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SPRI Physical Sciences Seminar Series

SPRI Physical Sciences Seminar Series

Lent Term 2009-10

Wednesday 20th January
Andrew Sole (University of Aberdeen)
The effects of coastal ocean warming and increased supra-glacial run-off on water temperature and circulation in Kangerdlugssuaq Fjord, East Greenland
Recent studies have suggested that regional changes in ocean temperatures could be a potential trigger for retreat and acceleration of Greenland tidewater outlet glaciers. There is therefore a need to understand how these changes are propagated along fjords to the glaciers' calving termini. We use the Bergen Ocean Model to simulate ocean circulation in Kangerdlugssuaq Fjord to assess the impact that warmer coastal waters and increased supra-glacial run-off could have on the submarine melt rate of Kangerdlugssuaq Gletscher. The model includes tidal and freshwater runoff forcing and is able to replicate well observed temperature and salinity profiles. We find that warm coastal water flows into the fjord at several distinct depths as a result of freshwater outflow near the surface and at intermediate depth. The deeper (~400m) warm water plume reaches the terminus of Kangerdlugssuaq Gletscher and increases submarine melt rates. The magnitude of supraglacial runoff is crucial in controlling the penetration of warm water into the fjord because of the compensatory inflow at depth.
Wednesday 3rd February
Paul Berkman (University of Cambridge)
Environmental Protection in the Arctic Ocean
The Arctic Ocean is crossing an environmental threshold expected to transform it from a perpetually ice-covered region to a seasonally ice-free sea within the next few decades. This environmental change has awakened global interests in Arctic energy, fishing, shipping, and tourism. The Arctic could slide into a new era featuring jurisdictional conflicts, increasingly severe clashes over the extraction of natural resources, and the emergence of a new "great game" among the global powers. However, the environment provides a physical and a conceptual framework to link government interests in the Arctic Ocean, as well as a template for addressing transboundary security risks cooperatively.
Wednesday 17th February
Anthony Seale
Automatic satellite monitoring of East Greenland's calving glacier fronts: seasonal signals and southern retreat
Whilst completing my M.Phil at SPRI I developed a new automated system for tracking Greenland tidewater glacier frontal positions using MODIS (satellite) data. By reducing the amount of researcher labour required to gather glacier positions, the method allowed data to be collected from 105,536 glacier images, giving a detailed account of East Greenland glacier retreat and other behaviour during the rapid speed-up events of the past decade. Large scale retreat was found on southern glaciers, with little change further north. Widespread seasonal patterns were also found to exist on many glaciers. The role of the ocean in controlling retreat is considered, attempting to explain the observations. This talk will be of interest to remote sensors, glaciologists and M.Phil students beginning their research.
Wednesday 3rd February
Bernd Kulessa (Swansea University)
Flow, fracture and modelled present stability of the Larsen C ice shelf
We modelled the flow of the Larsen C ice shelf using an adapted continuum-mechanical model, and applied a fracture criterion to the simulated velocities to investigate its present-day stability. Constraints come from satellite data and geophysical measurements in the 2008-09 austral summer. We obtained excellent agreements between modelled and measured ice-flow velocities, and inferred and observed distributions of rifts and crevasses. Ice-shelf thickness was derived from BEDMAP and ICESat data and depth-density profiles inferred from our seismic data. Notable exceptions occur in regions of modelled basal accretion down flow of promontories, thus placing the first quantitative constraints on their mechanical effects. Anomalously soft marine ice, advected into the ice shelf in flow-parallel bands, controls rates of rift propagation downstream. In this presentation I will assess the implications of these findings for the current stability of the Larsen C ice shelf, as compared with the pre-collapse dynamic evolution of the Larsen B ice shelf. I will also present initial analyses and findings from extensive ground-penetrating radar surveys in the 2009-10 austral summer in a prominent zone of basal accretion down-flow of the Joerg Peninsula.

Michaelmas Term 2009-10

NOTE: Seminars will be held in the Friends' Room during this term due to the refurbishment of the museum. The Friends' room is accessed via the Library (1st floor). Talks will be sign-posted.

