LGM isoscape of central North America; implications for an ice-proximity climate gradient

Sarah Dendy-Metz, Jessica L. Conroy, David Grimley, William Guenthner, Phillip Kerr, Jeffrey S. Pigati

Research output: Chapter in Book/Report/Conference proceedingConference contribution


Widespread, abundant, terrestrial paleoclimate proxies dating to the last glacial maximum (LGM) are rare. Land snails are preserved in Quaternary loess and palustrine deposits worldwide. The stable oxygen isotope (delta (super 18) O) values of land snail shells provide a record of past climate variables, including precipitation, temperature, and the delta (super 18) O value of precipitation. Modern land snail delta (super 18) O values throughout North America are largely driven by average annual precipitation delta (super 18) O values. Here we investigate land snail delta (super 18) O values from deposits dated to the LGM in the upper Midwest USA and Mississippi River Valley. We present 387 measurements of delta (super 18) O and delta (super 13) C values from 12 gastropod taxa (including Succineidae, Vertigo, Discus, Carychium and Stenotrema). Gastropod shells were collected from 7 sites distributed along a north-south transect, following the Mississippi River from northern Illinois to the Gulf of Mexico, and from 5 sites along a west-east transect from Iowa to Indiana. The delta (super 18) O and delta (super 13) C values range from 2.9 ppm to -3.8 ppm and from -0.5 ppm to -10.9 ppm, respectively. We hypothesize that spatial variability in shell delta (super 18) O values is influenced by the presence of the Laurentide Ice Sheet due to its effect on temperature and atmospheric circulation. We observe a gradient in mean Succineidae delta (super 18) O values from Iowa to southern Illinois, with lower delta (super 18) O values from higher latitude samples closer to the ice margin. Lower delta (super 18) O values in samples closer to the ice sheet margin may be caused by increased warm-season storminess and lower precipitation delta (super 18) O values, due to the steepened land-ice meridional temperature gradient during the LGM. There is no observed north-south trend in delta (super 13) C values. However, a trend with proximity to the ice margin may provide more insight.
Original languageEnglish (US)
Title of host publicationGeological Society of America, 2021 annual meeting; GSA connects 2021
PublisherGeological Society of America (GSA), Boulder, CO, United States
StatePublished - 2021


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