Had it not been the Land of the Long White Cloud (Aotearoa), in 1769 Young Nick and Captain Cook might have sailed right past the island microcontinent that is New Zealand. Instead, after sighting and then circumnavigating and mapping "the land uplifted high" (see the volume Frontispiece, parts A-C), Cook proceeded westward to chart also the east coast of Australia. He thus demonstrated to his European audience the existence of the Tasman Sea and established the geographic importance of New Zealand as the western margin of the main Pacific Ocean Basin (Fig. F1).
Almost exactly 200 years later, two other Northern Hemisphere vessels sailed New Zealand waters in pursuit of a global understanding of the nature of continents, ocean basins, and the tectonically active volcanic interface between them that is exemplified by the circum-Pacific mobile belt. In 1962, the vessel Eltanin was assigned to the U.S. National Science Foundation (NSF) for use as a research ship in support of the Foundation's Antarctic and Southern Ocean research program. During 1962-1972, the Eltanin conducted an extensive series of 55 pioneering voyages that laid the basis for our understanding of the oceanography and geology of the Southern Ocean (e.g., Glasby, 1990). Many of the Eltanin results were published in more than 40 volumes of the Antarctic Research Series of the American Geophysical Union (for Pacific geology, especially volumes 15 and 19) (cf. Houtz et al., 1967; Ewing et al., 1969; Hayes and Pitman, 1972; and summary in Davey, 1977). These achievements were followed, in 1972-1974, by the accomplishment of drilling Legs 21, 28, and 29 by the Glomar Challenger (Fig. F2) under the aegis of the NSF Deep Sea Drilling Project (DSDP), which formed part of the then rapid development of our understanding of the mechanisms of global tectonics and of the new discipline of paleoceanography (e.g., Burns, Andrews, et al., 1973; Kennett, Houtz, et al., 1975; Andrews, 1977; Burns, 1977). At that time, perhaps most astonishing was the fact that shipborne measurements and conclusions, drawn mostly by persons unfamiliar with New Zealand geology, should provide such powerful insights into both global geological mechanisms (Molnar et al., 1975; Weissel et al., 1977) and regional geological history (Ballance, 1976; Carter, R., and Norris, 1976).
The science achieved by these Eltanin-Glomar Challenger cruises revolutionized our understanding of southwest Pacific geology and oceanography just as surely as Cook, earlier, had revolutionized our appreciation of its geography. The first plate tectonic interpretations made it apparent that the northeast-trending active volcanic and earthquake zones of New Zealand—in the North Island the Taupo Volcanic Zone-Hikurangi Subduction Zone and in the South Island the transform Alpine fault—marked the modern plate boundary between the Pacific and the Australian plates (Isacks et al., 1968; Le Pichon, 1968; Molnar et al., 1975; Sutherland, 1995). The Tasman Sea represents an abandoned spreading center located entirely on the Australian plate (Hayes and Ringis, 1973; Weissel and Hayes, 1977). Thus, the New Zealand Plateau or microcontinent—comprising the emergent islands together with the flanking submarine Campbell Plateau, Chatham Rise, and Lord Howe Rise—forms not only the geographic but also the geologic and oceanographic southwestern margin of the Pacific Ocean Basin.
Meanwhile, onland, more than one 100 years of investigation by the staff of the New Zealand Geological Survey (Grindley et al., 1959) and by university and museum researchers had established that New Zealand's younger geology encompassed a richly fossiliferous record with a widely varying representation of both nonmarine and marine sediment facies (e.g., Cotton, 1955; Fleming, 1975; Suggate et al., 1978). The essentially unbroken nature of the postrifting succession of sediments is well summarized in the quotation from Cotton at the head of this review (cf. volume Frontispiece, part D). This Cretaceous-Cenozoic succession was termed the Notocenozoic by Cotton (1955) and classified as the Kaikoura Sequence (now Kaikoura Synthem) by Carter, R., et al. (1974). (Use of the term synthem as a replacement for sequence, in the sense of Sloss, 1963, after the latter term had been usurped by sequence stratigraphers, follows the usage of the International Commission on Stratigraphic Nomenclature. Synthems retain great usefulness as high-level terms for the widespread, unconformity-bounded packets of strata that make up regional geological successions; cf. Chang, 1975).
