Mobilization of dissolved organic carbon (DOC) from permafrost due to arctic coastal erosion

Michael.Fritz [ at ]


Arctic permafrost coasts make up ~34% of the world’s coastline (ca. 400,000 km) and are often made of ice-rich unconsolidated sediments. This makes them highly susceptible to coastal erosion, and it is likely that large quantities of carbon are released, because permafrost soils are considered to hold approximately 50% of the global soil organic carbon pool. Current estimates of the carbon released by coastal erosion focus solely on particulate organic carbon (POC). Dissolved organic carbon (DOC) is generally not included in these calculations, because estimations of DOC contents in ground ice, which is overwhelmingly present along Arctic coasts, do not exist. In some cases, ground ice occupies as much as 90% of coastal bluffs with 40 m in height, where the coastline erodes at rates approaching 20 m/yr at its maximum. Here, we report DOC contents within permafrost from different ground ice types throughout the Arctic (Canada, Alaska, Siberia). We put them into context of Arctic organic carbon pools and fluxes, and evaluate their contribution to the Arctic carbon budget against the background of increasing permafrost degradation and enhancing coastal erosion in the future. For example, DOC concentrations in massive ground ice bodies including ice wedges range between <1.0 and 28.6 mg/L, while ice wedges have the greatest potential as DOC pool due to their wide spatial distribution in late Pleistocene and Holocene polygonal ground. Siberian Ice Complex deposits (Yedoma) are thought to consist of up to 50% of ice wedges by volume and are therefore a substantial pool of DOC. Intrasedimental ice (non-massive) like ice lenses and pore ice are another important part of unconsolidated permafrost deposits. DOC concentrations within intrasedimental ice differ in orders of magnitude compared to massive ice and rise up to 1200 mg/L. Although these numbers might be still small compared to the POC stocks in peat and mineral soils, DOC is chemically labile and may directly enter local food webs of the near-shore zone. Moreover, due to its lability, DOC is quickly mineralized and returned to the atmosphere when released due to permafrost degradation. Robust estimations of how much organic carbon is potentially released from permafrost are crucial for predicting the strength and timing of carbon-cycle feedback mechanisms in the Arctic. This approach shall lead to an improved understanding of how important permafrost thaw in general and the erosion of permafrost coasts in particular are for the climate development this century and beyond. This is especially important in the Arctic before the background of expected rising air and sea surface temperatures, prolongation of the open-water season, increasing storm frequency and accelerating eustatic sea level rise.

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Conference (Talk)
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4th European Conference on Permafrost, 18 Jun 2014 - 21 Jun 2014, Évora, Portugal.
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Fritz, M. , Tanski, G. , Herzschuh, U. , Couture, N. J. , Opel, T. , Meyer, H. and Lantuit, H. (2014): Mobilization of dissolved organic carbon (DOC) from permafrost due to arctic coastal erosion , 4th European Conference on Permafrost, Évora, Portugal, 18 June 2014 - 21 June 2014 .

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