United States

In this paper we analyze how oceanic circulation affects sediment deposition along a sector of the Ross Sea continental margin, between the Iselin Bank and the Hillary Canyon, and how these processes evolved since the Late Miocene. The Hillary Canyon is one of the few places around the Antarctic continental margin where the dense waters produced onto the continental shelf, mainly through brine rejection related to sea ice production, flow down the continental slope and reach the deep oceanic bottom layer (Gales et al., 2021). At the same time the Hillary Canyon represents a pathway for relatively warm waters, normally flowing along the continental slope within the Antarctic Slope Current, to reach the continental shelf. The intrusion of warm waters onto the continental shelf produces basal melting of the ice shelves, reduces their buttressing effect and triggers instabilities of the ice sheet that represents one of the main uncertainties in future sea level projections. For this study we use seismic, morpho-bathymetric and oceanographic data acquired in 2017 by the R/V OGS Explora. Age models from two drilling sites (U1523 and U1524) of the Integrated Ocean Discovery Program (IODP) Expedition 374 (McKay et al., 2019). Oceanographic data, together with a regional oceanographic model, are used to support our reconstruction by showing the present-day oceanographic influence on sediment deposition. Regional correlation of the main seismic unconformities allows us to identify eight seismic sequences. Seismic profiles and multibeam bathymetry show a strong influence of bottom current activity on sediment deposition since the Early Miocene and a reduction in their intensity during the mid-Pliocene Warm Period. Oceanographic data and modelling provide evidence that the bottom currents are related to the dense waters produced on the Ross Sea continental shelf and flowing out through the Hillary Canyon. The presence of extensive mass transport deposits and detachment scarps indicate that also mass wasting participates in sediment transport. Through this integrated approach we regard the area between the Iselin Bank and the Hillary Canyon as a Contourite Depositional System (ODYSSEA CDS) that offers a record of oceanographic and sedimentary conditions in a unique setting. The hypotheses presented in this work are intended to serve as a framework for future reconstructions based on detailed integration of lithological, paleontological, geochemical and petrophysical data.

SGI 2021

Bottom current control on sediment deposition between the Iselin Bank and the Hillary Canyon (Antarctica) since the late Miocene: an integrated seismic-oceanographic approach

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L'Istituto Nazionale di Oceanografia e Geofisica Sperimentale - OGS e il Dipartimento di Matematica e Geoscienze dell'Università di Trieste sono orgogliosi di ospitare il 90° Congresso della Società Geologica Italiana a Trieste dal 14 al 16 settembre 2021. La modalità del congresso è interamente online.

Con il motto "Geologia senza frontiere" questo evento mira a promuovere le Scienze della Terra come disciplina scientifica proiettata nel futuro, oltre i confini geografici, politici e disciplinari, per comprendere meglio l'interno del Pianeta Terra e la struttura del sottosuolo, difendere la società da pericolosi eventi geologici, comprendere meglio la variabilità climatica, pianificare l'utilizzo delle georisorse in modo etico e nel rispetto dell'ambiente.


**Please note, times listed in the SCHEDULE tab (calendar icon) reflect YOUR LOCAL TIME ZONE. The main timezone for this conference will be Central European Summer Time.**

The National Institute of Oceanography and Experimental Geophysics - OGS and the Department of Mathematics and Geosciences of the University of Trieste are proud to host the 90th Congress of the Italian Geological Society in Trieste on 14-16 September 2021.  The Congress will be held entirely online.

With the motto "Geology Without Borders" this event aims to promote Earth Sciences as a scientific discipline projected into the future, beyond geographical, political and disciplinary boundaries, to better understand the interior of Planet Earth and the structure of the subsurface, defend society from dangerous geological events, better understand climatic variability, plan the use of geo-resources in an ethical way and respecting the environment.


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Earth Sciences should be understood not only as necessary for a better understanding of the interior of the planet Earth, but also as a defense of society from dangerous geological events, for the understanding of climatic variations, for the planning and use of georesources in a ethical and respecting and protecting the environment.

