Dating deep-lake sediments by using amino acid racemization in fossil ostracodes

The long-term rate of racemization for amino acids preserved in fossil ostracode shells was determined by using independently dated sediment cores from five deep lakes. The racemization rates for aspartic and glutamic acids in the common ostracode genus Candona were calibrated for the past 100 k.y., providing the basis for an age equation with a realistic age uncertainty of ∼±20%. The new age equation can be applied to other hypolimnic settings because the temperature below the thermocline of deep lakes from middle- and high-latitude regions can reasonably be assumed to remain close to 4 °C. The sample size required for analysis is an order of magnitude less than for ¹⁴C dating and presents new opportunities to date deposits that are organic-matter poor or those with large ¹⁴C reservoir effects.