GSA Annual Meeting in Phoenix, Arizona, USA - 2019

Paper No. 224-4
Presentation Time: 2:30 PM


LACHNIET, Matthew S., Geosciences, University of Nevada Las Vegas, 4505 S. Maryland Parkway, University of Nevada Las Vegas, Mailstop 4022, SEB, Las Vegas, NV 89154, WINTER, Amos, Earth and Environmental Systems, Indiana State University, Science Bldg. 159, 600 Chestnut St., Terre Haute, NV 47809, ZANCHETTIN, Davide, Dept. of Environmental Sc., Informatics and Statistics, University Ca’ Foscari of Venice, Via Torino 155, Mestre, 30172, Italy, VIETEN, Rolf, Institute of Earth Sciences, Hebrew University of Jerusalem, Jerusalem, Israel and CHENG, Hai, School of Human Settlement and Civil Engineering, Xi’an Jiaotong University, Xi’an, 710049, China

We present a Holocene speleothem δ18O record from Cueva del Rey Marcos (15.43°N, 90.28°W, 1460 m), Alta Verapaz, Guatemala which spans from 11,400 years to ~300 yr BP and provides a long-term climatic context for ecosystem and cultural change in the southern Maya highlands. We interpret the speleothem δ18O variations to indicate changes in the strength of regional convection associated with the seasonal rain cycle derived from Caribbean Sea air masses. The modern rainfall regime has remained strong since ~9000 yr BP when a sea surface temperature threshold was exceeded in the nearby tropical oceans as the Atlantic meridional overturning circulation strengthened. Our data do not show a clear insolation-paced rainfall weakening over the Holocene as would be predicted from a local summer insolation driver, suggesting that regional temperatures are more important than summer insolation in controlling rainfall amount. Over the Late Holocene, a dry interval at 4200 yr BP terminated abruptly to produce peak wet conditions at 3800 yr BP, and rainfall has gradually decreased toward modern. Three successively drier intervals are superimposed upon the drying trend of the last two millennia, each separated by wetter conditions: drying interval 1 between 1630-1310 yr BP (320-640 CE), drying interval 2 between 1220-1010 yr BP (730-940 CE) around the Terminal Classic, and drying interval 3 between 480-780 yr BP (1170 to 1470 CE), with peak dryness of the past four millennia achieved at 600 yr BP (1350 CE). Finally, our record shows a subtle trend to drier conditions over the past 2000 years which contrasts with a wetting trend as inferred from the δ18O record from Tzabnah Cave, Northern Yucatan. Taken at face value, this observation suggests a northward shift of the latitude of heaviest rainfall over last two millennia on the Caribbean Slope of Central America and the Yucatan, and opens the possibility that rainfall variability has differed sub-regionally over the Holocene.