Southern South China Sea Research Articles

Symbiotic Zooxanthellae Drive the δ13C Changes of Tridacna gigas Shell in the Southern South China Sea

AbstractThe carbon isotope (δ13C) in marine biogenic carbonate is a valuable tool for comprehending the marine carbon cycle. However, the absence of monthly resolved δ13C records before the instrumental era (since 1850) hinders us to fully understand the global carbon cycle. In this study, we present a δ13C record from a modern Tridacna gigas shell (δ13Cshell) collected from the southern South China Sea (SCS) with an average resolution of ∼10 days. The δ13C record illustrates seasonal and interannual cycles which are superimposed by long‐term decreasing trend. We investigate the environmental controls influencing the δ13Cshell on different time scales. We suggest that more positive δ13Cshell values observed during the juvenile stage (first 8–10 years), which correspond to a high growth rate, can be attributed to 13C enrichment of the internal dissolved inorganic carbon pool. This resulted from the exponential increase of symbiotic zooxanthellae, and preferential 12C sequestration by the accelerated buildup of productive tissues. On the interannual time scale, changes in δ13Cshell were likely affected by both internal (vital effect) and external processes (sea water δ13C), as well as being disturbed by the super El Niño‐La Niña event. Seasonal changes of δ13Cshell were mainly dominated by the intensity of photosynthesis and respiration of symbiotic zooxanthellae, which depend on the seasonal solar irradiance variations in association with precipitation and the South Asian summer monsoon. Our study sheds light on the controlling factors of δ13Cshell variations on seasonal timescale and the long‐term trend, providing insight into the carbon cycle over geological history.

Late Quaternary mangrove biogeography and paleoenvironments in the reef area of the South China Sea based on analysis of palynomorph assemblages

In this study, we analyse the development of mangroves around the South China Sea (SCS) over the last 40 kyrs BP. Findings are based on 208 palynological samples obtained from a sediment core (NS07–25) in the reef area of the SCS. These palaeo-records are interpreted in the context of 161 surface sediment palynological samples obtained from across the SCS that serve as a modern reference set. Employing the Near Analysis function in ArcGIS, mangrove pollen in modern surface sediment comprises two major assemblages: dominant Rhizophoraceae (subtropical, wind- and animal-pollinated taxa) in the northern SCS and diverse Sonneratia (tropical, animal-pollinated taxa) in the southern SCS. The distribution field of these modern mangrove pollen assemblages is bounded by the Nansha Islands and reefs, which may act to obstruct pollen transportation between the northern and southern parts of the SCS. In our late Quaternary core, concentrations of Rhizophoraceae and Sonneratia pollen assemblages gradually increase in the late stage of Marine Isotope Stage 3 and during the Last Glacial Maximum, as a result of falling sea level and mangrove colonization of the exposed marine shelf, whereas they rapidly decrease in the Deglacial period, coincident with an increase in sea level and coastal retreat. The occurrence of Rhizophoraceae pollen assemblages in the southern SCS during the Last Glacial Maximum indicates that these communities disperse southward in response to climate change. Our findings highlight the complex effects of growth conditions, varied pollinators, and transportation patterns on the preservation of Rhizophoraceae and Sonneratia pollen assemblages with implications for understanding change in climate and sea level since 40 kyr BP.

Comprehensive Investigation on Spatiotemporal Variations of Tropical Cyclone Activities in the Western North Pacific, 1950–2019

