Physical controls on North Atlantic organic carbon export from eddying ocean models

Abstract. Organic carbon export from the surface mixed layer to the ocean interior is a central component of the biological carbon pump, yet physically driven subduction export of particulate and dissolved organic carbon (POC and DOC, respectively) remains poorly constrained. The North Atlantic is a critical region for organic carbon export, where strong physical and biological contrasts generate substantial spatial and temporal variability in export pathways. Here, we employ an eddy-present global ocean–sea ice model configuration with an embedded eddy-rich Atlantic to quantify the spatial and temporal variability of subduction export in the North Atlantic and to evaluate its sensitivity to model resolution. We divide total organic carbon export into gravitationally driven sedimentation export and physically driven subduction export, the latter comprising advective and mixed-layer exports. Regionally, subduction export contributes up to 34 % of total POC export across the examined bioregions (from south to north: subtropical, intermediate, subpolar, and ice-covered regions) and is consistently partitioned between advective and mixed-layer export in an ∼2:1 ratio except in the ice-covered region; total DOC export is also dominated by the advective component within subduction, accounting for up to 94 %. This broadly uniform partitioning persists despite the pronounced south-to-north patterns in the net export fluxes of both total POC and DOC. Seasonally, a winter–spring peak in advective export precedes the spring maximum in mixed-layer export, and is followed by a spring–summer maximum in sedimentation export in most regions, a pattern common to both POC and DOC, indicating a first-order role of subduction export alongside sedimentation export in shaping seasonal carbon export. Comparison between eddy-present and eddy-rich simulations shows generally higher export for both tracers in the eddy-rich simulation, with differences peaking at mid-to-high latitudes and reaching up to 64 % of the eddy-rich export for DOC in the ice-covered region. The advective component is particularly sensitive to model resolution, underscoring the need to better resolving the physical processes that regulate subduction export. Together, these results provide a further constraint on physically driven subduction export in the North Atlantic and a stronger basis for understanding its role in ocean carbon cycling.