Seasonal Characteristics of Water Masses in Muir Inlet, a Fjord with Tidewater Glaciers

Abstract

The presence of two distinct seasonal water masses with transitions between them has been revealed in Muir Inlet, a fjord with tidewater glaciers in southeast Alaska. In spring a homogeneous water mass was found in which over 70% of the water fell into the ranges 31.0–31.2‰ salinity and 3.0–3.5 C. Heterogeneous water masses were found in summer and fall. The transition from the homogeneous to the heterogeneous water mass is explained on the basis of an entrainment mechanism during the summer high runoff period. It is suggested that the homogeneous spring condition derives from the intrusion of water from outside the fjord over the entrance sill which continues into early summer. This water exchange is driven primarily by tidal energy and depends upon denser water being available outside the sill during fall and spring. The differences between inlets with and without tidewater glaciers result from the melting of glacial ice in contact with warm, saline water masses. The melting of glacial ice appeared to continue at all seasons in Muir Inlet. The dissolved oxygen content confirms tha almost continuous renewal, showing only relatively small seasonal variations.