The ocean circulation in the Antarctic Sector of the Pacific is dominated by the continuous eastward-flowing Antarctic Circumpolar Current (ACC), a deep-reaching current driven by strong, prevailing westerly winds. Waters with diverse properties are entrained into the ACC all along its path and are subsequently blended into a more or less zonally uniform flow. The southernmost waters in the Pacific Ocean are therefore more similar to their counterparts in the Atlantic and Indian Oceans than they are to the waters further north in the Pacific. Because of their distinct and relatively homogeneous properties, the waters within and to the south of the ACC are collectively referred to as the Southern Ocean.

Besides being important as the primary connecting link between the three major ocean basins, the Southern Ocean is also the region of the major oceanic heat loss that drives the meridional circulation of the world ocean thermally. Heat advected poleward within the deep water is lost by radiation and either direct or indirect interaction with the cold Antarctic atmosphere and ice. The newly-formed cold water masses then spread northward at intermediate (~ 1,000 m) and abyssal (> 4,000 m) depths.

In this chapter, we present a general review of the descriptive physical oceanography of the Antarctic Sector of the Pacific Ocean, whose geographic limits and major bathymetric features are shown in Fig. 3.1. The Pacific constitutes by far the largest sector of the Southern Ocean, but its influence on the water mass properties of the ACC and the adjacent oceans is relatively weak in contrast to that of the Atlantic, which contains major sources of both deep and bottom waters. The chief influence of the Pacific is its contribution of a dissolved oxygen minimum and nutrient maximum to the Upper Circumpolar Deep Water. There are also identifiable sources of Antarctic Bottom Water (AABW) within the Ross Sea and along the Adelie Coast (130°E to 150°E), but their influence seems to be confined to the vicinity of the sources.

Ocean circulation within the Pacific Sector is driven by both wind and thermohaline forcing. Both modes of circulation are influenced by bottom topography and the earth's rotation. The review begins with a description of the mean wind-driven circulation in the Pacific Sector. This is followed by a discussion of the velocity structure of the ACC, its interaction with bottom topography, and its estimated volume transport. The tendency for water properties to vary from north to south (meridionally) but to be uniform from east to west (zonally) has led to a characterization of the ACC as consisting of broad, distinct and continuous zones separated by narrow fronts. This "zonation" of the ACC is described in some

Fig. 3.1. Major bathymetric features of the Pacific Sector of the Southern Ocean. Dashed line is the 3,500 m isobath.

detail and is followed by a brief discussion of mesoscale variability within the ACC. The next section presents a discussion of the large-scale thermohaline circulation and includes a description of sources, formation mechanisms, identifying properties, and circulation of the major water masses present in the Pacific Sector. The final section presents a summary and identifies some of the major gaps in our knowledge of this vast and remote area.

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