Mid-Pleistocene benthic foraminiferal record in the Southwest Pacific

Benthic foraminiferal faunas from three bathyal sequences provide a proxy record of oceanographic changes through the mid-Pleistocene transition (MPT) on either side of the Subtropical Front (STF), east of New Zealand. Canonical correspondence analyses show that factors related to water depth, latitude and climate cycles were more significant than oceanographic factors in determining changes in faunal assemblage composition over the last 1 Ma. Even so, mid-Pleistocene faunal changes are recognizable and can be linked to inferred palaeoceanographic causes. North of the largely stationary STF the faunas were less variable than to the south, perhaps reflecting the less extreme glacial-interglacial fluctuations in the overlying Subtropical Surface Water. Prior to Marine Isotope Stage (MIS) 21 and after MIS 15, the northern faunas had fairly constant composition, but during most of the MPT faunal composition fluctuated in response to climate-related food-supply variations. Faunal changes through the MPT suggest increasing food supply and decreasing dissolved bottom oxygen. South of the STF, beneath Subantarctic Surface Water, mid-Pleistocene faunas exhibited strong glacial-interglacial fluctuations, inferred to be due to higher interglacial nutrient supply and lower oxygen levels. The most dramatic faunal change in the south occurred at the end of the MPT (MIS 17- 12). with an acme of Abditodentrix pseudothalmanni, possibly reflecting higher carbon flux and lower bottom oxygen. This study suggests that the mid-Pleistocene decline and extinction of a group of elongate, cylindrical deep-sea foraminifera may have been related to decreased bottom oxygen concentrations as aresult of slower deep-water currents.

The CMCC Eddy-permitting Global Ocean Physical Reanalysis (C-GLORS v5, 1980-2014), links to NetCDF files

The CMCC Global Ocean Physical Reanalysis System (C-GLORS) is used to simulate the state of the ocean in the last decades. It consists of a variational data assimilation system (OceanVar), capable of assimilating all in-situ observations along with altimetry data, and a forecast step performed by the ocean model NEMO coupled with the LIM2 sea-ice model. KEY STRENGTHS: - Data are available for a large number of ocean parameters - An extensive validation has been conducted and is freely available - The reanalysis is performed at high resolution (1/4 degree) and spans the last 30 years KEY LIMITATIONS: - Quality may be discontinuos and depend on observation coverage - Uncertainty estimates are simply derived through verification skill scores

Quaternary isotope stratigraphy of DSDP Hole 90-593 from the Challenegr Plateau, South Tasman Sea

A moderate-resolution isotope stratigraphy (with an average of one sample per 17,500 yr.) derived from the benthic foraminifer Uvigerina (or Cibicides), the planktonic foraminifer Globigerina bulloides, and calcareous nannofossil concentrates is presented for the entire Quaternary (and latest Pliocene) section of mid-upper bathyal calcareous oozes from DSDP Site 593, western Challenger Plateau, south Tasman Sea. Superimposed on a trend of gradually increasing average delta18O values through the Pleistocene, reflecting the progressive buildup of polar ice sheets, is a record of highfrequency but generally low amplitude (0.5-1?) isotope fluctuations in the early Quaternary (1.9-1.0 m.y.), followed by a greatly increased intensity (1.5-2.0 ?) of glacial-interglacial fluctuations during the late Quaternary (< 1.0 m.y.). The standard late Quaternary isotope stages 1 to 24 are mainly resolvable. Significant excursions in both delta18O and delta13C values at various times during the Quaternary are suggested to be due to periodic, fundamental changes in ocean circulation properties over the plateau. For example, intensified upwelling of Antarctic Intermediate Waters during several glacial periods is indicated by the convergence of benthic and planktonic foraminiferal delta18O data, and productivity variations may account for certain delta13C spikes in the record. With increasingly higher resolution analysis this core will provide a useful Quaternary isotope reference section for southern temperate waters in the southwest Pacific, centered on New Zealand.

