Humid Pleistocene−Holocene transition and early Holocene in sub‐tropical northern Mexico and possible Gulf of California forcing

Abstract

A new geochemical record from the paaleolake Santiaguillo documents the hydrological variability of subtropical northern Mexico over the last ∼14 cal. ka. Summer-season runoff, lake water salinity and deposition of sediments by aeolian activity were reconstructed from concentrations of K, Ca and Zr/K in bulk sediments. More-than-average runoff during c. 12.3-9.3 cal. ka BP represented an interval of enhanced summer precipitation. Arid intervals of c. 14-12.3 cal. ka BP and c. 6-4.3 cal. ka BP were characterized by average and more-thanaverage aeolian activity. Comparison with proxy records of summer as well as winter precipitation from tropical and sub-tropical North America and sea surface temperatures from the Atlantic and Pacific provides insight into the source of moisture and possible forcing. The wet Pleistocene−Holocene transition and early Holocene was contemporary with warmer conditions in the Gulf of California. We suggest that the Atlantic had minimal influence on the summer precipitation of the western part of sub-tropical northern Mexico and that the source of moisture was dominantly Pacific.

The Holocene history of the North American Monsoon: ‘known knowns’ and ‘known unknowns’ in understanding its spatial and temporal complexity

“…The increase of winter precipitation in the northern part of the NAM under glacial-type background conditions is a well established idea, but how far south this influence reached and the actual balance between winter and summer precipitation is difficult to establish using the proxies available, most of which have limited seasonal discrimination. There have been suggestions that wetter conditions at this time in the northern NAM area were associated with an early re-establishment of the NAM (Roy et al, 2014 and references therein). Midden records from San Pedro Martir in northern Baja California (Holmgren et al, 2011) show increasing proportions of C4 grasses and summer flowering plants from 13,600 cal yr BP, which are interpreted as reflecting the onset of summer, monsoonal rainfall.…”

“…There has been work on new sites (e.g. Ortega-Rosas et al, 2008a, b), but Holocene chronologies are often rather poor and there is more focus on longer records extending back into the last glacial (Roy et al, 2014). Unfortunately, there have been very few new packrat midden records published from Mexico in recent years (but see Holmgren et al, 2011).…”

Subsurface fire and subsidence at Valle del Potosí (Nuevo León, Mexico): Preliminary observations

“…However, the replication of a similar mechanism is not possible at Valle del Potosí due to the fact that northern Mexico is arid and there is no major river nearby. The paleoclimatic records from the region show a tendency towards reduced rainfall over the last 2,000 years (Roy et al, 2013(Roy et al, , 2014. Similarly, the increasing activity of El Niño Southern Oscillation in the modern era has reduced the amount of rainfall in northern Mexico (Magaña et al, 2003).…”

Past vegetation influence on the hydrological cycle in the Chihuahuan Desert, North Mexico as indicated by data of four pollen sites

“…Recent contributions to palaeo-hydrological change in subtropical North-Central Mexico have been made in studies of trace elements linked to changes of detrital accumulation and thus surface run-off in playa-lake deposits (Roy et al, 2012(Roy et al, , 2014, following methods also used in perennial lake basins in tropical Mexico. The temporal patterning of past precipitation changes is also a focus of these analyses using lake sediments, originally in more tropical areas of Mexico (Davies et al, 2004;Metcalfe et al, 2010), where diatoms as well as detrital titanium reconstruct a high-resolution pattern for the Late Holocene.…”

“…2). This (LM) basin is a focus of present study at the sites of LM Cuota 2 and LM Cuota 7, and smaller basins indeed have been a focus of climate history studies in the region (e.g., Metcalfe et al, 2002;Roy et al, 2014) with a view to changing hydrological conditions since the Pleistocene. However, a limitation in many studies is that pollen data are sparse, and particularly after the Pleistocene.…”