The central Arctic is an important component of the global climate system, not only by atmospheric teleconnections but also by links in ocean circulation to lower latitudes. There, the gyre circulation and the meridional overturning may be affected by the release of freshwater from the Arctic reservoir.

Long-term observations in the Arctic Ocean by a multitude of observational platforms allow estimates of annual mean liquid freshwater content in the upper Arctic basins (Figure).

In addition to research cruises by icebreaking ships, e.g. Polarstern and air-supported spring expeditions, autonomous ice-tethered buoy systems like FRAM or MIDO have enabled a nearly year-round, Arctic basin-wide coverage of temperature and salinity profile observations since 2006. These measurements not only provide estimates of basin-wide integrated quantities but also improve our understanding of long-term changes in ice drift, snow cover, atmospheric pressure and ocean circulation; and of the role of local processes in these large-scale changes.