Climatic Variation in the Western Part of Subtropical North America during Late Last Glacial and Deglaciation: Some New Records and a Synthesis

Abstract:

Late Quaternary climate of western subtropical North America is related to the dynamics of summer as well as winter precipitation. During the last glacial maximum, it was hypothesized that the frequent winter storms provided more precipitation (COHMAP members, 1988) as the southern branch of the jet streams carried more moisture into the region (Kutzbach and Wright, 1985). However, the new global climate simulations do not provide indication of the jet stream split and some even suggest that the southern branch of the jet was weaker (Kim et al., 2008; Toracinta et al., 2004). In the last few years, the proxy records from the region have provided new information and suggested new hypothesis (Barron et al., 2012; Lyle et al., 2012; Roy et al., 2013). We present some new records of paleohydrological changes occurred over the late last glacial and deglaciation from the northwestern México. A compilation of all the important records from the region provides information about the geographic coverage of summer and winter precipitation. Minimal influence of summer as well as winter precipitation caused drier conditions over a large part of northern and northwestern Mexico (i.e. 29°-31°N) during the late last glacial (27-18 cal ka BP). Summer precipitation was restricted to the southern part of subtropical North America during >18 cal ka BP and it expanded to higher latitudes and covered different regions over the deglaciation (18-10 cal ka BP). We relate the different geographical coverage of summer precipitation to moisture flow sourced from the tropical and subtropical Pacific and Gulf of California during different intervals.