Beschreibung: The Action Group called ‘Standardized methods across Permafrost Landscapes: from Arctic Soils to Hydrosystems’ (SPLASH) is a community-driven effort aiming to provide a suite of standardized field strategies for sampling mineral and organic components in soils, sediments, and water across permafrost landscapes. This unified approach will allow data from different landscape interfaces, field locations and seasons to be shared and compared, thus improving our understanding of the processes occurring during lateral transport in circumpolar Arctic watersheds.

Beschreibung: Warming in the Arctic causes strong environmental changes with permafrost degradation being among the most striking effects. Active layer deepening and permafrost erosion can result in the mobilization and lateral transport of organic carbon (OC), which potentially alters carbon cycles in the Arctic substantially. Although the understanding of ground ice contents and permafrost OC release is improving, still little is known of permafrost OC release rates, lateral transport pathways and its driving mechanisms on a landscape scale. In this study we investigate ground ice characteristics and OC composition of the most dominant landscape units of the Yukon coastal plain. In total, 12 permafrost cores were taken from moraine, lacustrine, fluvial and glaciofluvial deposits with a SIPRE corer. Ground ice and sediment contents were analysed using computed tomography and k-means classification. Active layer and upper permafrost were subsampled to analyse OC contents and isotopes of bulk material and a leaching-incubation experiment was conducted with active layer and permafrost sediments to assess potential dissolved OC export and degradation rates. Preliminary results show that ground ice contents vary significantly between landscape units. Ground ice contents in permafrost average 72.4 vol.-% with highest contents in moraines (78.3 vol.-%) and lowest contents in fluvial deposits (53.2 vol.-%). We expect highest dissolved OC leaching and loss rates from permafrost in contrast to active layer and from fluvial and lacustrine deposits, as they simply contain more OC. Yet, lateral OC transport is more likely for landscapes with a topographic gradient such as ground ice-rich moraines. We conclude that due to the high ground ice contents on the Yukon coastal plain, substantial changes of the permafrost landscape will occur under current warming trends. This will include subsidence, abrupt erosion, changes in hydrology and OC degradation processes, which will differ between landscape units.

Beschreibung: Thermal erosion of permafrost coasts delivers large quantities of organic carbon (OC) to arctic coastal waters. While deposition of permafrost OC in nearshore sediments potentially attenuates the ‘permafrost carbon feedback’, continued resuspension of sediments by waves, storms and currents potentially enhances greenhouse gas production in the nearshore zone. Recent studies, focusing on bulk sediments, suggest that permafrost OC derived from coastal erosion is predominantly deposited in the nearshore zone. However, hydrodynamic gradients in the coastal zone allow sorting processes to strongly influence the OC distribution and fate, which cannot be assessed by using bulk sediment approaches. Here, we study soils and sediments fractionated by density (1.8 g/cm-3 cutoff), separating the organic from the mineral-associated fraction, and size (63 µm), separating sand-associated from silt and clay-associated OC. We sampled sediments along a transect from an active retrogressive thaw slump at the coast of Herschel Island - Qikiqtaruk (Yukon, Canada), to the nearshore zone, towards an offshore sedimentary basin. Each sediment fraction was analysed for its elemental content (TOC, TN), carbon isotope signature (δ13C, Δ14C), molecular biomarkers (n-alkanes, n-alkanoic acids, lignin phenols, cutin acids), and mineral surface area. Preliminary data show that the OC partitioning between the sediment fractions changes considerably over the transect, suggesting that hydrodynamic sorting processes take place. Additionally, the OC characteristics of the fractions are significantly different from each other. For example, the low-density organic fraction shows a slightly less degraded signal than the high-density silt- and clay-associated OC fraction in several molecular biomarker proxies, and has a higher average TOC/TN ratio (24 ±3 versus 12 ±2). We aim to disentangle sorting processes and degradation mechanisms of permafrost OC along this transect of fractionated soils and sediments in the nearshore zone, and give new insights into pathway of this material upon erosion.