Climate-induced storminess forces major increases in future storm surge hazard in the South China Sea region

It is vital to robustly estimate the risks posed by extreme sea levels, especially in tropical regions where cyclones can generate large storm surges and observations are too limited in time and space to deliver reliable analyses. To address this limitation for the South China Sea region, we force a hydrodynamic model with a new synthetic database representing 10,000 years of past/present and future tropical cyclone activity, to investigate climate change impacts on extreme sea levels forced by storm surges (± tides). We show that, as stronger and more numerous tropical cyclones likely pass through this region over the next 30 years, both the spatial extent and severity of storm surge hazard increases. While extreme storm surge events in this location become generally a more frequent occurrence in the future, larger storm surges around Vietnam and China coastlines are projected to regionally amplify this hazard. This threatens low-lying, densely-populated areas such as the Red and Mekong River deltas, while sections of the Cambodian and Thai coastline face previously unseen storm surge hazards. These future hazards strongly signal that coastal flood management and adaptation in these areas should be reviewed for their resilience against future extreme sea levels.

Petrogenesis of Dacites in a Triassic Volcanic Arc in the South China Sea: Constraints From Whole Rock and Mineral Geochemistry

Triassic volcanic rocks, including basalts and dacites, were drilled from Meiji Atoll in the South China Sea (SCS), which represents a rifted slice from the active continental margin along the Cathaysia Block. In this study, we present apatite and whole rock geochemistry of Meiji dacites to decipher their petrogenesis. Apatite geochronology yielded U-Pb ages of 204–221 Ma, which are identical to zircon U-Pb ages within uncertainty and thus corroborate the formation of the Meiji volcanic rocks during the Late Triassic. Whole rock major elements suggest that Meiji dacites mainly belong to the high-K calc-alkaline series. They display enriched patterns in light rare earth elements (LREE) and flat patterns in heavy rare earth elements (HREE). They show enrichment in large-ion lithophile elements (LILE) and negative anomalies in Eu, Sr, P, Nb, Ta, and Ti. The dacites have initial 87Sr/86Sr ratios of 0.7094–0.7113, εNd(t) values of -5.9–-5.4 and εHf(t) values of -2.9–-1.7, whereas the apatite has relatively higher initial 87Sr/86Sr ratios (0.71289–0.71968) and similar εNd(t) (-8.13–-4.56) values. The dacites have homogeneous Pb isotopes, with initial 206Pb/204Pb of 18.73–18.87, 207Pb/204Pb of 15.75–15.80, and 208Pb/204Pb of 38.97–39.17. Modeling results suggest that Meiji dacites can be generated by <40% partial melting of amphibolites containing ∼10% garnet. Therefore, we propose that the Meiji dacites were produced by partial melting of the lower continental crust beneath the South China block, triggered by the underplating of mafic magmas as a response to Paleo-Pacific (Panthalassa) subduction during the Triassic. Meiji Atoll, together with other microblocks in the SCS, were rifted from the South China block and drifted southward due to continental extension and the opening of the SCS.