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The calibration of D[Sr/Ca] versus sea-surface temperature relationship for
... Accordingly, there is the potential for these chemical records to fill knowledge gaps surrounding the palaeoenvironment and the complex ecology of marine organisms (Campana, 1999;Weber, 1973). The use of this method to do so has been successful (Beck et al., 1992;de Villiers et al., 1994;McCulloch et al., 1994;Shen et al., 1996). ...
... Strontium has been examined more extensively than barium in past literature (Thorrold et al., 1998). Specifically, the use of strontium as an environmental proxy for temperature (Beck et al., 1992;Coutant and Chen, 1993;de Villiers et al., 1994;Halden et al., 1995;Kalish, 1990;Limburg, 1995;Mazloumi et al., 2017;McCulloch et al., 1994;Otake and Uchida, 1998;Secor et al., 1995;Shen et al., 1996). Numerous studies have examined the relationship and use of otolith elemental Sr:Ca and Ba:Ca as an environmental proxy for both temperature and salinity. ...
... S.J. Morrissey, et al. Journal of Experimental Marine Biology and Ecology 527 (2020) 151375 negative relationships exist between Sr:Ca and temperature in the aragonite skeletons of corals (Alibert and McCulloch, 1997;Beck et al., 1992;de Villiers et al., 1994;McCulloch et al., 1994;Shen et al., 1996). These relationships, although inverse to the relationship presented in this study, highlight the potential use of these relationships between elemental chemistry and environmental variation. ...
... Discrepancies between these samples provide further evidence that the reliability of the Sr/Ca proxy may be sensitive to local environmental conditions. To the authors' knowledge, there have been only two studies (Shen et al., 1996;Swart, Elderfield, and Greaves, 2002) that obtained in situ time-series measurements of seawater Sr/Ca around corals sampled for Sr/Ca SST proxy. ...
... Between September 2009 and December 2010, seawater Sr/Ca ratios ranged from a minimum of 8.90 to a maximum of 9.36 mmol/mol, with an average value of 9.06 mmol/mol (Table 2). Overall, Sr/Ca values from Apra Harbor are enriched by~0.5 mmol/mol relative to previously reported Sr/Ca values from the Pacific (de Villiers, Shen, and Nelson, 1994;Shen et al., 1996). The time series for each cation concentration (Table 2 and Figure 5a) shows it to be essentially uniform and stable over the study period. ...
... For the reconstruction of historical SST, these questions are important because the utility of the Sr/Ca-SST coral proxy is based on the assumption that seawater Sr is constant, primarily as a function of its long residence time (.4 Ma) relative to oceanic mixing (10 3 y; Broecker 1963) and its conservative nature (e.g., homogeneous distribution spatially). However, the fidelity of the coral-derived Sr/Ca thermometry can be compromised by several factors, including variable calcification and extension rates (e.g., Cohen et al., 2004;de Villiers, Shen, and Nelson, 1994), variability in seawater Sr/Ca composition (e.g., de Villiers 1999;Shen et al., 1996;Sun et al., 2005), and interspecies differences (see DeLong et al., 2011) that can influence the Sr/Ca-SST calibration. In some cases, these factors can be addressed by accounting for growth rate (e.g., Goodkin, Hughen, and Cohen, 2007;Saenger et al., 2008), employing microsampling (see summary by Jones et al., 2009) and avoiding sampling sites sensitive to riverine or submarine ground discharge that can alter the seawater composition (DeLong et al., 2011(DeLong et al., , 2014Flannery and Poore, 2013;Maupin, Quinn, and Halley, 2008). ...
Located on the northern edge of the West Pacific Warm Pool and having a developed economy and modern infrastructure, Guam is well positioned and equipped for obtaining natural records of the west Pacific maritime paleoclimate. This study was a proof of concept to explore whether useful climate proxy records might be obtained from coral at readily accessible, even if geochemically nonoptimal, coastal sites. A 50-year Sr/Ca record (1960-2010) was thus obtained from a shallow-water, near-shore Porites lutea colony at a recreational facility inside Guam's Apra Harbor and compared with local and regional meteorological records, including the El NiñoNi˜Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) indices. The accessibility of the site enabled documentation of relevant environmental variables for): seawater d 18 O, pH, seawater cations, and nitrate. Time series of seawater d 18 O, pH, and cations show evidence of freshwater input from direct rainfall and stream discharge into the harbor. An anomalously higher mean and variable concentrations of Ba suggest the presence of river-borne, fine-grained terrigenous sediment. Nevertheless, the Sr/Ca time series reproduces a long-term warming trend seen in historical records of local air temperature and regional sea-surface temperature (SST) and closely tracks the ENSO and PDO indices over the entire 50-year record. The consistency of the results with Guam's historical instrumental records, previous coral d 18 O results from Guam obtained by others, and previous Sr/Ca proxy results for SST in similar environments elsewhere demonstrate that accessible near-shore sites-where environmental conditions can be monitored-can produce useful Sr/Ca records of local and regional climate phenomena.
... Discrepancies between these samples provide further evidence that the reliability of the Sr/Ca proxy may be sensitive to local environmental conditions. To the authors' knowledge, there have been only two studies (Shen et al., 1996;Swart, Elderfield, and Greaves, 2002) that obtained in situ time-series measurements of seawater Sr/Ca around corals sampled for Sr/Ca SST proxy. ...
... Between September 2009 and December 2010, seawater Sr/Ca ratios ranged from a minimum of 8.90 to a maximum of 9.36 mmol/mol, with an average value of 9.06 mmol/mol (Table 2). Overall, Sr/Ca values from Apra Harbor are enriched by~0.5 mmol/mol relative to previously reported Sr/Ca values from the Pacific (de Villiers, Shen, and Nelson, 1994;Shen et al., 1996). The time series for each cation concentration (Table 2 and Figure 5a) shows it to be essentially uniform and stable over the study period. ...
... For the reconstruction of historical SST, these questions are important because the utility of the Sr/Ca-SST coral proxy is based on the assumption that seawater Sr is constant, primarily as a function of its long residence time (.4 Ma) relative to oceanic mixing (10 3 y; Broecker 1963) and its conservative nature (e.g., homogeneous distribution spatially). However, the fidelity of the coral-derived Sr/Ca thermometry can be compromised by several factors, including variable calcification and extension rates (e.g., Cohen et al., 2004;de Villiers, Shen, and Nelson, 1994), variability in seawater Sr/Ca composition (e.g., de Villiers 1999;Shen et al., 1996;Sun et al., 2005), and interspecies differences (see DeLong et al., 2011) that can influence the Sr/Ca-SST calibration. In some cases, these factors can be addressed by accounting for growth rate (e.g., Goodkin, Hughen, and Cohen, 2007;Saenger et al., 2008), employing microsampling (see summary by Jones et al., 2009) and avoiding sampling sites sensitive to riverine or submarine ground discharge that can alter the seawater composition (DeLong et al., 2011(DeLong et al., , 2014Flannery and Poore, 2013;Maupin, Quinn, and Halley, 2008). ...
Located on the northern edge of the West Pacific Warm Pool and having a developed economy and modern infrastructure, Guam is well positioned and equipped for obtaining natural records of the west Pacific maritime paleoclimate. This study was a proof of concept to explore whether useful climate proxy records might be obtained from coral at readily accessible, even if geochemically nonoptimal, coastal sites. A 50-year Sr/Ca record (1960-2010) was thus obtained from a shallow-water, near-shore Porites lutea colony at a recreational facility inside Guam's Apra Harbor and compared with local and regional meteorological records, including the El Niño-Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) indices. The accessibility of the site enabled documentation of relevant environmental variables for 16 months (September 2009-December 2010): seawater λ ¹⁸ O, pH, seawater cations, and nitrate. Time series of seawater λ ¹⁸ O, pH, and cations show evidence of freshwater input from direct rainfall and stream discharge into the harbor. An anomalously higher mean and variable concentrations of Ba suggest the presence of river-borne, fine-grained terrigenous sediment. Nevertheless, the Sr/Ca time series reproduces a long-term warming trend seen in historical records of local air temperature and regional sea-surface temperature (SST) and closely tracks the ENSO and PDO indices over the entire 50-year record. The consistency of the results with Guam's historical instrumental records, previous coral λ ¹⁸ O results from Guam obtained by others, and previous Sr/Ca proxy results for SST in similar environments elsewhere demonstrate that accessible near-shore sites - where environmental conditions can be monitored - can produce useful Sr/Ca records of local and regional climate phenomena.
... A few key genera of reef-building corals are used in most paleoclimate studies to reconstruct tropical climate Saenger et al., 2008]. Porites is the genus most commonly used in the Pacific [e.g., Gagan et al., 2012;McGregor and Gagan, 2003;Shen et al., 1996]. In the Atlantic region, Montastrea is the genus most successfully used in paleoclimate studies Saenger et al., 2008;Watanabe et al., 2002]. ...
... Many previous calibration studies Shen et al., 1996] have defined the slope using single coral colonies, but Goodkin et al. [2007] pointed out that multi-colony calibrations are inherently more accurate for paleoclimate reconstructions than those that use individual coral specimens selected from a random population of a particular species. In this study, I develop calibration slopes from multiple modern corals to provide a more robust relationship for this species. ...
... These data include a signal from the seasonal cycle ( Figure 15) and interannual variability in the anomalies from the seasonal cycle ( Figure 16) Although many studies have demonstrated the consistency of Sr/Ca ratios among coral colonies Stephans et al., 2004], there is some evidence that different coral colonies growing near each other can have colony-specific offsets in mean Sr/Ca ratios [de Villiers et al., 1994]. Potential factors that might cause such offsets include species effects, growth rate differences, water depth differences and seawater Sr/Ca differences [Goodkin et al., 2005;Pfeiffer et al., 2008;Shen et al., 1996]. Mean Sr/Ca ratio offsets in the corals from this study cannot be explained by species effects because all the samples are the same species. ...
Tropical sea surface temperature (SST) has been implicated as a driver of climate changes during the Medieval Climate Anomaly (MCA, 950-1300 CE) but little data exist from the tropical oceans for this time period. I collected multiple Diploria strigosa coral colonies from Anegada, British Virgin Islands (18.73°N, 63.33°W) in order to reconstruct climate in the northeastern Caribbean and tropical North Atlantic during the MCA. My Sr/Ca-temperature calibration results derived from three modern Diploria strigosa corals suggest that the temperature sensitivity for Diploria strigosa is -0.048 (±0.001) mmol/mol°C-1. My reconstruction of MCA climate suggests cooler and wetter conditions in the northeastern Caribbean during the late MCA, indicating that a Pacific La Niña-type climate pattern may have influenced local conditions. Additional analysis indicates that the North Atlantic Oscillation (NAO) was the principal driver of interannual climate variability during the late MCA.
... The linear regression equations for the coral proxies and SST are shown in Table 2. The regression indicates a Sr/Ca/SST calibration slope ranging from − 0.0650 to − 0.0465 mmol/mol • C − 1 , which is very close to the values of other SCS corals (e.g., − 0.06 to − 0.04 mmol/mol • C − 1 , Shen et al., 1996;Yu et al., 2005;Bolton et al., 2014;Krawczyk et al., 2020;Zhou et al., 2021). It is worth noting that the reported slope of coral δ 18 O/SST ranges from − 0.18 to − 0.12‰/ • C in the SCS (e.g., Shen et al., 1996;He et al., 2002;Shen et al., 2005;Yu et al., 2005;Su et al., 2006;Bolton et al., 2014) is far lower than the mean value (~0.22‰/ • C) in other sea areas of the Pacific Ocean (e.g., Epstein et al., 1953;Fairbanks and Dodge, 1979;Weber and Woodhead, 1972). ...
... The regression indicates a Sr/Ca/SST calibration slope ranging from − 0.0650 to − 0.0465 mmol/mol • C − 1 , which is very close to the values of other SCS corals (e.g., − 0.06 to − 0.04 mmol/mol • C − 1 , Shen et al., 1996;Yu et al., 2005;Bolton et al., 2014;Krawczyk et al., 2020;Zhou et al., 2021). It is worth noting that the reported slope of coral δ 18 O/SST ranges from − 0.18 to − 0.12‰/ • C in the SCS (e.g., Shen et al., 1996;He et al., 2002;Shen et al., 2005;Yu et al., 2005;Su et al., 2006;Bolton et al., 2014) is far lower than the mean value (~0.22‰/ • C) in other sea areas of the Pacific Ocean (e.g., Epstein et al., 1953;Fairbanks and Dodge, 1979;Weber and Woodhead, 1972). The slope value of δ 18 O/SST in this study, between − 0.1527 and − 0.1332‰/ • C, is within the range of previous relationships derived for SCS corals. ...
