Showing papers by "Martin Heimann published in 2023"

Impact of the Long-Term Drainage on the Eddy-Covariance Fluxes in Northern High Latitude Permafrost Regions

Abstract: In the context of global climate change, permafrost thaw in northern high-latitude territories is becoming a major concern due to the vast amount of organic carbon that is stored within this region. To accurately predict the feedback between Arctic permafrost carbon pools and future climate change, detailed insight into current carbon cycle processes and their environmental controls is imperative. A highly valuable data source for this purpose are continuous observations of turbulent exchange fluxes of carbon (e.g. CO2 and CH4 fluxes) and energy (e.g. fluxes of sensible and latent heat) with the eddy-covariance technique, in combination with the monitoring of environmental parameters such as e.g. air or soil temperature and moisture, radiation,  atmospheric turbulence, water table levels, precipitation, and snow depth.In this study, we evaluate the effect of drainage on vertical carbon fluxes and environmental parameters within a Northeast Siberian wet tundra permafrost ecosystem. Our experiment includes two co-located eddy-covariance sites, one reflecting disturbed conditions affected by a drainage system which was built in 2004, and the other as an undisturbed control site. Both towers were identically outfitted with eddy covariance instruments mounted on 5 m tall towers on the floodplain of the Kolyma River near Chersky (68.75 º N, 161.33º E) in Northeast Siberia, Russia. The dataset analyzed here covers the period from July 2013 to December 2021, including continuous coverage throughout the winter seasons. We present a statistical analysis of the long-term trends in the environmental parameters and surface-atmosphere exchange fluxes at both sites. In addition, we relate the carbon and heat fluxes at both sites in the spectral and temporal domain to the inter-annual variability in climate conditions, which include extremes in both summer (temperature, precipitation) and winter (snow cover) conditions. Finally, we show the annual carbon budget of both sites, with a specific focus on the long-term impact of the drainage on carbon cycle process.

Can thawing permafrost alter the general circulation of the atmosphere?

Abstract: Thawing Arctic permafrost has been assigned increasing importance as a key element in the global climate system over the past decades. One quarter of land surface of the northern hemisphere are permafrost regions, containing about 50% of the global below-ground carbon pool. Permafrost degradation and the associated climate feedback pose a potential tipping element that might be reached even within 1.5 °C global warming. Besides the potential release of additional carbon, permafrost degradation also holds the potential to significantly alter the surface characteristics of affected landscapes, resulting in further feedback processes that are poorly understood so far.In the presented study, we investigate the impact of permafrost degradation onto the structure of the atmospheric boundary layer (ABL) as a first feedback link to the global circulation. High-resolution Large Eddy Simulations (LES) are used to quantify the role of surface heterogeneity as a particular driver for boundary layer characteristics. Our virtual experiments simulate the structural changes of the ABL linked to long-term enhanced permafrost thaw, including e.g. the formation of new ponds and lakes, or increased spatial heterogeneity in vegetation structure with the establishment of different grass and shrubs species. Such changes may result in shifted fingerprints of heat and momentum fluxes into the atmosphere. Through this connection, ongoing climate change may lead to permanently altered influences of thawed permafrost on temperature and moisture profiles within the Arctic atmosphere, including changes in the boundary layer height. A particular focus of our study will be placed on the potential loss of water being drained away from the ecosystem after permafrost degradation, where the dried out soil not only changes the carbon cycle processes but also exhibits new surface characteristics. We quantify how the ABL reacts to those changes in idealized LES experiments, and investigate how atmospheric changes may further affect permafrost degradation.

Spatio-temporal patterns in carbon distribution in supra-permafrost groundwater at a small-scale site in North-East Siberia

Abstract: Climate warming can influence a variety of landscape processes, including the transformation and transfer  of water, carbon and nutrients. In the Northern Hemisphere, permafrost underlays large parts of the land surface and represents a large reservoir of  organic carbon that is extremely vulnerable to changing climate conditions. Accelerated thaw can decompose permafrost carbon, and lead to modified exchange processes with the atmosphere (vertical pathway) and hydrosphere (lateral pathways). These carbon export rates are highly dependent on soil water conditions, suprapermafrost groundwater table location, and vegetation community. Depending on depth of thaw and dry or wet soil conditions, changes in the production and availability patterns of dissolved organic carbon (DOC), particulate organic carbon (POC) and dissolved inorganic carbon (DIC), the three main carbon components in water, are expected. Shifts in lateral carbon export become more relevant for quantifying the total local carbon budget with predicted future permafrost degradation due to climate warming and resulting drier soil conditions. This study focuses on carbon distribution patterns of the three main carbon components (DOC, POC, DIC) within a floodplain tundra site near Chersky, Northeast Siberia. We compared a wet control site with a dry site affected by a drainage ring built in 2004. A network of piezometers was established to continuously monitor water table trends during the summer season (July to September) in 2017. On several key locations within that network, water was sampled to determine carbon concentrations (DOC, POC, DIC) and carbon isotopes (∆14C-DOC, δ13C-DOC, δ13C-DIC) in 2017. Here, we analyze and discuss the spatio-temporal carbon distribution on both sites with linkages to hydrological conditions (e.g. saturated zone) and carbon isotopic observations. The highest concentrations throughout both sites were found for DOC, followed by DIC and POC. DIC is relatively higher at wet sites compared to dry sites. Reversely, the organic carbon components, DOC and POC, were higher at dry sites. ∆14C-DOC can be associated with fresh material and decreased at all measurement sites with time of the season. Within that range, ∆14C-DOC decreased more at dry sites, when thaw depths were deepest within that site and where water tables were lower compared to wet sites, indicating the release of older carbon. Our results show that the distribution of carbon and the respective carbon isotopes are directly related to hydrological flow patterns. Understanding the carbon redistribution processes in these ecosystems is of relevance for assessing the carbon budget in disturbed permafrost areas. These findings will therefore be used to compare climate warming induced permafrost degradation at the dry (drained) site with the wet (control) site.