Bathymetry and Geomorphology of Shelikof Strait and the Western Gulf of Alaska

Abstract

We defined the bathymetry of Shelikof Strait and the western Gulf of Alaska (WGOA) from the edges of the land masses down to about 7000 m deep in the Aleutian Trench. This map was produced by combining soundings from historical National Ocean Service (NOS) smooth sheets (2.7 million soundings); shallow multibeam and LIDAR (light detection and ranging) data sets from the NOS and others (subsampled to 2.6 million soundings); and deep multibeam (subsampled to 3.3 million soundings), single-beam, and underway files from fisheries research cruises (9.1 million soundings). These legacy smooth sheet data, some over a century old, were the best descriptor of much of the shallower and inshore areas, but they are superseded by the newer multibeam and LIDAR, where available. Much of the offshore area is only mapped by non-hydrographic single-beam and underway files. We combined these disparate data sets by proofing them against their source files, where possible, in an attempt to preserve seafloor features for research purposes. We also attempted to minimize bathymetric data errors so that they would not create artificial seafloor features that might impact such analyses. The main result of the bathymetry compilation is that we observe abundant features related to glaciation of the shelf of Alaska during the Last Glacial Maximum including abundant end moraines, some medial moraines, glacial lineations, eskers, iceberg ploughmarks, and two types of pockmarks. We developed an integrated onshore–offshore geomorphic map of the region that includes glacial flow directions, moraines, and iceberg ploughmarks to better define the form and flow of former ice masses.

Passes of the Aleutian Islands: First detailed description

“…Hunt and Stabeno (2005) summarize several significant ecological impacts of this western/eastern division in water masses at Samalga Pass, including differences in primary production; zooplankton species composition; species diversity of cold‐water corals; groundfish species richness, abundance, diet composition, and growth rates; seabird foraging guilds; Steller sea lion diets ( Eumetopias jubatus ); and cetacean distributions. The location of this division of water masses at Samalga Pass makes bathymetric sense because the minimum opening of Shelikof Strait (6.504 km 2 : Zimmermann et al., 2019) is approximately equal to the sum of the eastern Aleutians passes through Samalga (6.189 km 2 , including the 15,800 m 2 estimate of False Pass from Zimmermann & Prescott, In Review). Samalga is by far the largest and deepest of these eastern passes, accounting for 61% of the group's cross‐sectional area, and thus, its size may dictate the importance of its location.…”

“…A new volumetric analysis of water transport, taking into account ACC depth and speed, along with our new pass size and shape estimates, might improve our understanding of this important oceanographic process. The oceanographic connection between the narrowest opening of Shelikof Strait is about 1,200 km to the east of Samalga Pass, across the glacially sculpted western Gulf of Alaska (Zimmermann et al., 2019), so it is highly unlikely that there is a direct, one‐to‐one relationship between water flow through these two features.…”

False Pass, Alaska: Significant changes in depth and shoreline in the historic time period

“…We attempted to use ArcMap's Cost Distance tool to derive algorithmically the minimal cross‐sectional openings of the False Pass area, as we did for all of the other Aleutian passes (Zimmermann & Prescott, In Review). This method is different than the user drawing straight lines (Interpolate Line tool) across a depth surface, which we have utilized in past analyses (e.g., Zimmermann et al., 2019). The Cost Distance tool groups together raster‐derived points from the edge of the depth raster near one shore (potential starting points), groups together a second set of raster edge points from the neighboring shore (potential ending points), and then determines the minimal path by summing depths between the two groups of points (https://desktop.arcgis.com/en/arcmap/latest/tools/spatial-analyst-toolbox/understanding-cost-distance-analysis.htm).…”

“…We attempted to use ArcMap's Cost Distance tool to derive algorithmically the minimal cross-sectional openings of the False Pass area, as we did for all of the other Aleutian passes (Zimmermann & Prescott, In Review). This method is different than the user drawing straight lines (Interpolate Line tool) across a depth surface, which we have utilized in past analyses (e.g., Zimmermann et al, 2019). The…”

The International Bathymetric Chart of the Arctic Ocean Version 4.0

“…Bathymetric data that have been contributed without metadata are not listed, although used in the compilation where no other data are available. Alaska Fisheries Science Center of the US National Oceanic and Atmospheric Administration’s National Marine Fisheries Service (NOAA Alaskan Fisheries) Bathymetry data from the Alaska bathymetry compilations for the Aleutian Islands, central and western Gulf of Alaska and Norton Sound: https://www.afsc.noaa.gov/RACE/groundfish/Bathymetry/default.htm Digitized chart soundings, Alaska: Proofed digitized historical chart soundings from “smooth sheets” covering Alaskan waters 44 – 47 Alfred Wegener Institute (AWI) 81 Cruises of Multibeam data in the Atlantic and Indian Ocean region . 11 Cruises of multibeam data in the South and West Pacific: https://www.pangaea.de/ https://www.pangaea.de/expeditions/cr.php/Polarstern https://webapp-srv1a.awi.de/eBathy/datasets2.php National Institute of Oceanography and Applied Geophysics (OGS), Infrastructures Division; Barcelona University (UB), Department of Stratigraphy, Paleontology and Marine Geosciences (now Department of Earth and Ocean Dynamics); University of Bremen, MARUM – Center for Marine Environmental Sciences; University of Tromsø (UiT), The Arctic University of Norway, CAGE, Centre for Arctic Gas Hydrate; Italian Navy, Italian Hydrographic Institute OGS provided a combined grid of the following datasets Multibeam bathymetry from EGLACOM cruise with RV OGS-Explora in 2008 to the western Barents Sea margin 48 Multibeam bathymetry from SVAIS cruise with RV Hesperides 2007 to the western Barents Sea margin 49 Multibeam bathymetry from DEGLABAR cruise with RV OGS-Explora in 2015 to the western Barents Sea margin 50 Multibeam bathymetry from EDIPO cruise with RV OGS-Explora in 2015 to the western Barents Sea margin 51 Multibeam bathymetry by MARUM from MSM30 (CORIBAR) cruise with RV M.S.…”