Fourteen years (2000–2014) of bottle chemistry data collected during the North Pole Environmental Observatory were compiled to examine variations in the composition of freshwater (meteoric water, net sea-ice meltwater, and Pacific water) over mixed layer of the Central Arctic Ocean. In addition to significant spatial and interannual variability, there was a general decrease in meteoric water (MW) fractions at the majority of stations reoccupied over the duration of the program that was approximately balanced by a concomitant increase in freshwater from sea-ice melt (SIM FW) between 2000 and 2012. Inventories (0–120 m) of MW and SIM FW computed using available data between 2005 and 2012 exhibited similar variations over the study area, allowing for first-order estimates of the mean annual changes in MW (–389±194 km³ yr^-1) and SIM FW (292±97 km³ yr^-1) for the Central Arctic region. These mean annual changes were attributed to the diversion of Siberian river runoff to the Beaufort Gyre and the overall reduction of sea ice volume across the Arctic, respectively. In addition to this lower-frequency variability, spatial gradients and interannual variations in MW, SIM FW, and Pacific water contributions to specific locations were attributed to shifts in the Transpolar Drift that advects waters of eastern and western Arctic origin through the study area.

Freshening in the Canada basin of the Arctic Ocean began in the 1990s and continued to at least the end of 2008. By then, the Arctic Ocean might have gained four times as much fresh water as comprised the Great Salinity Anomaly of the 1970s, raising the spectre of slowing global ocean circulation. Freshening has been attributed to increased sea ice melting and contributions from runoff, but a leading explanation has been a strengthening of the Beaufort High — a characteristic peak in sea level atmospheric pressure — which tends to accelerate an anticyclonic (clockwise) wind pattern causing convergence of fresh surface water. Limited observations have made this explanation difficult to verify, and observations of increasing freshwater content under a weakened Beaufort High suggest that other factors must be affecting freshwater content.

Here we use observations to show that during a time of record reductions in ice extent from 2005 to 2008, the dominant freshwater content changes were an increase in the Canada basin balanced by a decrease in the Eurasian basin. Observations are drawn from satellite data (sea surface height and ocean-bottom pressure) and in situ data. The freshwater changes were due to a cyclonic (anticlockwise) shift in the ocean pathway of Eurasian runoff forced by strengthening of the west-to-east Northern Hemisphere atmospheric circulation characterized by an increased Arctic Oscillation index. Our results confirm that runoff is an important influence on the Arctic Ocean and establish that the spatial and temporal manifestations of the runoff pathways are modulated by the Arctic Oscillation, rather than the strength of the wind-driven Beaufort Gyre circulation.

Long-term moored measurements of temperature, salinity, and velocity over the abyssal plain near the North Pole show a rich array of eddy-like structures over a wide range of depths. Here we demonstrate an anticyclone that extends from the surface to at least 1700 m, is about 60 km across, and has a likely origin along the Eurasian continental margin.