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Subsurface fluxes of mass and energy at the accumulation zone of Lomonosovfonna ice cap, Svalbard
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. Uppsala University. (ice and climate)ORCID iD: 0000-0003-4785-4532
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. , p. 52
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1601
Keywords [en]
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: urn:nbn:se:uu:diva-334178ISBN: 978-91-513-0158-7 (print)OAI: oai:DiVA.org:uu-334178DiVA, id: diva2:1159174
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: 2018-03-08
List of papers
1. A plot-scale study of firn stratigraphy at Lomonosovfonna, Svalbard, using ice cores, borehole video and GPR surveys in 2012–14
Open this publication in new window or tab >>A plot-scale study of firn stratigraphy at Lomonosovfonna, Svalbard, using ice cores, borehole video and GPR surveys in 2012–14
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2017 (English)In: Journal of Glaciology, ISSN 0022-1430, E-ISSN 1727-5652, Vol. 63, no 237, p. 67-78Article in journal (Refereed) Published
Abstract [en]

Spatial heterogeneity of snow and firn properties on glaciers introduces uncertainty in interpretation of point and profile observations and complicates modelling of meltwater percolation and runoff. Here we present a study of the temporal and spatial dynamics of firn density and stratigraphy at the plot-scale (approximate to 10 m x 10 m x 10 m) repeated annually during 2012-14 at the Lomonosovfonna ice-field, Svalbard. Results from cores, video inspections in boreholes and radar grid surveys are compared. Ice layers 0.1-50 cm thick comprised approximate to 8% of the borehole length. Most of them are 1-3 cm thick and could not be traced between boreholes separated by 3 m. Large lateral variability of firn structure affects representativeness of observations in single holes and calls for repeated studies in multiple points to derive a representative stratigraphy signal. Radar reflections are poorly correlated with ice layers in individual boreholes. However, the match between the high amplitude peaks in the grid-averaged radar signal and horizons of preferential ice layer formation revealed by averaging the video surveys over multiple boreholes is higher. These horizons are interpreted as buried firn layers previously exposed to melt-freeze or wind-driven densification and several of them are consistently recovered throughout three field campaigns.

Keywords
borehole video, firn core, radar, stratigraphy
National Category
Physical Geography Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-308681 (URN)10.1017/jog.2016.118 (DOI)000394435300006 ()
Funder
Swedish Research Council, 621-2014-3735
Available from: 2016-11-29 Created: 2016-11-29 Last updated: 2018-01-13Bibliographically approved
2. Parameterizing deep water percolation improves subsurface temperature simulations by a multilayer firn model
Open this publication in new window or tab >>Parameterizing deep water percolation improves subsurface temperature simulations by a multilayer firn model
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2017 (English)In: Frontiers in Earth Science, ISSN 1096-231X, E-ISSN 1664-8021, Vol. 5, no 16Article in journal (Refereed) Published
Abstract [en]

Deep preferential percolation of melt water in snow and firn brings water lower along the vertical profile than a laterally homogeneous wetting front. This widely recognized process is an important source of uncertainty in simulations of subsurface temperature, density, and water content in seasonal snow and in firn packs on glaciers and ice sheets. However, observation and quantification of preferential flow is challenging and therefore it is not accounted for by most of the contemporary snow/firn models. Here we use temperature measurements in the accumulation zone of Lomonosovfonna, Svalbard, done in April 2012-2015 using multiple thermistor strings to describe the process of water percolation in snow and firn. Effects of water flow through the snow and firn profile are further explored using a coupled surface energy balance - firn model forced by the output of the regional climate model WRF. In situ air temperature, radiation, and surface height change measurements are used to constrain the surface energy and mass fluxes. To account for the effects of preferential water flow in snow and firn we test a set of depth-dependent functions allocating a certain fraction of the melt water available at the surface to each snow/firn layer. Experiments are performed for a range of characteristic percolation depths and results indicate a reduction in root mean square difference between the modeled and measured temperature by up to a factor of two compared to the results from the default water infiltration scheme. This illustrates the significance of accounting for preferential water percolation to simulate subsurface conditions. The suggested approach to parameterization of the preferential water flow requires low additional computational cost and can be implemented in layered snow/ firn models applied both at local and regional scales, for distributed domains with multiple mesh points.

Keywords
firn, firn modeling, preferential flow, internal accumulation, Lomonosovfonna, Svalbard, firn water content
National Category
Physical Geography
Identifiers
urn:nbn:se:uu:diva-321136 (URN)10.3389/feart.2017.00016 (DOI)000395736600001 ()
Funder
Swedish Research Council, 621-2014-3735
Available from: 2017-05-02 Created: 2017-05-02 Last updated: 2018-01-13Bibliographically approved
3. Thermal conductivity of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements
Open this publication in new window or tab >>Thermal conductivity of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements
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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:nbn:se:uu:diva-334156 (URN)
Available from: 2017-11-21 Created: 2017-11-21 Last updated: 2018-01-13Bibliographically approved
4. Water content of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements
Open this publication in new window or tab >>Water content of firn at Lomonosovfonna, Svalbard, derived from subsurface temperature measurements
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

The potential of capillary forces to retain water in pores is an important property of snow and firn at glaciers. Melt water suspended in pores does not contribute to runoff and is likely to refreeze during winter, by this affecting the climatic mass balance. However, retrieving of empirical data on snow/firn water content is challenging due to the subtle balance between the solid and liquid phases of water. Here we use subsurface temperature and density measured at 1200 m a.s.l.: at Lomonosovfonna, Svalbard, to derive water content of the firn profile after the melt season in 2014. For that measured and simulated rates of freezing front propagation are compared. The resulting volumetric volumetric water content of the subsurface profile is ca 1–2.5 vol.% above the depth of 3 m and below 0.5 vol.% below with a prominent lateral variability. These values are considerably lower than what is commonly used in snow/firn models, which is interpreted as a result of preferential water flow at Lomonosovfonna leaving extensive dry pockets in snow/firn above the fingering front. This calls for implementation of preferential flow description in snow/firn models.

National Category
Physical Geography
Identifiers
urn:nbn:se:uu:diva-334153 (URN)
Available from: 2017-11-21 Created: 2017-11-21 Last updated: 2018-01-13

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