Early Diagenesis in the Hypoxic and Acidified Zone of the Northern Gulf of Mexico: Is Organic Matter Recycling in Sediments Disconnected From the Water Column?
Early Diagenesis in the Hypoxic and Acidified Zone of the Northern Gulf of Mexico: Is Organic Matter Recycling in Sediments Disconnected From the Water Column?
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DOI：
10.3389/fmars.2021.604330
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发表时间：
2021-03
期刊：
影响因子：
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通讯作者：
C. Rabouille;B. Lansard;Shannon M. Owings;N. Rabalais;B. Bombled;E. Metzger;Julien Richirt;Eryn M. Eitel;Anthony Boever;J. Beckler;M. Taillefert
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作者：
C. Rabouille;B. Lansard;Shannon M. Owings;N. Rabalais;B. Bombled;E. Metzger;Julien Richirt;Eryn M. Eitel;Anthony Boever;J. Beckler;M. Taillefert
缺氧和相关的酸化对沿海地区的生态系统和生物地球化学循环越来越令人关切。墨西哥湾（nGoM）的北方经历了大规模的季节性缺氧几十年来与大陆架的富营养化由密西西比河营养排放燃料。沉积物在维持缺氧和酸化的底层沃茨方面起着关键作用，但这一作用仍未完全了解。在2017年夏天，当nGoM中缺氧区的表面积是有史以来最大的记录时，我们调查了大陆架上的四个站点，这些站点受到密西西比河-阿查法拉亚河系统的河流输入和季节性缺氧的不同影响。我们研究成岩过程下常氧，缺氧，和近缺氧的底部沃茨耦合安培，电位，伏安微剖面与高分辨率的扩散平衡薄膜（DET）配置文件和孔隙水分析。此外，我们使用了2017年5月至11月的底层水溶解氧的时间序列，这表明与有机碳循环有关的底层沃茨中的O2消耗强烈。在沉积物-水界面（SWI），我们发现，与有机物循环的耗氧量是大的扩散摄氧量（DOU）的8和14 mmol m-2 d-1，除了当氧浓度接近缺氧（5 mmol m-2 d-1）。除了位于密西西比河出口附近的站外，地下孔隙水硫酸盐浓度的降低有限，碱度、溶解无机碳（DIC）、铵和磷酸盐的增加很少，这表明低氧条件并没有如预期那样促进缺氧成岩作用。我们认为，低缺氧成岩作用强度的有机基质供应的限制，可能与减少生物扰动在缺氧的春季和夏季。
Hypoxia and associated acidification are growing concerns for ecosystems and biogeochemical cycles in the coastal zone. The northern Gulf of Mexico (nGoM) has experienced large seasonal hypoxia for decades linked to the eutrophication of the continental shelf fueled by the Mississippi River nutrient discharge. Sediments play a key role in maintaining hypoxic and acidified bottom waters, but this role is still not completely understood. In the summer 2017, when the surface area of the hypoxic zone in the nGoM was the largest ever recorded, we investigated four stations on the continental shelf differentially influenced by river inputs of the Mississippi-Atchafalaya River System and seasonal hypoxia. We investigated diagenetic processes under normoxic, hypoxic, and nearly anoxic bottom waters by coupling amperometric, potentiometric, and voltammetric microprofiling with high-resolution diffusive equilibrium in thin-films (DET) profiles and porewater analyses. In addition, we used a time-series of bottom-water dissolved oxygen from May to November 2017, which indicated intense O2 consumption in bottom waters related to organic carbon recycling. At the sediment-water interface (SWI), we found that oxygen consumption linked to organic matter recycling was large with diffusive oxygen uptake (DOU) of 8 and 14 mmol m–2 d–1, except when the oxygen concentration was near anoxia (5 mmol m–2 d–1). Except at the station located near the Mississippi river outlet, the downcore pore water sulfate concentration decrease was limited, with little increase in alkalinity, dissolved inorganic carbon (DIC), ammonium, and phosphate suggesting that low oxygen conditions did not promote anoxic diagenesis as anticipated. We attributed the low anoxic diagenesis intensity to a limitation in organic substrate supply, possibly linked to the reduction of bioturbation during the hypoxic spring and summer.