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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]

Aim: In this study, we investigated whether environmental factors can effectively control the spatial distribution of various benthic algae and examined the critical ecological impacts of algae on corals across the South China Sea (SCS). Relationships between benthic algae and environmental factors were assessed, and potential ecological impacts of algae on coral communities were evaluated across spatial scales. Location: A total of 104 sites at 12 coral reefs in four coral reef regions (CRRs) of the SCS (latitude range of 9–22° N). Taxa: Turf algae, macroalgae (including fleshy macroalgae and Halimeda), crustose coralline algae (CCA), coral and juvenile coral. Methods: Using diver‐based surveys (2015–2018), we investigated four CRRs with different reef distance to mainland (RDM) across the SCS. We obtained field data on benthic algal composition and cover, coral cover and diversity, and juvenile coral density. We also measured and collected the environmental factors (including seawater environmental parameters and reef fish diversity). Results: The cover of turf algae and CCA gradually decreased and increased, respectively, with an increase in RDM, which had a strong relationship with the gradually changing environmental factors. Random forest models suggested that nutrients, reef fish diversity, seawater transparency and temperature were the most important factors for predicting turf algae and CCA cover. Linear regression analyses showed a significant relationship between the turf algae, macroalgae, and CCA covers, and juvenile coral density. Main conclusions: Our results showed that gradually changing environmental factors were correlated with the spatial distributions of turf algae and CCA. However, the natural biophysical relationships between macroalgae and environmental factors may be disrupted by turf algal overgrowth and nutrient subsidies. Increases in all benthic algal groups significantly impacted coral recruitment, highlighting the critical role of benthic algae in determining the recovery trajectory of the Indo‐Pacific reefs that are threatened by human activities. [ABSTRACT FROM AUTHOR]

The El Niño–Southern Oscillation (ENSO) dominates interannual climate variability worldwide and has important environmental and socio‐economic consequences. However, determining the evolution of ENSO variability and its long‐term response to climate forcing remains an ongoing challenge owing to the limited instrumental records. In this study, we quantified ENSO variability via an empirically calibrated threshold and sliding variance windows using monthly sea‐surface temperature (SST) anomalies based on Porites coral Sr/Ca records from the Xisha Islands in the northern South China Sea. Instrumental SST anomalies from the Xisha Islands correctly captured increasing ENSO variability in the twentieth century, with ENSO detection skills similar to those for Niño3.4 regions. Coral Sr/Ca‐SST anomalies can also serve as sensitive and robust proxies for ENSO variability. Sub‐fossil coral Sr/Ca‐SST anomalies indicated intensified ENSO variability at the end of the Medieval Climate Anomaly (MCA) from 1149 to 1205 ± 4.9 (2σ) Common Era (CE). Combining our records with other ENSO‐sensitive proxy reconstructions from the tropical Pacific, we observed fluctuating ENSO variability during the MCA and intensified ENSO variability for the late MCA. Considering the fewer and low intensity fluctuations associated with external climate forcing and the absence of a coherent temporal correspondence of ENSO activity with solar irradiance and volcanic eruption during the MCA, we hypothesized that the internal dynamics of the climate system play a prominent role in modulating ENSO variability and its evolution, which is supported by unforced climate model simulations and coral reconstructions across the tropical Pacific. Key Points: Coral Sr/Ca‐sea‐surface temperature variations from the northern South China Sea are a reliable proxy of El Niño–Southern Oscillation variabilityIntensified El Niño–Southern Oscillation variability occurred during the late Medieval Climate AnomalyUnforced internal variability within the climate system likely play a prominent role in modulating El Niño–Southern Oscillation variability [ABSTRACT FROM AUTHOR]

The knowledges of trophic status (i.e., autotrophy/heterotrophy) of corals are helpful for understanding the mechanisms driving their environmental stress tolerance and bleaching resilience. We conducted this study to elucidate the differences in trophic status among corals of different genera and then explore the implication of trophic status for their different environmental stress tolerance. In this study, 117 coral samples including five genera (i.e., relatively stress‐tolerant massive genera Porites, Favites, and Favia and relatively vulnerable plating genus Pavona and branching genus Acropora) were collected from Weizhou Island, northern South China Sea. The symbiotic zooxanthellae density, δ13C of host tissues (δ13Ch), and symbiotic zooxanthellae (δ13Cz) were measured. Besides, the difference in values between δ13Ch and δ13Cz (i.e., △h‐z 13C) was analyzed. Our results indicated that both zooxanthellae density and δ13Cz values of Porites, Favites, and Favia are higher than that of Pavona and Acropora and indicate that autotrophic photosynthesis intensity of symbiotic zooxanthellae of Porites, Favites, and Favia is higher than that of Pavona and Acropora. Besides, both δ13Ch and △h‐z 13C of Porites, Favites, and Favia are lower than that of Pavona and Acropora and indicate a higher contribution of heterotrophic predation to the coral host of Porites, Favites, and Favia. These comparisons suggest that trophic status of relatively stress‐tolerant Porites, Favites, and Favia is more plasticity than vulnerable Pavona and Acropora, which is conducive to maintain a positive energy budget. This is one of important factors leading to different environmental stress tolerance and bleaching resilience among corals of different genera. Key Points: Autotrophic photosynthesis and heterotrophic predation of massive corals are higher than that of plating and branching coralsTrophic status of relatively stress‐tolerant massive corals is more plasticity than that of vulnerable plating and branching coralsDifferent trophic status is one of important factors leading to different environmental stress tolerance and bleaching resilience [ABSTRACT FROM AUTHOR]

