Yuanfu Yue, Lichao Tang, Kefu Yu, Rongyong Huang. Coral records of Mid-Holocene sea-level highstands and climate responses in the northern South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2264-9
Citation:
Yuanfu Yue, Lichao Tang, Kefu Yu, Rongyong Huang. Coral records of Mid-Holocene sea-level highstands and climate responses in the northern South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2264-9
Yuanfu Yue, Lichao Tang, Kefu Yu, Rongyong Huang. Coral records of Mid-Holocene sea-level highstands and climate responses in the northern South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2264-9
Citation:
Yuanfu Yue, Lichao Tang, Kefu Yu, Rongyong Huang. Coral records of Mid-Holocene sea-level highstands and climate responses in the northern South China Sea[J]. Acta Oceanologica Sinica. doi: 10.1007/s13131-023-2264-9
School of Marine Sciences, Coral Reef Research Center of China, Guangxi University, Nanning 530004, China
2.
Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Nanning 530004, China
Funds:
The National Natural Science Foundation of China under contract Nos 42366002 and 41702182; the National Key R&D Program of China under contract No. 2017YFA0603300; the Guangxi Scientific Projects under contract No. 2018GXNSFAA281293.
High-resolution sea-level data and high-precision dating of corals in the northern South China Sea (SCS) during the Holocene provide a reference and historical background for current and future sea-level changes and a basis for scientific assessment of the evolutionary trend of coral reefs in the SCS. Although sporadic studies have been performed around Hainan Island in the northern SCS, the reconstructed sea level presents different values or is controversial because the indicative meaning of the sea-level indicators were neither quantified nor uniform criteria. Here, we determined the quantitative relationship between modern living coral and sea level by measuring the top surfaces of 27 live Porites corals from the inner reef flat along the east coast of Hainan Island and assessed the accuracy of results obtained using coral as sea-level indicators. Additionally, three in situ fossil Porites corals were analyzed based on elevation measurements, digital X-Ray radiography, and U-Th dating. The survey results showed that the indicative meanings for the modern live Porites corals is (−146.09 ± 8.35) cm below the mean tide level (MTL). It suggested that their upward growth limit is constrained by the sea level, and the lowest low water is the highest level of survival for the modern live Porites corals. Based on the newly defined indicative meanings, 6 new sea-level index points (SLIPs) were obtained and 19 published SLIPs were recalculated. Those SLIPs indicated a relative sea level fluctuation between (227.7 ± 9.8) cm to (154.88 ± 9.8) cm MTL between (5 393 ± 25) cal a BP and (3 390 ± 12) cal a BP, providing evidences of the Mid-Holocene sea-level highstand in the northern SCS. Besides that, our analysis demonstrated that different sea-level histories may be produced based on different indicative meanings or criteria. The dataset of 276 coral U-Th ages indicates that coral reef development in the northern SCS comprised the initial development, boom growth, decline, and flourishing development again. A comparison with regional records indicated that synergistic effects of climatic and environmental factors were involved in the development of coral reefs in the northern SCS. Thus, the cessation of coral reef development during the Holocene in the northern SCS was probably associated with the dry and cold climate in South China, as reflected in the synchronous weakening of the ENSO and East Asian summer monsoon induced by the reduction of the 65°N summer insolation, which forced the migration of the Intertropical Convergence Zone.
Figure 1. A geographic map of South China Sea, showing the location of Hainan Island. a. Surface-ocean circulation patterns in the South China Sea during the East Asian summer monsoon (EASM) and b. the East Asian winter monsoon (EAWM), modified after Yu and Liu (1993) and Morton and Blackmore (2001). c. Coral reefs are distributed along the coast of Lei-Qiong and d. The elevation survey and sampling during the field investigation from Wenchang southward to Qionghai along the east coastal Hainan Island in July 2020.
Figure 2. Cross-section sketches showing distribution of biological-geomorphological zones of typical fringing coral reefs based on our field investigation in July 2020 on the eastern coast of Hainan in the northern SCS.
Figure 3. Precise height measurement results of the top surface elevation of the 27 live Porites corals from Tongguling along the coast of Wenchang, Hainan Island. It showed that the upper surface elevations of those live Porites corals were 146.09 cm below the MTL on average. The depth range of live Porites corals heights is relative to 1985 National Elevation Benchmarks and the predicted tidal levels at Qinlan Port tide gauge. The mean tide level (MTL) lies 103 cm above 1985 National Elevation Benchmarks, the mean low water (MLW) is 58 cm, the mean high water (MHW) is 147 cm, the highest high water (HHW) is 315 cm, the lowest low water (LLW) is −28 cm, the mean tidal range is 89 cm, and the maximum tidal range is 255 cm (China Nave Hydrographic Office, 2022).
Figure 4. Left images showing macro-structures and preservation status of Holocene fossil Porites corals on the east coastal Hainan in the northern SCS. The diameters in Images a, b and c are 101.5 cm, 253 cm, and 191 cm, respectively.
Figure 5. Distribution of the δ 234U (T) variations (a), the U concentrations (b) and U-Th ages (c) for the 276 in-situ dead Porites, Porites microatolls and coral-related debris from the northern SCS. Episodes of corals growth from the northern SCS during the Holocene based on the U-Th ages order and its’ two standard deviations (50-year interval) of the age determination errors (±2σ) (d).
Figure 6. U-Th age-elevation data for our 6 new SLIPs and 19 recalculated SLIPs from east costal Hainan Island in the northern SCS. Vertical uncertainties are uniformly ±9.8 cm (±2σ).
Figure 7. Comparison of Mid-Holocene RSL data (a) with the predictions of the ICE-4G model (Wang et al., 2012) and the outputs of the final ice-volume equivalent sea-level model from Bradley et al. (2016), coral U-Th ages distribution pattern (c, d) derived from the in situ dead corals on the coast of northern SCS, storm records from Lingyang Reef (Yue et al., 2019) (b), the reconstructed temperature (relative to the present) from China (Wang and Gong, 2000) (e), subtropical evergreen broadleaved percentage (Yue et al., 2012) (f), the sea surface temperatures (SSTs) of Core MZ01 from the continental shelf of the East China Sea (Pan et al., 2020) (g, h), reconstruction of El Niño occurrences from Laguna Pallcocha, Ecuador (Moy et al., 2002) (i), δ 18O records (‰, VSMOW) from the stalagmite of Dongge Cave (Wang et al., 2005) (j), and the 65°N summer insolation in July in the Northern Hemisphere (Berger and Loutre, 1991) (k).
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