Abstract: The Traill island model of Gilg et al. (2003) is a landmark attempt at mechanistic modelling of the cyclic population dynamics of rodents, focusing on a high Arctic community. It models the dynamics of one prey, the collared lemming, and four predators : the stoat, the Arctic fox, the long-tailed skua and the snowy owl. In the present short note, we first summarize how the model works in light of theory on seasonally forced predator-prey systems, with a focus on the temporal dynamics of predation rates. We show notably how the impact of generalist predation, which is able here to initiate population declines, differs slightly from that of generalist predation in other mechanistic models of rodent-mustelid interactions such as Turchin & Hanski (1997). We then provide a low-dimensional approximation with a single generalist predator compartment that mimics the essential features of the Traill island model: cycle periodicity, amplitude, shape, as well as generalist-induced declines. This simpler model should be broadly applicable to model other lemming populations that predominantly grow under the snow during the winter period. Matlab computer codes for Gilg et al. (2003), its two-dimensional approximation, as well as alternative lemming population dynamics models are provided.

Abstract: Soils of circumpolar regions store large amounts of carbon (C) and are a crucial part of the global C cycle. Yet, little is known about the distribution of soil C stocks among geomorphological terrain units of glacial valleys in the Arctic. Soil C and nitrogen (N) content for the top 100 cm of the dominant vegetated geomorphological terrain units (i.e., alluvial fans, humid polygons, mesic polygons) at Qarlikturvik Valley, Bylot Island, Canada have been analyzed. Soil C content was greatest in humid low-center ice-wedge polygons (82 kg m?2), followed by mesic flat-center ice-wedge polygons (40 kg m?2), and alluvial fan area (16 kg m?2), due to prevailing geomorphological processes, differences in vegetation and soil characteristics, as well as permafrost processes. Soil N content was greatest in humid polygons (4 kg m?2), followed by mesic polygons (2 kg m?2), and alluvial fan area (1 kg m?2). Vertically, C and N decreased with increasing depth except for a peak in C at depth in humid polygons, a likely result of past changes in vegetation cover. At Qarlikturvik Valley, which has a size of 121.7 km2, alluvial fans store 0.226 Tg organic C and humid and mesic polygons store 1.643 and 0.218 Tg organic C, respectively in the top 100 cm of soil. Findings like these are important to further constrain pan-Arctic soil C and N stock estimates and thus climate models.

Abstract: Standard proxies for reconstructing surface mass balance (SMB) in Antarctic ice cores are often inaccurate or coarsely resolved when applied to more complicated environments away from dome summits. Here, we propose an alternative SMB proxy based on photolytic fractionation of nitrogen isotopes in nitrate observed at 114 sites throughout East Antarctica. Applying this proxy approach to nitrate in a shallow core drilled at a moderate SMB site (Aurora Basin North), we reconstruct 700 years of SMB changes that agree well with changes estimated from ice core density and upstream surface topography. For the under-sampled transition zones between dome summits and the coast, we show that this proxy can provide past and present SMB values that reflect the immediate local environment and are derived independently from existing techniques.