Improvement to the International Bathymetric Chart of the Arctic Ocean (IBCAO): Updating the Data Base and the Grid Model

The project to develop the IBCAO grid model was initiated in 1997 with the objective of providing to the Arctic research community an improved portrayal of the seabed north of 64-deg N, in a form suitable for digital manipulation and visualization. The model was constructed from a compilation of all single-beam and multibeam echo soundings that were available for the polar region, complemented where appropriate by newly released contour information. The grid features a cell size of 2.5 x 2.5 km on a polar stereographic projection; it is constructed on the WGS 84 datum, with true scale at 75-deg N. Designated the Beta Version, a preliminary implementation of IBCAO was introduced to the geophysical community in December 1999, and released four months later as a digital grid that could be downloaded from a project website hosted by the National Geophysical Data Center in Boulder, CO. Since that release, the Beta Version has seen widespread use in Earth Science applications, with the website continuing to garner between 500 and 1000 visitors per week; this reportedly makes it one of the most heavily-visited of all NGDC websites. IBCAO has since been updated with the development of Version 1.0, which incorporates new information and formats, along with an expanded range of bathymetric products that will be released for public use through the same project website. Improvements include corrections to errors that were identified off Svalbard, in Canada Basin, and in Barrow Strait, as well as contributions of significant new data sets that were collected by the Norwegian Petroleum Directorate and the Alfred Wegener Institute off Norway and Svalbard, in Fram Strait, and over the Lomonosov Ridge. In addition, the portrayal of the Alaskan landmass was enhanced with a new topographic model extracted from NGDC\u27s GLOBE data set. New formats include downloadable Cartesian grids that can be imported directly into ArcInfo and Intergraph\u27s module Terrain Analyst. A geographic grid has been produced as well, with a resolution of 1\u27 x 1\u27 for compatibility with the global grid of bathymetry that is now under construction by a working group operating under the auspices of the General Bathymetric Chart of the Oceans (GEBCO). New products include a suite of bathymetric contours derived from the grid at depths ranging from 20 metres to 5000 metres, and poster-sized Postscript maps showing isobaths printed over a shaded relief background. These latest developments reflect a commitment to maintain IBCAO as a `live\u27 product for the foreseeable future, with periodic upgrades to improve its quality and usefulness

The International Bathymetric Chart of the Arctic Ocean (IBCAO): An Improved Morphological Framework for Oceanographic Investigations

The IBCAO initiative set out in late 1997 to assemble and merge all available bathymetric observations from northern regions, with the intent of constructing a reliable and up-to-date portrayal of the Arctic seabed in digital and printed form. In early 2000, a provisional grid and map were placed in circulation for public review and comment. Available for free downloading from a website hosted by the U.S. National Geophysical Data Center, these products won immediate acceptance from a broad spectrum of Arctic investigators who recognized the potential worth of the new information in a variety of applications ranging from straightforward map production to analysing the influence of underwater topography on ocean circulation. At the same time, error reports and new data sets were being forwarded to the creators of IBCAO, so that by the middle of 2002 a new and more definitive grid was ready to be placed into circulation. This was soon followed by the construction of a prototype shaded relief map that has been proposed as a successor to Sheet 5.17 of the General Bathymetric Chart of the Oceans (GEBCO)

The Grounding of an Ice Shelf in the Central Arctic Ocean: A Modeling Experiment

A numerical ice sheet model was used in a first test towards evaluating the hypothesis that, during a period of large-scale glaciation, an ice shelf emanating from the Barents/Kara Seas grounded across parts of the Lomonosov Ridge to a depth of around 1000 m below present sea level (Jakobsson, 1999; Polyak et al., 2001). Despite that we not include complex ice shelf physics or grounding line mechanics in our model and treat the process of marine melting in a simple manner, our experiments are the necessary first steps toward providing a comprehensive reconstruction of the former ice-sheet/ice-shelf system in the Arctic Ocean. A series of model runs was performed where ice shelf mass balance and ice shelf strain per unit time (strain rate) were adjusted. The mass balance and shelf ice strain rate are the key model parameters that govern the flux of ice into the Arctic Ocean. Grounding on the Lomonosov Ridge was not modeled when the ice shelf strain rate was 0.005 year-1 (i.e. a free flowing ice shelf). Even with low rates (\u3c10 cm/year) of basal melting, the ice shelf thickness was always less than 100 m over the central part of the ridge. Our experiment suggests that grounding on the Lomonosov Ridge by a free-flowing ice shelf is not possible. When the strain rate in the shelf ice was reduced to zero, however, the shelf thickness increased substantially. Such conditions are likely only to have occurred during periods of large-scale glaciation if substantial stagnant and thickened sea ice was present in the ocean, buttressing the ice shelf flowing from the Barents Sea. A comprehensive study using a coupled icesheet/ shelf/sea-ice model would build on these preliminary results and have the potential to further constrain the history of circum-Arctic Ocean ice sheets

