FY 1978

Deep water exchange in Alaskan subarctic fjords

Muench, R.D., and D.T. Heggie

In Estuarine Transport Processes, B. Kjerfve (ed.), Univ. of So. Carolina, Columbia, SC, 239–267 (1978)

Oceanographic conditions in deep waters of six different subarctic Alaskan fjords are discussed and related to circulation and mixing processes. The fjords are divided upon the basis of entrance sill depth into shallow, intermediate, and deep-silled fjords depending on whether the sill depth is less than, equal to, or greater than a level where there is minimum annual density variation in source waters from the Gulf of Alaska. Deep water renewal in shallow-silled fjords occurs principally during winter, while that in deep-silled fjords occurs during late summer; in intermediate-silled fjords it occurs on a year-round basis. Renewal of deep waters is dependent upon both the annual variation of density in the source waters and upon vertical mixing decreasing the density of the deep water between renewal periods. Inflow of source water at sill depth may be due in part to local winds and tidal currents and occurs despite restricted silled fjord entrances. In deep-silled fjords, inflow appears to be strongly influenced by longshore winds in the Gulf of Alaska as these raise or lower isopycnal surfaces. The frequencies of renewal are adequate to prevent the anoxic conditions observed farther south from occurring in these systems. Estimated values for oxygen utilization in the deep waters and for vertical eddy mixing coefficients agree with previously determined values, supporting the hypothesis for periodic deep water renewals between which distributions are controlled primarily by vertical mixing.