Compared with land-based geological studies, knowledge of the offshore geology and oceanography of the New Zealand region lagged and only developed during the second half of the twentieth century. Two events were pivotal to improving our knowledge of the geology of offshore territories. The first was the creation in 1954 of the New Zealand Oceanographic Institute (NZOI), initially as a branch of the Department of Scientific and Industrial Research (DSIR) but since 1992 encompassed within the National Institute of Water and Atmosphere (NIWA). The creation of a strong marine geological capability followed, as reflected in the major advances made by NZOI staff in understanding New Zealand's undersea geology and sedimentology during the second half of the twentieth century; Thompson (1994) presented a summary of this activity. Second, increasing numbers of petroleum exploration wells were drilled in New Zealand offshore waters from the 1960s onward. Under a far-sighted licensing policy, the seismic and stratigraphic databases collected during commercial exploration became open file reports, available through the Petroleum Section of the Geological Survey of New Zealand (e.g., McLernon, 1972). Analysis of this offshore data in conjunction with the onland geology had a markedly beneficial effect on the regional understanding of Cretaceous-Cenozoic stratigraphy, as exemplified by the appearance of the first regionally comprehensible and modern account of New Zealand's eight or so major Kaikoura sedimentary basins (Katz, 1968, updated in Ballance, 1993a; Laird, in press).
Each of New Zealand's post-Gondwana sedimentary basins, of course, contains an idiosyncratic local history, but all the eastern basins conform to the same regional pattern of initiation by rifting during the Late Cretaceous creation of the Pacific margin of the New Zealand microcontinent; thermal subsidence and marine transgression during the Cretaceous-Eocene phase of passive margin drift that accompanied mid-Pacific seafloor spreading; sediment starvation and current erosion during the Oligocene, by which time land areas and terrigenous sediment sources were greatly reduced and Southern Ocean current flows had started; and increased terrigenous sedimentation under the accelerating influence of volcanic and tectonic activity along the developing New Zealand plate boundary from the early Miocene onward (volume Frontispiece, part A) (Ballance, 1976; Carter, R., and Norris, 1976; Carter, R., 1988b; Ballance, 1993b; Laird, in press). Most of the sediments from which these generalizations are drawn were deposited in shallow or intermediate-depth marine waters, say <1500 m deep. Nonetheless, even the earliest studies recognized that these waters represented merely the shallow edge of a much larger and deeper Pacific Ocean Basin. This leads us to discuss the development of paleoclimatic and paleoceanographic studies in New Zealand.
Pelagic marine macro-organisms, such as nautiloids, occur only rarely as Cenozoic fossils. Thus, the abundant and diverse New Zealand Cretaceous-Cenozoic macrofossil record, like most, is overwhelmingly dominated by the remains of benthic organisms of limited zoogeographic distribution. Not surprisingly, the rich New Zealand literature on the interpretation of these fossil assemblages has been concerned mostly with discussion of their evolutionary and geographic origins and overseas affinities, as exemplified, for instance, by Finlay (1925). By the 1960s, however, the greatly increased knowledge of the invertebrate fossil faunas and the development of micropaleontological studies led to a burst of papers in which zoogeographic analysis was used also to infer New Zealand's changing climate history, as summarized by Fleming (1962; updated in 1975) and Hornibrook (1992). About the same time, the first direct physical measurements related to oceanic paleotemperature were provided from oxygen isotope analyses by Devereux (1967), and papers by Kennett (1968) and Vella (1973) provided early assessments of the past distribution of oceanic water masses in the southwest Pacific based on analysis of planktonic microfossils. These studies—which were based on organisms as diverse as mollusks, brachiopods, echinoderms, corals, foraminifers, nannoplankton, and trees (nuts, seeds, and pollen)—converged to provide a clear consensus regarding the history of Cenozoic climate in the New Zealand region (Fig. F3).
