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A Landform Based 3D Reconstruction of Glacier Ice at the Last Glacial Maximum in the Southern Alps, New Zealand

James, William Henry Meurig (2016) A Landform Based 3D Reconstruction of Glacier Ice at the Last Glacial Maximum in the Southern Alps, New Zealand. PhD thesis, University of Leeds.

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Abstract

New Zealand fills a large geographic gap in the global glacial record, with landforms and near-surface deposits preserving a remarkable footprint of Quaternary glaciation. As one of the few land masses in the Southern Hemisphere, the record of glacial geomorphology is of great importance for research into the natural behaviour of the Earth’s climate system. This thesis presents a 3D simulation of the New Zealand Southern Alps glaciers at the Last Glacial Maximum (LGM, c. 30 to 18 ka) in an attempt to constrain glacial geometry of that period. To achieve this, the REVOLTA (Reconstruction of Volume and Topography Automation) model was developed, a Python script tool for ArcGISTM that requires just a DEM of glacier bed conditions and the down-valley extent of glaciation as initial inputs. Ice thickness is initially estimated at points along an automatically generated centreline network based on the perfect-plasticity rheology assumption, taking into account a valley side drag component of the force balance equation. Distributed ice thickness is subsequently interpolated using a glaciologically correct algorithm. Results indicate a total LGM ice volume of 6771.9 km3, in good correspondence of previous studies using a climate-driven ice dynamics approach. Combined with an estimate of contemporary ice volume (50.67 km3), this result reinforces the notion that New Zealand has lost almost the entirety (99.25 %) of its glacial ice since the LGM, although this volume has contributed to just 17.02 mm of global sea level rise. Analysis of the LGM distributed ice thickness output shows a large number of nunataks and exposed ridges in the central Mt. Cook and northern regions, with a localised icefield in the Fiordland area. LGM Equilibrium Line Altitudes (ELAs) automatically calculated using the Accumulation Area Ratio (AAR) method reveals an average lowering of 1074 m from present, with those to the west of main divide 461m lower than those to the east on average. LGM climatic conditions were estimated using the ELAs and scaled versions of contemporary temperature and precipitation distributions, suggesting a temperature reduction of between 5.6°C to 10.3°C and precipitation change of +4.3 % to +100.4% from present. When considering these new estimates in conjunction with critically evaluated previous evidence, an average LGM cooling of 6.5 °C to 8°C is proposed, a refinement on the wide range of previously published values. Importantly, there is large spatial variability between catchments, with eastern regions experiencing significantly greater cooling and greater precipitation increases (or less decrease) than their western counterparts. Increased westerly circulation and reduced sea level altering the relative position of the orographic barrier is a suggested potential mechanism for the predicted precipitation pattern changes, whilst increased southerly flow bringing cool air up the east coast is a possible cause of the temperature change differential predicted. The proportion of precipitation falling as snow or rain was also found to be an important factor when considering New Zealand LGM conditions, with up to 50% estimated to be falling as rain at the LGM ELA, with a strong east-west differential. Input dataset generation for REVOLTA resulted in several important research outcomes. A DEM approximating LGM bed conditions was created, using a variety of novel techniques to modify the existing DEM. These included the estimation of contemporary ice thickness distribution using the VOLTA (Volume and Topography Automation) model for removal from the DEM, merging offshore and lake bathymetry and considering Holocene in-fill sediments. Furthermore, an in-depth review of the most up to date literature and datasets regarding the lateral extent of LGM glaciation was also carried out, generating an updated ‘outline’ of LGM glaciation.

Item Type: Thesis (PhD)
Keywords: New Zealand, glacier, ice volume, last glacial maximum, climate
Academic Units: The University of Leeds > Faculty of Environment (Leeds) > School of Geography (Leeds)
Depositing User: Mr William Henry Meurig James
Date Deposited: 27 Feb 2017 12:21
Last Modified: 27 Feb 2017 12:21
URI: http://etheses.whiterose.ac.uk/id/eprint/16345

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