Palsa
[4] The lack of thermal insulation provided by thick snow permits much deeper freezing in winter.
[7] In cross-section, the ice cores of a palsa show layering, which is caused by the successive winter freezing intervals.
The fact that palsas in various stages of growth and decay occur together shows that their collapse is not necessarily indicative of climatic change.
[6][11] Therefore, the collapsed form of the palsas are common in these areas which can be seen as rounded ponds, open peat surfaces or low circular rim ridges.
[9][12] The core of palsas stays frozen permanently, including summertime, as the peat layer creates an insulating effect.
In the initial aggrading stage of development, the palsas have smooth surfaces with no cracks in the peat layer and no visible signs of erosion can be seen.
Buoyant rise of the core occurs which freezes when the permafrost reaches the area and creates the ice layers.
[5] In the stable, mature phase, the surface has risen further to a level at which the snow cover during winter is thinned by the wind which in turn makes it possible for deeper freezing.
Adjacent to palsas in the degrading stage often several individual ponds are found, due to thawing of the frozen core.
When block erosion occurs the mineral soil is often exposed along the cracks, especially when the peat layer is thin.
[6][12] They are almost exclusively associated with the presence of peat[12] and commonly occur in areas where the winters are long and the snow cover tends to be thin.
In the southern hemisphere palsa remains from the last glacial maximum have been identified on the Argentine side of Isla Grande de Tierra del Fuego just north of Cami Lake.
[14] Remainders of Ice-Age palsas are to be found also in Hochmooren of Central Europe, such as Hohen Venn in the German-Belgian border area.
[8] Measurements from meteorological stations in the area show that the mean annual temperature rose 0.8 °C between the time periods of 1901–1930 and 1961–1990.
This phenomenon has been observed in the Dovrefjell in the last decades and is caused by a larger change in the climatic condition where the temperature has risen to a level at which the palsas cannot fully initiate their cyclic development.
Additionally, more active-layer monitoring and its correlation to local weather conditions is needed to better determine the effect of climate change on palsa mires.
[5] Because the top mounds of the palsas are more dry and nutrient poor than their wet surroundings, they create a mosaic of microhabitats within the mire.
The expanding wetness is projected to benefit sphagnum mosses and graminoids, at the expense of the dryer palsa vegetation.
Climate change causes an increase in the average annual temperature, which must lay under 0 °C (32 °F) for palsas to persist.
Conversely, increased rainfall in the summer months can result in higher ground thermal conductivities and greater heat transfer to the palsa core.
The effects are already visible: many studies[19][20][8][9] report degradation of palsa mires during the last decades with the primary cause for the loss of habitat area being climate change.
A typical palsa mire has a high level of biodiversity, ranging from several different types of bird species to tiny organisms like bacteria.
This is largely because of particularly due to its outstanding minerotrophic-ombrotrophic and water table gradients, which enables the presence of several microhabitats distributed in different degrees of wetness.
Palsa mires are listed as a priority habitat type by the European Union, and climate change may pose a great risk to its ecosystems.
[22] Although much research has been carried out on degradation of palsa mires, there is still an enormous information gap on what implications on biodiversity disruptions in ecosystems may have.
It is vital to gain more knowledge about the distribution of these organisms, as well as patterns of species richness long-term, in order to understand and predict possible implications of potential loss of palsa.
In palsa mire zones in Northern Europe, abundance of bird species breeding finds it peak.
This will likely have a negative impact on certain species of breeding birds as well as other organisms inhabiting palsa mires permanently or seasonally.
Palsas, however, do not necessarily require positive hydrostatic pressure (to inject water), since the boggy soil is water-saturated and therefore has sufficient supply for the growing ice core.
Similarly, palsas can laterally decrease in size while maintaining their height; the decay of pingos follows a different pattern.