In outline, New Zealand fossil assemblages reveal the dominance of warm temperate to subtropical temperatures during the Paleocene and Eocene, followed by a sharp reduction of temperature across the Eocene/Oligocene boundary (33.7 Ma), and then warming in the late Oligocene. Gradual warming continued up until the occurrence of another subtropical climatic optimum in the early middle Miocene (Altonian-Clifdenian; peaking at ~16.5 Ma), followed by reducing temperatures through the remainder of the Miocene and Pliocene, with the final disappearance of most warm-water taxa and the appearance of subantarctic immigrants at ~2.4 Ma. Superimposed on this long-term climatic change, from ~3.5 Ma onward increasing tectonic uplift resulted in the exposure onland of sections containing a superb cyclothemic record of Pliocene-Pleistocene glacial-interglacial fluctuations (Fleming, 1953; Beu and Edwards, 1984; Haywick et al., 1992; Abbott and Carter, R., 1994; Naish and Kamp, 1995; Journeaux et al., 1996; Saul et al., 1999).
Because of the richly fossiliferous nature of the sedimentary record, environmental inferences about past New Zealand seas are common in the local geological literature from the late nineteenth century onward. Thus Marshall (1912, p. 41) commented that the characteristics of outcropping Oligocene glauconitic marls "tell us that much of the present land was during this period 1200 to 1800 feet below the sea level" and that "limestone succeeds the greensand and indicates deeper submergence and probably the climax of the (downward) movement." These, of course, are paleoceanographic inferences. Fleming's comprehensive summary (Fleming, 1975) of this largely qualitative phase of paleoceanographic and paleogeographic study was, appropriately, published a little after the pioneering reconstruction by Devereux (1967) of the world's first Cenozoic-long oxygen isotope paleotemperature record. Although based on mixed samples from both micro- and macrofossils, Devereux's New Zealand curve broadly mirrors current high-resolution global isotope curves (e.g., Zachos et al., 2001) and included a clear delineation of the abrupt, major temperature decline across the Eocene/Oligocene boundary.
Modern paleoceanography arose from using similar new and sensitive analytical techniques applied to the long, undisturbed, and uninterrupted oceanic sediment cores that became available from the late 1960s. In this regard, the hydraulic piston corer, precursor of the advanced piston corer (APC), was first deployed successfully during DSDP Leg 64 in the Gulf of California in 1982, and the first volume of the journal Paleoceanography appeared in 1986. The 1983 drilling of DSDP Leg 90, a latitudinal transect of sites with paleoceanographic targets, provided the first lengthy piston cores from the New Zealand region (Kennett, von der Borch, et al., 1986). This drilling marked the inception of modern paleoceanographic research in the southwest Pacific Ocean, 10 years after Vella (1973, p. 318) concluded a discussion of the onland evidence for Neogene movements of the subtropical front (STF) with the prescient remark that "...to obtain more direct, more reliable and more complete results, the research must be reoriented towards paleo-oceanography."
DSDP Sites 593 and 594, drilled during Leg 90, were situated west and east of New Zealand, respectively, in subtropical waters on the Lord Howe Rise and subantarctic waters on the southern flank of the Chatham Rise (Kennett, von der Borch, et al., 1986). Subsequent study of material from these and earlier DSDP sites provided the first high-resolution sedimentary, geochemical, and climatic records for the southwest Pacific (Kennett et al., 1975; Kennett, von der Borch, et al., 1986; Nelson, 1986), contributed to the integration of onland New Zealand stratigraphy with international zonation schemes (Hornibrook, 1980, 1981, 1982, 1984; Scott, 1992), and provided evidence toward establishing the late Neogene timetable of mountain building along the Australian/Pacific plate boundary (Lewis et al., 1985). More expressly, paleoceanographic results from Site 594 were concerned with the synchroneity of glacials and interglacials between the hemispheres (Nelson et al., 1986a), the more general Neogene climatic deterioration (Lazarus and Caulet, 1993), the history of supply of Antarctic Intermediate Water (AAIW), and the historic properties and evolution of the STF and the Subantarctic Front (SAF) (Nelson et al., 1986a, 1993; Kowalski and Meyers, 1997) (Fig. F4). Of the three earlier DSDP sites in the vicinity, Sites 275 and 276 were rotary drilled at locations on the edge of the Campbell Plateau where erosion had removed a large part of the record and DSDP Leg 29 Site 277, in the Emerald Basin just west of the Campbell Plateau, recovered an exceptional late Eocene-early Oligocene isotope record (Shackleton and Kennett, 1975).