Tropical Cyclones (TCs) are the most severe natural disasters in the Western North Pacific Ocean (WNP). While previous studies reported evident changes over certain regions or seasons between typical periods, there is a lack of a complete picture of the long-term variations in TC activities in the WNP. This study carried out a comprehensive investigation on the spatiotemporal variations in TC genesis locations and transit pathways in the WNP, based on the TC best-track datasets from the China Meteorological Administration Shanghai Typhoon Institute. The results showed that the TC genesis and occurrence frequencies showed drastic decreases and westward shifts in the WNP from 1950 to 2019. The greatest decrease in TC genesis occurred for Tropical Depressions (TDs: 10.8−17.1 m/s) and Typhoons (TYs: > 32.7 m/s). The number of Tropical Storms (TSs: 17.2−32.6 m/s) and the mean intensity (2 min maximum sustained wind speed) of TCs overall showed no evident change. The decadal average of TC genesis frequency increased by 63% in the near-coast seas (WNPO), but decreased by 46% near the central Pacific Ocean (WNCP), demonstrating a westward shift for TC genesis locations. The TC genesis and occurrence frequencies also showed significant declines in the southern Philippine Sea (SPS) and South China Sea (SCS), while they showed a lower reduction in the Eastern East China Sea (EECS), the northern ocean edge of TC genesis areas, resulting in an increase in the average latitude of TC genesis locations, a spurious northward shift. The La Niña and El Niño years showed contrasting effects on TC genesis frequency and landfall ratios. There were greater instances of TC genesis and greater landfall ratios during the La Niña mature phase, while there were fewer TC formations and lower landfall ratios during the short duration (SD) El Niño developing phase. The TC genesis locations showed a distinct northwestward shift during La Niña years compared to those during El Niño years.

Spatial Distribution of Total 210Pb in the Marine Sediment of Peninsular Malaysia: Radioactivity Level Variations in the Sunda Shelf Seas

Radiochemical separation techniques were applied to measure 210Pb radioactivity in samples to determine spatial distribution of total 210Pb radionuclide in surface sediments and water column for the main waters on the Sunda Shelf. The average 210Pb radioactivity level recorded for the Malacca Strait (MS) is significantly higher than that of the southern South China Sea (sSCS); this is attributed to the supply of input from the Andaman Sea in its northern areas, and massive terrestrial processes from bordering land masses. The results reveal that the decreasing trend of total 210Pb in Peninsular Malaysia’s marine sediment starts with the north maritime zone of Malacca Strait (64.28 ± 5.97 Bq/kg) > south maritime zone of Malacca Strait (50.88 ± 6.15 Bq/kg) > east maritime zone of sSCS (41.01 ± 3.07 Bq/kg) > south maritime zone of sSCS (40.78 ± 3.16 Bq/kg). The Kelantan and Pahang Deltas have been identified as two of the main anthropogenic sources of input for total 210Pb in the sSCS with atmospheric transboundary mobilization affecting total 210Pb in the water column. In the Malacca Strait, however, the distribution of total 210Pb might be influenced mainly by in situ processes of the strait’s seafloor and sources origin of sediment. HIGHLIGHTS The Malacca Strait has a significantly higher level of 210Pb radioactivity compared to the southern South China Sea (sSCS), due to input from the Andaman Sea and terrestrial processes from adjacent land masses The decreasing trend of total 210Pb in Peninsular Malaysia’s marine sediment starts with the north maritime zone of Malacca Strait > south maritime zone of Malacca Strait > east maritime zone of sSCS > south maritime zone of sSCS The Kelantan and Pahang Deltas are identified as two of the main anthropogenic sources of input for total 210Pb in the sSCS, while in the sh Strait, the distribution of total 210Pb may be influenced mainly by in situ processes of the strait’s seafloor and sources origin of sediment GRAPHICAL ABSTRACT

Assessment of the Sea Surface Salinity Simulation and Projection Surrounding the Asian Waters in the CMIP6 Models

Sea surface salinity (SSS) is a crucial indicator that is used to monitor the hydrological cycle in the ocean system. In this study, we evaluated the simulation skill of the Coupled Model Intercomparison Project Phase 6 (CMIP6) models in reproducing the SSS in the Asian Marginal Seas (AMSs). The results show that the AMSs’ SSS simulated by most CMIP6 models is generally in good agreement with the observations in terms of spatial patterns and seasonal variability. However, these models tend to overestimate the SSS in the Eastern Arabian Sea and the Bay of Bengal by up to 1.3 psu, while they underestimate the SSS in the Bohai Sea, the Yellow Sea, the Southern South China Sea, and the Indonesian Seas, with the bias exceeding −1.5 psu. Additionally, the seasonal variations in the Sea of Okhotsk, the Bay of Bengal, and the Arabian Sea exhibit large biases with phase shift or reversal in some CMIP6 models. Notably, the observed magnitudes in the AMSs are significantly higher than the global average of 0.2 psu, ranging from 0.22 to 1.19 psu. Furthermore, we calculated the projected trends in sea surface salinity under different future scenarios by using the CMIP6 models. The results reveal relatively larger SSS freshening trends in the second half of the 21st century compared to the first half. Specifically, the freshening trends for the Shared Socio-Economic Pathway (SSP) of low- (global radiative forcing of 2.6 W/m2 by the year 2100), medium- (global radiative forcing of 4.5 W/m2 by 2100), and high-end (8.5 W/m2 by 2100) pathways are 0.05–0.21, 0.12–0.39, and 0.28–0.78 psu/century, respectively. The most rapid freshening trends of SSS are observed in the East China Seas and the Indonesian Seas, which are over two times greater than the global mean. On the other hand, the SSS freshening trends in the Arabian Sea are slightly lower than the global mean SSS freshening trend.