The Indo-western Pacific Ocean capacitor (IPOC) effect induces coherent climate variations over the Indo-western Pacific Ocean with significant sea-surface temperature (SST) anomalies over the South China Sea (SCS). Most IPOC events are related to El Niño-Southern Oscillation (ENSO), occurring in the post-ENSO years. The coral δ¹⁸O and Sr/Ca precisely recorded climate variations as proxies for SST. This study investigated the IPOC via a reduced major axis (RMA) regression analysis based on coral records in the SCS. The coral records of Yongxing Island show a double SST peak during El Niño events after the 1960s, one in the mature phase and the other in the post-El Niño summer. Tropical Indian Ocean warming persists into summer and anchors an anomalous anticyclonic circulation over the western North Pacific, extending the ENSO effect on the SCS SST through the IPOC effect, despite the decay of El Niño. The corals from Yongle Atoll, Dongsha Atoll, and the region off central Vietnam well recorded the IPOC impacts associated with two strong El Niño events (2009–2010 and 1997–1998) on SST anomalies in summer. According to coral records off central Vietnam, the 1959 IPOC effect occurred without an antecedent El Niño event. The results show that coral proxies could capture the IPOC events in the SCS and prove that IPOC could act as an intrinsic climate mode in the Indo-western Pacific Ocean.
... are common in the Indo-Pacific and known for preserving reliable paleoclimate information. Although some factors (e.g., changes in coral vital effects or Sr/Ca of sea water) have been identified as possible sources of non-temperature influences on the coral Sr/Ca paleothermometer (e.g., (de Villiers et al., 1995;Shen et al., 1996;de Villiers, 1999;Cohen et al., 2001;Cohen et al., 2002;Allison and Finch, 2004;Alibert and Kinsley, 2008;Grove et al., 2013;Alpert et al., 2016;Kuffner et al., 2017), many studies have shown success in accurately reconstructing SST from coral Sr/Ca (McCulloch et al., 1994;Marshall and McCulloch, 2001;Goodkin et al., 2005;DeLong et al., 2007;Goodkin et al., 2007;Cahyarini et al., 2009;Pfeiffer et al., 2009;DeLong et al., 2011;DeLong et al., 2013;Wu et al., 2013;Bolton et al., 2014;Ramos et al., 2017;Pfeiffer et al., 2019). Also, a recent study investigating variability in Sr/Ca-SST calibrations across large SST gradients showed that the Sr/Ca-SST slopes do not change randomly but vary systematically with mean SST (Murty et al., 2018). ...
... We also observed weakened interannual Sr/Ca-SST correlations relative to monthly for KOS, which may be due to the greatly reduced range of SST variability, the influence of terrestrial area within a large 1° × 1° SST grid, or the impact of 'landmass' effects from Kosrae Island (Palacios, 2002;Elliott et al., 2012). Our multi-site study leaves room to speculate about spatiotemporal changes in seawater Sr/Ca ratios impacting mean Sr/Ca in corals (Shen et al., 1996;Sun et al., 2005). However, measurements of Sr/Ca in seawater within the WPWP are sparse, non-continuous, and distant from our study sites (de Villiers, 1999). ...
Constraining past variability in ocean conditions in the Western Pacific Warm Pool (WPWP) and examining how it has been influenced by the El-Niño Southern Oscillation (ENSO) is critical to predicting how these systems may change in the future. To characterize the spatiotemporal variability of the WPWP and ENSO during the past three decades, we analyzed climate proxies using coral cores sampled from Porites spp. from Kosrae Island (KOS) and Woleai Atoll (WOL) in the Federated States of Micronesia. Coral skeleton samples drilled along the major growth axis were analyzed for oxygen isotopes (δ18 Oc ) and trace element ratios (Sr/Ca), used to reconstruct sea surface salinity and temperature (SSS and SST). Pseudocoral δ18O time series (δ18 Opseudo ) were calculated from gridded instrumental observations and compared to δ18 Oc , followed by fine-tuning using coral Sr/Ca and gridded SST, to produce age models for each coral. The thermal component of δ18 Oc was removed using Sr/Ca for SST, to derive δ18O of seawater (δ18O sw ), a proxy for SSS. The Sr/Ca, and δ18 O sw records were compared to instrumental SST and SSS to test their fidelity as regional climate recorders. We found both sites display significant Sr/Ca-SST calibrations at monthly and interannual (dry season, wet season, mean annual) timescales. At each site, δ18Osw also exhibited significant calibrations to SSS across the same timescales. The difference between normalized dry season SST (Sr/Ca) anomalies from KOS and WOL generates a zonal SST gradient (KOSWOL SST), capturing the east-west WPWP migration observed during ENSO events. Similarly, the average of normalized dry season δ18Osw anomalies from both sites produces an SSS index (KOSWOL SSS) reflecting the regional hydrological changes. Both proxy indices, KOSWOL SST and KOSWOL SSS , are significantly correlated to regional ENSO indices. These calibration results highlight the potential for extending the climate record, revealing spatial hydrological gradients within the WPWP and ENSO variability back to the end of the Little Ice Age.
... Based on the annual density bandings on X-ray photographs, the growth rate of this coral is estimated to be 7e8 mm/year. Subsample cubes (1 Â 1 Â 1 mm 3 ), 7e8 per year, spanning from 2002 to 2005, were cut along the maximum growth axis of the coral slice using the micro-surgical subsampling technique (Shen et al., 1996). After crushing into powder, the subsamples were cleaned with 10% H 2 O 2 and ultrapure water in an ultrasonic bath. ...
... Coralline aragonite Sr/Ca is considered as a robust SST proxy (Shen et al., 1996). Coral trace elemental records are thus calendared by matching Sr/Ca maxima (Fig. 2C) to the instrumental SST minima and an assumed constant intraannual growth rate (Fig. 2D). ...
We present a monthly dataset (AD 2002–2005) of rare earth elements (REEs) recorded in Porites coral, which were obtained from the Weizhou Island (WZI), Beibu Gulf, northwest of South China Sea (SCS). This offshore coral shows a strong seasonal cycle in REE/Ca ratios, with enriched REEs (total REEs, 100~140 ppb) in winter and depleted REEs (40~60 ppb) in summer. Since the influence of the river discharge is limited to the river mouth, its contribution to the dissolved REEs is negligible for the offshore area of WZI. Given the similar seasonal pattern of Ba/Ca, we suggest that the remobilization of REEs from river-transported sediments on the shelf of SCS through winter monsoon-driven mixing is the major source of REEs to WZI. Moreover, the peak time of the Nd/Yb ratio (occurred in spring) is not coupled with the occurrence of the maximum REEs, which could mainly be attributed to the degradation of biogenic particles that causes more light REE released in comparison to heavy REE. The Ce anomaly also displays a distinct seasonality (i.e., enhanced anomaly in winter and summer and diminished anomaly in spring), likely reflecting the microbial oxidation activities driven by seasonal temperature and nutrient cycles. Large Gd anomaly (Gd/Gd* up to 1.7) recorded in coral skeletons is unlikely originated from the natural sources, but reflects anthropogenic activities through the recent excessive use of Gd complexes by magnetic resonance imaging of medical examination in this region. Keywords: Coral, Rare earth element, Winter monsoon, South China sea
... Cohen et al., 2001;Cohen & Hart, 2004;Ferrier-pagès et al., 2002;Goodkin et al., 2005;Kuffner et al., 2012;de Villiers et al., 1994de Villiers et al., , 1995Weber, 1973), although this is not always the case (e.g. Alibert 1997; Allison & Finch, 2004;Hayashi et al., 2013;Shen et al., 1996;Smith et al., 1979;Wei et al., 2000). ...
... To date, Sr/Ca has been the most widely used coral paleothermometer (e.g. Calvo et al., 2007;Corrège et al., 2000;Fallon et al., 1999Fallon et al., , 2003Gagan et al., 1998;Heiss et al., 1997; Linsley et al., 2000;Marshall & McCulloch, 2001;McCulloch, 1999;Mitsuguchi et al., 1996;von Reumont et al., 2018;Shen et al., 1996;Sinclair et al., 1998;Zinke et al., 2004). However, separating the effects of temperature from the influence of 'vital effects' on Sr/Ca has long proven difficult (Alibert & McCulloch, 1997;Corrège, 2006;de Villiers et al., 1995). ...
Coral skeletons are the most commonly used high‐resolution temperature proxy in the tropical oceans, providing paleoclimate reconstructions dating back centuries to millennia. However, physiological differences in skeletal formation modes together with artifacts arising from coral biomineralization (vital effects) can confound the temperature dependence of single element‐to‐calcium ratios. In efforts to reduce vital effects and isolate temperature, new approaches have been developed based on Sr‐U and Li/Mg, which combine Sr/Ca and U/Ca and Li/Ca and Mg/Ca, respectively. Here we examine the systematics of Sr/Ca, Sr‐U, and Li/Mg paleothermometry in 33 colonies of branching (Acropora, Pocillopora, and Stylophora) and foliose (Turbinaria) genera. To address the calibration of these morphologically complex calcifiers, we conducted repeat field trips every 1 to 3 months and collected the most recent (~1 month) uppermost growth of individual colonies over ~18‐ to 24‐month periods. This enables seasonally resolved calibration of genera that exhibit rapid extension and slower secondary calcification. Based on this experimental design, we show that all three proxies capture seasonal to annual temperature variations for their respective growth intervals, providing calibrations across an 11 °C range. Species effects on the temperature dependence were largest for Sr/Ca (22.7%) yet minor for Li/Mg (7.2%) and Sr‐U (6.3%). Residuals from proxy‐temperature regressions were correlated between Sr/Ca and Li/Mg, indicating similar biological processes may influence Sr/Ca and Li/Mg thermometry. The implications of this study are that Sr‐U and to a lesser extent Li/Mg are applicable to fossil branching coral skeletons identified to genus level without the need for modern‐day calibration. We further show that all three paleothermometers provide complementary temperature constraints, with Li/Mg and the more species‐dependent Sr/Ca showing greater effectiveness at resolving seasonal variability and Sr‐U showing greater reliability at capturing mean annual temperature.
... A chronology for coral geochemical records was established by assigning d 18 O coral maxima to SST minima in January (based on on-site SST data) [Shen et al., 1996;Chiang et al., 2010] for each annual cycle and then interpolating monthly intervals (12 points/yr) following the approach of Charles et al. [1997] and Al-Rousan et al. [2002]. We also followed previous studies [Felis et al., 2009;Yamazaki et al., 2016] to build 1 and 3 year running averaged records to suppress local intraannual variability of solar insolation and SST. ...
... A neg- ligible correlation (R 5 20.03) between precipitation and d 18 O coral is observed (supporting information Fig- ure S2). Hence, the d 18 O coral data pri- marily reflect seasonal SST changes of about 58C (IGOSS SST; Figure 2a Figure S1b), considered to be primarily controlled by SST [Shen et al., 1996;Yu et al., 2005;DeLong et al., 2007DeLong et al., , 2012, also supports this view. ...
The Kuroshio Current (KC), one of the most important western boundary currents in the North Pacific Ocean, strongly affects regional hydroclimate in East Asia and upper ocean thermal structure. Limited by few on-site observations, the responses of the KC to regional and remote climate forcings are still poorly understood. Here we use monthly coral δ¹⁸O data to reconstruct a KC transport record with annual to interannual resolution for the interval 1953–2004. The field site is located in southern Taiwan on the western flank of the upstream KC. Increased (reduced) KC transport would generate strong (weak) upwelling, resulting in relatively high (low) local coral δ¹⁸O. The upstream KC transport and downstream transport, off Tatsukushi Bay, Japan, covary on interannual and decadal time scales. This suggests common forcings, such as meridional drift of the North Equatorial Current bifurcation, or zonal climatic oscillations in the Pacific. The intensities of KC transport off southeastern and northeastern Taiwan are in phase before 1990 and antiphase after 1990. This difference may be due to a poleward shift of the subtropical western boundary current as a response to global warming.
... The "sclerochronology" studies aim to characterize the isotopic and geochemical composition of the environment through the geochemical record in carbonate biogenic structures. The organisms with carbonate structures can present a wide range of growth rates and can register daily changes (induced by local environmental variations), seasonal (inter-monthly variations), annual and long-term environmental changes and climatic oscillations (Shen et al., 1996;Gillikin et al., 2005b;Schöne et al., 2005;. ...
