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To evaluate the relationships between coral calcification, thermal stress, and sedimentation and eutrophication linked to human impact (hereafter referred to as \"land development\") by river discharge, we analyzed growth characteristics in the context of a paleoenvironment that was reconstructed from geochemical signals in modern and fossil (1.2 cal kyr BP and 3.5 cal kyr BP, respectively) massive Porites corals from Nagura Bay (\"Nagura\") and from modern Porites corals from the estuary of the Todoroki River, Shiraho Reef (\"Todoroki\"). Both sites are on Ishigaki Island, Japan, and Nagura is located approximately 12 km west of Todoroki. At Nagura, the individual corals provide time windows of 13 (modern), 10 (1.2 cal kyr BP), and 38 yr in length (3.5 cal kyr BP). Here, we present the coral annual calcification for Nagura and Todoroki, and (bi) monthly resolved records of Sr/Ca (a proxy of sea surface temperature (SST)) and Ba/Ca (a proxy of sedimentation and nutrients related to land development) for Nagura. At Nagura, the winter SST was cooler by 2.8°C in the 1.2 cal kyr BP, and the annual and winter SSTs in the 3.5 cal kyr BP were cooler by 2.6°C and 4.6°C, respectively. The annual periodicity of Ba/Ca in modern coral is linked to river discharge and is associated with land development including sugar cane cultivation. Modern coral calcification also has declined with SST warming and increasing Ba/Ca peaks in winter. However, calcification of fossil corals does not appear to have been influenced by variations in Sr/Ca and Ba/Ca. Modern coral growth characteristics at Nagura and Todoroki indicate that coral growth is both spatially and temporally influenced by river discharge and land development. At Nagura, our findings suggest that land development induces negative thermal sensitivity for calcification in winter due to sugar cane harvest, which is a specifically modern phenomenon.

The historical record of daily light cycle in tropical and subtropical regions is short. Moreover, it remains difficult to extract this cycle in the past from natural archives such as biogenic marine carbonates. Here we describe the precise analysis of Sr/Ca, Mg/Ca, and Ba/Ca ratios in a cultivated giant clam shell, using a laterally high-resolution secondary ion mass spectrometer with 2 μm resolution. The Sr/Ca ratio exhibits striking diurnal variations, reflecting the daily light cycle. A clear seasonal variation in Sr/Ca is also observed in another longer set of measurements with 50 μm resolution. Light-enhanced calcification and elemental transportation processes, in giant clam and symbiotic algae, may explain these diurnal and annual variations. This opens the possibility to develop the Sr/Ca ratio from a giant clam shell as an effective proxy for parameters of the daily light cycle. A record of the daily light cycle in tropical regions is difficult to extract from biogenic marine carbonates such as shells. Here, the precise analysis of Sr/Ca ratios is shown in a cultivated giant clam shell, revealing variations that reflect the daily light cycle and the potential for future development of a proxy.

The response of Acropora digitifera to ocean acidification is determined using geochemical proxy measurements of the skeletal composition of A. digitifera cultured under a range of pH levels. We show that the chemical composition (δ 11 B, Sr/Ca, Mg/Ca, and Ba/Ca) of the coral skeletons can provide quantitative constraints on the effects of seawater pH on the pH in the calcification fluid (pH CF ) and the mechanisms controlling the incorporation of trace elements into coral aragonite. With the decline of seawater pH, the skeletal δ 11 B value decreased, while the Sr/Ca ratio showed an increasing trend. The relationship between Mg/Ca and Ba/Ca versus seawater pH was not significant. Inter-colony variation of δ 11 B was insignificant, although inter-colony variation was observed for Ba/Ca. The decreasing trend of pH CF calculated from δ 11 B was from ~8.5, 8.4, and 8.3 for seawater pH of ~8.1, 7.8, and 7.4, respectively. Model calculations based on Sr/Ca and pH CF suggest that upregulation of pH CF occurs via exchange of H + with Ca 2+ with kinetic effects (Rayleigh fractionation), reducing Sr/Ca relative to inorganic deposition of aragonite from seawater. We show that it is possible to constrain the overall carbonate chemistry of the calcifying fluid with estimates of the carbonate saturation of the calcifying fluid ( Ω CF ) being derived from skeletal Sr/Ca and pH CF (from δ 11 B). These estimates suggest that the aragonite saturation state of the calcifying fluid Ω CF is elevated by a factor of 5–10 relative to ambient seawater under all treatment conditions.