Geochemical characteristics of sediment and pore water affected by cold seeps in southern South China Sea

Cold seep, characterized by active material circulation and methane seepage, is of great importance to reconstruct the paleo-marine environment and trace the origin of life and the occurrence of minerals. Southern South China Sea (SCS) with ample oil and gas resources is an ideal platform for cold seep study, but information and researches on cold seeps here are rather deficient. We studied the geochemical characteristics of sediment cores and pore water combined with seismic profile information in the Beikang Basin, aiming to further understand the nature of cold seeps in this area. Results show the extremely low δ 13CDIC of pore water in each core and we also found sulfate content decreases with depth, the high content of inorganic carbon (DIC) and the corresponding minimumδ 13CDIC in pore water, the kink-type depth profiles of Sr, Ba and Ni enrichment factors and Sr/Mg in the sediments of BH-CL37, the reducing sedimentary environment constrained by the features of Mo, U and REE. The extremely negative δ 13CDIC in the pore water of the sediment cores indicates strong AOM effect in cold seeps and the main biogenic origin of methane. The SO42- depth variation trends of pore water, the high DIC content and the lowest value of δ 13CDIC can define the approximate SMTZ depth of each sediment core effectively. We thought that fluid fluxes and tectonic settings greatly influence the sedimentary environment and geochemistry, leading to the manifest regional differences in the properties and activities of cold seeps. This study of cold seep in southern SCS proves the variation of cold seep in time and space, stressing the necessity of further region-specific analysis towards different cold seeps; and the complex conditions of SCS do function well in offering multiple types of cold seeps.

Relationship between South China Sea Summer Monsoon and Western North Pacific Tropical Cyclones Linkages with the Interaction of Indo-Pacific Pattern

The South China Sea (SCS) summer monsoon (SCSSM) and Western North Pacific tropical cyclones (TCs) are both tropical systems that interact with each other on multiple scales. This study examines the differences in TCs activity characteristics between anomalous strong and weak SCSSM years, and explores the possible mechanisms behind these differences through the coupling relationship between tropical atmospheric circulation and oceanic surface conditions. Results show that the destructiveness of TCs over the Western North Pacific is stronger during weak SCSSM years than in strong years, whereas the opposite occurs for TCs over the SCS. The interaction between the tropical Indo-Pacific ocean and atmosphere plays a key role in the relationship between SCSSM intensity and TCs activity. In strong (weak) SCSSM years, the sea surface temperature anomaly (SSTA) in the tropical Pacific Ocean tends to correspond to a La Niña-like (El Niño-like) distribution, whereas the tropical Indian Ocean shows an Indian Ocean dipole-negative (positive) phase distribution. Moreover, Walker circulations in both the Indian and Pacific Oceans are coupled during these years, which creates a seesaw-like relationship in the conditions for TCs formation between the SCS and the Western Pacific Ocean. During weak SCSSM years, the formation and activity of TCs over the SCS are suppressed due to the weakened water vapor transport caused by abnormal easterly winds from the eastern Indian Ocean to the southern SCS. Meanwhile, the higher SSTA in the Western Pacific Ocean enhances the TCs activity. In strong SCSSM years, the enhanced monsoon drives a stronger monsoon trough, improving the convective environment over the SCS, whereas in contrast, the Western Pacific Ocean is covered by colder water, resulting in poorer conditions for TCs genesis.

