Abstract
Ocean acidification (OA) threatens coral calcification by reducing the carbonate ion concentration that corals need to build their skeletons. However, assessments of the impacts of long-term OA are scarce, limiting our understanding of the response and acclimatization of corals to high pCO2 levels. Here we present a 42-year (1968–2010) seasonal δ11B and B/Ca records from Porites corals at Dongsha Atoll, located in the northern South China Sea. Our results reveal a rapid decline in seawater pH over this period, at a rate of −0.0021 ± 0.0008 pH units per year. Of special interest is that the interannual variability in seawater pH appears to be primarily co-regulated by hydrological changes in the Pearl River and fluctuations in the strength of Kuroshio intrusion. These factors are linked to large-scale climate systems and interannual-to-decadal variability, including the Pacific Decadal Oscillation, El Nino-Southern Oscillation, and East Asian Winter Monsoon. Meanwhile, reconstructed carbonate chemistry from the coral calcifying fluid suggests that Porites corals at Dongsha Atoll are able to physiologically modulate their internal pH. This up-regulation of internal pH not only buffers seasonal fluctuations in the aragonite saturation state and sustains stable calcification rates year-round, but also aids in long-term resistance to the detrimental effects of OA.
Plain Language Summary
Ocean acidification poses a major threat to coral reefs by reducing the concentration of carbonate ions essential for coral skeleton formation. However, long-term assessments of ocean acidification impacts on coral calcification are scarce, limiting our understanding of coral resilience and their potential for acclimation to ocean acidification. Using a 42-year Porites coral δ11B and B/Ca records, we investigated long-term variability in pHsw and the carbonate chemistry of the coral calcifying fluid (e.g., pHcf and Ωcf) in the northern South China Sea. Our results reveal a significant decline in pHsw over the past four decades. The interannual variability in pHsw is primarily co-modulated by hydrological changes in the Pearl River system and variations in the strength of Kuroshio intrusion. Physiological modulation of pHcf up-regulation in Dongsha corals plays a key role in minimizing seasonal fluctuations in Ωcf, maintaining stable year-round calcification rates, and contributing to their long-term resistance to the adverse effects of ocean acidification over the past 42 years.
Key Points
- A 42-year δ11B and B/Ca records from Dongsha corals reveals rapid OA and physiological adjustment of calcifying fluid carbonate chemistry
- Interannual pHsw variability is primarily co-modulated by hydrological changes in the Pearl River and variations in the Kuroshio intrusion
- Under a rapid OA rate (−0.0021 ± 0.0008 pHsw yr−1), calcifying fluid Ωcf remains constant, suggesting that DSA corals are resistant to OA
Chen H. Y. & Huang K. F., 2025. Rapid ocean acidification and coral calcification response in the northern South China Sea: insights from δ11B and B/Ca records in Porites coral. Global Biogeochemical Cycles 39(10): e2024GB008348. doi: 10.1029/2024GB008348. Article (restricted access).
