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Abstract Dissolved organic and inorganic carbon (DOC and DIC) influence water quality, ecosystem health, and carbon cycling. Dissolved carbon species are produced by biogeochemical reactions and laterally exported to streams via distinct shallow and deep subsurface flow paths. These processes are arduous to measure and challenge the quantification of global carbon cycles. Here we ask: when, where, and how much is dissolved carbon produced in and laterally exported from the subsurface to streams? We used a catchment‐scale reactive transport model, BioRT‐HBV, with hydrometeorology and stream carbon data to illuminate the “invisible” subsurface processes at Sleepers River, a carbonate‐based catchment in Vermont, United States. Results depict a conceptual model where DOC is produced mostly in shallow soils (3.7 ± 0.6 g/m2/yr) and in summer at peak root and microbial respiration. DOC is flushed from soils to the stream (1.0 ± 0.2 g/m2/yr) especially during snowmelt and storms. A large fraction of DOC (2.5 ± 0.2 g/m2/yr) percolates to the deeper subsurface, fueling deep respiration to generate DIC. DIC is exported predominantly from the deeper subsurface (7.1 ± 0.4 g/m2/yr, compared to 1.3 ± 0.3 g/m2/yr from shallow soils). Deep respiration reduces DOC and increases DIC concentrations at depth, leading to commonly observed DOC flushing (increasing concentrations with discharge) and DIC dilution patterns (decreasing concentrations with discharge). Surprisingly, respiration processes generate more DIC than weathering in this carbonate‐based catchment. These findings underscore the importance of vertical connectivity between the shallow and deep subsurface, highlighting the overlooked role of deep carbon processing and export.
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This content will become publicly available on April 1, 2026
Drivers of inorganic and organic carbon removal in aged oceanic crust
Large volumes of fluid flow through aged oceanic crust. Given the scale of this water flux, the exchange of organic and inorganic carbon that it mediates between the crust and deep ocean can be significant. However, off-axis carbon fluxes in older oceanic crust are still poorly constrained because access to low-temperature fluids from this environment is limited. At North Pond, a sedimented depression located on 8-million-year-old crust on the flank of the Mid-Atlantic Ridge, circulating crustal fluids are accessible through drilled borehole observatories. Here, fluids are cool (≤ 20°C), oxygenated and bear strong geochemical similarities to bottom seawater. In this study, we report concentrations and isotopic composition of dissolved organic and inorganic carbon from crustal fluids that were sampled six years after the installation of borehole observatories, which better represent the fluid geochemistry prior to drilling and perturbation. Radiocarbon-based signatures within carbon reservoirs support divergent shallow and deep fluid pathways within the crust. We also report a net loss of both dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) from the fluid during isolation in the crust. The removal of DOC is isotopically selective and consistent with microbe-mediated DOC oxidation. The loss of DIC is consistent with carbonate precipitation, although geochemical signatures of DIC addition to the fluids from DOC oxidation and basalt weathering are also evident. Extrapolated to global fluxes, systems like North Pond could be responsible for a net loss of ~10^11 mol C/yr of DIC and ~10^11 mol C/yr of DOC during the circulation of fluids through oceanic crust at low temperatures.
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- Award ID(s):
- 2023656
- PAR ID:
- 10633918
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Geochimica et Cosmochimica Acta
- Volume:
- 394
- Issue:
- C
- ISSN:
- 0016-7037
- Page Range / eLocation ID:
- 1 to 14
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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