Porewater δ13CDOC Indicates Variable Extent Of Degradation In Different Talik Layers Of Coastal Alaskan Thermokarst Lakes

Thermokarst lakes play an important role in permafrost environments by warming up and insulating the underlying permafrost. As a result, thaw bulbs of unfrozen ground (taliks) are formed. Since these taliks remain perennially thawed, they are zones of increased degradation where microbial activity a...

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Main Authors: Meisel, Ove H., Dean, Joshua F., Vonk, Jorien E., Wacker, Lukas, Reichart, Gert-Jan, Dolman, A. Johannes
Format: Text
Language:English
Published: 2020
Subjects:
Online Access:https://doi.org/10.5194/bg-2020-439
https://bg.copernicus.org/preprints/bg-2020-439/
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spelling ftcopernicus:oai:publications.copernicus.org:bgd91331 2023-05-15T15:02:46+02:00 Porewater δ13CDOC Indicates Variable Extent Of Degradation In Different Talik Layers Of Coastal Alaskan Thermokarst Lakes Meisel, Ove H. Dean, Joshua F. Vonk, Jorien E. Wacker, Lukas Reichart, Gert-Jan Dolman, A. Johannes 2020-12-15 application/pdf https://doi.org/10.5194/bg-2020-439 https://bg.copernicus.org/preprints/bg-2020-439/ eng eng doi:10.5194/bg-2020-439 https://bg.copernicus.org/preprints/bg-2020-439/ eISSN: 1726-4189 Text 2020 ftcopernicus https://doi.org/10.5194/bg-2020-439 2020-12-21T17:22:15Z Thermokarst lakes play an important role in permafrost environments by warming up and insulating the underlying permafrost. As a result, thaw bulbs of unfrozen ground (taliks) are formed. Since these taliks remain perennially thawed, they are zones of increased degradation where microbial activity and geochemical processes can lead to increased greenhouse gas emissions from thermokarst lakes. It is not well understood though to what extent the organic carbon (OC) in different talik layers below thermokarst lakes is affected by degradation. Here, we present two transects of short sediment cores from two thermokarst lakes on the Arctic Coastal Plain of Alaska. Based on their physiochemical properties two main talik layers were identified. A <q>lake sediment</q> at the top with low density, sand and silicon content but high porosity. Underneath a <q>deeper talik</q> (former permafrost soil) of high sediment density and rich in sand but lower porosity. Loss on ignition (LOI) measurements show that the organic matter (OM) content in the <q>lake sediment</q> of 28 ± 3 wt % (1σ, n = 23) is considerably higher than in the underlying <q>deeper talik</q> soil with 8 ± 6 wt % (1σ, n = 35), but dissolved organic carbon (DOC) leaches from both layers in high concentrations: 40 ± 14 mg/l (1σ, n = 22) and 60 ± 14 mg/l (1σ, n = 20), respectively. Stable carbon isotope analysis of the porewater DOC (δ 13 C DOC ) showed a relatively wide range of values from −30.74 ‰ to −27.11 ‰ with a mean of −28.57 ± 0.92 ‰ (1σ, n = 21) in the <q>lake sediment</q>, compared to a relatively narrow range of −27.58 ‰ to −26.76 ‰ with a mean of −27.59 ± 0.83 ‰ (1σ, n = 21) in the <q>deeper talik</q> soil (one outlier at −30.74 ‰). The opposite was observed in the soil organic carbon (SOC), with a narrow δ 13 C SOC range from −29.15 ‰ to −27.72 ‰ in the <q>lake sediment</q> (−28.56 ± 0.36 ‰, 1σ, n = 23) in comparison to a wider δ 13 C SOC range from −27.72 ‰ to 25.55 ‰ in the underlying <q>deeper talik</q> soil (−26.84 ± 0.81 ‰, 1σ, n = 21). The wider range of porewater δ 13 C DOC values in the <q>lake sediment</q> compared to the <q>deeper talik</q> soil, but narrower range of comparative δ 13 C SOC , along with the δ 13 C-shift from δ 13 C SOC to δ 13 C DOC together indicates increased stable carbon isotope fractionation due to ongoing processes in the <q>lake sediment</q>. Increased degradation of the OC in the <q>lake sediment</q> relative to the underlying <q>deeper talik</q> are the most likely explanation for these differences in δ 13 C DOC values. As thermokarst lakes can be important greenhouse gas sources in the Arctic it is important to better understand the degree of degradation in the individual talik layers as an indicator for their potential in greenhouse gas release. Especially, as predicted warming of the Arctic in the coming decades will likely increase the number and extent (horizontal and vertical) of thermokarst lake taliks. Text Arctic permafrost Thermokarst Alaska Copernicus Publications: E-Journals Arctic Talik ENVELOPE(146.601,146.601,59.667,59.667)
institution Open Polar
collection Copernicus Publications: E-Journals
op_collection_id ftcopernicus
language English
