The following selected abstracts are from the linked: "Proceedings of the Wellington Symposium", held 12–17 February 2017
Wellington, New Zealand
https://www.igsoc.org/symposia/2017/newzealand/proceedings/proceedings.html75A2218
The RICE ice core: timing and drivers of the deglaciation in the Ross Sea region
Nancy Bertler, Howard Conway, Dorthe Dahl-Jensen
Corresponding author: Nancy Bertler
Corresponding author e-mail: nancy.bertler@vuw.ac.nz
Geological evidence and modelling experiments suggest that the removal of ice shelves from marine-based ice sheets can lead to catastrophic collapse. Roosevelt and Ross Islands are thought to be stabilization anchors for the Ross Ice Shelf and thus the West Antarctic Ice Sheet. As part of the Roosevelt Island climate evolution (RICE) project, a 763 m deep ice core was recovered during 2011–13 from Roosevelt Island, at the northern edge of the Ross Ice Shelf. The ice at Roosevelt Island is grounded 210 m below sea level and accumulates in situ, with the Ross Ice Shelf flowing around the rise. High-resolution radar surveys show a well developed Raymond Bump at the divide of the ice dome. The RICE age model is developed using high-resolution methane data tied to the WAIS Divide ice core record, supported with annual layer count, tephra ages and a glacial flow model. Here we show data spanning the past 30 ka and discuss reconstructions of sea surface and air temperature, sea-ice extent, atmospheric circulation patterns and ice-shelf grounding-line retreat. An ensemble of sensitivity modelling experiments is used to determine thresholds for the removal of ice on Roosevelt Island and correlated grounding-line and ice-volume changes of the Ross Ice Shelf and the West Antarctic Ice Sheet. Our data suggest that the delayed onset of the Ross Ice Shelf grounding-line retreat during the deglaciation was driven at least in part by the early onset of deglaciation in West Antarctica as recorded in the WAIS ice core. The Ross Ice Shelf grounding line started to retreat rapidly with the initiation of an ice shelf cavity. RICE TEAM: Bertler N, Conway H, Dahl-Jensen D, Baccolo G, Baisden T, Blunier T, Brightley H, Brook E, Buizert C, Carter L, Ciobanu G, Dadic R, Delmonte B, Dongqi Z, Edwards R, Eling L, Ellis A, Emanuelsson D, Fudge T, Golledge N , Hindmarsh R, Hawley R, Jiao Y, Johnson K, Keller L, Kingslake J, Kipfstuhl S, Kjær H, Korokikth E , Kurbatov A, Lee J, Lowry D, Mayewski P, Naish T, Neff P, Scherer R, Schoeneman S, Severinghaus J, Simonsen M, Steig E, Ulaylottil Venugopal A, Vallelonga P, Waddington E, Winton H
75A2226
Sea ice drives the large-scale Southern Ocean overturning circulation
Violaine Pellichero, Jean-Baptiste Sallée, Sunke Schmidtko, Fabien Roquet, Jean-Benoît Charrassin
Corresponding author: Violaine Pellichero
Corresponding author e-mail: violaine.pellichero@locean-ipsl.upmc.fr
In the Southern Ocean, deep waters well up towards the ocean surface under sea ice, where water masses are transformed in the mixed layer and re-injected back in deeper or shallower layers. The role of the Southern Ocean in ventilating global deep waters and redistributing heat and fresh water within the upper ocean is particularly important for the climate as a whole. However, significant uncertainty exists about the processes responsible for the Southern Ocean water mass overturning circulation south of 30° S. Working on elephant-seal-derived data as well as ship-based observations and Argo float data, we have investigated the processes that lead to the under-ice transformation of the upper circumpolar deep water (UCDW) and Antarctic intermediate water (AAIW). Air–sea flux data from several sources and in situ observations are used to describe the diapycnal flux at the ocean surface from one density class to the next, including UCDW and AAIW density ranges. In the sea-ice sector, our results show that surface buoyancy fluxes drive an upwelling of about 6 Sv in the UCDW ranges and a subduction of about 4.5 Sv in the AAIW ranges. The freshwater flux dominates over most of the density ranges, highlighting the role of the sea ice in driving this Southern Ocean branch of the meridional overturning circulation and fresh-water transport. Moreover, the regional distribution of the cross-isopycnal flux is computed in order to identify the regions where the UCDW upwells and AAIW sinks around the Antarctic continent. Our conclusions suggest that changes in regional sea-ice distribution or sea-ice seasonal cycle duration, as currently observed, would widely affect the buoyancy budget of the underlying mixed layer, and impacts large-scale water-mass formation and transformation
75A2272
Paleoclimate earth system modelling of cryosphere–ocean interactions in the Southern Hemisphere
Elizabeth Keller, Nicholas Golledge, Richard Levy
Corresponding author: Elizabeth Keller
Corresponding author e-mail: l.keller@gns.cri.nz
We present paleoclimate model experiments designed to explore ocean–ice interactions in the Southern Hemisphere under warmer-than-present conditions. We examine the changes in ocean circulation and biochemistry associated with the retreat of the West Antarctic Ice Sheet (WAIS) with steady-state simulations of Pliocene and Miocene interglacials, and the role of ocean dynamics in the expansion and retreat of WAIS during glacial/interglacial transitions. We use intermediate-complexity earth system models LOVECLIM and the UVic ESCM for initial exploration, with the goal of moving to a full GCM and a high-resolution ocean model to examine more detailed ice–ocean dynamics and processes.