The main aim of this work is to demonstrate that the Laser ablation multi-collector inductively coupled plasma mass spectrometry (LA-MC-ICP-MS) is a powerful tool for the analysis of strontium (Sr) isotopes in corals. This work discusses certification strategies for Sr isotopes determination, using reference material (RM) analyses and the results treatment based on detailed data acquired in biological materials, a coral sample. To obtain reliable results, it is essential to properly adjust the mass spectrometer and laser ablation system. Adjusting the equipment to its maximum intensity does not always result in correct 87Sr/86Sr ratios. Therefore, the optimization of the mass spectrometer was performed using the reference material NIST SRM-987 (solution) and adjusting the correct Sr isotope ratio to the reference material (USGS MACS3 and NIST-612, solids) before each analytical session. The protocol applied the solid reference material USGS MACS3 with an isotopic ratio 87Sr/86Sr of 0.72000. The values obtained for this RM varied between 0.7012 and 0.7014, with a correction factor calculated between 0.990 and 0.988. In order to account for potential drifts in the mass spectrometer during an analytical session, the application of bracketing correction and the use of the most convenient reference material are suggested. The analytical uncertainty of Sr data obtained by LA-MC-ICP-MS is comparable to studies carried out on other carbonate materials. The results of ablation techniques are reproducible within the analytical error, which implies that this technique produces robust results when applied to coral carbonates. In addition, several comparative measurements of different reference materials (e.g. USGS MACS3 and NIST 612) and the comparison of the 87Sr/86Sr ratios highlight the robustness of the method. The results along the coral growth axes showed a decrease in the 87Sr/86Sr ratio from the inner to the outer layer of the coral (from 0.70920 to 0.70627), which indicate variations in the availability of particulate matter during the coral growth, probably related to local marine environmental changes.
... While Sr/Ca ratios are mostly used to assess the shell preservation of fossil specimens (Brand and Veizer, 1980), this ratio also constitutes a potential marine paleothermometer applicable to brachiopod shells, as is the case for corals (McCulloch et al., 1994;Shen et al., 1996;Marshall and Mc-Culloch, 2002;Swart et al., 2002;Ayling et al., 2006;De-Long et al., 2011). Previous studies already suggested Sr/Ca ratios as marine paleothermometers for brachiopod shells owing to their correlations with oxygen isotope ratios and seawater temperature (Lowenstam, 1961;Mii and Grossman, 1994;Pérez-Huerta et al., 2008;Butler et al., 2015;Ullmann et al., 2017). ...
Most of our knowledge of past seawater temperature history is based on δ18O values of calcium carbonate fossil shells. However, the determination of past temperatures using this proxy requires the knowledge of past seawater δ18O values, which is generally poorly constrained. Other paleothermometers using carbonate archives, such as Mg/Ca ratios and clumped isotopes (Δ47), have been developed to allow for paleotemperatures to be estimated independently and to allow past ocean δ18O values to be calculated using various groups of calcifying organisms. Articulated brachiopod shells are some of the most commonly used archives in studies of past oceanic geochemistry and temperature. They are abundant in the fossil record since the Cambrian, and for decades, their low Mg–calcite mineralogy has been considered relatively resistant to diagenetic alteration. Here, we investigate the potential of brachiopod shells as recorders of seawater temperatures and seawater δ18O values using new brachiopod shell geochemical data by testing multiple well-established or suggested paleothermometers applied to carbonate archives.
Modern articulated brachiopod shells covering a wide range of temperatures (-1.9 to 25.5 ∘C), depths (5 to 3431 m) and salinities (33.4 to 37.0 PSU) were analysed for their stable isotope compositions (δ13C, δ18O and Δ47) and their elemental ratios (Mg/Ca, Sr/Ca, Na/Ca and Li/Ca). Our data allowed us to propose a revised oxygen isotope fractionation equation between modern-brachiopod shell calcite and seawater: 1T=-5.0(±0.2)(δ18Oc-δ18Osw)+19.4(±0.4), where δ18Oc is in ‰ VPDB, δ18Osw is in ‰ VSMOW, and T is in ∘C. Our results strongly support the use of clumped isotopes as an alternative temperature proxy but confirm significant offsets relative to the canonical relationship established for other biogenic and abiogenic calcium carbonate minerals. Brachiopod shell Mg/Ca ratios show no relationship with seawater temperatures, indicating that this ratio is a poor recorder of past changes in temperatures, an observation at variance with several previous studies. Despite significant correlations with brachiopod living temperature, brachiopod shell Sr/Ca, Na/Ca and Li/Ca values indicate the influence of environmental and biological factors unrelated to temperature, which undermines their potential as alternative temperature proxies. Kinetic effects (growth rates) could explain most of the deviation of brachiopod shell calcite from expected isotopic equilibrium with seawater and part of the distribution of Sr/Ca, Na/Ca and Li/Ca ratios.
... In the 20th century, the main stress on coral reefs in the Nansha Islands was more or less related to the climatic and environmental variation controlled by the monsoon without the effect of the mainland and coastal industry (Yu et al., 2006. Sr/Ca ratios and Δδ 18 O are widely used as the most stable and appropriate proxies in coral reefs in reconstructing past variations in SST and SSS at different temporal resolution (Bolton et al., 2014;Cahyarini et al., 2008;Chen et al., 2013;DeLong et al., 2013;Deng et al., 2009;Gagan et al., 1998;Schrag, 1999;Shen et al., 1996;Wei et al., 2000;Yu et al., 2005aYu et al., , 2005b. Hence, a monthly resolution analysis of past SST and SSS variations by Sr/Ca and Δδ 18 O could allow us to approach the seasonal and environmental information of the mortalities, hiatuses, negative δ 13 C shifts or other episodes, which would be vital proof to determine their causes. ...
To better understand the long-term survival of modern coral reefs under global warming, the history of past coral bleaching events prior to modern marine ecological surveys must be investigated. Here, 11 dead Porites and 2 Porites with growth hiatuses growing in the 20th century were collected from the Nansha Islands, southern South China Sea (SCS) for monthly Sr/Ca, δ¹⁸O and δ¹³C analyses to explore the climatic conditions and metabolic information corresponding to these growth structures. Among the 13 episodes, the results showed that 8 mortalities occurred in the summers, coral MJ8 died in spring, and the other 2 mortalities and 2 growth hiatuses occurred in the cooling season. In addition to the dead surface of the coral mortalities, stress bands with significantly reduced growth rates could also be observed in the corals. Negative shifts in δ¹³C occurred prior to 5 coral mortalities and most stress bands were caused in summer, suggesting a sharp reduction in photosynthesis by decreased symbiotic zooxanthellae or photosynthetic pigments. Overall, the mortalities can be concluded to have occurred in summer and stress bands with abrupt δ¹³C decreases in the last century were mainly caused by thermal coral bleaching in the southern SCS. This in turn suggests that the repeated coral bleaching and mortalities occurred much earlier before the 1980s, which is a longer-term response to modern global warming during the last century.
... C'est sur cette base qu'a notamment été développé dans les années 1970 le rapport élémentaire Sr/Ca, proxy largement utilisé dans les coraux, particulièrement pour les espèces tropicales (Weber, 1973;Smith et al., 1979;Corrège, 2006). En effet, le rapport Sr/Ca est inversement proportionnel à la température de l'eau dans laquelle le corail précipite (Weber, 1973;Smith et al., 1979;Shen et al., 1996;Sinclair et al., 1998;Fallon et al., 2003; Figure 11). Le Strontium possède un long temps de résidence dans l'Océan, de l'ordre de 3 à 5.10 6 années, suggérant un rapport Sr/Ca constant dans les eaux de mers au cours du temps pour les derniers cycles climatiques (Beck et al., 1992). ...
La calibration du paléo-thermomètre Li/Mg a ici été revisitée pour 15 espèces de corail mises en culture ou issues de contextes environnementaux variés, allant des régions tropicales aux eaux profondes Antarctiques. Ces travaux de thèse ont montré que ce nouveau proxy retrace bien toute la gamme de température de l’océan allant de -1 à 29°C, avec une précision de l’ordre de± 1,0°C. Cependant, la présence dans le squelette de matière organique ou de calcite diagénétique peut biaiser les températures reconstruites. Il a également été montré que ces effets peuvent être corrigés par un nettoyage chimique adapté ou par des analyses spécifiques à micro-échelle. Une analyse des données Li/Mg dans les coraux tropicaux indique que les incertitudes de reconstruction sont plus élevées pour les eaux de surface chaudes et soumises aux variations saisonnières des facteurs environnementaux (SST, lumière, précipitations, etc.). Les processus de calcification ou le mode de croissance de ces espèces à zooxanthelles, contrôlés par leur localisation (lagon) et par les variations saisonnières, semblent altérer la précision du traceur Li/Mg. Toutefois, en combinant les rapports élémentaires Li/Mg et Sr/Ca dans une approche multi-proxy, ces incertitudes peuvent être considérablement réduites, de l’ordre de ± 0,6°C. En première application et après analyse de calibrations globales ou locales, l’évolution historique des températures a été retracée à partir d’une colonie de Siderastrea siderea prélevée vivante en Martinique. La série temporelle obtenue couvrant les 2 derniers siècles trace clairement le réchauffement climatique en cours dans la région des Caraïbes, en accord avec les données existantes. Une seconde application concerne l’utilisation du Li/Mg dans des coraux profonds fossiles de la Mer Méditerranée et permet de reconstruire l’évolution des températures depuis 55 000 ans des eaux intermédiaires de la Méditerranée, tracées particulièrement froides au LGM, et cela en réponse au dernier cycle glaciaire/interlgaciaire.
... Sr:Ca ratios were used as a proxy for the seawater temperatures experienced by jellyfish. This approach has been used before for corals and fishes (Beck et al. 1992;De Villiers et al. 1994;McCulloch et al. 1994McCulloch et al. , 2005Shen et al. 1996;Campana 1999;Campana and Thorrold 2001;Elsdon and Gillanders 2003;Tabouret et al. 2010). Our estimates of the temperatures that A. alata experienced through life were based on the experimental findings for variation in Sr:Ca with temperature from the cubozoan Chironex fleckeri (Morrissey et al. 2020). ...
Movements undertaken by marine organisms occur for varying reasons and knowledge surrounding them is critically important for understanding population structures, ecology and for effective management and conservation of species. The objective of this study was to test a hypothesis that the cubozoan jellyfish Alatina alata spends a large part of its life at great depths by utilising the recently validated technique of statolith elemental chemistry. The approach was to ground-truth estimates of temperature based on a previous manipulative laboratory-based experiment, determine Sr:Ca and Ba:Ca ratios in the statoliths of A. alata at different life-history stages and use elemental chemistry as an environmental marker to estimate their life-time movements. High Sr:Ca values in the core and edge of the statoliths were found which corresponded with the time jellyfish were in shallow waters. Ambient water temperatures estimated for the end period of the jellyfish’s lives closely matched known sea surface temperatures in Hawaii, hence supporting a correlation between statolith Sr:Ca and temperature. For the middle section of the statoliths, strong evidence from both Sr:Ca and Ba:Ca ratios suggested that the jellyfish reached depths of at least 200–400 m. Ba:Sr maxima further supported this as Ba concentrations are usually higher below the thermocline. Individual Sr:Ca tracks also suggested that individuals moved over a depth range of tens to hundreds of meters through undertaking regular vertical movements. This study demonstrates that the use of elemental chemistry within cubozoan statoliths has the potential to determine vertical and horizontal movements where temperature gradients are strong.
... Palaeo-climate reconstructions present a challenge for times beyond historical archives and instrumental records (Gagan et al., 2000;Grottoli, 2001). Among other natural archives typically used for climate reconstructions (e.g., tree rings, ice or sediment cores), scleractinian corals are considered one of the best recorders of environmental changes in shallow-water tropical oceans, offering a valuable window into past climatic oscillations in these regions (Beck et al., 1992;de Villiers et al., 1995;Min et al., 1995;McCulloch et al., 1996;Mitsuguchi et al., 1996;Shen et al., 1996;Schrag, 1999;Zinke et al., 2004). This is due to the uptake of trace element and isotope (TEI) signatures during biomineralisation processes accompanying coral growth, which act as sensitive chemical recorders -proxies -of environmental changes over the lifetime of the organism. ...
