Ross Sea dynamics: what we learned from the Italian PNRA cruises. Andrea Bergamasco. National Research Council, CNR-ISMAR, Venice, Italy

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1 Ross Sea dynamics: what we learned from the Italian PNRA cruises Andrea Bergamasco National Research Council, CNR-ISMAR, Venice, Italy The Polar Regions are considered to be more sensitive to global warming than the lower latitude areas. In this presentation we focus our attention on the Ross Sea water masses and their dynamics. Ross Sea is an embayment located south of the line ideally joining Cape Adare to Cape Colbeck, and characterized by a westward rocky coastline, the Ross Ice Shelf (RIS) along the southern boundary, and featuring a wide, deep continental shelf with alternating banks and depressions at the sea bed. The depth of the shelf (offshore areas are mostly deeper than 200 m, with maximum depths reaching more than 1000 m in the Drygalski basin) is due to the isostatic reaction to ice load during the last Great Ice Age. The RIS is a large ice shelf about 250m thick and underneath seawater can freely circulate for hundreds of kilometers southward, reaching the grounding line. A subset of World Ocean Database 2001, referring to the Ross Sea (containing data in this region since 1928) was merged with all data collected by the Italian expeditions (mainly CLIMA Project dataset and other PNRA Projects, since 1994 up to now). From this extended dataset, climatologies of the Ross Sea water masses have been drawn and some dynamic behavior inferred. The comparison between the WOD01 dataset and the CLIMA ones showed some significant changes occurred during the last decades: a freshening of the Ross Sea shelf waters and some relevant variations of the MCDW masses, which appeared to reduce their presence and to deepen. Variations in the MCDW properties and extension could have relevant consequences, e.g. a decreased Ross Ice Shelf basal melting and may also be indicative of a reduced thermo-haline circulation within the Ross Sea. Shelf Waters (SW) having neutral density γ n > 28.7 Kg m-3, which contribute to form the densest Antarctic Bottom Waters (AABW), showed a large volumetric decrease in the 1994/ /04 decade, most likely as a consequence of the SW freshening.

2 Small eddies and large tides: Modeling the Ross Sea Stefanie Mack Applied Physics Lab University of Washington Seattle, WA USA The Ross Sea, Antarctica is a region that is dominated by large diurnal tides. Tides affect bottom water formation and export, vertical mixing, and ice shelf basal melt rates. The effect of mesoscale eddies is not so prominent. Due to weak winter stratification and small baroclinic radius of deformation, eddies are a difficult feature to model in the Ross Sea and may not make a large contribution to circulation or ice shelf basal melt rates. In this talk, I will present an overview of recent updates to our ROMS model of the Ross Sea, a summary of the key results, and a wish list for future improvements.

3 The change of the bathymetry in the Ross Sea : how and why we reconstructed it Laura De Santis Istituto Nazionale di Oceanografia e di Geofisica Sperimentale OGS Borgo Grotta Gigante 42/c Sgonico Trieste, Italy ldesantis@inogs.it The Antarctic Ice Sheets stores frozen water equivalent to 60 m of global sea level rise. It is then of vital importance for the World population living along the coast, to understand how the Antarctic Ice Sheets reacts to warmer conditions. Antarctic ice shelves are currently thinning, but causes and rates of the ongoing processes and tipping points are still unknown. Sea level rise and basal melting due to Ocean warming is inferred to cause dismantling of ice sheets, grounding on landward dipping sea bed, once they are no longer buttressed by ice shelves. Changes in the bathymetry of the continental shelf are the important component of ice sheet and circulation models for understanding the Antarctic Ice Sheet mass balance controls. The Ross Sea ( S) is one of the best studied areas of the Antarctic margin, allowing combination of large geophysical data set and high-resolution geological records with status of the art ice sheet and general circulation ocean models. Here we aim to reconstruct past environmental settings at the transition from the greenhouse world, with high CO2 concentration, like those projected for the next 100 years, to the ice house world, when CO2 and temperatures drop and continental ice accumulated in Antarctica and then fluctuated, driven by orbital forcing. The stratigraphic information from the IODP Exp. 374 and previous drill sites combined with the geophysical data grid allow us to reconstruct paleobathymetric maps of the main seismic unconformities and to provide a measure of the geomorphological changes under the action of the ice sheet and ocean circulation. The Italian and US collaboration in the frame of the MAECI GSLAISSS Global Sea Level Rise & Antarctic Ice Sheet Stability predictions: guessing future by learning from past project is aimed at reconstructing Ross Sea paleobathymetry maps, ice sheet extension and ocean current circulation at significant time shifts of the Cenozoic climate cooling history.

4 Regional Antarctic ocean/sea ice/ice shelf modeling at Old Dominion University: Current work and future plans Michael Dinniman Center for Coastal Physical Oceanography Old Dominion University 4111 Monarch Way Norfolk, VA 23508, USA Current and past members of the Center for Coastal Physical Oceanography (CCPO) at Old Dominion University have created regional ocean circulation models for various areas around Antarctica to study high latitude coastal ocean dynamics, ocean-ice interactions, and connections between ocean physics and polar ecosystems. The primary tool for this is the Regional Ocean Modeling System (ROMS), some versions of which now include processes necessary for simulations at high latitudes, including dynamic sea ice and floating extensions of land ice (ice shelves). A sampling of results from regional ROMS ocean/sea ice/ice shelf circulation models for the Amundsen Sea, West Antarctic Peninsula coast, Ross Sea, and entire Southern Ocean will be presented. In order to help identify areas of potential future collaborations, a short summary will be given of current and new Antarctic projects at CCPO.

