Mette Gillespie - Academia.edu (original) (raw)

Papers by Mette Gillespie

Journal of Glaciology

Observations remain sparse for peripheral glaciers and ice caps in Greenland. Here, we present th... more Observations remain sparse for peripheral glaciers and ice caps in Greenland. Here, we present the results of a multi-frequency radar survey of Lyngmarksbræen Ice Cap in West Greenland conducted in April 2017. Radar measurements show thick ice of up to ~120 m in subglacial valleys associated with the largest outlet glaciers, while relatively thin ice cover the upper plateau ice divides, suggesting future vulnerability to ice cap fragmentation. At the time of the radar survey, Lyngmarksbræen Ice Cap had a total volume of 0.82 ± 0.1 km3. Measurements show a 1.5–2 m thick end-of-winter snowpack, and that firn is largely absent, signifying a prolonged period of negative mass balance for most of the ice cap. The thermal regime of Lyngmarksbræen Ice Cap is investigated through analysis of scattering observed along radar profiles. Results show that the ice cap is largely below the pressure melting point, but that temperate ice exists both in deep basal pockets and in shallow zones that som...

Earth System Science Data, Jul 17, 2023

One of the key components of this research has been the mapping of Antarctic bed topography and i... more One of the key components of this research has been the mapping of Antarctic bed topography and ice thickness parameters that are crucial for modelling ice flow and hence for predicting future ice loss and the ensuing sea level rise. Supported by the Scientific Committee on Antarctic Research (SCAR), the Bedmap3 Action Group aims not only to produce new gridded maps of ice thickness and bed topography for the international scientific community, but also to standardize and make available all the geophysical survey data points used in producing the Bedmap gridded products. Here, we document the survey data used in the latest iteration, Bedmap3, incorporating and adding to all of the datasets previously used for Bedmap1 and Bedmap2, including ice bed, surface and thickness point data from all Antarctic geophysical campaigns since the 1950s. More specifically, we describe the processes used to standardize and make these and future surveys and gridded datasets accessible under the Findable, Accessible, Interoperable, and Reusable (FAIR) data principles. With the goals of making the gridding process reproducible and allowing scientists to re-use the data freely for their own analysis, we introduce the new SCAR Bedmap Data Portal (https://bedmap.scar.org, last access: 1 March 2023) created to provide unprecedented open access to these important datasets through a web-map interface. We believe that

This has been a long journey, which has taken me to one of the most remarkable places on the plan... more This has been a long journey, which has taken me to one of the most remarkable places on the planet, and I would like to thank all of the people that have helped me on my way. First of all, a big thank you to my three supervisors Wendy Lawson, Wolfgang Rack and Brian Anderson. You have all helped me move forward when I most needed it, and I especially enjoyed the discussion and stories shared during dinner in a small yellow tent. During my studies I have had had the privilege of working alongside helpful and enthusiastic people in the Department of Geography and Gateway Antarctica, some of whom I will mention here. Bryan Storey introduced me to the Antarctic environment for which I will always be grateful. Peyman Zawar-Reza inspired me about meteorological datasets and Ian Owens, with his wealth of knowledge, offered timely and important advice. I would also like to thank Irfon Jones who taught me about cartography with patience and humour, Justin Harrison and Nick Key who helped organise and plan my fieldwork, Marney Brosnan who twice 'volunteered' for the ungrateful task of designing my posters while I was away, and Graham Furniss and Steven Sykes who made the modelling part of this work possible with their knowledge of computers and programming. I would also like to acknowledge the expertise and help offered by people from outside the department. In particularly, I would like to thank David Pollard for allowing me to use his model in my work and for providing invaluable advice along the way, and Donald D. Blankenship and his team for adjusting their ICECAP field campaign to include airborne radar measurements over the DHGS and letting me use these in my work. I am also grateful for the advice on GPR processing and interpretation offered by Mike Finnemore, Matt Nolan and David Nobes, which significantly improved this part of my work. Thank you also to Dean Arthur for his great company and ability to keep us safe during the fieldwork. Also of importance to this work is the SPIRIT DEM which was made available through the project IPY ASAID (Co-PI: W. Rack). Without the financial and logistical support of Antarctic New Zealand, none of this could have been possible, and I thank the staff in Christchurch and at Scott Base for an enjoyable working relationship. Education New Zealand has supported me throughout this research with a New Zealand International Doctoral Research Scholarship, and my participation in a course in Italy was financed by the Department of Geography and Gateway Antarctica. Finally, I would like to thank my family and friends at home and in New Zealand, who have supported me with humour and love in whatever adventure I have embarked upon. I especially thank Mark, who despite these last crazy months, still plans to marry me this autumn. interaction between glacier and ocean (Anderson et al. 2004; Johnson and Staiger 2007). The research presented in this these aims to further investigate the present and past dynamic behaviour of the DHGS. This will lead to an increased understanding of slow-moving TAM glaciers and the results provide additional constraint to the magnitude of Holocene change of the WAIS and EAIS.

