Abstract
Abstract. Permafrost deposits in the Beringian Yedoma region store large amounts of organic carbon (OC). Walter Anthony et al. (2014) describe a previously unrecognized pool of 159 Pg OC accumulated in Holocene thermokarst sediments deposited in Yedoma region alases (thermokarst depressions). They claim that these alas sediments increase the previously recognized circumpolar permafrost peat OC pool by 50 %. It is stated that previous integrated studies of the permafrost OC pool have failed to account for these deposits because the Northern Circumpolar Soil Carbon Database (NCSCD) is biased towards non-alas field sites and that the soil maps used in the NCSCD underestimate coverage of organic permafrost soils. Here we evaluate these statements against a brief literature review, existing data sets on Yedoma region soil OC storage and independent field-based and geospatial data sets of peat soil distribution in the Siberian Yedoma region. Our findings are summarized in three main points. Firstly, the sediments described by Walter Anthony et al. (2014) are primarily mineral lake sediments and do not match widely used international scientific definitions of peat or organic soils. They can therefore not be considered an addition to the circumpolar peat carbon pool. We also emphasize that a clear distinction between mineral and organic soil types is important since they show very different vulnerability trajectories under climate change. Secondly, independent field data and geospatial analyses show that the Siberian Yedoma region is dominated by mineral soils, not peatlands. Thus, there is no evidence to suggest any systematic bias in the NCSCD field data or maps. Thirdly, there is spatial overlap between these Holocene thermokarst sediments and previous estimates of permafrost soil and sediment OC stocks. These carbon stocks were already accounted for by previous studies and they do not significantly increase the known circumpolar OC pool. We suggest that these inaccurate statements made in Walter Anthony et al. (2014) mainly resulted from misunderstandings caused by conflicting definitions and terminologies across different geoscientific disciplines. A careful cross-disciplinary review of terminologies would help future studies to appropriately harmonize definitions between different fields.
Highlights
Soils and sediments of the northern permafrost region have accumulated large stocks of organic carbon (OC) over millennia (Tarnocai et al, 2009)
Following initial permafrost degradation and thermokarst, these basins have typically been terrestrialized and re-aggraded permafrost. We examine these important statements by evaluating the findings and data presented by Walter Anthony et al (2014) against (1) a brief review of vulnerability to climatic changes and scientific definitions of peat, peatlands, organic soils and thermokarst sediments, (2) independent field data as well as independent geospatial databases showing the extent of organic soils and/or peatlands in the Siberian Yedoma region and (3) by analyzing the spatial overlap between these new estimates and existing data sets of Yedoma region soil and sediment OC storage
There is no evidence or reasoning to suggest that these deposits increase the northern peatland pool or that the Northern Circumpolar Soil Carbon Database (NCSCD) is systematically biased against upland soils
Summary
Soils and sediments of the northern permafrost region have accumulated large stocks of organic carbon (OC) over millennia (Tarnocai et al, 2009). Following initial permafrost degradation and thermokarst, these basins have typically been (partly) terrestrialized (e.g., through lake drainage or evaporation of lake water) and re-aggraded permafrost We examine these important statements by evaluating the findings and data presented by Walter Anthony et al (2014) against (1) a brief review of vulnerability to climatic changes and scientific definitions of peat, peatlands, organic soils and thermokarst sediments, (2) independent field data as well as independent geospatial databases showing the extent of organic soils and/or peatlands in the Siberian Yedoma region and (3) by analyzing the spatial overlap between these new estimates and existing data sets of Yedoma region soil and sediment OC storage
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