The successful completion of DSDP Leg 90 provided a strong impetus for the development of paleoceanographic studies of the New Zealand region, aided by the growth of allied research programs at Waikato University and within NIWA (including a shipborne capability on Rapahuia and Tangaroa), with staff and students often working in collaboration with overseas scientists aboard visiting research vessels such as the Sonne, Atalante, and Marion Dufresne. Consequently, the last two decades have witnessed a burgeoning of papers on the paleoceanography of the southwest Pacific Ocean and Tasman Sea (Thiede, 1979; Griggs et al., 1983; Stewart and Neall, 1984; Nelson et al., 1985, 1986b, 1993, 2000; Hodell and Kennett, 1986; Carter, L., and Mitchell, 1987; Carter, L., and Carter, R., 1988; Dudley and Nelson, 1988, 1989; Carter, L., 1989; Proctor and Carter, 1989; Carter, L., et al., 1990, 1995, 1996, 1999, 2000, 2002a, 2002b; Dersch and Stein, 1991; Fenner et al., 1992; Barnes, 1994; Carter, L., and McCave, 1994, 1997; Head and Nelson, 1994; Hesse, 1994; Heusser and van de Geer, 1994; Martinez, 1994; van der Lingen et al., 1994; Flower and Kennett, 1995; Wright et al., 1995; Weaver et al., 1997, 1998; Ayress et al., 1997; Hiramatsu and De Deckker, 1997; Kowalski and Meyers, 1997; Swanson and van der Lingen, 1997; Thiede et al., 1997; Wells and Connell, 1997; Wells and Okada, 1997; Lean and McCave, 1998; Lewis et al., 1998; Schuur et al., 1998; Wei, 1998; Barrows et al., 2000; King and Howard, 2000; Nelson et al., 2000; Sikes et al., 2000, 2002; Hayward et al., 2001; McGlone, 2001; McMinn et al., 2001; Nelson and Cooke, 2001; Stickley et al., 2001; Cooke et al., 2002; Findlay and Giraudeau, 2002; Kawahata, 2002; Neil et al., submitted [N1]). Increasingly, similar high-resolution stratigraphic studies are being pursued for New Zealand onland sections as well (e.g., Vella, 1973; Hollis et al., 1995; Strong et al., 1995; Kaiho et al., 1996; Morgans et al., 1999, 2002; Graham et al., 2000; Killops et al., 2000; Crouch et al., 2001; Hancock et al., 2003; Hollis, 2003, and papers therein). Paul Vella must be well satisfied!
Globally, it is very clear that geological boundaries have a profound influence on the oceans; after all, land is land, sea is sea, and the continents are geologically different from the ocean basins. Thus the presence of land masses and their submerged extensions plays a dominant role in shaping the disposition of the major ocean currents. Since the advent of plate tectonics, it has been apparent that it is the dance of the geological plates that controls the opening of ocean basins and the position of their gateways and that therefore ultimately shapes the flow of the world ocean (e.g., Berggren and Hollister, 1977) and the distribution of marine organisms that possess planktonic larvae or life habits (e.g., Jenkins, 1993). To a large degree, tectonics also control the location and magnitude of the major sources of terrigenous sediment that is contributed to the world ocean. The resulting interaction between tectonics, sediment supply, and ocean current flows is well epitomized in the New Zealand area. There, the concept of an Eastern New Zealand Sedimentary System (ENZOSS) (Carter, L., et al., 1996) was used to characterize a regionally extensive system within which ~2% of the world's marine terrigenous sediment flux is currently being provided from—and then recycled by oceanographic, tectonic, and volcanic processes through—the southwest Pacific sector of the Australian/Pacific plate boundary (see Frontispiece, parts A-E).