Then as now for El Niño Coarse resolution palaeoclimate proxy evidence has suggested that the Pliocene warm period (PWP) between 3 million and 5 million years ago was characterized by permanent El Niño conditions in which the equatorial Pacific was uniformly warm, instead of having the modern-day 'cold tongue' extending westward from South America. New high-resolution climate proxy data from fossil corals raise doubts over this assertion. Well-preserved PWP-era fossil corals with clear skeletal annual bands, discovered in the Philippines, show that ocean conditions in the western Pacific during the PWP were characterized by El Niño variations that are similar to those we see today. Coarse-resolution palaeoclimate proxy evidence has suggested that the Pliocene warm period (∼3–5 million years ago) was characterized by permanent El Niño conditions in which the equatorial Pacific was uniformly warm, instead of having the modern-day 'cold tongue' extending westward from South America. This study uses high-resolution climate proxy information from fossil corals to challenge this assertion and shows that ocean conditions in the western Pacific during the Pliocene warm period were characterized by El Niño variations similar to modern-day variations. The El Niño/Southern Oscillation (ENSO) system during the Pliocene warm period (PWP; 3–5 million years ago) may have existed in a permanent El Niño state with a sharply reduced zonal sea surface temperature (SST) gradient in the equatorial Pacific Ocean 1 . This suggests that during the PWP, when global mean temperatures and atmospheric carbon dioxide concentrations were similar to those projected for near-term climate change 2 , ENSO variability—and related global climate teleconnections—could have been radically different from that today. Yet, owing to a lack of observational evidence on seasonal and interannual SST variability from crucial low-latitude sites, this fundamental climate characteristic of the PWP remains controversial 1 , 3 , 4 , 5 , 6 , 7 , 8 , 9 , 10 . Here we show that permanent El Niño conditions did not exist during the PWP. Our spectral analysis of the δ 18 O SST and salinity proxy, extracted from two 35-year, monthly resolved PWP Porites corals in the Philippines, reveals variability that is similar to present ENSO variation. Although our fossil corals cannot be directly compared with modern ENSO records, two lines of evidence suggest that Philippine corals are appropriate ENSO proxies. First, δ 18 O anomalies from a nearby live Porites coral are correlated with modern records of ENSO variability. Second, negative-δ 18 O events in the fossil corals closely resemble the decreases in δ 18 O seen in the live coral during El Niño events. Prior research advocating a permanent El Niño state may have been limited by the coarse resolution of many SST proxies, whereas our coral-based analysis identifies climate variability at the temporal scale required to resolve ENSO structure firmly.

The response of Acropora digitifera to ocean acidification is determined using geochemical proxy measurements of the skeletal composition of A. digitifera cultured under a range of pH levels. We show that the chemical composition ( delta super(11)B, Sr/Ca, Mg/Ca, and Ba/Ca) of the coral skeletons can provide quantitative constraints on the effects of seawater pH on the pH in the calcification fluid (pH sub(CF)) and the mechanisms controlling the incorporation of trace elements into coral aragonite. With the decline of seawater pH, the skeletal delta super(11)B value decreased, while the Sr/Ca ratio showed an increasing trend. The relationship between Mg/Ca and Ba/Ca versus seawater pH was not significant. Inter-colony variation of delta super(11)B was insignificant, although inter-colony variation was observed for Ba/Ca. The decreasing trend of pH sub(CF) calculated from delta super(11)B was from ~8.5, 8.4, and 8.3 for seawater pH of ~8.1, 7.8, and 7.4, respectively. Model calculations based on Sr/Ca and pH sub(CF) suggest that upregulation of pH sub(CF) occurs via exchange of H super(+) with Ca super(2+) with kinetic effects (Rayleigh fractionation), reducing Sr/Ca relative to inorganic deposition of aragonite from seawater. We show that it is possible to constrain the overall carbonate chemistry of the calcifying fluid with estimates of the carbonate saturation of the calcifying fluid ( Omega sub(CF)) being derived from skeletal Sr/Ca and pH sub(CF) (from delta super(11)B). These estimates suggest that the aragonite saturation state of the calcifying fluid Omega sub(CF) is elevated by a factor of 5-10 relative to ambient seawater under all treatment conditions.

