Role of advection in Arctic Ocean lower trophic dynamics: A modeling perspective

The Arctic Ocean (AO) is an oligotrophic system with a pronounced subsurface Chl-a maximum dominating productivity over the majority of the basin. Strong haline stratification of the AO and substantial ice cover suppress vertical mixing and restrict the vertical supply of nutrients to the photic zone. In such a vertically stratified oligotrophic system, the horizontal supply of nutrients by advection plays an important role in sustaining primary production. In this paper, we attempt to characterize the role of nutrient advection in the maintenance of the subsurface Chl-a maximum, using timescales to determine the connectivity between the photic zone of the deep AO, nutrient-rich Pacific and Atlantic inflow waters, and bottom waters of the wide continental shelves of the AO. Our study uses output from a general circulation model, Nucleus for European Modeling of the Ocean, coupled to a model of ocean biogeochemistry, Model of Ecosystem Dynamics, carbon Utilization, Sequestration, and Acidification. A Lagrangian particle tracking approach is used to back-track water from where it forms subsurface Chl-a maxima to the points of entry into the AO and to analyze nutrient transformation along the route. Our experiments show that advective timescales linking subsurface layers of the central AO with the nutrient-rich Pacific and Atlantic waters do not exceed 15-20 years and that the advective supply of shelf nutrients to the deep AO occurs on the timescale of about 5 years. We show substantial role of the continental shelf pump in sustaining up to 20% of total AO primary production.