poster

The Northern Adriatic Sea hosts a rich biodiversity, in both the Italian and Slovenian offshore and nearshore zones. Peculiar habitats, locally known as Trezze and Tegnue, mostly represented by the coralligenous outcrops and colonized by serpulids, red algae, bryozoans, bivalves, and dead corallites of Cladocora caespitosa, Cymodocea nodosa and Zostera marina associated with the presence of Pinna nobilis are investigated in the North Italian offshore, and in marine protected areas of Debeli rtič Natural Monument and the Strunjan Nature Park of Strunjan, in Slovenia. This research is carried out  in the frame of the INTERREG ITA-SLO TRETAMARA Project, which aims to provide an integrated and strengthened management of the Northern Adriatic marine-coastal habitats with high ecological value. They are characterize by a fragile biological equilibrium, due to the slow-growing calcareous organisms considered as non renewable resources, and the dredging and bottom trawling pressure that strongly threatens the physical characteristics of the habitat and negatively affect the associated biota. Here we present the preliminary results of cross-border pilot actions supporting biodiversity of these precious marine-coastal habitats. They consist of high quality seafloor images obtained by Multibeam and Side Scan Sonar surveys, aimed at: (1) mapping the Trezze and Tegnue buildups for better understanding  their origins, which are still debated (e.g., Gordini et al., 2012; Tosi et al., 2017; Donda et al., 2015 and 2019), and the seagrass meadows and Pinna nobilis settlement; 2. Collecting the Management Plans, Conservation Measures, and Regulations actions relating to marine-coastal Natura 2000 areas, aimed at producing a review document for the integrated management of the Northern Adriatic Sea marine habitats with high ecological value. This document will play a key role to promote cross-border sustainability and governance of such fragile environments.

Unveiling the secrets of the Northern Adriatic Sea: the TRETAMARA project for their management, valorization and conservation

In January 2020, International Ocean Discovery Program (IODP) Expedition 378 drilled in South Pacific and recovered a continuously cored, multiple-hole Paleogene sedimentary section at Site U1553 (Thomas, Röhl, Childress, et al., 2020). The aim was to replicate the sedimentary record of DSDP Site 277, the best known Paleogene paleoceanographic site in the South Pacific, drilled during Leg 29 (Kennett et al., 1975). From this site, classic oxygen isotope records were generated that first defined the climatic evolution through the Eocene (e.g., Shackleton & Kennett, 1975). Improved coring technologies and core-log integration resulted in the development of multiple core stratigraphic splices representing a more complete succession than the single succession of Site 277. This area in the South Pacific Ocean is critical for high-latitude climate reconstructions across the Paleocene to late Oligocene. Research on Site U1553 is in-progress for studying in detail the major events preserved in this high-latitude sedimentary record (Hollis et al., 2015). Here we report on the preliminary results of a study on calcareous nannofossil assemblages in an expanded upper Eocene to upper Oligocene sequence. The biostratigraphic data confirm the validity of the biozonation scheme proposed for the Southern Ocean (Fioroni et al., 2012) and suggest that further refinements on biostratigraphy can be obtained, thanks to the rich and well preserved nannofossil assemblages observed. In a preliminary paleoecological analysis, performed at low resolution, the considered major groups, each including cool, temperate, eutrophic and oligotrophic taxa, provide a revealing signal for paleotemperature and nutrient concentration in line with previous studies at high latitude sites (Villa et al., 2014). Further analyses at high resolution will certainly help in reconstructing changes in South Pacific temperature, circulation, and productivity associated with the greenhouse–icehouse transition (Eocene/Oligocene) and the early Oligocene.

Calcareous nannofossils at IODP Site U1553, a reference paleoceanographic record for the Paleogene

The main objective of this study is to reconstruct the Late Quaternary (<60 ka) palaeoceanographic and paleoclimatic variability recorded in the Isfjorden sediment drift located on the western margin of Svalbard (Arctic). The study is based on the sedimentological analyses on two calypso cores: core GS191-02PC, located at 1320 m water depth, that was collected during the expedition of the R/V G.O.Sars, in the framework of Eurofleets-2 PREPARED Project (Lucchi et al., 2014), and core CAGE-19-3-KH-15-GPC01, located at 1580 m water depth, that was collected during the “Calypso giant piston coring in the Arctic-Atlantic gateway” expedition on the R/V Kronprins Haakon (Knies et al., 2019). The cores were studied with X-ray, physical properties obtained through a Multi-sensor core logger (magnetic susceptibility and wet bulk density), digital photographs of the fresh sediment surface, visual logging, and sediment composition through XRF-core scan (chemical composition) and XRD analyses (clay mineral assemblage). A high-resolution age model was reconstructed for core GS191-02PC (Caricchi et al., 2019). In this poster, we present the results of sedimentological analysis from the two calypso cores providing information on the down-slope (glacial) vs along-slope (contour currents) sedimentary processes that occurred at the Isfjorden drift during last 60 ka.

