Spring snowmelt and midwinter thaw and refreeze north of 60°N based on Seawinds QuikScat 2000-2009

The scatterometer SeaWinds on QuikSCAT provided regular measurements at Ku-band from 1999 to 2009. Although it was designed for ocean applications, it has been frequently used for the assessment of seasonal snowmelt patterns aside from other terrestrial applications such as ice cap monitoring, phenology and urban mapping. This paper discusses general data characteristics of SeaWinds and reviews relevant change detection algorithms. Depending on the complexity of the method, parameters such as long-term noise and multiple event analyses were incorporated. Temporal averaging is a commonly accepted preprocessing step with consideration of diurnal, multi-day or seasonal averages.

Snow-pit measurements on Atka Bay landfast sea ice during ANT-Land 2012/2013 season

Up to now, snow cover on Antarctic sea ice and its impact on radar backscatter, particularly after the onset of freeze/thaw processes, are not well understood. Here we present a combined analysis of in situ observations of snow properties from the landfast sea ice in Atka Bay, Antarctica, and high-resolution TerraSAR-X backscatter data, for the transition from austral spring (November 2012) to summer (January 2013). The physical changes in the seasonal snow cover during that time are reflected in the evolution of TerraSAR-X backscatter. We are able to explain 76-93% of the spatio-temporal variability of the TerraSAR-X backscatter signal with up to four snowpack parameters with a root-mean-squared error of 0.87-1.62 dB, using a simple multiple linear model. Over the complete study, and especially after the onset of early-melt processes and freeze/thaw cycles, the majority of variability in the backscatter is influenced by changes in snow/ice interface temperature, snow depth and top-layer grain size. This suggests it may be possible to retrieve snow physical properties over Antarctic sea ice from X-band SAR backscatter.

Climate and soil characteristics and soil arthropod abundance on Anchorage, Signy and Falkland Islands

Over a 2-year study, we investigated the effect of environmental change on the diversity and abundance of soil arthropod communities (Acari and Collembola) in the Maritime Antarctic and the Falkland Islands. Open Top Chambers (OTCs), as used extensively in the framework of the northern boreal International Tundra Experiment (ITEX), were used to increase the temperature in contrasting communities on three islands along a latitudinal temperature gradient, ranging from the Falkland Islands (51°S, mean annual temperature 7.5 °C) to Signy Island (60°S, -2.3°C) and Anchorage Island (67°S, -3.8°C). At each island an open and a closed plant community were studied: lichen vs. moss at the Antarctic sites, and grass vs. dwarf shrub at the Falkland Islands. The OTCs raised the soil surface temperature during most months of the year. During the summer the level of warming achieved was 1.7 °C at the Falkland Islands, 0.7 °C at Signy Island, and 1.1 °C at Anchorage Island. The native arthropod community diversity decreased with increasing latitude. In contrast with this pattern, Collembola abundance in the closed vegetation (dwarf shrub or moss) communities increased by at least an order of magnitude from the Falkland Islands (9.0 +/- 2 x 10**3 ind./m**2) to Signy (3.3 +/- 8.0 x 10**4 ind./m**2) and Anchorage Island (3.1 +/- 0.82 x 10**5 ind./m**2). The abundance of Acari did not show a latitudinal trend. Abundance and diversity of Acari and Collembola were unaffected by the warming treatment on the Falkland Islands and Anchorage Island. However, after two seasons of experimental warming, the total abundance of Collembola decreased (p < 0.05) in the lichen community on Signy Island as a result of the population decline of the isotomid Cryptopygus antarcticus. In the same lichen community there was also a decline (p < 0.05) of the mesostigmatid predatory mite Gamasellus racovitzai, and a significant increase in the total number of Prostigmata. Overall, our data suggest that the consequences of an experimental temperature increase of 1-2°C, comparable to the magnitude currently seen through recent climate change in the Antarctic Peninsula region, on soil arthropod communities in this region may not be similar for each location but is most likely to be small and initially slow to develop.

Soil characteristics and Collembola and Acari abundance in control and warming plots at Abisco Research Station

Extreme weather events can have negative impacts on species survival and community structure when surpassing lethal thresholds. Extreme winter warming events in the Arctic rapidly melt snow and expose ecosystems to unseasonably warm air (2-10 °C for 2-14 days), but returning to cold winter climate exposes the ecosystem to lower temperatures by the loss of insulating snow. Soil animals, which play an integral part in soil processes, may be very susceptible to such events depending on the intensity of soil warming and low temperatures following these events. We simulated week-long extreme winter warming events - using infrared heating lamps, alone or with soil warming cables - for two consecutive years in a sub-Arctic dwarf shrub heathland. Minimum temperatures were lower and freeze-thaw cycles were 2-11 times more frequent in treatment plots compared with control plots. Following the second event, Acari populations decreased by 39%; primarily driven by declines of Prostigmata (69%) and the Mesostigmatic nymphs (74%). A community-weighted vertical stratification shift occurred from smaller soil dwelling (eu-edaphic) Collembola species dominance to larger litter dwelling (hemi-edaphic) species dominance in the canopy-with-soil warming plots compared with controls. The most susceptible groups to these winter warming events were the smallest individuals (Prostigmata and eu-edaphic Collembola). This was not apparent from abundance data at the Collembola taxon level, indicating that life forms and species traits play a major role in community assembly following extreme events. The observed shift in soil community can cascade down to the micro-flora affecting plant productivity and mineralization rates. Short-term extreme weather events have the potential to shift community composition through trait composition with potentially large consequences for ecosystem development.

Analysis of soils from King George Island and Casey station, Antarctica

A comparative study was carried out on soils of the maritime (Arctowski, King George Island) and the continental (Casey, Wilkes Land) Antarctic. Soil sampIes are described for surface layers (0-10 cm) by their in situ temperature profiles as well as by field and laboratory analyses of grain sizes, pH and nutrient contents. Active cryoturbation is a main factor of mixing processes in surfaces with high silt and clay content. In both regions processes of podzolisation were recognized. Microclimatic conditions show the importance of small scale processes which are of special importance for freeze-thaw cycles. The distribution of nutrients and other inorganic components is rather homogeneous in regosols and leptosols. But in soils with organic top layers by lichen and moss cushions (crusts) accumulation occurs as well as displacement of metal ions into deeper layers (>10 cm). Histosols show patterns of brown soils. Special attention is given to the origin of nitrogen compounts and the different ways of import of other components (e.g. chloride) into the Antarctic system are discussed.