Radiocarbon age-offset measurements reveal shifts in the transport mechanism and age of permafrost-derived organic carbon from Burial Lake, arctic Alaska from MIS 3 to present

IF 3.2 1区 地球科学 Q1 GEOGRAPHY, PHYSICAL
Hailey Sinon , Mark Abbott , Eitan Shelef , Brad Rosenheim , Devon Firesinger , Melissa Griffore , Matt Finkenbinder , Bruce Finney , Mary Edwards
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引用次数: 0

Abstract

The stability of arctic permafrost and the carbon it contains are currently threatened by a rapidly warming climate. Burial Lake, situated in northwestern arctic Alaska, is underlain by continuous permafrost and has a uniquely rich set of paleoclimate proxy data that comprise a 40-ka record of climate and environmental change extending well into Marine Isotope Stage (MIS) 3. Here, we examine the relationship between erosion, subsurface hydrology, and primary productivity from the Burial Lake sediments to improve our understanding of the links between climate, hydrology, sediment transport, and carbon mobility. The record is developed with radiocarbon (14C) age-offsets from two independent methods used to date the lake sediments: 1) 14C measurements on paired bulk sediment and plant macrofossils from the same stratigraphic layer of lake sediment and 2) ramped pyrolysis-oxidation (RPO) 14C analysis that separates fractions of organic carbon (OC) from a single bulk sediment sample based on thermochemical differences through continuous heating. As lakes capture and archive OC transported from the watershed, changes in the amount and relative age of permafrost-derived OC mobilized during past climatic variations can be documented by examining how age-offsets change over time. The Burial Lake sediment revealed higher age-offsets during the cold Last Glacial Maximum (LGM; ∼29-17 ka) than the comparatively warmer post-glacial (∼17 ka-present) and the MIS 3 interstadial (∼40-29 ka) periods. The relatively warm, wet climate of the post-glacial period promoted both terrestrial and aquatic productivity, resulting in increased OC deposition, and it likely favored transport via subsurface flow of dissolved OC (DOC) sourced from soils. This resulted in a greater flux of contemporary OC relative to ancient OC into the lake sediment, lowering the average age offset to ∼2 ka. In contrast, the low-productivity conditions of the LGM resulted in slow soil accumulation rates, leaving ancient OC in a shallower position in the soil profile and allowing it to be easily eroded in the form of particulate OC (POC). Although the amount of total OC deposited in the lakebed during the LGM is small relative to post-glacial deposition, the majority is ancient, which leads to a relatively high average age offset of ∼9 ka. Finally, climate and environmental conditions of the MIS 3 interstadial were intermediate between those of the post-glacial and the LGM. As with post-glacial sediments, a relatively large amount of OC is present; however, the vast majority of it is ancient (more similar to the LGM), and it produces an average age offset of ∼6 ka. The Burial Lake radiocarbon record demonstrates the complexities of the thaw and mobilization of permafrost OC in arctic Alaska, including the balance between production, transport, deposition, remobilization, and preservation. This record highlights the importance of considering factors that both enhance and inhibit erosion (i.e. vegetation cover, lake level, precipitation) and the mechanisms of OC transport (i.e. subsurface flow or erosion) in predictions of future permafrost response to changes in climate.
放射性碳年龄偏移测量揭示了从 MIS 3 到现在阿拉斯加北极 Burial 湖永久冻土有机碳迁移机制和年龄的变化
北极永久冻土的稳定性及其所含的碳目前正受到气候迅速变暖的威胁。埋骨湖位于阿拉斯加西北部的北极地区,被连续的永久冻土覆盖,拥有独特的丰富的古气候代用数据,这些数据构成了 40-ka 的气候和环境变化记录,一直延伸到海洋同位素阶段(MIS)3。在这里,我们研究了埋骨湖沉积物中的侵蚀、地下水文和初级生产力之间的关系,以加深我们对气候、水文、沉积物迁移和碳流动之间联系的理解。该记录采用了两种独立的方法对湖泊沉积物进行放射性碳(14C)年龄测定:1) 对来自同一湖泊沉积物地层的成对块状沉积物和植物大化石进行 14C 测量;2)斜坡式热解-氧化(RPO)14C 分析,该分析通过持续加热,根据热化学差异从单一块状沉积物样本中分离出有机碳(OC)组分。由于湖泊会捕获并存档从流域迁移过来的有机碳,因此可以通过研究年龄偏移随时间的变化,记录在过去的气候变迁中永冻土来源的有机碳的数量和相对年龄的变化。埋骨湖沉积物显示,在寒冷的末次冰川极盛时期(LGM;29-17 ka),年龄偏移高于相对温暖的后冰川时期(17 ka至今)和MIS 3间冰期(40-29 ka)。后冰期相对温暖湿润的气候促进了陆生和水生生产力,导致 OC 沉积增加,并可能有利于来自土壤的溶解 OC(DOC)通过地表下的流动进行迁移。这导致进入湖泊沉积物的当代 OC 相对于远古 OC 有更大的通量,从而将平均年龄偏移降低到 ∼2 ka。与此相反,LGM时期的低生产力条件导致土壤积累速度缓慢,使得古OC在土壤剖面中的位置较浅,容易以颗粒OC(POC)的形式被侵蚀。虽然相对于冰川期后的沉积物而言,大冰川时期沉积在湖床中的总 OC 量较少,但大部分都是古 OC,这就导致平均年龄偏移相对较高,为 ∼9 ka。最后,MIS 3间期的气候和环境条件介于后冰期和全新世之间。与后冰期沉积物一样,这里也有相对较多的 OC,但绝大部分是古 OC(与全新世更为相似),其产生的平均年龄偏移为 6 ka。埋骨湖放射性碳记录显示了阿拉斯加北极地区永久冻土 OC 解冻和移动的复杂性,包括生成、迁移、沉积、再移动和保存之间的平衡。该记录突出表明,在预测未来永久冻土对气候变化的反应时,必须同时考虑促进和抑制侵蚀的因素(即植被覆盖、湖泊水位、降水)以及 OC 运输机制(即地下流动或侵蚀)。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
Quaternary Science Reviews
Quaternary Science Reviews 地学-地球科学综合
CiteScore
7.50
自引率
15.00%
发文量
388
审稿时长
3 months
期刊介绍: Quaternary Science Reviews caters for all aspects of Quaternary science, and includes, for example, geology, geomorphology, geography, archaeology, soil science, palaeobotany, palaeontology, palaeoclimatology and the full range of applicable dating methods. The dividing line between what constitutes the review paper and one which contains new original data is not easy to establish, so QSR also publishes papers with new data especially if these perform a review function. All the Quaternary sciences are changing rapidly and subject to re-evaluation as the pace of discovery quickens; thus the diverse but comprehensive role of Quaternary Science Reviews keeps readers abreast of the wider issues relating to new developments in the field.
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