Alaska Bathymetry, Sediments, and Smooth Sheets
NOAA is mandated to identify Essential Fish Habitat (EFH) by provisions of the Magnuson-Stevens Act, but the necessary data sets are not always available. In the marine environment, depth and sediment type are often the most important determinants.
NOAA is mandated to identify Essential Fish Habitat (EFH) by provisions of the Magnuson-Stevens Act, but the necessary data sets are not always available. In the marine environment, depth and sediment type are often the most important determinants of EFH for fish that live on the bottom. Bathymetry data can be further analyzed into important habitat descriptors such as slope and roughness. Marine researchers are familiar with National Ocean Service (NOS) nautical charts, which are often considered the most useful source of EFH information in Alaskan waters. The small scale (often 1:100,000 or smaller) means that the nautical charts lack significant fish habitat details. However, what most marine researchers do not know is that these NOS nautical charts are derived from more detailed, larger-scale (often 1:20,000) charts called "'smooth sheets," which are the final published product from the original charting surveys.
Digital files of the soundings from these smooth sheets are available at the National Geophysical Data Center, but the files contain numerous errors and thus need to be proofed and edited prior to use.
Scientists within the Groundfish Assessment Program at the Alaska Fisheries Science Center have developed the methods for proofing and editing smooth sheets, and representing the seafloor in full detail such that individual features, such as lumps and dips, are clearly depicted (Zimmermann and Benson, 2013). Producing maps that depict accurate bathymetry, bathymetric derivatives (slope, roughness, etc.), substrate information (sand, gravel), and features (rocks, islets, kelp) provide the basis to delineate EFH. While these data sets are not for navigation, they have a wide variety of research uses.
What are Smooth Sheets?
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Physically, a paper smooth sheet with muslin backing was the final product of a hydrographic survey. The soundings were drawn on a smooth sheet, along with the shoreline, geographic features (e.g., kelp beds, rocky reefs, islets, rocks), seafloor substrates (e.g., gravel, sand, mud), and the navigational signals to provide a visual record of the hydrographic survey, which could be annotated as new information became available.
Though more detailed than navigational charts, smooth sheets are not intended for use in navigation. Instead, the smooth sheets, many dating back to the 1930s, were used as internal documents by the Hydrographic Office. Only after they were scanned, digitized, and posted to NGDC (Wong et al. 2007) did they become widely used by non-hydrographers. The NOS navigational charts (not smooth sheets) are the legal standard for safe navigation on the ocean (Title 33 Code of Federal Regulations 164).
Most likely, scientists who conduct research on the ocean have used the small-scale navigational charts for a variety of cruise planning and data analysis tasks. They might not know that perhaps ten times as much information is available from the precursor hydrographic surveys, represented by the smooth sheets. Others who are aware of the smooth sheet resource might not understand some of the details about successfully using this rich data resource. Therefore, now that electronic copies of the smooth sheets are readily available, it is worthwhile for non-hydrographers to understand how to use them.
Bathymetry of Aleutian Islands
Bathymetric surface of Aleutian Islands compiled from National Ocean Service hydrographic surveys and supplemented with some non-hydrographic surveys.
AFSC scientists with the RACE Groundfish Program corrected, digitized, and assembled 2.1 million National Ocean Service bathymetric soundings from 290 hydrographic surveys represented by smooth sheets, extending 1,900 km along the Aleutian Islands from Unimak Island in the east to the Russian border in the west.
The original, uncorrected smooth sheet bathymetry data sets are available from the National Geophysical Data Center (NGDC), which archives and distributes data that were originally collected by the NOS and others. Details of our processing methods can be found in Smooth Sheet Bathymetry of the Aleutian Islands, NOAA Tech Memo NMFS-AFSC-250.
Sediments of the Aleutian Islands
Map of National Ocean Service verbal sediment descriptions.
We also digitized 25,000 verbal surficial sediment descriptions from 234 of the smooth sheets, providing the largest single source of sediment information for the Aleutian Islands.
