Carbon Burial (in)Efficiency: Tracking the Molecular Fingerprint of In Situ Organic Matter Burial Using a 30-Year Freeze-Core Series From a Northern Boreal Lake (Nylandssjön, Sweden)

IF 3.7 3区 环境科学与生态学 Q2 ENVIRONMENTAL SCIENCES
Richard Bindler, Julie Tolu, Christian Bigler, Johan Rydberg, Antonio Martínez Cortizas
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Abstract

Organic carbon (OC) burial rates in northern lakes are estimated to have increased by 2–3 fold over the past 150 years. However, assessing OC burial efficiency is challenging because (a) long-term (decadal) process are difficult to study in situ, and (b) sediment organic matter (OM) consists of thousands of different compounds from both terrestrial and aquatic sources, which are subject to different degrees of degradation, transformation, or preservation. Here, we used pyrolysis–gas chromatography/mass spectrometry to track changes in the organic molecular composition of individual varve years in a series of sediment freeze cores collected during 1979–2010, allowing us to assess diagenetic changes over ≤31 years (or 12.5 cm depth). As predicted from previous work, the greatest losses over time/depth (18–19 years; 8.5 cm) are for compounds indicative of fresh OM, both terrestrial (e.g., levosugars with 58%–77% lost) and particularly aquatic origin (e.g., phytadiene and phytene amongst chlorophylls with 40%–82% lost). This high variability in degradation of specific compounds has implications for interpreting past changes in C and N. Although OM composition changes only slightly beyond 20 years (8.5 cm), the chlorophyll:lignin ratio (fresh vs. degraded compounds) continues to decline to 31 years (12.5 cm) and is predicted to continue up to 100 years (37 cm depth). In most northern lakes, indications of OM degradation to these depths correspond to sediment ages of 50 to >150 years, suggesting that much of the recent increase in OC burial in northern lakes does not represent permanent sequestration of C.

Abstract Image

碳埋藏效率:利用北北方湖泊30年冻核序列追踪原位有机质埋藏的分子指纹(Nylandssjön,瑞典)
据估计,在过去150年里,北部湖泊的有机碳埋藏率增加了2-3倍。然而,评估有机碳埋藏效率是具有挑战性的,因为(a)长期(年代际)过程很难在原位研究,(b)沉积物有机质(OM)由来自陆地和水生的数千种不同化合物组成,这些化合物会受到不同程度的降解、转化或保存。在这里,我们使用热解-气相色谱/质谱法跟踪了1979-2010年收集的一系列沉积物冻结岩心中各个年份有机分子组成的变化,使我们能够评估≤31年(或12.5 cm深度)的成岩变化。根据以前的工作预测,随着时间/深度的变化,损失最大(18-19年;8.5 cm)用于表示新鲜有机质的化合物,包括陆生(例如,损失58%-77%的左旋糖)和特别是水生来源(例如,叶绿素中的植二烯和植烯,损失40%-82%)。特定化合物降解的这种高变异性对解释过去C和n的变化具有重要意义。尽管有机质组成在20年(8.5 cm)以后仅发生轻微变化,但叶绿素:木质素比率(新鲜化合物与降解化合物)继续下降到31年(12.5 cm),并预计将持续到100年(37 cm深度)。在大多数北部湖泊中,这些深度的有机质降解迹象对应于50至150年的沉积物年龄,这表明北部湖泊中最近增加的大部分碳埋藏并不代表碳的永久封存。
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来源期刊
Journal of Geophysical Research: Biogeosciences
Journal of Geophysical Research: Biogeosciences Earth and Planetary Sciences-Paleontology
CiteScore
6.60
自引率
5.40%
发文量
242
期刊介绍: JGR-Biogeosciences focuses on biogeosciences of the Earth system in the past, present, and future and the extension of this research to planetary studies. The emerging field of biogeosciences spans the intellectual interface between biology and the geosciences and attempts to understand the functions of the Earth system across multiple spatial and temporal scales. Studies in biogeosciences may use multiple lines of evidence drawn from diverse fields to gain a holistic understanding of terrestrial, freshwater, and marine ecosystems and extreme environments. Specific topics within the scope of the section include process-based theoretical, experimental, and field studies of biogeochemistry, biogeophysics, atmosphere-, land-, and ocean-ecosystem interactions, biomineralization, life in extreme environments, astrobiology, microbial processes, geomicrobiology, and evolutionary geobiology
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