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Tropical cyclones (TCs) lead to huge economic losses and casualties in coastal regions, but multi‐decadal variation of TC remains poorly understood due to the limited length of observational records and low‐resolution reconstructions. Porites corals provide continuous and monthly resolved records that allow for the determination of weather‐timescale (weekly to monthly) extreme events, including TC, to overcome the above limitations. Here we synthesize five coral Δδ18O records from the South China Sea (SCS) and develop a coral TC frequency index, in good agreement with post‐1980 instrumental records and sediment‐based TC reconstructions over the past century. Our results indicate that TC frequency in the SCS exhibits pronounced decadal variations, with active TCs corresponding to the negative phase of the Pacific Decadal Oscillation. Our findings here provide novel evidence for past TC changes in the SCS and a constraint for predicting future TC changes. Plain Language Summary: The impact of tropical cyclones (TCs) on coastal regions results in significant economic losses and casualties. Due to the relatively short observations or low‐resolution records, assessing long‐term changes of TCs has suffered from large uncertainties. Porites corals are sensitive to environmental changes and can provide century‐long, monthly resolved records, which could serve as a potential archive for reconstructing past TCs. Here we present five coral Δδ18O records from the South China Sea (SCS) and develop two TC frequency indexes. Both the TCs generated in the SCS and those entering the SCS from the Western North Pacific are reflected in our coral‐based TCs reconstruction. In addition, our reconstruction suggests that the TCs in the SCS were increased in 1878–1888, 1894–1904, 1934–1952, 1971–1978, and 1995–2004, which corresponded to the negative phase of the Pacific Decadal Oscillation over the past century. Our findings provide new evidence for historical changes in TCs in the SCS and a valuable constraint for predicting future TC variations. Key Points: The low residual oxygen isotope values of coral strongly respond to tropical cyclones in the South China SeaExcluding temperature, we reconstruct tropical cyclone activities in the South China Sea over the past century using coral oxygen isotopesPacific Decadal Oscillation modulates tropical cyclones in the South China Sea over the past century [ABSTRACT FROM AUTHOR]

Significant differences in environmental conditions between nearshore and offshore coral reefs lead to different symbiotic zooxanthellae density (ZD) of corals. From the perspective of energy supply, different ZD lead to different energy provided by the photosynthesis of zooxanthellae to the coral host. However, few studies have conducted a comparative analysis of coral trophic status (i.e., autotrophic photosynthesis of zooxanthellae and heterotrophic feeding of the host) between nearshore and offshore reefs. In this study, 70 coral samples of Favia palauensis were collected from the nearshore Sanya reefs, and offshore Xisha, Nansha reefs in the South China Sea (SCS). The ZD, δ15N of seawater particulate organic matter (δ15NPOM), host tissue (δ15Nh), zooxanthellae (δ15Nz) and the difference between δ15Nh and δ15Nz (i.e., △h−z 15N = δ15Nh−δ15Nz) were measured and statistically analyzed. The purpose is to elucidate the differences in the energy maintenance mechanisms of corals between nearshore and offshore reefs. Results show that ZD is significantly positively correlated with δ15Nz in all three reefs (p < 0.05). Corals in nearshore Sanya have higher autotrophic abilities than corals from offshore Xisha and Nansha reefs. By contrast, corals in offshore reefs are more dependent on heterotrophic feeding of the host to obtain energy. Our research demonstrate that corals can adjust their trophic status, especially improve their heterotrophic feeding intensity to meet energy needs under different environmental conditions. This dynamic adjustment of energy supply patterns is of great significance to improve coral's environmental adaptability. Plain Language Summary: Coral reefs are mainly divided into nearshore fringing reefs, barrier reefs and offshore atolls according to geographical distribution. Therein, ambient seawater in nearshore reefs are significantly affected by human activities and has relatively higher nutrient levels. In contrast, corals in offshore atolls are less affected by human activities as they are far away from the mainland, but they will be potentially affected by abnormal natural conditions. Different environmental conditions lead to significant differences in the physiological parameters of corals, such as symbiotic zooxanthellae density (ZD). From the perspective of energy supply, different ZD may lead to different energy provided by the photosynthesis of zooxanthellae to the coral host. However, few studies have conducted a comparative analysis of coral trophic status between nearshore and offshore reefs. Based on the δ15N labeling technology, we find that corals in nearshore fringing reefs have higher autotrophic abilities than corals from offshore reefs. By contrast, corals in the offshore reefs are more dependent on heterotrophic feeding of the host to obtain energy. This means that corals can adjust their trophic status to meet energy needs under different environmental conditions. This dynamic adjustment of energy supply patterns is of great significance to improve coral's environmental adaptability. Key Points: The δ15N can record coral trophic status changes between nearshore and offshore reefsCorals in nearshore reefs have higher autotrophic photosynthesis and heterotrophic energy than corals in offshore reefsCoral can independently adjust trophic status under different environmental conditions between nearshore and offshore [ABSTRACT FROM AUTHOR]

Cadmium (Cd) geochemical cycle plays a significant role in the composition and function of the marine ecosystem. Skeletal cadmium‐to‐calcium (Cd/Ca) ratios in hermatypic corals have been applied to reconstruct the historical changes of oceanic and climatic processes, yet there was no systematic evaluation of this tracer's natural variability in high resolution over time. Here, we reported a coral skeletal Cd/Ca record in monthly resolution from 1999 to 2008 CE and reconstructed the history of Cd contents in surface seawater in the northern South China Sea. A significant seasonal variation (higher in the winter but lower in the summer) of Cd contents in surface seawater can be identified. We found that the seasonal variations in coral skeletal Cd/Ca ratios exhibited significant trends coupled with the surface wind speeds, indicating that strong winds had likely driven the vertical seawater mixing process and then induced the process of sediment remobilization on the shelf, which significantly increased Cd contents in surface seawater. The reduction in Cd contents in surface seawater due to biological processes might be masked by the impacts of surface winds. Importantly, we also observed that coral skeletal Cd/Ca records in the winter showed significant correlations with the winter monsoon index, highlighting the possibility as a new proxy of winter monsoon in the non‐upwelling shelf environments. Plain Language Summary: Cadmium (Cd) is a nutrient element absorbed by phytoplankton in surface seawater, showing a distribution of low surface content and high bottom content. In order to determine the seasonal variations of Cd content in surface seawater in the northern South China Sea, we analyzed the coral skeletal Cd/Ca ratios in monthly resolution (1999–2008 CE) and finally concluded that the process of sediment resuspension and vertical mixing of seawater driven by winter monsoons is the main reason. The reduction of Cd contents in surface seawater due to biological processes was masked by the impacts of surface winds. In the past, Cd content in seawater/coral has been used to track the history of upwelling and El Niño Southern Oscillation, but the potential indicative on winter monsoon has not been reported so far. Considering that the trend between coral skeletal Cd/Ca ratios and average wind speeds showed a great agreement, we suggested that coral skeletal Cd/Ca ratios in the winter might be a potential proxy of winter monsoon. Key Points: Coral skeletal Cd/Ca ratios in monthly resolution were first reportedSeawater mixing process and sediments resuspension caused by winter monsoon are responsible for Cd seasonal variations in surface seawaterCoral skeletal Cd/Ca ratios have potential to be a novel proxy for winter monsoon [ABSTRACT FROM AUTHOR]