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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]

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]

Coralline algae are excellent archives for recording paleo-water depth, but to date few studies have used them for long-term paleo-water depth reconstruction. This study focuses on the Plio-Pleistocene section of Well CK2, which was drilled in the northern South China Sea. The section consists of 55.2 m of volcanic basement overlain by 873.55 m of carbonates. The chronological framework of Well CK2 has been well established using magnetostratigraphy and bulk sediment strontium isotope ratios. The Plio-Pleistocene section includes the uppermost 341 m (5.18 Ma). Based on observations of 201 petrologic thin sections, we identified nine coralline algae genera (nongeniculate: Mesophyllum , Spongites , Lithothamnion , Lithoporella , Lithophyllum , and Hydrolithon ; articulated: Amphiroa , Jania , and Corallina), and five coralline algal assemblages (Mesophyllum assemblage, Spongites assemblage, Lithothamnion assemblage, Mesophyllum - Lithophyllum assemblage, and Lithoporella - Lithophyllum assemblage). The Mesophyllum assemblage dominates in the interval between 341 and 312 m (5.18–4.36 Ma; early Zanclean) and developed in a water depth between 15 and 25 m. The Spongites assemblage dominates in the interval between 312 and 309 m (4.36–4.28 Ma; middle Zanclean) and is characterized by subspherical rhodoliths (3 to 9 cm in diameter). This assemblage is probably related to the very shallow (0 to 5 m) water of the distal reef flat/reef crest. The Lithothamnion assemblage dominates in the interval between 309 and 200 m (4.28–2.20 Ma) and developed in a reef platform zone at a water depth of more than 25 m. The Mesophyllum - Lithophyllum assemblage dominates in the interval between 200 and 80 m (2.20–1.16 Ma) and developed in a water depth between 15 and 20 m. The Lithoporella - Lithophyllum assemblage dominates in the interval between 80 and 0 m (1.16–0 Ma) and develops in a water depth of 15 m or less. Our paleo-water depths are basically in agreement with global sea-level variations over time, indicating that paleo-water depths in the South China Sea were controlled mainly by eustatic variations. Based on the relationship between coral reef development and water depth, we further divided the Quaternary intervals into four long-term developmental stages. They consist of two catch-up stages: 1) from 5.18 to 4.28 Ma and 2) from 2.2 to 1.16 Ma; a give-up stage from 4.28 to 2.2 Ma; and a keep-up stage from 1.16 Ma to present. Our results confirm that the coralline algae in the coral reefs of the South China Sea can accurately record past water depth variations. Unlabelled Image • Nine genera and five coralline algae assemblages recognized. • Reconstruction of the sequences of coralline algal assemblages of the South China Sea. • The Plio-Pleistocene paleo-water depth of the SCS has decreased over a long-term scale. • Coral reef development of the South China Sea is discussed. [ABSTRACT FROM AUTHOR]

The East Asian Monsoon (EAM) has significantly influenced various depositional and diagenetic processes in carbonate sediments in much of East and South Asia during the Cenozoic. The relationship between the EAM and marine carbonate platforms, which are widely developed in this region, however, remains largely unknown. Based on petrographic, mineralogical, and geochemical analyses of the carbonate succession (∼237 m thick) on the Xisha Islands, South China Sea, meteoric diagenesis and its relationship with the East Asian Summer Monsoon (EASM) during the Pleistocene were studied. Various petrographic features, stable isotopes (δ13C, δ18O), and trace elements (Sr, Fe, Mn, Rare Earth Elements and Y) indicate that this succession was extensively altered by meteoric diagenesis, producing four exposed surfaces embedded in the shallow coral reef sediments. Given this data, we suggest that the meteoric diagenesis that affected this succession occurred during periods of low sea-level, and was potentially related to the relative intensity of the EASM. During strong EASM periods, particularly during the Mid-Pleistocene Transition ∼0.9 Ma, meteoric diagenesis was intense, as suggested by the complete alteration of unstable minerals, extreme dissolution, the presence of reddish-brown iron oxides, and a large negative excursion of δ13C (−6.2‰). The influence of the EASM on meteoric diagenesis of Pleistocene carbonate platforms can be identified throughout the South China Sea. This study sheds light on the relationship between meteoric diagenesis and paleo-climate conditions in carbonate platform regions that are influenced by monsoons. • Meteoric diagenesis was controlled by the relative intensity of EASM. • The sensitivity of geochemical parameters to meteoric diagenesis is different. • EASM had influenced meteoric diagenesis since Pleistocene. • Meteoric diagenetic transformation of Xisha platform was most intense at ∼0.9 Ma. [ABSTRACT FROM AUTHOR]

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