Late Quaternary paleohydrology in the North American Great Plains inferred from the geochemistry of endogenic carbonate and fossil ostracodes from Devils Lake, North Dakota, USA

Devils Lake, North Dakota is a closed-basin lake in which water chemistry is responsive to hydrological changes, making it a valuable resource for documenting paleoclimate conditions. Ostracode trace-element and bulk-carbonate geochemistry in a core are used to generate a 12,000-year record of salinity fluctuations. The relative amounts of Sr, Ca and Ba in the bulk-carbonate fraction can be linked mechanistically to changes in sediment mineralogy (calcite/aragonite) and/or solute chemistry, whereas the elemental geochemistry of ostracode valves reflect solute chemistry. Associated minima in Sr/Ca, and maxima in Mg/Ca, in ostracode valves from the Devils Lake core may be due to aragonite mediation of Sr chemistry during the precipitation of multiple mineral phases during more saline intervals. The Devils Lake record can be divided into four hydrological periods on the basis of the geochemical proxies: (a) 12.5-9 k.y.: Low salinity; (b) 9.5-4.5 k.y.: Fluctuating, saline conditions with a maximum at about 8 k.y.; (c) 4.5-3.5 k.y.: Low salinity phase, but probably not as fresh as at 12.5-9 k.y.; (d) 3.5 k.y.-Present: Saline phase, although generally less so than 9.5-4.5 k.y. However, a large degree of variability characterizes the entire record, suggesting the absence of long-term climatic stability in this region.