Possible Sources and Preservation of Biogenic Pterins in the Sediments of the Southern South China Sea
Abstract

Pterins are vital metabolic precursor organic molecules in living organisms. Recent investigations reveal that the distribution of microbial pterins in the water column is primarily governed by biomass, productivity, and microbial community composition. Nevertheless, the sources, preservation, and degradation pathways of these compounds in surface and subsurface sediments remain poorly constrained. Specifically, the fate and controlling factors of the three major biogenic pterins—neopterin, biopterin, and isoxanthopterin—during their transition from the water column to surface sediments and subsequent burial remain unclear. To address this, the present study quantifies the occurrence, distribution, and provenance of pterins in sediment cores retrieved from the southern South China Sea (SCS) basin and Dongshan Bay. Cores were collected from Site Y1 (strong terrigenous influence) and Site A2 (weak terrigenous influence) during the 2024 TKK cruise, and from nearshore Dongshan Bay in 2025. Biopterin was identified as the predominant pterin species across all records, with concentrations and relative abundances generally declining with depth. While only biopterin was detected in the open-ocean SCS cores (with higher levels at Y1 than A2), three biogenic pterin compounds were identified in the Dongshan Bay core, albeit dominated by biopterin. Concentrations ranged from 0.07 to 9.07 nmol kg⁻¹ at A2, 0.05 to 1.32 nmol kg⁻¹ at Y1, and 1.07 to 9.80 nmol kg⁻¹ in Dongshan Bay. Notably, peak values in Dongshan Bay were slightly higher than those at Y1, and both were significantly higher than at A2, suggesting that enhanced terrigenous input plays a critical role in biopterin preservation. Furthermore, a significant positive correlation between biopterin and chlorophyll a indicates a photosynthetic origin, reflecting variations in input and preservation linked to regional primary productivity. These findings demonstrate that microbial-derived pterins in the water column are modulated by plankton community structure and abundance, clarifying the transfer and compositional evolution of these compounds in sedimentary environments. This study provides new insights into the utility of biogenic pterins as proxies for paleoproductivity and terrestrial input in coastal and oceanic biogeochemical cycles.

Key words: Pterins, South China Sea, metabolic precursor, Sedimentary preservation