Late Eocene—early Miocene provenance evolution of the Crocker Fan in the southern South China Sea

Late Eocene—early Miocene provenance evolution of the Crocker Fan in the southern South China Sea

Influence of Synoptic‐Scale Waves on the Interdecadal Change in Tropical Cyclone Activity Over the Western North Pacific in the Early 2010s

AbstractIn this study, we investigated the interdecadal change in tropical cyclone (TC) activity over the western North Pacific (WNP) in the early 2010s. At the western boundary of the WNP, the interdecadal change in TC activity exhibited a meridional tripole pattern. In contrast to the reduced activity over the northern South China Sea (SCS) and Taiwan, TC activity increased over the southern SCS and to the north of Shanghai after the early 2010s. Herein, we focused on the northern WNP. Over the last decade, frequent TC occurrences have affected East China, Korea and Japan. In this work, we examined the influence of synoptic‐scale waves (SSWs) on the interdecadal change in TC activity. During the 2011–2021 period, SSWs tended to propagate northward, resulting in more TC tracks affecting the northern WNP and surrounding countries. In contrast, the westward‐propagating SSWs before the early 2010s were more likely to favor westward‐moving TCs.

Southern South China Sea Dynamics: Sea Level Change from Coupled Model Intercomparison Project Phase 6 (CMIP6) in the 21st Century

Sea level rise will significantly impact coastal areas around the world. As a coastal country, Malaysia’s rising sea levels are a significant concern because they would affect 70% of its population. The study of sea level rise is important in order to implement effective mitigation and adaptation strategies. This study investigates the performance of CMIP6 Global Climate Models (GCMs) in simulating sea level rise in the Malaysian seas using various statistical methods. The models’ performances were evaluated by comparing historic CMIP6 GCM runs from 1993 to 2010 with sea level measurements from the satellite altimetry AVISO+ using the Taylor diagram. The SCS (SCSPM and SCSEM) had a higher sea level range and trend in both selected areas than the SM and SS. With 1.5 °C warmings, the multi-model ensemble means predicted that the SCS would rise by 16 mm near the Peninsular, with sea levels increasing by 0.908 m at a rate of 1.5 mm/year, and by 14.5 mm near East Malaysia, with sea levels increasing by 0.895 m at a rate of 1.1 mm/year. In contrast, 2.0 °C warmings project that SCSPM and SCSEM would cause sea levels to rise by 20.2 mm and 21.5 mm, respectively, at a rate of 0.6 mm/year and 0.7 mm/year. This information will provide an insight into Malaysian sea levels between now and the end of the twenty-first century, which will be beneficial for government agencies, academics, and relevant stakeholders.

Spatial Distribution and Trends of Wind Energy at Various Time Scales over the South China Sea

In this study, the spatial distribution and trends of wind energy (as measured by wind and wind power density) were investigated from 1979 to 2021 across various time scales over the South China Sea (SCS)by utilizing ERA5 reanalysis data. The results indicate that the SCS possesses abundant wind energy. In addition, due to the fact that the East Asian monsoon dominates the SCS, the wind energy exhibits obvious seasonal changes. It is in winter and autumn that the winter monsoon (i.e., the northeast wind) prevails over the SCS. Here, the wind energy is abundant and reaches its maximum in December. In summer, the summer monsoon (i.e., the southwest wind) prevails over the SCS. Here, the wind energy is abundant over the southwestern SCS. In spring, however, the wind energy is poor. The annual mean wind energy shows a decreasing trend along the northern coast and an increasing trend over the central SCS. The trends of seasonal mean wind energy in winter, spring, and summer demonstrate a similar pattern to the annual mean wind energy. With respect to the intensity of the trends, they are strongest in winter, followed by spring and autumn, and weakest in summer. The trend of wind energy in autumn almost demonstrates the opposite pattern in comparison with the other seasons, i.e., both decreasing and increasing trends over the northern and southern SCS, respectively. The decreasing trend of wind energy along the northern coast of the SCS occurs in February, April, July, September, and November, whereas the increasing trend over the central SCS appears from the period of December to June. The spatial distribution and trends of wind energy over the SCS can help with issuing a more informed recommendation with respect to offshore wind energy planning.

