Coral carbonate-bound isotopes reveal monsoonal influence on nitrogen sources in Southeastern China's Greater Bay Area from the mid-Holocene until the Anthropocene

作者：Cybulski, Jonathan D.^*; Duprey, Nicolas N.; Thibodeau, Benoit; Yasuhara, Moriaki; Geeraert, Naomi; Leonard, Nicole; Vonhof, Hubert B.; Martinez-Garcia, Alfredo; Baker, David M.^*

来源：Marine Pollution Bulletin, 2023, 197: 115757.

DOI：10.1016/j.marpolbul.2023.115757

• Nitrogen
• Stable-isotopes
• China's Greater Bay Area
• Coral
• Denitrifier method

Most anthropogenic nitrogen (N) reaches coastal waters via rivers carrying increasing loads of sewage, fertilizer, and sediments. To understand anthropogenic N impacts, we need to understand historical N-dynamics before human influence. Stable isotope ratios of N preserved in carbonates are one way to create temporal N records. However, records that span periods of human occupation are scarce, limiting our ability to contextualize modern N dynamics. Here, we produce a fossil-bound N-record using coral subfossils, spanning 6700 years in China's Greater Bay Area (GBA). We found that during the mid-to-late Holocene, the GBA's coastal N was dominated by fluvial sources. The weakening of the Asia monsoon throughout the late-Holocene decreased river outflow, leading to a relative increase of marine nitrate. This source shift from riverine-to-ocean dominance was overprinted by anthropogenic N. During the late 1980s to early 1990s, human development and associated effluent inundated the coastal system, contributing to the decline of coral communities.

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