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Strontium isotopes (87Sr/86Sr) are commonly used to assess the age of Cenozoic dolostones found on many isolated oceanic islands. The possible influence of Rubidium (Rb) content on the 87Sr/86Sr ratios, however, has generally been ignored. This critical issue is assessed by examining the 87Sr/86Sr ratios and elements (Rb, Sr, Al, Ti and K) of seventy‐one samples that came from a ca 339 m thick cored interval of Cenozoic dolomite on the Xisha Islands, South China Sea. For the dolomite from the upper Pliocene Yinggehai Formation (180.5 to 308.5 m; average 23% dolomite) there is a positive correlation between the 87Sr/86Sr ratios and Rb concentrations, whereas for the dolomite from the lower late Miocene Huangliu Formation (308.5 to 519 m; average >98% dolomite) such a correlation is not evident. Combined with high‐temperature experiments, correlation between Al, Ti, K, Rb and 87Sr/86Sr indicates that Rb containing old 87Rb from terrestrial materials modified the 87Sr/86Sr ratios of the Yinggehai dolomite, but not those from the Huangliu dolomite. This is mainly attributed to the different sources of terrestrial dust carried by different East Asian monsoon systems between the late Miocene and Pliocene, and probably also influenced by the dolomitization process to some extent. To test for 87Rb contamination, extrapolation of results from the Yinggehai dolomite and Huangliu dolomite indicate that concentrations of Rb < 1 ppm, Al < 1000 ppm, Ti < 15 ppm and K < 250 ppm in the dolomite indicates that terrestrial inputs are minimal and that the measured 87Sr/86Sr ratios can be used for determining the dolomitization age. Potentially, these concentration thresholds may serve as a screening criterion for assessing the reliability of Sr isotope chronostratigraphy of other island dolostones throughout the world. [ABSTRACT FROM AUTHOR]

Coral skeleton δ13C is a routinely measured indicator in modern insolation change research, but the knowledge of environmental and climatic signals recorded in its seasonality during geological time is sparse. In this study, we present eight Porites coral δ13C records from the mid‐late Holocene to the present from the northern South China Sea (NSCS). Compared with the main control factors for modern δ13C changes, coral δ13C seasonality in the NSCS since the mid‐Holocene shows a long‐term decreasing trend, which is consistent with the change trend as orbital‐induced (precession) insolation seasonal amplitude. By excluding other influencing factors, we speculate that the stronger coral δ13C seasonality (18.8%) over the mid‐Holocene than modern period is attributable to the metabolic effect, which predicts the stronger coral δ13C seasonality under stronger insolation seasonality. Our study has implications for coral δ13C seasonality as a potential indicator to record past insolation information under different climatic backgrounds. Plain Language Summary: Numerous studies have documented the seasonal features of fast‐growing modern coral skeleton δ13C in response to insolation variation. The environmental and climatic signals recorded by coral δ13C seasonality in the geological period remain unclear owing to the relatively short length of observation records. Here we present monthly resolved δ13C records in seven fossil Porites corals (5.6–3.6 ka BP, before 1950 CE) and one modern Porites coral (1987–2001 CE) from the northern South China Sea (NSCS). Compared with the widely accepted prevailing control factors for modern coral δ13C, our results indicated that the stronger coral δ13C seasonality (18.8%) over the mid‐Holocene compared to the modern period is consistent with the orbital‐induced (precession) insolation changes, which indicate a declining seasonality from the mid‐Holocene to present. By excluding other influencing factors, we infer that a tendency toward higher δ13C seasonality during the mid‐Holocene was primarily driven by the metabolic fractionation caused by the enhanced insolation seasonality. This study highlighted coral δ13C seasonality as a potential indicator for recording past insolation information. Key Points: The seasonal variation of modern coral skeleton δ13C in the northern South China Sea (NSCS) is primarily controlled by solar insolationCoral δ13C seasonality in the NSCS since the mid‐Holocene shows a long‐term decreasing trendThe decrease of orbital‐induced (precession) insolation seasonal amplitude led to the declining trend of δ13C seasonality [ABSTRACT FROM AUTHOR]

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]

Epigenetic modifications based on DNA methylation can rapidly improve the potential of corals to adapt to environmental pressures by increasing their phenotypic plasticity, a factor important for scleractinian corals to adapt to future global warming. However, the extent to which corals develop similar adaptive mechanisms and their specific adaptation processes remain unclear. Here, to reveal the regulatory mechanism by which DNA methylation improves thermal tolerance in Pocillopora damicornis under fluctuating environments, we analyzed genome-wide DNA methylation signatures in P. damicornis and compared the differences in the methylation and transcriptional responses of P. damicornis from fluctuating and stable environments using whole-genome bisulfite sequencing and nanopore-based RNA sequencingtranscriptome sequencing. We discovered low methylation levels in P. damicornis (average methylation 4.14%), with CpG accounting for 74.88%, CHH for 13.27%, and CHG for 11.85% of this methylation. However, methylation levels did not change between coral samples from the fluctuating and stable environments. The varied methylation levels in different regions of the gene revealed that the overall methylation level of the gene body was relatively high and showed a bimodal methylation pattern. Methylation occurs primarily in exons rather than introns within the gene body In P. damicornis , there was only a weak correlation between methylation and transcriptional changes at the individual gene level, and the methylation and gene expression levels generally exhibited a bell-shaped relationship, which we speculate may be due to the specificity of cnidarian species. Correlation analysis between methylation levels and the transcriptome revealed that the highest proportion of the top 20 enriched KEGG pathways was related to immunity. Additionally, P. damicornis collected from a high-temperature pool had a lower metabolic rate than those collected from a low-temperature pool. We hypothesize that the dynamic balance of energy–expenditure costs between immunity and metabolism is an important strategy for increasing P. damicornis tolerance. The fluctuating environment of high-temperature pools may increase the heat tolerance in corals by increasing their immunity and thus lowering their metabolism. • Scleractinian corals are more tolerant in fluctuating reef-dwelling environments. • Low methylation levels in P. damicornis. • Thermal acclimation increase tolerance in corals by increasing coral immunity and thus lowering their metabolism. • Dynamic balance of energy–expenditure costs between immunity and metabolism is an important strategy. [ABSTRACT FROM AUTHOR]

Beachrock is considered a good archive for past sea-levels because of its unique formation position (intertidal zone). To evaluate sea-level history in the northern South China Sea, three well-preserved beachrock outcrops (Beigang, Gongshanbei, and Hengling) at Weizhou Island, northern South China Sea were selected to examine their relative elevation, sedimentological, mineralogical, and geochemical characteristics. Acropora branches with well-preserved surface micro-structures were selected from the beachrocks and used to determine the ages of these beachrocks via U-series dating. The results show that the beachrocks are composed of coral reef sediments, terrigenous clastics, volcanic clastics, and various calcite cements. These sediments accumulated in the intertidal zone of Weizhou Island were then cemented in a meteoric water environment. The U-series ages of beachrocks from Beigang, Gongshanbei, and Hengling are 1712–768 ca. BP, 1766–1070 ca. BP, and 1493–604 ca. BP (before 1950 AD) respectively. Their elevations are 0.91–1.16 m, 0.95–1.24 m, and 0.82–1.17 m higher than the modern homologous sedimentary zones, respectively. Therefore, we concluded that the sea-level in the Meghalayan age (1766–604 ca. BP) was 0.82–1.24 m higher than the present, and that the sea-level over this period showed a declining trend. [ABSTRACT FROM AUTHOR]

