The Impact of Initial Tracer Profile on the Exchange and On-Shelf Distribution of Tracers Induced by a Submarine Canyon

摘要

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 vertical local mean of the 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 downstream extension of the pool of low oxygen water depends on the onshore flux of water through the canyon and the oxygen profile. 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.