Geochemical and palynological measurements from the ODP Leg 189 at Site 1172 on the East Tasman Plateau

A brief (~150 kyr) period of widespread global average surface warming marks the transition between the Paleocene and Eocene epochs, ~56 million years ago. This so-called "Paleocene-Eocene thermal maximum" (PETM) is associated with the massive injection of 13C-depleted carbon, reflected in a negative carbon isotope excursion (CIE). Biotic responses include a global abundance peak (acme) of the subtropical dinoflagellate Apectodinium. Here we identify the PETM in a marine sedimentary sequence deposited on the East Tasman Plateau at Ocean Drilling Program (ODP) Site 1172 and show, based on the organic paleothermometer TEX86, that southwest Pacific sea surface temperatures increased from ~26 °C to ~33°C during the PETM. Such temperatures before, during and after the PETM are >10 °C warmer than predicted by paleoclimate model simulations for this latitude. In part, this discrepancy may be explained by potential seasonal biases in the TEX86 proxy in polar oceans. Additionally, the data suggest that not only Arctic, but also Antarctic temperatures may be underestimated in simulations of ancient greenhouse climates by current generation fully coupled climate models. An early influx of abundant Apectodinium confirms that environmental change preceded the CIE on a global scale. Organic dinoflagellate cyst assemblages suggest a local decrease in the amount of river run off reaching the core site during the PETM, possibly in concert with eustatic rise. Moreover, the assemblages suggest changes in seasonality of the regional hydrological system and storm activity. Finally, significant variation in dinoflagellate cyst assemblages during the PETM indicates that southwest Pacific climates varied significantly over time scales of 103 - 104 years during this event, a finding comparable to similar studies of PETM successions from the New Jersey Shelf.

Petrogenesis of Cenozoic volcanic rocks in the NW sector of the Gharyan volcanic field, Libya

The north-western sector of the Gharyan volcanic field (northern Libya) consists of trachytic-phonolitic domes emplaced between similar to 41 and 38 Ma, and small-volume mafic alkaline volcanic centres (basanites, tephrites. alkali basalts. hawaiites and rare benmoreites) of Middle Miocene-Pliocene age (similar to 12-2 Ma). Two types of trachytes and phonolites have been recognized on the basis of petrography, mineralogy and geochemistry. Type-1 trachytes and phonolites display a smooth spoon-shaped REE pattern without negative Europium anomalies. Type-2 trachytes and phonolites show a remarkable Eu negative anomaly, higher concentration in HFSE (Nb-Ta-Zr-Hf), REE and Ti than Type-1 rocks. The origin of Type-1 trachytes and phonolites is compatible with removal of clinopyroxene, plagioclase, alkali feldspar, amphibole. magnetite and titanite starting from benmoreitic magmas. found in the same outcrops. Type-2 trachytes and phonolites could be the result of extensive fractional crystallization starting from mafic alkaline magma, without removal of titanite. In primitive mantle-normalized diagrams, the mafic rocks (Mg#= 62-68, Cr up to 514 ppm, Ni up to 425 ppm) show peaks at Nb and Ta and troughs at K. These characteristics, coupled with low Sr-87/Sr-86(i) (0.7033-0.7038) and positive epsilon(Nd) (from +4.2 to + 5.3) features typical of the mafic anorogenic magmas of the northern African plate and of HIMU-OIB-like magma in general. The origin of the mafic rocks is compatible from a derivation from low degree partial melting (3-9%) shallow mantle sources in the spinel/gamet facies. placed just below the rigid plate in the uppermost low-velocity zone. The origin of the igneous activity is considered linked to passive lithospheric thinning related to the development of continental rifts like those of Sicily Channel (e.g.. Pantelleria and Linosa) and Sardinia (e.g., Campidano Graben) in the Central-Western Mediterranean Sea. (C) 2012 Elsevier B.V. All rights reserved.

