19 Jan 2021
19 Jan 2021
On the influence of erect shrubs on the irradiance profile in snow
- 1Takuvik Joint International Laboratory, Université Laval (Canada) and CNRS-INSU (France), Québec City, QC, G1V 0A6, Canada
- 2Centre d’Études Nordiques, Université Laval, Québec City, QC, Canada
- 3Department of Geography, Université Laval, Québec City, QC, Canada
- 4Department of Chemistry, Université Laval, Québec City, QC, Canada
- 5Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, Grenoble, France
- 6Météo-France – CNRS, CNRM UMR 3589, CEN, Grenoble, France
- 1Takuvik Joint International Laboratory, Université Laval (Canada) and CNRS-INSU (France), Québec City, QC, G1V 0A6, Canada
- 2Centre d’Études Nordiques, Université Laval, Québec City, QC, Canada
- 3Department of Geography, Université Laval, Québec City, QC, Canada
- 4Department of Chemistry, Université Laval, Québec City, QC, Canada
- 5Univ. Grenoble Alpes, CNRS, IRD, Grenoble INP, IGE, Grenoble, France
- 6Météo-France – CNRS, CNRM UMR 3589, CEN, Grenoble, France
Abstract. The warming-induced expansion of shrubs in the Arctic is transforming snowpacks into a mixture of snow, impurities and buried branches. Because snow is a translucent medium into which light penetrates up to tens of centimeters, buried branches may alter the snowpack radiation budget with important consequences for the snow thermal regime and microstructure. To characterize the influence of buried branches on radiative transfer in snow, irradiance profiles were measured in snowpacks with and without shrubs near Umiujaq in the Canadian Low Arctic (56.5° N, 76.5° W) in November and December 2015. Using the irradiance profiles measured in shrub-free snowpacks in combination with a Monte Carlo radiative transfer model revealed that the dominant impurity type was black carbon (BC) in variable concentrations up to 185 ng g−1. This allowed the separation of the radiative effects of impurities and buried branches. Irradiance profiles measured in snowpacks with shrubs showed that the impact of buried branches was generally weak, except for layers where branches were also visible in snowpit photographs, suggesting that branches influence snow locally (i.e. a few centimeters around branches). The local-effect hypothesis was further supported by observations of localized melting and depth hoar pockets that formed in the vicinity of branches. Buried branches therefore affect snowpack properties, with possible impacts on Arctic flora and fauna and on the thermal regime of permafrost. Lastly, the unexpectedly high BC concentrations in snow are likely caused by nearby open-air waste burning, suggesting that cleaner waste management plans are required for northern community and ecosystem protection.
Maria Belke-Brea et al.
Status: final response (author comments only)
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RC1: 'Comment on bg-2020-461', Anonymous Referee #1, 11 Feb 2021
Belke-Brea et al. present interesting work on the difficult subjects of measuring and modelling light transmission in snow with buried shrubs. The introduction makes shrubs sound rather like invasive species that have only recently arrived in the tundra; they are actually natural (albeit expanding) components of tundra biomes. Trapping of snow by shrubs is likely to have more influence on the insulating properties of a snowpack, but absorption of light by buried branches clearly does have an influence and has received less attention. The title to could be modified to reflect that a lot of this paper is about the influence of soot.
A wind rose would be a nice addition to Figure 2 in place of the wind direction arrows, if the AWS can provide. Do you have any information on the frequency and volume of waste burning in winter?
The measured absorption coefficients in Figure 4 clearly cannot be fitted well by adding dust to the snow, but Figure 4(b) does not look like the best possible fit for 400-450 nm (a negative bias could be removed).
How close together and how comparable were the sites for snow pits without shrubs? Table 1 shows that snow depth increased by 7 cm between 22 and 28 November. Doesn’t that mean that the clean snow in ZOI4 on 28 November was already on the ground when the snow was judged to be dirty on 22 November?
Comparing with Figure 5, I think that the ZOI depths in Table 2 are wrong.
Above 700 nm, the increased grain size of depth hoar will have an effect of decreasing absorption coefficients. Could the large grains and voids in the snow around shrub branches act as pipes for transmission of near-infrared light (just to make modelling radiative transfer even harder)?
- RC2: 'Comment on bg-2020-461', Inge Grünberg, 23 Feb 2021
Maria Belke-Brea et al.
Maria Belke-Brea et al.
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