The ENZOSS terrigenous sediment budget is dominated by two major sources. First, a background supply of sediment is derived from the erosion of actively uplifting mountain chains in South and North Islands, and, second, an intermittent but voluminous volcaniclastic contribution was provided by large eruptions in the Coromandel and Taupo volcanic zones of the North Island. The Southern Alps, which are delimited to the west by the Alpine Fault plate boundary, have similar maximum rates of uplift and summit erosion (up to 10 mm/yr) and therefore approximate a "steady-state" mountain chain (Wellman, 1979; Adams, 1980; Koons, 1989; Willett and Brandon, 2002). Sediment is shed eastward from the alpine summits into about eight major river systems, three of which coalesce to form the 300-km-long braid-plain of the Canterbury Plains (e.g., Leckie, 1994). The estimated ENZOSS sediment input from South Island rivers at the east coast is ~40 Mt annually (Griffiths and Glasby, 1985), despite the presence of large sediment traps en route in abandoned glacial lake basins (Carter, L., and Carter, R., 1990). Given adequate precipitation, at glacial lowstands the east coast sediment input can therefore be expected to have been considerably higher (Carter, L., et al., 2000). On reaching the coast, the riverine sediment is entrained within a north-traveling transport system (Carter, L., and Herzer, 1979; Gibb, 1979; Gibb and Adams, 1982), where most of it is initially deposited in coastal or inner shelf depocenters (Andrews, 1973; Herzer, 1981; Carter, R., et al., 1985; Carter, L., and Carter, R., 1986). Abundant terrigenous material is also provided to the North Island shelf (Lewis, 1973). Griffiths and Glasby (1985) estimated that eastern North Island rivers provide ~66 Mt of sediment to the east coast annually. Given such an abundant sediment supply, inshore sedimentation rates are locally very high in eastern New Zealand, for instance attaining >5 m/k.y. in the Clutha River and Poverty Bay depocenters (Carter, L., and Carter, R., 1986; Foster and Carter, L., 1997). Nonetheless, given the efficiency of nearshore sediment entrapment and the presence of vigorous oceanic currents on both the North (south-traveling East Auckland-East Coast Current) and South (north-traveling Southland Current) Island shelves (e.g., Heath, 1985) (Fig. F4), the offshore shelf is commonly starved of terrigenous sediment (Carter, L., 1975). For instance, the outer shelf off northern and western North Island (Nelson et al., 1981; Norris and Grant-Taylor, 1989) and eastern South Island (Powell, 1950; Carter, R., et al., 1985) is the locus of extensive bryozoan-molluscan carbonate deposition (shelly detritus which often overspills onto the adjacent upper slope; Orpin et al., 1998), a major field of phosphatic nodules and glauconite is developed along the crest of the Chatham Rise (Cullen, 1980), glauconitic sediment also occurs on outer shelf highs east of North Island (Pantin, 1966), and current-swept exposed rock platforms occur outside the shore-connected terrigenous prisms on the outer shelf off Kaikoura, South Island (Carter, L., et al., 1982) and under the influence of the East Coast Current off East Cape, North Island (Carter, L., unpubl. data).
If most modern terrigenous sediment is confined to coastal and inner shelf depocenters and the outer shelf is characterized by condensed carbonate-rich sediment or is swept clean by currents, how then does terrigenous sediment from New Zealand reach the deep sea?
