Interpreting the seasonality of precipitation in northern Baja California for the last ~45,000 cal yr BP

Abstract:

The Sierra de Juarez of Northern Baja California lies in a region that is heavily influenced by the El Niño Southern Oscillation (ENSO), which brings winter precipitation and the North American Monsoon (NAM), which brings summer precipitation to the region. Little is known about the impacts that the seasonality of precipitation have had on fire and vegetation throughout the region, especially extending into the early Holocene and Pleistocene. Fire regimes and ciénega processes, as indicate by loss on ignition, magnetic susceptibility, and charcoal data, appear to be controlled by the amount of precipitation to the region and groundwater levels. This study will analyze seasonality of precipitation based on certain taxa that are associated with summer wet or winter wet moisture patterns. Preliminary pollen analysis shows that when summer-wet taxa are more prevalent on the landscape, winter-wet taxa declines. Based on existing ENSO and NAM data, we know that the influences of both phenomena have changed in their intensities and spatial boundaries throughout time. Our study sites (Ciénega Chimeneas, 32^o 14’ N and 116 ^o 06’ W, and Ciénega San Faustino, 32° 12’ 30.4” N 116° 09’ 55” W, spanning the last ~45,000 cal yrs BP) are located in a region that can help define when and where changes in the seasonality of precipitation have occurred since the late Pleistocene. Additional dating and pollen analysis will allow us to further validate the relationships between ENSO and NAM like activity and ecosystem processes for this site.