Ron Macnab

New grid of Arctic bathymetry aids scientists and mapmakers

For over two decades, Sheet 5.17 of the Fifth Edition of the General Bathymetric Chart of the Oceans (GEBCO) [Canadian Hydrographic Service, 1979] has been considered the authoritative portrayal of the sea floor north of 64 N.This sheet was constructed from publicly available bathymetric data sets, which in the late 1970s were rather sparse, consisting almost entirely of underway measurements collected from ice-breakers, drifting ice islands, and point measurements obtained along snow-mobile tracks or using air support. Data coverage tended to be fairly good at lower latitudes where ice cover was not a hindrance, but at higher latitudes, where ice was more prevalent, major features such as the Amerasian and Eurasian Basins were not well delineated. This situation posed problems not only for expedition planners but also for scientific investigators, who needed an accurate description of the sea floor to design field experiments and to link their research with processes affecting or affected by the shape of the seabed (for example, sea level change, ocean circulation, sediment transport,seafloor spreading, and Pleistocene glaciation).

Physiographic provinces of the Arctic Ocean seafloor

The International Bathymetric Chart of the Arctic Ocean (IBCAO) grid model has been used to define the first-order physiographic provinces of the Arctic Ocean, which in this study is taken to consist of the oceanic deep Arctic Ocean Basin; the broad continental shelves of the Barents, Kara, Laptev, East Siberian, and Chukchi Seas; the White Sea; and the narrow continental shelves of the Beaufort Sea and the Arctic continental margins of the Canadian Arctic Archipelago and northern Greenland. The first step in this classification is an evaluation of seafloor gradients contained in a slope model that was derived from the IBCAO grid. The evaluation of this slope model, which emphasizes certain process-related seafloor features that are reflected in the bathymetric information, is subsequently used along with the bathymetry to classify the first-order physiographic provinces. The areas of the provinces so classified are individually calculated, and their morphologies are subsequently discussed in the context of the geologic evolution of the Arctic Ocean Basin as described in the published literature. In summary, this study provides a physiographic classification of the Arctic Ocean seafloor according to the most up-to-date bathymetric model, addresses the geologic origin of the prominent features, and provides area computations of the defined first-order physiographic provinces and of the most prominent second- order features.

New database documents the magnetic character of the Arctic and North Atlantic

Magnetic observations of the Arctic and North Atlantic Oceans and adjacent land areas have been compiled in a new database that offers an unprecedented look at the magnetic anomalies over the continents and oceans of the study area. The most visible result of this compilation is the shaded relief map shown in Figure 1, which offers one of the most complete and coherent perspectives to date of the regions magnetic character. When combined with other types of observations, this information promises to shed new light on the breakup of the continents and the creation of the seafloor. Another product of the compilation is a grid of magnetic anomalies with wavelengths shorter than 400 km. Defined at regular intervals of 5 km, these grid values are well suited to quantitative tectonic investigations and to the automated production of accurate maps. Upon conclusion of the project in the first quarter of 1996, a digital version of the final grid will be released into the public domain for free and unrestricted use by investigators, along with full documentation and regional magnetic anomaly maps.

Magnetic imprints of continental accretion in the U.S.S.R

The evidence for these events has been studied extensively by Soviet investigators, who in recent years have applied the concepts of plate tectonics to the geological framework and evolution of the continental U.S.S.R. and summarized their findings in a series of tectonic reconstructions. The results of these studies have been synthesized, and their English publication “e.g., Khain, 1987; Zonenshain et al, 1990a,b” has provided Western investigators with a modern and comprehensive overview of the geological structure and history of the Soviet Union. Complementing these recent publications is a new digital grid of about 16 million points describing the magnetic anomaly field of the U.S.S.R. This data set was produced from a series of 18 maps, scale 1:2,500,000, published by the U.S.S.R. Ministry of Geology “Makarova, 1974” and digitized recently by the U.S. Naval Oceanographic Office in Bay St. Louis, Miss.

A compilation of magnetic observations from the Arctic and North Atlantic Oceans and adjacent land areas

Progress made in a new compilation of magnetic observations from the Arctic & North Atlantic Oceans and adjacent l and a reas , c a r r i e d o u t a t t h e A t l a n t i c Geoscience Centre of the Geological Survey of Canada, a l lows the p roduc t ion of a new preliminary map (see Figure). P rocedures app l i ed to p rocess the magnetic observations and incorporate them in to a da ta base a re b r ie f ly d i scussed . The new magnetic data base w i l l s e r v e a s a t o o l t o s t u d y p l a t e tec ton ic p rocesses in the nor the rn hemisphere.

Compiling all the world's magnetic anomalies

When the ultimate textbook of geology is written, several thematic maps of the world will be cited as conclusive evidence of global tectonics. Examples would be the map of global seismicity that shows just how neatly the vast majority of earthquakes are confined to the plate margins [Simkin et al., 1989] and the map showing the ocean floor topography that has been created, mostly during the last 150 Ma of Earths history [Smith and Sandwell, 1997]. Visionaries worked out the principles of plate tectonics on much more limited datasets, but extending the principles to understanding the geology of the most remote corners of the globe—and seeing world geology as a true global entity—demands global maps. The magnetic “stripes” of the ocean floor and their symmetry around spreading-axes can be demonstrated on a few profiles but, so far, only for the North Atlantic and Arctic Oceans have complete magnetic anomaly maps been published [Verhoef et al., 1996]. The much more complex geology of the remaining 90% of Earths history is preserved in the continents and uniquely revealed—even below extensive areas of younger cover—by continental magnetic anomaly maps. A magnetic anomaly map of the whole world would be a map of some significance alongside these others.

Submarine Elevations and Ridges: Wild Cards in the Poker Game of UNCLOS Article 76

Submarine elevations and ridges present an array of definitional uncertainties to coastal states that are engaged in the high-stakes process of delimiting extended continental shelves. Faced with the imprecise terminology of Article 76, with the nonspecific wording of the Scientific and Technical Guidelines of the Commission on the Limits of the Continental Shelf (CLCS), and with the Commissions rules of confidentiality that hamper the open exchange of information concerning ridge and elevation assessments in previous continental shelf implementations, a coastal state needs to develop its own evaluations of what might and might not pass the “test of appurtenance.” Significant components of a continental shelf submission might thus be formulated on the basis of these national evaluations, only to have the CLCS question them, which could necessitate a potentially expensive and time-consuming reworking of the submission. This article outlines the ramifications of this wild card effect.

Houston, We Have a Problem: Satellite Altimetry Skews Ocean Depths

In the decades after the space program began, several research missions produced global maps of ocean bathymetry. While these maps do an adequate job of portraying generally the seabed on a worldwide or even a regional basis, they fail to convey accurate and detailed pictures of seabed topography over more restricted areas when compared with renditions that can be obtained with multibeam sounding systems. As more and more laypeople come into contact with seafloor altimeter data through systems such as Google MapsTM, the public erroneously is starting to believe that all of the seafloor has been mapped in fine detail. To prevent this, ocean scientists must take active roles in petitioning those who fund science research that a broad campaign to survey the ocean floor through multibeam sounding systems is as critically needed as studies from space.