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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. [ABSTRACT FROM AUTHOR]

Compared with other ocean basins, annual resolution long-term series of sea-level records in the South China Sea (SCS) are still rare. Here we first analyzed the correlation mechanism between the oxygen stable isotopes (δ18O) of Porites coral and instrumental sea-level, sea surface salinity (SSS), sea surface temperature (SST) and rainfall of the SCS, and NINO 3.4 SST during 1980–2015 CE (Common Era); and we then quantitatively reconstructed sea-level at an annual resolution based on the coral δ18O in the SCS. The results show that the sea-level fell slightly (−0.73 ± 0.27 mm/yr) during 1850–1900 CE; then has continuously risen (1.31 ± 0.06 mm/yr) with a total increase of 152 ± 7 mm from 1900 to 2015 CE. On the inter-annual timescale, ENSO by mediating the overflow effect of seawater in the Western Pacific Warm Pool and the location of storm genesis in the western Pacific, indirectly affects sea-level, rainfall and SSS, which is finally reflected in changes in coral δ18O in the SCS. On the long-term timescale, especially since the 1900s, the gradual increase in SST and glaciers and ice sheets meltwater injected into the ocean due to the continuous warming mainly caused by human activities has not only promoted the rise of sea-level, but also caused a gradual negative bias of δ18O seawater (i.e. a gradual decrease of SSS), these processes are faithfully recorded by coral δ18O. Compared with SST, SSS or δ18O seawater may play a more important role in promoting the negative bias of coral δ18O in the SCS. Our study not only provides a better understanding of sea-level history and relationship mechanism around the SCS during 1850–2015 CE, but also may have the potential to provide a valuable proxy for the accurate quantitative reconstruction of sea-level at an annual resolution over a longer time scale for recent past periods. • On the interannual timescale, ENSO is the main driver of coral δ18O via its indirect effects on seawater δ18O in the SCS • On the long-term timescale, SST and injection of meltwater are the main driver of changes in coral δ18O and sea-level • Both SSS and SST are bridges between coral δ18O and sea-level • Coral δ18O is an ideal proxy to indicate sea-level, which has risen by 152 ± 7 mm in total from 1900 to 2015 CE in the SCS [ABSTRACT FROM AUTHOR]

Few reconstructions of sea-surface temperature (SST) have focused on seasonal and interannual variability, two major components of the global climate system, due to the limited temporal resolution of proxies. This study presents a combined 228-year-long, monthly resolved strontium to calcium ratios (Sr/Ca) record covering the period of 2070–1740 a BP (years before 1950 CE (Common Era)) extracted from three U-series-based sub-fossil Porites corals located on the Xisha Islands, northern South China Sea (SCS). The composite time series allowed for accurate assessment of the natural range of SST variations during snapshots of the Roman Warm Period (RWP). Reconstructed SST revealed that the RWP was characterized by cooler conditions compared with the 20th century, consistent with climatic variations in the western Pacific and East Asia. The amplitude of SST seasonality was within the modern range, except for a lower value at 1980–1928 a BP. Interannual variability associated with El Niño–Southern Oscillation (ENSO) activity was enhanced by 39% relative to 1980–2014 CE. The results of the sliding window demonstrate that ENSO variability persistently strengthened during 2070–2010 a BP, followed by an overall fluctuating attenuation during 1980–1928 a BP. Then, the trends of rising first before descending twice during 1852–1800 a BP appeared. Furthermore, ENSO activity played a leading role in steering short-term changes in SST seasonality in the northern SCS, manifested as stronger ENSO activity with more frequent El Niño events and decreased SST seasonality. Considering that the frequency of extreme ENSO events may strengthen in the future under global warming, the climate in the northern SCS might become more variable and complex. • 228-year monthly SST derived from coral Sr/Ca for snapshots of the Roman Warm Period. • Cooler conditions and variable SST seasonality characterize the 2070–1740 a BP. • Stronger interannual variability and ENSO evolution for the RWP are investigated. • ENSO activity modulates changes of SST seasonality in the northern South China Sea. [ABSTRACT FROM AUTHOR]

