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

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 similar to 39% of particulate nitrogen (PN) in the surface ocean were derived from bacteria. Most of the bacterial POM (similar to 87%) was labile or semi-labile, and similar to 85% of bacterial POM was removed between depths of similar to 100-300 m. Bacterial POM constituted only similar to 8% and similar to 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.