Regionally Variable Contribution of Dissolved Organic Phosphorus to Marine Annual Net Community Production

Abstract

AbstractMarine dissolved organic phosphorus (DOP) serves as an organic nutrient to marine autotrophs, sustaining a portion of annual net community production (ANCP). Numerical models of ocean circulation and biogeochemistry have diagnosed the magnitude of this process at regional to global scales but have thus far been validated against DOP observations concentrated within the Atlantic basin. Here we assimilate a new marine DOP data set with global coverage to optimize an inverse model of the ocean phosphorus cycle to investigate the regionally variable role of marine DOP utilization by autotrophs contributing to ANCP. We find ∼25% of ANCP accumulates as DOP with a regionally variable pattern ranging from 8% to 50% across nine biomes investigated. Estimated mean surface ocean DOP lifetimes of ∼0.5–2 years allow for transport of DOP from regions of net production to net consumption in subtropical gyres. Globally, DOP utilization by autotrophs sustains ∼14% (0.9 Pg C yr−1) of ANCP with regional contributions as large as ∼75% within the oligotrophic North Atlantic and North Pacific. Shallow export and remineralization of DOP within the ocean subtropics contributes ∼30%–80% of phosphate regeneration within the upper thermocline (<300 m). These shallow isopycnals beneath the subtropical gyres harboring the preponderance of remineralized DOP outcrop near the poleward edge of each gyre, which when combined with subsequent lateral transport equatorward by Ekman convergence, provide a shallow overturning loop retaining phosphorus within the subtropical biome, likely helping to sustain gyre ANCP over multiannual to decadal timescales.