Despite organophosphate esters (OPEs) are widely prevalent in the environment, however, limited information is available regarding their occurrence, trophodynamics, and exposure risks in coral reef ecosystems. In this study, 11 OPEs were investigated in a tropical marine food web (7 fish species and 9 benthos species) from the Xisha (XS) Islands, South China Sea (SCS). The ∑ 11 OPEs were 1.52 ± 0.33 ng/L, 2227 ± 2062 ng/g lipid weight (lw), 1024 ± 606 ng/g lw, and 1800 ± 1344 ng/g lw in seawater, fish, molluscs, and corals, respectively. Tris (2-chloroisopropyl) phosphate (TCIPPs) were the dominant OPEs in seawater, fish, and molluscs, while tris (2-butoxyethyl) phosphate (TBOEP) predominated in coral tissues. Abiotic and biotic factors jointly affect the OPEs enrichment in marine organisms. Trophic magnification factors (TMFs) (range: 1.31–39.2) indicated the biomagnification potency of OPEs. A dietary exposure risk assessment indicated that OPEs at current levels in coral reef fish posed a low risk to human health but were not negligible. Overall, this study contributes to a further understanding of the environmental behaviors of OPEs in coral reef ecosystems. [Display omitted] • OPEs profiles in seawater and marine organisms are different. • Fish tend to enrich Cl-alkyl OPEs and benthos prefer to accumulate aryl OPEs. • Abiotic and biotic factors jointly affect the OPEs enrichment in marine organisms. • OPEs pose a low risk to human health by coral reef fish ingestion. • Emerging pollutants are dominating the pollution status in the Xisha Islands. [ABSTRACT FROM AUTHOR]

Recent studies have indicated that coral mucus plays an important role in the bioaccumulation of a few organic pollutants by corals, but no relevant studies have been conducted on organochlorine pesticides (OCPs). Previous studies have also indicated that OCPs widely occur in a few coral reef ecosystems and have a negative effect on coral health. Therefore, this study focused on the occurrence and bioaccumulation of a few OCPs, such as dichlorodiphenyltrichloroethanes (DDTs), hexachlorobenzene (HCB) and p , p ′-methoxychlor (MXC), in the coral tissues and mucus as well as in plankton and seawater from a coastal reef ecosystem (Weizhou Island) in the South China Sea. The results indicated that DDTs were the predominant OCPs in seawater and marine biota. Higher concentrations of OCPs in plankton may contribute to the enrichment of OCPs by corals. The significantly higher total OCP concentration (∑ 8 OCPs) found in coral mucus than in coral tissues suggested that coral mucus played an essential role in resisting enrichment of OCPs by coral tissues. This study explored the different functions of coral tissues and mucus in OCP enrichment and biodegradation for the first time, highlighting the need for OCP toxicity experiments from both tissue and mucus perspectives. [Display omitted] • OCPs were firstly studied in coral mucus in the South China Sea. • Plankton may have an influence on coral enrichment of OCPs. • Obvious higher ∑ 8 OCPs occurred in coral mucus than in coral tissues. • Coral mucus showed lower metabolic capability of DDTs than coral tissues. • Coral mucus may resist the enrichment and metabolism of OCPs by coral tissues. [ABSTRACT FROM AUTHOR]

