Last 3000 years of hydroclimate variability in western Mexico

Sediment rock-magnetic records from Laguna Minucua, (Oaxaca) Mexico, have been used to develop a detailed proxy environmental record of hydroclimate variability (wet/dry cycles) for the last 3000 years. Rock magnetic intensities (ARM, SIRM, CHI) estimate the clastic flux to Laguna Minucua due to variable rainfall/outwash. The rock magnetic ratio, ARM/CHI, estimates the overall clastic grain size versus time. These rock-magnetic proxies and a revised chronostratigraphy define a detailed multi-decadal/centennial scale of hydrologic cyclicity for the last 3000 years. This pattern is also noted in four other published paleoclimate records from western Mexico. This cyclicity is synchronous (<±25 years) among these five records for the entire time period of overlap. This synchrony suggests that western Mexico from Baja, California to Oaxaca, Mexico, and west of the Sierra Madre Occidental crest define a coherent regional hydroclimate pattern of variability. The multi-decadal/centennial scale cyclicity varies slowly over time from a period of less than 100 years (today) versus 150–200 years 3000 years ago. All of the regional records identify notable long (>20-yr) droughts, several of which have been noted before in other paleoclimate/archeological studies. There is also evidence for a longer alternation in wet/dry conditions, consistent among all our studied records, with four 200–400 years wet intervals, individually preceeded by a notable long drought, and followed by increasingly drought conditions for the next several 100 years.