Surface cloud radiative forcing from broadband radiation measurements on the Antarctic plateau

Surface based measurements systems play a key role in defining the ground truth for climate modeling and satellite product validation. The Italian-French station of Concordia is operative year round since 2005 at Dome C (75°S, 123°E, 3230 m) on the East Antarctic Plateau. A Baseline Surface Radiation Network (BSRN) site was deployed and became operational since January 2006 to measure downwelling components of the radiation budget, and successively was expanded in April 2007 to measure upwelling radiation. Hence, almost a decade of measurement is now available and suitable to define a statistically significant climatology for the radiation budget of Concordia including eventual trends, by specifically assessing the effects of clouds and water vapor on SW and LW net radiation. A well known and robust clear sky-id algorithm (Long and Ackerman, 2000) has been operationally applied on downwelling SW components to identify cloud free events and to fit a parametric equation to determine clear-sky reference along the Antarctic daylight periods (September to April). A new model for surface broadband albedo has been developed in order to better describe the features the area. Then, a novel clear-sky LW parametrization, based on a-priori assumption about inversion layer structure, combined with daily and annual oscillations of the surface temperature, have been adopted and validated. The longwave based method is successively exploited to extend cloud radiative forcing studies to nighttime period (winter). Results indicated inter-annual and intra-annual warming behaviour, i.e. 13.70 W/m2 on the average, specifically approaching neutral effect in summer, when SW CRF compensates LW CRF, and warming along the rest of the year due prevalentely to CRF induced on the LW component.

TALDICE-1 age scale of the Talos Dome deep ice core, East Antarctica

A new deep ice core drilling program, TALDICE, has been successfully handled by a European team at Talos Dome, in the Ross Sea sector of East Antarctica, down to 1620 m depth. Using stratigraphic markers and a new inverse method, we produce the first official chronology of the ice core, called TALDICE-1. We show that it notably improves an a priori chronology resulting from a one-dimensional ice flow model. It is in agreement with a posteriori controls of the resulting accumulation rate and thinning function along the core. An absolute uncertainty of only 300 yr is obtained over the course of the last deglaciation. This uncertainty remains lower than 600 yr over Marine Isotope Stage 3, back to 50 kyr BP. The phasing of the TALDICE ice core climate record with respect to the central East Antarctic plateau and Greenland records can thus be determined with a precision allowing for a discussion of the mechanisms at work at sub-millennial time scales.

Centennial mineral dust variability in high-resolution ice core data from Dome C, Antarctica

Ice core data from Antarctica provide detailed insights into the characteristics of past climate, atmospheric circulation, as well as changes in the aerosol load of the atmosphere. We present high-resolution records of soluble calcium (Ca2+), non-sea-salt soluble calcium (nssCa2+), and particulate mineral dust aerosol from the East Antarctic Plateau at a depth resolution of 1 cm, spanning the past 800 000 years. Despite the fact that all three parameters are largely dust-derived, the ratio of nssCa2+ to particulate dust is dependent on the particulate dust concentration itself. We used principal component analysis to extract the joint climatic signal and produce a common high-resolution record of dust flux. This new record is used to identify Antarctic warming events during the past eight glacial periods. The phasing of dust flux and CO2 changes during glacial-interglacial transitions reveals that iron fertilization of the Southern Ocean during the past nine glacial terminations was not the dominant factor in the deglacial rise of CO2 concentrations. Rapid changes in dust flux during glacial terminations and Antarctic warming events point to a rapid response of the southern westerly wind belt in the region of southern South American dust sources on changing climate conditions. The clear lead of these dust changes on temperature rise suggests that an atmospheric reorganization occurred in the Southern Hemisphere before the Southern Ocean warmed significantly.

Change in dust variability in the Atlantic sector of Antarctica at the end of the last deglaciation

We present a Rare Earth Elements (REE) record determined on the EPICA ice core drilled at Dronning Maud Land (EDML) in the Atlantic sector of the East Antarctic Plateau. The record covers the transition from the last glacial stage (LGS) to the early Holocene (26 600–7500 yr BP) at decadal to centennial resolution. Additionally, samples from potential source areas (PSAs) for Antarctic dust were analyzed for their REE characteristics. The dust provenance is discussed by comparing the REE fingerprints in the ice core and the PSA samples. We find a shift in variability in REE composition at ~15 000 yr BP in the ice core samples. Before 15 000 yr BP, the dust composition is very uniform and its provenance was most certainly dominated by a South American source. After 15 000 yr BP, multiple sources such as Australia and New Zealand become relatively more important, although South America remains the major dust source. A similar change in the dust characteristics was observed in the EPICA Dome C ice core at around ~15 000 yr BP, accompanied by a shift in the REE composition, thus suggesting a change of atmospheric circulation in the Southern Hemisphere.