Data Available for Download
Data Not to be Used for Navigation
- 100-m Resolution Grid (Raster Surface) of the Bathymetry
- Bathymetry Grid Metadata
- Shape File of Sediment Point Data
- Sediment Metadata
Bathymetry of Cook Inlet
- Digitizing the inshore features, such as rocks, islets, rocky reefs, and kelp beds.
- Digitizing the shoreline.
- Replacing some areas of older, lower resolution smooth sheet bathymetry data with more modern, higher resolution multibeam bathymetry data.
The smaller area of Cook Inlet, greater amount of project time, and higher quality of smooth sheets than in the Aleutian Islands made these additions possible. The Alaska Regional Office's Essential Fish Habitat funding made much of this work possible.
A total of 1.4 million National Ocean Service (NOS) bathymetric soundings from 98 hydrographic surveys represented by smooth sheets in Cook Inlet were corrected, digitized, and assembled.
Overall, the inlet is shallow, with an area-weighted mean depth of 44.7 m, but is as deep as 212 m at the south end near the Barren Islands. The original, uncorrected smooth sheet bathymetry data sets are available from the National Geophysical Data Center (NGDC), which archives and distributes data that were originally collected by the NOS and others.
Sediments of Cook Inlet
A total of 9,000 verbal surficial sediment descriptions from 96 smooth sheets were digitized, providing the largest single source of sediment information for Cook Inlet.
There were 1,172 unique verbal descriptions, with most of the sediment description categories (58%) only having a single occurrence. That means that most descriptions were fairly lengthy and specific.
Of the sediment descriptions which occurred more than once, Hard (n = 1335), Sand (n = 721), Rocky (n = 608), and Mud (n = 365) were the most common, which ranged from Rock to Clay, Sand ridges to Mud flats, Weeds to Stumps, and Mud to Coral.
The 20 most common sediment categories are depicted along a color gradient in the Figure, where red shows larger/harder sediments such as Rock, Rocky, and Boulders, and green shows smaller/softer sediments such as Mud, Soft, and Sticky.
Smooth sheet features of Cook Inlet.
Smooth Sheet Features of Cook Inlet
A total of 12,000 features such as rocky reefs, kelp beds, rocks, and islets were digitized from the smooth sheets and added to the original files from NGDC, resulting in a total of 18,000 features.
Almost 10,000 of these points indicated the edge of rocky reefs, covering much of the shore in Kamishak Bay, the southern shore of Kachemak Bay, and near Chisik Island, but reefs were rare north of there.
More than 7,000 rocks and more than 800 islets were found along most of the Cook Inlet shore. There were less than 300 kelp beds, almost all of which occurred in outer Kachemak Bay.
Altogether there were almost 18,000 rocks or rock ally features such as rocky reefs, kelp beds, and islets, which were added to the sediment data set.
Shoreline features of Cook.
A total of 95,000 individual shoreline points were also digitized, describing 2,418.3 km of mainland shoreline and 528.9 km of island shoreline from 507 individual islands, providing the most detailed shoreline of Cook Inlet.
The shoreline is defined on the smooth sheets as MHW (Mean High Water), the same vertical tidal datum as the bathymetry, which typically ranges only as shallow as MLLW (Mean Lower Low Water), defined as zero meters depth.
The MHW shoreline was highest in the northern end of Cook Inlet, ranging up to -9.2 m in Turnagain Arm, and -9.1 m in Knik Arm, and lowest at Augustine Island and Kamishak Bay (-4.4 to -3.4 m, respectively).
By adding the digitized shoreline to the digitized bathymetry, a complete bathymetry map for Cook Inlet was assembled without the typical gaps between the shallowest soundings and the shoreline. Thus, researchers were able to determine that at high tide (MHW) the total volume of the inlet is 1,024.1 km3 and the total surface area is 20,540 km2. When the tide drops from MHW to MLLW, the Inlet loses 99.7 km3 of water, or 9.7% of its volume, and exposes 1,616 km2 of seabed, or 7.9% of its surface area.
