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Abstract The Sr/Ca ratio of modern coral skeletons can record local seawater temperature (T) and is an important tool for reconstructing 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. The 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 adds midpoint alignments between the min/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.

One of the fundamental hypotheses in aquatic ecology deals with the recognition of fish stocks. The present study tested the spatial dynamics of starry sturgeon stocks across environmental gradients by spatial variability in strontium to calcium in the pectoral fin spine. Forty samples of starry sturgeon were collected from the north and south of the Caspian Sea. A quantitative method was used to examine stocks using digested pectoral fin spine, reflecting habitat characters of fish. Parts of pectoral fin spines from adult starry sturgeon were separated and analyzed using Inductively Coupled Plasma- Mass Spectrometry (ICP-MS). Comparisons of Sr/Ca ratios in digested spines of the fish from north and south of the Caspian Sea demonstrated that Sr/Ca varied in the region and this significance was reflected in the spine as well. Our results for starry sturgeon support the use of spine Sr/Ca as a proxy for ambient levels throughout their life-history, confident interpretation of life history from spine Sr/Ca chronologies, however likely require matching time series of ambient Sr/Ca in the water bodies of interest.

Coral geochemical tracers have been used in studies of the paleoclimatology and paleoceanography of the tropics and subtropics. We measured Sr/Ca and oxygen isotope ratios (δ18O) in a coral sample collected from the southern part of Lombok Strait, a significant outlet of the Indonesian Throughflow (ITF) to the Indian Ocean, to reconstruct the historical record of sea surface temperature (SST) and seawater δ18O. Seawater δ18O can be used to approximate sea surface salinity (SSS) because it reflects the balance of evaporation and precipitation. The resulting time series reconstructed SST and SSS, covering the period 1962–2012, shows no clear trend of global warming, although the record includes a large cooling event (~4°C) during 1996–1997. Although neither SST nor SSS shows a systematic relationship with El Niño–Southern Oscillation and Indian Ocean Dipole (IOD), weak but significant correlations are found partly. In addition, the coral data show signals of major IOD and El Niño events in 1994 and 1997, respectively, although climatic trends recorded in the coral are not consistent with those found along the Java-Sumatra coast. To evaluate other influences on the ITF in Lombok Strait, we compared our coral record with coral records from sites in the Java Sea, the southern part of Makassar Strait, and Ombai Strait. During the northwest monsoon (December–January–February), variations in SST and SSS at Lombok Strait site are similar to those at the Java Sea and southern Makassar sites for the period 1962–1995, which suggests that low-salinity water from the Java Sea is carried at least to the southern part of Makassar Strait where it suppresses the ITF upstream from Lombok Strait. However, the SST and SSS records differ at the three sites during the southeast monsoon (June–July–August), indicating that surface conditions in Lombok Strait vary separately from those in the Java Sea. In the longer term, although global warming has been widely identified in the Indonesian Seas, the coral record shows no clear warming trend in the southern part of Lombok Strait, where fluctuations in the ITF may be modulating the distribution of heat in the surface waters of the western Pacific and eastern Indian Ocean.

Oxygen isotope composition (δ18O) in Porites coral skeletons at the micrometer scale has been proposed to be uninfluenced by temperature in previous studies. Considering that temperature is the main controlling factor of coral δ18O at the macro scale, the effect of temperature on the δ18O variations at the micrometer scale should be evaluated carefully. To better understand the climatic and biological significance of high-resolution δ18O in coral skeletons, in situ δ18O values were analyzed in three modern Porites corals from the South China Sea and the Great Barrier Reef by a Cameca IMS 1280-HR secondary ion mass spectrometry (SIMS). A twice vacuum impregnation procedure for sample mount preparation and a subsection calibration method based on multiple controlling points for coral matrix effect correction were used for SIMS analysis. The derived SIMS coral δ18O time series exhibit consistent long-term variations with the monthly δ18O (measured by conventional gas isotope ratios mass spectrometry), monthly Sr/Ca, and daily sea surface temperature, first highlighting the dominant temperature control on micrometer-scale coral δ18O. The 1.5‰ fluctuation amplitude of SIMS coral δ18O at the scales of 400–800 μm can be explained by the combined SST effects of ~10-day variation and day–night fluctuation, whereas the effects of seawater δ18O and growth rate on SIMS coral δ18O seem not dominant. Some abnormally negative δ18O values possibly resulted from the primary ion bombardment on indistinguishable centers of calcification.

