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Different models indicate a marked increase in ice-volume in Antarctica (approx. 50%) during the late Messinian, that culminate in large glaciations (TG22, 20 and 18) when the Antarctic ice-sheet was probably larger than today. Until recently there were only limited late Messinian records that could be used to investigate the influence of these Antarctic ice-sheet expansions on paleoclimatic and palaeoceanographic variability. A key location where this influence is poorly known is the boundary between the Indian and the Atlantic Ocean, which is an integral inter-ocean link in the global thermohaline circulation. In 2016 the International Ocean Discovery Program (IODP) Expedition 361 (“SAFARI”) recovered a complete highresolution Messinian sedimentary succession at 3 drilling locations on the southeast African margin and in the Indian-Atlantic Ocean gateway. Here we present results from Site U1475 (Agulhas Plateau), a location proximal to the entrance of North Atlantic Deep Water (NADW) to the Southern Ocean and South Indian Ocean. The site is located over sedimentary drift deposits in 2669 m water depth and comprised of carbonate-rich sediments (74 – 85 wt % CaCO3). Based on high-resolution data sets of density, velocity, natural gamma radiation, X-ray fluorescence (XRF) core-scanning data, colour reflectance, grain size distributions and planktonic foraminifera oxygen isotope data, we reconstruct major circulation changes in bottom current as well variations in orbitally controlled climate variability that can be linked to the Antarctic ice-sheet expansions.

Next to atmospheric CO2 concentrations, iceproximal oceanographic conditions are a critical factor for

Australasian IODP Regional Planing Workshop (2017. Sidney), Instituto Geológico y Minero de España, España, Instituto Andaluz de Ciencias de la Tierra, Consejo Superior de Investigaciones Científicas, España, Istituto Nazionale di Oceanografia e Geofisica Sperimentale, Italia, San Diego State University, Estados Unidos

Palmer Deep sediment cores are used to produce the first high-resolution, continuous late Pleistocene to Holocene time-series from the Antarctic marine system. The sedimentary record is dated using accelerator mass spectrometer radiocarbon methods on acid insoluble organic matter and foraminiferal calcite. Fifty-four radiocarbon analyses are utilized in the dating which provides a calibrated timescale back to 13 ka BP. Reliability of resultant ages on organic matter is assured because duplicates produce a standard deviation from the surface age of less than laboratory error (i.e., ±50 years). In addition, surface organic matter ages at the site are in excellent agreement with living calcite ages at the accepted reservoir age of 1260 years for the Antarctic Peninsula. Spectral analyses of the magnetic susceptibility record against the age model reveal unusually strong periodicity in the 400,–200 and 50-70 year frequency bands, similar to other high-resolution records from the Holocene but, so far, unique for the circum-Antarctic. Here we show that comparison to icecore records of specific climatic events (e.g., the ’Little Ice Age‘, Neoglacial, Hypsithermal, and the Bølling/Allerød to Younger Dryas transition) provides improved focus upon the relative timing of atmosphere/ocean changes between the northern anid southern high latitudes.

Warm intervals within the Pliocene epoch (5.33–2.58 million years ago) were characterized by global temperatures comparable to those predicted for the end of this century1 and atmospheric CO2 concentrations similar to today2, 3, 4. Estimates for global sea level highstands during these times5 imply possible retreat of the East Antarctic ice sheet, but ice-proximal evidence from the Antarctic margin is scarce. Here we present new data from Pliocene marine sediments recovered offshore of Adélie Land, East Antarctica, that reveal dynamic behaviour of the East Antarctic ice sheet in the vicinity of the low-lying Wilkes Subglacial Basin during times of past climatic warmth. Sedimentary sequences deposited between 5.3 and 3.3 million years ago indicate increases in Southern Ocean surface water productivity, associated with elevated circum-Antarctic temperatures. The geochemical provenance of detrital material deposited during these warm intervals suggests active erosion of continental bedrock from within the Wilkes Subglacial Basin, an area today buried beneath the East Antarctic ice sheet. We interpret this erosion to be associated with retreat of the ice sheet margin several hundreds of kilometres inland and conclude that the East Antarctic ice sheet was sensitive to climatic warmth during the Pliocene.

