(Appendix) Analysis of benthic foraminifera from ODP Leg 181 and DSDP Leg 90

Canonical correspondence analysis indicates that the distribution of Neogene benthic foraminiferal faunas (>63 µm) in seven DSDP and ODP sites (500-4500 m water depth) east of New Zealand (38-51°S, 170°E-170°W) is most strongly influenced by depth (water mass stratification), and secondly by age (palaeoceanographic changes influencing faunal composition and biotic evolution). Stratigraphic faunal changes are interpretted in terms of the pulsed sequential development of southern, and later northern, polar glaciation and consequent cooling of bottom waters, increased vertical and lateral stratification of ocean water masses, and increased overall and seasonal surface water productivity. Oligocene initiation of the Antarctic Circumpolar Current and Deep Western Boundary Current (DWBC), flowing northwards past New Zealand, resulted in extensive hiatuses throughout the Southwest Pacific, some extending through into the Miocene. Planktic foraminiferal fragmentation index values indicate that carbonate dissolution was significant at abyssal depths throughout most of the Neogene, peaking at upper abyssal depths in the late Miocene (11-7 Ma), with the lysocline progressively deepened thereafter. Miocene abyssal faunas are dominated by Globocassidulina subglobosa and Oridorsalis umbonatus, with increasing Epistominella exigua after 16 Ma at upper abyssal depths. Peak abundances of Epistominella umbonifera indicate increased input of cold Southern Component Water to the DWBC at 7-6 Ma. Faunal association changes imply establishment of the modern Oxygen Minimum Zone (upper Circumpolar Deep Water) in the latest Miocene. Significant latitudinal differences between the benthic foraminiferal faunas at lower bathyal depths indicate the existence of an oceanic front along the Chatham Rise (location of present Subtropical Front), since the early late Miocene at least, with more pulsed productivity (higher E. exigua) along the south side. Modern Antarctic Intermediate Water faunal associations were established north of the Chatham Rise at 10-9 Ma, and south of it at 3-1.5 Ma. Middle-upper bathyal faunas on the Campbell Plateau are dominated by reticulate bolivinids during the early and middle Miocene, indicative of sustained productivity above relatively sluggish, suboxic bottom waters. Faunal changes and hiatuses indicate increased current vigour over the Campbell Plateau from the latest Miocene on. Surface water productivity (food supply) appears to have increased in three steps (at times of enhanced global cooling) marked by substantially increased relative abundance of: (1) Abditodentrix pseudothalmanni, Alabaminella weddellensis, Cassidulina norvangi (16-15 Ma, increased pulsed productivity); (2) Bulimina marginata f. aculeata, Nonionella auris, Trifarina angulosa, Uvigerina peregrina (3-1.5 Ma, increased overall productivity); and (3) Cassidulina carinata (1-0.5 Ma, increased overall productivity). Three intervals of deep-sea benthic foraminiferal taxonomic turnover are recognised (16-15, 11.5-10, 2-0.5 Ma) corresponding to intervals of enhanced global cooling and possible productivity changes. The late Pliocene-middle Pleistocene extinction, associated with increasing Northern Hemisphere glaciation, culminating in the middle Pleistocene climatic transition, was more significant in the study area than the earlier Neogene turnovers.

Late Pleistocene oxygen isotope record of biognic silica

We determined the isotopic composition of oxygen in marine diatoms in eight deep-sea cores recovered from the Atlantic sector of the Southern Ocean. The analytical reproducibility and core-to-core consistency of the isotopic signal suggests that diatom delta18O can be used as a new paleocenographic tool to reconstruct past variations in surface water characteristics and to generate 18O -isotope-based stratigraphy for the Southern Ocean. The data indicate that diatom delta18O reflects sea surface temperature and seawater isotopic composition and that diatoms retain their isotopic signal on timescales of a least 430 ka. The delta18O analyses of different diatom assemblages reveal that the isotopic signal is free of species effects and that the common Antarctic species have the same water-opal fractionation. The transition from the last glacial maximum (LGM) to the Holocene is fully recorded in high sedimentation rate cores. An 18O enrichment during the LGM, a post-LGM meltwater spike and an input of meltwater during the late Holocene are the main isotopic features observed in down core records. The origin of this meltwater was very likely melting icebergs and/or continental ice or by melting sea ice that had accumulated snow. The most pronounced meltwater effects are recorded in cores that are associated with the Weddel gyre. Our results provide the basis for extending isotope studies to oceanic regions devoid of carbonate; further, isotopic stratigraphies may be constructed for records and regions where they were previously not possible.