Seasonal variability of satellite-derived primary production in the South China Sea from an absorption-based model

Seasonal patterns of marine net primary production (NPP) are crucial for understanding the marine ecosystem and biogeochemical cycles. Uncoupling of seasonal variations between NPP and phytoplankton chlorophyll-a over different areas has attracted much attention. In this study, following a review of previous studies, monthly climatological NPP data from 2003 to 2020, estimated using the Size-fractioned Phytoplankton Pigment Absorption (aph)-based NPP Model (SABPM), were selected to study the seasonal variability of NPP in the South China Sea (SCS). Results showed the spatial differences of NPP seasonality and its departures from climatology in extreme El Niño-Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) years. Cluster analysis for climatological monthly data identified significant differences of NPP seasonality in five typical regions. In coastal regions along the northern SCS and off eastern Vietnam, NPP exhibited the most obvious seasonal cycle with maximum (minimum) values in summer (winter), attributable mainly to river discharge and summer upwelling. In regions off northwestern Luzon and coast of southern SCS, NPP showed peaks in winter, which were related to strong mixing and upwelling. In northwestern SCS, NPP was high during May–September in phase with sea surface temperature and the primary controlling factors were found to be shallow nutricline depth and wind-driven mixing. Owing to the deep nutricline depth in the central basin, NPP exhibited little seasonal variability; only a weak signal was observed in spring in phase with photosynthetically active radiation. Local dynamics on regulating the nutrient supply and light availability contribute to these regional differences in NPP seasonality, which could also be affected by extreme climate events. The largest anomalies of the NPP seasonal cycle coincide with 2015/2016 ENSO and super IOD in 2020. During these events, enhanced (weakened) westerly winds caused fall (rise) of SLA and increase (decrease) of NPP in coastal regions along the northern SCS and that off eastern Vietnam. Overall, theaph-based model shows a new perspective to study the spatiotemporal variations of NPP in the SCS.

The Natuna Waters Conflict between Indonesia and Vietnam: How is it resolved in International Law?

Indonesia is one of the largest archipelagic countries in the world consisting of thousands of islands. Part of Indonesia, namely the Natuna Islands, its position protrudes to the north which is located in the southern South China Sea. The Natuna Sea has natural resources, such as minerals and fish, and is an international sea crossing for ships coming from the Indian Ocean to enter the industrial countries around the sea and also to the Pacific Ocean. The problem of conflicts that occur between Indonesia and Vietnam in Natuna waters is one of the cases that are within the scope of International Law, especially specifically on International Sea Law. The Republic of Indonesia is one of the countries affected by the southern China sea conflict. Because the Indonesian EEZ region in the Natuna waters region is included in the Vietnam unilateral claim map. Therefore, Indonesia seeks to resolve, prevent and make resolutions regarding the South China Sea conflict which seriously threatens national interests and State sovereignty. One of the strategies implemented by Indonesia is the policy to enforce Vietnamese-flagged vessels carrying out illegal fishing in Natuna waters and also directing the combat fleet in the form of warships to intensify patrol in the region. In this regard, Indonesia conducted various negotiations and diplomacy to ensure that it resolved issues concerning the waters of southern China.

Borneo Vortices in a warmer climate

Borneo Vortices (BVs) are weather systems that are responsible for devastating hydro-climatic extremes and significant losses of life and property in Southeast Asia. The typical resolution of most current climate models is insufficient to resolve these high-impact, synoptic-scale weather systems. Here, an ensemble of high-resolution models projects that future BVs may become less frequent and more stationary, driven by the weakening of the Northeast monsoon flow and associated cold surges across North Borneo. However, substantial increases in both the intensity and the total amount of precipitation from BVs are projected. Such changes are driven by the more humid and convectively unstable lower troposphere. As a result, the contribution of BVs to the accumulation of both total precipitation and extreme precipitation is projected to increase considerably in the vicinity of the southern South China Sea, making individual BVs more threatening to the adjacent coastal regions.

