Groundwater dominated lakes are an important feature of many landscapes. Their sediments are a particularly valuable source of paleoenvironmental information in semiarid regions where perennial lakes may otherwise be scarce. Where groundwater and lake composition are favorable, carbonate mineral precipitation, evaporative concentration of lake water, and microbial processes can combine to strongly deplete dissolved Ca relative to influent groundwaters. The authigenic carbonate flux (ACF) can then become limited by water column cation availability and thereby be coupled to groundwater inflow rates and aquifer recharge. Here we analyze sedimentary records from two marl-producing, groundwater-controlled lakes and demonstrate a link between one-dimensional ACF and the Palmer Drought Severity Index (PDSI), a measure of land surface wetness. In a restricted outflow lake with high-carbonate alkalinity, ACF is enhanced during historically wet climatic periods in response to increased aquifer recharge rates. ACF in this lake declines during droughts. A neighboring dilute lake with a high rate of groundwater outflow shows comparatively weak coupling between ACF and PDSI history. Ionic chemistry, carbonate mineral equilibria, and δ13C patterns of dissolved inorganic carbon show that the sensitivity of the ACF signal depends on the degree of evaporative evolution of lake water and the mineral saturation state of the water column under conditions of stratification and ice cover.
|Original language||English (US)|
|Number of pages||17|
|Journal||Geochimica et Cosmochimica Acta|
|State||Published - May 15 2005|
Bibliographical noteFunding Information:
We wish to thank Larry Benson, Avner Ayalon, and an anonymous reviewer for careful critiques of this manuscript, which benefited in important ways from their suggestions. We also thank Eric Grimm and Dan Engstrom for critical contributions to core recovery and sediment dating. Geof and Kathy Foote, Jim and Colleen Stone, Gary and Sharon Jacobsen, and Price, Laura, and Justin Williams provided generous access to private lands and invaluable logistical assistance in the field. The senior author’s contribution to this research was supported by the U.S. National Science Foundation through the University of Minnesota Department of Geology and Geophysics GeoFluids Program and the UM Paleorecords Research Training Group, and by the U.S. Department of Education through the UM Department of Geology and Geophysics GAANN Program. Critical support was provided by facilities and personnel of LRC LacCore facility. This is Limnological Research Center Contribution #601.