AN ANNUALLY RESOLVED RECORD OF CLIMATE VARIABILITY FROM THE SOUTHERN MEXICAN HIGHLANDS

We present preliminary analysis of an annually resolved reconstruction of climate over the last millennia for Southern Mexico. The reconstruction is derived from a varved lake record from Laguna Minucua located in the highlands of Oaxaca, which spans the last 5000 years. Prior work by Goman et al. (2018) characterized the morphology and geochemistry of the varves, which are composed of light and dark couplets. The dark couplets contain coarse material deposited during the rainy season and the lighter couplets finer-grained clays and authigenic hydrous sulfate minerals deposited during the dry season.

We discuss high resolution magnetic susceptibility and varve width measurement record for the past 1000 years, which shows significant shifts in concentration and size from the preceding 1500 years. Subtle shifts in the two proxies occurred during the Medieval Climatic Anomaly (MCA: C.E. 1000-1400) and Little Ice Age (LIA: C.E. 1400-1850); although there is decadal variability exhibited within these shifts. The MCA is characterized by lower magnetic susceptibility and greater varve width variability, possibly indicative of wetter conditions, while the LIA exhibits higher magnetic susceptibility, smaller varves and reduced variability, likely reflecting drier climatic conditions. Varve formation ceased around C.E. 1880, and magnetic susceptibility data indicate major declines towards the present.

We place the findings within the context of other high and low resolution climate data from Mesoamerica and the broader Caribbean region. Our preliminary analysis indicates association of varve formation with the North American Monsoon and variations within the dynamics of that system. The climate history is further compared to significant cultural events in Western Mesoamerica.