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Marine heterotrophicBacteria(or referred to as bacteria) play an important role in the ocean carbon cycle by utilizing, respiring, and remineralizing organic matter exported from the surface to deep ocean. Here, we investigate the responses of bacteria to climate change using a three-dimensional coupled ocean biogeochemical model with explicit bacterial dynamics as part of the Coupled Model Intercomparison Project Phase 6. First, we assess the credibility of the century-scale projections (2015–2099) of bacterial carbon stock and rates in the upper 100 m layer using skill scores and compilations of the measurements for the contemporary period (1988–2011). Second, we demonstrate that across different climate scenarios, the simulated bacterial biomass trends (2076–2099) are sensitive to the regional trends in temperature and organic carbon stocks. Bacterial carbon biomass declines by 5–10% globally, while it increases by 3–5% in the Southern Ocean where semi-labile dissolved organic carbon (DOC) stocks are relatively low and particle-attached bacteria dominate. While a full analysis of drivers underpinning the simulated changes in all bacterial stock and rates is not possible due to data constraints, we investigate the mechanisms of the changes in DOC uptake rates of free-living bacteria using the first-order Taylor decomposition. The results demonstrate that the increase in semi-labile DOC stocks drives the increase in DOC uptake rates in the Southern Ocean, while the increase in temperature drives the increase in DOC uptake rates in the northern high and low latitudes. Our study provides a systematic analysis of bacteria at global scale and a critical step toward a better understanding of how bacteria affect the functioning of the biological carbon pump and partitioning of organic carbon pools between surface and deep layers.
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Bacterial Control of Metabolic Balance in the Sargasso Sea Near Bermuda: Insights From Data‐Assimilative Biogeochemical Modeling
Heterotrophic marine bacteria are key players in the ocean carbon cycle. However, their exact contributions to net community production (NCP)—a crucial metric for the biological pump that indicates the metabolic balance and sets the upper limit for carbon export—remain unquantified due to limited bacterial integration in ocean biogeochemical models. In this study, we addressed this knowledge gap and quantified the role of bacterial dynamics in controlling total heterotrophic respiration (HR) and NCP at the Bermuda Atlantic Time‐series Study (BATS) site. To do this, we developed and employed a one‐dimensional data‐assimilative ocean biogeochemical model. Our results demonstrated that bacteria contributed 88% of HR, playing a dominant role in regulating NCP through respiration rates comparable to net primary production (NPP). Under future climate conditions, annual NCP remained stable in the upper ocean due to offsetting increases in bacterial respiration (BR) and NPP. However, distinct seasonal and vertical patterns emerged that intensified with the severity of climate change: increased NCP in winter and early spring surface waters, decreased NCP in late spring and at depth during mixing periods, and less pronounced increases during summer‐fall stratification. The increased BR rates resulted from complex interactions between temperature‐enhanced metabolic rates and adaptive substrate utilization, where bacteria maintained their metabolism despite increased labile organic matter limitation by utilizing a semi‐labile pool. Our results highlight bacteria's critical influence on upper ocean carbon cycling, providing key insights into their biogeochemical role under climate change.
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- Award ID(s):
- 2318940
- PAR ID:
- 10671941
- Publisher / Repository:
- AGU/Wiley (Journal of Geophysical Research)
- Date Published:
- Journal Name:
- Journal of Geophysical Research: Biogeosciences
- Volume:
- 130
- Issue:
- 10
- ISSN:
- 2169-8953
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1029/2025JG008919
