Regionally variable contribution of dissolved organic phosphorus to
marine annual net community production
Abstract
Marine dissolved organic phosphorus (DOP) can serve as an organic
nutrient to marine autotrophs, helping to sustain 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 dataset 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 – 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 multi-annual to decadal timescales.