Reconstructing seawater δ18O from paired coral δ18O and Sr/Ca ratios: Methods, error analysis and problems, with examples from Tahiti (French Polynesia) and Timor (Indonesia)

Abstract

We compare several statistical routines that may be used to calculate d 18 O sw and SSS from paired coral Sr/Ca and d 18 O measurements. Typically, the d 18 O coral -SST relationship is estimated by linear regression of coral d 18 O vs. SST. If this method is applied, evidence should be given that at a particular site SST and SSS do not co-vary. In the tropical oceans, SST and d 18 O sw (SSS) often co-vary, and this will bias the estimate of the regression slope of d 18 O coral -SST. Using a stochastic model, we show that covariance leads to a bias in the coefficients of the univariate regression equations. As the slope of the d 18 O coral -SST relationship has known, we propose to insert this value for c 1 in the regression models. This requires that the constants of the regression equations are removed. To omit the constants, we propose to center the regression equations (i.e., to remove the mean values from the variables). The statistical error propagation is calculated to assess our ability to resolve past variations in d 18 O sw (SSS). At Tahiti, we find that the combined analytical uncertainties of coral d 18 O and Sr/Ca equal the amplitude of the seasonal cycle of d 18 O sw (SSS). Therefore, we cannot resolve the seasonal cycle of SSS at Tahiti. At Timor, the error of reconstructed d 18 O sw (SSS) is lower than the magnitude of seasonal variations of d 18 O sw (SSS), and the seasonal cycle of d 18 O sw (SSS) can be resolved.

Pronounced interannual variability in tropical South Pacific temperatures during Heinrich Stadial 1

“…1). Consequently, modern Tahiti coral Sr/Ca-based SST records 20 do not reveal significant variance at typical ENSO periods (Fig. 3b), in contrast to our HS1 coral Sr/Ca record.…”

“…S8). The two longer records of modern corals from the Teahupoo (TH1) and Vairao (TH2) lagoons in southeastern Tahiti 20 were used as a benchmark with respect to interannual variability.…”

“…This is not necessarily in conflict with the Sr/Ca results as δ 18 O reflects variations in both temperature and δ 18 O seawater , which is closely related to salinity. Modern coral δ 18 O records from the Tahiti region reveal significant variance at ENSO periods of 2-5 years, although the ENSO signal is not well pronounced 20,29 (Fig. 3e).…”

Reconstruction of Sea Surface Temperature Data based on the Sr/Ca of Porites Coral in Ambon Bay

“…The huge coral resources in Indonesia can be used to solve this problem. Besides the function of coral as a habitat for marine biota, coral also serves as natural recording medium for environmental parameters such as sea surface temperature (SST) [6][7][8][9] and sea surface salinity (SSS) [10][11][12]. These parameters are recorded by corals in the form of geochemical proxy.…”

Akurasi Rekonstruksi Suhu Permukaan Laut Dan 18o Air Laut (Salinitas) Untuk Interpretasi Iklim Masa Lampau Dari Karang Mati (Fosil)

“…Kandungan unsur geokimia dalam karang seperti Sr/Ca dan  18 O telah banyak digunakan untuk rekonstruksi suhu permukaan laut (SPL) (Cahyarini et al, 2009;Zinke et al,2004) dan rekonstruksi kandungan  18 O air laut (Cahyarini et al, 2008;Ren et al, 2002). Kandungan  18 O air laut ini selanjutnya dapat digunakan untuk merekonstruksi salinitas air laut.…”