Abstract Reconstructing intermediate and bottom‐water temperature in the Arctic Ocean is key for understanding paleoclimatic phenomena, such as the region's interactions with warm Atlantic waters, stratification, and sea‐ice dynamics. However, benthic proxy archives are sparse throughout the Arctic circle compared to lower latitudes. Trace‐element ratios (E/Ca) derived from ostracodes, a group of bivalved microscopic crustaceans, have shown promise in this regard. Samples for E/Ca measurements typically require rigorous cleaning prior to analysis, and signs of contamination are routinely monitored through the presence of other trace elements such as Al, Fe, and Mn, which are associated with suspected sources of overprinting. However, there has not yet been an intra‐valve investigation of all of these trace elements, which may hinder our ability to effectively identify geochemical overprinting. Here, we present several elemental concentration and E/Ca ratio measurements in two ostracode genera, Krithe and Polycope, extracted from Chukchi Sea sediment samples. We further investigate the intra‐valve distribution of elements within single shells of adult and juvenile specimens using electron probe microanalysis (EPMA). Our findings suggest that brushing and bleach treatments may not be effective for completely eliminating clays from the edges of valves, which can bias paleoclimatologically relevant trace‐element proxies such as Mg/Ca ratios, particularly in the case of incomplete or small samples with low amounts of calcite material. In addition, we report the first trace‐element data from the genus Polycope, which shows potential as a new Arctic paleotemperature archive.

DOI:10.17014/ijog.2.1.43-51Indonesia is an interesting and important location for a climate study, because it is located in the centre of a warm pool and adjacent to Pacific and Indian Oceans. Long records of climate data are required from this region to more understand the climate variability and the response of global warming. Geochemical proxies derived from Porites corals are believed to be an excellent climate recorder. Sr/Ca content in Porites corals from Kendari, Southeast Sulawesi shows that seasonal variability of SST is resolved by coral Sr/Ca from this region. The monsoon strongly influences reconstructed SST from coral Sr/Ca. Coral SST shows strong power spectrum at the 2.75 year period. Annual to interannual coral SST signal is stronger than the decadal to interdecadal signal. Both ENSO and IOD influence coral SST at two-month and three-month lags respectively.

Early-life stages of reef-building corals are vital to coral existence and reef maintenance. It is therefore crucial to study juvenile coral response to future climate change pressures. Moreover, corals are known to be reliable recorders of environmental conditions in their skeletal materials. Aposymbiotic Acropora millepora larvae were cultured in different seawater temperature (27 and 29°C) and pCO2 (390 and 750 μatm) conditions to understand the impacts of “end of century” ocean acidification (OA) and ocean warming (OW) conditions on skeletal morphology and geochemistry. The experimental conditions impacted primary polyp juvenile coral skeletal morphology and growth resulting in asymmetric translucent appearances with brittle skeleton features. The impact of OA resulted in microstructure differences with decreased precipitation or lengthening of fasciculi and disorganized aragonite crystals that led to more concentrations of centers of calcifications. The coral skeletal δ11B composition measured by laser ablation MC-ICP-MS was significantly affected by pCO2 (p = 0.0024) and water temperature (p = 1.46 × 10−5). Reconstructed pH of the primary polyp skeleton using the δ11B proxy suggests a difference in coral calcification site and seawater pH consistent with previously observed coral pH up-regulation. Similarly, trace element results measured by laser ablation ICP-MS indicate the impact of pCO2. Primary polyp juvenile Sr/Ca ratio indicates a bias in reconstructed sea surface temperature (SST) under higher pCO2 conditions. Coral microstructure content changes (center of calcification and fasciculi) due to OA possibly contributed to the variability in B/Ca ratios. Our results imply that increasing OA and OW may lead to coral acclimation issues and species-specific inaccuracies of the commonly used Sr/Ca-SST proxy.

