ECOLOGICAL DISTRIBUTION OF BENTHIC FORAMINIFERA, OFFSHORE NORTHEAST NEW ZEALAND BRUCE W. HAYWARD 1 ,HUGH R. GRENFELL 1 ,ASHWAQ T. SABAA 1 ,CLARE M. HAYWARD 1 AND HELEN L. NEIL 2 ABSTRACT Northeast of New Zealand, nine benthic foraminiferal associations are recognized and mapped (50–3800 m depth) based on cluster analysis of faunal census data (.63 mm, 235 species, 56 samples). Similar associations are identified using cluster analysis based on the presence or absence of species. Canonical correspondence analysis shows that the associa- tions correlate most strongly with factors related to water depth, especially decreasing food supply (organic carbon flux) with increasing depth. The depth-stratified distribution of lower bathyal to abyssal (.1000 m) associations accords well with the deep water masses, and is attributed in part to lower oxygen concentrations in the bottom waters. The two deepest associations, dominated by Alabaminella weddellensis, Epis- tominella exigua, Bulimina marginata f. aculeata, Globocas- sidulina subglobosa, and Oridorsalis umbonatus, underlie the oxygen minimum zone of Circumpolar Deep Water. A mid- lower bathyal association dominated by Cassidulina carinata, Alabaminella weddellensis, Abditodentrix pseudothalmanni, and Trifarina occidentalis, underlies Antarctic Intermediate Water. In addition to their bathymetric stratification, mid shelf to upper bathyal (50–600 m) associations also show latitudinal variation that may reflect differences in terrige- nous mud (abundant Eilohedra vitrea), bottom current strength, food supply (more abundant Cassidulina carinata) and nutrient remineralization on the seafloor. At depths of ,1000 m, the benthic foraminiferal assem- blages of this study are more similar to those off the west coast than those further south down the east coast. This may reflect lower levels of phytoplankton productivity and consequent benthic food supply, than occurs in the vicinity of the Subtropical Front, east of central New Zealand. Individual foraminiferal faunas off northeast New Zealand are more species rich (Fisher Alpha Index, a 14–18) than those further south (a 10–13). Total foraminiferal species richness (.50 m depth) is similar off northeast (235 species) and eastern (246 species) New Zealand and higher than off the west coast (150 species). INTRODUCTION This paper documents the present-day ecological distri- bution of benthic foraminiferal faunas off the northeast coast of New Zealand, and uses multivariate analysis techniques and proxy environmental data to determine the more significant environmental causes of the observed patterns. Studies elsewhere have shown that the ecological distribution of deep-sea benthic foraminifera is determined by the complex interplay of a number of physical and biological factors (e.g., Murray, 1995). The resulting distributional patterns usually exhibit zonations that are roughly coincident with increasing water depth, but absolute depths and taxonomic composition of these zonations vary from region to region (e.g., Culver, 1988; Murray, 1991). Knowledge of these depth-related distribu- tional patterns and the factors responsible for them are essential ingredients in paleoecological reconstructions and basin analyses based on fossil foraminiferal faunas (e.g., Hayward and Buzas, 1979; Hayward, 2004). This is the third of a series of regional studies designed to investigate the geographic and bathymetric distribution of deep sea benthic foraminifera around New Zealand. The two earlier studies documented similar .63 mm faunas from east of central New Zealand (Hayward and others, 2001, 2002) and west of the North Island (Hayward and others, 2003). The only other quantitative studies of deep water foraminifera (.100 m) around New Zealand are in the unpublished theses of Thompson (1975) and Hoskins (1978), both east of northern New Zealand. Several early taxonomic studies (Brady, 1884; Cushman, 1919; Heron-Allen and Earland, 1922) described faunas from samples within the present study area. Recent studies have documented the ecological distribution of benthic foraminifera in shallow water (,100 m) around the fringes of the study area (Hayward, 1982; Hayward and others, 1984; 1997; Hayward and Grace, 1981; Hayward and Grenfell, 1994; Reid and Hayward, 1997). LOCATION AND PHYSIOGRAPHIC SETTING The study region of ,180,000 sq. km lies off the east coast of the northern half of the North Island of New Zealand (Fig. 1) at latitudes 33.5–37.5uS and longtitudes 173–178uE. Samples were chosen to provide general coverage of the area with transects from the shelf down the continental slope and out to abyssal depths of 3800 m. The area studied extends from the Three Kings Ridge in the northwest, out into the South Fiji Basin to the north, and is bounded by the Colville Ridge and Havre Trough to the southeast and coast of the North Island to the west (Fig. 1). It includes a broad continental shelf, a narrow continental slope, the bathyal Northland Plateau and the flat floor of the South Fiji Basin (abyssal). Bathymetric terminology in this paper follows Kennett (1982) for shelf depths and van Morkhoven and others (1986) for bathyal and abyssal depths: mid shelf 5 30–100 m, outer shelf 5 100–200 m, upper bathyal 5 200– 600 m, mid-bathyal 5 600–1000 m, lower bathyal 5 1000– 2000 m, abyssal 5 2000–5000 m. SEAFLOOR SEDIMENT Pelagic carbonate sandy mud (.75% mud) covers the floor of the South Fiji Basin and most of the Northland 1 Geomarine Research, 49 Swainston Rd, St Johns, Auckland, New Zealand. E-mail: b.hayward@geomarine.org.nz 2 National Institute of Water and Atmosphere, P.O. Box 14 901, Kilbirnie, Wellington, New Zealand. Journal of Foraminiferal Research, v. 36, no. 4, p. 332–354, October 2006 332