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Abstract. Four adjacent lakes (Arco, Budd, Deming, and Josephine) within Itasca State Park in Minnesota, USA, are reported to be meromictic in the scientific literature. However, seasonally persistent chemoclines have never been documented. We collected seasonal profiles of temperature and specific conductance and placed temperature sensor chains in two lakes for ∼1 year to explore whether these lakes remain stratified through seasonal mixing events and what factors contribute to their stability. The results indicate that all lakes are predominantly thermally stratified and are prone to mixing in isothermal periods during spring and fall. Despite brief, semi-annual erosion of thermal stratification, Deming Lake showed no signs of complete mixing from 2006–2009 and 2019–2022 and is likely meromictic. However, the other lakes are not convincingly meromictic. Geochemical data indicate that water in Budd Lake, which contains the most water, is predominantly sourced from precipitation. The water in the other three lakes is of the calcium–magnesium–bicarbonate type, reflecting a source of water that has interacted with the deglaciated landscape. δ18OH2O and δ2HH2O measurements indicate the lakes are supplied by precipitation modified by evaporation. Josephine, Arco, and Deming lakes sit in a valley with likely permeable sediments and may be hydrologically connected through wetlands and recharged with shallow groundwater, as no streams are present. The water residence time in meromictic Deming Lake is short (100 d), yet it maintains a large reservoir of dissolved iron, indicating that shallow groundwater may be an additional source of water and dissolved ions. All four lakes develop subsurface chlorophyll maxima layers during the summer. All lakes also develop subsurface oxygen maxima that may result from oxygen trapping in the spring by rapidly developed summer thermoclines. Documenting the mixing status and general chemistry of these lakes enhances their utility and accessibility for future biogeochemical studies, which is important as lake stratification and anoxia are becoming more prevalent due to changes in climate and land use. 

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. 

Abstract Laminated sediments can record seasonal changes in sedimentation of material from anoxic waters, including minerals of the redox‐sensitive elements Fe, Mn, and S that form under varying oxygen levels, mineral saturation conditions, and from microbial metabolism. However, preserving the oxygen‐sensitive minerals for identification is challenging when preservation of the spatial arrangement of laminae is also required. In this study, we compare methods for embedding sedimentary materials from anoxic waters and sediments from Brownie Lake, Minnesota, USA for analysis of the speciation for Fe, Mn, and S using synchrotron‐based X‐ray absorption near edge spectroscopy (XANES). We found that acetone dehydration and resin replacement in a 100% N₂glovebox successfully preserved the speciation of Fe and Mn minerals within laminated sediments. However, acetone removed some sulfur species from sediments, and epoxies contained sulfur species, which challenged identification of native sulfur species. Results from this study will aid researchers who are interested in spatial analysis of oxygen sensitive sediments, soils, or microbial mats in choosing a preservation method. 

The dataset is comprised of analyses of sediment cores and sediment trap samples from ferruginous and meromictic Brownie Lake, Minnesota, U.S.A from January 2018 through February 2021. The dataset includes bulk sediment characteristics including water content, grain size, major and minor elements. Voltammetric scans were collected on porewaters and lake waters. Sediment porewaters were analyzed for pH, total alkalinity, ferrous iron, and dissolved sulfur species contents. Sediment samples were maintained under the exclusion of oxygen for analysis by synchrotron-based X-ray absorption spectroscopy. 

Depth profiles of water column chemical and physical properties were assessed with seasonal-scale frequency from two meromictic lakes in the upper Midwest, U.S.A. from 2015 to 2019. Brownie Lake in Minneapolis, MN and Canyon Lake in the Huron Mountains of MI both contain elevated hypolimnetic dissolved iron (i.e. “ferruginous”). 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.