Elevated anthropogenic CO2 invasion and stimulated carbonate dissolution in the South China Sea Basin

Great concern has been drawn in how marginal seas respond to elevated atmospheric carbon dioxide (CO2) and changes of carbonate system during absorbing anthropogenic CO2 (Cant). Decades of Cant absorption had prominently changed the carbonate system in the South China Sea (SCS). The Cant penetrated 1200–1800 m in the SCS in 2015, deeper than it in 1997. While the inventory of Cant reached 0.66 Gt C in the entire SCS, approximately 10% higher than it in 1997.With the invasion of the Cant, the average saturated depth of aragonite and calcite became shallower. The organic carbon pump and carbonate pump in the central and southern SCS Basin were less efficient than those in the northern SCS Basin especially in the intermediate waters, which were probably caused by the different biogenic compositions and residence time from north to south. The less calcite carbonate (CaCO3) load and longer residence time in the southern SCS Basin enhanced organic matter remineralization therein and thus resulted in a less efficient organic carbon pump. The decomposition of organic matter enhanced the CaCO3 dissolution while more CaCO3 dissolution enhanced the ability of buffering the atmospheric CO2 especially in the intermediate waters. In the foreseeable future, the SCS will absorb more Cant and continue decreasing the saturation depth of CaCO3. Plain language summaryThe ocean absorbs more atmospheric carbon dioxide (CO2) and changes its carbonate system under increasing emission of anthropogenic CO2 (Cant) since the industrial evolution. Decades of Cant absorption resulted in a deeper penetration depth by several hundred meters from 1997 to 2015 in the South China Sea (SCS), and enhanced the inventory of Cant in the meantime. During the invasion of the Cant, although changes of carbonate system could not be found from the dissolved oxygen, apparent oxygen utilization (AOU), normalized dissolved inorganic carbon (NDIC) and normalized total alkalinity in the upper 1000 m between 1997 and 2015 since the discrepancies were not significant enough. But the signals of acidification in the SCS became more severe, resulting in a shallower saturated depth of aragonite and calcite.The distribution of NDIC and AOU showed distinct pattern from north to south in the SCS Basin especially in the intermediate water, indicating a less efficient organic carbon pump and carbonate pump in the central and southern SCS Basin than those in the northern SCS Basin. The composition of carbonate (CaCO3) and residence time contributed to the discrepancies of these two pumps. Under the invasion of Cant, more CaCO3 dissolved and enhanced the ability of absorbing atmospheric CO2. In the foreseeable future, the SCS will absorb more Cant and continue decreasing the saturation depth of CaCO3.

Discovery of pockmarks in the Zengmu Basin, southern South China Sea and the implication

Discovery of pockmarks in the Zengmu Basin, southern South China Sea and the implication

Holocene transgression and sea level change offshore Peninsular Malaysia (innermost Sunda Shelf) as indicated by benthic foraminiferal, lithologic and geochronologic data

The history of Holocene sedimentation on the Sunda Shelf (southern South China Sea), one of the largest shelves in the world, has received little attention, particularly off Peninsular Malaysia. We present here evidence of Holocene transgression from most of the inner shelf of Peninsular Malaysia, based on lithologic and foraminiferal analyses of 24 cores from 13.5 m to 46.8 m water depth encompassing the coastal sand wedge and the immediately adjacent shelf. Six benthic foraminifera biofacies occur within these cores and, together with lithologic data and five AMS radiocarbon age estimates, enable recognition of three units previously defined in cores taken from 52 m to 77 m water depth. Eleven of 24 cores contain Unit 3, earliest Holocene coastal plain semi-consolidated peaty, sandy clay deposits that represent the lowest part of the post-last glacial maximum transgressive systems tract (TST). In a single core, Unit 4 open marine, inner shelf sandy mud deposits of the early Holocene upper part of the TST overlie Unit 3. In 23 cores Unit 3 is directly overlain by Unit 5, open marine, inner shelf sandy mud deposits of the highstand systems tract (HST) and laterally equivalent sediments within the coastal sand wedge that accumulated after the mid-Holocene sea-level maximum.

