Terrestrial and hydrological responses during the Younger Dryas Chronozone in the Cuatrociénegas Basin,Mexico

High-resolution analysis of pollen from Poza Cortador, Cuatrociénegas, Mexico was conducted for the period 13,600–11,300 cal yr BP. Results indicate that rapid cooling, coincident with the Younger Dryas chronozone, led to rapid shifts in the vegetation of the Chihuahuan Desert. Prior to the Younger Dryas, desert taxa like Acacia were increasing in abundance. This expansion was suppressed by apparent cooling and shifts in regional hydrology. The interval associated with the Younger Dryas has two phases. An initial phase from 13,010 to 12,455 cal yr BP had an expansion of mixed conifer woodlands with co-mingled pine, juniper, and oaks. From 12,455 to 11,915 cal yr BP, juniper became dominant in these woodlands. Wetland dynamics show concomitant hydrologic changes impacting the region. Seagrass (Ruppia) pollen spiked near 13,010 cal yr BP, suggesting a shift from fresh- to brackish marsh condition early in the Younger Dryas chronozone. A subsequent freshening of the marshes is suggested with increases in sedges for most of this initial period. The second phase of the Younger Dryas, when Juniper became began to dominate woodland composition at 12,455 cal yr BP, coincides with a loss of macrophytes and dominance of the marsh by salt-tolerant grasses, asters and forbs. Detailed analysis of pollen through this period of rapid climate change provides insights into the natural rate of change in aridland ecosystems and the resiliency of these systems to both temperature and hydrologic change.