Chronologies of glacier deposits in the Transantarctic Mountains provide important constraints on... more Chronologies of glacier deposits in the Transantarctic Mountains provide important constraints on grounding-line retreat during the last deglaciation in the Ross Sea. However, between Beardmore Glacier and Ross Island-a distance of some 600 km-the existing chronologies are generally sparse and far from the modern grounding line, leaving the past dynamics of this vast region largely unconstrained. We present exposure ages of glacial deposits at three locations alongside the Darwin-Hatherton Glacier System-including within 10 km of the modern grounding line-that record several hundred meters of Late Pleistocene to Early Holocene thickening relative to present. As the ice sheet grounding line in the Ross Sea retreated, Hatherton Glacier thinned steadily from about 9 until about 3 ka. Our data are equivocal about the maximum thickness and Mid-Holocene to Early Holocene history at the mouth of Darwin Glacier, allowing for two conflicting deglaciation scenarios: (1) ∼ 500 m of thinning from 9 to 3 ka, similar to Hatherton Glacier, or (2) ∼ 950 m of thinning, with a rapid pulse of ∼ 600 m thinning at around 5 ka. We test these two scenarios using a 1.5-dimensional flowband model, forced by ice thickness changes at the mouth of Darwin Glacier and evaluated by fit to the chronology of deposits at Hatherton Glacier. The constraints from Hatherton Glacier are consistent with the interpretation that the mouth of Darwin Glacier thinned steadily by ∼ 500 m from 9 to 3 ka. Rapid pulses of thinning at the mouth of Darwin Glacier are ruled out by the data at Hatherton Glacier. This contrasts with some of the available records from the mouths of other outlet glaciers in the Transantarctic Mountains, many of which thinned by hundreds of meters over roughly a 1000-year period in the Early Holocene. The deglaciation histories of Darwin and Hatherton glaciers are best matched by a steady decrease in catchment area through the Holocene, suggesting that Byrd and/or Mulock glaciers may have captured roughly half of the catchment area of Darwin and Hatherton glaciers during the last deglaciation. An ensemble of three-dimensional ice sheet model simulations suggest that Darwin and Hatherton glaciers are strongly buttressed by convergent flow with ice from neighboring Byrd and Mulock glaciers, and by lateral drag past Minna Bluff, which could have led to a pattern of retreat distinct from other glaciers throughout the Transantarctic Mountains.

Geomorphology, Apr 1, 2019

Glacier revisited: Constraining ice dynamics, landform formations and glaciomorphological changes... more Glacier revisited: Constraining ice dynamics, landform formations and glaciomorphological changes in the early quiescent phase following the 1995-98 surge event. Geomor (2019),