Conclusion
While the Alaska Fisheries Science Center has been conducting marine research for decades in Alaskan waters, a lot of basic information about the seafloor, such as depth, is generally not known beyond what is depicted on small scale (1:100,000) NOS Navigational Charts. Therefore, AFSC scientists have been creating more detailed bathymetry and sediment maps to provide a better understanding of how studied animals interact with their environment. This information from the Aleutian Islands is being used by NOAA’s Deep Sea Coral Research and Technology Program to predict the presence/absence and abundance of corals and sponges. More information on these studies is featured in the AFSC research report Determining the Distributions of Deep-sea Corals and Sponges Throughout Alaska.
Scientists who conduct AFSC stock assessment bottom trawl surveys are also using the information to delimit areas that cannot be sampled effectively with bottom trawls. The results from the AFSC mapping project may result in an alternative survey method such as underwater cameras or acoustics to assess the abundance of fish in untrawlable areas. This will help researchers quantify changes in abundance across trawlable and untrawlable areas.
An inter-agency collaboration, the Gulf of Alaska Integrated Ecosystem Research Program (GOA-IERP), sponsored by the North Pacific Research Board, is using the detailed bathymetry and sediment information to predict the preferred settlement habitat of juveniles of five important groundfish species. Results from GOA-IERP will be used towards developing a better understanding of the ecosystem processes that regulate the recruitment of young fish into the population.
The Alaska Regional Office will investigate use of the bathymetry and sediment information to oversee sustainable fisheries, conduct Essential Fish Habitat (EFH) reviews, and manage protected species. The Bureau of Ocean Energy Management may use the information for preparing National Environmental Policy Act (NEPA), Essential Fish Habitat (EFH), and Endangered Species Act (ESA) documents for the possibility of a federal lease sale in lower Cook Inlet.
Details of the processing methods for the smooth sheet data for Cook Inlet are available in Smooth sheet Bathymetry of Cook Inlet, Alaska. NOAA Tech. Memo. NMFS-AFSC-275.
Bathymetry of Central Gulf of Alaska
The geographic extent of this project matches the area of interest for the North Pacific Research Board's Gulf of Alaska Integrated Ecosystem Research Program (GOA-IERP), which is examining the physical and biological factors that influence the growth and survival of five species of juvenile groundfish in the Gulf of Alaska. Funding from the NOAA Fisheries Alaska Regional Office's Essential Fish Habitat made some of this work possible.
Cartographic Features of Central Gulf of Alaska
About 96,000 cartographic features such as rocky reefs, kelp beds, rocks, islets and others were proofed, edited and digitized from the smooth sheets and charts. The most common feature was kelp beds (it should be noted that kelp beds are seasonal and their size and location are variable from year to year). The second-most common feature was rocks, at just less than 29,000, with the majority occurring in the Kodiak, Kenai and Sitka areas. Rocky reefs were third in occurrence, and there were 15,000 islets almost equally split between western and eastern sides of the CGOA.
Multibeam Data of Central Gulf of Alaska.
Multibeam Data of Central Gulf of Alaska
Geological Features of Central Gulf of Alaska.
Geological Features of Central Gulf of Alaska
Kayak Trough
The depressions within Kayak Trough, a glacial feature composed of a flat floor bordered by steep edges along its inland margins, are about 70 m deep on the eastern side and about 20 m deep on the western side. These depressions are remnants of a deeper Kayak Trough, the center of which has been filled with sediment (Sean Gulick, Research Assoc. Prof., Institute for Geophysics, Jackson School of Geosciences, Univ. Texas at Austin, personal communication, 2012; Worthington et al. 2008) from the Copper River (Jeager et al., 1998). Currents may play an important role in forming (scouring) and maintaining these depressions (Sean Gulick, personal communication, 2012).
