Atmospheric changes in North America during the last deglaciation from dune-wetland records in the Midwestern United States

Reconstructing moisture conditions during the early retreat of the Laurentide Ice Sheet (LIS) may help define the phase relationship of deglacial conditions and atmospheric changes over North America. Here, we report two sediment successions near the concurrent ice margins in the Midwest of the U.S.A. to show that dune formation was active from 17.7 to 14.7 and from 12.8 to 11.8 thousand years ago (ka) and lowland soils formed at 14.7 and wetland sediments developed from 13.5 to 12.8 ka. Our results suggest that moisture conditions in the Midwestern U.S.A. were inversely phased with those in the southwestern U.S.A. During the Heinrich event 1 (H1) and Younger Dryas (YD) stadials, the northern area became drier and southern area became wetter, whereas during the Bølling/Allerød (B/A) interstadials, the northern area became wetter and southern area became drier. This pattern is also observed on phase change levels within the H1 interval. In detail, from 17.7 to 16.5 ka during the H1b phase, major aridity in the Midwest corresponded to wet conditions in the Southwest U.S.A. From 16.5 to 15.0 ka during the H1a phase, climate reversed from dry to wet in the Midwest, whereas conditions went from wet to dry in the Southwest. From 15.0 to 14.7 ka during the transition to the Bølling/Allerød (t-B/A) phase, a return of aridity in the Midwest corresponded to a return of humidity in the Southwest.

► Dune-wetland successions showing H1 and YD aridity and B/A wetness in the Midwestern U.S.A.
► Evidence of moisture variability within the H1 stadial on regional scales.
► Inversed pattern of moisture distributions between Northern and Southern U.S.A.
► Constraints of polar jet stream/rain belt shifts during the last deglaciation across North America.