Sedimentary processes at the Isfjorden continental margin: preliminary results from lithological study of two long Calypso cores

The presence of different types of glacial and sub-glacial features near the shelf edge indicates that the Western Antarctic Ice Sheet (WAIS) was grounded near the shelf break in many sectors of the Eastern Ross Sea (ERS) during the Last Glacial Maximum (LGM) (Shipp et al., 1999; Mosola & Anderson, 2006; Halberstadt et al., 2016; Anderson et al., 2018; Gales et al., 2021). However, mechanisms and timing of the post-LGM retreat are still debated. Studying sediments collected along the continental slope could help to reconstruct the LGM and post-LGM history of the ice sheet. This study focused on the analysis of three box cores collected east of the Hillary Canyon, which carves the ERS continental slope and is connected to the Glomar Challenger and Pennell Troughs on the shelf, south-east to the Iselin Bank. Multidisciplinary analysis (grain size, organic matter, biogenic silica and water content, magnetic susceptibility and chemical composition (XRF core scanner)) were conducted in order to reconstruct the sedimentary dynamics. Three samples for each box core were dated by using organic matter (14C AIO dates). Here, we present the results of these analysis. These box cores were collected during the XXIX PNRA (National Antarctic Research Program) expedition (2013-2014) and studied in the frame of the ROSSLOPE II (2013/AN2.01) PNRA project and the STREAM Project (Late Quaternary evolution of the ocean-ice sheet interactions: the record from the Ross Sea continental margin, Antarctica; period 2019-2021). The latter is funded by the Italian Ministry of Foreign Affairs and International Cooperation and the National Research Foundation of Korea.

Holocene sedimentary dynamics by multidisciplinary analysis of three box cores collected East to the Hillary Canyon (Eastern Ross Sea, Antarctica)

During the Last Glacial Maximum (LGM, 21’000 yrs BP) the Antarctic ice sheet was extended over the continental shelves. In the Ross Sea sector, only a restricted portion of the continental shelf was ice free, restricting main coastal circulation to the continental slope. How this impacted on the oceanic circulation in the open ocean and on the basal melting at the grounding line of the Antarctic ice sheet remains unknown. Here we present the implementation of the ocean model MITgcm on a regional grid of the Ross Sea at 5 km resolution. The numerical model includes the sub ice-shelf cavity and interactive sea-ice, while tides are not accounted for. This implementation was used to run a transient control simulation over 1993-2018 forced by state-of-the-art atmospheric and ocean reanalyses. As for the LGM, the model was spun up with steady-state climatic conditions and run transiently for 20 years. Atmospheric and oceanic forcing were taken from a global climate transient simulation (TraCE-21ka, Liu et al., 2009). The comparison of model output with oceanographic in situ data, demonstrates that it is able to simulate the main features of the oceanic circulation: the warm Circumpolar Deep Water (CDW) is advected by the southern branch of the Ross Sea Gyre towards the shelf-break, where it crosses the Antarctic Slope Front (ASF) and intrudes onto the shelf where it mixes with ambient waters (mCDW). In the Western shelf, production of High Salinity Shelf Water (HSSW) occurs by wind-induced brine rejection in winter months. The HSSW and mCDW are advected below the Ross ice shelf at different depths, the first at the grounding line, the second at the front, therefore impacting in different ways on ice shelf dynamics. A preliminary comparison of the present-day and LGM runs shows that the simulated LGM circulation was totally different. Almost all the shelf was covered by grounded ice, except for the three main troughs in the Western side: Drygalski, Joides, Pennel (Halberstadt et al., 2016), where sub-ice shelf cavities presumably were developed. The CDW in the open ocean was ~2 °C cooler than the present, and ~2 PSU saltier. The ASF was largely missing, due to the weak density contrast between shelf and open ocean waters. Most oceanic processes occurring at present on the continental shelf, such as coastal polynyas, HSSW production and dense water formation still took place, but were confined to the continental slope, with increased intensity due to the more extreme climatic conditions at the LGM.

