View of the MIS 2—MIS 1 transition from paleosol archives within loess of the North American central Great Plains

The transition from MIS 2 to MIS 1 was characterized by a rapid succession of discrete climatic phases (Bølling-Allerød, Younger Dryas, Pre-Boreal, and Boreal), during which there was an overall reduction in Global atmospheric dust flux. Within the North American central Great Plains, the upland loess mantle stabilized sufficiently for effective pedogenesis, resulting in soil formation that persisted for nearly 5 k yrs. This remarkable pedostratigraphic feature, preserved beneath Holocene loess, is well manifest along the proximal boundary of the Last Glacial regional loess plume. In this source-proximal corridor, the soil was particularly sensitive to perturbations in the waning loess transport and associated environmental fluctuations. Age of the soil has been well-constrained through recent AMS 14C and OSL dating of localities east-west along the proximal boundary. Pedogenesis began about 14.2 ka during the Bølling-Allerød and continued uninterrupted to about 10.1 ka within the early Boreal, at which time a threshold level of dust influx and a decrease in effective moisture caused soil development to wane and finally to cease at about 9.4 ka. Increased loess flux, accompanied by widespread sand dune and sheet activation, persisted within the region until about 6.5 ka. Archives of information preserved within this soil document environmental change during the course of pedogenesis. Soil architecture is that of a mature mollisol, exhibiting a cumulic A, underlain by Bk-C horizonation. Profiles of δ13C values derived from total soil organic carbon display a transition from C3 to C4 plant dominance with time, though retardation in this rate of change occurs during the Younger Dryas. Notable consistency exists within the isotopic record for a range of spatial scales, attesting to the viability and inherent region-wide nature of the signal. Biogenic opal data further document the temporal decrease in C3 plants and attendant increase in C4 short grasses during pedogenesis, including a short interval of C4 tall grass appearance subsequent to the Younger Dryas (11.5-10.1 ka). Particle-size, elemental, and rock-magnetic signals further articulate the environmental change during this extended period of pedogenesis. Though this episode of pedogenesis largely integrated changes in climate during the Pleistocene-Holocene transition, it nonetheless contains salient manifestations of the shift in Global climate.