Surface freshening of the Canada Basin, 2003-2007: River runoff versus sea ice meltwater

The extent of summer Arctic sea ice has reduced dramatically in recent years and, simultaneously, we have observed surface freshening over the Canada Basin in 2006 and 2007. In order to identify the source of this fresh water, either meteoric or sea ice meltwater, salinity, δ18O, and alkalinity were analyzed. Results show that sea ice meltwater increased in the surface water over the central part of the basin in 2006 and 2007, corresponding to the melting of an additional 2.7 m (1.3 m a−1) of sea ice. Anomalously fresh surface water observed in the southern part in 2007, however, was mostly attributed to Mackenzie River water extending into the basin interior, a source that was mainly absent in the early 2000s. Comparison with previous data shows that the meltwater component of surface water in the southern part of the Canada Basin has progressively increased at a mean rate of 0.27 m a−1 since 1987. This can be explained by a reduction of winter sea ice formation rate by 0.45 m or more during the past two decades. The runoff component showed larger variability in the southern basin but no obvious temporal trend. In the central basin, the river runoff component showed an increasing trend of 0.7 m a−1.