An assessment of Arctic Ocean freshwater content changes from the 1990s to the 2006–2008 period

Unprecedented summer-season sampling of the Arctic Ocean during the period 2006–2008 makes possible a quasi-synoptic estimate of liquid freshwater (LFW) inventories in the Arctic Ocean basins. In comparison to observations from 1992 to 1999, LFW content relative to a salinity of 35 in the layer from the surface to the 34 isohaline increased by 8400±2000 km3 in the Arctic Ocean (water depth greater than 500 m). This is close to the annual export of freshwater (liquid and solid) from the Arctic Ocean reported in the literature.Observations and a model simulation show regional variations in LFW were both due to changes in the depth of the lower halocline, often forced by regional wind-induced Ekman pumping, and a mean freshening of the water column above this depth, associated with an increased net sea ice melt and advection of increased amounts of river water from the Siberian shelves. Over the whole Arctic Ocean, changes in the observed mean salinity above the 34 isohaline dominated estimated changes in LFW content; the contribution to LFW change by bounding isohaline depth changes was less than a quarter of the salinity contribution, and non-linear effects due to both factors were negligible.

Research highlights
► Unprecedented Arctic-basin-wide sampling in 2006 – 2008 enables freshwater budgets.
► Liquid freshwater content increased by 8400±2000 km3 (20%), relative to the 1990s.
► Changes largely due to freshening of upper Arctic Ocean (river input and ice-melt).
► Changes partly due to regional Ekman Pumping.
► Results from ice-ocean model (NAOSIM) compare well on basin scales.