The El Niño-Southern Oscillation (ENSO) is the most influential climatic phenomenon on an interannual timescale. Studying the relationship between sea surface temperature (SST) and ENSO events during typical geological periods is helpful for understanding the trends of ENSO activities in the future, especially under the background of global warming. Here we quantitatively reconstructed a 115-year history of SST and ENSO activity around 282 ka during Marine Isotope Stage 8 (MIS8) by using the growth rate of Porites corals from Xisha Islands in the South China Sea. The results show that the average coral growth rate (6.0 ± 1.0 mm/yr (1σ)) around 282 ka was only 56.1% of the modern average value (10.7 ± 0.9 mm/yr; 1937–2014 CE), and the average SST (26.0 ± 0.3 °C (1σ)) was 0.7 ± 0.4 °C and 1.1 ± 0.4 °C lower than that in the Little Ice Age (LIA; 1520–1676 CE; 26.7 ± 0.2 °C) and the present (1937–2014; 27.1 ± 0.2 °C), respectively. The reconstructed results show that there was significant ENSO activity with moderate intensity or above at 282 ka, while the frequency of ENSO activity at that time was lower than that of the LIA and the present. This seems to indicate that the frequency of moderate intensity ENSO activity increases with rising SST. Given the current rapid warming, the future trend of ENSO activities deserves close attention. • The growth rate of Porites coral is a reliable paleoenvironmental proxy. • The coral growth rate at 282 ka was only equivalent to 56.1% of the present. • Coral–SST at 282 ka was 0.7 °C and 1.1 °C lower than the LIA and present, respectively. • The ENSO frequency at 282 ka was lower than the present. [ABSTRACT FROM AUTHOR]

As one of the most abundant metals in heavy oils, Ni has suffered so notably increasing impacts from industrial and traffic activities that anthropogenic Ni emissions have altered natural geochemical processes. The coral Ni/Ca has become a reliable proxy for characterizing marine pollution, but this potential has been unexploited for highlighting oil pollution. Here, we utilized a high-resolution record of geochemical parameters (Ni/Ca, δ18O, and δ13C) in a Porites coral of an offshore island in the northern South China Sea to reconstruct of Ni distribution patterns in surface seawater from 1984 to 2015. The coral Ni/Ca ratios exhibit minor fluctuations, except for multiple mutation peaks (0.20 ± 0.42 μmol/mol) during the period from 1984 to 1993. The ratio was low and stable (0.10 ± 0.09 μmol/mol) from 1994 to 2008, and then increased rapidly with significant variations (1.60 ± 4.56 μmol/mol) from 2009 to 2015. The coral Ni/Ca ratios captured all significant Ni discharges, and this demonstrates its potential for recording oil spill episodes. The historical variations in the contributions of Ni indicate that industrial and traffic activities should be responsible for changes in the anthropogenic input. The leaks and consumptions of petroleum likely account for the primary Ni emission sources. [Display omitted] • Anthropogenic Ni input has altered the geochemical processes of oceanic Ni. • Coral Ni/Ca records have potentials to be novel proxies for surface winds. • Temporal emissions of anthropogenic Ni can be captured by coral Ni/Ca records. [ABSTRACT FROM AUTHOR]

Antibiotics have been the subject of much attention in recent years due to their widespread use and the potential ecological risks and resistance risks. In this study, we conducted an extensive survey of 19 antibiotics in a wide range of waters of the Beibu Gulf during summer and winter (154 samples). The total concentrations of the 19 antibiotics (Σ 19 ABs, ng/L) were significantly higher in winter (n.d.–364) than in summer (n.d.–70.1) and were mainly concentrated in areas of seagoing rivers (1.50–364). The primary route for antibiotics entering Beibu Gulf was through riverine input. Precisely, florfenicol (FF) (n.d.–278 ng/L) discharged from livestock and poultry farms upstream of Nanliu River, predominantly in swine farming, constitutes the main pollutant in Beibu Gulf throughout the year. The Nanliu River (988 kg/a) accounts for 85% of the gulf's total annual antibiotic emission flux. Source analysis identified livestock and poultry farming, particularly swine farming, as the primary pollution source, contributing 58% in summer. Risk assessment reveals that algae (0.51 ± 0.56) exhibited relatively high sensitivity to antibiotics, presenting a medium-high risk at specific sites in Nanliu River during winter. Additionally, FF discharged from swine farming demonstrates a certain level of antibiotic resistance risk. Therefore, reinforcing control measures for antibiotic discharges from livestock and poultry farming, especially upstream of Nanliu River, can effectively mitigate antibiotic-related risks in the water bodies of Beibu Gulf. [Display omitted] • Antibiotic levels in Beibu Gulf coastal water are higher in winter than summer. • The Nanliu River is the primary contributor of antibiotics through riverine inputs. • Livestock farming discharge is the primary source of antibiotics in Beibu Gulf. • Algae have a higher risk sensitivity to antibiotics than crustaceans and fish. [ABSTRACT FROM AUTHOR]

