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Fieldwork

Spring Multibeam Cruise in Glacier Bay Provides Spectacular Images


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Paul Carlson and Andy Stevenson of CMG Menlo Park joined Philip Hooge and four other biologists from the BRD Glacier Bay Field Station on a 9-day cruise (May 28th-June 5th) that acquired superb multibeam imagery from Glacier Bay, Alaska. The scientists collected data at resolutions of 5 m per pixel and better using a RESON SeaBat 8111 system on the M/V Davidson, a former NOAA vessel. The cruise was funded by a joint GD-BRD grant (to Hooge and Carlson) plus an equal share of the cost provided by Glacier Bay National Park. The GD-BRD cruise was linked to a preceding cruise off Southeast Alaska financed by the Alaska Department of Fish and Game, and a subsequent cruise off the Semidi Islands financed by NOAA. These cooperative ventures were mutually productive because of the high mobilization costs for work in Alaskan waters. Contractor Thales GeoSolutions (Pacific), Inc., of Anchorage collected the data on all three cruises. Bathymetric data are already under study, and co-located backscatter data are being edited and prepared by the contractor.

Glacier Bay: Map of Alaska and Glacier Bay. Red lines show glacial terminus positions and dates during retreat of the Little Ice Age glacier. Green polygon outlines approximate area mapped by multibeam system in May-June 2001.
map showing location of Glacier Bay on the panhandle of Alaska, and glacial terminus positions within Glacier Bay

Previous sidescan-sonar data had given some indication of the geomorphic complexity of the floor of Glacier Bay, but none of the project members had any idea of the widespread nature of Little Ice Age gouges in the lower bay. The gouges in the lowermost portions of Glacier Bay are shown in the multibeam image of Sitakaday Narrows (see image below). Sidescan-sonar imagery from Whidbey Passage, collected in 1998 as part of a study of benthic habitats, first revealed the presence of complex iceberg-gouge patterns in gravelly mud in more than 100 m of water. Some gouges are >10 m wide, >800 m long, and 1 to 2 m deep. The glacier that filled Glacier Bay during the Little Ice Age began its retreat from the mouth of the bay more than 200 years ago and has exposed a magnificent fjord system about 100 km long. The massive glacier retreated past Sitakaday Narrows ~190 years ago, retreated past Whidbey Passage ~160 years ago, and reached the upper end of the main bay by 1860 (~140 years ago). There the glacier bifurcated and the multibeam data set terminates. The amount of fine sediment reaching the lower bay is largely restricted to local runoff and plankton debris. In addition, the currents through Sitakaday Narrows can be as fast as 7 kt, scouring the bottom of fine sediment. So a long history of morphologies is clearly visible on the bottom.

Sitakaday Narrows: Numerous iceberg gouges are visible in this multibeam image of the bathymetry of the moraine and adjacent fjord floor in Sitakaday.
sidescan-sonar image of the seafloor of Sitakaday Narrows in Glacier Bay

The multibeam data collected in the recent cruise will be used in a joint study of the biological and physical characteristics of bay-floor habitats, especially as related to Dungeness crab and halibut. Results of the study will provide guidance to the National Park Service in its management of recreational and commercial fishing in the Bay.


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in this issue: Fieldwork cover story:
Mapping Puget Sound

Biscayne Nat'l Park

Glacier Bay Cruise

Tripod Deployment

Outreach GIS Group Teaches Science

Juneteenth Celebration

Meetings Geochemical Processes

Geologic Discipline EMAC

Wetlands Meeting

Awards Closing the Circle

Staff & Center News Eric Thompson

NAGT Summer Interns

Woods Hole Interns

Jerry Parker Memorial

Gaye Farris Re-Elected to STC Exec Board

Publications "Natural Gas Hydrates" Book

July Publications List


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