Atsuhito Ennyu

Yokohama Institute of Ocean Sciences

Downcore oxygen and carbon stable isotope records of planktonic and benthic foraminifers and fine-fraction carbonate from the southern high latitudes provide critical paleohydrographic constraints on the evolution of the Southern Ocean climate. In particular, the potential effects of an intensified Antarctic Circumpolar Current on the thermal isola...

In this data report, we present carbon stable isotope (δ 13 C) analy- ses of dissolved inorganic carbon (DIC) in interstitial water sam- ples from Integrated Ocean Drilling Program Expedition 303 Sites U1305, U1306, and U1307 on the Eirik Drift in the Labrador Sea. A total of 84 interstitial water samples extracted on board were analyzed postcruise...

The IODP Expeditions 303 and 306 drilling sites were chosen for two reasons: (1) to capture Miocene-Quaternary millennial-scale climate variability in sensitive regions at the mouth of the Labrador Sea and in the North Atlantic ice-rafted debris (IRD) belt (Ruddiman et al., 1977), and (2) to provide the sedimentary and paleomagnetic attributes, inc...

Paleoclimate proxy records from the southern high latitudes can provide key constraints on the possible role of ocean circulation as a cause of the middle Miocene global cooling event and the major development of the Antarctic cryosphere. Here we present oxygen and carbon stable isotope records of multispecific planktic and benthic foraminifera and...

The mudstone of the Yezo Group exposed in Central Hokkaido yields abundant microfossils of calcareous nannofossils, foraminifers, radiolarians and dinoflagellates. Benthic foraminifers consisting of both agglutinated and calcareous species occur abundantly and consistently throughout the sequence, while specimens of planktonic foraminifers are gene...

The middle Miocene encompasses one of the major steps in a global cooling trend towards the permanent establishment of east Antarctica ice sheet (EAIS), as inferred from the worldwide ca. 1\permil increase in benthic foraminiferal delta18O. It has been suggested that an intensified Antarctic Circumpolar Current (ACC) prompted the mid-Miocene coolin...

We have measured stable isotopic compositions of Miocene pelagic fine-fraction (<63 μm) carbonates from oligotrophic deep-sea sites in the Pacific and Atlantic oceans and compared them with those of coexisting foraminifers to test their utility as near sea-surface indicators. Fine-fraction carbonates (primarily polyspecific nannofossils) and surfac...

One of the great stories of geoscience is how Gondwana broke up and the other southern continents drifted northward from Antarctica, which led to major changes in global climate.The recent drilling of Ocean Drilling Project (ODP) Leg 189 addressed in detail what happened as Australia drifted away from Antarctica and the Tasmanian Gateway opened. Th...

A diagnostic model of the mean annual cycles of oxygen, dissolved inorganic carbon (DIC) and nitrate below the mixed layer at the Bermuda Atlantic Time-Series Study (BATS) site is presented and used to estimate organic matter remineralization in the seasonal thermocline. The model includes lateral and vertical advection as well as vertical diffusio...

ODP Leg 189 was designed to test the hypothesis that opening of the Tasmanian Seaway and initiation of circumpolar circulation contributed to the thermal isolation of Antarctica, leading to the development of initial ice-sheet and oceanic thermohaline circulation. The clay assemblages of the Tasmanian region contain the traces of two tectonic stage...

ResumeLe but du leg ODP 189 etait de tester l'hypothese selon laquelle l'ouverture oceanique au sud de la Tasmanie, isolant le continent antarctique au-dela des courants circumpolaires, serait a l'origine du developpement des glaces et des eaux antarctiques, moteurs importants de la circulation thermohaline actuelle. Les argiles terrigenes du secte...

Palaeogene ocean opening south of Tasmania, and palaeoceanographic implications: preliminary results of clay mineral analyses (ODP Leg 189). ODP Leg 189 was designed to test the hypothesis that opening of the Tasmanian Seaway and initiation of circumpolar circulation contributed to the thermal isolation of Antarctica, leading to the development of...

The focus of the expedition was to better document the climatic and oceanographic consequences of the opening of the gateway during the transition from warm Eocene climates to cool Oligocene climates. The relatively shallow region off Tasmania (Exon and Crawford, 1997) is one of the few places where well-preserved and almost complete marine Cenozoi...