A 9-m sediment core from Crystal Lake, Illinois (U.S.A.) has yielded pollen, ostracode, and ostracode biogeochemical records dating from 16.1 cal ka to the present. Crystal Lake has yielded a nearly continuous ostracode record spanning the Bølling, Allerød, Younger Dryas, and early Holocene; coeval sediments from other local deep-lakes are barren of ostracodes. Preservation of ostracode valves in the Crystal Lake record is attributed to a leaky basin, a moisture budget that includes about 50% groundwater input, watershed geology composed of dolomite-rich till and outwash, and water residence time of < 1 yr. Published reconstructions of past seasonal moisture and temperature based on an expanded response surface technique of no-analogue pollen spectra indicate excessive moisture (primarily as winter snow) from 14.2 to 11.5 cal ka^-1. The biogeochemistry of adult valves of Candona ohioensis and other ostracode species supports these conclusions. Particularly sensitive is Sr/Ca_m, a proxy for alkalinity and salinity in hard-water lakes that do not precipitate aragonite. Modern analogs indicate that mid-Holocene total dissolved solids (TDS) averaged about 500 mg/L suggesting that Younger Dryas values were about 200 mg/L, approximately the calcite saturation level (below which calcite dissolves). Modern analogs of the mid-Holocene ostracode assemblages from Crystal Lake indicate a total dissolved solid (TDS) value of about 500 mg/L. Today, Crystal Lake’s TDS is about 450 mg/L. Sr/Ca_m values suggest TDS values at or below 200 mg/L for the interval 13.77-9.25 cal ka. The evidence in the core of fresher water, and hence, greater-than-modern P-E is supported by very low valve counts, barren zones, low ostracode diversity, and modern analog reconstructions of salinity.
^-1 Gonzales et al., 2009. doi:10.1016/j.quascirev.2009.09.005