New constraints on the gas age-ice age difference along the EPICA ice cores, 0-50 kyr

Gas is trapped in polar ice sheets at ~50–120 m below the surface and is therefore younger than the surrounding ice. Firn densification models are used to evaluate this ice age-gas age difference (Δage) in the past. However, such models need to be validated by data, in particular for periods colder than present day on the East Antarctic plateau. Here we bring new constraints to test a firn densification model applied to the EPICA Dome C (EDC) site for the last 50 kyr, by linking the EDC ice core to the EPICA Dronning Maud Land (EDML) ice core, both in the ice phase (using volcanic horizons) and in the gas phase (using rapid methane variations). We also use the structured 10Be peak, occurring 41 kyr before present (BP) and due to the low geomagnetic field associated with the Laschamp event, to experimentally estimate the Δage during this event. Our results seem to reveal an overestimate of the Δage by the firn densification model during the last glacial period at EDC. Tests with different accumulation rates and temperature scenarios do not entirely resolve this discrepancy. Although the exact reasons for the Δage overestimate at the two EPICA sites remain unknown at this stage, we conclude that current densification model simulations have deficits under glacial climatic conditions. Whatever the cause of the Δage overestimate, our finding suggests that the phase relationship between CO2 and EDC temperature previously inferred for the start of the last deglaciation (lag of CO2 by 800±600 yr) seems to be overestimated.

Where to find 1.5 million yr old ice for the IPICS "Oldest-Ice" ice core

The recovery of a 1.5 million yr long ice core from Antarctica represents a keystone of our understanding of Quaternary climate, the progression of glaciation over this time period and the role of greenhouse gas cycles in this progression. Here we tackle the question of where such ice may still be found in the Antarctic ice sheet. We can show that such old ice is most likely to exist in the plateau area of the East Antarctic ice sheet (EAIS) without stratigraphic disturbance and should be able to be recovered after careful pre-site selection studies. Based on a simple ice and heat flow model and glaciological observations, we conclude that positions in the vicinity of major domes and saddle position on the East Antarctic Plateau will most likely have such old ice in store and represent the best study areas for dedicated reconnaissance studies in the near future. In contrast to previous ice core drill site selections, however, we strongly suggest significantly reduced ice thickness to avoid bottom melting. For example for the geothermal heat flux and accumulation conditions at Dome C, an ice thickness lower than but close to about 2500 m would be required to find 1.5 Myr old ice (i.e., more than 700 m less than at the current EPICA Dome C drill site). Within this constraint, the resolution of an Oldest-Ice record and the distance of such old ice to the bedrock should be maximized to avoid ice flow disturbances, for example, by finding locations with minimum geothermal heat flux. As the geothermal heat flux is largely unknown for the EAIS, this parameter has to be carefully determined beforehand. In addition, detailed bedrock topography and ice flow history has to be reconstructed for candidates of an Oldest-Ice ice coring site. Finally, we argue strongly for rapid access drilling before any full, deep ice coring activity commences to bring datable samples to the surface and to allow an age check of the oldest ice.

Phase Structure of Radar Stratigraphic Horizons Within Antarctic Firn

We have recorded reflection profiles of firn through large areas of West Antarctica and part of the East Antarctic plateau using 400 MHz short-pulse radar. The locations show accumulation rates that vary from well above to well below the vertical radar resolution. Most reflection horizons have extensive lateral continuity, and are composed of distinctive wavelets with a consistent phase polarity sequence within their successive half-cycles. We modeled these waveforms, and conclude that they arise from thin, double layers of ice over hoar, which is consistent with the standard model of firn stratification. In addition, we conclude that ice/hoar layers are extensive throughout West Antarctica and also present (although more sparsely) beneath the Antarctic Plateau.

The role of seasonality of mineral dust concentration and size on glacial/interglacial dust changes in the EPICA Dronning Maud Land ice core

We present a record of particulate dust concentration and size distribution in subannual resolution measured on the European Project for Ice Coring in Antarctica (EPICA) Dronning Maud Land (EDML) ice core drilled in the Atlantic sector of the East Antarctic plateau. The record reaches from present day back to the penultimate glacial until 145,000 years B.P. with subannual resolution from 60,000 years B.P. to the present. Mean dust concentrations are a factor of 46 higher during the glacial (~850–4600 ng/mL) compared to the Holocene (~16–112 ng/mL) with slightly smaller dust particles during the glacial comparedto the Holocene and with an absolute minimum in the dust size at 16,000 years B.P. The changes in dust concentration are mainly attributed to changes in source conditions in southern South America. An increase in the modal value of the dust size suggests that at 16,000 years B.P. a major change in atmospheric circulation apparently allowed more direct transport of dust particles to the EDML drill site. We find a clear in-phase relation of the seasonal variation in dust mass concentration and dust size during the glacial (r(conc,size) = 0.8) but no clear phase relationship during the Holocene (0