Holocene coral reef development is valuable to understanding the behavior and impacts of paleoclimate and sea level changes. This study focuses on the Holocene carbonate sequences of a drill core extracted from Well CK2 in the northern South China Sea (SCS). This drill core consists of an 873.55 m thick carbonate layer overlying 55.20 m of volcanic basement. High precision U-series dating of 22 coral samples suggests that the Holocene coral reef, which has a thickness of 16.7 m, initiated at ~7800 yr BP (years before 1950 CE) and stopped vertical accretion at 3900 yr BP. The mean vertical accretion rate in the Holocene in Well CK2 was 3.48 m kyr−1, varying from 6.44 m kyr−1 during 7800–6000 yr BP to 0.87 m kyr−1 during 6000–3900 yr BP. After 3900 yr BP, the vertical development of the reef ceased, indicating that the reef development likely involved lateral accretion. The Holocene section mostly consists of unconsolidated coarse sediments, mainly including corals, coralline algae, large benthic foraminifera, and mollusks. Based on the relationship between coral reef development and sea level, together with the age profile, we determined that the relative sea level near Chenhang Island rose rapidly between 7800 and 6000 yr BP, slowed at ~6000 yr BP, and reached a position of about 2 m above the present-day mean sea level by 3900 yr BP. After 3900 yr BP, the sea level was stable or fell, resulting in a cessation in the reef's upward development. • 22 230Th ages of a SCS reef core suggest the Holocene reef initiated at 7800 yr BP. • Vertical development decreased from 6.44 to 0.87 m kyr−1 at 3900 yr BP. • Sea level at 7800 yr BP was ~13.8 m below present and rose rapidly. • Sea level has stabilized/fallen since 3900 yr BP, as indicated by reef development. [ABSTRACT FROM AUTHOR]

Global warming and sea-level rise (SLR) induced by rising atmospheric CO2 concentrations can cause coral bleaching, death, and submergence of the world's coral reefs. Adopting the GIS and RS methods, we modeled how these two stressors combine to influence the future growth of the atolls and table reefs of three archipelagoes in the South China Sea (SCS), based on geomorphic and ecological zones. A large-scale survey of the coral communities in Xisha Islands in 2014, Dongsha Islands in 2014–2016 and Nansha Islands in 2007 provided zone-specific process datasets on the range of reef accretion rates. Sea surface temperature and extreme (minimum and maximum) SLR data above 1985–2005 levels by 2100 in the SCS were derived from the Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) models forced with the Representative Concentration Pathways (RCPs). Our model projected that: (1) the Xisha Islands and Dongsha Islands may have a better growth status, because the reef flat biotic sparse zone may be recolonized with hard coral and become a biotic dense zone; (2) the southern Nansha Islands reefs have a risk of stopping growing due to their earlier annual bleaching years. The increasing of water depths of these reefs is stronger in the RCP with more emissions. Our approach offers insights into the best-case and worst-case impacts of two global environmental pressures on potential future reef growth under a changing climate. [ABSTRACT FROM AUTHOR]

Most studies on coral bleaching alerts use common Degree Heating Week (DHW) thresholds; however, these may underestimate historical patterns of heat stress for coral reef ecosystems. Taking an optimized DHW threshold for coral bleaching alerts for Coral Reef Watch (CRW) and Coral Reef Temperature Anomaly Database (CoRTAD) products, we analyzed the precise spatial and temporal pattern of heat stress on China's coral reefs from 2010 to 2021 in the South China Sea (SCS) and the Beibu Gulf (BG). We compared acute heat stress using common and optimized thresholds. Results indicated that the ocean warming rate in 2010–2021 was approximately 0.43 ± 0.22 °C/10a, showing a significant increase in the northern SCS and the BG. More severe bleaching events were predicted by the optimized thresholds and the high-frequency areas were mainly in the northern SCS. The number and intensity of years with severe heat stress anomalies was in the order 2020 > 2014 > 2010 > 2015. Heat stress duration was the longest in the Xisha Islands among offshore archipelagos, and longest in 2020–2021 in Weizhou Island in BG in the relative high-latitude inshore reefs. These abnormal events were mainly caused by El Niño, but La Niña was also involved in 2020. • The most intense severe heat stress anomaly years were 2010 > 2014>2020 > 2015. • The anomaly duration of offshore islands was Xisha > Dongsha > Zhongsha > Nansha Islands. • High-latitude reefs were predicted not to be future thermal refuges for SCS reefs. • The optimized DHW threshold more accurately predicted spatiotemporal heat stress. [ABSTRACT FROM AUTHOR]

