Campbell Plateau is a submerged continental platform protruding into the southwest Pacific Ocean for ∼1100 km from the southeastern margin of South Island, New Zealand (Figure 1). For much of its area, plateau depths are 1000–600 m, shoaling to 250 m, and comprising a number of broad rises and depressions. Surface expression occurs in the form of several Subantarctic Island groups, including the volcanic Auckland and Campbell Islands. The Plateau margins are precipitous, plunging from 1000 m to more than 4000 m, often at gradients of 1:4. Campbell Plateau is separated from Chatham Rise in the north by the Bounty Trough [Carter and Carter, 1993], and from the adjacent Bounty Plateau by the ∼1400 m deep Pukaki Saddle which forms a distinct breach in the major topographic boundary steering the SAF of the ACC [Summerhayes, 1969].
 The interior of Campbell Plateau is mantled by pelagic carbonate sediments. Similar sediments are also present on the flanks but the cover is patchy due to erosion by the powerful ACC [e.g., Glasby, 1976; Carter, 1989], with mass failure also playing a role. At depths >2000 m, the Deep Western Boundary Current (DWBC), aided by the ACC, have redistributed sediment and formed thin drifts along the plateau base [Carter and McCave, 1997; Carter et al., 1999]. The extensive biopelagic cover is generally fine-grained, white and homogeneous, consisting mainly of foraminifera, coccolith plates, and noncarbonate material (typically ∼10–20%). Quartz-dominant terrigenous sediment and biosiliceous remains of radiolaria and sponge spicules are main constituents of the sand fraction in the noncarbonate component. Holocene carbonate content averages 85% with no distinct variation with depth or geographical location across the shallow plateau [Summerhayes, 1969; Carter et al., 2000]. Sedimentation rates are generally low over Campbell Plateau and dominated by pelagic deposition [Carter et al., 2000].
 Campbell Plateau margin separates Subantarctic from Circumpolar surface waters, as well as constricting the flow of the eastward flowing ACC [Burling, 1961; Gordon, 1972; Orsi et al., 1995]. Constriction causes a pronounced northward deflection of the leading edge of the ACC, marked by the SAF, along the eastern plateau margin [Heath, 1981; Carter and Wilkin, 1999]. As a result, the flow is topographically intensified with mean current speeds of 27–39 cm s−1 recorded within a ∼150 km wide swath centered on the plateau slope [Stanton and Morris, 2004]. Nevertheless, sectors of the ACC resume their eastward flow at ∼55°S [e.g., Orsi et al., 1995] and at ∼50°S [e.g., Bryden and Heath, 1985; Carter et al., 1998]. The western plateau also hosts a northward current, this time associated with the STF. Termed the Southland Current, it has a mean speed of ∼20 cm s−1 [Chiswell, 1996; Sutton, 2003].
 At depth the flow is dominated by a large DWBC [Carter and McCave, 1994], which enters the New Zealand region through gaps and around Macquarie Ridge. This thermohaline inflow, extending from 2000 to ∼5000 m deep, finds the western boundary presented by Campbell Plateau and passes north in consort with the ACC to about 50°S, where divergence from the ACC occurs, leaving the DWBC to continue over Bounty Trough, while the ACC veers east across the Pacific Ocean.
 Surface oceanographic conditions off southernmost New Zealand are influenced by two distinctly different regimes of circulation: the intense and variable ACC, and weak, gyre-like circulation on Campbell Plateau. The ACC is a composite flow bounded by the strong zonal jets associated with the SAF and Antarctic Polar Front to the north and south respectively [e.g., Peterson and Whitworth, 1989; Paterson and Whitworth, 1990]. The intervening flow is generally weaker. Sharp transitions in water properties and current speed along the fronts extend deep into the water column. Strong northeastward flow in the SAF, and its entrained Subantarctic Mode Water (SAMW), is confined to the shelf edge along Campbell Plateau flanks [Morris et al., 2001] (Figure 2). Trajectories of deep floats reported by Davis  show large eastward displacements, indicating a swift, deep current within the ACC, south of New Zealand. Several deep float tracks head north trapped within the SAF. Other trajectories are more complicated especially in the vicinity of Bounty Plateau and Bounty Trough, although there is a strong tendency to align with the bathymetry and either turn eastward into the southwest Pacific Ocean or pass through Pukaki Saddle, to continue as a cyclonic flow around the head of Bounty Trough [Morris et al., 2001] (Figures 1 and 2).