Water stable oxygen isotope records from six Antarctic ice core sites for the present and last interglacial periods

We compare the present and last interglacial periods as recorded in Antarctic water stable isotope records now available at various temporal resolutions from six East Antarctic ice cores: Vostok, Taylor Dome, EPICA Dome C (EDC), EPICA Dronning Maud Land (EDML), Dome Fuji and the recent TALDICE ice core from Talos Dome. We first review the different modern site characteristics in terms of ice flow, meteorological conditions, precipitation intermittency and moisture origin, as depicted by meteorological data, atmospheric reanalyses and Lagrangian moisture source diagnostics. These different factors can indeed alter the relationships between temperature and water stable isotopes. Using five records with sufficient resolution on the EDC3 age scale, common features are quantified through principal component analyses. Consistent with instrumental records and atmospheric model results, the ice core data depict rather coherent and homogenous patterns in East Antarctica during the last two interglacials. Across the East Antarctic plateau, regional differences, with respect to the common East Antarctic signal, appear to have similar patterns during the current and last interglacials. We identify two abrupt shifts in isotopic records during the glacial inception at TALDICE and EDML, likely caused by regional sea ice expansion. These regional differences are discussed in terms of moisture origin and in terms of past changes in local elevation histories, which are compared to ice sheet model results. Our results suggest that elevation changes may contribute significantly to inter-site differences. These elevation changes may be underestimated by current ice sheet models

(Appendix A) Geochemical composition of snow and eolian mineral dust from Berkner Island ice sheet, Antarctica

The Sr and Nd isotopic composition of dust extracted from recent snow layers at the top of Berkner Island ice sheet (located within the Filchner-Ronne Ice Shelf at the southern end of the Weddell Sea) enables us, for the first time, to document dust provenance in Antarctica outside the East Antarctic Plateau (EAP) where all previous studies based on isotopic fingerprinting were carried out. Berkner dust displays an overall crust-like isotopic signature, characterized by more radiogenic 87Sr/86Sr and much less radiogenic 143Nd/144Nd compared to dust deposited on the EAP during glacial periods. Differences with EAP interglacial dust are not as marked but still significant, indicating that present-day Berkner dust provenance is distinct, at least to some extent, from that of the dust reaching the EAP. The fourteen snow-pit sub-seasonal samples that were obtained span a two-year period (2002-2003) and their dust Sr and Nd isotopic composition reveals that multiple sources are at play over a yearly time period. Southern South America, Patagonia in particular, likely accounts for part of the observed spring/summer dust deposition maxima, when isotopic composition is shifted towards 'younger' isotopic signatures. In the spring, possible additional inputs from Australian sources would also be supported by the data. Most of the year, however, the measured isotopic signatures would be best explained by a sustained background supply from putative local sources in East Antarctica, which carry old-crust-like isotopic fingerprints. Whether the restricted East Antarctic ice-free areas produce sufficient eolian material has yet to be substantiated however. The fact that large (> 5 µm) particles represent a significant fraction of the samples throughout the entire time-series supports scenarios that involve contributions from proximal sources, either in Patagonia and/or Antarctica (possibly including snow-free areas in the Antarctic Peninsula and other areas as well). This also indicates that additional dust transport, which does not reach the EAP, must occur at low-tropospheric levels to this coastal sector of Antarctica.

Baseline surface radiation during the International Polar Year 2007-2009

Downwelling and upwelling shortwave and longwave radiation components from six active polar sites, taking part of the Baseline Surface Radiation Network (BSRN), were selected for the period of the last International Polar Year (March 2007 to March 2009), and included in the BSRN-IPY dataset, along with metadata and supplementary data for some of the stations. Two sites, located at Svalbard archipelago (Ny Ålesund) and Alaska (Barrow), represent Arctic sea-level conditions. Four Antarctic stations represent both sea-level (Dronning Maud Land and Cosmonaut Sea) and high-elevation conditions (South Pole and East Antarctic Plateau). The BSRN-IPY dataset content and quality are discussed.