this study, SST variabilities in the two different local coastal areas were reconstructed, which demonstrated ocean responses to the trade winds. The long term SST reconstruction, which predates observation records suggested that the decadal-scale changes of trade wind intensity controls local SST variabilities.
Modern Porites sp. coral cores sampled at eastern and western side of Oahu Island, were used in this study. X-ray photo of the coral slabs were used to determine maximum growth axis as measurement line. Coral powders were obtained at 0.2mm intervals using a micro drill. Sr/Ca was analyzed using inductively coupled plasma optical emission spectrometer (ICP-OES). Age model for the Sr/Ca profile was made by anchoring the timing of maxima (minima) of Sr/Ca to the minima (maxima) of reference SST. For calibrating Sr/Ca for SST, skeletal Sr/Ca in eastern coral and satellite-based SST time series which was corrected by in-situ SST, were used. Applying the calibration result on Sr/Ca ratio in coral from eastern and western Oahu, long term SST records for each location were reconstructed and compared.
Sr/Ca ratio was highly correlated to reference SST, and the calibration result of coral Sr/Ca-SST from eastern Oahu coral was comparable to the previously reported values from other regions (Gagan, 2000; Swart, 2002; Corrège, 2006). The standard SST error (1σ) was <1°C, suggesting a reliable calibration of the high resolution (bi-weekly) Sr/Ca record. Applying the coral-based thermometry, SST variability was reconstructed from 1920s and 1950s in eastern and western Oahu respectively. Seasonal amplitude was subtracted to the reconstructed SST to show each long-term variability. The eastern and western Oahu SST records did not show covariance. Interestingly, the east-west SST difference during overlapping period showed decadal variability with an amplitude of approximately ±2℃, which could be correlated to northeastern winds intensity (m/s). The windward eastern (leeward western) SST were higher when northeastern winds were stronger (weaker). Based on the previous studies, the prevailing winds around the Hawaiian Islands is trade winds outflow from the northeastern subtropical high pressure (Sanderson et al., 1993; Garza et al., 2012), and the wind stress curl derived by the trade winds drives SST variation in the open ocean around the Hawaiian Islands (Xie et al., 2001). In this study, SST variabilities in the two different local coastal areas were reconstructed, which demonstrated ocean responses to the trade winds. The long term SST reconstruction, which predates observation records suggested that the decadal-scale changes of trade wind intensity controls local SST variabilities.