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Thermal conductivity of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (ice and climate)ORCID iD: 0000-0003-4785-4532
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The subsurface processes in the snow and firn layer at glaciers and ice sheets are to a great extent controlled by the temperature therein and are closely linked with the mass and energy fluxes at the surface. Thus an accurate description of the feedbacks linking such phenomena as the glacier-induced sea level rise, runoff from glaciated catchments and glacier ice flow is dependent on our understanding of the subsurface properties responsible for temperature evolution. In the absence of liquid water the temperature evolution in snow and firn is driven by the conductive heat exchange, which is controlled by its effective thermal conductivity (keff). Here we reconstruct the effective thermal conductivity firn at Lomonosovfonna, Svalbard, using an optimization routine minimizing the misfit between simulated and measured subsurface temperatures. The results are complemented by sensitivity experiments showing the potential uncertainties in the estimates that may be caused by the errors in employed empirical data. The optimized keff values lie in the range from 0.6 to 1.3 J (smK)-1 and increase downwards. Compared to commonly used density-based parameterizations they are consistently larger, suggesting an underestimation in simulated conductive heat fluxes in firn.

National Category
Physical Geography
Identifiers
URN: urn:nbn:se:uu:diva-334156OAI: oai:DiVA.org:uu-334156DiVA: diva2:1158869
Available from: 2017-11-21 Created: 2017-11-21 Last updated: 2017-11-23Bibliographically approved
In thesis
1. Subsurface fluxes of mass and energy at the accumulation zone of Lomonosovfonna ice cap, Svalbard
Open this publication in new window or tab >>Subsurface fluxes of mass and energy at the accumulation zone of Lomonosovfonna ice cap, Svalbard
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Glaciers cover ca 10% of the Earth's land and are found in the high altitudes and latitudes. They are important components of environmental systems due to the multiple feedbacks linking them with the atmosphere, hydrosphere and periglacial landscapes. The cold sloping surfaces of glaciers change the patterns of atmospheric circulation at different scales and at the same time glaciers are largely controlled by climate. They are commonly used as climatic archives for reconstruction of the past environmental changes based on evidences from the areas affected by glaciation at the moment and in the past. Glaciers are the largest fresh-water reservoirs on our planet and runoff thereof significantly affects the global sea level and life in glaciated catchments. However, melt- and rain-induced runoff from glaciers greatly depends on the subsurface conditions which thus need to be taken into account, particularly in a changing climate.

This thesis focuses on the processes of subsurface mass and energy exchange in the accumulation zones of glaciers, which are largely driven by the climate at the surface. Results are largely based on empirical data from Lomonosovfonna ice cap, Svalbard, collected during field campaigns in 2012-2017. Observations of subsurface density and stratigraphy using shallow cores, video records from boreholes and radar surveys returned detailed descriptions of the snow and firn layering. The subsurface temperature data collected using multiple thermistor strings provided insights into several subsurface processes. The temperature values measured during three summer seasons were used to constrain the suggested parameterization of deep preferential water flow through snow and firn. The part of data recorded during the cold seasons was employed for an inverse modelling exercise resulting in optimized values of effective thermal conductivity of the subsurface profile. These results are then used to compute the subsurface water content by comparing the simulated and measured rates of freezing front propagation after the melt season in 2014.

The field observations and quantitative estimates provide further empirical evidences of preferential water flow in snow/firn packs at glaciers. Results presented in the thesis call for implementation of description of the process in layered models simulating the subsurface fluxes of energy and mass at glaciers. This will result in a better understanding of glacier response to the past and future climatic changes and more accurate estimates of glacier runoff.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. 52 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1601
Keyword
glacier, ice sheet, sea level, runoff, ice, firn, snow, stratigraphy, density, core, radar, thermistor, temperature, preferential water flow, thermal conductivity, water content
National Category
Physical Geography
Research subject
Earth Science with specialization in Physical Geography
Identifiers
urn:nbn:se:uu:diva-334178 (URN)978-91-513-0158-7 (ISBN)
Public defence
2018-01-19, GM128 Axel Hambergsalen, Villavägen 16, Uppsala, 09:00 (English)
Opponent
Supervisors
Projects
Stability and Variations of Arctic Land Ice (SVALI)
Available from: 2017-12-13 Created: 2017-11-21 Last updated: 2017-12-13

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Marchenko, Sergeyvan Pelt, WardPohjola, VeijoPettersson, RickardLötstedt, Per

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