GLERL 2000 Milestone Reports

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GOAL: SUSTAIN HEALTHY COASTS.

OBJECTIVE 2: PROMOTE CLEAN COASTAL WATERS TO SUSTAIN LIVING MARINE RESOURCES AND ENSURE SAFE RECREATION, HEALTHY SEAFOOD AND ECONOMIC VITALITY.

PM: Number of coastal and Great Lakes states provided with improved predictive capabilities and understanding of environmental processes. Milestone: Complete and publish new Lake Ontario high resolution bathymetry.

Scientists: D.F. Reid and T.L. Holcombe

Accomplishment

The bathymetry of Lake Ontario was completed with 2m contour resolution and a color poster map depicting the bathymetry of the lake was published in December 1999. It is the latest in a series of NOAA Great Lakes bathymetry poster maps and data sets that are being made available to the public. The scale of the new 36" x 50" poster map is 1:275,000, and the bathymetric contour interval is 2 meters. In addition to the main map, insets are included showing details of bottom relief in part of the Rochester Basin, the main basin in the eastern end of the lake, and in the vicinity of Charity Shoal near the outlet to the St. Lawrence River. Also included are text explanations of the geology and geomorphology of the main lakefloor features, and a list of references for further reading.

map: color rendering of bathymetry of Lake Ontario

Color Rendering of the Bathymetry of Lake Ontario Red = shallowest; dark-blue = deepest

Background

Bathymetry is the science of measuring and mapping the depths of water bodies (oceans, seas, lakes) to show the topography of their basins. Bathymetric maps are two-dimensional representations of the 3-dimensional shape of these basins and provide the perspective and geospatial reference needed to understand the field relationships between sample locations and habitat types, or depth of the water column, or proximity to major underwater features.

Extensive geological and geophysical data were collected in the Great Lakes during the last 150 years and there are substantial holdings of sounding data in both U.S. and Canadian government archives. It is estimated that total data holdings between the U.S. and Canada collectively include several million soundings. Until the 1990s, these data were unutilized for bathymetry purposes and therefore, unavailable to the potential user communities in both the United States and Canada. Since the early 1990s, the following organizations have been cooperating on a joint project to develop highly detailed bathymetric maps of the Great Lakes:

NOAA/OAR/Great Lakes Environmental Research Laboratory (GLERL), Ann Arbor, MI;
NOAA/NESDIS/National Geophysical Data Center, Boulder, Colorado;
Canadian Hydrographic Service (CHS), Ottawa, Canada;
Cooperative Institute for Limnology and Ecosystems Research (CILER) at the University of Michigan, Ann Arbor, and the
Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado, Boulder.

Constituents

Bathymetric information is specifically needed for habitat mapping. For example, high resolution bathymetry was requested by the U.S.G.S. Biological Resources Division to allow better definition of the boundaries of the proposed Six Fathom Bank Lake Trout Refuge in Lake Huron. Some fisheries are depth dependent and one key statistic of interest to many fishery scientists is the total bottom area between two depth contours, which can only be obtained from detailed processed bathymetric information. We have had numerous requests for such data. Bathymetric information is necessary for accurate circulation and coastal forecasting models and our data are being incorporated into coastal forecasting models for the Great Lakes as soon as they become available. Bathymetry is also the only way to visualize underwater topography for educational purposes, and we have had numerous requests from educators and educational institutions for these products, as well as from Sea Grant Extension agents throughout the Great Lakes region. >From the public standpoint, our products have been requested by sports and commercial fishing interests, museums, schools, and citizens groups. Several engineering firms have requested our the information in connection with siting of pipes and cables.

Significance

This is the first high-resolution rendering of the bathymetry of Lake Ontario. The merging of sounding records from both the U.S. and Canada effectively doubled the data available, and resulted in new information and understandings of the lake's bottom topography. Many earlier interpretations of Lake Ontario geomorphology are confirmed by the new high resolution bathymetry, and some new features have emerged. For example:

Linear and parallel ridges (1-2 km spacing, 15-30m relief) have been found across the floor of the Rochester Basin in a NE-SW arc. These features resemble the grooved topography in onshore drumlin fields north of the lake, and therefore probably reflect the flow direction of advancing ice and/ or subglacial meltwater.
A small circular depression (1000m in diameter, 15-20m relief) with a continuous encircling rim coincides with the feature referred to on nautical charts as Charity Shoal. The origin of the feature remains unproven, but it bears close resemblance to, and characteristics of, a simple impact crater. The Canadian Geologic Survey plans to sample the bottom rocks surrounding the feature during the summer of 2000 in search of direct evidence that it is of meteoric origin

3-D view of Charity Shoal in Lake Ontario

Map and 3-D views of feature known as Charity Shoal in Lake Ontario.

Next Steps

A CD-ROM containing the entire Lake Ontario bathymetry data set in various formats, plus images from sections of the map, will be published late 2000. Compilation and contouring of the bathymetry of Lake Superior has been initiated and will take about two more years to complete. The latter will mark completion of this project.

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Last updated: July 9, 2002 mbl