Summary: Environmental conditions between the outer reef slope (ORS) and lagoon in tropical atolls are significantly different, but the variations of juvenile coral‐microbiomes in the two environments and their relationship with coral thermal acclimatization are poorly understood. We explored this issue based on local water conditions and the microbiome of juvenile corals in the ORS and lagoon in the central South China Sea. Coral‐symbiotic Symbiodiniaceae showed significant differences among coral species; Pocillopora verrucosa and Pachyseris rugosa in the ORS, and Acropora formosa in the lagoon were dominated by Durusdinium, but other corals were dominated by Cladocopium. Although A. formosa in the ORS were dominated by Cladocopium (C3u), they were dominated by Durusdinium (D1/D1a) and Cladocopium (C50) in the lagoon. Other coral species were both dominated by Cladocopium in the lagoon and ORS. The relative abundance of bacteria in the Deinococcus–Thermus was generally higher in the lagoon corals than in the ORS corals. Our study indicates that P. verrucosa, P. rugosa and Porites lutea may have high thermal tolerance based on the relatively high abundance of heat‐tolerant Durusdinium and Thermus scotoductus. Likewise, A. formosa in the lagoon may acclimatize to the thermal environment based on a high relative abundance of heat‐tolerant Durusdinium. [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]

El Niño-Southern Oscillation (ENSO) is the largest source of interannual climate variability over the globe. Knowledge of ENSO variability back to the pre-instrumental period (and earlier) can help to enhance our understanding of its mechanisms and impacts. Here we use the coral record from the northern South China Sea, where the interannual climate variability is associated with ENSO activity, to reconstruct ENSO variability over the past 150 years. Our record, together with other ENSO chronologies, indicated not only the weakened ENSO activity between ~1930s and ~1960s but also the larger variations of El Niño activity relative to that of La Niña based on the sliding window method. The comparison between the SCS and Pacific ENSO band coral records revealed the relatively stronger climatic coupling between the SCS and the equatorial central-eastern Pacific compared with that between SCS and western Pacific, indicating the reliability of teleconnection relationship between the SCS climate and ENSO. Our result indicated that the coral δ 18O record from the SCS could contribute to the pan-Pacific ENSO reconstructions. [ABSTRACT FROM AUTHOR]

As one of the microcontinents dispersed in the South China Sea (SCS), the Xisha microcontinent lacks the petrological evidence of the Cenozoic magmatic activity and basement. Well CK‐2, as a full‐coring kilometre‐scale major scientific drilling in Xisha Islands in the northwestern SCS, drilled through the thick reefal limestone and into the underlying basaltic pyroclastic rocks basement. This paper presents zircon U–Pb age and mineral chemistry of clinopyroxenes from the basaltic pyroclastic rocks. Mineral composition of the clinopyroxenes suggests that most of the clinopyroxenes are composed of diopside, which contains relatively high Al(w (Al2O3) = 5.03%–10.25%) and Ti(w (TiO2) = 2.2%–4.95%). The clinopyroxene discrimination diagrams show that the primary magma is alkaline basalt and likely generated in an intraplate tectonic setting. U–Pb dating of zircons by LA‐ICP‐MS yielded a wide range of ages: 36–33, 116–104, 148–140, 207–196, 255–236, 440, 808–749, and 2,440–1185 Ma. The youngest group has an average age of 35.5 ± 0.9 Ma, which is considered as the maximum age of the basalt eruption. The 2440 ± 19 Ma, which is the oldest zircons in the SCS, are firstly found in the basaltic pyroclastic rocks from the SCS, suggesting that the SCS may contain very old materials. The ages of the inherited zircons are comparable to magmatic activities that occurred around the SCS, implying that they were probably once linked and an integrated part of Gondwana. The ancient continental basement has experienced multistages magmatic events. [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]

Abstract Frequent storm surges often cause catastrophic impacts on human lives and the global economy; however, these phenomena are not well understood. In this study, a regional storm reconstruction is performed based on a grain-size analysis and stratigraphic modelling of the accelerator mass spectrometry radiocarbon dates of benthic foraminifera from two neighbouring lagoon cores from Lingyang Reef in the Xisha Islands located in the northern South China Sea of the western Pacific. The dating results from the lagoon cores reveal a ~3500-year depositional history. Three different depositional units are recognized based on a time series of distinct grain-size variations that correspond to the following three stages of storm activity: intense and frequent storms from ~3500 to 3100 cal yr BP and ~1800 cal yr BP to present and weak and infrequent storms from ~3100 to 1800 cal yr BP. A high sedimentation rate remarked by reverse and chaos age is observed from ~2800 to 2600 cal yr BP in both cores, and it was likely associated with a tsunami event. In addition, grain-size variability may be associated with changes over time caused by the synchronous Asian monsoon and may also be correlated with climate records retrieved from the ice cores from Greenland; thus, this variability could indicate pervasive global climatic teleconnections. The overall temporal patterns of the isolated coral branches and shells from the sediment sequences are well correlated with the high sea surface temperatures in the western tropical Pacific. We suggest that increasing sea surface temperatures in the future may lead to more intense storm activity in the western Pacific warm pool as the planet warms. Highlights • Reconstructed storm activity since late Holocene in Xisha Islands of South China Sea, in West Pacific • Intense and frequent storms mainly centre during the period of ~3500–3100 cal yr BP and ~1800 cal yr BP to present. • The intense and frequent tropical storms activities are generally coeval with the relative high SST. • 3500-year western Pacific storm record warns of additional storm activity in a warming warm pool. [ABSTRACT FROM AUTHOR]

Abstract As a natural laboratory for testing various paleoclimatological and paleoceanographic hypotheses, the Pliocene-Pleistocene stratigraphic sequence from a full-coring major scientific drilling (Well CK2 with total length: 928.75 m) in Yongle atoll of Xisha Islands, northern South China Sea was studied. The Petrography of studied section of the core was dominated by reef carbonate limestones which contain abundant shallow marine organisms, e.g., coralline algae, corals, and foraminifera, which almost consisted of pure carbonates and preserved the primary geochemical message since Pliocene. According to the isolation of Well CK2 and the provenance of elements, the systematic changes and abrupt points of isotope and element geochemical compositions (rare earth element parameters, SiO 2 content, Al/Ti ratio, etc.) from coral reef carbonate record presented the elevated terrigenous influences related to the East Asian monsoon after ~2.6 Ma BP, as part of the Pliocene-Pleistocene climate transition. Our results demonstrated that the continental weathering controlled by the East Asian summer monsoon dominated the surface seawater compositions of study area before ~2.6 Ma BP, when the winter monsoon was not strong enough to exert significant influences. Then, the effects of eolian dust associated with the intensity of East Asian winter monsoon, the precipitation driven by summer monsoon, and the global temperature, which played different roles at different periods after ~2.6 Ma BP, should be considered. Our results confirmed that the potentials and significances of shallow-water carbonate deposition from coral reefs, and provided a unique perspective to shed light on the carbonate record of climate changes. Highlights • Shallow-water carbonates from coral reefs can contribute to record of climate change. • Continental weathering dominated the surface seawater composition before ~2.6 Ma BP. • Eolian dusts contributed distinctly to surface seawater composition after ~2.6 Ma BP. [ABSTRACT FROM AUTHOR]