Geological Features of Central Gulf of Alaska
Fairweather Fault Zone
A trace of the Fairweather Fault Zone was found in the soundings from Survey H04529, a 1925 small-scale (1:100,000) smooth sheet (A), off of Yakobi and Chichagof Islands, just south of Cross Sound. The fault zone is imaged as an east facing scarp (cliff face) and a western uplifted structural block (plateau or ridge) about 25 km long. Shallower soundings in the north (B), center (C) and south (D) show the rough outline of the uplifted structural block.
The explanation of the Fairweather Fault Zone's presence in the area, provided by Peter Haeussler Research Geologist, US Geological Survey, (personal communication, 2011), is corroborated by a single-beam echosounder pass across the structure (E) collected during the 2005 GOA trawl survey (Raring 2007).
Middleton Island Submerged Marine Terraces
Kodiak Fault Zone
Narrow Cape Fault and the Kodiak Fault Zone (KFZ) on Southern and Middle Albatross Banks, south of Kodiak Island, as depicted by slope (A), or depth change (von Huene et al. 1980; Carver et al. 2008, see Plate 1). The KFZ appears to consist of an elevated platform and a steep south-facing scarp in the slope data. The inset of a single-beam echogram (B) shows a depth change from 62 to 50 m over a distance of about 200 m as the KFZ is approached from the south (indicated with black arrow), south of Sitkinak Island, which images a south-facing scarp and associated uplifted northern platform.
Seafloor Changes of Central Gulf of Alaska
Great Alaska Earthquake of 1964
An added difficulty in describing bathymetry across this vast area is that it is changing faster than it is being surveyed. The best known example of seafloor change is the great Alaska earthquake of 1964 (magnitude 9.2), centered near Valdez, which abruptly altered the seascape across a large expanse of the CGOA (National Research Council 1972). A comparison of smooth sheet surveys conducted before and after the 1964 earthquake showed sinking of 0.2 to 9.8 m in Resurrection Bay, rising of 6.1 m at Cape Clear, and rising of 1.6 to 4.2 m at Middleton Island.
Katalla Bay Shoreline
Other significant bathymetry changes are more localized. For example, a shoreline accretion of about 600-800 m in Katalla Bay, near the Copper River, occurred between the 1905 (H02768) to 1971 (H09207) surveys, perhaps as a result of heavy sediment deposition in this area (Jeager et al., 1998).
Taylor Bay Shoreline
There was approximately 4500 m horizontal change in the location of the shoreline of Taylor Bay between the 1901 survey of H02558 (green) and the 1992 survey of H10425 (red) due to isostatic uplift of about 20mm/year (Freymueller et al. 2008) and significant possible sedimentation (Jeff Freymueller, Professor of Geophysics, Geophysical Institute and Dept. of Geology and Geophysics, Univ. of Alaska Fairbanks, personal communication 2014). This figure was created by plotting the partially transparent smooth sheet of the older survey on top of the smooth sheet of the newer survey, resulting in some imagery faintness. The shallowest modern soundings occur on top of 26 fathom soundings from the old survey.
Bathymetry of Norton Sound
The Norton Sound project includes smooth sheet bathymetry editing, the digitizing of sediments, inshore features, and shoreline, as well as incorporating higher resolution multibeam bathymetry data, where available, to supersede some areas of older, lower resolution smooth sheet bathymetry.
Over 230,000 National Ocean Service (NOS) bathymetric soundings from 39 smooth sheet surveys in Norton Sound were corrected, digitized, and assembled, as well as over 6000 soundings from a GAP research cruise, and three NOS multibeam surveys. The bathymetry compilation ranged geographically from the eastern point of St. Lawrence Island, southeast to the Yukon River delta and north along the Seward Peninsula and around the point of Cape Prince of Wales.