75A2296
Role of tropical teleconnections in changes in the Southern Ocean dynamics and Antarctic sea-ice extent in the ACME Earth System Model
Rahul Sivankutty, Diana Francis, Eayrs Clare, David Holland, Stephen Price
Corresponding author: Rahul Sivankutty
Corresponding author e-mail: rs5521@nyu.edu
Recent studies suggest that changes in the Southern Ocean, particularly the Antarctic Circumpolar Current, can influence the thermal structure of the upper ocean and thus affect sea-ice concentration in the Antarctic region. The poleward shifting of subtropical westerlies can result in changes in ocean circulation pattern. The changes in the Southern Annular Mode, and its linkage to tropical SST variability, prove that tropical teleconnections can play an important role in Antarctic climate variability. Using a state-of-the-art Earth system model – the US Department of Energy’s Accelerated Climate Model for Energy (ACME) – which includes coupled representations of all of the components of the physical climate system (atmosphere, land, ocean, sea ice and land ice), we study the tropical linkages to the variability in the Southern Ocean and Antarctic sea ice. The study validates the model’s ability to capture the observed teleconnection patterns. The mechanisms by which the tropical climate influences the dynamics of the Southern Ocean and thereby Antarctic sea ice variability are highlighted.
75A2308
Glacial Antarctic warm events as captured by RICE ice core
Abhijith UV, Nancy Bertler, Giuseppe Cortese
Corresponding author: Abhijith UV
Corresponding author e-mail: Abhijith.Uv@vuw.ac.nz
The last glacial period in Antarctica has been punctuated by several episodes of warm events, where air temperature rose between 1 and 3°C, which are referred to as Antarctic isotope maxima (AIM). On correlating high-resolution Antarctic and Greenland ice-core records for AIM events, an out-of-phase relationship has been observed between both the hemispheres, with Antarctica warming when Greenland is under a cold phase and Antarctica cooling when Greenland stays in a warm state. This out-of-phase relationship is called the ‘bipolar seesaw’. Possible explanations include oceanic teleconnections via a shift in strength of the Atlantic Meridional Overturning Circulation (AMOC) and Antarctic bottom water (AABW) formation. A recent comparison between the WAIS Divide and NGRIP records identified a Northern Hemisphere lead of about 218 ± 92 a and 208 ± 96 a for the onset and termination of Dangaard/Oeschger and AIM events, further evidence for an important oceanic role in the interhemispheric energy distribution. Roosevelt Island is a local ice rise at the northern edge of the Ross Ice Shelf. A 764 m deep ice core, the Roosevelt Island Climate Evolution (RICE) core, was obtained over two field seasons in 2011/12 and 2012/13. Due to its proximity to the Ross Sea, one of the major contributors to AABW, the RICE records have the potential to provide new insights into the drivers and consequences during the evolution of AIM events. Here, we will present preliminary data of the major ion record from the RICE ice core covering an age range of 18–60 ka with the main focus of understanding core aspects of AABW during AIM events, including its strength and mode of formation and further to test the bipolar seesaw hypothesis.