Coral-based reconstructions of sea surface temperatures (SSTs) using Sr/Ca, U/Ca and δ¹⁸O are important tools for quantitative analysis of past climate variabilities. However, post-depositional alteration of coral aragonite, particularly early diagenesis, restrict the accuracy of calibrated proxies even on young corals. Considering the diagenetic effects, we present new Mid to Late Holocene SST reconstructions on well-dated (U/Th: ∼70 yr to 5.4 ka) fossil Porites sp. collected from the Society Islands, French Polynesia. For few corals, quality pre-screening routines revealed the presence of secondary aragonite needles inside primary pore space, resulting in a mean increase in Sr/Ca ratios between 5-30%, in contrast to the massive skeletal parts. Characterized by a Sr/Ca above 10 mmol/mol, we interpret this value as the threshold between diagenetically altered and unaltered coral material. At a high-resolution, observed intra-skeletal variability of 5.4 to 9.9 mmol/mol probably reflects the physiological control of corals over their trace metal uptake, and individual variations controlled by CaCO3– precipitation rates. Overall, the Sr/Ca, U/Ca and δ¹⁸O trends are well correlated, but we observed a significant offset up to ± 7°C among the proxies on derived palaeo-SST estimates. It appears that the related alteration process tends to amplify temperature extremes, resulting in increased SST-U/Ca and SST-Sr/Ca gradients, and consequently their apparent temperature sensitivities. A relative SST reconstruction is still feasible by normalizing our records to their individual mean value defined as ΔSST. This approach shows that ΔSST records derived from different proxies agree with an amplitudinal variability of up to ± 2°C with respect to their Holocene mean value. Higher ΔSST values than the mean SSTs (Holocene warm periods) were recorded from ∼1.8 to ∼2.8 ka (Interval I), ∼3.7 to 4.0 ka (Interval III) and before ∼5 ka, while lower ΔSST values (Holocene cold periods, Interval II and IV) were recorded in between. The ensuing SST periodicity of ∼1.5 ka in the Society Islands record is in line with the solar activity reconstructed from ¹⁰Be and ¹⁴C production (Vonmoos et al., 2006), emphasizing the role of solar activity on climate variability during the Late Holocene.
... Note that the axes were inverted to facilitate comparison among overall trends.(e.g.,Alibert & McCulloch, 1997, Alpert et al., 2016, Sayani et al., 2019, Corrège et al., 2004. Compared with previous Porites-based Sr/Ca-SST and δ 18 O-SST sensitivities in Nanwan Bay (i.e., −0.051 and − 0.053 mmol·mol −1 ·°C −1 ,Shen et al., 1996; and − 0.14‰°C −1 , Chiang et al., 2010), our monthly calibration slopes (i.e., −0.067 mmol·mol −1 ·°C −1 and −0.22‰°C −1 ) are steeper regardless of the regression method used (i.e., OLS regression results in an SST dependence of −0.064 mmol·mol −1 ·°C −1 and −0.19‰°C −1 ) ...
Reconstructions of key climate parameters prior to anthropogenic influences serve to constrain decadal to multicentury natural climate variability. In the western Pacific region, relatively few reconstructions exist north of the Western Pacific Warm Pool (WPWP), a region critical to global climate. In this study, we collected a coral core from Houbihu, southern Taiwan, and generated a 225‐year reconstruction of annual and wintertime sea surface temperature, dry season sea surface salinity, and wet season rainfall records derived from paired Porites Sr/Ca and δ¹⁸O profiles extending back to the end of the Little Ice Age (1850 CE). Multidecadal sea surface temperature trends generally track regional surface temperature reconstructions, indicating the dominant influence of solar and volcanic radiative forcings. Reconstructed dry season sea surface salinity reflects an advection signal linked to the East Asian Winter Monsoon and the Pacific Decadal Oscillation, both influencing variations in the Kuroshio Intrusion across the Luzon Strait. Reconstructed wet season rainfall, on the other hand, reveals influence of the Pacific Decadal Oscillation on the decadal variability of local and regional rainfall patterns. Relative to the late 1900s, our climate reconstructions document cooler and drier (high salinity and low rainfall) conditions during the end of the Little Ice Age, supporting other lines of evidence of a retracted WPWP region during this period. In the late 20th to early 21st century, our climate reconstructions record warming and freshening (low salinity and high rainfall) trends, highlighting the potential impact of anthropogenic forcing in the extension of the WPWP.
... Similarly, linear extension of P. damicornis from the GBR is reported to increase with SST to an optimal value at 26.7°C . These findings from the GBR are supported by an earlier study on branching pocilloporids from subtropical Hawaiian reefs (Kaneohe Bay, 21°24′N), where annual SST range (23-28°C, Shen et al. 1996) is comparable to Myrmidon Reefs (22.8-29.7°C), in which calcification rates of P. damicornis reached their optimum growth at around 27°C (Clausen and Roth, 1975). ...
As oceans continue to warm under climate change, understanding the differential growth responses of corals is increasingly important. Scleractinian corals exhibit a broad range of life-history strategies, yet few studies have explored interspecific variation in long-term growth rates under a changing climate. Here we studied growth records of two coral species with different growth forms, namely branching Isopora palifera and massive Porites spp. at an offshore reef (Myrmidon Reef) of the central Great Barrier Reef (GBR), Australia. Skeletal growth chronologies were constructed using a combination of X-radiographs, gamma densitometry, and trace element (Sr/Ca) analysis. General additive mixed-effect models (GAMMs) revealed that skeletal density of I. palifera declined linearly and significantly at a rate of 1.2% yr-1 between 2002 and 2012. Calcification was stable between 2002 and 2009, yet declined significantly at a rate of 12% yr-1 between 2009 and 2012 following anomalously high sea surface temperatures (SST). Skeletal density of massive Porites exhibited a significant non-linear response over the 11-year study period (2002-2012) in that density was temporarily reduced during the 2009-2010 anomalously hot years, while linear extension and calcification showed no significant trends. Linear extension, density and calcification rates of I. palifera increased to maximum growth of 26.7-26.9 °C, beyond which they declined. In contrast, calcification and linear extension of Porites exhibited no response to SST, but exhibited a significant linear decline in skeletal density with increasing SST. Our results reveal significant differences in coral growth patterns among coral growth forms, and highlight both the resistant nature of massive Porites and sensitivity of branching I. palifera. Future research should target a broad range of coral taxa within similar environments to provide a community-level response of ocean warming on coral reef communities.
... As the distribution coefficient of Sr into coral aragonite is close to 1, a fundamental assumption is that the past Sr 2+ /Ca 2+ seawater value has not changed through time. Similar to Li, Mg and Ca it has been shown that seawater Sr/Ca ratios changed over long time periods (Coggon et al., 2010), on glacial/interglacial timescales by 5%-10% (Stoll et al., 1999) and may even vary by location by up to 0.1 mmol/ mol (Shen et al., 1996;De Villiers, 1999). This phenomenon is intriguing as Sr has a residence time of 2-4 Myr (Hodell et al., 1990) and therefore its concentration and isotopic composition should be well mixed in the oceans. ...
Cold‐water coral reefs and mounds are and have been biodiversity hotspots of the deep sea. As their occurrence depends on specific environmental parameters, gaining hindsight on changing ocean conditions under on‐going climate change is the key to a better understanding of cold‐water coral mound development through time. A convenient technique for reconstructing the palaeoenvironment during periods of cold‐water coral mound growth is by extracting geochemical proxies from biologically mediated carbonates. Here, we focus on probably the two most abundant calcareous archives, i.e. cold‐water Scleractinia and Foraminifera, with an overview of the geochemical proxies (selection) used in these aragonitic and calcitic skeletons from cold‐water coral mounds. A particular emphasis is set on constraining proxies for for temperature, salinity, seawater density, seawater carbonate systems parameters (pH, CO32‐), nutrients, oxygen and water mass tracers.
... The first is the fresh water input, including river water, ground water and precipitation. (Beck et al., 1992;Beck et al., 1997;Correge et al., 2000;Linsley et al., 2000;McCulloch et al., 1996;Reynaud et al., 2007;Shen et al., 1996). The fact of no obvious correlation found between 87 Sr/ 86 Sr ratio were negligible (Fig. 3.2). ...
Monthly resolution 87Sr/86Sr records of living coral Porites heads, collected in the Nanwan Bay, southernmost Taiwan (21o55’N, 120o47’E), were analyzed by a MC-ICP-MS at the Department of Geosciences, National Taiwan University. For stable Sr isotopic analysis, a 84Sr/86Sr double spike method was applied on TIMS at Institute of Earth Sciences, SINICA. The data show no relationship between δ88/86Sr and seawater temperature. Between the time window of 1992 and 2002, 87Sr/86Sr ratios show good relationship with the ENSO index. No relationship is found between 87Sr/86Sr and climate proxy data, both Sr/Ca and
δ18O, which suggests that the effect of temperature and fresh water input are negligible to the observed fluctuations of 87Sr/86Sr in these corals. By checking 87Sr/86Sr in Nanwan water, it shows that a simple two end-member mixing model cannot explain the observations. A profound magnitude of subsurface water upwelling with low 87Sr/86Sr should be included to contribute low Sr isotopic ratio in southern Taiwan. Compare to the Niño 3.4 index, the results show that during strong El Niño years such like 1994-1995 and 1998, 87Sr/86Sr ratios were lower than the average. On the contrary, in 1999 and 2000 La Niña years, 87Sr/86Sr values were higher than the others. This suggests that the variation of radiogenic Sr isotopes probably related to ENSO variability (Fig. 4.2). ENSO related Luzon
Strait transport and the corresponding remix of surface and subsurface seawater were found (Hsu and Liu, 2004; Qu et al., 2004), and these events in the past may be traced by 87Sr/86Sr in corals.
... In order to investigate the impact of the global-warming hiatus on the stability of the IOD teleconnection in the western Indian Ocean, we developed biweekly-resolved records (0.5 mm sampling interval) of seawater oxygen isotopes (δ 18 O sw ) and strontium/calcium ratios (Sr/Ca) from a 26-year long coral core drilled in the Gulf of Oman, Arabian Sea (Fig. 1). Previous coral studies have demonstrated that Sr/Ca reflects SST variations 13,14 , while oxygen isotopes (δ 18 O coral ) are influenced both by SST and δ 18 O SW . Therefore, δ 18 O SW can be estimated by subtracting the SST contribution inferred from Sr/Ca from δ 18 O coral . ...
The Indian Ocean Dipole (IOD) is an interannual mode of climate variability in the Indian Ocean that has intensified with 20th century global-warming. However, instrumental data shows a global-warming hiatus between the late-1990s and 2015. It is presently not clear how the global-warming hiatus affects modes of climate variability such as the IOD, and their basin-wide ocean-atmosphere teleconnections. Here, we present a 26-year long, biweekly record of Sr/Ca and δ18O from a Porites coral drilled in the Gulf of Oman. Sea surface temperature (SSTanom) is calculated from Sr/Ca ratios, and seawater δ18O (δ18Osw-anom) is estimated by subtracting the temperature component from coral δ18O. Our δ18Osw-anom record reveals a significant regime shift in 1999, towards lower mean δ18Osw values, reflecting intensified upwelling in the western Indian Ocean. Prior to the 1999 regime shift, our SSTanom and δ18Osw-anom show a clear IOD signature, with higher values in the summer of positive-IOD years due to weakened upwelling. The IOD signature in SSTanom and δ18Osw-anom disappears with the overall intensification of upwelling after the 1999 regime shift. The inferred increase in upwelling is likely driven by an intensified Walker circulation during the global-warming hiatus. Upwelling in the Western Indian Ocean uncouples from the IOD.
... Skeletal proxies circumvent the spatio-temporal limitations of instrumental records and provide insight into long-term anthropogenic and climatic impacts on water quality and, in turn, ecosystems. For example, the ratio of strontium to calcium (Sr/ Ca) in coral skeleton has been shown to respond predictably to changes in sea temperature, and is used extensively as a proxy-based paleo-thermometer (Shen et al., 1996;Alibert and McCulloch, 1997;Marshall and McCulloch, 2002;Goodkin et al., 2005;Bolton et al., 2014). ...
The ratio of barium to calcium in coral skeletons (Ba/Ca coral ) is broadly used as a proxy for tracking terrestrial/river runoff. There are, however, inconsistencies in Ba/Ca coral records that have prompted caution in its reliability as an environmental proxy. Direct comparisons between in-situ seawater measurements and coral Ba/Ca are therefore needed to ensure accurate proxy calibration and interpretation. The current study represents the first to test Ba/Ca coral against years-long monthly-resolution contemporaneous measurements of several in-situ seawater parameters i.e. dissolved seawater barium (Ba SW ), temperature, salinity, suspended sediments, sedimentation rate and photosynthetically active radiation. We analysed the Ba/Ca coral of six Porites lutea corals sampled from two turbid reefs in Singapore, and explored relationships with in-situ seawater parameters over the period 2008–2015. Our study found poor agreement in Ba/Ca coral from replicate corals sampled from the same reef, and only one of the six colonies analysed showed significant but weak Ba/Ca coral –Ba SW and Ba/Ca coral –Ba/Ca SW relationships. There was also no clear relationship between Ba/Ca coral and skeletal luminescence G/B (a coral proxy strongly linked with salinity and river runoff). This implies that (1) the incorporation of terrestrially derived humic-like substances into the coral is independent of Ba, and (2) it is likely factors other than freshwater discharge/flood events are driving the poor reproducibility of Ba/Ca coral and disconnect with Ba SW at our study sites. We found a positive relationship between Ba/Ca coral and organic suspended solids for 4 of the 6 colonies analysed that suggests biological mechanisms such as feeding could be driving skeletal Ba incorporation. A negative relationship between Ba/Ca coral and total sedimentation rate was also found, suggesting that within reef sediment fluxes may be influencing spatio-temporal variability of the Ba-supply. Ba incorporation into coral skeleton, especially in dynamic, turbid settings such as those found in Singapore, is likely more complex than previously thought. Our results highlight the possibility of high heterogeneity in coral responses to environmental conditions, and the need for careful selection of colonies and a site-specific, replicated approach when attempting to apply Ba/Ca coral as a trace element proxy.