Our Norton Sound coverage is very shallow, with a maximum depth of 63 meters in the outer waters along the Bering Sea, while the sound itself, bounded by the westernmost point on the Yukon River delta along the south and Nome on the North, has an average depth of just 13 meters. The original, uncorrected smooth sheet bathymetry data sets are available from the National Geophysical Data Center (NGDC), which archives and distributes data that were originally collected by the NOS and others. These data are not to be used for navigational purposes.
Alaska Regional Office's Essential Fish Habitat (EFH) and Habitat and Ecological Processes Research (HEPR) funding made this work possible. This Norton Sound bathymetry and sediment work was done in response to a NOAA Fisheries AKRO (Alaska Regional Office) request to provide information for a new predictive modeling effort examining Norton Sound red king crab and potential effects of offshore marine mining activities on their habitat. The Alaska Regional Office will also investigate use of the bathymetry and sediment information to oversee sustainable fisheries, conduct Essential Fish Habitat (EFH) reviews, and manage protected species. This Norton Sound bathymetry compilation is part of a GAP (Groundfish Assessment Program) effort to create more detailed bathymetry and sediment maps in order to provide a better understanding of how studied animals interact with their environment.
We digitized 4,305 verbal sediment descriptions present in 32 of the 39 surveys. There were 120 unique verbal descriptions, with over half of the categories having only a single occurrence. Of the sediment descriptions which occurred more than once, Hard (n=1623), Soft (n=1289), and Sticky (n=591) were the most prevalent.
Smooth sheet features are shown; Rocks in red, Islets in black, and all other features grouped together in teal. Not to be used for navigational purposes.
Features of Norton Sound
A total of 312 features were digitized from the smooth sheets. Only 14 of the 39 smooth sheet surveys contained features. They were predominantly rocks and islets.
The MHW is shown, in meters. The highest shoreline, in red, is located in the inner sound while low shoreline is depicted in blue, near Sledge Island and the Yukon River delta. Not to be used for navigational purposes.
Shoreline of Norton Sound
A total of 107,112 individual shoreline points were digitized, describing 2,142 km of mainland and 837 km of island shoreline. The shoreline is defined on the smooth sheets as MHW (Mean High Water), the same vertical tidal datum as the bathymetry, which typically ranges only as shallow as MLLW (Mean Lower Low Water), defined as zero meters depth. The MHW shoreline ranged from -1.28 m in the Norton Bay area to -0.18 m north of Sledge Island.
By adding the digitized shoreline to the digitized bathymetry, a complete bathymetry map for Norton Sound was assembled without the typical gaps between the shallowest soundings and the shoreline. Thus, researchers were able to determine that at high tide (MHW) the total volume of Norton Sound is 435.8 km3, while the surface area of the sound is 31,379.3 km2.
With the addition of the shoreline, a comparison with similar work in Cook Inlet shows how shallow Norton Sound is. While Norton Sound has a larger surface area, 31,379.3 km2 to Cook Inlet’s 20,540 km2, it has less than half the MHW volume, 435.8 km3 compared to 1,024.1 km3.
Additional Resources
- Smooth Sheet Bathymetry: How to Work With Them in a GIS to Derive Bathymetry, Features and Substrates
- Alaska Bathymetry Data and Publications
- Alaska Bathymetry Map
- Alaska Bathymetry Smooth Sheet Metadata
- Smooth Sheet Bathymetry of the Aleutian Islands
- Smooth Sheet Bathymetry of the Central Gulf of Alaska
- Smooth Sheet Bathymetry of Cook Inlet, Alaska
- Smooth Sheet Bathymetry of Norton Sound Alaska
- Bathymetry Sediment Point Data
- Alaska Bathymetry: 100-m Resolution Grid (Raster Surface) of the Bathymetry
- Bathymetry Grid Metadata
- Alaska Essential Fish Habitat Research Plan: A Research Plan for the National Marine Fisheries Service's Alaska Fisheries Science Center and Alaska Regional Office
- Smooth Sheets Hosted by National Centers for Environmental Information (NCEI)