Seasonal and spatial variations in the water mass characteristics of Muir Inlet, Glacier Bay, Alaska

Abstract

Muir Inlet, a Southeast Alaska fjord with tidal glaciers, is investigated. Its water masses show definite seasonal and spatial responses in temperature, salinity, and dissolved oxygen distributions and in circulation patterns. Its basin water is continually renewed. Two seasonal parameter structures are found. The winter - spring structure is characterized by the homogeneity of the water masses, with up to 84% of the fjord water having a temperature between 3.0 - 3.5°C and up to 55%, a salinity of 31.3 - 31.4%. The summer - fall fjord water masses are heterogeneous, with temperatures ranging from 0.5 - 7.5°C., salinities from 13.0 - 32.0% and dissolved oxygen levels ranging from 1.8 - 0.5 milliliters per liter. The heterogeneous state develops gradually from April through November. The homogeneous state is regained abruptly in late fall. The salinity of water below the pycnocline continually increases from late fall through early summer. The salinity of the surface water decreases from mid-spring through early fall. Several spatial parameter patterns are observed. Both salinities and temperatures decrease progressively from the Pacific Ocean to the head of the fjord. The tidal glaciers serve both as heat sinks and as freshwater sources, producing negative temperature and salinity gradients upfjord. The data are consistent with a three-layer flow system: outflowing brackish surface layer, intermediate zone of net upward transport, and a higher salinity deep layer with an upfjord transport. Advective inflows and thermohaline convection may occur from late fall through early summer.