Ancient hydrocarbon slicks recorded by a coral atoll in the South China Sea

The intensifying oil slicks exert deleterious effects on coral reefs, hence attracting many investigations on coral's tolerance and resilience to anthropogenic oil pollution. We hypothesize that intense seafloor hydrocarbon seepages in the past could also produce oil slicks and subsequently contaminate coral reefs nearby, which may provide clues on their responses to natural oil contamination. Here, a long coral reef core (NK1) drilled in the isolated Meiji Atoll in the southern South China Sea is analyzed for aliphatic hydrocarbons to test this hypothesis. Two depth intervals, centered at 45–65 m and 95–110 m, corresponding to ages of ca. 0.3–0.6 Ma and 1.3–1.5 Ma, respectively, are characterized by geological-configured hydrocarbons indicative of ancient natural oil pollution. Because the Meiji Atoll stands on a volcanic seamount and in isolation in the sea, we deem that natural oils were incorporated into contemporary coral reefs by surface oil slicks, which were derived from hydrocarbon seepages at the seafloor of the adjacent petroliferous basins. The natural hydrocarbon seepages should result from regional tectonic movements that occurred extensively in the middle and late Pleistocene, likely in association with the arc-continent collision in the Taiwan region since 2 Ma. Albeit the two significant contamination events, it appears that they exerted insignificant disturbances on the growth and development of coral reefs, perhaps protected by certain holobiotic oil-degrading bacteria as indicated by excess production of bacterial branched fatty acids during the events. Our study thus suggests a high resilience of coral reefs to oil pollution under natural conditions, which, of course, does not mean that they would survive readily from the abrupt and intense anthropogenic pollution.

Observation of Near-Inertial Internal Gravity Waves in the Southern South China Sea

Two sets of more than 850 days of mooring records and satellite altimeter data are used to explore the features and spatiotemporal evolution of near-inertial waves (NIWs) near Nansha Island in the southern South China Sea (SCS). The observed NIWs are dominated by clockwise (downward energy propagation) motions and show a clear blue shift with a distinct peak frequency of 1.09 f during two large NIW events. The near-inertial kinetic energy (NIKE) is primarily concentrated in the upper layer and radiated downward. The largest value of depth-integrated NIKE reaches 3.5 KJ/m2. Besides, the NIWs are dominated by the first three modes, which account for 80% of the total NIKE. Moreover, the depth-integrated NIKE exhibits an apparent seasonal variation, with the largest NIKE in winter, which is almost three times larger than that in other seasons. Every large NIKE event is attributed to the passage of storms and is dominated by mode-2 NIWs. The dominance of the mode-2 NIWs is likely caused by the interaction between NIWs and mesoscale eddies.

Coexistence of savanna and rainforest on the ice-age Sunda Shelf revealed by pollen records from southern South China Sea

Exposure of the presently submerged continental shelf of Southeast Asia during low sea-level stands of the Quaternary is thought to be deeply involved in the biogeographic evolution of this biodiversity hotspot. Inland proxy records are mounting to argue grassland expansions over Southeast Asia during glacial periods, lending supports to the existence of a transequatorial “savanna corridor” as hypothesized. However, pollen records retrieved from marine sediments have indicated widespread rainforests on the exposed northern Sunda Shelf. To reconcile these seemingly conflicting observations, here we present new, multisite marine pollen records from the southern South China Sea focusing on the Last Glacial Maximum (LGM) time interval. It is found that the sites in front of the Sunda Shelf palaeo-rivers contain substantially more Poaceae pollen, in particular a smaller size fraction, than the site offshore North Borneo. Among the sites, abundant lowland tree pollen with similar major taxa is also observed. The co-occurrence of grass and rainforest pollen suggests a longitudinal climate gradient with increasing aridity toward the interior of glacial Sundaland. Combining our results with various palynological evidence from marine sediments seems to indicate that the vegetation on the exposed Sunda Shelf might not be fully recognized by previous studies. This is likely due to an admixture of pollen from other source regions, particularly Borneo where the rainforest was retained during glacial periods. Therefore, the extant vegetation records, from both terrestrial and marine archives, support the hypothesis of a “savanna corridor” over the LGM sundaland.