Rapid Cycling of Bacterial Particulate Organic Matter in the Upper Layer of the Western Pacific Warm Pool

• Published in: Geophysical research letters Vol. 50; no. 11
• Main Authors: Guo, Jinqiang, Zhou, Bu, Achterberg, Eric P., Yuan, Huamao, Song, Jinming, Duan, Liqin, Li, Xuegang
• Format: Journal Article
• Language: English
• Published: Washington John Wiley & Sons, Inc 16.06.2023; Wiley
• Subjects: Abundance; amino acids; Bacteria; bacterial organic matter; Carbon capture and storage; Carbon dioxide; Carbon sequestration; Cycles; cycling; Detritus; High temperature; Metabolism; Oceans; Organic carbon; Organic matter; Particulate organic carbon; Particulate organic matter; Respiration; Suspended particulate matter; Upper ocean; Uptake; Western Pacific Warm Pool
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2023GL102896

Bacterial metabolism largely drives the sequestration of refractory organic matter in the ocean. However, a lack of understanding exists regarding the abundance and reactivity of bacterial particulate organic matter (POM). Here we report the bacterial contributions to suspended POM collected in the oligotrophic Western Pacific Warm Pool (WPWP). Around 27% of particulate organic carbon (POC) and ∼39% of particulate nitrogen (PN) in the surface ocean were derived from bacteria. Most of the bacterial POM (∼87%) was labile or semi‐labile, and ∼85% of bacterial POM was removed between depths of ∼100–300 m. Bacterial POM constituted only ∼8% and ∼13% of refractory POC and PN, respectively. The rapid cycling of bacterial POM in upper waters was likely related to oligotrophic conditions and facilitated by higher temperatures in the WPWP. Taken together, these observations indicate that bacterial POM plays a crucial role in supplying energy for bacterial respiration. Plain Language Summary Bacteria transform a large fraction of the organic matter made by primary producers and contribute to long‐term oceanic carbon sequestration with bacterial detritus, thereby contributing to ocean uptake of atmospheric carbon dioxide. The abundance and reactivity of bacterial organic matter are critical to consider in this carbon storage pathway. Here we collected suspended particulate organic matter (POM) in the Western Pacific Warm Pool (WPWP) and assessed the bacterial POM contribution. A substantial proportion of bacterial POM was found in the surface ocean, but most (∼85%) was rapidly removed between depths of 100–300 m as particles sink. The high temperature and oligotrophic features of WPWP facilitate the use of bacterial POM as an energy source for bacterial respiration. This rapid turnover of bacterial POM in the upper ocean results in a contribution of only ∼8% to long‐term carbon sequestration. Our results suggest that bacterial POM exhibits high reactivity and only a small fraction can lead to long‐term carbon sequestration. Key Points We assess bacterial contributions to suspended particulate organic matter (POM) in the Western Pacific Warm Pool on the basis of D‐amino acid biomarkers Bacterial organics constitute 27% of surface ocean particulate organic carbon (POC) and 39% of particulate nitrogen (PN), but majority (∼87%) is labile or semi‐labile Rapid cycling of bacterial POM in the upper ocean results in a contribution of only ∼8% to refractory POC and ∼13% to PN