title: Transformation of terrestrial organic matter along thermokarst-affected permafrost coasts in the Arctic.
abstract: The changing climate in the Arctic has a profound impact on permafrost coasts, which are subject to intensified thermokarst formation and erosion. Consequently, terrestrial organic matter (OM) is mobilized and transported into the nearshore zone. Yet, little is known about the fate of mobilized OM before and after entering the ocean. In this study we investigated a retrogressive thaw slump (RTS) on Qikiqtaruk - Herschel Island (Yukon coast, Canada). The RTS was classified into an undisturbed, a disturbed (thermokarst-affected) and a nearshore zone and sampled systematically along transects. Samples were analyzed for total and dissolved organic carbon and nitrogen (TOC, DOC, TN, DN), stable carbon isotopes (δ13C-TOC, δ13C-DOC), and dissolved inorganic nitrogen (DIN), which were compared between the zones. C/N-ratios, δ13C signatures, and ammonium (NH4-N) concentrations were used as indicators for OM degradation along with biomarkers (n-alkanes, n-fatty acids, n-alcohols). Our results show that OM significantly decreases after disturbance with a TOC and DOC loss of 77 and 55% and a TN and DN loss of 53 and 48%, respectively. C/N-ratios decrease significantly, whereas NH4-N concentrations slightly increase in freshly thawed material. In the nearshore zone, OM contents are comparable to the disturbed zone. We suggest that the strong decrease in OM is caused by initial dilution with melted massive ice and immediate offshore transport via the thaw stream. In the mudpool and thaw stream, OM is subject to degradation, whereas in the slump floor the nitrogen decrease is caused by recolonizing vegetation. Within the nearshore zone of the ocean, heavier portions of OM are directly buried in marine sediments close to shore. We conclude that RTS have profound impacts on coastal environments in the Arctic. They mobilize nutrients from permafrost, substantially decrease OM contents and provide fresh water and nutrients at a point source.
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany; Potsdam University, Institute of Earth and Environmental Sciences, Potsdam, Germany. Electronic address: George.Tanski@awi.de.
authors.forename: George
authors.initials: G
authors.lastname: Tanski
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany; Potsdam University, Institute of Earth and Environmental Sciences, Potsdam, Germany. Electronic address: Hugues.Lantuit@awi.de.
authors.forename: Hugues
authors.initials: H
authors.lastname: Lantuit
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany; Potsdam University, Institute of Earth and Environmental Sciences, Potsdam, Germany. Electronic address: saskia.ruttor@gmail.com.
authors.forename: Saskia
authors.initials: S
authors.lastname: Ruttor
authors.affiliation: University of Hamburg, Institute of Soil Sciences, Hamburg, Germany. Electronic address: Christian.Knoblauch@uni-hamburg.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Knoblauch
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany; Potsdam University, Institute of Earth and Environmental Sciences, Potsdam, Germany. Electronic address: Boris.Radosavljevic@awi.de.
authors.forename: Boris
authors.initials: B
authors.lastname: Radosavljevic
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany. Electronic address: Jens.Strauss@awi.de.
authors.forename: Jens
authors.initials: J
authors.lastname: Strauss
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany; Potsdam University, Institute of Earth and Environmental Sciences, Potsdam, Germany. Electronic address: Juliane.Wolter@awi.de.
authors.forename: Juliane
authors.initials: J
authors.lastname: Wolter
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany; Potsdam University, Institute of Earth and Environmental Sciences, Potsdam, Germany. Electronic address: Anna.Irrgang@awi.de.
authors.forename: Anna M
authors.initials: AM
authors.lastname: Irrgang
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany; Potsdam University, Institute of Earth and Environmental Sciences, Potsdam, Germany. Electronic address: Justine.Ramage@awi.de.
authors.forename: Justine
authors.initials: J
authors.lastname: Ramage
authors.affiliation: Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research, Periglacial Research Unit, Potsdam, Germany. Electronic address: Michael.Fritz@awi.de.
authors.forename: Michael
authors.initials: M
authors.lastname: Fritz
keywords: Biogeochemistry; Canadian Arctic; Carbon degradation; Coastal erosion; Retrogressive thaw slump