Distribution of convective Lower Halocline Water in the eastern Arctic Ocean

We investigate the distribution of convectively formed Lower Halocline Water (cLHW) in the eastern Arctic Ocean using observational and climatological data. The cLHW can be defined as the water mass in the cold halocline layer formed by winter convection. The presence of cLHW is indicated by temperatures close to the freezing point and a sharp bend in the Theta-S curve near the salinity of cLHW. Results from ice-drifting buoy observations in 2002 show differences in water mass characteristics in the upper ocean among the Amundsen Basin, over the Arctic Mid-Ocean Ridge, and in the Nansen Basin. In 2000-2002, cLHW was present over the Arctic Mid-Ocean Ridge and the Nansen Basin, but was largely absent from the Amundsen Basin. Using climatological data, we find that cLHW was confined to the Nansen Basin prior to 1990. In the early 1990s, cLHW still covered only the Nansen Basin, but extended to the northern side of the Arctic Mid-Ocean Ridge in the mid-1990s and covered the whole of the Amundsen Basin by the late 1990s. In the early 2000s, the area of cLHW moved back to its present boundary on the northern side of the Arctic Mid-Ocean Ridge. These results correspond roughly to other changes in the Arctic Ocean circulation and water mass structure, but with a time delay. We hypothesize that general circulation changes and the cutoff of source water for advective-convective modification of the LHW are causes of the change in cLHW distribution. The lag in changes to cLHW distribution behind other changes in the atmosphere and upper ocean are likely related to differences in circulation change with depth and the transit time from cLHW formation.