Time lapse imagery of the ice-on event at Darfáljávri (Lake Tarfala), Kebnekaise mountains, northern Sweden, autumn 2025
Johanna Dahlkvist, Nina Kirchner, Tarfala Research Station staff
This dataset contains images of Darfáljávri taken every 2 hours (irrespective of day- or night time) during the period from 15 September, 2025 to 26 October, 2025. During this period, the surface of Darfáljávri transitions from being ice-free to ice-covered, an event referred to as "ice-on".
The dataset can be used to observe the ice-on event and to assign a date to it. Knowledge of lake ice phenology, i.e. seasonal formation and loss of the lacustrine ice cover, is of importance since the timing of ice-on impacts lake processes such as stratification and vertical mixing.
The pictures were acquired using a camera positioned on the mountain flank along Darfáljávri’s north-eastern shore, at 1220 m above sea level. In total, there are 498 images.
LacustrineHydrologyDarfáljávriLake TarfalaTarfalaLake iceLake ice phenologyIce-on
Download dataScientific highlights
This dataset allows to assign a precise date to the ice-on event at Darfáljávri in autumn 2025. Defining ice-on as the first occasion after the ice-free summer season on which the lake becomes completely ice-covered and remains so for the rest of the winter, it was attained on 21 October 2025.
Some notable events in the time-lapse imagery of the diminishing lake ice cover include:
Pre-ice-on
- 4 October: Onset of snowfall that will not undergo melting throughout the season (picture 234).
- 20 October: Ice starts to form on the western shore by Isfallsglaciären and Norra Klippberget (picture 423).
- 21 October: Ice has formed except for by the eastern shore at 10:00 (picture 435), in two hours you can see the ice grow closer to the shoreline at 12:00 (picture 436).
Ice-on
- 21 October : Ice on 14:00 (picture 437).
- 22 October: Snowfall clearly displays that ice has formed over the entire lake (picture 448).
- 23 October: Ice surface appears wet (picture 462). Coincides with positive air temperatures after previous prevailing negative temperatures.
- 26 October: Snow accumulating and thickening over entire frozen lake surface (picture 495).
Picture numbers in the scientific highlights correspond to picture numbers in the dataset. Note that the camera produces black-white images under certain light conditions, such as during low-visibility weather conditions.
On 5 October, the camera lense was apparently partly frozen (pictures 235 – 255).
Name
Version
Citation
References
Kirchner N, Jansen J (2023) Water temperatures from the arctic-alpine Lake Tarfala (Darfáljávri), Northern Sweden, 2019 – 2020 and 2021 – 2022. Dataset version 1. Bolin Centre Database. https://doi.org/10.17043/tarfala-kirchner-2023-lake-temperature-1
Kirchner N, Weckström J, Jansen J, Schenk F, Barnett J, Granebeck A, Leppäranta M, Korhola A (2024) Water temperature, mixing, and ice phenology in the arctic–alpine Lake Darfáljávri (Lake Tarfala), northern Sweden. Arctic, Antarctic, and Alpine Research 56. https://doi.org/10.1080/15230430.2023.2287704
Data description
The dataset consists of image files (JPG) of Darfáljávri, with the date and time (Swedish daylight saving time, UTC+2) included in each photo. Image file names are numbered in chronological order.
The pictures were acquired using a camera positioned on the mountain flank along Darfáljávri’s north-eastern shore, at ~67.9° N, 18.6° E, at 1220 m above sea level.
The data were collected using a Hunter Orion Trail Camera 4G. The camera elevation is 1.8 m above ground. Each JPG file has a size of ~992 KB. The total size of the dataset is ~499MB.
During a few short periods, fog, snow and/or rain obscures the view of the lake.
Comments
Kirchner et al. (2024) gives an example of how the time-lapse imagery is used in connection with modelled ice phenology and lake water temperatures (see Kirchner & Jansen 2023) and mixing processes.
Project
Data is collected as part of Tarfala Research Station's base program since 2023 as a continuation of the Avenue Spearhead Research project made in collaboration between Stockholm University and the University of Helsinki, Finland, that ran between 2019 and 2022.
Publisher
Bolin Centre Database
License
Creative Commons Attribution 4.0 International License (CC BY 4.0)
First name
Johanna
Last name or organisation
Dahlkvist
Email address
Address
Baltic Sea Centre; Stockholms universitet
Postal code
SE-106 91
City
Stockholm
Country
Sweden
GCMD science keyword
Earth science > Climate indicators > Terrestrial hydrosphere indicators > River/lake ice freeze
GCMD location
Continent > Europe > Northern Europe > Scandinavia > Sweden
Dataset language
English
Begin date
2025-09-15
End date
2025-10-26