... Coral 18 O, Sr/Ca, and Mg/ Ca are the most widely used tracers in coral-based paleoenvironmental reconstructions (Yu et al. 2005). The indicators of 18 O, Sr/Ca, and Sr content of reef corals recording the sea surface temperature (SST) signals with month-scale resolution and high precision have been used for the SST reconstruction and many high-resolution results were reported (Shen et al. 1996;Linsley et al. 2000;Urban et al. 2000;Wei et al. 2000;Sun et al. 2004;Yu et al. 2005;Wei et al. 2007;Yu 2012). In the South China Sea (SCS) and the Hainan Island, some researchers found a significant positive correlation between coral winter δ 18 O and the East Asian Winter Monsoon (EAWM), namely, the lower the δ 18 O is, the higher the SST is, and the weaker the EAWM is (Yu et al. 2001;Peng et al. 2003;Deng et al. 2009;Su et al. 2010). ...
The instrumental observations of dust storm (DS) in China and in most countries of the world have only a history of 50–60 years, and the DS variability beyond this timescale cannot be understood properly. Here, we show that the DS frequency can be reconstructed using the coral reef environment records as a proxy. Based on the high-resolution sea surface temperature (SST) records previously reconstructed by Liu et al. (2008) and Sun et al. (2004), we reconstructed the variations of DS frequency and strong wind frequency in China from 1908 to 1959, using the 5-year moving average of the longitudinal SST gradient (GX-H,SST,5m) in the northern South China Sea (SCS) as an indicator. The calibration equation shows that GX-H,SST,5m explains 66% of the variation in the 5-year average of the DS frequency (FDS,5m) and 86% of the variation in the 5-year moving average of strong wind (FSW,5m) in China, respectively. A comparison between the reconstructed long series (1908–1990) and the observed short series (1960–1990) FDS,5m indicates that the mean, maximum, and minimum of the latter series is 10.8, 20.9, and 36.1% smaller than that of the former, demonstrating that the DS frequency strongly depends on timescales; the statistical characteristics over short timescales are quite different from those over long timescales.
... In particular, SSTs have been successfully measured using Sr/Ca ratios from the coral aragonite, as the substitution of Sr for Ca in aragonite is largely temperature dependent (Beck et al., 1992;Alibert and McCulloch, 1997). Sr/Ca is the most common trace element proxy for SST due to the relatively high Sr content of coral skeletons (∼7500 μg/g (Sun et al., 1999)), however the dependence of coral Sr/Ca on temperature is small (∼0.06 mmol/mol per degree) and thus the seasonal variation of Sr/Ca in corals is also quite low (∼3%) and requires highly precise measurements for accurate analysis of SST (Beck et al., 1992;Mitsuguchi et al., 1996;Shen et al., 1996). The Sr/Ca temperature proxy has been widely applied to coral records for reconstructing modern and past SSTs including in the tropical Pacific Ocean (DeLong et al., 2007;Wu et al., 2013Wu et al., , 2014, Indian Ocean (Marshall and McCulloch, 2001;Abram et al., 2007;Zinke et al., 2016) and South China Sea (Sun et al., 2004;Chen et al., 2013). ...
The use of X-Ray Fluorescence (XRF) Core Scanning for continuous high-resolution analysis of Sr/Ca in corals is investigated here as a new method for analyzing coral material. Corals are valuable archives for generating high resolution palaeoclimate records of sea surface temperatures of the tropical oceans, but traditional methods of analyzing coral geochemistry involve extensive subsampling and wet chemistry techniques to obtain high precision elemental records. More recent developments of micro-beam techniques have limitations in the length of core that can be scanned at any one time. XRF core scanning provides a fast, non-destructive method of analyzing long sections of coral cores whilst maintaining a high sampling resolution. Here we apply this method to two modern corals, from the Sunda Strait, Indonesia and One Tree Island, Great Barrier Reef Australia. We find that results show that XRF core scanning of corals produce Sr/Ca records that capture the annual cycle, particularly from reef sites with a large sea surface temperature range. Coupled density measurements of the coral skeleton also aid in increasing the utility of XRF measurements obtained from coral material, although difficulties remain in reliably reconstructing interannual temperature variability using XRF Sr/Ca determinations. We recommend that XRF can provide a valuable method of quick and non-destructive screening of coral material, prior to more targeted analysis using traditional destructive geochemical analysis.
... This indicates that skeletal Sr/Ca signals also were modulated partially by other drivers. Sr/Ca signals in Cyphastrea could be influenced by the coastal proximity wherein local runoff may have affected the Sr/Ca in the turbid water of Rat Island (Shen et al., 1996;Marshall and McCulloch, 2002;Fallon et al., 2003). Other biological factors (so called "vital effects") are also thought to modulate the skeletal Sr/Ca signatures in corals (De Villiers et al., 1994;De Villiers et al., 1995;Allison and Finch, 2004;Sinclair, 2005a;Sinclair et al., 2006;Saenger et al., 2008;Cohen and Gaetani, 2010;Grove et al., 2013;Deng et al., 2014), and slower growing corals, like Cyphastrea, are more susceptible to such vital effects (Deng et al., 2014). ...
Coral reef ecosystems maintain high biodiversity and have great economic value. Nonetheless, inshore coral reefs of the Great Barrier Reef (GBR) are facing threats from poor water quality due to extensive modification of coastal catchments following European settlement. Ba/Ca ratios in coral skeletons have been used to infer past water quality, but in order to use a proxy to infer past environments, it is critical to develop a firm understanding of the parameters that control the proxy. This study investigated various environmental, climatic and oceanographic factors to understand a long-term (1976 to 2016) record of biogeochemical cycling of Ba/Ca preserved in a Cyphastrea sp. coral colony recovered from near-shore Rat Island (near Port Curtis), southern GBR. Our Cyphastrea was found to have simple skeletal microstructure, similar to that of Porites, with unaltered skeletal preservation, clear annual density banding, and an extended growth history with seasonally resolved Sr/Ca signals. This combined with a wide geographic distribution make Cyphastrea coral a potential new palaeoenvironmental archive. Although Rat Island is located near the mainland and is influenced directly by discharge from the Calliope and Boyne rivers, temporal oscillations of Ba/Ca did not show peaks associated with high runoff during summers. Rather, Cyphastrea's high-resolution Ba/Ca data shows, for the first time, consistent seasonal cycles with a gradual decrease from spring through summer and gradual rise from autumn through winter. Biogeochemical cycling of Ba in the semi-confined turbid water of Port Curtis may be controlled by active or passive planktic uptake during the spring bloom stage and removal of barite minerals formed in decaying phytoplankton during post-bloom stage. The subsequent increase of Ba/Ca from autumn through winter may be attributed to reduction of phytoplankton abundance. The semi-enclosed embayment of Port Curtis has restricted water turnover with a large terrigenous runoff load that may have significant influence on phytoplankton dynamics. Our work suggests that Ba cycling, and hence, the Ba/Ca coral proxy, may differ greatly depending on local geographic factors and thus, we recommend that geographic and oceanographic conditions should be taken into account in coral-based Ba/Ca proxy studies used to reconstruct water quality.
... Due to their apparent sensitivity to physical and chemical changes in the marine environment, reefbuilding corals have provided potentially useful proxies for interpreting past environments and chemistry of ambient seawater for several decades (e.g. Shen and Boyle, 1987;Shen et al., 1992;Delaney et al., 1993;Shen et al., 1996;Fallon et al., 2002). The internal growth bands that massive scleractinian corals accumulate (related to annual periodicity) can preserve changes in seawater properties, nutrient levels, and even pollution entering the marine environment during the coral lifetime as continuous time-series records and provide time markers for the development of long chronologies (Knutson et al., 1972;Scoffin et al., 1992) which permit subannual dating resolution and permit accurate sampling. ...
In this paper the adaptive abilities of coral reefs in the changing marine environment were reviewed. The parameters assessed were sedimentation, nutrient loading, trace element fluctuations, thermal stress, carbon dioxide increase, ocean acidification and the economic damage of climate change. It was found that many studies have analysed different elements, stressors and proxies, but not many studies have looked at a combination of the stressors. It is imperative that future studies look at a combination of stressors and proxies coupled with factors such as skeletal extension, zooxanthellae density and coral abundance to determine whether specific combinations of factors negatively affect coral reefs more than others. Once these questions can be confidently answered, only then can we establish proper policies and management procedures that will reduce the amount of stress placed upon the coral reefs.
... Also in our experiments, the D Sr values varied between 0.90 and 1.13 with a value of 1.04 in the control treatment. The D Sr value we report for our control treatment is consistent with previously published values for several coral species (Porites cylindrica, Porites lutea, Porites lobata, Pavona clavus, and Pocillopora eydouxi) grown in standard seawater between 25 and 26°C (De Villiers et al., 1994;Shen et al., 1996;Armid et al., 2011). In our experiments, the D Sr values vary as a function of seawater Ca concentrations (Fig. 5b), but there is no significant relationship between D Sr values with seawater Mg concentrations (Fig. 5c), as was previously suggested by Swart (1981). ...
The skeletal composition of calcifying organisms, in particular Mg/Ca and Sr/Ca ratios, have been widely used to understand fluctuations in seawater chemistry throughout the Phanerozoic. While the success of applying these data to the geologic record depends on a knowledge of the distribution coefficients for these elements (DMg and DSr), there are scarcely any studies which have described how these values vary as a result of changing seawater Mg/Ca ratios. To address this, we have cultured the scleractinian coral, Pocillopora damicornis, in seawater with ranges of Mg and Ca concentrations. Here, we demonstrate that Mg/Ca and Sr/Ca ratios of coral skeletons correlate with total seawater Mg/Ca and Sr/Ca molar ratios, but that apparent DMg and DSr values do not remain constant across the range of experimental seawater treatments, with DMg values significantly increasing with seawater Mg/Ca ratios and DSr values significantly increasing with seawater Ca concentrations. These trends are not rate dependent and may be best explained by a Rayleigh distillation model, in which the calcifying space is semi-isolated from seawater during skeletogenesis (i.e. leaky). As there is a slight increase in DMg and decrease in DSr values between our “Jurassic” and “Modern” seawater treatments, the application of a constant distribution coefficient to estimate changes in ancient seawater chemistry may underestimate seawater Mg/Ca ratios overestimate Sr/Ca throughout the Mesozoic and Cenozoic. We suggest that interpretations of seawater chemistry from fossil corals may be improved by using the relationships derived for skeletal and seawater Mg/Ca and Sr/Ca ratios established by our experiments, as they incorporate the effect of seawater Mg/Ca ratios on skeletal Mg/Ca and Sr/Ca ratios.
... Nonetheless, both species generated SST reconstructions that are within error of each other (Figures 2b and 2c). Both calibration slopes are within the range of slopes reported in other paired columella Diploastrea Sr/Ca records (e.g., À0.054 to À0.062 mmol/mol°C À1 ) [Bagnato et al., 2004;Correge et al., 2004], other Porites-based studies from the same region as our site (e.g., À0.042 to À0.061 mmol/mol°C À1 ) [Mitsuguchi et al., 1996;Shen et al., 1996;Sun et al., 2005;Yu et al., 2005;Wei et al., 2000] and other slow-growing corals, i.e., less than 0.8 cm/yr (e.g., À0.045 to À0.059 mmol/mol°C À1 ) [Cardinal et al., 2001;Goodkin et al., 2005Goodkin et al., , 2007DeLong et al., 2011;Xu et al., 2015]. These results give indication that Diploastrea Sr/Ca has SST sensitivity similar to that of Porites. ...
