ORBITAL AND INTERNAL FORCING OF CLIMATE ON THE YUCATAN PENINSULA FOR THE PAST CA.36-KA

A 19.6 m sedimentary sequence from Lake Quexil, Guatemala, is presente d as a proxy record of climatic change on the low-lying Yucatan Penins ula over the last ca. 36 ka. Long-term climatic fluctuations are attri buted to orbital forcing of insolation, while abrupt changes during th e late glacial period are the result of internal forcing mechanisms th at remain imperfectly modelled. GCMs simulating meltwater cooling of t he Gulf of Mexico may predict some but not all climatic responses in t he Circum-Caribbean. Lake Quexil did not experience greater aridity th an predicted by orbital forcing during late glacial zones Q-LG 1 and 2 , which were drier only in comparison with Holocene conditions. Q-LG 1 appears to have been colder than expected based on insolation alone, and is contemporary with the Younger Dryas event between meltwater pul ses 1A and 1B. Thus, other feedbacks also may have cooled surface temp eratures in the Gulf of Mexico, such as unique late glacial circulatio n patterns, increased albedo for the Florida and Yucatan Peninsulas, o r surface temperatures on the North American continent. Additional ter restrial sequences are needed to improve the chronology and confirm th e distribution of sub-regional climatic variability in the Circum-Cari bbean.