Three mechanisms operate to transfer sediment of New Zealand origin to the deep sea. First is the direct air fall of volcanic ash. For instance, 120 km3 of epiclastic material was associated with the historic Taupo eruption of A.D. 186 (Walker, 1980; Carter, L., et al., 1995), and the older Kawakawa (~26.6 ka) and Rangitawa (~340 ka) eruptions are estimated to have ejected ~550 km3 (Carter, L., et al., 1995) and ~700 km3 (Froggatt et al., 1986) of ash, respectively (cf. Frontispiece, part A, inset). Carter, L., et al. (1996) estimated an average air fall ash input into ENZOSS of ~45 Mt/yr (~0.025 km3/yr) since the last glacial maximum, and thus individual large volcanic eruptions contribute volumes of detrital sediment equivalent to ~9,500-12,000 yr of typical riverine supply from North and South Island combined. The second transfer mechanism is the collapse of an underconsolidated or oversteepened outer shelf or upper slope seabed, a common accompaniment of rapid sediment deposition (e.g., Herzer, 1979) or accretionary wedge tectonics (Lewis et al., 1998). Seafloor failure is particularly characteristic of the Hikurangi subduction margin in North Island (Lewis, 1971; Barnes and Lewis, 1991; Lewis and Pettinga, 1993), where the Matakoa and Ruatoria avalanches have been estimated to attain volumes of 600 and 3150 km3, respectively (Carter, L., 2001; Collot et al., 2001). Thus, individual slides may transfer material downslope equivalent to ~17,000-88,000 yr of riverine supply to the New Zealand east coast margin. Third, and regionally most widespread, sediment is transferred to the deep sea through three recently described submarine channels, each of which debouch into the abyssal Deep Western Boundary Current (DWBC). In the south, erosional products are transferred from the mountainous Fiordland region via Southland rivers, Solander Trough, and Solander Channel to the Emerald Basin and beyond (Carter, L., and McCave, 1997; Schuur et al., 1998). East of South Island, the Bounty Channel (Carter, R., and Carter, L., 1987; Carter, L., and Carter, R., 1988; Carter, L., et al., 1990) forms the conduit between the South Island shelf and East Otago canyon-fan complex and the abyssal Bounty Fan (Carter, L., and Carter R., 1993; Carter, R., et al., 1994), which builds out directly into the path of the DWBC at the mouth of the Bounty Trough (Carter, R., and Carter, L., 1996). Near the northeastern tip of South Island, the head of the third Hikurangi Channel, marked by the Kaikoura and Pegasus canyons, lies at the terminus of the north-traveling South Island shelf sediment system (Carter, L., and Herzer, 1979; Carter, L., et al., 1982; Lewis and Barnes, 1999). This channel then passes north along almost the entire North Island margin (Lewis, 1994) before turning east at latitude 39°S to deliver its sediment load to the Hikurangi Fan-drift, located beneath the DWBC and 1500 km northward and downstream from the Bounty Fan (Carter, L., and McCave, 1994; McCave and Carter, L., 1997). Of the three channels, the Hikurangi Channel is unusual because the nearshore location of its head ensures that it is abundantly supplied with terrigenous sediment today and, therefore, also during past sea level highstands. In contrast, both the Solander (Schuur et al., 1998) and Bounty (Carter, R., and Carter, L., 1992) channels, the heads of which lie well offshore, are inferred to have received a greater terrigenous sediment supply during periods of Quaternary glacial sea level lowstand. Thus, in a sense, a fourth mechanism of sediment transfer to the deep sea is eustatic sea level fall, which operated particularly strongly during the Pliocene-Pleistocene. Indeed, it is argued by McCave (2002) that on a global basis and a 105 yr timescale, "sea level pumping" was the principal method of sediment delivery from the continents to the deep sea throughout the Pliocene-Pleistocene.
The circulation of cold, deep Antarctic Bottom Water (AABW) is one of the controlling factors in the Earth's heat budget and, ultimately, climate (Figs. F4, F5). Today, 40% of the flux of cold bottom water entering the major ocean basins does so through the southwest Pacific Ocean, as the Pacific DWBC (Frontispiece, part E) (Warren, 1981). The DWBC is constituted of Circumpolar Deep Water (CDW), which is derived through dense waters sinking around Antarctica and through the entrainment and mixing of deep Atlantic and Indian Ocean waters by the wind-driven Antarctic Circumpolar Current (ACC). The DWBC attains an average volume transport of 16 ± 11.9 Sv (= 106 m3/s) at 32°30´S (Whitworth et al., 1999) and, in the southwest Pacific, comprises three main divisions: lower CDW, a mixture of new bottom waters generated around Antarctica (cf. Stickley et al., 2001); middle CDW, derived from North Atlantic Deep Water (NADW) and marked by a characteristic salinity maximum; and upper CDW, derived mainly from Indian Ocean outflow and characterized by strong nutrient enrichment and oxygen depletion. At the approach to the Pacific Ocean, the ACC passes around and through gaps in Macquarie Ridge and then flows northeast along and around the eastern edge of the Campbell Plateau. There, the DWBC is reinforced by the ACC at an estimated rate of 50 Sv and velocities up to 70 cm/s (Carter and Wilkin, 1999; Stanton and Morris, in press). At the southern edge of the Bounty Trough (46°S), the main body of the ACC veers east and continues across the Pacific, leaving the DWBC to flow northward at depths between ~5000 and ~2000 m, across the Bounty Fan, around the eastern end of the Chatham Rise through Valerie Passage, northwestward across the eastern boundary of the Hikurangi Plateau, and finally northward toward the equator along the Tonga-Kermadec Ridge (Fig. F4).
