Hydrographic Evidence for Dense Shelf Water Contributions to the Arctic and Nordic Basins
James H. Swift
UCSD Scripps Institution of Oceanography
1. INTRODUCTION
'Hydrographic characteristics at and below mid-depth in most regions of the Arctic Ocean and Nordic seas can be derived only if dense shelf waters are added to the products of the "arctic" gyres of the Nordic Seas, which produce dense, well-ventilated waters in winter. Here I examine the σ0, range 27.8 to 28.1, corresponding to Denmark Strait Overflow Water (DSOW).
2. RESULTS
The surface waters of the Nordic Seas have a vast potential to influence subsurface water mass structure. The Atlantic water becomes very dense as it cools, and by the time it reaches the northern Norwegian Sea it can supply salt to the Nansen Basin water column from below the halocline to the saline water in theσ0, range 27.95 to 28.03 found in the central Nansen Basin (see Figure 1). The Nordic Seas do not, however, provide the freshening of subhalocline Arctic Ocean waters less dense thanσ0 = 28.0. The Arctic shelf seas must instead account for that freshening. The Makarov and Canada basins, the most remote from Fram Strait, are the freshest in the DSOW density range.
Oxygen distributions in the DSOW density range (Figure 2) show that Greenland Sea waters, if permitted to penetrate the Arctic Ocean, can supply substantial ventilation whereσ0, > 28.0. The high oxygen concentrations in the Nansen Basin in the rangeσ0, 27.9 to 28.O are coupled with high salinity, and so are unlikely to be derived from the Greenland Sea. Makarov Basin subhalocline waters with σ0 < 27.96 are relatively well ventilated. The bathymetric isolation of the deep Makarov and Canada basins is clear in the oxygen distributions. The low oxygen concentrations in the Norwegian Basin nearσ0 = 28.04 are more surprising, considering the proximity of the Greenland Sea.
The evolution of the water properties of the boundary current waters around the periphery of the Arctic Ocean basin provides clear evidence of the nature of the contributions from each of the
1 Corresponding author address:
James H. Swift, SIO, 95O0 Gilman Dr., La Jolla, CA 92093-0214, USA; email jswift@ucsd.edu