The Indo-Pacific coral Diploastrea heliopora reveals regional multi-decadal to centennial scale climate variability using coral carbonate δ18O (δ18Oc) as a combined proxy for sea surface temperature (SST) and sea surface salinity (SSS). However, to assess the coral's full potential in resolving climatic events, an independent SST proxy would be more advantageous. We examined both Sr/Ca and δ18O of Diploastrea against an adjacent Porites lobata core collected from northeast Luzon, Philippines. Winter Sr/Ca data from Diploastrea show a significant correlation to SST (r = -0.41, p < 0 .05, RMSR = 0.81 °C) and provide a proxy with similar sensitivity as Porites (r = -0.57, p < 0.05, RMSR = 0.62 °C). An inter-species SST record is shown to be robust and used for a reconstruction of the Pacific Decadal Oscillation (PDO) during boreal winter (r = -0.70, p = 0.02). While we were unable to generate a robust Diploastrea δ18O-SSS calibration at inter-annual timescale, the freshening trend towards the present, commonly observed in the region, is qualitatively captured in Diploastrea δ18O. Comparison with Porites δ18O and instrumental SSS records shows that the magnitude of freshening is consistent between coral species. Wet and dry season Porites δ18O provide support for the relative influence of El Niño Southern Oscillation (ENSO) events and local precipitation to SSS variability at our site. The multi-proxy, multi-species approach of this study further strengthens the evidence for Diploastrea as an alternate climate archive in the Indo-Pacific region, and seals its potential in helping resolve less understood global-scale climate phenomena.
... In the culture-based experiments, the use of filters that eliminates particulates in pumped seawater is necessary to maintain a healthy environment for the corals. According to Shen et al. (1996), the value for Sr/Ca in seawater changes according to the filtrations technique used, and filtration membranes reduce the Sr/Ca values because seawater with 0.45-5.0 μm particulates had the highest Sr/Ca ratios. ...
Coral skeletons preserve useful archival indicators from which to reconstruct past environments. We conducted temperature-controlled culture experiments (20, 22, 27, and 31 °C) with primary polyps of Acropora digitifera to accurately assess the impact of a wide range of temperatures on the calcification rate and to methodically evaluate the skeletal trace elements (Sr/Ca, Mg/Ca, and Na/Ca ratios). Water temperatures positively affected the calcification rate up to 31 °C, which exceeds the temperature threshold for this species. The calcification rates also varied widely (> 20%) during each of the four temperature treatments. The skeletal Sr/Ca ratio was most strongly correlated with water temperature (R² = 0.68, p < 0.001), whereas the Mg/Ca and Na/Ca ratios showed lower correlations (R² = 0.53, p < 0.001; R² = 0.34, p = 0.011, respectively). The variations in the skeletal Sr/Ca, Mg/Ca, and Na/Ca ratios at the four different temperatures were 0.36%–1.20%, 0.83%–3.76%, and 0.52%–3.24%, respectively. Thus, the Sr/Ca ratio showed the least variation, despite the wide variations in the calcification rate. We confirm that the Sr/Ca ratio of A. digitifera juveniles is a robust proxy of temperature, regardless of variations in the calcification rate and the wide range of ambient temperatures. In addition, our results regarding skeletal Mg/Ca and Na/Ca ratios further our understanding of coral calcification processes.
... Furthermore, the distribution coefficient of coral skeletons is often close to that of abiogenic aragonite. For example, for Porites sp., Shen et al. (1996) reported a K Sr=Ca D value of 1.06 which is close to that of synthetic aragonite (1.19;Dietzel et al., 2004) at the same temperature (25 °C). With increasing water temperature, decreasing amounts of Sr 2+ substitute for Ca 2+ in the crystal lattice. ...
It remains a challenging task to reconstruct water temperatures from Sr/Ca ratios of bivalve shells. Although in many aragonitic species, Sr/Ca is negatively correlated to temperature – which is expected based on abiogenic precipitation experiments –, the incorporation of Sr into the shell of bivalves is strongly controlled by physiological processes and occurs away from predicted thermodynamic equilibrium. Strontium-to-calcium ratios of aragonitic shells remain far below that of the ambient water. Moreover, Sr concentrations vary considerably among shell portions consisting of different microstructures and / or organic content. Values observed at annual growth lines and within the intervening shell portions (= annual growth increments) deviate much stronger from each other than expected from a change in temperature or Sr/Cawater. As demonstrated here by ultra-high-resolution chemical analysis (EPMA, NanoSIMS) of a Cerastoderma edule shell, Sr concentrations are also heterogeneously distributed at approximately micrometer resolution. For example, in the outer portion of the outer shell layer, Sr/Ca ratios were statistically significantly (t-, u-tests) higher at circatidal growth lines (irregular simple prismatic structure; arithmetic mean ± 1 standard deviation = 2.86 ± 0.38 mmol/mol; n = 53) than within circatidal increments (nondenticular prismatic structure; 2.42 ± 0.25 mmol/mol; n = 51). S/Cashell, a representative of the concentration of organics, showed the opposite pattern, i.e., significantly higher values in circatidal increments (2.37 ± 0.29 mmol/mol; n = 51) than at circatidal growth lines (2.13 ± 0.47 mmol/mol; n = 53). Overall highest values of Sr/Cashell (3.47 ± 0.65 mmol/mol; n = 3) and S/Cashell (3.98 ± 0.65 mmol/mol; n = 3), however, were typically associated with annual growth lines and larger biomineral units. The intimate link between Sr/Cashell, S/Cashell and shell architecture may indicate that microstructures or the processes controlling their formation exert a strong control over the incorporation of strontium into shells of C. edule. Analytical techniques with lower sampling resolution, e.g., LA-ICP-MS, cannot resolve such fine-scale Sr variations. As a result, the signal-to-noise ratio decreases and the data generated by such techniques may therefore not seem to provide useful paleotemperature data. Future studies should therefore employ a combined analysis of Sr/Cashell and shell microstructures, and interpret Sr/Ca values of shell portions with different microstructures separately.
... While d 18 O is more universally applied, especially in the Pacific, d 18 O varies as a function of SST and sea-surface salinity (SSS), whereas Sr/Ca varies primarily as a function of SST. Porites lutea and P. lobata are common species of choice for paleoclimate work in the Pacific [Shen et al., 1996], but since the genus Porites is only represented by small-colony (e.g., Porites astreoides, see Busch et al. [2015]) or branching species in the western Atlantic, the Sr/Ca proxy is being developed for other species in this region [Sadler et al., 2014]. Because of its longlived, massive morphology, well-sampled and comprehensive growth record [Hudson, 1981b;Hudson et al., 1994], and widespread regional distribution, Orbicella faveolata (formerly Montastraea faveolata, and before that, M. annularis) was explored first as a proxy archive [Swart et al., 2002;Smith et al., 2006;Kilbourne et al., 2008] and sampling methods further refined [Leder et al. 1996;Flannery and Poore, 2013]. ...
Massive corals provide a useful archive of environmental variability, but careful testing of geochemical proxies in corals is necessary to validate the relationship between each proxy and environmental parameter throughout the full range of conditions experienced by the recording organisms. Here we use samples from a coral-growth study to test the hypothesis that Sr/Ca in the coral Siderastrea siderea accurately records sea-surface temperature (SST) in the subtropics (Florida, USA) along 350 km of reef tract. We test calcification rate, measured via buoyant weight, and linear extension (LE) rate, estimated with Alizarin Red-S staining, as predictors of variance in the Sr/Ca records of 39 individual S. siderea corals grown at four outer-reef locations next to in-situ temperature loggers during two, year-long periods. We found that corals with calcification rates<1.7 mg cm⁻² d⁻¹ or<1.7 mm yr⁻¹ LE returned spuriously high Sr/Ca values, leading to a cold-bias in Sr/Ca-based SST estimates. The threshold-type response curves suggest that extension rate can be used as a quality-control indicator during sample and drill-path selection when using long cores for SST paleoreconstruction. For our corals that passed this quality control step, the Sr/Ca-SST proxy performed well in estimating mean annual temperature across three sites spanning 350 km of the Florida reef tract. However, there was some evidence that extreme temperature stress in 2010 (cold snap) and 2011 (SST above coral-bleaching threshold) may have caused the corals not to record the temperature extremes. Known stress events could be avoided during modern calibrations of paleoproxies.
... In the case of Parola, its age model was refined further by constructing an independent age model based from comparisons between its Sr/Ca concentration ratios (Ramos, 2016) and sea surface temperature (SST) variations in the SCS, as estimated by NOAA's Extended Reconstructed Sea Surface Temperature (Smith et al., 2008). Coral Sr/Ca, in general, inversely follows SST variations (Shen et al., 1996). Parola coral subsample ages were estimated by matching Sr/Ca peaks (as a function of distance from the top part of the coral core) to annual SST minima in the SCS, which commonly occurs during January or February. ...
Iodine-129 is a long-lived fission product that is majorly released in human nuclear activities (HNA) such as nuclear bomb testing, nuclear fuel reprocessing, and nuclear accidents. It is a good environmental tracer and former measurements of (129)I in corals from the southern hemisphere show the increasing trend of (129)I concentrations in the marine environment caused by HNA. Here we show time series of (129)I/(127(stable))I isotopic ratios in two coral cores from the northern hemisphere (Philippines) and how these record (129)I released from HNA in even greater, unprecedented detail. Corals were taken from the Pacific Ocean (Baler) and South China Sea (Parola) sides of the Philippines. We observed nearly identical peaks ((129)I/(127)I ∼ 31.5 × 10(-12)) in both the Baler and Parola records, each attributed to the year 1962 - the year with the highest recorded amount of (129)I release from nuclear bomb testing. This 1962 (129)I bomb signal offers a new time marker that can be used to establish or confirm age models of corals, comparable to or possibly better than the well-known coral (14)C bomb peak. We also observed nuclear fuel reprocessing and Chernobyl accident (129)I signals in years 1977, 1980, and 1986, concurrently in Parola and with 9 to 11-year lags in Baler. This discrepancy in timing suggests that (129)I was transported to the South China Sea and Pacific Ocean sides of the Philippines directly from the atmosphere and through prevailing ocean currents, respectively. Lastly, we observed surprisingly high (129)I/(127)I isotopic ratios (i.e., 22.8 to 38.9 × 10(-12)) in the Parola record after the year 1996, which is in contrast to the decreasing trend observed in the Baler record and in published (129)I releases of different HNA. These results possibly indicate the presence of unknown sources of (129)I in the South China Sea region.
... Our results are consistent with previous research indicating that species-specific temperature effects can influence partition coefficients for metals such as Ba and Mg, confirming the need for validation studies prior to interpreting values in wild-caught fish (Elsdon & Gillanders 2002, Bath Martin et al. 2004, Miller 2009, 2011). Our observation that there was no temperature effect on D Sr for either species contrasts with the behavior of the Sr/Ca ratio in biogenic aragonite in different taxa observed by others (Shen et al. 1996, Elsdon & Gil - landers 2002, Zacherl et al. 2003, Bath Martin et al. 2004), which may be explained by the magnitude and relatively narrow temperature range tested in our study. These differences highlight a need for more investigation into the biological control over Sr incorporation that is exerted by different kinds of organisms. ...
Characterizing the behavior of larvae prior to settlement is integral to understanding population dynamics because coastal oceanography may facilitate or limit settlement. Otolith microchemistry can be used to determine patterns of fish movement, although there is a limited understanding of how this tool can be applied in coastal marine systems. Our goal in this study was to evaluate the application of otolith microchemistry to characterize water mass associations of settlement-stage marine fish in a coastal upwelling region using a 3-step approach. First, we characterized seawater chemistry of coastal water mass types across multiple years, finding differences in the chemical signatures of strong upwelling, weak upwelling, and relaxation events. Second, we experimentally determined the effect of temperature on the partitioning of trace elements in otoliths for 2 rockfishes (Sebastes spp.) to find that the effect of temperature on otolith partition coefficients was element-and species-specific. Finally, we compared coeval changes in seawater and otolith chemistry of settlement-stage rockfishes that were exposed to naturally variable conditions over an upwelling-relaxation cycle. We subsequently evaluate whether laser ablation inductively coupled plasma mass spectrometry effectively measures otolith chemistry over ecologically relevant time scales. We discovered that elemental concentrations in otoliths respond rapidly to changes in seawater chemistry and reflect equivalent proportional changes. This study provides evidence that elemental signatures are valuable tools for reconstructing larval histories of marine fish in coastal upwelling regions.
... In general, co-precipitation of Sr to Ca in aragonite decreases with temperature increases due to a declining distribution coefficient, which has been both measured and derived theoretically (Dietzel et al., 2004). The negative correlation between skeletal Sr/Ca ratios observed in some massive corals with ambient seawater temperature has been widely established and applied to reconstruct paleo-seawater temperature (Beck et al., 1992;Corrège, 2006;de Villiers, 1999;McCulloch et al., 1994;McCulloch et al., 1996;Shen et al., 1996;Weber, 1973;Yan et al., 2013;Yu et al., 2005). However, these relationships may be biased by the influence from symbionts causing an apparent vital effect Cohen et al., 2002;Cohen et al., 2006;Stevenson et al., 2014) or by ontogenetic age, grow rates, metabolic activity related to temperature and/or salinity (Purton et al., 1999). ...
