Horizontal advection critical for maintaining an Antarctic biological hotspot

Abstract

Along the Western Antarctic Peninsula, ecological hotspots are spatially coherent with submarine canyons and have persisted for millennia. Palmer Deep Canyon, a representative hotspot, is known to have higher phytoplankton biomass than the surrounding non-canyon regions. The physical mechanisms that maintain and deliver phytoplankton and Antarctic krill biomass, potentially increasing prey availability to predators, are not well known. To better understand these important mechanisms, we deployed a purpose built integrated polar observatory consisting of high frequency radar, coordinated gliders, and moorings. The gliders identified a depth dependent influence of the underlying canyon bathymetry on physical and biological variability. A series of simulated particle release experiments in the HF radar current maps were used to estimate surface residence time and connectivity across the canyon. With an average residence time of 2 days, our analysis indicates that the elevated phytoplankton biomass over the central canyon is transported into and out of the hotspot on time scales much shorter than the observed phytoplankton growth rate, suggesting that the canyon may not act as an incubator of phytoplankton productivity as previously suggested. It may instead serve more as a conveyor belt of phytoplankton biomass produced elsewhere, continually replenishing the phytoplankton biomass for the local krill community, which in turn supports numerous top predators.