The response of Acropora digitifera to ocean acidification is determined using geochemical proxy measurements of the skeletal composition of A. digitifera cultured under a range of pH levels. We show that the chemical composition (δ^sup 11^B, Sr/Ca, Mg/Ca, and Ba/Ca) of the coral skeletons can provide quantitative constraints on the effects of seawater pH on the pH in the calcification fluid (pH^sub CF^) and the mechanisms controlling the incorporation of trace elements into coral aragonite. With the decline of seawater pH, the skeletal δ^sup 11^B value decreased, while the Sr/Ca ratio showed an increasing trend. The relationship between Mg/Ca and Ba/Ca versus seawater pH was not significant. Inter-colony variation of δ^sup 11^B was insignificant, although inter-colony variation was observed for Ba/Ca. The decreasing trend of pH^sub CF^ calculated from δ^sup 11^B was from ~8.5, 8.4, and 8.3 for seawater pH of ~8.1, 7.8, and 7.4, respectively. Model calculations based on Sr/Ca and pH^sub CF^ suggest that upregulation of pH^sub CF^ occurs via exchange of H^sup +^ with Ca^sup 2+^ with kinetic effects (Rayleigh fractionation), reducing Sr/Ca relative to inorganic deposition of aragonite from seawater. We show that it is possible to constrain the overall carbonate chemistry of the calcifying fluid with estimates of the carbonate saturation of the calcifying fluid ([Omega] ^sub CF^) being derived from skeletal Sr/Ca and pH^sub CF^ (from δ^sup 11^B). These estimates suggest that the aragonite saturation state of the calcifying fluid [Omega] ^sub CF^ is elevated by a factor of 5-10 relative to ambient seawater under all treatment conditions.

To evaluate the relationships between coral calcification, thermal stress, and sedimentation and eutrophication linked to human impact (hereafter referred to as \"land development\") by river discharge, we analyzed growth characteristics in the context of a paleoenvironment that was reconstructed from geochemical signals in modern and fossil (1.2 cal kyr BP and 3.5 cal kyr BP, respectively) massive Porites corals from Nagura Bay (\"Nagura\") and from modern Porites corals from the estuary of the Todoroki River, Shiraho Reef (\"Todoroki\"). Both sites are on Ishigaki Island, Japan, and Nagura is located approximately 12 km west of Todoroki. At Nagura, the individual corals provide time windows of 13 (modern), 10 (1.2 cal kyr BP), and 38 yr in length (3.5 cal kyr BP). Here, we present the coral annual calcification for Nagura and Todoroki, and (bi) monthly resolved records of Sr/Ca (a proxy of sea surface temperature (SST)) and Ba/Ca (a proxy of sedimentation and nutrients related to land development) for Nagura. At Nagura, the winter SST was cooler by 2.8 degree C in the 1.2 cal kyr BP, and the annual and winter SSTs in the 3.5 cal kyr BP were cooler by 2.6 degree C and 4.6 degree C, respectively. The annual periodicity of Ba/Ca in modern coral is linked to river discharge and is associated with land development including sugar cane cultivation. Modern coral calcification also has declined with SST warming and increasing Ba/Ca peaks in winter. However, calcification of fossil corals does not appear to have been influenced by variations in Sr/Ca and Ba/Ca. Modern coral growth characteristics at Nagura and Todoroki indicate that coral growth is both spatially and temporally influenced by river discharge and land development. At Nagura, our findings suggest that land development induces negative thermal sensitivity for calcification in winter due to sugar cane harvest, which is a specifically modern phenomenon.