Geochemical Characterization of Two Ferruginous Meromictic Lakes in the Upper Midwest, USA
Geochemical Characterization of Two Ferruginous Meromictic Lakes in the Upper Midwest, USA
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DOI：
10.1029/2018jg004587
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发表时间：
2018-10
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影响因子：
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通讯作者：
N. Lambrecht;C. Wittkop;S. Katsev;M. Fakhraee;E. Swanner
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作者：
N. Lambrecht;C. Wittkop;S. Katsev;M. Fakhraee;E. Swanner
为了阐明地球早期海洋中铁和碳循环的（生物）地球化学过程的作用，需要具有类似地球化学条件的现代环境。由于前寒武纪海洋的化学、物理和生物属性在时间和空间上一定是不同的，因此不同成分的湖泊有助于提出和回答不同的问题。热带马塔诺湖（印度尼西亚），已知最大的铁质湖，和帕文湖（法国），一个半裂火山口湖，是两个研究最好的前寒武纪海洋类似物。在这里，我们提出了季节性地球化学数据从冰川形成的温带铁质湖泊：布朗尼湖（MN）和峡谷湖（MI）在上中西部，美国。多年季节性监测的结果表明：（1）每个湖都是部分混合的，有一个密集的缺氧的单一层，由一个尖锐的化学跃层与密度较小的缺氧的混合层分隔开;（2）在这个化学跃层之下是含铁的沃茨，最大溶解铁浓度>1 mM;（3）布朗尼湖的部分混合主要是人为的，而峡谷湖的部分混合是自然的;（4）布朗尼湖的浅化学跃层和高磷水库使其成为研究无氧光合作用、元素比值和矿物学的理想模拟物;（5）峡谷湖的深穿透性亚氧带可能支持未来的亚氧微生物活动或矿物转化研究。
To elucidate the role of (bio)geochemical processes that fueled iron and carbon cycling in early Earth oceans, modern environments with similar geochemical conditions are needed. As the range of chemical, physical, and biological attributes of the Precambrian oceans must have varied in time and space, lakes of different compositions are useful to ask and answer different questions. Tropical Lake Matano (Indonesia), the largest known ferruginous lake, and Lake Pavin (France), a meromictic crater lake, are the two best studied Precambrian ocean analogs. Here we present seasonal geochemical data from two glacially formed temperate ferruginous lakes: Brownie Lake (MN) and Canyon Lake (MI) in the Upper Midwest, USA. The results of seasonal monitoring over multiple years indicate that (1) each lake is meromictic with a dense, anoxic monimolimnion, which is separated from the less dense, oxic mixolimnion by a sharp chemocline; (2) below this chemocline are ferruginous waters, with maximum dissolved iron concentrations >1 mM; (3) meromixis in Brownie Lake is largely anthropogenic, whereas in Canyon Lake it is natural; (4) the shallow chemocline of Brownie Lake and high phosphorus reservoir make it an ideal analog to study anoxygenic photosynthesis, elemental ratios, and mineralogy; and (5) a deep penetrating suboxic zone in Canyon Lake may support future studies of suboxic microbial activity or mineral transformation.