Abstract

Submarine canyons enhance cross-shelf mass exchanges, which are a key component of on-shelf nutrient budgets and biogeochemical cycles. Previous studies assume that canyon-induced tracer flux onto the shelf only depends on canyon-induced water upwelling. This paper investigates the validity of this dependence for nutrients, carbon and dissolved gasses. To estimate the canyon-induced tracer upwelling flux and its spatial distribution on the shelf, we performed numerical experiments simulating an upwelling event near an idealized canyon, adding 10 passive tracers with initial profiles representing nutrients, carbon and dissolved gasses. This paper presents a scaling estimate for canyon-induced tracer upwelling and for the on-shelf distribution of a given tracer. We find that tracer upwelling depends on the mean initial vertical tracer gradient within the canyon, the depth of upwelling and the upwelling flux. We identify a pool of low oxygen and high nutrient concentration, methane, dissolved inorganic carbon and total alkalinity on the shelf bottom, downstream of the canyon. The horizontal extension of the pool depends on the canyon-induced advective fluxes feeding the pool and the initial background distribution of tracers on the shelf. This canyon-induced distribution of tracers has the potential to impact demersal and benthic ecosystems by lowering dissolved oxygen levels and spreading corrosive waters along the shelf.