Browsing by Author "Vyverman, W"
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- ItemLate quaternary changes in the westerly winds over the Southern Ocean – a progress report(VII Southern Connection Congress 2016, 2016-01-18) Hodgson, DA; Roberts, S; Perren, B; Saunders, KM; Verleyen, E; van Nieuwenhuyze, W; Vyverman, W; Sime, LThe Southern Hemisphere westerly winds (SHW) are the strongest time-averaged oceanic winds. They drive the circulation of the Southern Ocean and changes in their strength and position are thought to modify the upwelling of carbon rich deep water, exerting significant control on the ocean-atmosphere balance of CO2. Thus changes in the SHW, such as the recently observed intensification, could influence whether the Southern Ocean acts as a net source or sink of atmospheric CO2, with major implications for global climate. At present the relationships between wind strength, CO2 and climate are poorly understood and there are very few studies within the core belt of the SHW in the sub-Antarctic zone c.46 to 60 deg South. We have been attempting to address this by producing centennial to decadal reconstructions of changes in SHW strength at sub-Antarctic islands in each of the major sectors of the Southern Ocean. In this talk we will show how lake sediments and peat deposits on the west coasts of these islands can yield proxy-based reconstructions of past changes in the SHW. We will review the statistical performance of our inference models, their application down selected sediment cores, and compare them with complimentary proxies of changes in wind strength based on precipitation and minerogenic inputs. The next phase of the project will use GCM simulations to help understand the patterns seen in the observational data and identify the drivers of past changes in the SHW.
- ItemA luminescence study of porous diatoms(European Materials Research Society, 2004-05) Butcher, KSA; Ferris, JM; Phillips, MR; Wintrebert-Fouquet, M; Jong Wah, JW; Jovanovic, N; Vyverman, W; Chepurnov, VA
- ItemLuminescence study of porous diatoms(Elsevier, 2005-12) Butcher, KSA; Ferris, JM; Phillips, MR; Wintrebert-Fouquet, M; Jong Wah, JW; Jovanovic, N; Vyverman, W; Chepurnov, VAThe cathodoluminescent and photoluminescent properties of the nanoporous silica frustules of various diatom strains and of natural diatom samples are presented. The spectra are observed to be similar to that of pure silica glass and the phenology is therefore believed to also be somewhat similar. A strong U-V-blue luminescence peak is commonly observed as well as a yellow peak at 2.15 eV For the more heavily silicified field-collected freshwater benthic samples, a strong red peak at 1.95 eV is also observed. The 2.15 eV peak is also more strongly evident for the field-collected samples. The U-V-blue peak is related to common silica defect structure but cathodoluminescent microanalysis shows that this emission is highly localized in the diatom samples. © 2005, Elsevier Ltd.
- ItemRetreat history of the East Antarctic ice sheet since the last glacial maximum(Elsevier, 2014-09-15) Mackintosh, AN; Verleyen, E; O'Brian, PE; White, DA; Jones, RS; McKay, RM; Dunbar, R; Gore, DB; Fink, D; Post, AL; Miura, H; Leventer, A; Goodwin, ID; Hodgson, DA; Lilly, K; Crosta, X; Golledge, NR; Wagner, B; Berg, S; van Ommen, TD; Zwartz, D; Roberts, SJ; Vyverman, W; Massé, GThe East Antarctic Ice Sheet (EAIS) is the largest continental ice mass on Earth, and documenting its evolution since the Last Glacial Maximum (LGM) is important for understanding its present-day and future behaviour. As part of a community effort, we review geological evidence from East Antarctica that constrains the ice sheet history throughout this period (∼30,000 years ago to present). This includes terrestrial cosmogenic nuclide dates from previously glaciated regions, 14C chronologies from glacial and post-glacial deposits onshore and on the continental shelf, and ice sheet thickness changes inferred from ice cores and continental-scale ice sheet models. We also include new 14C dates from the George V Land – Terre Adélie Coast shelf. We show that the EAIS advanced to the continental shelf margin in some parts of East Antarctica, and that the ice sheet characteristically thickened by 300–400 m near the present-day coastline at these sites. This advance was associated with the formation of low-gradient ice streams that grounded at depths of >1 km below sea level on the inner continental shelf. The Lambert/Amery system thickened by a greater amount (800 m) near its present-day grounding zone, but did not advance beyond the inner continental shelf. At other sites in coastal East Antarctica (e.g. Bunger Hills, Larsemann Hills), very little change in the ice sheet margin occurred at the LGM, perhaps because ice streams accommodated any excess ice build up, leaving adjacent, ice-free areas relatively unaffected. Evidence from nunataks indicates that the amount of ice sheet thickening diminished inland at the LGM, an observation supported by ice cores, which suggest that interior ice sheet domes were ∼100 m lower than present at this time. Ice sheet recession may have started ∼18,000 years ago in the Lambert/Amery glacial system, and by ∼14,000 years ago in Mac.Robertson Land. These early pulses of deglaciation may have been responses to abrupt sea-level rise events such as Meltwater Pulse 1a, destabilising the margins of the ice sheet. It is unlikely, however, that East Antarctica contributed more than ∼1 m of eustatic sea-level equivalent to post-glacial meltwater pulses. The majority of ice sheet recession occurred after Meltwater Pulse 1a, between ∼12,000 and ∼6000 years ago, during a period when the adjacent ocean warmed significantly. Large tracts of East Antarctica remain poorly studied, and further work is required to develop a robust understanding of the LGM ice sheet expansion, and its subsequent contraction. Further work will also allow the contribution of the EAIS to post-glacial sea-level rise, and present-day estimates of glacio-isostatic adjustment to be refined. © 2014 The Authors. CC-BY Licence.
- ItemSmall angle neutron scattering on an absolute intensity scale and the internal surface of diatom frustules from three species of differing morphologies(Springer, 2013-05-01) Garvey, CJ; Strobl, M; Percot, A; Šaroun, J; Haug, J; Vyverman, W; Chepurnov, VA; Ferris, JMThe internal nanostructure of the diatoms Cyclotella meneghiniana, Seminavis robusta and Achnanthes subsessilis was investigated using small angle neutron scattering (SANS) to examine thin biosilica samples, consisting of isotropic (powder) from their isolated cell walls. The interpretation of SANS data was assisted by several other measurements. The N-2 adsorption, interpreted within the Branuer-Emmet-Teller isotherm, yielded the specific surface area of the material. Fourier transform infrared (FTIR) and Raman spectroscopy indicates that the isolated material is amorphous silica with small amounts of organic cell wall materials acting as a filling material between the silica particles. A two-phase (air and amorphous silica) model was used to interpret small angle neutron scattering data. After correction for instrumental resolution, the measurements on two SANS instruments covered an extended range of scattering vectors 0.0011 nm(-1) < q < 5.6 nm(-1), giving an almost continuous SANS curve over a range of scattering vectors, q, on an absolute scale of intensity for each sample. Each of the samples gave a characteristic scattering curve where log (intensity) versus log (q) has a -4 dependence, with other features superimposed. In the high-q regime, departure from this behaviour was observed at a length-scales equivalent to the proposed unitary silica particle. The limiting Porod scattering law was used to determine the specific area per unit of volume of each sample illuminated by the neutron beam. The Porod behaviour, and divergence from this behaviour, is discussed in terms of various structural features and the proposed mechanisms for the bio-assembly of unitary silica particles in frustules. © 2013, Springer.