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Gross primary productivity, chlorophyll, and quantum yield of photosynthesis data among phytoplankton in Deming Lake, Minnesota from 2023 - 2024. The PhytoPAM II (Walz) was used for all measurements. The data is comprised of taxa-specific gross primary productivity (GPP), chlorophyll, rapid light curves (RLCs), andquantum yields of photosynthesis across depths including the SCML and O2 max. This dataset contains two .csv files and a .zip folder with additional exported .csv files from the PhytoPAM II. 

Counts of photosynthetic and non-photosynthetic cells across four depths depths including the O2 max and SCML in Deming Lake, Minnesota from August 2023. We used flow cytometry for cell counts and distinguished between photosynthetic and non-photosynthetic cells based on autofluorescence. The dataset contains one .csv file. 

Abstract The greenhouse gas methane (CH4) contributed to a warm climate that maintained liquid water and sustained Earth’s habitability in the Precambrian despite the faint young sun. The viability of methanogenesis (ME) in ferruginous environments, however, is debated, as iron reduction can potentially outcompete ME as a pathway of organic carbon remineralization (OCR). Here, we document that ME is a dominant OCR process in Brownie Lake, Minnesota (midwestern United States), which is a ferruginous (iron-rich, sulfate-poor) and meromictic (stratified with permanent anoxic bottom waters) system. We report ME accounting for ≥90% and >9% ± 7% of the anaerobic OCR in the water column and sediments, respectively, and an overall particulate organic carbon loading to CH4 conversion efficiency of ≥18% ± 7% in the anoxic zone of Brownie Lake. Our results, along with previous reports from ferruginous systems, suggest that even under low primary productivity in Precambrian oceans, the efficient conversion of organic carbon would have enabled marine CH4 to play a major role in early Earth’s biogeochemical evolution. 

Depth profiles of water column chemical and physical properties were assessed with seasonal-scale frequency from four lakes in the Itasca State Park from 2006-2009 and from 2019-2023. The data was used to assess the mixing status and major geochemical constituents within the lakes. Several parameters were routinely measured with deployable probes at meter or sub-meter resolution at the deepest location in each lake. Water samples were also collected for laboratory analysis. Bathymetry data collected in 2022 is supplied as rasters.