MEPS 364:257-268 (2008)  -  DOI: https://doi.org/10.3354/meps07547

ABSTRACT: The magnitude of fluxes in the carbon cycle of subtropical and tropical marine habitats is determined by the supply of inorganic nutrients. These habitats have low sea-surface concentrations of nitrate (NO₃^–) and chlorophyll (dubbed LNLC regions), sustain relatively low rates of organic matter production and export, and represent global ocean minima in carbon sequestration potential. The low NO₃^– resupply should select for nitrogen (N₂)-fixing bacteria, termed diazotrophs, provided all other growth-limiting nutrients are available. Several recent field efforts have been aimed at enhancing N₂ fixation in LNLC regions through mesoscale fertilization with iron and phosphorus (or both) and we hypothesize herein that controlled upwelling of nutrient-enriched deep water may also be effective. Based on a quantitative assessment of the vertical distribution of NO₃^–, phosphate (PO₄^3–) and dissolved inorganic carbon (DIC) at Station ALOHA (22°45’ N, 158°W), we hypothesize that the process of controlled upwelling of low NO₃^–:PO₄^3– seawater may lead to enhanced N₂ fixation, organic matter production and net carbon sequestration. Furthermore, based on a long-term (20 yr) data set from Station ALOHA, we predict that the upwelling of water from a depth of 300 to 350 m during summer months will trigger a 2-stage phytoplankton bloom. The first stage will be characterized by a NO₃^–-supported Redfield ratio (e.g. C₁₀₆:N₁₆:P by atoms) diatom bloom. Following quantitative NO₃^– removal, the residual PO₄^3– from the low N:P (<16:1) upwelled nutrient pulse will stimulate a N₂-fixing bacterial bloom, leading to net sequestration of carbon. However, any strategic benefit of controlled upwelling for enhancing the long-term carbon sequestration will depend on the spatial and temporal uncoupling of organic matter production and remineralization, which is ultimately controlled by the microbial response to these perturbations.

KEY WORDS: N₂ fixation · Diazotroph · Nutrients · Carbon sequestration · North Pacific gyre

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Cite this article as: Karl DM, Letelier RM (2008) Nitrogen fixation-enhanced carbon sequestration in low nitrate, low chlorophyll seascapes. Mar Ecol Prog Ser 364:257-268. https://doi.org/10.3354/meps07547 Export citation Share:    Facebook - - linkedIn