Figure 2. (a). Geostrophic velocities (black and gray vectors) relative to the bottom during hydrographic surveys in May 1998, December 1998, and August 1999. Note the strong geostrophic flow in the SAF along the eastern flank of Campbell Plateau. (b) Time average results for the three surveys for Campbell Plateau section only; note change of scale. The flow vectors on the Campbell Plateau are an order of magnitude smaller than those around the flanks. (c) Repeat upper ocean temperature sections along the southeast track shown in Figure 2a, from South Island, New Zealand, over Campbell Plateau and off the shelf edge. Note the occurrence of seasonal stratification during summer and weak stratification during winter over Campbell Plateau. The contour interval is 0.5°C.
Download figure to PowerPoint
 In sharp contrast, current velocities on Campbell Plateau itself are weak, with a mean flow of <10 cm s−1 [Morris et al., 2001] (Figure 2). Although sluggish, these currents are persistent, with weak anticyclonic circulation occurring around Pukaki Rise [Morris et al., 2001], a counter flow inshore of the ACC and cyclonic circulation centered between Campbell Island and Pukaki Rise (Figure 2).
 At shallow depths the water over Campbell Plateau is cool, fresh Subantarctic Surface Water (SAW). This water mass is hydrologically and biologically distinct from warmer, saltier Subtropical Surface Water (STW) to the north, and colder, fresher Circumpolar Surface Water (CSW) in the south. These waters overlie Antarctic Intermediate Water (including a shallow SAMW component north of the SAF) and Circumpolar Deep Water (CPDW). Immediately north of the SAF, mixing occurs to ∼400 m; this deep mixing can extend over the Plateau flanks during winter. Additionally, extending from the SAF is a region of low temperature stratification associated with SAMW which extends between ∼200 m and the Campbell Plateau seabed at 600–1000 m depth (Figure 2). Consequently, waters over a large portion of the plateau are weakly stratified during winter, with few periods of active mixing observed. In summer the plateau waters are strongly stratified due to seasonal heating (Figure 2) [Morris et al., 2001].
 North of Campbell Plateau lies the Subtropical Front (STF), the northern limit of the Southern Ocean and the boundary with STW. Like the SAF, the STF is deflected around New Zealand. Presently it approximates 45°S in the Tasman Sea, but is deflected around the South Island continental margin to form the Southland Front [Heath, 1985; Chiswell, 1996]. The Southland Front resumes as the STF at Chatham Rise (∼43°S), before shifting south once free of Chatham Rise crest [e.g., Heath, 1985; Chiswell, 1994] (Figure 1).
2.4. Wind Systems
 Campbell Plateau currently lies within the influence of the vigorous “Roaring Forties” westerly wind system. Fluctuations in strength and latitude of the westerlies occur seasonally, with the winds expanding northward in winter and receding southward during summer [Markgraf et al., 1992]. Autumn is the windiest season, followed by spring [Reid and Penny, 1982; Reid and Collen, 1983]. Mean wind speeds of 30 km hr−1 with gusts of 96 km hr−1, occur on average for 106 days a year at Campbell Island [New Zealand Meteorological Service, 1981]. During glacial times, atmospheric circulation in the southwest Pacific was enhanced due to an increased pole-equatorial thermal gradient with expanding Antarctic ice shelves and sea ice [Thiede, 1979; Markgraf et al., 1992]. The core of the strengthened westerlies probably shifted significantly northward, and may have lain over New Zealand during such times [e.g., Thiede, 1979; Stewart and Neall, 1984].