Frontiers in Earth Science, Jun 13, 2022

Folgefonna consists of three ice caps which are rapidly retreating in response to warmer temperat... more Folgefonna consists of three ice caps which are rapidly retreating in response to warmer temperatures. The melting of Folgefonna has implications for meltwater drainage and hydropower production, as well as the potential for geohazards and impacts to tourism, the communities and infrastructures surrounding the glacier. To support future adaptation strategies, we need to know the subglacial topography of the ice caps to identify water divides and possible areas for geohazards. Therefore, we mapped the subglacial topography at Sørfonna, the largest of the Folgefonna ice caps, using an ice-penetrating radar (2.5 MHz antennas; 1,000 × 500 m grid). The results show a highly irregular subglacial landscape, with deep valleys and high mountain peaks. The maximum ice thickness is 570 m and the mean ice thickness is 190 m. We examined the retreat pattern of Sørfonna using the subglacial topography map in combination with a simple ice flow model and simulated the ice retreat 150 years into the future. We used two climate scenarios (one with a 1.5°C warming and a 3% increase in precipitation, and a second with a 3.5°C warming together with 15% increase in precipitation) and focused on how the glacial retreat will cause hydrological changes in the catchments surrounding the glacier. The main drainage pattern shifts during glacial retreat, with a larger proportion of southward drainage compared to the present day. The ice flow modelling also reveals that the southern part of Sørfonna is more durable during climate change whereas the thinner part of the ice cap, in the north, melts faster. We suggest that increased winter precipitation in a future warmer climate makes the southern part of Sørfonna more resilient than many other glaciers in southern Norway. The subglacial topography map and the retreat pattern also reveal areas that may accumulate water and could potentially generate a future glacial outburst flood. Sediments from distal glacier-fed lakes around Sørfonna have been used to constrain the thresholds identified on the subglacial topography map. Combining sedimentological evidence from distal glacier-fed lakes with the new subglacial topography map confirms that the retreat of specific outlet glaciers, such as Bondhusbreen, Buerbreen, and Møsevassbreen, will have a large impact on meltwater routing, as they are situated behind bedrock thresholds in the upper part of the glacier's catchment area.

AGU Fall Meeting Abstracts, Dec 1, 2019

AGU Fall Meeting Abstracts, Dec 1, 2018

I am extremely grateful to have had the opportunity to study geology in a place like Svalbard. Th... more I am extremely grateful to have had the opportunity to study geology in a place like Svalbard. This would not have been possible without financial support from the University Centre in Svalbard (UNIS) and the University of Aarhus. Water level measurements were kindly provided by Ole Humlum, Adjunct Professor at UNIS, while meteorological data were provided by the Norwegian Meteorological Institute. I wish to thank all the people who helped me during fieldwork. Karoline Baelum for great teamwork and many enjoyable hours during GPR data acquisition, Henrik Rasmussen and Rico Behlke for scooter assistance, Jannick Schültz for his help with digging snow pits and Helena Grev and Ken Martinussen for their help with water sampling. I also wish to thank all the people who decided to join me on my daily walks to Longyearbreen, and who paid me social calls during periods of camping. It was much appreciated. A special thank you also goes to Marie Kirkegaard Sørensen and Anne Camilla Stavnsgaard Nielsen for always offering a place to sleep during my stays in Aarhus. Furthermore, I would like to thank the staff at UNIS and Aarhus University, especially Berit Jakobsen, librarian at UNIS, for always finding the references I needed and those I did not know I needed. Fred Skancke Hansen, head of logistics and safety at UNIS, for help arranging the fieldwork and for not naming my fieldwork the most stupid fieldwork he had ever heard about. Bente Rasmussen, laboratory technician at the University Aarhus, for guiding me through the laboratory work and Ruth Nielsen, technical assistant at the University of Aarhus, for her map design and technical support. I wish to thank my supervisor Professor Niels Tvis Knudsen, University of Aarhus and associated Professor Hanne Hvidtfeldt Christiansen, University Centre in Svalbard for advice and encouragement during the fieldwork and writing process. In addition, I wish to thank Ph.D. Jacob Yde, University of Aarhus for his help and support during the entire making of this thesis. Finally, I wish to express my gratitude to my family, especially my mum, dad and brother, who have been there all the way, as always. And I wish to thank Mark, who made my time on Svalbard so amazing and who continues to inspire me every day. Front page photograph: Aerial photograph of the study area. The characteristic Sarkofagen mountain separates the two glaciers Larsbreen (furthest to the left) and Longyearbreen. Longyearbreen acts as a major transport routes for snow scooter traffic in the winter and spring and a scooter track is visible on the glacier (photograph: Rico Behlke, April 2004).

