inflowing Pacific water which is less saline than Atlantic water (∼2500 km^3 yr−1).
These freshwater inputs lead to a shallow mixed layer over a pronounced halocline.
Arctic sea ice is a ∼17,300 km^3 reservoir of freshwater. As the Arctic continues
warming, freshwater inputs will continue to increase.
(^) When the polar atmospheric high-pressure cell is well developed, the Beaufort gyre
extends over most of the Canadian Basin, and Pacific-derived water is found in the
Makarov Basin all the way to the Lomonosov Ridge. When the high-pressure cell is
weak, the Beaufort gyre is weak and displaced toward the American continent,
reducing the Pacific inflow and its extension toward the Atlantic. The front between
the Atlantic- and Pacific-derived waters has shifted over the last several decades from
the Lomonosov Ridge to the Mendeleyev Ridge (McLaughlin et al. 1996)
Production Controls
(^) The Canadian Basin, and the Beaufort, Chuckchi, and East Siberian Seas have low-
salinity surface water overlying the warmer but saltier Atlantic water. Nutrient
concentrations vary with the proportions of Pacific versus Atlantic waters, with
Pacific water having three-fold more nitrate, phosphate, and silicate at a given salinity
(Fig. 11.18). Nutrients can be depleted seasonally in the surface water, but tend to
range from 2 to 4 μM nitrate throughout the year in the Eurasian Basin. Elevated
nitrate, phosphate, and silicate are apparent in shelf water that is advected into the
basins forming a subsurface nutrient maximum associated with the halocline. There
are distinct nutrient and salinity signatures for Pacific- and Atlantic-derived waters
(Wheeler et al. 1997).
Fig. 11.18 Nutrients versus salinity plots for a 1994 Arctic Ocean section. Stations
with Pacific-derived characteristics (×); stations with intermediate chemical
characteritics (filled circles); stations with Atlantic-derived characteristics (open
circles). At a given salinity, Pacific-derived water has much higher nutrient
concentrations than Atlantic-derived water.
(^) (After Wheeler et al. 1997.)