A Modeling Experiment on the Grounding of an Ice Shelf in the Central Arctic Ocean During MIS 6

High-resolution chirp sonar subbottom profiles from the Lomonosov Ridge in the central Arctic Ocean, acquired from the Swedish icebreaker Oden in 1996, revealed large-scale erosion of the ridge crest down to depths of 1000 m below present sea level [Jakobsson, 1999]. Subsequent acoustic mapping during the SCICEX nuclear submarine expedition in 1999 showed glacial fluting at the deepest eroded areas and subparallel ice scours from 950 m water depth to the shallowest parts of the ridge crest [Polyak et al., 2001]. The directions of the mapped glaciogenic bed-forms and the redeposition of eroded material on the Amerasian side of the ridge indicate ice flow from the Barents-Kara Sea area. Core studies revealed that sediment drape the eroded areas from Marine Isotope Stage (MIS) 5.5 and, thus, it was proposed that the major erosional event took place during Marine Isotope Stage (MIS) 6 [Jakobsson et al., 2001]. Glacial geological evidence suggests strongly that the Late Saalian (MIS 6) ice sheet margin reached the shelf break of the Barents-Kara Sea [Svendsen et al. in press] and this gives us two possible ways to explain the ice erosional features on the Lomonosov Ridge. One is the grounding of a floating ice shelf and the other is the scouring from large deep tabular iceberg. Here we apply numerical ice sheet modeling to test the hypothesis that an ice shelf emanating from the Barents/Kara seas grounded across part of the Lomonsov Ridge and caused the extensive erosion down to a depth of around 1000 m below present sea level. A series of model experiments was undertaken in which the ice shelf mass balance (surface accumulation and basal melting) and ice shelf strain rates were adjusted. Grounding of the Lomonosov Ridge was not achieved when the ice shelf strain rate was 0.005 yr-1 (i.e. a free flowing ice shelf). However this model produced two interesting findings. First, with basal melt rates of up to 50 cm yr-1 an ice shelf grew from the St. Anna Trough ice stream across the section of the ridge where there is evidence for grounding. Second, even with ultra low rates of basal melting, the ice shelf thickness was always less than 200 m over the ridge. We conclude that grounding of the Lomonosov Ridge by a free-flowing ice shelf is not possible. When the strain rate was reduced to zero, however, the shelf thickness increased substantially. Such conditions are likely only to have occurred during periods of large-scale glaciation across the Eurasian Arctic such as in the Saalian, and if a substantial stagnant thickened sea ice was present in the ocean, buttressing the shelf flowing from the Barents Sea. Our results are interpreted using new techniques for dynamic 3Dvisualization

Analysis of Data Relevant to Establishing Outer Limits of a Continental Shelf under Law of the Sea Article 76

Coastal states may extend the limits of their juridically defined continental shelf beyond 200 nautical miles from their baselines under the provisions set forth in Article 76 of the United Nations Convention on the Law of the Sea (UNCLOS). In a preparatory desktop study, the University of New Hampshire’s Center for Coastal and Ocean Mapping/Joint Hydrographic Center analysed existing U.S. bathymetric and geophysical data holdings, identified data adequacy, and survey requirements to prepare a U.S. claim beyond the Exclusive Economical Zone (EEZ). In this paper we describe the methodology for our desktop study with particular emphasis on how we assembled and evaluated the existing data around the shelf areas of the United States, and estimated where additional surveys may be required