Over the past 60 years, scientists have strived to understand the past, present and future of the... more Over the past 60 years, scientists have strived to understand the past, present and future of the Antarctic Ice Sheet. One of the key components of this research has been the mapping of Antarctic bed topography and ice thickness parameters that are crucial for modelling ice flow and hence for predicting future ice loss and ensuing sea level rise. Supported by the Scientific Committee on Antarctic Research (SCAR), the Bedmap3 Action Group aims not only to produce new gridded maps of ice thickness and bed topography for the international scientific community, but also to standardize and make available all the geophysical survey data points used in producing the Bedmap gridded products. Here, we document the survey data used in the latest iteration, Bedmap3, incorporating and adding to all of the datasets previously used for Bedmap1 and Bedmap2, including ice-bed, surface and thickness point data from all Antarctic geophysical campaigns since the 1950s. More specifically, we describe the processes used to standardize and make these and future survey and gridded datasets accessible under the 'Findable, Accessible, Interoperable and Reusable' (FAIR) data principles. With the goals to make the gridding process reproducible and to allow scientists to re-use the data freely for their own analysis, we introduce the new SCAR Bedmap Data Portal (bedmap.scar.org, last access: 18 October 2022) created to provide unprecedented open access to these important datasets, through a user-friendly webmap interface. We believe that this data release will be a valuable asset to Antarctic research and will greatly extend the life cycle of the data held within it. Data are available from the UK Polar Data Centre: https://data.bas.ac.uk.

The Darwin-Hatherton glacial system (DHGS) drains from the East Antarctic Ice Sheet (EAIS) and th... more The Darwin-Hatherton glacial system (DHGS) drains from the East Antarctic Ice Sheet (EAIS) and through the Transantarctic Mountains (TAM) before entering the Ross Embayment. Large ice-free areas covered in glacial sediments surround the DHGS, and at least five glacial drift sheets mark the limits of previous ice extent. The glacier belongs to a group of slow-moving EAIS outlet glaciers which are poorly understood. Despite this, an extrapolation of a glacial drift sheet boundary has been used to determine the thickness of the EAIS and the advanced West Antarctic Ice Sheet (WAIS) during the Last Glacial Maximum (LGM). In order to accurately determine the past and present contributions of the Antarctic ice sheets to sea level changes, these uncertainties should be reduced. This study aims to examine the present and LGM ice dynamics of the DHGS by combining newly acquired field measurements with a 3-D numerical ice sheet-shelf model. The fieldwork included a ground penetrating radar sur...

Master Thesis, 2006 (Revised Edition) Department of Earth Sciences, University of Aarhus Departme... more Master Thesis, 2006 (Revised Edition) Department of Earth Sciences, University of Aarhus Department of Geology, University Centre in Svalbard (UNIS)

Journal of Glaciology, 2008

The ionic and isotopic characteristics of bulk waters emanating from the cold-based Longyearbreen... more The ionic and isotopic characteristics of bulk waters emanating from the cold-based Longyearbreen, central Svalbard, in 2004 are examined to determine lithological, hydrological and glaciological controls on water composition, solute provenance and chemical denudation. The geology consisted of reactive coal seams and associated sedimentary rocks. Acidity caused by microbial-mediated oxidation of sulfides and, to a lesser extent, nitrogen-bearing minerals was neutralized by congruent dissolution of dolomite and incongruent weathering of silicates in open-system subglacial drainage channels. The ablation season was divided into an early melt season, a peak-flow period and a late melt season. The runoff distribution during these periods was 1.7%, 89.7% and 8.6%, respectively, whereas the solute flux distribution was 1.9%, 82.1% and 16.0%, respectively. Comparisons between different annual solute flux estimation methods indicated that extrapolation of peak-flow period data significantly...

Earth System Science Data