Preserved particulate organic carbon is likely derived from the subsurface sulfidic photic zone of the Proterozoic Ocean: evidence from a modern, oxygen-deficient lake

IF 2.7 2区 地球科学 Q2 BIOLOGY
Geobiology Pub Date : 2024-03-12 DOI:10.1111/gbi.12593
Ashley B. Cohen, Lisa N. Christensen, Felix Weber, Milana Yagudaeva, Evan Lo, Gregory A. Henkes, Michael L. McCormick, Gordon T. Taylor
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Abstract

Biological processes in the Proterozoic Ocean are often inferred from modern oxygen-deficient environments (MODEs) or from stable isotopes in preserved sediment. To date, few MODE studies have simultaneously quantified carbon fixation genes and attendant stable isotopic signatures. Consequently, how carbon isotope patterns reflect these pathways has not been thoroughly vetted. Addressing this, we profiled planktonic productivity and quantified carbon fixation pathway genes and associated organic carbon isotope values (δ13CPOC) of size-fractionated (0.2–2.7 and >2.7 μm) particulate matter from meromictic Fayetteville Green Lake, NY, USA. The high-O2 Calvin-Benson-Bassham (CBB) gene (cbbL) was most abundant in the <2.7 μm size fraction in shallow oxic and deep hypoxic waters, corresponding with cyanobacterial and eukaryote algal populations. The low-O2 CBB gene (cbbM) was most abundant near the lower oxycline boundary in the larger size fraction, coincident with purple sulfur bacteria populations. The reverse citric acid cycle gene (aclB) was equally abundant in both size fractions in the deepest photic zone, coinciding with green sulfur bacteria populations. Methane coenzyme reductase A (mcrA), of anaerobic methane cyclers, was most abundant at the lower oxycline boundary in both size fractions, coinciding with Methanoregula populations. δ13CPOC values overlapped with the high-O2 CBB fixation range except for two negative excursions near the lower oxycline boundary, likely reflecting assimilation of isotopically-depleted groundwater-derived carbon by autotrophs and sulfate-reducers. Throughout aphotic waters, δ13CPOC values of the large size fraction became 13C-enriched, likely reflecting abundant purple sulfur bacterial aggregates. Eukaryote algae- or cyanobacteria-like isotopic signatures corresponded with increases in cbbL, cbbM, and aclB, and enrichment of exopolymer-rich prokaryotic photoautotrophs aggregates. Results suggest that δ13CPOC values of preserved sediments from areas of the Proterozoic Ocean with sulfidic photic zones may reflect a mixture of alternate carbon-fixing populations exported from the deep photic zone, challenging the paradigm that sedimentary stable carbon isotope values predominantly reflect oxygenic photosynthesis from surface waters.

保存下来的颗粒有机碳可能来自新生代海洋的次表层硫酸光化带:一个现代缺氧湖泊提供的证据。
新生代海洋中的生物过程通常是通过现代缺氧环境(MODE)或保存沉积物中的稳定同位素来推断的。迄今为止,很少有 MODE 研究同时量化碳固定基因和相应的稳定同位素特征。因此,碳同位素模式如何反映这些途径还没有得到彻底审查。为了解决这个问题,我们对来自美国纽约州费耶特维尔绿湖(Fayetteville Green Lake)的分光镜颗粒物(0.2-2.7 和大于 2.7 μm)的浮游生产力进行了剖析,并量化了碳固定途径基因和相关的有机碳同位素值(δ13 CPOC)。高氧卡尔文-本森-巴萨姆(CBB)基因(cbbL)在大粒径分馏物的下氧环边界附近最为丰富,与紫硫细菌种群相吻合。反向柠檬酸循环基因(aclB)在光照区最深处的两个大小分段中含量相同,与绿色硫细菌种群相吻合。厌氧甲烷循环器的甲烷辅酶还原酶 A(mcrA)在氧环下边界的两个大小分段中含量最高,与 Methanoregula 群体相吻合。CPOC δ13 值与高氧气 CBB 固定范围重叠,但在下氧环边界附近有两次负偏移,这可能反映了自养生物和硫酸盐还原器对同位素贫化的地下水源碳的同化作用。在整个虹吸水域,大粒径部分的 δ13 CPOC 值变得富含 13 C,这可能反映了丰富的紫硫细菌聚集。真核藻类或蓝藻类同位素特征与 cbbL、cbbM 和 aclB 的增加以及富含外聚物的原核光自养菌聚集体的富集相对应。研究结果表明,原生代海洋硫酸光化带地区保存的沉积物的δ13 CPOC值可能反映了从深部光化带输出的交替固碳种群的混合物,这对沉积物稳定碳同位素值主要反映来自表层水的含氧光合作用的范式提出了挑战。
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来源期刊
Geobiology
Geobiology 生物-地球科学综合
CiteScore
6.80
自引率
5.40%
发文量
56
审稿时长
3 months
期刊介绍: The field of geobiology explores the relationship between life and the Earth''s physical and chemical environment. Geobiology, launched in 2003, aims to provide a natural home for geobiological research, allowing the cross-fertilization of critical ideas, and promoting cooperation and advancement in this emerging field. We also aim to provide you with a forum for the rapid publication of your results in an international journal of high standing. We are particularly interested in papers crossing disciplines and containing both geological and biological elements, emphasizing the co-evolutionary interactions between life and its physical environment over geological time. Geobiology invites submission of high-quality articles in the following areas: Origins and evolution of life Co-evolution of the atmosphere, hydrosphere and biosphere The sedimentary rock record and geobiology of critical intervals Paleobiology and evolutionary ecology Biogeochemistry and global elemental cycles Microbe-mineral interactions Biomarkers Molecular ecology and phylogenetics.
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