Hydrodynamic sorting and degradation of permafrost organic matter in the nearshore zone of Herschel Island (Yukon, Canada)

• Main Authors: Jong, Dirk J., Bröder, Lisa, Tesi, Tommaso, Tanski, George, Oudenhuisen, Mickolai, Fritz, Michael, Lantuit, Hugues, Haghipour, Negar, Eglinton, T. I., Vonk, Jorien E.
• Format: Conference Object
• Language: unknown
• Published: 2020
• Subjects: Arctic; Canada; Herschel Island; Yukon; Herschel; permafrost
• Online Access: https://epic.awi.de/id/eprint/53645/; https://eventmobi.com/ac2020/agenda/f92b9476-9fb3-4428-9a5e-3e2177a30b97/8e14a10e-c0d9-4f35-b203-84809eb5c41f; https://hdl.handle.net/10013/epic.66f29a49-2acf-4c12-b2ae-a3be8a36b087

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.