75A2377
Subsurface geomorphology and post-Last-Glacial-Maximum deglaciation of Pine Island Glacier, Antarctica
Gerhard Kuhn, Johann Philipp Klages, Claus-Dieter Hillenbrand, James A. Smith, Frank O. Nitsche, Karsten Gohl, Sabine Kasten
Corresponding author: Gerhard Kuhn
Corresponding author e-mail: gerhard.kuhn@awi.de
Subglacial meltwater largely facilitates rapid but nonlinear ice flow beneath concurrent ice streams, and there is widespread evidence for a dynamic subglacial water system beneath the Antarctic Ice Sheet. It steers and affects the pattern of ice flow and is a direct result of boundary processes acting at the ice sheet bed, i.e. pressure-induced basal melting. Consequently, the occurrence of subglacial meltwater plays an important role in bedrock erosion, subsequent re-deposition, and shaping of the topography of ice-sheet beds. Here we present new geological and geochemical data from sediment cores recovered from the West Antarctic continental shelf in Pine Island Bay. We have interpreted the data as a reliable indicator for deposition in palaeo-subglacial lakes beneath the formerly expanded West Antarctic Ice Sheet, presumably following the Last Glacial Maximum (LGM). Characteristic changes of sedimentary facies and geochemical profiles within these cores taken on RV Polarstern expeditions ANT-XXIII/4 (2006) and ANT-XXVI/3 (2010) support the presence of an active and expanded subglacial lake system in at least five basins that were carved into bedrock during the last glaciations and filled with some meters of post-LGM sediments. These findings have important implications for palaeo ice-sheet dynamics, suggesting the presence of considerable amounts of water lubricating the ice–bed interface, eventually leading to the subglacial deposition of water-saturated subglacial lake sediments and soft tills. Based on our recent findings, we suggest the transition from a subglacial lake to an ocean-influenced environment took place during deglaciation at the transition from glacial marine isotope stage (MIS) 2 to the early Holocene. We suggest that the ice sheet thinned and the sub-ice lakes successively transformed to sub-ice cavities flushed by tidal currents at this time. Based on bathymetric maps, a glacial isostatic adjustment model, a global sea level curve and age information, we estimate ice thickness for buoyancy at the grounding line, as this grounding line retreated further inland across the rim of the subglacial lake. Our findings may have implications for ice-sheet models, which have to consider the predominantly non-linear effects related to subglacial hydrology
75A2401
IODP Expedition 374: ocean–ice-sheet interactions and West Antarctic Ice Sheet vulnerability
Rob McKay, Laura De Santis, Denise Kulhanek
Corresponding author: Rob McKay
Corresponding author e-mail: robert.mckay@vuw.ac.nz
Observations from the past several decades indicate that the Southern Ocean is warming significantly, while Southern Hemisphere westerly winds have migrated southward and strengthened due to increasing atmospheric CO2 concentrations and/or ozone depletion. These changes have been linked to thinning of Antarctic ice shelves and marine-terminating glaciers. Results of geologic drilling on Antarctica’s continental margins indicate late Neogene marine-based ice-sheet variability and numerical modeling indicates a fundamental role for oceanic heat in controlling this variability over at least the past 20 million years. While ice-sheet variability has been observed, sedimentologic sequences from the outer continental shelf are still required to evaluate the extent of past ice-sheet variability and the role of oceanic heat flux in controlling ice-sheet mass balance. IODP Expedition 374 is scheduled to be drilled in January 2018 and proposes a latitudinal and depth transect of sixdrill sites from the outer continental shelf and rise in the eastern Ross Sea to resolve the relationship between climatic/oceanic change and West Antarctic Ice Sheet evolution through the Neogene and Quaternary. This location was selected because numerical ice-sheet models indicate that it is highly sensitive to changes in ocean heat flux and sea level. The proposed drilling is designed for optimal data–model integration, which will enable an improved understanding of the sensitivity of Antarctic Ice Sheet mass balance during warmer-than-present climates (e.g. the early Pliocene and middle Miocene). Additionally, the proposed transect links ice proximal records from the inner Ross Sea continental shelf (e.g. ANDRILL sites) to deep southwest Pacific drilling sites/targets to obtain an ice proximal to far-field view of Neogene climate and Antarctic cryosphere evolution.
