Factors influencing the distribution patterns of Recent deep-sea benthic foraminifera, east of New Zealand, Southwest Pacific Ocean

Abstract

This study investigates which combination of environmental factors most strongly influences the distribution patterns of benthic foraminferal tests (>0.63 μm) in a region bisected by the Subtropical Front, east of New Zealand. Seafloor sample sites extend from outer shelf (90 m) to abyssal (4700 m) depths, across substrates ranging from biogenic/terrigenous gravelly sand to hemipelagic mud, and occur under the influence of Antarctic intermediate water (AAIW) and circumpolar deep waters as well as receiving detritus from both Subtropical and Subantarctic surface water masses. Elevated values of the planktic foraminiferal fragmentation index and reworked small Paleogene planktic foraminifera at outer shelf and bathyal depths coincide with areas of strong bottom currents. Q-mode cluster analysis on the census counts of 398 benthic species clusters the 66 samples into three large groups (shallow, bathyal, abyssal), and at a lower level 10 mappable associations are recognised. A combination of canonical correspondence analysis and a correlation coefficient matrix was used to relate the faunal data to a set of measured environmental proxies. These analyses show that factors that have a relationship with depth are the most significant in determining foraminiferal distribution. The principal environmental factors which appear to most strongly influence this benthic foraminiferal distribution are: dissolved oxygen content in bottom waters; sustainability of organic carbon flux rates; seasonality of food supply; lateral advection of water masses; bottom water carbonate corrosiveness; energetic state at the benthic boundary layer; grain-size composition of substrate; salinity and temperature of the bottom waters. Shallow water associations (90–1250 m), dominated by Cassidulina carinata and Trifarina angulosa, occur within coarse substrates under well-oxygenated, high energy regimes and sustained food input. The occurrence of the bathyal associations (230–2840 m), dominated by C. carinata, Alabaminella weddellensis and Abditodentrix pseudothalmanni, closely mirrors the distribution of AAIW within a region of variable food supply. The sustainability of food supply combined with bottom water type and associated ventilation and dissolution strongly influence the composition of abyssal associations (1200–4700 m), mostly dominated by Epistominella exigua and A. weddellensis.