Abstract On Xisha Islands, located in the South China Sea, the Neogene succession includes the unconformity-bounded Huangliu Formation that is 210.5 m thick in well CK-2 and formed almost entirely of dolostones. The diverse biota in the Huangliu Formation, which includes corals, algae, bivalves and foraminifera, indicates that the original carbonate sediments accumulated in water that was <30 m deep. The dolostones are formed of various mixtures of low- and high‑calcium calcian dolomite with limpid dolomite lining the walls of many cavities. The 18O and 13C stable isotopes suggest that dolomitization was mediated by slightly modified seawater. The 87Sr/86Sr ratios from the dolostones suggest that dolomitization took place ~9.4 and 2.3 Ma ago, with the age of dolomitization becoming progressively younger towards the top of the formation. "Island dolostones" like these, found on many islands throughout the Pacific Ocean and the Caribbean Sea, have commonly been linked to eustatic changes in sea-level with dolomitization taking place during lowstands, highstands, or transgressive phases. Data from the Huangliu Formation in well CK-2 suggests that dolomitization was associated with (semi-)continuous transgressive conditions that were controlled by the interaction of tectonic subsidence and eustatic changes in sea level. Highlights • Dolostones in the Huagliu Formation (Miocene) on the Xisha Islands are similar to island dolostones found on other isolated oceanic islands, including the Cayman Islands. • Dolomitization of the Miocene limestones on Xisha Islands, which took place ~9.4 to 2.3 Ma, appears to have been a (semi-)continuous time-transgressive process. • Critically, the similarity in the style and pattern of dolomitization on the Xisha Islands and other islands (e.g. Grand Cayman, Cayman Brac, Kita-daito-jima, Little Bahama Bank, San Salvador) suggests that the process of dolomitization may have been related to a worldwide phenomenon. • Available evidence indicates that dolomitization on the Xisha Islands influenced by eustatic changes in sea-level and tectonic subsidence of the Xisha Platform. [ABSTRACT FROM AUTHOR]

The importance of submarine groundwater discharge (SGD) is becoming increasingly recognized because of its potential significance as a source of dissolved species. To explore the probable coral geochemical signal of SGD and verify the validity of potential reliable proxies, multiple geochemical proxies over the last 137 years were identified from a Porites coral near a subterranean estuary in the northern South China Sea, where the SGD was reported to be the predominant flux of terrestrial waters to the coastal ocean. Results indicated that the SGD in the coastal zone was the dominant source of trace elements, especially REE and Ba, due to the various dissolution reactions occurring during groundwater flow in the karst terrain. The time- and frequency-domain comparison between the coral geochemical proxy and the local/regional precipitation indicated that coral REE/Ca ratios are predominantly impacted by the SGD associated with local precipitation, while coral Ba/Ca ratios are also affected by the primary productivity and allochthonous seawater Ba from surrounding areas. The REE signal from coral allows us to reconstruct the coastal surface seawater REE concentrations and the SGD rates on the coast of Sanya during 1870–2006. In a novel approach to developing a proxy for historic SGD to coastal waters, this study provides evidence that the coral REE/Ca record from the karst coast with large SGD has potentials to be a promising paleohydrological indicator. [ABSTRACT FROM AUTHOR]

Yongle Atoll is a complex atoll composed of 13 separated small atolls/reefs in the Xisha Islands, northern-central South China Sea. Wide, deep channels connect the Yongle Atoll lagoon with the open ocean. The sea surface partial pressure of CO 2 ( p CO 2 ) and sea–air CO 2 flux was measured at different geomorphological locations on the atoll. Atmospheric p CO 2 generally showed small diurnal variations, while seawater p CO 2 showed large diurnal variations. Lingyang Reef lagoon, an atoll within Yongle Atoll, was used to check the spatial difference in seawater p CO 2 and air–sea CO 2 flux. The diurnal variation in seawater p CO 2 was greater in the lagoon (258–748 μatm) than outside the lagoon area (354–476 μatm). Differences were also observed in the air–sea CO 2 fluxes depending on geomorphological zone. The mean seawater p CO 2 at Yongle Atoll is in the order of Lingyang Reef lagoon > inner reef slope of the Yongle Atoll > Yongle Atoll channel slope ≈ outer reef slope of the Yongle Atoll. The degree mixing between the lagoon and open sea through channels may have a key role in the horizontal distribution of seawater p CO 2 in the Yongle Atoll. Additional analyses indicated that the daily variations in surface seawater p CO 2 are significantly influenced by biological metabolic processes. The mean air–sea CO 2 flux in the Yongle Atoll was ~ 3.2 mmol CO 2 m −2 d −1 , indicating that the Yongle Atoll acts as a net source of CO 2 to the atmosphere. [ABSTRACT FROM AUTHOR]

Oil, is one kind of natural product of biological origin which is depleted in 13 C. Coral skeletal δ 13 C is an important archive of environmental and climatic change. However, few studies have been conducted on the effect of oil spill on the coral skeletal δ 13 C at present. This kind of research is useful for us to obtain environmental and climatic information from coral skeletal δ 13 C. In this study, two continuously growing Porites corals (W1 and W3), aged 22 and 31 years (1994–2015 and 1985–2015), respectively, were collected from the fringing reef of Weizhou Island in October 2015, coral skeletal δ 13 C and δ 18 O were analyzed. Besides, seawater was collected during an oil spill in 28 January 2018, and was used for δ 13 C DIC (δ 13 C values of DIC) analysis. The purpose is to explore the potential impact of oil spills on δ 13 C DIC and coral δ 13 C. δ 13 C DIC value during oil spill was significantly lower than that of normal seawater (Δδ 13 C≈-2.38‰). Coral δ 13 C of both two coral colonies showed lower values since 2008 (average value of δ 13 C before and after 2008 change from −2.04 ± 0.48‰ to −3.33 ± 0.55‰ ‰ and −1.77 ± 0.49‰ to −2.88 ± 0.54‰ of W1 and W3 respectively), especially, several abrupt negative shifts in 2008, 2009, 2011, 2012 and 2014 when oil spills occurred (extent of δ 13 C variation were W1：−3.08‰, −1.82‰, −1.82‰, −1.53‰, −1.37‰; W3：−3.27‰, −1.8‰, −1.91‰, −1.21‰, −1.13‰ respectively). Our results clearly show that degradation of oil by microorganisms when oil spill occurs should render a decrease in the 13 C/ 12 C ratio of the seawater dissolved inorganic carbon (DIC) which is the ultimate carbon source of coral calcification. [ABSTRACT FROM AUTHOR]

As a gauge for ocean precipitation conditions, sea surface salinity (SSS) is suspected to be an excellent indicator for variations in the global hydrological cycle. The SSS conditions in the South China Sea (SCS) are closely related to precipitation changes of the East Asian monsoon. However, the characteristics and driving mechanisms of the meridional pattern of East Asian monsoon rainfall during the warm periods of the late Holocene are not well understood because of a lack of high-resolution proxies from the SCS. Here, we present three precise chronologies of monthly stable coral skeleton oxygen isotopes (δ18O) and pair them with established composite strontium/calcium (Sr/Ca) records from the Xisha Islands to obtain a continuous reconstruction of the residual δ18O (Δδ18O, regarded as seawater δ18O) during 1980–2007 CE (Common Era), 1149–1205 CE, and 2070–2011 a BP (years before 1950 CE). The results confirm that coral Δδ18O is a good tracer for reconstructing SSS and precipitation changes in the northern SCS on seasonal and interannual timescales, with higher Δδ18O values implying more saline conditions and less precipitation. The mean value of fossil coral Δδ18O for 1149–1205 CE was higher than that of modern coral, suggesting the existence of salty surface waters and notable dry climate episodes in the northern SCS during the late Medieval Climate Anomaly (MCA). In contrast, the average coral Δδ18O for 2070–2011 a BP was significantly lighter by about 0.404‰ compared to that of recent decades, indicating that less saline and more humid conditions occurred in the northern SCS during the early Roman Warm Period (RWP). Synthesizing our coral records with other published precipitation reconstructions from eastern China suggested a meridional dipole spatial pattern of moisture variation over East Asia during the historical warm periods of the Holocene. During the MCA, drier conditions generally prevailed in the region south of the Yangtze River, and more humid conditions in the north. This may be closely related to the contemporaneous strong El Niño activity occurring at this time, which probably enhanced the East Asian summer monsoon (EASM) and caused a northward shift of the intertropical convergence zone (ITCZ), possibly inducing increased water vapor transport from the SCS to North China. During the RWP, the relatively weak El Niño–Southern Oscillation (ENSO) variability may weaken the intensity of the EASM and shift the ITCZ southward, possibly resulting in a spatial pattern of "wet south and dry north" in East Asia. • 145-year monthly seawater δ18O derived from corals in the northern South China Sea. • Salty surface waters for 1149–1205 CE and less saline for 2070–2011 a BP. • Meridional pattern of moisture over East Asia for the warm periods of late Holocene. • El Niño-Southern Oscillation modulates the strength of East Asian monsoon. [ABSTRACT FROM AUTHOR]