A method for high-throughput boron purification coupled with total evaporation thermal ionization mass spectrometry was developed to allow investigation of how the seawater pH varies spatially and temporally with respect to elevated atmospheric carbon dioxide level, and the impacts of ocean acidification on marine organisms. Using this method, we are able to measure boron isotopic composition in carbonate with less then 1 ng of boron in the sample and further reconstruct calcification pH for biogenic carbonate as a biogeochemical archive. In this dissertation, we applied this method to investigate how environmental factors influence the boron incorporation in two unconventional biogenic carbonate archives: aragonite bivalve shells and calcite coccolithophores. In the bivalve shell Arctica islandica study, we found that shells regulate their calcification pH, and that boron incorporation into the shell has a potential temperature dependence. Therefore, a culture experiment with fixed temperature and salinity, but variable pH is required to evaluate the species-specific relationship between boron and ambient seawater pH and the potential use of this proxy in this species. In the coccolithophorid species Pleurochrysis carterae study, we observed an ability for this organisms to adapt to ocean acidification. The boron isotopic composition in the coccoliths suggests it regulates vesicle pH to sustain calcification with decreasing environmental pH. With other geochemical constraints including the particulate inorganic carbon to particulate organic carbon ratio (PIC/POC) and stable isotopic compositions we found this coccolitophorid species is likely to change usage of inorganic carbon species from HCO3- to CO2(aq) as ambient medium pH decreases. This dissertation work provides insights on the diverse response of marine organisms to ocean acidification. Extending work on boron to pH calibration in unconventional species will help reconstruct seawater pH records over a wide geographic range through geologic time. Further applications in different marine calcifiers will help us better understand the mechanisms for diverse biological responses to ocean acidification and to predict the potential capacity to sequestrate exceeded atmospheric CO2 in the ocean.
... The applicability of these calibrations, however, needs to be scrutinized, e.g., Smith et al. [2006] explained similar differences in calibrations (for Montastraea) with variations in water chemistry not accounted for in the regression analysis. Their explanation is supported by the work of several investigators indicating that Sr/Ca of seawater, especially in the realm where corals grow, cannot be considered constant through time and space [de Villiers et al., 1994;Shen et al., 1996;de Villiers, 1999;De Deckker, 2004]. Furthermore, the strength and pattern of surface water circulation and therefore heat fluxes and associated heat accumulation within a reef system are strongly dependent on the systems morphology and its exposure to the open ocean [Roberts et al., 1975;Farrow and Patterson, 1993;Monismith et al., 2006;McCabe et al., 2010]. ...
The rising temperature of the world's oceans is affecting coral reef ecosystems by increasing the frequency and severity of bleaching and mortality events. The susceptibility of corals to temperature stress varies on local and regional scales. Insights into potential controlling parameters are hampered by a lack of long term in situ data in most coral reef environments and sea surface temperature (SST) products often do not resolve reef-scale variations. Here we use 42 years (1970-2012) of coral Sr/Ca data to reconstruct seasonal- to decadal-scale SST variations in two adjacent but distinct reef environments at Little Cayman, Cayman Islands. Our results indicate that two massive Diploria strigosa corals growing in the lagoon and in the fore reef responded differently to past warming events. Coral Sr/Ca data from the shallow lagoon successfully record high summer temperatures confirmed by in situ observations (>33°C). Surprisingly, coral Sr/Ca from the deeper fore reef is strongly affected by thermal stress events, although seasonal temperature extremes and mean SSTs at this site are reduced compared to the lagoon. The shallow lagoon coral showed decadal variations in Sr/Ca, supposedly related to the modulation of lagoonal temperature through varying tidal water exchange, influenced by the 18.6-year lunar nodal cycle. Our results show that reef-scale SST variability can be much larger than suggested by satellite SST measurements. Thus, using coral SST proxy records from different reef zones combined with in situ observations will improve conservation programs that are developed to monitor and predict potential thermal stress on coral reefs. This article is protected by copyright. All rights reserved.
... The basic assumption is that coral-Sr/Ca varies with temperature and that the composition of Sr and Ca in seawater is invariant on millennial timescales due to their long residence times in the ocean [Beck et al., 1992] . Hence, the Sr/Ca ratio in coral skeletons is considered a reliable proxy for deriving high-resolution records of past SST [Shen et al., 1992 [Shen et al., , 1996 McCulloch et al., 1994; Alibert and McCulloch, 1997; Wei et al., 2000; Swart et al., 2002; Zinke et al., 2004; Yu et al., 2005; Hetzinger et al., 2006 Hetzinger et al., , 2010 Pfeiffer and Dullo, 2006; DeLong et al., 2007 DeLong et al., , 2011 Pfeiffer et al., 2009; Cahyarini et al., 2009]. Other than temperature, biological controls and other environmental factors can also influence coral-Sr/Ca ratios [de Villiers et al., 1994 [de Villiers et al., , 1995. ...
Here we present the first record of Sr/Ca variability in a massive Porites lutea coral from the Lakshadweep Archipelago, Arabian Sea. The annual mean sea surface temperature (SST) in this region and the surrounding areas has increased steadily in the recent past. During some major El Ninõ events, SSTs are even higher, imposing additional thermal-stress on corals, episodically leading to coral bleaching. We infer from the coral-Sr/Ca record (1981-2008) that during some of these events high and persistent SSTs lead to a dampening of the temperature signal in coral-Sr/Ca, impairing the coral's ability to record full scale warming. Thus, coral-Sr/Ca may provide a history of past El Ninõ Southern-Oscillation (ENSO) induced thermal-stress episodes, which are a recurrent feature also seen in cross-spectral analysis between coral-Sr/Ca and the Nino3.4 index. Despite the impact of episodical thermal-stress during major El Ninõ events, our coral proxy faithfully records the seasonal monsoon-induced summer cooling on the order of μ2.3°C. Calibration of coral-Sr/Ca with instrumental grid-SST data shows significant correlation to regional SST and monsoon variability. Hence, massive Porites corals of this region are highly valuable archives for reconstructing long-term changes in SST, strongly influenced by monsoon variability on seasonal scales. More importantly, our data show that this site with increasing SST is an ideal location for testing the future effects of the projected anthropogenic SST increase on coral reefs that are already under thermal-stress worldwide.
... A few key genera of reef-building corals are used in most paleoclimate studies to reconstruct tropical sea surface temperature (SST) (Corrège, 2006;DeLong et al., 2007;Saenger et al., 2008). Porites is the genus most often used in the Pacific (e.g., Corrège, 2006;Gagan et al., 2012;McGregor and Gagan, 2003;Shen et al., 1996), whereas the Montastraea annularis species complex (now formally assigned to the genus Orbicella (Budd et al., 2012)) is commonly used in the Atlantic (e.g., Kilbourne et al., 2008;Saenger et al., 2008;Smith et al., 2006;Swart et al., 2002;Watanabe et al., 2001Watanabe et al., , 2002. ...
The coral species Diploria strigosa is a promising archive for paleoclimate reconstruction in the tropical Atlantic, but limited work has been accomplished thus far to quantify the relationship between strontium to calcium ratios and sea surface temperatures in this species. In this study, we collected three modern D. strigosa coral colonies from Anegada, British Virgin Islands to refine the use of this species as a paleoclimate archive. Three regression techniques including ordinary least squares, reduced major axis, and weighted least squares were used to assess how assumptions implicit in these regression methods influence the calibration. Our analysis demonstrated that regression slopes were strongly impacted by the assumptions about data uncertainty. We recommend using the unbiased weighted least squares regression technique for calibrating the Sr/Ca paleothermometer, especially when precise local sea surface temperature data are unavailable. Combining our Sr/Ca data with previously published data from this species results in a multi-site, multi-colony temperature sensitivity of - 0.046(±. <. 0.001) mmol/mol/°C for mean-centered monthly data, - 0.059(±. 0.001) mmol/mol/°C for monthly anomalies, and - 0.063(±. 0.004) for annual anomalies. We suggest these relationships are the best available characterization of the temperature dependence of Sr/Ca in D. strigosa, and can be utilized in future paleoclimate reconstructions.
The Kuroshio intrusion (KI) is a northwestward‐flowing branch of the Kuroshio Current, which enters the South China Sea (SCS) and regulates its temperature, salinity, and water mass exchanges. However, limited direct observations hinder our understanding of KI's mechanisms and responses to climate change. Here, we present a 60‐year bi‐monthly resolved coral oxygen isotope (δ¹⁸Oc) record from Dongsha Atoll, the northern SCS. The dry‐season (December–March) δ¹⁸Oc record reveals interannual to decadal variabilities of the KI. The impact of the East Asian winter monsoon (EAWM) on Dongsha δ¹⁸Oc was more pronounced during the 1970s and 1980s and after the early 2000s, while the influence of the El Niño‐Southern Oscillation (ENSO) on Dongsha δ¹⁸Oc was higher between the 1980s and 1990s. The Pacific Decadal Oscillation (PDO) may have a relatively minor effect on KI strength or may indirectly modulate KI strength through its influence on ENSO activities. Our Dongsha δ¹⁸Oc record highlight the importance of the EAWM, ENSO, and PDO in predicting future KI changes.
The Sr/Ca ratio of modern coral skeleton can record local seawater temperature (T) and is an important tool to reconstruct past environments. However, site-specific calibrations are required to ensure accurate temperature reconstructions. Here, we examine three modern coral skeletons collected at contrasting sites on the island of Oahu, Hawaii to establish the first accurate calibrations for this region and investigate site specific influences on the calibration process. Satellite T data, which is used for many calibrations, may not be able to derive an accurate thermometer. For our shallow lagoonal sites, satellite T had smaller seasonal T ranges which resulted in significantly higher slopes of Sr/Ca-T compared to using in situ T. Traditional age model based on aligning only min/max values can lead to errors in the Sr/Ca-T calibration due to variable growth rates. An enhanced age model which add midpoints alignments between the mim/max peak values can account for seasonal changes in growth rate and reduce the error. On the same island, site and time period specific conditions can cause notable differences in the Sr/Ca-T calibrations. The coral from an estuarine embayment showed a high Sr/Ca offset, likely due to high Sr/Ca in ambient seawater. For corals which experienced thermal stress, lower slopes were observed probably due to elevated Sr/Ca values during the period of thermal stress.
The strontium‐to‐calcium (Sr/Ca) ratio of coral is widely used as a paleothermometer for tropical sea surface temperature (SST) at subannual resolutions. The fidelity of Sr/Ca‐derived SST estimates largely depends on the properties of the monthly age model selected. Here, we develop a revised monthly age model for coral Sr/Ca estimation from the northern South China Sea based on specific tie points and evaluate the impacts of different age models on SST reconstruction. Our results indicate that our revised monthly age model reduces conversion errors by up to nearly 20%–30% relative to previously reported values, thereby improving the precision of seasonal SST estimates and enabling better paleoclimate interpretations, such as El Niño–Southern Oscillation variability. The revised monthly age model provides a generalized approach for developing more robust seasonal resolution Sr/Ca–SST reconstructions in other regions.
A 4-year time-series of surface seawater Sr/Ca ratios was assembled across a section of the Florida Keys Reef Tract, in order to uncover any variability that might explain previously reported anomalies in regional calibrations of the coral aragonite Sr/Ca paleotemperature proxy. Samples were collected semiannually on a grid of 54 sites, from September of 2016 until January of 2020. The 325-km 2 grid extended from the ocean shore to the forereef wall and from the east end of Long Key to the west end of Marathon. A novel ICP-AES method was used to measure the Sr/Ca ratio, with ratio calibration and normalization against an in-house seawater reference, yielding a long-term precision of better than 0.2%. Significant variations (2%–3%)
of the seawater Sr/Ca ratio were found. While it was relatively constant offshore, near the coast the ratio alternated seasonally between higher and lower values, generally resulting in seaward Sr/Ca gradients that were markedly negative in summer but reversed in winter. Inshore seawater Sr/Ca ratios ranged from a summer high of 8.83 mmol/mol to a winter low of 8.54 mmol/mol, the difference corresponding to a potential bias of ∼5.5°C in terms of the coral Sr/Ca paleotemperature proxy. This seasonal variation should diminish the slope of empirical Sr/Ca–SST calibration lines, as has indeed been observed in prior studies with local coral species. Open ocean samples obtained from the Atlantic, Indian, and Pacific enlarge the published Sr/Ca data set for surface seawater and show a much smaller variability of 8.646 ± 0.018 mmol/mol (0.2%).
