Microfossil abundances and stable isotope composition of foraminifera from DSDP Hole 90-594 off southeastern New Zealand

High-resolution textural, carbonate, microfossil, and oxygen (delta18O) and carbon (delta13C) stable isotopic analyses are presented for the late Quaternary (isotopic stages 1 to 6) interval of a core at Deep Sea Drilling Project site 594, situated just south of the present Subtropical Convergence in northernmost Subantarctic surface waters on the southern flank of Chatham Rise in the southwest Pacific. Downcore alternations of pelagic and hemipelagic oozes correspond to interglacial and glacial episodes, respectively. Interglacial oozes contain a northern Subantarctic assemblage of planktonic foraminifera, with rare cool subtropical species, while glacial oozes are characterized by species typical of southern(most) Subantarctic waters and include radiolaria with affinity for Antarctic waters. The planktonic delta18O record for the site supports a 3°-6°C temperature change in near-surface waters between interglacial and glacial stages and indicates that during stage 5e, the near-surface waters were about 1°C warmer than at present. A pronounced cooling during stage 5d matches that of the Vostok ice core deltaD record, and negative excursions at the end of stages 2 and 6 support a southern latitude warming preceding northern hemisphere deglaciation. Benthic foraminifera typical of cold intermediate to deep waters can increase dramatically in abundance in the hemipelagic ooze intervals when delta18O results suggest a temperature drop in glacial stage bottom waters of 2°-4°C, possibly a result of upward displacement of Antarctic Intermediate Water by Circumpolar Deep Water at the site. The foraminiferal delta13C records support a reduced influence of North Atlantic Deep Water in the southwest Pacific during glacial stages, when nutrient enhancement occurred in both bottom and surface waters. Despite the pronounced changes between interglacial and glacial conditions inferred at site 594, contributed to by a substantial northward shift by at least 5° of latitude in the position of the Antarctic Convergence south of New Zealand during glacial episodes, we conclude that the Subtropical Convergence remained locked to Chatham Rise (approximately 44°S) throughout stages 1 to 6. Major compression of the intervening belt of Subantarctic water during glacial episodes, and the associated very steep thermal gradients and intensified atmospheric and oceanic circulation patterns that developed in this part of the southwest Pacific, account for the harsh, frigid environment reported for on-land southern New Zealand at these times