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.
|Original language||English (US)|
|Number of pages||20|
|Journal||Journal of Geophysical Research: Biogeosciences|
|State||Published - Oct 2018|
Bibliographical noteFunding Information:
This work was sponsored by the National Science Foundation (NSF) collaborative research grant (EAR- 1660691 to E. D. S., EAR-1660761 to C. W., and EAR-1660873 to S. K.) and by grants from the Huron Mountain Wildlife Foundation (HMWF) in 2015, 2016, and 2017. We would like to thank the HMWF for providing housing and access to Canyon Lake. We acknowledge the Minneapolis Parks and Recreation Board for permits to work on Brownie Lake and Amy Myrbo (LacCore) for discussion and assistance in the field. Many thanks to students who assisted with sampling and laboratory analysis including Duncan Widman, Ashley Grengs, Paige Bauer, Matt Pronschinske, Kelly Hunt, Josh Torgeson, Trevor Van Dyke, and Raisa Islam. The authors declare that they have no conflict of interest. Our data are all provided as supporting information.
©2018. American Geophysical Union. All Rights Reserved.
- early Earth