3.5.3.2 Lower North Atlantic Deep Water

Dense waters overflowing the sills between Greenland and Scotland supply the Lower North Atlantic Deep Water (LNADW). Both overflows freshened from the mid-1960s to the mid-1990s (Dickson et al., 2008). The salinity of the Faroe Bank overflow increased by 0.015 to 0.02 from 1997 to 2004, implying a density increase on the order of 0.01 kg m–3 (Hansen and Osterhus, 2007). The other main overflow, through Denmark Strait, shows large interannual variability in temperature and salinity, but no trends for the time period 1996–2011 (Jochumsen et al., 2012). Observations of the transport of the dense overflows are dominated by short-term variability and there is no evidence of a trend in the short time series available (see Section 3.6). As both overflow components descend into the North Atlantic, they entrain substantial amounts of ambient subpolar waters to create LNADW. As a whole, the LNADW in the North Atlantic cooled from the 1950s to 2005 (Mauritzen et al., 2012), a signal thus stemming primarily from the entrained waters, possibly an adjustment from an unusually warm period observed in the 1920s and 1930s (Drinkwater, 2006).