Mark Zimmermann

Smooth sheet bathymetry of the central Gulf of Alaska

We assembled 1.75 million bathymetric soundings from 225 lead-line and single-beam echosounder hydrographic surveys conducted from 1901 to 1999 in the central Gulf of Alaska. These bathymetry data are available from the National Geophysical Data Center (NGDC: http:// www.ngdc.noaa.gov), which archives and distributes data that were collected by the NOS (National Ocean Service), its predecessors, and others. While various bathymetry data have been previously downloaded 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. Our editing included deleting erroneous and superseded values, digitizing missing values, and properly aligning all data sets to a common, modern datum. There were several areas where these older surveys were superseded by more recent, higher quality multibeam surveys, mostly from the NOS (n = 106). Three of these were unprocessed NOS multibeam surveys in the Sitka area, which we edited and processed into final bathymetric surfaces. We reduced the resolution of these multibeam surveys to 100 m, since some may have sub-meter resolution and many exceed a million soundings, and added them to our bathymetry compilation. We proofed, edited, or digitized 96,000 cartographic features (mostly from the smooth sheets, some from the multibeam surveys), such as rocky reefs, kelp beds, rocks, and islets, creating the most thorough compilation of these typically shallow, inshore features. The depth surface and inshore features, intended for use in fisheries research, are available at the Alaska Fisheries Science Center (AFSC: http://www.afsc.noaa.gov), and were mostly produced at a map scale of 1:20,000. iii