5 The change of the bathymetry in the Ross Sea : how do we use it for ice sheet modeling Florence Colleoni 1 Istituto Nazionale di Oceanografia Sperimentale, Sgonico, 34010, Italy, *fcolleoni@inogs.it Understanding how the Antarctic ice sheet will respond to global warming relies on knowledge of how it has behaved in the past. The use of numerical models, the only means to quantitatively predict the future, is hindered by limitations to topographic data both now and in the past, and in knowledge of how subsurface oceanic, glaciological and hydrological processes interact. Over the past 34 Million years, the Antarctic continental shelf has gradually deepened, due to ice sheet loading, thermal subsidence, and erosion from repeated glaciations. The deepening recorded in the sedimentological deposits around the Antarctic margin indicates that after the mid Miocene Climate Optimum ( 15 Ma), Antarctic Ice Sheet (AIS) dynamical response to climate conditions changed. We explore endmembers for maximum AIS extent, based on ice-sheet simulations of a late Pleistocene and a mid- Miocene glaciation. Fundamental dynamical differences emerge as a consequence of atmospheric forcing, eustatic sea level and continental shelf evolution. We show that the AIS contributed to the amplification of its own sensitivity to ocean forcing by gradually expanding and eroding the continental shelf, which likely changed its tipping points through time. The lack of past topographic and bathymetric reconstructions implies that so far, we still have an incomplete understanding of AIS tipping points in response to past climate forcing, which is crucial to constrain its future evolution. Incorporating the variety and interplay of such processes, operating at multiple spatio-temporal scales, is critical to modeling the Antarctic s system evolution and requires direct observations in challenging locations.

6 Andrea Bergamasco Is a senior research scientist at the CNR ISMAR, National Research Council, Institute of Marine Science, Venice, Italy since He is a Physical Oceanographer, focused on water formation, dispersion and mixing processes. He works mainly in General Circulation Modeling, both in Polar Regions and in the Mediterranean seas. Actually his research is focused on: 1) dense water overflows and cascade processes characterizing the shelf-slope interactions, 2) abyssal renewal variability and its correlation with climate change, 3) stable isotopes multi-proxies study with seasonal to multi-decadal resolution, 4) sea-ice formation processes in polynya area. He led several cruises in the Mediterranean Sea and was a member of the scientific party of the CLIMA Project in the Southern Ocean Ross Sea cruises. He is a faculty member of the School of Doctorate in Environmental Sciences of the University Cà Foscari of Venice.

7 Florence Colleoni received a joint Ph.D in paleoclimate modelling from LGGE (CNRS, Grenoble, France) and Stockholm University in She is a glaciologist and her research focused on the modeling of past Northern Hemisphere glaciations, a topic that she investigated until recently. She is currently junior scientist at the National Institute of oceanography and experimental geophysics (OGS) in Trieste (Italy). Her current research interests migrated towards the Southern Hemisphere when she recently started to collaborate with the Italian polar community, and in particular with the OGS institute in Trieste. She is currently investigating different aspects of the Antarctic ice sheet, from ocean and atmosphere to ice-sheet dynamics and from deep past to future, with a particular focus on the integration of the different timescales at which processes occur. One her main objective is to develop the paleo and future ice-sheet modeling research in Italy with the support of the major national structures dealing with polar sciences in Italy

8 Laura De Santis Is researcher at OGS, Istituto Nazionale di Oceanografia e di Geofisica Sperimentale, Trieste, Italy since She obtained a PhD in Marine Geosciences at Univ. of Parma (Italy) in 1995 on Ross Sea (Antarctica) seismic stratigraphy. Her main interest and expertise is in marine geology and seismic facies analysis in polar continental margins. Laura sailed on oceanographic geophysical cruises in the Mediterranean Sea and in Antarctica between 1990 and She was a member of the scientific party of the Cape Roberts deep drilling project - 1 in 1998 and co-chief of IODP Exp. 374 (Ross Sea, 2018). Laura is co-chief officer of the SCAR/PAIS Past Antarctic Ice Sheet dynamics program since 2016 and Italian delegate (Alternate) at the European Consortium for Ocean Drilling ECORD Council since Laura has supervised several Master and PhD thesis in Polar Science at Univ. Trieste, Venice, Siena (Italy) and Univ. of Seul-KOPRI (Rep. South Korea). She is lecturer on Antarctic marine and geophysics at Univ. of Trieste since Laura has been actively promoting and contributing to outreach initiatives in Italy and published over 40 papers in peer review journals

9 Stefanie Mack Stefanie is a Future of Ice postdoc with an expertise in regional ocean modeling, focusing on Antarctic ice shelves using the ROMS model. She is currently developing a model of Pine Island Glacier ice shelf cavity to investigate ocean-ice shelf interactions, ocean cavity circulation, and offline coupling with an ice shelf model. Before joining Ian Joughin s team in PSC, Stefanie s doctorate research involved using a ROMS model of the Ross Sea to investigate the role of tides and mesoscale eddies, particularly on the transport of dissolved iron, a limiting micronutrient, from source locations to the surface mixed layer. Stefanie was recently elected to serve a three-year term as a Student Representative for The Oceanography Society through More information about Stefanie s work is available from:

10 Mike Dinniman is a research scientist at the Center for Coastal Physical Oceanography (CCPO) in the Department of Ocean, Earth and Atmospheric Science at Old Dominion University in Norfolk, Virginia, USA. After spending several years writing software for flight simulators, Mike went back to school where he received an M.S. in Meteorology from the University of Maryland and first learned about ocean modeling. He then worked for two years at the NASA Goddard Space Flight Center before coming to CCPO in Most of Mike's current research is on ocean/ice interaction and the connections between ocean physics and ecosystems around Antarctica. However, he has other research interests involving computer models to study bodies of water ranging from the Pacific Ocean and Gulf of Mexico to educational models of the Chesapeake Bay and Lake Superior.