AFSC/RACE/GAP/Zimmermann and Prescott: Eastern Bering Sea Slope Grid

We created a new, 100 m horizontal resolution bathymetry raster and used it to define 29 canyons of the eastern Bering Sea (EBS) slope area off of Alaska, USA. To create this bathymetry surface we proofed, edited, and digitized 18 million soundings from over 200 individual sources. Despite the vast size (~1250 km long by ~3000 m high) and ecological significance of the EBS slope, there have been few hydrographic-quality charting cruises conducted in this area, so we relied mostly on uncalibrated underway files from cruises of convenience. The lack of hydrographic quality surveys, anecdotal reports of features such as pinnacles, and reliance on satellite altimetry data has created confusion in previous bathymetric compilations about the details along the slope, such as the shape and location of canyons along the edge of the slope, and hills and valleys on the adjacent shelf area. A better model of the EBS slope will be useful for geologists, oceanographers, and biologists studying the seafloor geomorphology and the unusually high productivity along this poorly understood seafloor feature

The purpose for creating this data set was to provide the best available bathymetry of the eastern Bering Sea slope for geospatial analysis.

\\AKC0SS-n086\AKC_PubliC\Dropbox\Zimm\EBS_Slope\Bathy\EBS_bathy.zip

These data are not to be used for navigation.

These data are not to be used for navigation. As more bathymetry data becomes available, and as more time allows, additional bathymetry drafts will be completed. Our slow method of data editing and compilation, which relied on comparing the digitized soundings to the smooth sheets in a GIS, was critical to the discovery and elimination of numerous errors, such as incorrect, misplaced and missing soundings. Properly accounting for the horizontal shift from the original datum to NAD 1983 was the most important part of our error-checking. We consider this smooth sheet bathymetry and feature compilation a first draft.

Our editing included deleting erroneous and superseded values, digitizing missing values, vertically correcting some data sets and properly aligning all data sets to a common, modern datum.

While various bathymetry data have been downloaded previously from NGDC, compiled, and used for a variety of projects, our effort differed in that we compared and corrected the digital bathymetry by studying the original analog source documents - digital versions of the original survey maps, called smooth sheets. The edited smooth sheet bathymetry points, along with the digitized shoreline points, features with elevations, and superseding multibeam data set points, were processed into a solid surface of variably-sized triangles (Triangular Irregular Network or TIN) which utilized the points as corners of the triangles. The TIN was then converted by area-weighted (nearest neighbor) interpolation into a solid surface of 100 m squares (GRID). Those grid cells that appeared on land, or outside of the area covered by the smooth sheets, were eliminated and a new grid was made which only covered the water. Our bathymetry editing resulted in the redescription of numerous canyons. We also disproved the existance of the four pinnacles reported to be in the Zhemchug Canyon area.

Our editing included deleting erroneous and superseded values, digitizing missing values, vertically correcting some data sets and properly aligning all data sets to a common, modern datum.