Last glacial hydrological variations at the southern margin of sub-tropical North America and a regional comparison

ABSTRACT Geochemical and magnetic characteristics of sediments from paleolake La Salada provide information about the last glacial hydrological conditions at the southern margin of sub‐tropical North America. Proxy records of runoff, lake water salinity, brine composition and provenance of organic matter are based on multi‐element concentration, magnetic susceptibility, mineralogy, carbonate content and C/N relation. Runoff was higher than average during ca. 43–36k cal a BP and at ca. 33k cal a BP. A shift in mineralogical assemblage from calcite > protodolomite–halite to protodolomite–gaylussite suggests that the brine composition changed from Ca–(Mg–Na)–HCO3–(Cl) to Mg–Na–Ca–HCO3 because of more runoff after the desiccation event at ca. 28k cal a BP. In general, organic matter deposited during the intervals of more runoff and deeper lake conditions were sourced from lacustrine phytoplankton. The contribution of terrestrial vegetation dominates during the intervals of reduced runoff. Comparison with other records provides a regional perspective of moisture variability. Humid conditions at ca. 33k cal a BP could be due to more summer precipitation in northern Mexico as well as increased winter rainfall in the south‐western USA.