Antarctic sea ice impacts on the ocean-atmosphere heat and gas fluxes, the formation of deep and intermediate waters, the nutrient distribution and primary productivity, the so-called ‘biological carbon pump’, one of the most active in the global ocean. In this study, we explore the link between sea ice dynamic, biological production and nutrient cycling during the late Holocene (the last 2,000 yrs) in the Adélie Basin, East Antarctica, from the well-dated sediments of the Ocean Drilling Program (ODP) Site U1357. This archive, composed from ~32 meters of seasonal to annual laminated diatomaceous sequences, allows reconstructions at an unprecedented time resolution (5-10 yrs). Our study combines records of diatom census counts and diatom-specific biomarkers (a ratio (D/T) of di- and tri-unsaturated Highly Branched Isoprenoid lipids (HBI)) as indicators of sea ice and biological production changes, XRF data as markers for terrigenous inputs and bulk nitrogen isotopes (d15N) and d15N on chlorins as proxies for reconstructing nitrogen cycle. The diatom and HBI records reveal five distinct periods. From 0 to 350 yrs AD, decreasing occurrences of sea ice-related diatom species (e.g. Fragilariopsis curta + F. cylindrus) together with low D/T values and increasing open ocean diatom species (large centrics, Chaetoceros Resting Spores (CRS)) document a progressive decline of sea ice presence during the year (>9 months per year) with spring melting occurring earlier in the year and autumn sea ice formation appearing later. In contrast, between 350 and 750 yrs AD, high production of open ocean diatom species and low low D/T values and sea ice related species indicate a short duration of sea ice cover (~10 months per year) is illustrated by a pronounced increase of sea ice-associated diatom species and high D/T values. Between ~1400 and 1850 yrs AD, seasonal sea ice strongly declines (

During the middle and late Eocene (∼ 48-34 Myr ago), the Earth's climate cooled and an ice sheet built up on Antarctica. The stepwise expansion of ice on Antarctica induced crustal deformation and gravitational perturbations around the continent. Close to the ice sheet, sea level rose despite an overall reduction in the mass of the ocean caused by the transfer of water to the ice sheet. Here we identify the crustal response to ice-sheet growth by forcing a glacial-hydro isostatic adjustment model with an Antarctic ice-sheet model. We find that the shelf areas around East Antarctica first shoaled as upper mantle material upwelled and a peripheral forebulge developed. The inner shelf subsequently subsided as lithosphere flexure extended outwards from the ice-sheet margins. Consequently the coasts experienced a progressive relative sea-level rise. Our analysis of sediment cores from the vicinity of the Antarctic ice sheet are in agreement with the spatial patterns of relative sea-level change indicated by our simulations. Our results are consistent with the suggestion that near-field processes such as local sea-level change influence the equilibrium state obtained by an ice-sheet grounding line.

第3回極域科学シンポジウム 横断セッション「海・陸・氷床から探る後期新生代の南極寒冷圏環境変動」11月27日（火） 国立国語研究所 ２階講堂

The Integrated Ocean Drilling Program Expedition 318 to the Wilkes Land margin of Antarctica recovered a sedimentary succession ranging in age from lower Eocene to the Holocene. Excellent stratigraphic control is key to understanding the timing of paleoceanographic events through critical climate intervals. Drill sites recovered the lower and middle Eocene, nearly the entire Oligocene, the Miocene from about 17 Ma, the entire Pliocene and much of the Pleistocene. The paleomagnetic properties are generally suitable for magnetostratigraphic interpretation, with well-behaved demagnetization diagrams, uniform distribution of declinations, and a clear separation into two inclination modes. Although the sequences were discontinuously recovered with many gaps due to coring, and there are hiatuses from sedimentary and tectonic processes, the magnetostratigraphic patterns are in general readily interpretable. Our interpretations are integrated with the diatom, radiolarian, calcareous nannofossils and dinoflagellate cyst (dinocyst) biostratigraphy. The magnetostratigraphy significantly improves the resolution of the chronostratigraphy, particularly in intervals with poor biostratigraphic control. However, Southern Ocean records with reliable magnetostratigraphies are notably scarce, and the data reported here provide an opportunity for improved calibration of the biostratigraphic records. In particular, we provide a rare magnetostratigraphic calibration for dinocyst biostratigraphy in the Paleogene and a substantially improved diatom calibration for the Pliocene. This paper presents the stratigraphic framework for future paleoceanographic proxy records which are being developed for the Wilkes Land margin cores. It further provides tight constraints on the duration of regional hiatuses inferred from seismic surveys of the region.