description Thermokarst lakes play an important role in permafrost environments by warming up and insulating the underlying permafrost. As a result, thaw bulbs of unfrozen ground (taliks) are formed. Since these taliks remain perennially thawed, they are zones of increased degradation where microbial activity and geochemical processes can lead to increased greenhouse gas emissions from thermokarst lakes. It is not well understood though to what extent the organic carbon (OC) in different talik layers below thermokarst lakes is affected by degradation. Here, we present two transects of short sediment cores from two thermokarst lakes on the Arctic Coastal Plain of Alaska. Based on their physiochemical properties two main talik layers were identified. A <q>lake sediment</q> at the top with low density, sand and silicon content but high porosity. Underneath a <q>deeper talik</q> (former permafrost soil) of high sediment density and rich in sand but lower porosity. Loss on ignition (LOI) measurements show that the organic matter (OM) content in the <q>lake sediment</q> of 28 ± 3 wt % (1σ, n = 23) is considerably higher than in the underlying <q>deeper talik</q> soil with 8 ± 6 wt % (1σ, n = 35), but dissolved organic carbon (DOC) leaches from both layers in high concentrations: 40 ± 14 mg/l (1σ, n = 22) and 60 ± 14 mg/l (1σ, n = 20), respectively. Stable carbon isotope analysis of the porewater DOC (δ 13 C DOC ) showed a relatively wide range of values from −30.74 ‰ to −27.11 ‰ with a mean of −28.57 ± 0.92 ‰ (1σ, n = 21) in the <q>lake sediment</q>, compared to a relatively narrow range of −27.58 ‰ to −26.76 ‰ with a mean of −27.59 ± 0.83 ‰ (1σ, n = 21) in the <q>deeper talik</q> soil (one outlier at −30.74 ‰). The opposite was observed in the soil organic carbon (SOC), with a narrow δ 13 C SOC range from −29.15 ‰ to −27.72 ‰ in the <q>lake sediment</q> (−28.56 ± 0.36 ‰, 1σ, n = 23) in comparison to a wider δ 13 C SOC range from −27.72 ‰ to 25.55 ‰ in the underlying <q>deeper talik</q> soil (−26.84 ± 0.81 ‰, 1σ, n = 21). The wider range of porewater δ 13 C DOC values in the <q>lake sediment</q> compared to the <q>deeper talik</q> soil, but narrower range of comparative δ 13 C SOC , along with the δ 13 C-shift from δ 13 C SOC to δ 13 C DOC together indicates increased stable carbon isotope fractionation due to ongoing processes in the <q>lake sediment</q>. Increased degradation of the OC in the <q>lake sediment</q> relative to the underlying <q>deeper talik</q> are the most likely explanation for these differences in δ 13 C DOC values. As thermokarst lakes can be important greenhouse gas sources in the Arctic it is important to better understand the degree of degradation in the individual talik layers as an indicator for their potential in greenhouse gas release. Especially, as predicted warming of the Arctic in the coming decades will likely increase the number and extent (horizontal and vertical) of thermokarst lake taliks.
format Text
author Meisel, Ove H.
Dean, Joshua F.
Vonk, Jorien E.
Wacker, Lukas
Reichart, Gert-Jan
Dolman, A. Johannes
spellingShingle Meisel, Ove H.
Dean, Joshua F.
Vonk, Jorien E.
Wacker, Lukas
Reichart, Gert-Jan
Dolman, A. Johannes
Porewater δ13CDOC Indicates Variable Extent Of Degradation In Different Talik Layers Of Coastal Alaskan Thermokarst Lakes
author_facet Meisel, Ove H.
Dean, Joshua F.
Vonk, Jorien E.
Wacker, Lukas
Reichart, Gert-Jan
Dolman, A. Johannes
author_sort Meisel, Ove H.
title Porewater δ13CDOC Indicates Variable Extent Of Degradation In Different Talik Layers Of Coastal Alaskan Thermokarst Lakes
title_short Porewater δ13CDOC Indicates Variable Extent Of Degradation In Different Talik Layers Of Coastal Alaskan Thermokarst Lakes
title_full Porewater δ13CDOC Indicates Variable Extent Of Degradation In Different Talik Layers Of Coastal Alaskan Thermokarst Lakes
title_fullStr Porewater δ13CDOC Indicates Variable Extent Of Degradation In Different Talik Layers Of Coastal Alaskan Thermokarst Lakes
title_full_unstemmed Porewater δ13CDOC Indicates Variable Extent Of Degradation In Different Talik Layers Of Coastal Alaskan Thermokarst Lakes
title_sort porewater δ13cdoc indicates variable extent of degradation in different talik layers of coastal alaskan thermokarst lakes
publishDate 2020
url https://doi.org/10.5194/bg-2020-439
https://bg.copernicus.org/preprints/bg-2020-439/
long_lat ENVELOPE(146.601,146.601,59.667,59.667)
geographic Arctic
Talik
geographic_facet Arctic
Talik
genre Arctic
permafrost
Thermokarst
Alaska
genre_facet Arctic
permafrost
Thermokarst
Alaska
op_source eISSN: 1726-4189
op_relation doi:10.5194/bg-2020-439
https://bg.copernicus.org/preprints/bg-2020-439/
op_doi https://doi.org/10.5194/bg-2020-439
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