The Mekong River Delta (MRD) is an essential agricultural area for the worldwide rice supply. Floods and droughts triggered by El Niño southern oscillation (ENSO) have been threatening sustenance in the MRD. Sustainable food supplies require understanding the response of the MRD hydrology to the changing ENSO behaviour in recent decades. Here, we reconstructed the annual rainfall maxima in the MRD using the oceanic paleoclimate proxy from coral skeletons and compared them with ENSO indexes. Annual minima of coral-based seawater oxygen isotope (δ¹⁸Osw) correlated with annual rainfall maxima, which allowed to extend rainfall data from 1924 to the recent. The annual rainfall maxima based on δ¹⁸Osw negatively correlated with the central Pacific El Niño index. This suggested that La Niña and central Pacific El Niño events lead to heavy and light rainy seasons. The heavy rainy season had more serious impacts in recent decades, which likely increases the flood risk. In contrast, the frequency and rainfall amount of the light rainy season has not changed significantly, although a catastrophic drought has hit the MRD. Our finding concludes that the impact of the ENSO event on MRD hydrology is inconsistent in the past century.
The skeletons of massive corals inhabiting tropical and subtropical oceans grow over centuries. The chemical and isotopic compositions of their skeletons reflect changes in the marine environment and provide an archive of sea surface temperature (SST) and salinity at a high temporal resolution spanning decades to centuries. Stable oxygen isotope ratios in coral skeletons (δ¹⁸Oc) are an excellent proxy for SST and the stable oxygen isotopic composition in seawater (δ¹⁸Osw). Variations in δ¹⁸Osw serve as a hydrological proxy and are routinely estimated by subtracting the SST component from δ¹⁸Oc. The SST component of δ¹⁸Oc is inferred from coral Sr/Ca (SST proxy). Both Sr/Ca and δ¹⁸Oc are converted to SST units based on Sr/Ca‐ and (δ¹⁸Oc–δ¹⁸Osw)‐SST calibrations. However, the exact slope values of the Sr/Ca‐SST and (δ¹⁸Oc–δ¹⁸Osw)‐SST calibrations are challenging to assess, which hampers the reliable estimation of SST, δ¹⁸Osw, and their uncertainties. Here, we present a simple Monte Carlo approach to estimate variations in SST and δ¹⁸Osw together with their confidence intervals. Our approach improves on previous error propagation methods by including intercolonial differences of calibration slopes in addition to analytical errors. In addition, Monte Carlo experiments using adjusted errors suggest that uncertainties in the calibration slopes have a minor influence on estimates of SST and δ¹⁸Osw.
Hundreds of coral paleoclimate records have been developed over the past several decades, significantly extending the instrumental record and improving our understanding of tropical climate variability and change in otherwise data‐poor regions. Coral “proxy” records measure the change in skeletal geochemistry or growth as a function of ocean conditions at the time of calcification. Over the past decade (since 2010), new syntheses have identified coherent patterns of warming and variability that are unique within the paleo record (albeit not yet unprecedented). In turn, ocean warming and acidification have had a detrimental impact on coral growth, with reduced extension and increased stress banding. Methodological advances have constrained uncertainties and improved our understanding of the processes by which climate information is archived in coral skeletons. Models that describe these processes have been developed to facilitate proxy‐model comparisons, identify sources of uncertainties, and provide a benchmark upon which forced changes may be detected within a highly variable climate system. Finally, several innovative new proxies have expanded the climate and environmental information that may be obtained from corals, including: seawater pH, aragonite saturation, anthropogenic nitrogen, runoff, and trade winds. Further extending established and novel proxies should remain a priority, along with seawater monitoring and density measurements with which to screen and calibrate these records. As this critical climate archive is increasingly threatened by warming and ocean acidification, the community must work closely together to collect this invaluable climate data in an ecologically and culturally sensitive manner, before it is too late.
This article is categorized under: Paleoclimates and Current Trends > Paleoclimate
Longterm fluctuation content of heavy metal concentrations (Sr, Cr, Fe, Zn, and Pb) was traced through the analysis of coral skeletal growth bands of massive coral core Porites lutea. Annual growth band was examined using X radiography. Heavy metal samples were extracted from each yearly layer of the core section. Seven samples of the coral skeleton were analyzed using neutron activation analysis and atomic absorption spectrometry to detect metal concentrations. The oldest layer of coring corals obtained from the windward side started from 1940, while in leeward of the island starting from 1969. All five metals from both sides were still detected until 2014. There was significant increase over time of the four metals (Cr, Fe, Zn. and Pb), while the concentrations of strontium remained relatively stable.
Elevated CO2 caused by human activities is thought as a cause of future climate change driving global warming and ocean acidification. In order to predict global environments in the near future, it is required to understand the past environmental change and its process in detail. While it is well known that biogenic carbonates such as foraminifera and coccolithophorid are attractive tools to reconstruct the past environments, scleractinian corals also provide environmental data around tropical to subtropical region with much higher time resolution. In this review, I summarize previous works on paleo-environments based on chemical components of fossil and modern coral skeletons in order of the age from Pliocene to the present. Then recent studies concerning elemental variability in micro scales of skeletal surfaces and current issues accompanying with new findings from these studies are discussed. I hope that this review will inspire further study in this field.
Here we present coral Sr/Ca data of biweekly resolution from three modern coral cores drilled from living Porites corals from two different reef settings at Chagos (tropical Indian Ocean). Chagos lies at the eastern margin of the Seychelles-Chagos thermocline ridge and features open ocean upwelling. In situ temperatures have been recorded by temperature loggers since 2006. High-resolution satellite temperatures closely track the logger data. Two cores were collected from a patch reef in the lagoon of Peros Banhos, a site characterized by high mean temperatures and low-temperature variability. An open ocean core was collected at the outer reef slope of Diego Garcia, which experiences larger temperature fluctuations related to open ocean upwelling. The open ocean core shows clear seasonal cycles in Sr/Ca that closely track the satellite temperatures. The Sr/Ca records from the two lagoon corals show good reproducibility. Between 2007 and 2010, Sr/Ca tracks satellite temperatures. However, between 2003 and 2006 the Sr/Ca curves are almost flat and annual coral growth rates are low. During these years, warm sea surface temperatures and coral bleaching have been observed at Chagos. It is likely that the observed reduction in coral growth rates is a response to prolonged warming events, adding to the growing evidence that seemingly healthy and surviving corals are affected by thermal stress. Further, the high correlation between the Sr/Ca records of the two lagoon cores suggests that this effect is not limited to single coral colonies but may affect the entire reef setting.
Dust storms occur frequently in arid and semi-arid regions of China and other parts of the world, exerting a considerable influence on air quality in densely populated areas. Instrumental observations of dust storms are only available over the past 50 to 60 years, limiting our ability to understand dust storm variability over longer timescales. However, tropical sea surface temperatures have been reconstructed over the past four centuries, using geochemical records from corals. Here we show that tropical Pacific sea surface temperatures, as recorded by corals, can be used to reconstruct dust storm frequency at one-year resolution. Based on the coral-reconstructed annual sea-surface temperature anomaly data from two regions (the western Pacific; 25°N–25°S, 110–155°E, and the eastern Pacific; 10°N–10°S, 175°E–85°W) published by Tierney et al. (2015), we reconstructed the frequency of dust storms in northern China (DSFCN) for the period from 1617 to 1953 CE. The reconstructed DSFCN variation can be divided into several distinct periods: (1) DSFCN increased from 1617 to 1650, then (2) decreased from 1650 to 1675, (3) remained unchanged from 1675 to 1755, (4) increased again from 1755 to 1860, (5) remained unchanged from 1860 to 1925, and finally (6) decreased rapidly from 1925 to 1995. We propose the following causal chain to explain the observed relationship between DSFCN and SST: as tropical Pacific Ocean SST increases, the Siberian High weakens and the Eastern Asian Trough strengthens. As the air pressure difference weakens, the East Asian Winter Monsoon weakens, and strong wind frequency decreases, causing DSFCN to decrease as well. The statistical results support this interpretation of the causal chain.
Interglacial climate state are an important aspect of Quaternary climate, representing time of decreased global ice volume, and warm conditions similar to the present. Acquiring high- resolution paleoclimate data from these interglacial period critical for establishing the natural range of climate variability that exist in the absence of anthropogenic greenhouse gas forcing and/or under variable orbital forcing regimes. In addition paleoclimate data can shed light on how the climate system responded to various external or internal forcing mechanisms in the past, and also the thresholds and feedback systems that are in place. Stemming from this knowledge is a greater understanding of the modern climate system and thus predictive capabilities for what the future climate holds.
Seasonality is an intrinsic component of all climate systems, and has been linked to both large scale change in the growth and decay of the N. Hemisphere ice sheets, and abrupt climate change event such as Heinrich events and the Younger Dryas. Massive corals and giant clams are fast growing. High -resolution tropical climate archives that precipitate aragonite skeletons from sea water and preserve environmental information in their skeletal geochemistry. Fossil coral and clam records thus have the ability to provide ‘snapshots' of tropical climate and seasonality during earlier interglacial interval. Several seasonally resolved paleoclimate records exist for the In terglacial (–125 ka) however prior to this, few records exist, reasons being that limited samples are preserved beyond the Last Interglacial (fossil corals older than the Last Interglacial arc generally uncommon on tectonically stable sites) and diagenetic effect can alter the primary geochemistry of a sample. In addition. the applicability of modern day SST calibrations fossil specimens is questionable over interglacial/glacial timescales due to possible oceanic baseline change (∂180 and Sr/Ca) or biological effect.
In this thesis I attempt to overcome these problems using a multi-faceted approach that includes analysis of well preserved MIS 9 (339-303 ka) Porites coral from Henderson Island (25°S . 128°W) and MIS 11 5e (128-116 ka) and MIS 11 (423-360 ka) Tridacna clam from Huon Peninsula. Papua New Guinea (PNG ) (6°S, 148°E). Both sites have experienced uplift, thus preserving fossil reefs, and difference in location offer a unique opportunity to examine contrasting aspects of the paleo-climate system (sub-tropical climate vs. WP\VP ocean- atmosphere interaction ). The amplitude of the seasonal cycle of SST was reconstructed in a MIS 9 fossil Porites using 8180 and Sr/Ca average-slope calibration equations. The results suggest SST seasonality was similar or slightly larger (+18%) than present. Using the latitudinal relationship between insolation seaonality and SST seasonality, a new approach is investigated that uses the orbital forcing of seasonal SST cycle to place suborbital constraints on the timing of reef growth. The MIS 9 Porites specimen is con trained to one of two brief intervals: 327-320 ka, or 306-299 ka, which correlate to the MIS 9.3 and MIS
9.1 interstadials respectively.
Climate signals are also investigated in modern and fossil Tridacna gigas from Huon Peninsula, PNG, through analysis of stable isotope and a suite of trace clement ratios (Ba/Ca, Mg/Ca. Sr/Ca and B/Ca). 8180 is found to be a robust indicator of interannual variability associated with ENSO. and by applying modern threshold limits to a MIS 11 fossil
T. giga, a high-resolution paleo-ENSO record is generated. This MIS II record suggests El Nino events were reduced in frequency compared to present( 14 events/century vs. -26 events/century for the current regime). The ability of Tridacna to maintain geochemical integrity and allow high resolution climate records to be reconstructed over the last 400 k)•r, highlights the significant potential of this climate archive for future paleoclimate studies. Tridacna Ba/Ca and Mg/Ca also show potential as indicators of productivity and sea surface temperature respectively, though additional work is required to determine their fidelity as climate proxies. Although problems relating to baseline uncertainties prohibit absolute SST reconstructions in both fossil Porites and Tridacna, signal seasonality is a robust characteristic of these fossil records and provides some interesting insights into these Late Quaternary interglacial climates.
Paleoclimate studies are critically dependanton accurate dating method: in this the is the prospect of using a diffusion-adsorption model to obtain reliable U-series for fossil Tridacna is also investigated. by characterising the spatial distribution of secondary uranium in their skeletons using LA ICPMS techniques, and identifying possible uptake historic through simple open-system modelling. It is concluded that the D-A model can not be applied to fossil Tridacna to obtain age estimates, owing to their structural complexities and complex, multi-stage uranium-uptake histories.
抄録
後期更新世～完新世の陸上古気候記録媒体として石筍は優れた特徴を持ち，中国南部での石筍酸素同位体の結果は夏のアジアモンスーン強度を反映した標準的古気候記録として認知されている．しかし，石筍試料の安定同位体比や微量元素含有量は大気・土壌・鍾乳洞で起こる多くのプロセスに支配されており，プロキシから定量的に気温や降水量を見積もるには至っていない．石筍の酸素同位体比には降水強度・降水の季節性・温度・水の蒸発が，炭素同位体比には滴下水の供給量・植生・土壌湿度が反映される．また，滴下前に水が方解石を沈殿していた場合，石筍の微量元素含有量と炭素同位体比は影響を受ける．プロセスの複雑さにもかかわらず，異なる地点での石筍記録は同調することが多い．最終氷期以降の気候イベントの時間的一致は，降水量や気温の変化が広域的に起こっていたことを示唆する．石筍古気候学は気温と降水量の分離を目指し，今後進展していくだろう．
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