Nutrient enrichment is a widely recognized threat to coastal coral reefs. Yet its impact on open ocean reefs is largely unknown due to the lack of long-term observations at remote sites and the entanglement of various environmental factors affecting coral growth. Here we determined growth rates and the carbonate chemistry of calcifying fluid (CF) of massive corals over the last 550 years at a remote South China Sea reef ecosystem. We show that large growth variations cannot be fully explained by changes in seawater pH or temperature due to the antiphase relationship between growth rate and pH cf as well as small sea surface temperature variations before the 1960s. Instead, coral growth rate decreases proportionally with past seabird populations over the past centuries. We suggest that excess nutrient loads through monsoon pumping and seabird migration played an important role in controlling coral growth at this remote reef ecosystem. Specifically, episodic eutrophication as indicated by a ∼ 3 per mil increase in coral δ13C has depressed coral growth by ∼30% during 15th to 18th centuries, which is comparable to the modern decline. Thus, accurate projections of future coral growth for remote reefs under ongoing human activities and climate change needs to take into account the history of past nutrient inputs into these ecosystems under pre-anthropogenic conditions, which has been overlooked previously due to a lack of historical observations. • Coral cores from an open ocean reef that grew from ∼1450 to present were analyzed. • Temperature affects multi-decadal variability in coral calcifying fluid DIC but not pH. • Reef-water pH modified by monsoon controls calcifying fluid pH and [CO 3 2−] • Eutrophication caused by monsoon and seabirds depressed coral growth during the Little Ice Age • An analog to the responses of corals to the projected rise in anthropogenic nutrient inputs. [ABSTRACT FROM AUTHOR]

As emerging pollutants, the environmental geochemistry of organophosphate esters (OPEs) in the coastal zone with multiple functional areas are still less recognized. This study investigated spatiotemporal distribution, sources and risks of 11 widely used OPEs in surface waters from seagoing rivers and multiple coastal functional areas of the Beibu Gulf. The results indicated that significantly higher ∑ 11 OPEs (total concentrations of 11 OPEs, ng/L) occurred in summer (34.2–1227) than in winter (20.6–840), as a result of the high emission caused by climate reasons. In general, higher ∑ 11 OPEs occurred in rivers (41.2–1227) than in the coast (34.2–809) in summer, especially in the urban rivers, while in winter, higher ∑ 11 OPEs occurred in the coast (23.4–840 vs 20.6–319 in rivers) because of obviously higher ∑ 11 OPEs in marine fishery areas (99–840). Source identification revealed that fishery activity, especially fishing vessels, and urban rivers were the main sources of OPEs in the Beibu Gulf. For the individual OPE, only tri-n-butyl phosphate (TNBP) may have ecological risks to aquatic organisms in a few sites, but if considering the additive effects, the OPEs mixtures would pose a high risk to algae and low to medium threats to crustaceans and fish. [Display omitted] • OPEs' levels and sources were studied in the coastal water of Beibu Gulf (BG). • High temperature and rainfall may promote the release of OPEs to the environment. • Riverine discharge and fishery activities were the main sources of OPEs in the BG. • Ecological risk of OPEs at different trophic levels were assessed in BG. • They pose relatively high ecological risks to aquatic organisms, especially algae. [ABSTRACT FROM AUTHOR]