The decadal variability of ocean primary productivity (PP) has mainly been studied using relatively short term satellite data, limiting its in‐depth analysis. Here, by removing the influence of the 13C Suess effect, we extract the PP signal on decadal timescales using a record of coral δ13C values from the northern South China Sea (NSCS), where the physical‐biogeochemical conditions are influenced largely by the winter monsoon. Our results show that the PP in the NSCS increased from 1851 to the 1920s and decreased from the 1920s to 2007, and large superimposed decadal‐scale changes were observed. The in‐phase relationship observed between the PP reconstruction and winter monsoon records suggests that the changes in the PP in the NSCS are linked to decadal‐scale changes in the winter monsoon. Considering that the winter monsoon intensity may weaken in the future under global warming, the PP in the NSCS might decrease in the coming decades. Plain Language Summary: Marine phytoplankton contributes roughly half of the global primary production and thus constitutes a vital component of the marine ecosystem that serves as the foundation of the marine food web. Due to the relatively short length of observation records, evaluations of the long‐term changes in ocean primary productivity (PP) have suffered from large uncertainties, which have hampered further discussion of the decadal variability of PP in a long‐term context. To discuss the decadal variability of the PP beyond the range of satellite observations, we present a coral‐based PP reconstruction since 1851 CE from the northern South China Sea (NSCS), where the physical‐biogeochemical conditions are influenced largely by the winter monsoon. Our results show considerable decadal variability of the PP in the NSCS superimposed on a pre‐1920s increase and a post‐1920s decrease. We also found an in‐phase relationship between the decadal variability of the reconstructed PP and the winter monsoon records over the past 150 years, indicating that the PP in the NSCS is linked to changes in the winter monsoon forcing on decadal timescales. Considering that the winter monsoon intensity may weaken in the future under global warming scenarios, the PP in the NSCS might decrease in the coming decades. Key Points: The decadal variability of primary productivity was extracted from a coral δ13C record by removing the influence of the 13C Suess effectThe coral‐based primary productivity reconstruction for the past 150 years showed a pre‐1920s increase and a post‐1920s decreaseThe primary productivity of the northern South China Sea varied in phase with the intensity of the winter monsoon on decadal timescales [ABSTRACT FROM AUTHOR]

To date, the decadal variability of the Global Monsoon (GM) has been mainly studied using instrumental data collected over the last 50 years, and further discussion has been hampered by the limited data length. Here, we present a coral δ18O record from the northern South China Sea, where the hydrology is related to the seasonal Intertropical Convergence Zone (ITCZ) migration, and we use this record to reconstruct the decadal migration of the ITCZ since 1851 A.D. Combining our record with a synthesis of monsoon records reveals an anti‐phase inter‐hemispheric variability of the GM over the last 150 years, indicating that the decadal‐scale hydrologic variability in the tropics is modulated by the meridional migration of the ITCZ. The plausible relationship observed between the decadal variability of the GM and the Atlantic Multidecadal Oscillation suggests that the decadal variability of tropical hydrological changes is likely linked to the climate perturbations in the North Atlantic. Plain Language Summary: The prediction of monsoon variability in the coming decades will be of great importance for policy‐making and socio‐economic development. The Global Monsoon (GM) is the global‐scale seasonal atmospheric overturning associated with the migration of the Intertropical Convergence Zone (ITCZ). The variability and dynamics of the GM on decadal timescales are still unclear due to the limited length of the instrumental data (< 50 years). Here, we integrated a synthesis of the monsoon and the ITCZ records, including published records and our new coral record, and found that the GM varied in an anti‐phase inter‐hemispheric mode on decadal timescales associated with the ITCZ migration over the past 150 years, suggesting that the simultaneous intensification of the monsoons in both hemispheres since the ~1980s was unusual in a long‐term context. The linkage between the decadal variability of GM and the Atlantic Multidecadal Oscillation/Variability indicated that the North Atlantic has been driving the anti‐phase inter‐hemispheric variability of the GM on decadal timescales. Key Points: The coral δ18O record from the northern South China Sea captures the migration of the regional ITCZ on decadal timescalesThe Global Monsoon varied in an anti‐phase inter‐hemispheric mode on decadal timescales associated with the ITCZ migration since 1851 A.DThe decadal variability of the Global Monsoon was found to be linked to the Atlantic Multidecadal Oscillation [ABSTRACT FROM AUTHOR]