Marco Taviani

Obliquity-paced Pliocene West Antarctic ice sheet oscillations

Thirty years after oxygen isotope records from microfossils deposited in ocean sediments confirmed the hypothesis that variations in the Earth’s orbital geometry control the ice ages, fundamental questions remain over the response of the Antarctic ice sheets to orbital cycles. Furthermore, an understanding of the behaviour of the marine-based West Antarctic ice sheet (WAIS) during the ‘warmer-than-present’ early-Pliocene epoch (∼5–3u2009Myr ago) is needed to better constrain the possible range of ice-sheet behaviour in the context of future global warming. Here we present a marine glacial record from the upper 600u2009m of the AND-1B sediment core recovered from beneath the northwest part of the Ross ice shelf by the ANDRILL programme and demonstrate well-dated, ∼40-kyr cyclic variations in ice-sheet extent linked to cycles in insolation influenced by changes in the Earth’s axial tilt (obliquity) during the Pliocene. Our data provide direct evidence for orbitally induced oscillations in the WAIS, which periodically collapsed, resulting in a switch from grounded ice, or ice shelves, to open waters in the Ross embayment when planetary temperatures were up to ∼3u2009°C warmer than today and atmospheric CO2 concentration was as high as ∼400u2009p.p.m.v. (refs 5, 6). The evidence is consistent with a new ice-sheet/ice-shelf model that simulates fluctuations in Antarctic ice volume of up to +7u2009m in equivalent sea level associated with the loss of the WAIS and up to +3u2009m in equivalent sea level from the East Antarctic ice sheet, in response to ocean-induced melting paced by obliquity. During interglacial times, diatomaceous sediments indicate high surface-water productivity, minimal summer sea ice and air temperatures above freezing, suggesting an additional influence of surface melt under conditions of elevated CO2.

Antarctic records of precession‐paced insolation‐driven warming during early Pleistocene Marine Isotope Stage 31

Precisely dated Antarctic continental margin and Southern Ocean geological records show that the early Pleistocene interglacial Marine Isotope Stage 31 (MIS-31) was characterized by warmer than present surface waters with reduced sea-ice and enhanced high latitude marine carbonate production. Micropaleontologic, isotopic, and paleomagnetic evidence from drill cores at 77°S (Cape Roberts Project-1) and 53°S (ODP Site 1094) indicate circumantarctic changes in sea surface temperature and water mass stratification that are in phase with high southern latitude insolation changes during MIS-31. These changes imply a significant, though as yet unquantifiable reduction in Antarctic ice volume. This study supports the hypothesis that the interhemispheric antiphased relationship of the precession cycle attenuates a potentially significant Antarctic ice volume signal in the deep sea oxygen isotope record. The implications are that Antarctic marine ice sheets may be more susceptible to warming and high insolation driven retreat than has been widely recognized.

Antarctic ice sheet sensitivity to atmospheric CO2 variations in the early to mid-Miocene

Significance New information from the ANDRILL-2A drill core and a complementary ice sheet modeling study show that polar climate and Antarctic ice sheet (AIS) margins were highly dynamic during the early to mid-Miocene. Changes in extent of the AIS inferred by these studies suggest that high southern latitudes were sensitive to relatively small changes in atmospheric CO2 (between 280 and 500 ppm). Importantly, reconstructions through intervals of peak warmth indicate that the AIS retreated beyond its terrestrial margin under atmospheric CO2 conditions that were similar to those projected for the coming centuries. Geological records from the Antarctic margin offer direct evidence of environmental variability at high southern latitudes and provide insight regarding ice sheet sensitivity to past climate change. The early to mid-Miocene (23–14 Mya) is a compelling interval to study as global temperatures and atmospheric CO2 concentrations were similar to those projected for coming centuries. Importantly, this time interval includes the Miocene Climatic Optimum, a period of global warmth during which average surface temperatures were 3–4 °C higher than today. Miocene sediments in the ANDRILL-2A drill core from the Western Ross Sea, Antarctica, indicate that the Antarctic ice sheet (AIS) was highly variable through this key time interval. A multiproxy dataset derived from the core identifies four distinct environmental motifs based on changes in sedimentary facies, fossil assemblages, geochemistry, and paleotemperature. Four major disconformities in the drill core coincide with regional seismic discontinuities and reflect transient expansion of grounded ice across the Ross Sea. They correlate with major positive shifts in benthic oxygen isotope records and generally coincide with intervals when atmospheric CO2 concentrations were at or below preindustrial levels (∼280 ppm). Five intervals reflect ice sheet minima and air temperatures warm enough for substantial ice mass loss during episodes of high (∼500 ppm) atmospheric CO2. These new drill core data and associated ice sheet modeling experiments indicate that polar climate and the AIS were highly sensitive to relatively small changes in atmospheric CO2 during the early to mid-Miocene.

Chemosynthetic Bivalves of the Family Solemyidae (Bivalvia, Protobranchia) in the Neogene of the Mediterranean Basin

Abstract The Mediterranean area is the locus of a variety of deep-sea chemosynthetic environments that have been exploited by bivalves of the family Solemyidae during Cenozoic to present time. Large solemyids represented by the Solemya doderleini group were widely distributed in Neogene deep-sea reducing habitats, including cold vent hydrocarbon sites. Based upon the diagnostic structure of the ligament, Solemya doderleini (Mayer), 1861 and S. subquadrata (Foresti), 1879 are moved to the genus Acharax Dall, 1908. After the Messinian Salinity Crisis Acharax doderleini re-colonized deep-sea sulphide environments up to the Pliocene at least. At present, Acharax occurs in similar settings in the adjacent eastern Atlantic Ocean. Thus far, large solemyids are not documented from the present deep Mediterranean Sea in spite of a vast number of seep and reducing habitats with chemosynthetic biota, especially concentrated in its Eastern basin. Promisingly, however, a single live juvenile specimen of Solemyidae has been recently found at bathyal depth associated with a pockmark in the Nile Deep Sea Fan.

Late quaternary coastal landscape morphology and evolution of the Maltese Islands (Mediterranean Sea) reconstructed from high-resolution seafloor data

Abstract The current strong motivation to explore those traces of the archaeological and prehistoric human heritage that presently lie submerged on the continental shelf requires large-scale and precise underwater mapping. One Mediterranean sector deserving particular attention is the Sicily Channel, which is critical for a better understanding of the Africa–Europe migratory routes and early civilization patterns due to its large expanses of shallow seabed that were partially or totally exposed at times of lower relative sea levels. We have focused our attention on the submerged continental margin of the Maltese archipelago. A detailed bathymetric map is here presented, and is discussed in terms of features interpretable as former subaerial landforms and inundated by sea-level rise following the Last Glacial Maximum lowstand at approximately –130 m. Our datasets combine multibeam surveys, Light Detection And Ranging (LiDAR)-derived digital terrain models (DTMs), Chirp sub-bottom profiler records and bottom samples acquired between 2009 and 2012. The main features identified are former river incisions, alluvial plains, karst landscapes (sinkholes, limestone plateaus), slide deposits and palaeoshorelines. This study provides a detailed topographical reconstruction of the palaeolandscape of this key region that is relevant to any future archaeological exploration of the Maltese offshore area.