Diatom, pollen, and geochemical evidence for the palaeosalinity of Medicine Lake, S. Dakota, during the late-Wisconsin and early Holocene
✍ Scribed by Nancy Radle; Claire M. Keister; Richard W. Battarbee
- Book ID
- 104661446
- Publisher
- Springer Netherlands
- Year
- 1989
- Tongue
- English
- Weight
- 967 KB
- Volume
- 2
- Category
- Article
- ISSN
- 0921-2728
No coin nor oath required. For personal study only.
✦ Synopsis
Medicine Lake is a highly saline meromictic lake in eastern South Dakota. A lithostratigraphic and biostratigraphic study of the late-glacial and early post-glacial sediments shows that it was a relatively deep dilute freshwater lake during the period of the Picea pollen zone. When spruce forest changed to a Betula and then to a Quercus/Ulmus woodland in the early post-glacial period, the lake water became more concentrated but remained fresh. However, during the subsequent rapid transition to prairie in the early Holocene, when Gramineae, Ambrosia, and Artemisia dominated dry-land vegetation, the freshwater diatom flora was progressively replaced by a saline assemblage characterized by Cyclotella quillensis, Chaetoceros, and eventually Cyclotella caspia. The lake became permanently saline at about 9000 yr BP. A comparison of the fossil diatom assemblages with surface-sediment samples from a range of lakes in the Dakotas indicates that the change involved an increase in conductivity from about 500 #S c m -1 in the late-glacial period to > 10000 pS cm-a in the early Holocene. This rapid change is also marked by an abrupt increase in sulphate concentration in the sediment, the first appearance of bands of gypsum crystals, and the beginning of a well-laminated core sequence that continues through the remaining sediment record. Conditions of high salinity have prevailed to the present day.
* Contribution 299, Limnological Research Center. 1972;Brugam, 1980). These studies have shown that low-water levels occurred in this region in the mid-Holocene, a time when pollen evidence indicates an eastward migration of the prairie/forest border (McAndrews, 1966), probably in response to climatic warming associated with the hypsithermal period (Wright, 1976).
Until now studies in this region have been confreed to lakes with open drainage. In the prairie environment closed (saline) lakes are common. Lake-level fluctuations can be accompanied by major changes in water salinity, and associated