Data_Sheet_1_The Seasonal Flux and Fate of Dissolved Organic Carbon Through Bacterioplankton in the Western North Atlantic.pdf

The oceans teem with heterotrophic bacterioplankton that play an appreciable role in the uptake of dissolved organic carbon (DOC) derived from phytoplankton net primary production (NPP). As such, bacterioplankton carbon demand (BCD), or gross heterotrophic production, represents a major carbon pathway that influences the seasonal accumulation of DOC in the surface ocean and, subsequently, the potential vertical or horizontal export of seasonally accumulated DOC. Here, we examine the contributions of bacterioplankton and DOM to ecological and biogeochemical carbon flow pathways, including those of the microbial loop and the biological carbon pump, in the Western North Atlantic Ocean (∼39–54°N along ∼40°W) over a composite annual phytoplankton bloom cycle. Combining field observations with data collected from corresponding DOC remineralization experiments, we estimate the efficiency at which bacterioplankton utilize DOC, demonstrate seasonality in the fraction of NPP that supports BCD, and provide evidence for shifts in the bioavailability and persistence of the seasonally accumulated DOC. Our results indicate that while the portion of DOC flux through bacterioplankton relative to NPP increased as seasons transitioned from high to low productivity, there was a fraction of the DOM production that accumulated and persisted. This persistent DOM is potentially an important pool of organic carbon available for export to the deep ocean via convective mixing, thus representing an important export term of the biological carbon pump.

海洋中广泛分布着异养浮游细菌（heterotrophic bacterioplankton），这类微生物在摄取源自浮游植物净初级生产力（phytoplankton net primary production，NPP）的溶解有机碳（dissolved organic carbon，DOC）过程中发挥着重要作用。据此，浮游细菌碳需求（bacterioplankton carbon demand，BCD）即总异养生产，代表了一条关键的碳循环路径，其会影响表层海洋中DOC的季节性积累，并进而影响季节性积累的DOC潜在的垂直或水平输出。本研究针对西北大西洋（约沿西经40°、北纬39°至54°海域）在完整年度浮游植物水华周期内的生态与生物地球化学碳流路径展开研究，涵盖微生物环（microbial loop）与生物碳泵（biological carbon pump）相关路径，其中涉及浮游细菌与溶解有机物（dissolved organic matter，DOM）的贡献。本研究将现场观测数据与配套的DOC再矿化实验数据相结合，估算了浮游细菌利用DOC的效率，证实了支撑BCD的NPP占比存在季节变化，并为季节性积累的DOC的生物可利用性与持久性变化提供了证据。研究结果表明，尽管随着季节从高生产力阶段向低生产力阶段过渡，经由浮游细菌的DOC通量占NPP的比例有所上升，但仍有一部分DOM生产会发生积累并持续留存。这类持久性DOM或许是一类重要的有机碳库，可通过对流混合向深海输出，因此代表了生物碳泵的一项关键输出项。