Coral bleaching heat stress products provide real-time and rapid coral bleaching alerts for coral reefs globally. However, geographical variations in the alert accuracy of multi-source coral bleaching heat stress products exist. Taking the coral reefs in the South China Sea (SCS) as the study area, we evaluated and improved the coral bleaching alert capabilities of two coral bleaching heat stress products: Coral Reef Watch (CRW) and Coral Reef Temperature Anomaly Database (CoRTAD). Using in situ coral bleaching survey data and evaluation indicators, the optimized thresholds of degree heating weeks (DHWs) for coral bleaching alerts were determined. The results in the SCS indicated that, first, CRW was better than CoRTAD for coral bleaching event alerts. However, both products underestimated coral bleaching events using the common DHW thresholds of 4°C-weeks and 8°C-weeks. Second, the DHW optimized threshold for CRW was 3.32°C-weeks for coral bleaching event alerts and 4.52°C-weeks for severe coral bleaching event alerts. For CoRTAD products, the DHW optimized threshold was 2.36°C-weeks for coral bleaching event alerts and 4.14°C-weeks for severe coral bleaching event alerts. This study proposed a method to evaluate and optimize the alert capability of multi-source coral bleaching heat stress products, which can provide more accurate basic data for coral reef ecosystem health assessment and contribute to global coral reef ecosystem protection and restoration. • A method to evaluate and optimize the alert capability of coral bleaching heat stress products in the SCS. • Optimized DHW thresholds for coral bleaching alerts were 3.32°C-weeks for CRW and 2.36°C-weeks for CoRTAD. • Optimized DHW thresholds for coral severe bleaching alerts were 4.52°C-weeks for CRW and 4.14°C-weeks for CoRTAD. • CRW was better than CoRTAD for coral bleaching event alerts in the SCS. [ABSTRACT FROM AUTHOR]

Guo, J.; Yu, K.; Wang, Y.; Xu, D.; Huang, X.; Zhao, M.; Yang, H., and Zhang, R., 2017. Nutrient distribution in Coral Reef degraded areas within Sanya Bay, South China Sea. An investigation was conducted in August 2014 to explore the spatial distribution of dissolved inorganic nitrogen (DIN) and phosphate ( ) in overlying water, pore water, and surface sediment from Sanya Bay and living coral cover on Luhuitou fringing reef. Generally, nutrient contents gradually decreased from the estuary to the central bay, which confirmed that terrigenous inputs from Sanya River and Sanya Harbor were the primary nutrient sources. The results of K-means cluster analysis suggested the Luhuitou fringing reef is in danger of being affected by the pollution source. The results of nutrient diffusive fluxes at the sediment-seawater interface indicated diffusion from pore water to overlying water. Compared with other coral reef areas around the world, nutrient levels in Luhuitou fringing reef were at the medium level. Significant correlation between temporal variation of nutrients and living coral cover was not found, which suggests that low nutrient enrichment, ranging from 1.89 to 2.89 μmol/L for DIN and from 0.1 to 0.49 μmol/L for , may not be responsible for the coral reef decline on Luhuitou fringing reef from 2002 to 2014. [ABSTRACT FROM AUTHOR]

Coral bleaching has generally been recognized as the main reason for tropical coral reef degradation, but there are few long-term records of coral bleaching events. In this study, trace metals including chromium (Cr), copper (Cu), molybdenum (Mo), manganese (Mn), lead (Pb), tin (Sn), titanium (Ti), vanadium (V), and yttrium (Y), were analyzed in two Porites corals collected from Meiji Reef in the tropical South China Sea (SCS) to assess differences in trace metal concentrations in bleached compared with unbleached coral growth bands. Ti, V, Cr, and Mo generally showed irregular fluctuations in both corals. Bleached layers contained high concentrations of Mn, Cu, Sn, and Pb. Unbleached layers showed moderately high concentrations of Mn and Cu only. The different distribution of trace metals in Porites may be attributable to different selectivity on the basis of vital utility or toxicity. Ti, V, Cr, and Mo are discriminated against by both coral polyps and zooxanthellae, but Mn, Cu, Sn, and Pb are accumulated by zooxanthellae and only Mn and Cu are accumulated by polyps as essential elements. The marked increase in Cu, Mn, Pb, and Sn are associated with bleaching processes, including mucus secretion, tissue retraction, and zooxanthellae expulsion and occlusion. Variation in these trace elements within the coral skeleton can be used as potential tracers of short-lived bleaching events. [ABSTRACT FROM AUTHOR]

The study presents a detailed record of foraminiferal faunas from CK2 core, a 928.75 m long core drilled in the center of Xisha Islands, South China Sea, for biostratigraphy and palaeoenvironmental reconstruction of the study area. Coupling foraminiferal biostratigraphy and bulk-sediment strontium-isotope chronologic age revealed that carbonate deposition occurred from Early Miocene (~19.6 Ma) to present. Examination of 281 petrologic thin sections and 246 unconsolidated sediment samples revealed 141 foraminiferal taxa, among which the foraminiferal abundance and simple diversity peaked in the Middle Miocene and Pliocene to early Pleistocene strata. Nine foraminiferal assemblages (FAs) were distinguished, documenting eight distinct facies that indicated five intervals in the development of Xisha Islands. At the initial interval (19.6–17 Ma), a coral, coralline algal and shallow-water larger foraminifers (FA1 and FA2) association colonized the shallow platform facies, forming an aggrading sequence in response to tectonic subsidence and sea-level rise. Platform development slowed from 17 to 10.19 Ma, dominated by the miliolids and small benthic foraminifers as well as larger benthic foraminifers (FA3 and FA4) representing lagoonal to reef-flat facies with agradation to progradation (backreef infilling) associated with sea-level fall. At 10.19–4.35 Ma, a deepening sequence was indicated by the change from shallow-water benthic foraminifers (FA5) upward to deeper dwelling species (FA6), as a result of climatic cooling and abrupt sea-level fluctuation. As sea level rose, the platform was drowned from 4.35 to 2.18 Ma, as indicated by abundant planktic foraminifers and large, flat benthic foraminifers (FA7 and FA8). At 2.18–0.089 Ma, the platform aggraded rapidly with sea level fall indicated by the appearance of thick benthic foraminifers (FA9) and increased coral. The close association between the biofacies and regional paleobathymetry, which was in phase with the long-term global sea-level change, suggest that foraminiferal morphology and assemblage composition are ideal parameters for paleobathymetric and paleo-depositional environmental interpretations. • Nine foraminiferal assemblages were distinguished, documenting eight carbonate biofacies. • Two major transgressive-regressive palaeobathymetry cycles were recorded since about 19.6 Ma. • Five development phases of Xisha carbonate succession since Early Miocene were revealed. • Eustasy, tectonics, paleoclimatic and paleooceanographic change are the main factors affecting the carbonate production. [ABSTRACT FROM AUTHOR]

