Impact of an unusually large warm-core eddy on distributions of nutrients and phytoplankton in the southwestern Canada Basin during late summer/early fall 2010

[1] Recent freshening of the Arctic Ocean due to melting of sea ice and enhanced Ekman pumping has deepened the nutricline over the Canada Basin and reduced nutrient concentrations in the euphotic zone. Cold-core eddies frequently transport nutrient-rich shelf water to the Canada Basin, but the eddies are much deeper than the euphotic zone. Because warm-core eddies appear near the surface or at a depth range shallower than that of the cold-core eddies, they may play a crucial role in determining nutrient distributions in the euphotic zone and hence may affect primary production. During late summer/early fall 2010, we conducted detailed surveys of a warm-core eddy, which was unusually large (∼100 km in diameter). We suggest that this warm-core eddy which contained high-ammonium shelf water could supply ammonium to the euphotic zone in the southwestern Canada Basin and may sustain ∼30% higher biomass of picophytoplankton (<2 μm) than that in the surrounding water in the basin. The role of warm-core eddies in supplying nutrients to the euphotic zone and controlling phytoplankton distributions seems to be more important than previously because the recent deepening of the nutricline in the Canada Basin has decreased the nutrient supply to the euphotic zone.