Abstract The first of the four main parts of this chapter presents a short history of the European discovery of circumpolar lands and the Arctic Ocean from the earliest recorded voyages to the twentieth century. The story of geographic exploration of the Arctic regions has been told many times, and there is an enormous literature dealing with expeditions and geographic discoveries. Particularly useful in providing the historical setting for the growth of scientific knowledge of the Arctic Ocean area is the compilation by Kirwan (1959), who provides insights into the economic, strategic, political, and personal motives behind many of the explorations; and the scholarly analyses edited by Rey and others (1984), which trace the development of geographic and scientific knowledge of the Arctic as a result of myths, conjectures, genuine discoveries, and increasingly precise observations from antiquity to the eighteenth century. The next part deals with the mapping of the Arctic Ocean basin and floor during the last century, from sparse information that led to a shallow, single-basin concept to the complex sea- floor morphology that gradually emerged as a result of the more detailed surveys beginning with the Soviet explorations in 1937. This section ends with a description of the major modern bathymetric maps and charts that have appeared in print, from Bartholomew in 1897 to Perry and others (Plate 1, this volume). The third section is an outline of the history of the geoscien- tific work carried out within the Arctic Ocean region, from ships, from drifting stations, and

Abstract The oceanic regions located north of the Arctic Circle are the Arctic Ocean, the Norwegian-Greenland Sea, and Baffin Bay (Plate 1). The latter is described in Keen and Williams (1990). Despite the bold isobaths in Plate 1, the bathymetry of the Arctic Ocean is still poorly known. Most of the Norwegian-Greenland Sea, on the other hand, is quite precisely charted. Exceptions are the areas east of Greenland often covered by the pack ice that exits the Arctic Ocean in the East Greenland current. The names used for the physiographic features in this volume are those shown on Plate 1. Different names that have been applied to these features in the literature are given in Sweeney and others (this volume.)

Abstract This chapter describes the physiography plus the geological and geophysical character of the central Arctic. The available information is chiefly from work done on several ice station transits of the area together with aeromagnetic and satellite magnetic investigations. The data provide crude constraints on the nature and ages of the main sea-floor features of the central Arctic Ocean. The central area of the Arctic Ocean contains abyssal depths that are traversed by two subparallel submarine mountain ranges, the Lomonosov Ridge and the Alpha-Mendeleev Ridge complex. The wedge-shaped Makarov Basin separates these adjacent ranges, which are close to North America and are more than 500 km apart at their junction with the East Siberian continental margin (Fig. 1). Significant difference in overall morphology and geophysical properties between the Lomonosov and Alpha Ridges, despite their juxtaposition near North America, suggests a complex structural evolution for the central Arctic, whose origins are constrained loosely within the late Early Cretaceous-earliest Tertiary interval.

Abstract Free-air and Bouguer anomaly maps have been compiled from about 9,000 gravity measurements made throughout the Canadian Arctic Archipelago and the Arctic Ocean. These measurements form part of a major survey of the Arctic being carried out by the Canadian government. Correlation of Bouguer anomalies with geologic and physiographic features shows that negative anomalies generally occur over sedimentary basins and mountainous regions and positive anomalies occur over fold belts and the ocean basin. The major feature of the free-air anomaly map is a series of large, positive, elliptically shaped anomalies overlying the continental margin and striking parallel with the continental break. These anomalies, which are approximately 120 km in width and between 150 and 300 km in length, have amplitudes greater than 100 mgal and regional horizontal gradients as large as 2.5 mgal/km. Interpretation of the gravity data, using seismic and geologic data for control, indicates that these anomalies can be explained best by a composite structure consisting of a sedimentary layer up to 10 km in thickness and a crust which thins by as much as 17 km. The average free-air anomaly of the relatively flat archipelago (mean elevation of 15 m) west of 90°W long, is about 7 mgal; this value indicates that the region is in approximate isostatic equilibrium