Relatively little is known about the extent and distribution of damage to coral reefs by typhoons in the South China Sea, especially in remote reefs where typhoons occur frequently. A strong Typhoon, Wutip (JTWC Category 3), directly struck the Yongle Atoll on 29 September 2013, causing 62 deaths and sinking dozens of ships in the Yongle Atoll maritime area, Xisha Islands, South China Sea. Surveys on coral reefs at Yongle Atoll were conducted using scuba diving before (July 2013) and after (8 days) the typhoon sweep. The results show that the effects of Wutip on coral reefs were patchy as a result of varying coral reef geomorphology and depth. The typhoon caused significant damage to reef associated depths on the passage of the atoll, where currents generated by the typhoon produced the strongest energy. Coral destruction was most spectacular at the 2 m depth (46% living scleractinian corals were damaged). At 6 m and 15 m depths, damage to the coral reefs were minimal. The shallow fore-reef area on the steep slopes, the upper region of the outer slopes with depths between 2 and 6 m, were the principal zones of the typhoon effect. However, the vertical part of the steep slopes were mainly damaged indirectly waves rolling boulders or corals, which were less severely affected than the shallow fore-reef steep slope area. On the low angle slopes, the correlation between the typhoon damage to coral reefs and depth was low because the wave and current energy induced by the typhoon were homogenously attenuated along gentle slopes. Under the stress of global warming, destructive damage to coral reefs on the Xisha Islands is expected to increase, and will require frequent monitoring to determine trends in the near future. [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]

Reconstructing the precise timing of sea level fall is important for understanding earth system during the geologic time. However, previous studies are limited by the absence of effective indicators for sea level fall. To overcome this limitation, we investigated the 87Sr/86Sr and petrologic features of carbonate strata in a 928.75-m-long coral reef core (CK2) from Xisha Islands, northern South China Sea and their relationship to sea level fluctuations. Ten exposed surfaces were identified by their petrologic features. The Mn and Sr content, Mn/Sr, Sr/Ca and δ18O suggest that most of the coral reef carbonate in the CK2 core preserved the original seawater 87Sr/86Sr except at intervals of 672–616, 596–575, 521–491, 423–414, and 192.5–161 m, which suffered alteration of meteoric water and showed higher 87Sr/86Sr during low sea level period. The 160 carbonate 87Sr/86Sr showed a continuously increasing trend, which is consistent with that of seawater over the same period. The continuously increasing 87Sr/86Sr curve of CK2 was divided into seven units by six 87Sr/86Sr hiatuses. Inconsistency between the sedimentation rate of CK2 and tectonic subsidence rate in the Xisha area suggest that the continuously increasing 87Sr/86Sr was controlled by the coupled effect of tectonic subsidence and sea level change, and the hiatus and higher 87Sr/86Sr interval in the 87Sr/86Sr curve were controlled by sea level fall. The higher 87Sr/86Sr usually produced during low sea level (<5 m), 87Sr/86Sr hiatus usually produced when sea level changed from deeper to shallower. The depth of hiatuses and higher intervals of 87Sr/86Sr correspond well with the exposed surface in CK2 core, verifying that the hiatuses and higher intervals of 87Sr/86Sr in the coral reef carbonate succession provide an effective indicator of sea level fall. Using this indicator and the CK2 87Sr/86Sr profile, we identified eleven large-scale sea level falls and three dramatic regressions during 19.6–0.2 Ma and constrained the age based on strontium isotope stratigraphy. These interpreted sea level falls are mostly consistent with other records of global sea level changes, confirming the reliability of our records. The 87Sr/86Sr profile of a coral reef carbonate is an efficient indicator of past sea level falls, including their timing. • 87Sr/86Sr ratios of carbonate in a coral reef core from Xisha Islands. • The core indicated five hiatuses and six anomalously high ratios in Sr isotope. • Hiatus and high ratios in reef carbonate Sr isotope were produced by sea level fall. • Eleven major lower sea level and three dramatic regressions found during 19.6–0.2 Ma. • This method provides an effective indicator of past sea level fluctuation. [ABSTRACT FROM AUTHOR]

Strontium to calcium (Sr/Ca) ratios in annual bands of Porites corals are commonly used as past sea surface temperature proxy in tropical oceans, whereas studies that refer to Sr/Ca–SST calibration in high-latitude corals are rather rare in general. Here we present a 50-year (1961–2010) near-fortnightly Sr/Ca record in two Porites lutea corals living near the northern limit of reef-building corals in the subtropical northern South China Sea, where winter temperatures are extreme for hermatypic corals. The Sr/Ca time series shows a clear annual cyclicity, with marked sharp/narrow winter peaks. Comparison with an instrumental SST record (since 1961) indicates that this Sr/Ca record is chiefly modulated by SST. Two different methods are discussed for calibrating Sr/Ca with SST. The correlation between interpolated Sr/Ca and SST is significant, but the coefficient is relatively low, mainly attributed to extreme cold winter SSTs (<~16°C) which cause a significant decrease or even cessation of coral skeletal extension. Another modified method using only annual low Sr/Ca values which could clearly be matched with the same features in the instrumental SST record is more reliable. The modified regression equation does not encompass SSTs below 24°C. The fidelity of the coral-based Sr/Ca–SST calibration was assessed and the precision of the method is estimated to be 0.31±0.62°C based on the calibration–verification exercise. The modified method is suggested in marginal coral areas with extreme intra-annual SST variation (e.g., from 13 to 30°C). [ABSTRACT FROM AUTHOR]

Highlights: [•] We have studied the Raman spectra in different growth bands of Porites coral. [•] Raman spectra show vaterite could be the precursor of coral aragonitic skeleton. [•] The positional shift in the infrared spectra correlate significantly to minor elements. [ABSTRACT FROM AUTHOR]

We have previously shown that the coralline algal assemblages (CAAs) of the South China Sea may indicate post-Pliocene paleo-water depth changes; however, the pre-Pliocene coralline algal compositions and related sea-level significance remain to be elucidated. In the present study, we explore the Miocene coralline algal compositions and their role in recording the sea level, and show the distribution, classification, type, abundance, and diversity of Miocene coralline algae from 213 petrologic thin sections using a coral-reef carbonate sequence from the northern South China Sea. The diversity and abundance of coralline algae in the early and late Miocene are higher than those in the middle Miocene. Eleven genera were identified and grouped into seven CAAs, showing a water depth range from <5 m to >25 m. At 18.67–17.98 Ma, the coral reef was in a stagnation/drowning stage, with rising sea levels exceeding the development of the coral reef. At 17.98–16.78 Ma, the coral reef was in a rapid development during a rapid rise in sea level. Additionally, at 16.78–14.79 Ma, low coralline algal abundance was observed, and the corals were sporadically distributed at a relatively stable sedimentation rate, suggesting a decline in coral reef development. At 14.79–10 Ma, the coral reef development was remarkably slow or stagnant. Furthermore, at 10–5.3 Ma, the coral reefs developed slowly, indicating a gradual rise in the sea level. The sea-level changes indicated by coral reef development are consistent with the long-term global sea-level changes, indicating that the composition and assemblage of Miocene coralline algae can be used to accurately relay the sea-level history. • Eleven coralline algal genera were identified in a Miocene carbonate sequence. • Miocene coralline algae were divided into 7 coralline algal assemblages (CAAs). • Sea-level changes due to coral reef development were consistent with global values. [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]

The micro-conditions that control dolomitization processes were still not well known in natural environments. Cenozoic "island dolostones" are ideal for examining the processes since they are geologically young and have not experienced deep burial conditions. Miocene dolostones from the Xisha Islands, located in the South China Sea, are similar to those found on Grand Cayman Island, located in the Caribbean Sea. These dolostones are composed of low-Ca dolomite (LCD, < 55 mol % CaCO 3 ; hereafter referred to as %Ca) and high-Ca dolomite (HCD, > 55 %Ca). Individual dolomite crystals are commonly formed entirely of LCD or HCD, and/or HCD cores that are encased by LCD and alternating zones of HCD and LCD (1–10 μm thick). The crystal textures indicate that the LCD and HCD are primary growth features (no obvious recrystallization) that formed as the dolomite replaced the limestone precursor. The compositional features (%Ca in LCD and HCD, average %Ca, and proportion of LCD and HCD) and geochemical parameters (O/C isotopes, Sr, Fe and Mn) of dolomite indicate that the Mg was incorporated into dolomite crystals in an orderly manner that was mainly controlled by the interaction of fluid properties and crystal structure. The fact that dolomite stoichiometry varied laterally and vertically throughout the successions shows that micro-scale physicochemical conditions played a critical role in the evolution of individual dolomite crystals. The similarities between the dolostones of the Xisha Islands and Grand Cayman, which are 15,795 km apart, indicate that the factors that control the micro- and large-scale features of these dolostones must have undergone similar processes or experienced similar physicochemical conditions despite their disparate settings. • High similarity of the Miocene dolostones from the Xisha Islands (South China Sea) and Grand Cayman (Caribbean Sea). • Dolomite stoichiometry controlled by the interaction of properties of dolomitization fluids and dolomite crystal structure. • Micro-scale conditions played a critical role in the evolution of individual dolomite crystals. [ABSTRACT FROM AUTHOR]

