Organic‐Matter Accumulation and Degradation in Holocene Permafrost Deposits Along a Central Alaska Hillslope
Organic‐Matter Accumulation and Degradation in Holocene Permafrost Deposits Along a Central Alaska Hillslope
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DOI：
10.1029/2022jg007290
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发表时间：
2023-09
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影响因子：
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通讯作者：
Leah P. Marshall;Darrell S. Kaufman;R. S. Anderson;N. McKay;E. Schuur
中科院分区：
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作者：
Leah P. Marshall;Darrell S. Kaufman;R. S. Anderson;N. McKay;E. Schuur
多年冻土高地下富碳有机质（OM）的数量和保存，以及碳积累随千年气候变化的演变，是碳循环对气候变化反馈的不确定性的主要来源。我们调查了多年冻土有机质积累和降解的全新世断面的沉积物芯可以追溯到至少c。6 ka，来自阿拉斯加中部八英里湖流域的山坡。我们在上层泥炭下面发现分米级的富有机层（111 ± 45 kg C m−3）和贫有机层（49 ± 30 kg C m−3），在上层1 m中分别储存了35% ± 11%和41% ± 20%的碳。在有机质贫乏的地层中，分散的14 C年龄的植物宏化石和较高比例的退化Alnus和Betula花粉表明了冷扰动和山坡过程的改造。尽管有机碳与氮的比例通常表明有机质在核心上变新鲜，但氨基酸细菌生物标志物，包括d-对映体和γ-氨基丁酸，表明在5 ka之前降解增强。碳积累速率从10.4 g C m−2年− 1增加到14 g C m−2年−1。8 ~ 0.2ka，与区域性降温增湿相一致，这可能促进了有机质的积累。地表1米范围内的碳储量平均为66 ± 13 kg C m−2，从上斜坡埋藏洼地的77 kg C m−2到下坡的48 kg C m−2不等。我们的结论是保存OM的异质性反映了山坡地貌过程，冰冻扰动和全新世气候变化的组合。
The quantity and preservation of carbon‐rich organic matter (OM) underlying permafrost uplands, and the evolution of carbon accumulation with millennial climate change, are large sources of uncertainty in carbon cycle feedbacks on climate change. We investigated permafrost OM accumulation and degradation over the Holocene using a transect of sediment cores dating back to at least c. 6 ka, from a hillslope in the Eight Mile Lake watershed, central Alaska. We find decimeter‐scale organic‐rich (111 ± 45 kg C m−3) and organic‐poor (49 ± 30 kg C m−3) layers below an upper peat, which store 35% ± 11% and 41% ± 20% of the carbon in the upper 1 m, respectively. In organic‐poor layers, scattered 14C ages of plant macrofossils and higher percentages of degraded Alnus and Betula pollen indicate reworking by cryoturbation and hillslope processes. Whereas organic carbon to nitrogen ratios generally indicate OM freshening up‐core, amino acid bacterial biomarkers, including d‐enantiomers and gamma‐aminobutyric acid, suggest enhanced degradation prior to 5 ka. Carbon accumulation rates increased from ∼4 to 14 g C m−2 year−1 from c. 8 to 0.2 ka, coinciding with decreasing temperatures and increasing moisture regionally, which may have promoted OM accumulation. Carbon stocks within the upper 1 m average 66 ± 13 kg C m−2, varying from 77 kg C m−2 in a buried depression on the upper slope to 48 kg C m−2 downslope. We conclude that heterogeneity in preserved OM reflects a combination of hillslope geomorphic processes, cryoturbation, and climatic variations over the Holocene.