Evidence for increased cool season moisture during the middle Holocene

Isotopic analyses of three stalagmites from Cold Water Cave, northeast Iowa , United States, reveal nearly identical delta(13)C trends from ca, 7 to 2 ka, However, delta(18)O patterns differ by as much as 3 parts per thousand from 5.7 to 3.2 ka, These disparate delta(18)O values reflect evaporative O -18 enrichment in meteoric water prior to infiltration, suggesting that pre viously calculated temperatures based on a single Cold Water Cave stalagmit e overestimated middle Holocene warming. The coincidence of elevated middle Holocene growth rates in the stalagmites with the Lowest oxygen isotopic c ompositions indicates that the middle Holocene was marked by a predominance of cool-weather precipitation during a period of increased overall aridity .