This paper reviews both the recent and longer-term (Holocene) ecological history of coral reefs in the South China Sea (SCS). (1) Local ecological monitoring since the 1960s shows that the coral reefs in the South China Sea have declined dramatically, reflecting the rapid decrease of living coral cover and the great loss of symbiotic zooxanthellae. Collectively, this has led to a significant decrease of annual CaCO production. Heavy anthropogenic activities and global warming are recognized as major triggers of the observed coral reef degradation. Observations show that the modern coral reefs in the SCS are a source of atmospheric CO in summer. (2) Coral reefs of the SCS have been widely used to reveal longer-term environmental variations, including Holocene high-resolution sea surface temperature (SST) and abrupt climate events, millennial-scale El Niño variations, millennial- and centennial-scale sea level oscillations, strong and cyclic storm activities, East Asian monsoon intensities, variation in seawater pH, and recent seawater pollution. (3) Coral reefs of the southern SCS have experienced repeated episodes of bleaching over the last 200 years due to high SST and intense El Niño events; coral reefs of the northern SCS suffered high levels of mortality during several abrupt winter cold-water bleaching events during the middle Holocene warm period. On average, recovery after the middle Holocene cold-bleaching took 20-30 years; recovery following other middle Holocene environmental stresses took approximately 10-20 years. Such findings have significantly contributed to the understanding of the present ecological pressures faced by the coral reefs in the SCS, the histories of Holocene climate/environment changes, and the long-term models of coral reef responses to various past environmental changes. [ABSTRACT FROM AUTHOR]

As a typical contaminant in fossil fuels, vanadium has undergone dramatically increase due to the impacts from human activities. The excessive anthropogenic vanadium emissions have altered natural geochemical processes. However, research on vanadium geochemistry in the ocean, which is the major sink for vanadium mobilized on land, has lagged much behind relative to those of other contaminants. Here we reconstruct historical patterns of vanadium in surface seawater utilizing a high-resolution temporal record (1984–2015 CE) of geochemical proxies (vanadium/calcium (V/Ca), δ18O, δ13C, etc.) in a Porites coral colony from an offshore non-estuarine island in the northern South China Sea (SCS). We find a close association between the surface winds and the temporal patterns of coral V/Ca ratios, revealing great potential for documenting prehistoric changes in tropical cyclones. Moreover, the coral V/Ca record remarkably captured the temporal patterns of anthropogenic activities, offering a valuable and novel tool for testing the efficacy of specific legislation on pollution prevention. Combined with the other reported coral vanadium data, we recovered the historical changes in vanadium emissions in the northern SCS and identified that changing industrial practices should be responsible for the differences in anthropogenic vanadium emissions at each stage. Our results demonstrated that the coral V/Ca ratio at a high temporal resolution has great potential as a new and direct geochemical proxy for tropical cyclones after removing artificial disturbances in the ocean. [ABSTRACT FROM AUTHOR]

Abstract: Transported coral blocks scattered on reef flats have previously been identified as useful proxies for past storm occurrences. High-precision TIMS U-series dating and detailed field observations of 110 coral samples collected from 102 individual transported coral colonies (coral blocks) and 4 transported sections of reef matrix (reef blocks) from the northern side of Heron Reef (southern Great Barrier Reef) indicate that: (1) the youngest age of corals attached to reef blocks may represent the age of possible past storm occurrence, providing a proxy for historical storm reconstruction; (2) most ages of dated storm-transported coral and reef blocks match well relatively with known cyclone and storm events, further supporting that they are good indicators of past storm events; and (3) age distribution and relative probability frequency analysis of the dated coral and reef blocks suggest that there have been eight broad periods of storm occurrence since 1900AD (1904–1909, 1914–1916, 1935–1941, 1945–1960, 1965–1967, 1976–1977, 1983–1988 and 2001–2007), roughly showing decadal variations. The coral-based storm reconstruction therefore extended the database of past storm occurrences around Heron Reef area. These findings suggest that coral reefs in the southern Great Barrier Reef are frequently influenced by periods of high storm activity, and show strong resilience to natural disturbances over the past century. Additionally, our results show for the first time that the blue skeletal coral Heliopora coerulea (Order: Helioporacae) has U concentrations of only 0.12 to 0.30ppm, ~5–10% that of common reef building corals with white skeletons (Order: Scleractinia), which may be a unique chemical signature of the only living species of the Helioporidae family. [Copyright &y& Elsevier]

Rising atmospheric CO and warming of the global climate that have occurred since the industrial revolution are regarded as fatal threats to coral reefs. We analyzed the skeletal calcification rate of 14 massive Porites corals from the Meiji Reef in the southern South China Sea through X-ray photography of coral skeletons. A general pattern of change in coral skeletal calcification was determined. The change pattern of coral calcification on the Meiji Reef over the past two centuries can be divided into five periods: calcification increase in 1770-1830, 1870-1920, and 1980-2000 and calcification decline in 1830-1870 and 1920-1980. Over the past two centuries, the largest increase in calcification was 4.5%, occurring in 1770-1830, whereas the largest decline in calcification was 6.2%, occurring in 1920-1980. Coral calcification slightly increased in the recent 20 years (1980-2000). The response relationship of coral calcification to atmospheric CO and sea surface temperature (SST) shows that calcification was not correlated with atmospheric CO but responded nonlinearly to SST with maxima at ∼27.2°C in 1900-2000. On the Meiji Reef, increasing atmospheric CO had a negligible effect on coral growth in the past century. However, rising SST improved coral growth in the early and middle 20th century, and restricted coral growth in the recent 20 years. [ABSTRACT FROM AUTHOR]

Coral bleaching, characterized by a significant loss of symbiotic zooxanthellae, is the primary cause of mass coral mortality and reef degradation throughout the world. The characteristics, processes, and resistance of corals to bleaching varies significantly and is dependent on environmental conditions. We documented a mass coral bleaching event in June 2007 at the Meiji and Zhubi Reefs, Nansha Islands (NS), South China Sea using ecological surveys and measurement of coral zooxanthellae density and sea surface temperatures (SST). More than 35 species of corals (between 0-20 m in depth) were bleached. These bleached corals accounted for 15.6% of total corals in the investigated quadrats. The branching corals Pocillopora and Acropora were the most vulnerable species whereas the massive corals Porites and Favia were more tolerant of the high SSTs. Surprisingly, we found no evidence of bleaching in Agariciidae corals suggesting that this family is resistant to thermal stresses. The bleached corals had lost 72%-90% of their symbiotic zooxanthellae. Furthermore, corals that had no visual signs of bleaching had also lost 31%-53% of their zooxanthellae suggesting that most corals were experiencing the early stage of bleaching. The monthly mean SST during June 2007 was 30.8°C, the highest since 1998. Based on measurements of SST and the Hotspots and DHW data (NOAA), we conclude that it the extremely high SSTs triggered this coral bleaching event. Our results suggest that the previously accepted temperature thresholds used to predict coral bleaching based on satellite data are likely to underestimate the extent and intensity of coral bleaching, at least in the NS. [ABSTRACT FROM AUTHOR]

