Search

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

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