Effects of marine-ending glaciers with tidewater termini on fjord water properties
Bograd, Steven E.
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Oceanographic data collected in front of the San Rafael Glacier, Chile, indicate that mixing between subglacial stream discharge and laguna water was dependent on tidal stage and distance from the terminus. Maximum mixing occurred during flood tide and decreased away from the terminus. Based on studies in Alaska, high rates of sedimentation were expected in Chile. However, our oceanographic, bathymetric and suspended sediment data indicate that the San Rafael Glacier transports and releases two orders of magnitude less debris than glaciers in Glacier Bay, Alaska. In addition, suspended sediment samples collected in Chile consisted of approximately 60% sand and 40% mud, whereas debris released from glaciers in Alaska is dominated by mud. Therefore, it is probable that resulting lithofacies could differ among glaciers with similar climatic and glacial characteristics depending on bedrock types or weathering conditions. Utilization of a ROV allowed the collection of oceanographic data and visual observations directly at the termini of Grand Pacific and Muir Glaciers, Alaska. Temperature and salinity data were used to identify and document the mixing of different water types including: subglacial, englacial and deltaic stream discharge; direct ice melt; and far-field fjord water. Englacial, subglacial and deltaic stream discharge dominated during the ablation season while direct ice melt dominated during the accumulation season. Potential ice-melt rates for winter conditions were approximately 50% of the rates calculated for summer conditions. The detection of fresh water originating from morainal bank sediment indicates possible subglacial aquifer discharge. Comparison of ice proximal marine environments at San Rafael Glacier and Grand Pacific and Muir Glaciers also indicates a difference in termini stability. Deep water, active calving and subglacial stream discharge with low sediment concentrations describe an unstable situation for the San Rafael Glacier. Shallow water, decreased calving and the growth of morainal banks into ice contact deltas describe a more stable situation at Grand Pacific and Muir Glaciers.