Field measurements of air-sea CO2 exchange in three coral reef areas of the South China Sea (i.e. the Yongshu Reef atoll of the Nansha Islands, southern South China Sea (SCS); Yongxing Island of Xisha Islands, north-central SCS; and Luhuitou Fringing Reef in Sanya of Hainan Island, northern SCS) during the summers of 2008 and 2009 revealed that both air and surface seawater partial pressures of CO2 (pCO2) showed regular diurnal cycles. Minimum values occurred in the evening and maximum values in the morning. Air pCO2 in each of the three study areas showed small diurnal variations, while large diurnal variations were observed in seawater pCO2. The diurnal variation amplitude of seawater pCO2 was ~70 µmol mol-1 at the Yongshu Reef lagoon, 420-619 µmol mol-1 on the Yongxing Island reef flat, and 264-579 µmol mol-1 on the reef flat of the Luhuitou Fringing Reef, and 324-492 µmol mol-1 in an adjacent area just outside of this fringing reef. With respect to spatial relations, there were large differences in air-sea CO2 flux across the South China Sea (e.g. ~0.4 mmol CO2 m-2 d-1 at Yongshu Reef, ~4.7 mmol CO2 m-2 d-1 at Yongxing Island, and ~9.8 mmol CO2 m-2 d-1 at Luhuitou Fringing Reef). However, these positive values suggest that coral reef ecosystems of the SCS may be a net source of CO2 to the atmosphere. Additional analyses indicated that diurnal variations of surface seawater pCO2 in the shallow water reef flat are controlled mainly by biological metabolic processes, while those of deeper water lagoons and outer reef areas are regulated by both biological metabolism and hydrodynamic factors. Unlike the open ocean, inorganic metabolism plays a significant role in influencing seawater pCO2 variations in coral reef ecosystems. [ABSTRACT FROM AUTHOR]

Coral reefs worldwide are becoming increasingly and detrimentally impacted upon by a variety of factors including significant climate changes, such as global warming and increased El Niño-Southern Oscillation activity. Generally, the persistence of coral reefs, especially at low-latitudes, is governed, in part, by sea surface temperatures not exceeding the critical limit (∼30°C) at which mass mortality can occur. Thus, it is thought that corals living at high-latitudes (i.e., currently cooler sea surface temperatures) will likely respond more favourably to hypothesized future temperature increases than corals living at low-latitudes (i.e., currently warmer sea surface temperatures). Consequently, high-latitude coral communities may have the potential to act as regions of refugia for many coral species in the face of potential future global warming. The Daya Bay (22°31'-22°50'N), northern South China Sea, contains several high-latitude non-reefal coral communities and represents one of the most northerly distributions of scleractinian corals within the region. Significantly, Daya Bay has experienced dramatic warming in both air and sea surface temperatures throughout the past 50 years. In this paper, we analyze 25 years of change in the Daya Bay coral communities, based both on historic surveys and our latest 2006-2008 regional ecological surveys. Our results suggest that, contrary to predictions, there have been significant declines in coral cover within the Daya Bay during the past 25 years (i.e., 76.6% coral cover in 1983/1984 to only 15.3% coral cover by 2008). Such changes also reflect a significant shift in the most abundant coral species, from Acropora pruinosa to Favites abdita. Most of the modern coral communities became established between 15 and 30 years ago, corresponding to a period of increased winter sea surface temperature. However, very few colonies have become established within the last 15 years, despite a more intense period of warming. By taking into account additional factors, we hypothesize that direct anthropogenic impacts, rather than climatic events, have both restricted the development, and drove the decline, of Daya Bay coral communities in the last 15 years. The Daya Bay has also been subjected to occasional extreme cold events during the past 50 years, with the most recent occurring in early 2008 (13 January-13 February). During the 2008 cold event, the lowest air temperature reaches only 6.6°C, and the mean sea surface temperature for February fall to <14°C, including six continuous days at 12.3°C. Significantly, the sea surface temperatures fall below the hypothesized critical lower temperature threshold (∼13°C) that commonly leads to mass mortality in scleractinian coral communities. Surprisingly, our coral community surveys, conducted both before (August 2007) and after (late February 2008) the extreme 2008 cold event, demonstrate that the Daya Bay coral ecosystems are barely impacted upon during the cold period. Those observations suggest that the Daya Bay scleractinian coral communities have developed adaptations to low sea surface temperatures. Overall, our data support the hypothesis that high-latitude coral communities, such as Daya Bay, have the potential to act as areas of refugia for scleractinian corals in the advent of potential future global warming. [ABSTRACT FROM AUTHOR]

Coral reef bleaching is usually characterized by expulsion of symbiotic zooxanthellae, loss of zooxanthellae pigmentation, or both. We collected 128 samples comprising 39 species of 21 genera of reef-building corals from Luhuitou and Xiaodonghai in Sanya of Hainan Island and Daya Bay of Guangdong Province, respectively, and analyzed the symbiotic zooxanthellae population density. The results show that: (1) the symbiotic zooxanthella density varies from 0.67×106 to 8.48×106 cell/cm2, displaying significant interspecies variability, with branch corals usually having relatively less zooxanthellae (ranging from 0.67×106 to 2.47×106 cell/cm2) than massive species (from 1.0×106 to 8.48×106 cell/cm2); (2) corals inhabiting within 4 m water depth have higher levels of symbiotic zooxanthellae than those living at the bottom (-.7 m depth) of the reef area; (3) there is no discernable difference in the zooxanthellae density between corals from relatively high latitude Daya Bay (-22°N) and those from relatively low latitude Sanya (-18°N) at comparable sea surface temperatures (SST); (4) in partially-bleached corals, the density of zooxanthellae shows the following order: healthy-looking part> semi-bleached part > bleached part. Based on the above results, we suggest that (1) the zooxanthellae density difference between branching and massive coral species is the main cause that branching corals are more vulnerable to bleaching than massive corals. For example, symbiotic zooxanthellae levels are low in branching Acropora and Pocillopora corals and thus these corals are more susceptible to bleaching and mortality; (2) symbiotic zooxanthellae density can also be affected by environmental conditions, such as sediment loads, diving-related turbidity, and aquaculture-related nitrate and phosphate input, and their increase may reduce symbiotic zooxanthellae density in corals. [ABSTRACT FROM AUTHOR]

High-resolution Sr/Ca ratios of two Porites corals from Leizhou Peninsula were measured using inductively coupled plasma atomic spectrometry (ICP-AES). TIMS U-Th dating reveals that the life-spans of the two corals are 489–500 AD and 539–530 BC, respectively. Monthly sea surface temperatures (SSTs) during these two periods can be reconstructed from their skeletal St/Ca ratios. The results reveal that SSTs during 539–530 BC were roughly the same as those during 1990–2000 AD in this area, indicating a relative warm climate period. However, the period of 489–500 AD was significantly cooler, with annual mean SST, the 10-a average of minimum monthly winter SSTs and the 10-a average of maximum monthly summer SSTs being about 2, 2.9 and 1°C lower than that in the 1990s, respectively. Such climate patterns agree well with the phenological results recorded in the historic documents in other areas of China. [ABSTRACT FROM AUTHOR]

Analyzes the nature of Porites lutea from Nansha Islands, China. Determination on the carbon isotopic composition of Porites; Sensitivity of reef corals to environmental changes; Environmental factors influencing coral metabolism.

Examines the timing of Holocene sea-level highstands by mass spectroscopic U-series ages of coral reef from Leizhou Peninsula, South China Sea. Recognition on the episodes of coral growth; Emphasis on the marking of post-glacial stabilization of global sea level; Measurement on Dengloujiao reef flat.

Analyzes the oxygen isotropic composition of Porites lutea from the Nansha Islands in China. Indicators of sea surface and air temperature; Activities of El Nino events; Use of coral reefs in climate reconstruction.

