Analysis of the Spatial Variability of Vertical Carbon Export Efficiency in the Ross Sea Using a Coupled Ocean‐Sea Ice‐Biogeochemical Model

Abstract The vertical export of particulate organic carbon (POC) is a key component of the oceanic carbon cycling. However, the mechanisms underlying the spatial variability of vertical POC export in the Ross Sea remain unclear due to limited observations. To address this, a high‐resolution, three‐dimensional coupled ocean‐sea ice‐ecosystem model for the Ross Sea (ROSE) was developed to explore the seasonal and spatial variations in vertical POC flux and its ratio to net primary production (NPP), a measure of biological carbon pump efficiency. A decade‐long hindcast simulation (2010–2020) was conducted and evaluated against available observations, demonstrating that ROSE reasonably reproduces key features of the lower‐trophic‐level of the Ross Sea ecosystem. Model results show that vertical POC export through the upper 100 m follows the NPP seasonality, with a single peak occurring approximately 1 month after the NPP maximum. Regional variability in light and dissolved iron limitations shape the magnitude and duration of NPP peaks, producing two distinct seasonal patterns: sharp‐pulse and smooth‐pulse types. The Ross Sea exhibits substantial carbon export potential, with a mean 100 m export efficiency exceeding 40%, but displaying pronounced spatial heterogeneity. POC budget analyses indicate that these spatial differences are primarily governed by variations in the biological transfer efficiency of per‐unit NPP to POC, further modulated by plankton community structure. Smooth‐pulse NPP with greater diatom dominance relative to Phaeocystis antarctica supports higher mesozooplankton biomass and greater POC buildup, thereby enhancing vertical export efficiency. Lateral POC flux plays a significant amplifying role, while POC remineralization contributes minimally.