- © 2013 Cushman Foundation for Foraminiferal Research
Census counts (>63 μm) of 461 species in 361 samples are used as the basis for recognizing and mapping associations of deep-sea benthic foraminifera (50–5000-m depth) around New Zealand, southwest Pacific (28–60°S, 155°E–170°W). Fourteen faunal associations are identified by cluster analysis with five of these subdivided into 20 subassociations. The deepest associations, dominated by Nuttallides spp., Globocassidulina subglobosa, and diverse agglutinated species, occur at middle–lower abyssal depths (>3600 m) right around New Zealand, where they have been impacted by differing levels of taphonomic modifications. Two large associations are widespread throughout the region: one (Alabaminella weddellensis-Epistominella exigua) at lower bathyal–middle abyssal depths (~1500–4000 m) and the other (Cassidulina carinata-A. weddellensis-Abditodentrix pseudothalmanni) mostly at mid-bathyal–upper abyssal depths (~500–3000 m). Two deep-water associations occur on current-swept submarine highs: one (Trifarina angulosa-Ehrenbergina glabra) at lower bathyal–upper abyssal depths (1000–2400 m) along the southeastern margin of the Camp-bell and Bounty plateaux and the other (Bolivina robusta-Globocassidulina canalisuturata) at mid–upper bathyal depths in coarse sediment east and southeast of New Zealand. Two large associations occur at mid-shelf–uppermost-bathyal depths (50–400 m): one (Cassidulina carinata-Bulimina marginata-Gavelinopsis praegeri) around the coast beneath warm Subtropical Water and the other (C. carinata-T. angulosa-G. praegeri) further south beneath the cooler Subtropical Front and Subantarctic Water.
A major reason for this study was to understand the environmental drivers of foraminiferal faunal distribution in this region to assist in paleoenvironmental interpretations of fossil faunas which have a significant regional character. Canonical correspondence analysis indicates that the distribution of bathyal and abyssal associations is more strongly influenced by depth-related variables, while shallower associations are influenced by latitude-related differences in surface-water characteristics. Environmental variables that influence faunal patterns at abyssal and bathyal depths appear to be, in decreasing order: food supply (organic-carbon flux, chlorophyll-a proxies), bottom-oxygen concentration, and carbonate corrosiveness (Fragmentation Index, planktic % proxies). Latitude-related variables driving mid-shelf–uppermost bathyal faunal patterns are water temperature, followed by primary productivity (phosphate and chlorophyll-a proxies). Environmental variables related to bottom-current strength appear to drive the faunal composition of three associations at shelf and bathyal depths. Cluster analysis enables the recognition of 22 anomalously deep faunas that are inferred to have a significant displaced content. There are no significant diversity trends correlated with depth, but species diversity decreases with increasing latitude at all depths.