Late Quaternary benthic foraminiferal record of the Bounty Trough, east of New Zealand

The Bounty Trough, east of New Zealand, lies along the southeastern edge of the present-day Subtropical Front (STF), and is a major conduit via the Bounty Channel, for terrigenous sediment supply from the uplifted Southern Alps to the abyssal Bounty Fan. Census data on 65 benthic foraminiferal faunas (>63 µm) from upper bathyal (ODP 1119), lower bathyal (DSDP 594) and abyssal (ODP 1122) sequences, test and refine existing models for the paleoceanographic and sedimentary history of the trough through the last 150 ka (marine isotope stages, MIS 6-1). Cluster analysis allows recognition of six species groups, whose distribution patterns coincide with bathymetry, the climate cycles and displaced turbidite beds. Detrended canonical correspondence analysis and comparisons with modern faunal patterns suggest that the groups are most strongly influenced by food supply (organic carbon flux), and to a lesser extent by bottom water oxygen and factors relating to sediment type. Major faunal changes at upper bathyal depths (1119) probably resulted from cycles of counter-intuitive seaward-landward migrations of the Southland Front (SF) (north-south sector of the STF). Benthic foraminiferal changes suggest that lower nutrient, cool Subantarctic Surface Water (SAW) was overhead in warm intervals, and higher nutrient-bearing, warm neritic Subtropical Surface Water (STW) was overhead in cold intervals. At lower bathyal depths (594), foraminiferal changes indicate increased glacial productivity and lowered bottom oxygen, attributed to increased upwelling and inflow of cold, nutrient-rich, Antarctic Intermediate Water (AAIW) and shallowing of the oxygen-minimum zone (upper Circum Polar Deep Water, CPDW). The observed cyclical benthic foraminiferal changes are not a result of associations migrating up and down the slope, as glacial faunas (dominated by Globocassidulina canalisuturata and Eilohedra levicula at upper and lower bathyal depths, respectively) are markedly different from those currently living in the Bounty Trough. On the abyssal Bounty Fan (1122), faunal changes correlate most strongly with grain size, and are attributed to varying amounts of mixing of displaced and in-situ faunas. Most of the displaced foraminifera in turbiditic sand beds are sourced from mid-outer shelf depths at the head of the Bounty Channel. Turbidity currents were more prevalent during, but not restricted to, glacial intervals.

Quaternary surface-water stable isotope signal from calcareous nannofossils at DSDP Site 90-593, South Tasman Sea

Oxygen isotope values from calcareous nannofossils in four cores spanning the Quaternary from DSDP Site 593 in Tasman Sea are compared with the delta18O signal of planktonic and benthic foraminifers from the same samples. The classic mid-late Quaternary isotope stages are exhibited with stage 12 particularly well developed. When delta18O values of nannofossils are adjusted for coccolithophore vital effects they indicate larger (by 1-6°C) surface to bottom paleotemperature gradients and greater (by 1-3°C) changes in mean sea-surface temperature between full glacial and interglacial conditions than do delta18O values from planktonic foraminifers. Along with the foraminifers, the nannofossils record a bimodal distribution of delta18O between the early and mid-late Quaternary, indicating a significant change in global ice budget. The delta13C of nannofossils also shows a bimodal distribution, but is opposite to that for the foraminifers. Nannofossil delta18O values record a shift of c. -0.8? at isotope stage 8 corresponding to a major reduction in abundance of the previously dominant gephyrocapsids. A shift in delta13C of c. -1.5? also occurs at stage 8, and a shift in delta13C of c. +1.2? at around stage 14. The delta18O shift in nannofossils is at least a Pacific-wide phenomenon; the delta13C shifts are possibly global. The delta13C signal of nannofossils exhibits an antipathetic relationship to that of benthic foraminifers back to isotope stage 18 but no significant correlation beyond this level to the base of the Quaternary. This is interpreted as reflecting local productivity dominating global influences on delta13C since stage 18 at DSDP Site 593. The difference between nannofossil and benthic foraminifer delta13C signals (Delta13C) tends to be maximum during glacial stages and minimum during interglacials throughout the section, showing a strong correlation with the nannofossil delta180 signal. The increased partitioning of 13C between surface and bottom waters during the glacial periods may indicate heightened productivity in surface waters in the southern Tasman Sea at these times.