Background
The authors say their study was motivated "by reports of extraordinary change in the Arctic Ocean observed in recent decades."  Specifically, they refer to positive Atlantic Layer Core Temperature (ALCT) anomalies of up to 1°C in the 150- to 800-m depth interval that were observed by Carmack et al. (1995) and Woodgate et al. (2001).  In this regard, however, they note that the evaluation of these anomalies and, therefore, their true significance "requires an understanding of the underlying long-term variability" of the pertinent measurements, which they thus proceed to provide.

What was done
The data employed in the authors' study included temperature and salinity measurements from Russian winter surveys of the central Arctic Ocean carried out over the period 1973-79, which were derived from 1034 oceanographic stations and, in their words, "constitute the most complete set of arctic observations."  In addition, they utilized forty years of summer and winter observations from the Laptev Sea.  Based on these comprehensive measurements, they determined new statistical estimates of long-term variability in both ALCT and sea-surface salinity (SSS).

What was learned
The authors demonstrated that the standard dataset that had been used to suggest the existence of the apparent 1°C temperature anomalies of the 1990s "considerably underestimates variability."  In a specific case study, for example, they observed ALCT anomalies in the late 1970s that were fully as great as those of the 1990s.

What it means
In the carefully chosen words of the authors, they say that their new statistical analyses "place strong constraints on our ability to define long-term means, and hence the magnitudes of ALCT and SSS anomalies computed using synoptic measurements from the 1990s referenced to means from [earlier] climatologies."  In language a bit more blunt, we could just as well say that "the extraordinary change in the Arctic Ocean observed in recent decades" is not extraordinary at all, but merely a repeat of conditions that occurred but a few years earlier.

References
Carmack, E.C., Macdonald, R.W., Perkin, R.G., McLaughlin, F.A. and Pearson, R.J.  1995.  Evidence for warming of Atlantic water in the southern Canadian Basin of the Arctic Ocean: Results from the Larsen-93 expedition.  Geophysical Research Letters 22: 1061-1064.

Woodgate, R.A., Aagaard, K., Muench, R.D., Gunn, J., Bjork, G., Rudels, B., Roach, A.T. and Schauer, U.  2001.  The Arctic Ocean boundary current along the Eurasian slope and the adjacent Lomonosov Ridge: Water mass properties, transports and transformations from moored instruments. Deep Sea Research, Part I 48: 1757-1792.