DOI: 10.17014/ijog.v6i3.121Sea surface temperature (SST) is one of the important parameters for (paleo) climate studies. The long time series of SST data are required to understand more the climate change. Coral geochemical proxy such as Sr/Ca overcomes this problem. Coral can provide long time series of climate data continuously from present till hundreds years ago, even fossil (dead) coral can do it till thousand years ago. In this study, Sr/Ca content of Porites coral within 10 m deep from Labuan Bajo, Simeulue Island was analyzed to reconstruct SST. Coral Sr/Ca shows a strong correlation with local SST in seasonal scale as well as in the annual mean scale. Reconstructed SST data show that the monsoon between 1993 2007 strongly influence the SST variation in the Simeulue region. It supposed that the seasonal variation signal strongly influence local SST than the annual mean signal such as El Nino.

DOI: 10.17014/ijog.v5i2.96Sr/Ca content ratio in coral is a promising tool for a sea surface temperature reconstruction. In this study, Sr/Ca was analyzed from the top core of fossil coral from Central Mentawai, Indonesia (BLS). The dating of U/Th is used for the age determination of the fossil coral. Based on the U/Th dating, the fossil coral used in this study was deposited in 14th century which approximately has a time range 11 years. The result of this study shows that in the 14th century, the sea surface temperature increased by 3.20 C during 11 years period.

Sr/Ca has been analyzed from coral core from the Seribu Islands reef complex i.e Jukung Island. SST from ERSST dataset and air temperature measured at Jakarta is used for Sr/Ca calibration. The results show that Jukung Island coral Sr/Ca correlates better with SST than with air temperature. A comparison between the Sr/Ca records with the Nino 3.4 index shows that Jukung coral sites indicate warming sea surface temperatures during the beginning of El Nino events followed by cooling temperatures at the end of El Nino years.

A better understanding of the global climate system depends on our ability to expand the limited instrumental records of sea surface temperature (SST) of tropical regions. The Sr/Ca and Mg/Ca ratios contained in the growth bands of corals have proved to be an accurate tool to reconstruct SST variability. In this study we show the calibration obtained from the seasonal geochemical measurement of the Sr/Ca and Mg/Ca molar ratios in the skeleton of coral of the genus Porites from San Benedicto Island, in the Revillagigedo Archipelago, and SST. The geochemical ratios measured (precision ±0.2%, 2σ) showed a high seasonal covariation closely related to the region's SST. The calibration equation calculated for the Sr/Ca–SST relation (n = 52) was Sr/Ca (mmol mol–1) = 10.467 (±0.067) – 0.0524 (±0.003) × SST (r2 = 0.894), and for the Mg/Ca?SST relation it was Mg/Ca (mmol mol–1) = 1.550 (±0.095) + 0.0956 (±0.0043) × STT (r2 = 0.906). When comparing the SST time series reconstructed from the Sr/Ca and Mg/Ca ratios with the mean SST of a spatial grid of 2º × 2º (longitude × latitude) that comprises San Benedicto Island, we found a high concordance between both temperatures, showing the robustness of the procedure. A drawback of this method is that no unique calibration exists for the Sr/Ca–SST and Mg/Ca–SST relations, and the different calibrations published generate discrepancies of up to 8ºC in the calculated temperature, regardless of whether the thermal sensitivity (i.e., the slope of the paleotemperature equation) of corals is similar. We therefore concluded that the Sr/Ca and Mg/Ca paleothermometers are highly reliable in this region of the Pacific Ocean, provided that a specific equation exists for the area under study.