The Ross Sea sector oceanography: glacial vs present day

Ostracods, calcareous bivalve microcrustaceans, are the only metazoan organisms commonly preserved as microfossils in deep sea sediments in sufficient quantities for detailed paleoceanographic studies. Detailed investigations of modern and recent regional distribution of ostracod species from shelf, slope, bathyal, and abyssal environments indicate that their distribution is strongly influenced by the physico-chemical characteristics of water masses (e.g., temperature, salinity, nutrients, dissolved oxygen, etc.), as well as substrate type and food supply. The Quaternary Antarctic ostracod fauna is mostly composed of extant species. This appearance of most extant species during the Quaternary may suggest that rapid climate cooling during the Plio-Pleistocene triggered diversification of cryophilic ostracods. These cryophilic ostracods constitute the modern Antarctic fauna showing high endemism and only few of them are found from the South American continental shelf and the Magellan Strait. The scarce knowledge of the modern Antarctic ostracods and in particular of their relationship with environmental parameters and physico-chemical characteristics of the water masses actually represents a strong obstacle in particular for the definition and analysis of environmental, climatic and oceanographic changes that have affected older periods. For this purpose, for a possible interpretation of the environmental and climatic changes that affected the Ross Sea in particular during the Plio-Pleistocene, the ostracod associations found in ninety surface sediment samples taken during different oceanographic research cruises were analyzed. The data obtained were connected with the numerous physico-chemical data of the water masses taken since the 90's by the oceanographic research cruises organized by the National Research Program in Antarctica (PNRA) in the Western Ross Sea area. In this way we obtained the distribution (presence absence) of the ostracod modern species in the Westerns Ross Sea such as induced by the different oceanographic settings and environmental conditions. These results have been compared with high quanti/qualitative ostracod associations values recorded in three units recovered in the IODP_374 Site U1523 that show an equivalent fauna to the modern sediments. So we believe which could be possible, through the comparison between modern and past ostracod associations, to provide a possible reconstruction of the complex environmental, climatic and oceanographic changes that have affected the Ross Sea during the last 3.0 Ma.

Ostracods fauna from IODP_374 Site U1523: a comparison with modern ones from the Western Ross Sea Area.

Geophysical/geological data integration contribute to constrain the reconstruction of the deglaciation patterns imprinted on the seafloor (Anderson et al., 2018; Bart et al., 2020; Prothro et al., 2020). The Northern Drygalski Basin (Ross Sea western coast) shows a subglacial landscape tectonically and ice drainage controlled. Seismo-stratigraphic architectures, related to the fluctuations of the East Antarctic Ice Sheet, allow to interpret the glacial-deglacial sediment depocenters and the Grounding Zone Wedges in this area. Sedimentological, micropaleontological and geochemical analysis on two GLEVORS (Glacial Evolution in the north-western Ross Sea, offshore North Victoria Land – Antarctica)  Project Cores GC01 and GC02, result basic for a reliable geomorphic reconstruction in a context where ice landforms and bedforms were shaped and where grounding lines and melt-water processes took place. The sediment cores, considered as important time-snapshotscan provide a chronostratigraphic control on the past marine-based ice-sheet vulnerability and retreat and on the records of the ice streams draining catchments, the post-LGM biological, cryosphere/atmosphere and oceanographic processes (Kim et al., 2018; Post et al., 2020; Smith et al. 2020).

Ross Sea snapshots from the past – GLEVORS Project indirect and direct records

Over the last few decades, different researches have led to important advances in our understanding of late Quaternary Antarctic Ice Sheet (AIS) behavior. However, the continental shelf margin remains still poorly investigated. To address this issue, we aim to increase the knowledge of the last glacial/deglacial dynamics in the Central Basin (slope-basin system) using a multidisciplinary approach, including sedimentological, micropaleontological, and tephrochronological analyses performed on marine sediments cores. Based on grain size clustering and the sortable silt data, together with diatom, silicoflagellate and foraminifera assemblages, we recognize three stratigraphic units. Unit 1 (24-17 ka BP) documents the influence of the ice shelf calving zone vicinity, Unit 2 (17-10.2 ka BP) represents the progressive retreat of the ice shelf due to Circumpolar Deep Water inflow, and Unit 3 (10.2 ka BP-present) corresponds to the establishment of seasonal sea ice with a strengthening of bottom currents. The dominant and persistent process is the sedimentation controlled by contour currents, which tend to modulate intensity in time and space. The study also allowed us to document the presence of a primary volcanic ash layer dated 22 ka BP correlated with the explosive activity of Mount Rittmann. This study has been conducted in the framework of the STREAM Project (Late Quaternary evolution of the ocean-ice sheet interactions: the record from the Ross Sea continental margin, Antarctica) funded by the Italian Ministry of Foreign Affairs and International Cooperation and the National Research Foundation of Korea.

