Climate Change in Greenland: Timing of lake ice break-up and its consequences

APRI scientists from the CC-MoRe (Climate Change in Mountain Regions) research group at the University of Graz investigated the timing of the seasonal ice cover break-up of lakes in Greenland and identified its strong dependence on altitude. The temperatures of extreme years 2018 and 2019 are reflected in the observations of the timing of lake ice break-up. An earlier break-up of lakes in Greenland has implications for their energy balance due to solar radiation and influences the ecosystems of lakes and fjords.

APRI scientists Christoph Posch, Jakob Abermann and Tiago Silva from the University of Graz identified the timing of the annual break-up of lake ice cover in Greenland between 2017 and 2021 based on satellite data. Using an automated detection algorithm and climate data, they were able to determine the break-up timing of lakes, describe their temporal and spatial variability, and discuss their effects on the energy balance due to the disappearance of ice cover.

A lake in West Greenland during the break-up of the seasonal ice cover (Photo: J. Abermann).

The break-up of lake ice cover, i.e., the transition from a frozen surface to open water, can be detected using radar data from the European Sentinel-1 satellite mission. From an automated detection for approximately 500 lakes in South and West Greenland, the break-up timing showed to be significantly dependent on the altitude and varies by being 8 days earlier or later than the average in the observed period. “The break-up timing of lakes is around 3 days later per 100 m increase in altitude, which can be explained by the microclimatic conditions of steep coasts and fjord systems”, says Christoph Posch, the lead author of the study.

Median of break-up dates in Day of Year (a) as well as the break-up dates in the years 2018 (b) and 2019 (c) along the southern (S), southwest (SW), and northwest (NW) coast of Greenland. Lakes closer to the fjords and thus at lower altitudes (orange arrow) generally break-up earlier than lakes at higher elevations (blue arrow). The relatively late or early break-up dates in the years 2018 and 2019 reflect the particularly low and high air temperatures during these years, respectively. Average Break-up time 2018: 8 June (DOY 159), average Break-up time 2019: 10 July (DOY 191). (Posch et al., 2024)

The approximately 155,000 lakes outside the Greenland ice sheet cover about 3 % of Greenland’s non-glaciated area, roughly equivalent to 1.4-times the size of Austria. The timing of lake ice break-up is not only an indicator of prevailing air temperatures but also significantly influences how much solar radiation is delivered to the lakes as energy. An ice- and consequently often snow-covered lake surface can reflect up to 90 % of incoming solar radiation, while an open water surface typically only reflects up to 20 % of the solar radiation.

The Break-up and freezing of a lake in southwest Greenland during 2019 in Copernicus Sentinel-2 imagery. (Christoph Posch)

The additional energy input due to an earlier disappearance of ice cover has significant effects on the energy balance of lakes. A hypothetical 8-day earlier break-up of lakes, corresponding to the observed variability, would result in an additional energy input which could theoretically increase the temperature of a water volume by 1 °C, which could be translated to a water depth of about 35 m at each respective lake. To put this into perspective, this additional energy input summed up for all lakes along the entire South and West coast of Greenland is roughly equivalent to melting an ice cube with a side length of 7,4 km. “An earlier break-up or higher variability not only affects the ecosystem of lakes through changes in temperature regimes and oxygen content but also consequently impacts freshwater input into fjords and their ecosystems”, says Jakob Abermann, Assistant Professor and climate researcher at the Graz Geography Institute. “Considering climate scenarios and our findings, we expect an increasingly earlier annual break-up of lakes in Greenland and thus insufficiently described feedback mechanisms.”