It is early April. The deckhand is shoveling snow from the deck of the USGS science boat, the Gyre. Divers are preparing to put on rebreathing equipment and climb down the ladder into the water, then ride small bullet-shaped battery-powered scooters to take video footage of the seafloor near the mouth of the Bartlett River at Lagoon Island. They hope for a clear view in a turbulent, silt-laden environment. This trip was planned for just before the "spring bloom", when deep-water renewal, or nutrient enrichment brought about by mixing of the water columns due to zonal differences in water temperature, occurs. Once the bloom occurs, the visibility may not be as clear. Hence diving in cold early April! The divers are cold, must come back up in less than 40 minutes, or their hands ache, their bodies are tired. One diver radios up a signal, then surfaces from the deep.
DEEP WATER RENEWAL
by Elizabeth Hooge
A report titled FJORD OCEANOGRAPHIC PROCESSES IN GLACIER BAY, ALASKA was prepared by Philip N. Hooge and Elizabeth Ross Hooge, of the USGS at the Glacier Bay Field Station, for the NPS, Jan. 2001. The primary data used in this study were oceanographic surveys, made between 1992 and 2000, that sampled 24 central-channel stations from the mouth of the Bay to the heads of both the East and West Arms. An oceanographic instrument (a Conductivity-Temperature-Depth probe, or CTD) which records depth, temperature, salinity, light penetration, amount of sediment, and amount of phytoplankton, was used to obtain measurements at one-meter intervals throughout the water column to a depth of 300m at each station. Surveys were conducted up to 8 times a year in such a manner as to encompass the primary annual variation in oceanographic patterns.
Results include:
1. Deep-water renewal, or nutrient enrichment brought about by mixing of the water columns due to zonal differences in water temperature, is not limited to the winter months, but can and probably does occur regularly in the spring, summer and fall. A tidally mixed front provides conditions ideal for encouraging high primary productivity by phytoplankton.
2. Mixing phenomena are much more extensive than previously remarked upon in literature, leading to phenomenally high primary productivity. This includes large standing crops of phytoplankton, whose limits are not caused by zooplankton grazing or nutrient limitation, but by light penetration.
3. Water temperatures appear to have increased significantly since the early oceanographic work of the 1960s. This warming trend is up to 2 degrees C on average.
4. As a result of the oceanographic monitoring program, there is now an extensive body of oceanographic and weather data integrated into the Glacier Bay information management system and available on CD-ROM.
5. The need for maintenance of an oceanographic program in Glacier Bay is seen. In the words of the authors, Philip N. Hooge and Elizabeth Ross Hooge,
"Because of the importance of oceanography to understanding critical resource and research problems, the complexity of the Bay's oceanographic system, as well as the limited and contradictory prior work, it is imperative that a sustained, rigorous, and complete monitoring program be developed and implemented. The Exxon Valdez Trustee Council has identified a strong oceanographic program as the cornerstone for a biotic monitoring program in Prince William Sound, Alaska. Oceanography's importance in Glacier Bay is no less. "
****During June of 2001, a research cruise to map the benthic (sea floor) habitat using geological and oceanographic tools took place. The cruise resulted in crucial scientific data as well as fascinating discoveries:
ICE GOUGES, GROUND TRUTHING, AND MULTIBEAM MAPPING
As a support for effective management of the GBNP ecosystem, the USGS conducted multidisciplinary research to map benthic (seafloor) habitat and monitor oceanographic parameters. Marine biologists and geologists used a combination of remote sensing and direct observations to provide the data necessary to evaluate human disturbance in this naturally changing ecosystem. Data from looking at both oceanography and surficial geology will now be combined with biological data and placed within a flexible marine geographic information system (GIS) so that relationships can be seen.
The survey vessel R/V Davidson, with a hull-mounted multibeam mapping system, was used to image almost half of Glacier Bay's waters deeper than 30 meters. The vessel also used its oceanographic laboratory to obtain continuous measurements of phytoplankton density throughout the June, 2001 research cruise.
In addition to the vessel multibeam work, extensive ground-truthing was conducted by divers, drop cameras, and submersibles. The remotely sensed and ground-truthing data will be integrated into a marine GIS. Then geologists and biologists can produce benthic habitat maps identifying those geological and oceanographic features that significantly influence species abundance and distribution.
WHAT WAS FOUND?
Hundreds of gouges carved several meters into the bottom of Glacier Bay are visible in the multibeam acoustic imaging. These gouges were incised by the keels of large icebergs (up to 160 meters thick) that calved from the face of the glacier that once filled all of Glacier Bay. Grounded ice was driven by tidal currents through Sitakaday Narrows, which today experiences currents in excess of 8 knots.
WHAT MIGHT THIS RESEARCH LEAD TO?
The USGS hopes to see additional ground-truthing data and analysis for Glacier Bay. This will include new research sites and new research questions, multibeam work on the remaining portions of Glacier Bay, and development of integrated geological and oceanographic habitat models for the marine inhabitants in the bay. This work is a step toward determining the habitat relationships of critical species and resources within the Park.
For more information contact:
Dr. Philip N. Hooge, philip_hooge@usgs.gov; USGS, PO Box 140, Gustavus, AK 99826 OR Dr. Paul R. Carlson, pearlson@usgs.gov; USGS, 345 Middlefield Road, Menlo Park, CA 94025 OR these websites: www.absc.usgs.gov/glba OR http://walrus.wr.usgs.gov/nearshorehab
the OYSTERCATCHER 2002
edited by Kate Boesser
OTHER USGS WORK IN 2001
FISH, SEA OTTERS, CRABS, BEARS, AND TIDES
:
A.Small Schooling Fish Project
Small Schooling Fish Project1. Predator Surveys by Jim Bodkin2. Fish Surveys and Sampling by
John Piatt
a. Humpback Whale Prey Pilot Studyb. Netting/Trawling/Beach Seining
B.Continuing Sea Otter Surveys and Sea Otter Food Surveys
Continuing Sea Otter Surveys and Sea Otter Food Surveys C.MADS (Multi-Agency Dungeness Study) September Pot Survey by Jim Taggart:
MADS (Multi-Agency Dungeness Study) September Pot Survey by Jim Taggart:Taggart was pilot-testing methods to use for a study of movements of crab species (king, tanner, dungeness) and halibut that should start summer 2002.
Its goal is to test the efficacy of marine reserves here for those species.
D. Intertidal Monitoring Study by Gail Irvine
Intertidal Monitoring Study by Gail IrvineE.Bear - Human Interactions Study by Tom Smith
Bear - Human Interactions Study by Tom SmithFor more information on USGS projects,
contact www.absc.usgs.gov