Wednesday 28th October
Paul Holland (British Antarctic Survey)
Marine Ice in Larsen Ice Shelf
It is argued that Larsen Ice Shelf contains marine ice formed by oceanic freezing and other mechanisms. Missing basal returns in airborne radar soundings and observations of a smooth and healed surface coincide downstream of regions where an ocean model predicts freezing. Visible imagery suggests that marine ice currently stabilizes Larsen C Ice Shelf and implicates failure of marine flow bands in the 2002 Larsen B Ice Shelf collapse. Ocean modeling indicates that any regime change towards the incursion of warmer Modified Weddell Deep Water into the Larsen C cavity could curtail basal freezing and its stabilizing influence.
Wednesday 11th November
Alex Piotrowski (Earth Sciences, University of Cambridge)
Linking North and South Atlantic deep water circulation using Nd isotopes
Understanding changes in ocean circulation during the last deglaciation is crucial to unravelling the dynamics of glacial-interglacial and millennial climate shifts. Neodymium (Nd) isotope records measured on Fe-Mn oxide leaches from marine sediment cores have been used to reconstruct changes in Atlantic deep water mixing and structure. We present new tests of marine Nd extraction, and new widely distributed records. Taken as a whole, these records provide a coherent reconstruction of glacial Atlantic deep circulation, which is consistent with benthic d13C reconstructions, and suggests major changes in water mass strength and structure during the last deglaciation. Neodymium isotope measurements from deep western North Atlantic at the Bermuda Rise allow comparison of our deep water source record with overturning strength proxies. This comparison shows that both deep water mass source and overturning rate shifted rapidly and synchronously during the last deglacial transition. In contrast any freshwater perturbation caused by Heinrich event 1, could have only affected shallow overturning illustrating the difference between changes in upper-ocean overturning associated with millennial-scale events, and whole ocean deglacial climate events.
Wednesday 18th November
Alan Ashworth (Department of Geosciences, North Dakota State University)
Neogene terrestrial environment of Antarctica
The discovery of terrestrial fossil assemblages at several locations in the Transantarctic Mountains is transforming our understanding of the late Cenozoic environment of Antarctica. The most southerly fossil assemblage is at lat. 85.1°S, about 500 km from the South Pole. The environment was an active glacial margin in which plants, insects and freshwater mollusks inhabited sand and gravel bars and small lakes on an outwash plain. Initially the deposits were assigned a Pliocene age (3.5 Ma) but a mid- to early Miocene age is more probable (c. 14 – 25 Ma) based on correlation of fossil pollen from the deposits with 39Ar/40Ar dated pollen assemblages from the McMurdo Dry Valleys. Within the McMurdo Dry Valleys, the oldest fossiliferous beds are at least 19.76 Ma based on the 39Ar/40Ar age of a volcanic ash bed interbedded within a valley fill of diamictites, paleosols and lacustrine deposits. The valley floor during the non-glacial phases had poorly-drained soils and the extensive development of mossy mires. Wood and leaves of Nothofagus are abundant in lacustrine deposits. The silts of shallow fluvial channels contain abundant megaspores and spiky leaves of the aquatic lycopod Isoetes (Quillwort). The youngest fossiliferous beds within the Dry Valleys are 14.07 Ma. The fossils are mostly those of freshwater organisms including numerous species of diatoms and an ostracod species in which the soft anatomy is preserved. The base of the lake is marked by a moss bed with exceptionally well-preserved stems and leaves of the extant species Drepanocladus longifolius. Pollen evidence from marine cores in the Ross Sea basin suggests that tundra existed from the Oligocene to the Mid-Miocene. Fossil evidence from the Dry Valleys locations indicates organisms with complex life histories persisted in Antarctica until c. 14 Ma. At 14 Ma there was a shift in glacial regimes from wet- to cold-based, marking a profound and abrupt climatic shift likely causing widespread extinction. It seems probable that at least some of the mid-Miocene fossils had ancestors that evolved in Antarctica during the Paleogene or earlier. An important consequence of these studies is that the Cenozoic climate of Antarctica was warm enough until the mid-Miocene to support vascular plants and insects.
Wednesday 25 November
Screening of the Werner Herzog film "Encounters at the End of the World"
Instead of the usual seminar, there will be a screening of the Werner Herzog film "Encounters at the End of the World" - a documentary about the people and the science based out of McMurdo Station, Antarctica.
Wednesday 2 December
Christopher Talbot (Earth Sciences, University of Uppsala)
Subaerial salt extrusions in Iran as analogues of ice sheets, streams & glaciers
Ice (H20) and salt (halite, NaCl) form by different processes in mutually exclusive environments but share many physical properties and resemble each other in hand specimens and en-masse. Layyers of salt have to be buried by kilometres of other rocks over millions of years before they rise to the surface in piercing structures (diapirs) many of which extrude flows that simulate glaciers. Seismic profiles have revealed 1000s such salt sheets in over 35 basins worldwide in the last 25 years. As most of these are submarine the focus here will be on subaerial rivers of salt (namakiers) exposed in the deserts of Iran. Glaciers and namakiers will be compared and contrasted. Clear grain shape fabrics map streamlines that help understand how folds develop inside namakiers. Namakiers surge like glaciers but within 20 minutes of their TOP surfaces being wet by rain that cannot reach the basal contact.