Introduction

Glacier Bay is a diverse fjord ecosystem with multiple tidewater glaciers and complex biological, geological, and oceanographic patterns that vary greatly along its length. The bay was completely glaciated prior to the 1700's, and subsequently experienced the fastest glacial retreat recorded in historical times (Fig. 1). As a result, some of the highest rates of glacial sedimentation and uplift are observed here.

Figure 1. Location map of Glacier Bay National Park showing terminus positions and dates of retreat of the Little Ice Age glacier that completely filled the bay somewhat more than 200 yrs ago. The 1794 terminous line near the mouth of the bay is where Capt. George Vancouver and crew observed the massive glacier face during their hunt for the Northwest Passage. The 1879 glacier terminous position was mapped by John Muir during his first of several visits to Glacier Bay. Trapezoid outlines the Whidbey Passage study area. Modified from Seramur et al. (1996).

Glacier Bay is the deepest silled fjord in Alaska, with depths of over 450 meters. The variety of physical processes (for example icebergs gouging, see Fig. 2) and depths creates many diverse habitats within a relatively small area. Mapping benthic (seafloor) habitats is thus crucial to understanding and managing Glacier Bay's complex marine ecosystem and the marine species therein. High-resolution multibeam mapping of the bay, funded jointly by USGS and the National Park System, provides an unprecedented new baseline for resource and habitat assessment. Full integration of the new data set will require additional ground-truthing data (sampling) and analysis. The USGS goal is to develop integrated geological and oceanographic habitat models for the marine benthos in Glacier Bay, as a step toward determining the habitat relationships of critical species and resources within the Park.

Figure 2. Single icebergs that come in contact with the seafloor will produce grooves in unconsolidated sediments ranging from mud to coarse gravel. These iceberg gouges may change shape and direction in response to changes intidal currents. Illustration from Reimnitz et al. (1973).

This Open-File Report publishes the multibeam bathymetry along with images.

References

Seramur, Keith C., Powell, R.D., Carlson, P.R., 1996. Evaluation of conditions along the grounding line of temperate marine glaciers: an example from Muir Inlet, Glacier Bay, Alaska. Marine Geology 140, 307-327.

Reimnitz, E., P.W. Barnes, and T. R. Alpha, 1973, Bottom features and processes related to drifting ice on the Arctic Shelf, Alaska: USGS Miscellaneous Field Studies Map MF-532.

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