The snow melts in Antarctica

Melt pool

The Arctic sea ice cover has not only become smaller in the past decade, but also significantly younger and thinner. Where previously meter-thick, perennial ice drifted, today there are mainly thin annual clods that are covered over large areas with meltwater pools in the summer months.
The snow on the Arctic sea ice melts completely every summer - what remains are pools of meltwater. In large parts of the Arctic, these pools form within a few days, often in the first weeks of June. They only disappear again when the surface freezes in September. Most of these freshwater pools measure three to 20 meters in diameter. Their color depends mainly on the thickness of the ice under the pond, as the dark (black) ocean then shines through more or less strongly. As a result, it is more turquoise on thicker, perennial sea ice, and dark blue to black on thinner, annual ice.
In the context of the energy balance of the sea ice, melt pools play a major role, because in contrast to the surrounding white sea ice, the melt pools reflect only a fraction of the sunlight, but more penetrates into the sea ice and through the sea ice into the ocean. This is primarily because the pools do not have a surface of snow or disintegrated sea ice that reflects almost all of the light (albedo). If this "scattering layer" is no longer available due to the accumulation of meltwater, considerably more light penetrates the ice and can then also get through the ice into the ocean.
Young, thin ice with its many melting ponds allows around three times more light to pass than older sea ice. It also absorbs twice as much solar radiation. Conversely, both of these mean that this thin, puddle-covered ice reflects significantly less sun rays than the thick ice. Its reflection rate is around 37 percent. In addition, the young ice absorbs more heat with the solar energy, which promotes its melting - it melts "from the inside", so to speak.
Melt pools also affect measurements of sea ice from satellites, for example. They are registered by sensors on the satellites as open water, where in reality there is still sea ice. This can lead to considerable measurement inaccuracies. Measurements on site show that such melt pools can often cover up to 40 percent of the sea ice.