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. (2012). Observation of low shear wave velocity at the base of the polar ice sheets: evidence for enhanced anisotropy
. Geophysical Journal International , 190 (1 ), 391–405 .
Abstract: We analyse seismic data from the broad-band stations located on the Antarctic and Greenland ice sheets to determine the large-scale seismic parameters of the polar ice sheets. The P-to-S converted waves at the ice/rock interface and inside the ice sheets and their multiples (the P receiver functions) are used to estimate the in situ P velocity Vp and the P-to-S velocity ratio Vp/Vs of the polar ice. The thickness of the whole ice layer is precisely known either from radio echo soundings or from ice core drillings allowing thus an accurate determination of Vp and Vp/Vs. At some places in and near the Wilkes Basin, a sedimentary layer is probably squeezed between the ice and the bedrock. We find that the polar ice caps have a two-layer structure, the upper layer of variable thickness about 2/3 of the total thickness with velocities very close to the ice standard values and the lower layer preserving a standard Vp but with about 25 per cent smaller shear wave velocity and a more or less constant thickness. The shear-velocity drop in the lower layer may be the evidence of a strong anisotropy induced by preferred orientation of ice crystals and by fine layering of soft and hard ice layers. A large variation of ice viscosity with depth is therefore expected and heterogeneous flowing of the polar ice sheet. This heterogeneous flowing may invalidate the use at great depth of the ice dating models based on monotonic layer thinning.
Programme: 906
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Wittlinger G. & Farra V. (2007). Converted waves reveal a thick and layered tectosphere beneath the Kalahari super-craton. Earth Planet. Sci. Lett., 254, 404–415.
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Winton, H., Frey, M., Haigh, J., Mulvaney, R., Pyle, J., Savarino, J., Tuckwell, R., Weller, R., and Yang, X. (2018). Air-snow transfer of nitrate in Dronning Maud Land, East Antarctica. Bachelor's thesis, , .
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Winton V.H.L., Ming A., Caillon N., Hauge L. Jones A.E., Savarino J., Yang X., Frey M.M. (2020). (Vol. 20). Bachelor's thesis, , .
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Winters Kraig B, Bouruet-Aubertot Pascale, Gerkema Theo, . (2011). Critical reflection and abyssal trapping of near-inertial waves on a -plane
. Journal of Fluid Mechanics, 684, 111–136.
Abstract: ABSTRACT We consider near-inertial waves continuously excited by a localized source and their subsequent radiation and evolution on a two-dimensional $\ensuremath{\beta} $-plane. Numerical simulations are used to quantify the wave propagation and the energy flux in a realistically stratified ocean basin. We focus on the dynamics near and poleward of the inertial latitude where the local value of the Coriolis parameter $f$ matches the forcing frequency $\sigma $, contrasting the behaviour of waves under the traditional approximation (TA), where only the component of the Earths rotation aligned with gravity is retained in the dynamics, with that obtained under the non-traditional approach (non-TA) in which the horizontal component of rotation is retained. Under the TA, assuming inviscid linear wave propagation in the WKB limit, all energy radiated from the source eventually propagates toward the equator, with the initially poleward propagation being internally reflected at the inertial latitude. Under the non-TA however, these waves propagate sub-inertially beyond their inertial latitude, exhibiting multiple reflections between internal turning points that lie poleward of the inertial latitude and the bottom. The numerical experiments complement and extend existing theory by relaxing the linearity and WKB approximations, and by illustrating the time development of the steadily forced flow and the spatial patterns of energy flux and flux divergence. The flux divergence of the flow at both the forcing frequency and its first harmonic reveal the spatial patterns of nonlinear energy transfer and highlight the importance of nonlinearity in the vicinity of near-critical bottom reflection at the inertial latitude of the forced waves.
Programme: 1015
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. (2015). Explaining the disjunct distributions of austral plants: the roles of Antarctic and direct dispersal routes
. Journal of Biogeography, 42(7), 1197–1209.
Abstract: Aim. Dispersal explains the disjunct distributions of many austral plant lineages.
However, the role of Antarctica is largely uncertain and the routes of
dispersal have remained speculative. Based on niche conservatism we can make
predictions about the timing of disjunction establishment, as well as the availability
of direct transoceanic, Antarctic stepping-stone, and out-of-Antarctica
dispersal routes over time. We evaluate these predictions using molecular
divergence time estimates for the establishment of disjunct distributions across
multiple plant lineages.
Location. Southern Hemisphere.
Methods. We estimated the timing of disjunction establishment and determined
habitat affinities for 72 austral plant groups. We used Wilcoxon rank
sum tests to compare the timing of disjunction establishment between cold
and temperate climate lineages for the full data set, as well as within several
subsets. We compared our results with those from a literature survey.
Results. As niche conservatism predicts, the timing of disjunction establishment
in cold and temperate climate austral lineages is consistent with the availability
of the corresponding habitats over time. Our results also suggest that
disjunction establishment has involved a combination of Antarctic and direct
dispersal routes. For cold climate lineages, both out-of-Antarctica and direct
dispersal routes are required to explain the observed estimates, while stepping
stone routes cannot be ruled out. It appears that for these lineages the importance
of the three dispersal routes differs with environmental, geographical and
temporal context.
Main conclusions. Both direct and Antarctic dispersal routes are necessary to
explain the establishment of contemporary austral distributions. Evidence that
some taxa were, until recently, restricted to Antarctica changes how we view
the evolutionary histories of austral floras and the lineages they contain. Moreover,
that we detect differences in the importance of alternative dispersal routes
suggests that long-distance plant dispersal processes can be explicitly incorporated
into models of climate change response.
Programme: 1116
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Winkworth RC, Hennion F, Wagstaff SJ. (2013). Origins and evolution of plant diversity on the southern lands: new insights from large phylogenies. VII Southern Connection Congress, Dunedin, New-Zealand, 19-25 January 2013 .
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Winkworth RC, Hennion F, Prinzing A, Hermant M, Wagstaff SJ. (2013). Antarctica helped shape Southern Hemisphere plant distribution patterns. VII Southern Connection Congress, Dunedin, New-Zealand, 19-25 January 2013 .
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Winkworth R.C., Hennion F., Hermant M., Prinzing A. & Wagstaff S.J. (2009). The role of Antarctica and the subantarctic islands in south hemisphere plant dispersal.
Abstract: Xth SCAR International Biology Symposium, Sapporo, Japon, 26-31/07/2009
Programme: 136
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Winkworth R.C. (2012).
Abstract: invited seminar
Programme: 136
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