Environmental and Oceanographic Conditions at the Continental Margin of the Central Basin, Northwestern Ross Sea (Antarctica) since Last Glacial Maximum

The Eurofleets ANTSSS (Antarctic ice Sheet Stability from continental Slope process investigation) 2017 cruise and the IODP (International Ocean Discovery Program) 2018 Expedition 374 recovered new geological, geophysical, and oceanographic data from a latitudinal and depth transect across the continental shelf, slope and rise of the Ross Sea, Antarctica. This transect is located along one of the largest glacial valleys cut into the continental shelf by West Antarctic Ice Streams that feed into the Hillary Canyon, which debouches downslope onto the continental rise. It is also located along the oceanward flow pathway of dense and cold water, forming in the Ross Sea polynya and mixing with Circumpolar Deep Water at the continental shelf edge. The new morphobathymetric geological and oceanographic data highlight that processes acting here during glacial and interglacial cycles likely drove large-scale shifts in outer shelf and canyon head processes, and the build-up of channel-levees on the continental rise. The IODP Exp. 374 sites U1521 and U1522 recovered a Miocene to Plio-Pleistocene geological record of past expansion and retreat of ice streams emanating from the East and West Antarctic Ice Sheets across the Ross Sea continental shelf. Site U1523 targeted a Miocene to Pleistocene sediment drift on the outermost continental shelf and informs about the changing vigor of the eastward flowing Antarctic Slope Current (ASC) through time, a key control on regulating heat flux onto the continental shelf. Sites U1524 and U1525 cored a continental rise levee system near the flank of the Hillary Canyon, with a near-continuous record of the downslope flow of Ross Sea Bottom Water and turbidity currents, but also of ASC vigor and iceberg discharge. A 20 cm-thick tephra matches a c. 1.3 Ma deposit on the caldera rim of the Chang Peak volcano 1300 km from the U1524 coring site adds a new marker for dating, correlation, and synchronization of marine and continental early Pleistocene records of West Antarctica. Exp. 374 sediments are providing key chronological constraints on the major Ross Sea seismic unconformities, enabling reconstruction of paleo-bathymetry and assessment of the geomorphological changes associated with Neogene ice sheet and ocean circulation changes. Exp. 374 results are fundamental for improving the boundary conditions of numerical ice sheet, ocean, and coupled climate models, which are critically required for understanding past ice sheet and global sea level response during warm climate intervals. Such data, and improved model skill, will enable more accurate predictions of ice sheet behavior and sea level rise anticipated with future warming. 

IODP Exp. 374 provides clues into the dynamics of the Antarctic Ice Sheet during Cenozoic climate transitions

A biodiversity crisis was observed in the benthic community from a latest Triassic carbonate platform of western Tethys. The studied succession, i.e. Mt Sparagio section in NW Sicily, consists of a continuous Upper Triassic to Lower Jurassic peritidal carbonate succession organized in shallowing upward cycles. The Upper Triassic horizons can be sub-divided into two informal units on the base of the benthic fossils assemblage: at the base the Unit A (thickness about 111 m) consists of a high diverse fossiliferous assemblage comprising very large megalodontoids specimens (up to 40 cm); Unit B (about 179 m) shows a reduction of biodiversity with the occurrence of rare and small megalodontoids (Conchodon?) up to 15 cm in size. Both units are Rhaetian in age as indicated by the presence of large tested specimens of the benthic foraminifer Triasina hantkeni. The top of Unit B is marked by an oolitic level, and records the total disappearance of the Triassic benthic fossil assemblage. Upward, the subtidal members of peritidal cycles (Unit C) show the presence of an oligotypic assemblage with T. parvovesiculifera, which represents a survival zone, followed in turn by a gradual recovery of the Lower Jurassic benthic community (e.g. Siphovalvulina sp.). A negative excursion of δ18Ocarb, corresponding to an increase in temperature, matches the biodiversity reduction between Unit A and Unit B. This episode correlates the Initial Carbon Isotopic Excursion already individuated in this section and related to the first pulse of the CAMP volcanic activity. A second change in temperature that is characterized by a positive excursion of δ18Ocarb matches the total extinction of the Upper Triassic benthic community. These data well fit with the environmental parameters of the modern tropical shallow water platform (T-factory). In particular, the sea surface temperature (SST) of a T-factory range from 18 °C to 30.5 °C representing respectively the minimum SST for the carbonate factory persistence and the maximum SST that a T-factory can tolerate.

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Unveiling the secrets of the Northern Adriatic Sea: the TRETAMARA project for their management, valorization and conservation

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