Time lapse imagery of the ice-off event at Lake Tarfala, Kebnekaise Mountains, northern Sweden, summer 2020

Nina Kirchner, Annika Granebeck, Marnie Hancke

This dataset contains images of Lake Tarfala taken every 2 hours during the period from June 20, 2020, to September 14, 2020. During this period, the surface of Lake Tarfala changes from ice-covered to ice-free, an event referred to as "ice-off".

The dataset can be used to observe the ice-off event and to assign a date (or, rather, a time interval) to it. Knowledge of this is important because the timing of ice-off impacts lake processes, such as vertical mixing.

The pictures were acquired using a camera positioned on the mountain flank along Lake Tarfala’s north-eastern shore, at 1220 m above sea level. In total, there are 955 images.

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Scientific highlights

This dataset allows to assign a precise date to the ice-off event at Lake Tarfala in 2020. If ice-off is defined as the first occasion on which the lake is completely ice-free, it was attained on August 7, 2020.

Precise knowledge of the ice-off date can be used to:

1. Help understanding lake mixing processes.
2. Better constrain numerical models computing ice-off.
3. Provide a complement to ice-off dates derived from satellite imagery, which is notoriously difficult in polar alpine environments.
4. Lend support to alternative definitions of ice-off.

Some notable events in the time-lapse imagery of the diminishing ice cover include:

• 21⁠ – ⁠25 June: Growing numbers of features at the lake surface, mimicking surface meltwater-ponds.
• 5 July: Onset of pronounced melting along the entire south-western shoreline (in the background of the picture).
• 22 July: Retreat of ice from the south-eastern shoreline (in the foreground of the picture, during a few hours).
• 23 July: Onset of drifting lake ice, breaking up into floes.
• 25 July: Drift of ice floes into the northwestern lake-corner.
• 29 July: Inflow of streamwater of a distinctly different color into the lake during a few hours (at 21:00, 23:00).
• 31 July⁠ – ⁠7 August: Final disintegration of the seasons last drifting ice floes.

No pictures were taken at 19:00. In the visualization above, those are shaded. Note that the camera saves black-white images under certain light conditions, often occurring at 01:00.

Citation

Nina Kirchner, Annika Granebeck, Marnie Hancke (2021) Time lapse imagery of the ice-off event at Lake Tarfala, Kebnekaise Mountains, northern Sweden, summer 2020. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/tarfala-kirchner-2021-ice-off-1

References

Kirchner N, et al. (2021) Timing of ice-off and ice-on at Lake Tarfala, constrained by multiple datasets. (in preparation)

Data description

The dataset consists of image files (JPG) of Lake Tarfala, with the date and time (Swedish summer time, UTC+2) included in each photo.

The pictures were acquired using a camera positioned on the mountain flank along Lake Tarfala’s north-eastern shore, at ~67.9° N, 18.6° E, at 1220 m above sea level.

The data were collected using a SiFar Willfine Trail Camera 4.0CG. The camera elevation is 1.8 m above ground. Each JPG file has a size of ~2.5 MB. The total size of the dataset is ~2.2 GB.

During a few short periods, fog and/or rain obscures the view of the lake. From August 9 onwards, one or more pictures per day are dark because the period of midnight sun came to an end.

Comments

Please cite this dataset and the article by Kirchner et al. when using images from this dataset.

The support of our co-workers on the Arctic Avenue activity Lake thermal and mixing dynamics under changing climate (J. Weckström, K. Weckström, A. Korhola, and F. Schenk), and of our field assistants (M. Holmström, E. Kirchner) is gratefully acknowledged.