75A2402
An update on ice-shelf changes in Northern Greenland
Jérémie Mouginot, Eric Rignot, Bernd Scheuchl, Mathieu Morlighem, Ala Khazendar
Corresponding author: Jeremie Mouginot
Corresponding author e-mail: jmougino@uci.edu
Zachariæ Isstrøm, in northeast Greenland, is retreating and accelerating, most probably because of enhanced melting at its ice-shelf bottom followed by its break-up. Nioghalvfjerdsfjorden, its neighbor, is also showing signs of thinning close to its grounding line, as is Petermann Gletscher, located 800 km more to the west. Here, we investigate dynamic and geometrical changes of all the other glaciers located along the northern coast of Greenland, namely Humboldt Gletscher, Steensby Gletscher, Ryder Gletscher, Ostenfeld Gletscher, Marie Sophie Gletscher, Academy Gletscher and Hagen Bræ. Using satellite and airborne-based remote-sensing sensors, we reconstruct the time series of speed, grounding-line position, ice thickness and surface elevation changes since the 80s. We will provide an update of the glacier ice discharges and will discuss any large-scale pattern of enhanced melting of the northern Greenlandic ice shelves . We will conclude with the possibility of actual or future destabilization -or lack thereof- of the glaciers in this sector of Greenland.
75A2445
Rapid melting in the basal zone of a major Greenland outlet glacier
Poul Christoffersen, Tun Jan Young, Bryn Hubbard, Samuel Huckerby Doyle, Alun Hubbard, Marion Bougamont, Coen Hofstede, Keith Nicholls
Corresponding author: Poul Christoffersen
Corresponding author e-mail: pc350@cam.ac.uk
The Greenland ice sheet is losing mass and raising sea levels by 1 mm a–1. While melting of the ice sheet explains half of the net annual loss, the other half is caused by dynamic processes operating in the catchments of marine-terminating outlet glaciers. These processes are poorly understood because they are confined to the basal zone, which is often inaccessible. The Subglacial Access and Fast Ice Research Experiment (SAFIRE) is addressing this paucity of data by drilling to the bed of Store Glacier, the second-largest outlet glacier in West Greenland in terms of flux. Seven 600-m-deep boreholes were drilled to the base of the glacier, about 30 km inland from the calving terminus, at a location where ice flows at a rate of 700 m a–1. Sensors installed at the bed and within ice show that the glacier overrides a warm bed consisting of soft, water-saturated sediment. Basal motion comprised a combination of intense deformation of temperature basal ice as well as sliding. High basal water pressure with diurnal variations showed that water produced on the surface is transported subglacially in a distributed basal water system, which nevertheless was sufficiently efficient to cause rapid lowering of the water level in all seven boreholes, once the system was intercepted. To evaluate the quantify of heat transported from surface to bed, we measured rates of basal melting with a phase-sensitive, frequency-modulated continuous wave (FMCW) radar system installed autonomously at the borehole drill site. The radar captured internal and basal reflector ranges at high spatial (millimetre) and temporal (hourly) resolutions, producing a unique time series of ice deformation and basal melting, coincident with englacial and subglacial borehole measurements. Here, we show that the rate of basal melting was 3 m a–1 in winter, when heat at the bed is provided mainly by basal friction, and that it increases to 20 m a–1 in summer, when heat is also transported to the bed from the surface. Our measurements show that the flow of outlet glaciers from the Greenland Ice Sheet is influenced not only by their interaction with the ocean but equally by their interaction with the atmosphere, making them potentially more sensitive to climate change than thought so far.
75A2456
Future fate of the polar ice sheets and implications for global coastlines
Rob DeConto
Corresponding author: Rob DeConto
Corresponding author e-mail: deconto@geo.umass.edu
New climate and ice-sheet modeling, calibrated to past changes in sea level, is painting a stark picture of the future fate of the great polar ice sheets if greenhouse-gas emissions continue unabated. This is especially true for Antarctica, where a substantial fraction of the ice sheet rests on bedrock more than 500 m below sea level. Here, we will explore the sensitivity of the polar ice sheets to a warming atmosphere and ocean, using models that include previously underappreciated physical processes, including surface meltwater-driven hydrofracturing and structural failure of ice cliffs. Approaches to more precisely define the climatic thresholds capable of triggering rapid and potentially irreversible ice-sheet retreat will also be discussed, as will the potential for policy and aggressive mitigation strategies like those discussed at the 2015 Paris Climate Conference to substantially reduce the risk of extreme sea-level rise.