Higher in the water column, north-spreading AAIW, formed by subduction near the Antarctic Polar Front (AAPF), and Subantarctic Mode Water (SAMW), formed by seasonal convection at and north of the SAF, bathe the top and eastern upper flank of the Campbell Plateau at depths of 400-1500 m (Morris et al., 2001).
The upper ocean east of South Island contains two major frontal systems. At ~55°S, the east-flowing ACC is bounded to the north by the SAF (cf. Fig. F1), which here follows the southeastern edge of the Campbell Plateau (Orsi et al., 1995). South of the SAF, the annual mean surface water temperature is <10°C and the nutrient-rich polar ocean is rich in both phosphate and silica. About 10° latitude north of the SAF at 45°S, the STF separates subantarctic water from subtropical water (Heath, 1985; Belkin and Gordon, 1996). Cold (Southland Current) and warm (East Coast Current) currents that have passed around the extremities of New Zealand continue east along the south and north sides of the STF along Chatham Rise and merge east of the rise to form the 5-Sv South Pacific Current of Stramma et al. (1995). (The STF is termed the Subtropical Convergence, STC, in many previous papers, but this term also has a more general usage to describe the broad oceanic zone between ~20° and 50°S where wind stress drives downward Ekman pumping; therefore, we follow Stramma et al., 1995, in preferring to use the term STF for the sharp band of enhanced meridional gradients present at the contact of northern warm and saline subtropical water and southern cool and relatively fresh subantarctic water.) In the open ocean the SAF and STF have been shown to migrate laterally by as much as 6° of latitude during a glacial-interglacial cycle (e.g., Howard and Prell, 1992; Wells and Connell, 1997). However, modern seasonal movements of the fronts of at least 2° of latitude may occur also, as, for example, the STF east of New Zealand (Chiswell, 1994; Kawahata, 2002). In contrast to such seasonal mobility, over the longer term and through climatic cycles the STF appears to have remained topographically aligned along the shallow crest of the Chatham Rise (Fenner et al., 1992; Nelson et al., 1993; Weaver et al., 1998; Sikes et al., 2002).
When referring to ancient water masses whose properties can never be fully reconstructed, some authors prefer not to use the terminology of modern water masses. Thus Wright and Miller (1993) use the term Southern Component Water (SCW) for paleowater masses that originate in the Southern Ocean. Such terminology may be modified to take account of presumed depth of origin, as in Southern Component Intermediate Water (SCIW) or Southern Component Bottom Water (SCBW).
With respect to the preceding summary and discussion, the ENZOSS region occupies a key position on the route of the modern global thermohaline circulation system. Nearby tectonic developments affected it in two different, but interrelated, ways.
To investigate the development of the New Zealand sector of the global thermohaline system as well as related problems such as the eruptive history of the North Island volcanic arc and the integration of local biostratigraphic zonations into a global stratigraphy, a two-leg drilling program was designed. Ocean Drilling Program (ODP) Leg 181 represented the distillation of this wider program, with a particular focus on drilling sediment drifts; Table T1 comprises a listing of the sites drilled, and Table T2 is a summary of the relevant water masses and fronts. As always in frontier areas, stratigraphic surprises awaited the drill bit. Less of a surprise, given the latitudes and the late winter drilling period, was that storms disrupted the intended work program. Nonetheless and despite severe weather-imposed drilling setbacks at Sites 1120 and 1122, much was accomplished from our reconnaissance drilling. Leg 181 results confirm that the southwest Pacific is a critical region within which to pursue future studies of the history of the thermohaline current system, the movements of Southern Hemisphere oceanic fronts, and the production of thermocline water masses.