ALBERT

Description: Peat plateaus and palsas are characteristic morphologies of sporadic permafrost, and the transition from permafrost to permafrost‐free ground typically occurs on spatial scales of meters. They are particularly vulnerable to climate change and are currently degrading in Fennoscandia. Here we present a spatially distributed data set of ground surface temperatures for two peat plateau sites in northern Norway for the year 2015–2016. Based on these data and thermal modeling, we investigate how the snow depth and water balance modulate the climate signal in the ground. We find that mean annual ground surface temperatures are centered around 2 to 2.5 °C for stable permafrost locations and 3.5 to 4.5 °C for permafrost‐free locations. The surface freezing degree days are characterized by a noticeable threshold around 200 °C.day, with most permafrost‐free locations ranging below this value and most stable permafrost ones above it. Freezing degree day values are well correlated to the March snow cover, although some variability is observed and attributed to the ground moisture level. Indeed, a zero curtain effect is observed on temperature time series for saturated soils during winter, while drained peat plateaus show early freezing surface temperatures. Complementarily, modeling experiments allow identifying a drainage effect that can modify 1‐m ground temperatures by up to 2 °C between drained and water accumulating simulations for the same snow cover. This effect can set favorable or unfavorable conditions for permafrost stability under the same climate forcing.

Description: Polygonal tundra and ice-rich permafrost landscapes are widespread across the Arctic and prone to rapid transitions due to ground subsidence, thermokarst or thermoerosion. Such small-scale processes are typically not resolved in large-scale Earth System models. Our goal with this study was to develop a scalable modeling approach that is capable of simulating the degradation of ice-wedges and the corresponding geomorphological transition from low- to high-centered polygons. For this, we employed the land surface model CryoGrid3 and advanced it by a hydrological infiltration scheme. We simulated the lateral exchange of heat, water, and snow between polygon centers, rims and troughs by coupling multiple realizations. We proved our modeling approach to be capable of describing the evolution of ice-wedge polygons and analyzed the hydrological and climatic conditions, which are favorable for their degradation. With this, we contributed to the understanding of landscape transitions in ice-rich permafrost regions and their representation in large-scale models.

Description: Thawing of permafrost potentially affects the global climate system through the mobilization of greenhouse gases, and poses a risk to human infrastructure in the Arctic. The response of ice-rich permafrost landscapes to a changing climate is particularly uncertain, and challenging to be addressed with numerical models. A main reason for this is the rapidly changing surface topography resulting from melting of ground ice, which is referred to as thermokarst. It is expressed in characteristic landforms which alter the hydrology, the surface energy balance, and the redistribution of snow of the entire landscapes. Polygonal patterned tundra which is underlain by massive ice-wedges, is a prototype of a sensitive permafrost system which is increasingly subjected to thermokarst activity throughout the Arctic. In this talk I will present a scalable modeling approach, based on the CryoGrid land surface model, to investigate the degradation of ice-wedges. The numerical model takes into account lateral fluxes of heat, water, and snow between different topographic units of polygonal tundra and simulates topographic changes resulting from melting of excess ground ice (i.e., thermokarst), and from lateral erosion of sediment. We applied the model to investigate the influence of hydrological conditions on the development of different types of ice-wedge polygons in a study area in northern Siberia. We further used projections of future climatic conditions to confine the evolution of ice-wedge polygons in a changing climate, and assessed the amount of organic matter which could thaw under different scenarios. In a related study for a study site in northern Alaska, we demonstrated that the model setup can be used to study the effect of infrastructure on the degradation of ice-wedges. Altogether, our modeling approach can be seen as a blueprint to investigate complexly inter-related processes in ice-rich permafrost landscapes, and marks a step forward towards an improved representation of these landscapes in large-scale land surface models.

Description: Heinrich events are characterized by worldwide climate modifications. Over the Altiplano endorheic basin (high tropical Andes), the second half of Heinrich Stadial 1 (HS1a) was coeval with the highstand of the giant paleolake Tauca. However, the atmospheric mechanisms underlying this wet event are still unknown at the regional to global scale. We use cosmic-ray exposure ages of glacial landforms to reconstruct the spatial variability in the equilibrium line altitude of the HS1a Altiplano glaciers. By combining glacier and lake modeling, we reconstruct a precipitation map for the HS1a period. Our results show that paleoprecipitation mainly increased along the Eastern Cordillera, whereas the southwestern region of the basin remained relatively dry. This pattern indicates a southward expansion of the easterlies, which is interpreted as being a consequence of a southward shift of the Bolivian High. The results provide a new understanding of atmospheric teleconnections during HS1 and of rainfall redistribution in a changing climate.