IODP Leg 318 recovered sediment cores from the Antarctic Wilkes Land Margin dating back into the early Eocene, the warmest time interval of the Cenozoic era. These cores provide a first insight into environmental dynamics of an ice-free Antarctica. The onboard and postcruise studies have resulted in a well-constrained age model, and the multidisciplinary biogeochemical and micropaleontological data allows detailed paleoecological interpretations. Here we present the results of a high-resolution dinocyst study on the Eocene recovered at IODP Site U1356. We evaluate relative sea level and productivity fluctuations and put the record of dinocyst endemism in the context of the regional tectonic evolution of the Australo-Antarctic continental breakup

IODP Expedition 318 drilled several sites on the Wilkes Land margin of East Antarctica in Jan.–Feb. 2010. The principle objective of the cruise was to obtain a better understanding of the Cenozoic cryospheric evolution of Antarctica, in conjunction with the dating of major regional seismic unconformities WL-U3 thru U8. Unconformity WL-U3 was suggested to be related to the inception of Antarctic glaciation during the Eocene-Oligocene Transition (~34 Ma). Changes in biotic assemblages distinctly denote an ecological transition from warm, Eocene ice-free ‘greenhouse’ conditions to colder, highly productive, Oligocene ‘icehouse’ conditions, more akin to the modern shelf environment of Antarctica. Preliminary dinoflagellate, and TEX86 results will be discussed. In addition, our paleoecological interpretations provide constraints for on-going geophysical studies aimed at modelling changes in relative sea level in response to East Antarctic glaciation and ice-sheet arrival at the Wilkes Land margin

During IODP Expedition 318 (January–March 2010, Wellington to Hobart), ~2000 m of Eocene to Quaternary sediments were recovered from the Antarctic (Wilkes Land) margin, documenting the evolution of this margin from an ice-free “greenhouse Antarctica” to the present-day icehouse environment. Based on a bio- and magnetostratigraphically dated, late early to early middle Eocene record recovered at Site U1356, we have carried out palynological and organic geochemical analyses in order to gain insights into the terrestrial environmental dynamics on Antarctica under peak greenhouse conditions. Our preliminary palynological indicate that the vegetation along the Wilkes Land margin was highly diverse and contains thermophilous elements that today are widely distributed in the subtropics; along with our organic geochemical results, their presence suggests warm conditions at least in the coastal lowlands of the Wilkes Land margin. At the same time, taxa that today are typical for cool temperate settings are consistently present

Three case studies are used to exemplify the wide variety of controlling factors that combine to influence the development of modern turbidite systems, and how these vary with location and time. For example, Cascadia Basin in the Pacific Ocean off western North America, which is underlain by the Cascadia Subduction Zone, exhibits the dominant tectonic control of earthquake triggering for turbidity currents, the increased sediment-supply effects of the Mt. Mazama catastrophic volcanic eruption in 7626 yr B.P., the glacial climatic and sea-level lowstand control on rapid turbidite-system growth rates, and the recent anthropogenic control that reduces sediment supply rates. Lake Baikal in Russia shows how the rift-basin tectonic setting controls the number and type of sediment input points, the amount of sediment supply, and the consequent types of turbidite systems developed along different margins of the Baikal basin. Pleistocene glacial climatic changes, without changes in lake base level, causes increased sediment input and the rapid growth rate of Baikal turbidite systems that is three to five times greater than that during the Holocene interglacial climate. The Ebro turbidite systems in the northwest Mediterranean Sea exhibit control of system types by the Messinian salinity-crisis lowstand, of channel locations by oceanographic current patterns, and of sediment-supply increase by glacial climatic changes as well as recent decrease by anthropogenic changes.Both active-margin and passive-margin settings have some common controls such as climatic and sea-level changes, and develop similar types of turbidite systems such as base-of-slope aprons, submarine fans, and deep-sea or axial channels. Each margin also has specific local controlling factors, for example the volcanic events in Cascadia Basin, glacial climatic without erosional base-level control in Lake Baikal, and the Messinian extreme lowstand in the Mediterranean Sea. Comparison of modern turbidite systems points out new insights on external controls such as importance of: (1) earthquakes for triggering turbidity currents on active tectonic margins, (2) equal or greater Pleistocene climatic control compared to lowered base level for sediment supply, (3) direct glacial sediment input that results in doubled proximal channel size, (4) greatly reduced deposition rates in drained compared to ponded turbidite basins, (5) importance of ocean currents on location of turbidite systems and channel development, and (6) anthropogenic effects from river damming during the last century that sometimes reduces present sediment supply to turbidite systems by orders of magnitude.

Martech 2007 International Workshop on Marine Technology, 15-16 november 2007, Vilanova i la Geltrú, Spain.-- 2 pages, 1 figure, The authors acknowledge the support of the MCYT Acción Especial HITS (REN2000-2150-E), PRIME-PICABIA cruise to access to CALYPSO European Large Scale Facility (HPRI-CT2001-00120), EUROMARGINS program of the European Science Foundation SWIM project (01-LEG-EMA09F and REN2002-11234E-MAR), Spanish National Projects IMPULS (REN2003-05996MAR) and EVENT (CGL2006-12861-C02-02), and the EU project NEAREST (ref. 37110)

The Southwest Iberian Margin is caracterized by an intense and diffuse seismic activity due to the convergence between Eurasian and African plates...