Regional acclimatisation and microbial interactions significantly influence the resilience of reef-building corals facing anthropogenic climate change, allowing them to adapt to environmental stresses. However, the connections between community structure and microbial interactions of the endemic coral microbiome and holobiont acclimatisation remain unclear. Herein, we used generation sequencing of internal transcribed spacer (ITS2) and 16S rRNA genes to investigate the microbiome composition (Symbiodiniaceae and bacteria) and associated potential interactions of endemic dominant coral holobionts (Pocillopora verrucosa and Turbinaria peltata) in the South China Sea (SCS). We found that shifts in Symbiodiniaceae and bacterial communities of P. verrucosa were associated with latitudinal gradient and climate zone changes, respectively. The C1 sub-clade consistently dominated the Symbiodiniaceae community in T. peltata ; yet, the bacterial community structure was spatially heterogeneous. The relative abundance of the core microbiome among P. verrucosa holobionts was reduced in the biogeographical transition zone, while bacterial taxa associated with anthropogenic activity (Escherichia coli and Sphingomonas) were identified in the core microbiomes. Symbiodiniaceae and bacteria potentially interact in microbial co-occurrence networks. Further, increased bacterial, and Symbiodiniaceae α-diversity was associated with increased and decreased network complexity, respectively. Hence, Symbiodiniaceae and bacteria demonstrated different flexibility in latitudinal or climatic environmental regimes, which correlated with holobiont acclimatisation. Core microbiome analysis has indicated that the function of core bacterial microbiota might have changed in distinct environmental regimes, implying potential human activity in the coral habitats. Increased bacterial α diversity may lead to a decline in the stability of coral-microorganism symbioses, whereas rare Symbiodiniaceae may help to retain symbioses. Cladocopium , γ-proteobacteria, while α-proteobacteria may have been the primary drivers in the Symbiodiniaceae-bacterial interactions (SBIs). Our study highlights the association between microbiome shift in distinct environmental regimes and holobiont acclimatisation, while providing insights into the impact of SBIs on holobiont health and acclimatisation during climate change. Unlabelled Image • Coral microbial communities are linked to latitudinal/climatic environmental regime. • Core microbiome abundance change may lead to microbiota function variation. • Anthropogenic bacteria in core microbiome suggest large-scale human activity. • Microbial α diversity is closely associated with co-occurrence network complexity • Potential SBI may be driven by Cladocopium , γ-proteobacteria, and α-proteobacteria. [ABSTRACT FROM AUTHOR]

Some scleractinian corals exhibit high thermal adaptability to climate changes, although the mechanism of their adaptation is unclear. This study investigated the adaptability of scleractinian coral Pocillopora damicornis to thermally variable reef environments by applying a nanopore-based RNA sequencing method to characterize different transcription responses that promote heat tolerance of P. damicornis. We identified 1414 novel genes and optimized 6256 mis-annotated loci. Based on full-length transcriptome data, we identified complex alternative polyadenylation and alternative splicing events, which can improve our understanding of the genome annotation and gene structures of P. damicornis. Furthermore, we constructed differentially expressed lncRNA-mRNA co-expression networks, which may play a crucial role in the P. damicornis thermal adaptive response. KEGG function enrichment analysis revealed that P. damicornis from the high-temperature pool had a lower metabolic rate than that from the low-temperature pool. We hypothesize that metabolic readjustment, in the form of a lower metabolic rate, positively correlated with increased heat tolerance in P. damicornis in thermally variable reef environments. Our study provides novel insights into lncRNAs that promote thermally tolerance of scleractinian corals in the thermally variable reef environment, suggesting potential mechanisms for their adaptation to global warming in the future. [Display omitted] • Heat tolerance of P. damicornis is related to metabolic readjustments. • Non-coding RNA regulates scleractinian coral phenotype plasticity. • 6.86% of total transcripts resulted from alternative splicing. • We constructed lncRNA-mRNA co-expression networks of P. damicornis. • Thermally variable macrotidal reef habitat promotes heat tolerance of P. damicornis. [ABSTRACT FROM AUTHOR]

The trade winds cause strong upwelling in the eastern equatorial Pacific, and create the eastern Pacific Cold Tongue (EPCT) that has far‐reaching impacts on global climate. However, large discrepancies persist in quantifying 20th‐century EPCT sea surface temperature (SST) changes across different instrumental data sets. Here we synthesize four coral Sr/Ca‐SST records from the tropical central‐eastern Pacific to develop a Cold Tongue Index (CTI) reconstruction for 1887–1997. The coral CTI record shows a rapid 20th century warming of the EPCT, suggesting an underestimation of warming trends in instrumental CTI records. The decadal to multidecadal changes in reconstructed EPCT SST show an association with the Walker Circulation. Our reconstruction indicates that recent EPCT cooling during the global warming hiatus is not unusual in the context of the 20th century. Our results provide new evidence for 20th century EPCT SST changes and an observational constraint for predicting future tropical climate changes. Plain Language Summary: The tropical Pacific exhibits an asymmetric pattern of sea surface temperatures (SST) along the equator, with a warm pool in the west and a cold tongue in the east. The Eastern Pacific Cold Tongue (EPCT) plays a crucial role in influencing global climate. To date, however, considerable disagreement persists about changes and causes of the EPCT SST over the 20th century due to the sparse instrumental observations before ∼1960. Here we synthesize published coral Sr/Ca‐SST records from the tropical central‐eastern Pacific to develop a coral Cold Tongue Index (CTIcoral) for the period 1887–1997. The CTIcoral record correlates significantly with instrumental data since 1960, and thus allows reliable assessment of 20th century EPCT SST changes. Our record exhibits a rapid 20th century warming trend of the EPCT, indicating an underestimation of warming trends in instrumental CTI records. The decadal to multidecadal changes in CTIcoral also show an association with the Walker Circulation. Comparing the magnitude of the 1992–2011 trend in instrumental CTI with our reconstruction reveals that recent EPCT cooling during the global warming hiatus is not anomalous in the context of 20th century. Our findings have implications for predicting future EPCT SST changes by offering a constraint for model simulations. Key Points: Synthesizing coral Sr/Ca‐SST records yields robust estimates of 20th century warming trend in the eastern Pacific Cold Tongue (EPCT)A coral‐based reconstruction indicates an underestimation of 20th century EPCT warming trends in instrumental SST recordsRecent EPCT cooling during the global warming hiatus is not anomalous in the context of the 20th century [ABSTRACT FROM AUTHOR]

Scattered evidence indicates the occurrence of coral thermal bleaching events during the mid-Holocene. However, information on such occurrences is still very rare. Ten Porites coral cores were drilled from the Wenchang fringing reef of Hainan Island, northern South China Sea. These cores contain mortality surfaces and/or growth discontinuities dating from the mid-late Holocene between 3.4 and 5.7 thousand years ago (ka, before 1950 AD). Monthly Sr/Ca, δ18O and δ13C were analyzed to reconstruct sea-surface temperature (SST), sea-surface salinity (SSS), and photosynthesis intensity during the events. Results show that the mortality surfaces and growth discontinuities of five corals are associated with high SST of 30.3 °C–33.6 °C and high SSS of 34.3–38.3. The abrupt concurrent negative shifts of 1.8‰ or more in δ13C indicate a decrease in the photosynthesis intensity, most likely attributable to the loss of zooxanthellae. These lines of evidence imply that the mortality surfaces and growth discontinuities were the consequence of coral bleaching under abnormally high temperature. The observed recovery directly after bleaching events indicates that corals in the South China Sea are capable of rehabilitation after experiencing severe environmental stresses. • Ten Porites coral cores dated at 3.4–5.7 ka BP contain mortality surfaces/hiatuses. • Sr/Ca and δ18O suggest that mortality occurred in high SST and SSS environments. • Negative shifts of δ13C indicate a decrease in photosynthesis or zooxanthellae. • The geochemical proxies provide evidence of past coral bleaching and recovery. [ABSTRACT FROM AUTHOR]