Recent high-quality hydrographic measurements in the Arctic Ocean have
revealed a warming of up to 1 K of the Atlantic Layer when compared w
ith Russian climatologies of the 1940s to 1970s. About half of this wa
rming can be attributed to the different methods by which the two data
sets were obtained: the climatologies are based on discrete bottle da
ta in the vertical and necessarily involve smoothing in space and time
, whereas the modern, quasi-synoptic data are from continuously record
ing conductivity-temperature-depth sondes and give much better resolut
ion in the vertical. Modern surveys also focused more on boundary curr
ent regimes where narrow warm bands of Atlantic Water are present. The
remainder of the warming detected can be explained with the following
physical arguments: (1) an increased inflow of Atlantic Water in the
early 1990s and (2) a higher temperature of this inflowing water. Temp
erature time series in the Barents Sea since the beginning of this cen
tury suggest that the warming of the early 1990s is not a long-term cl
imate signal but, rather, is related to the inherent natural variabili
ty of the system with timescales of decades.