HOLOCENE CENTENNIAL CLIMATE VARIABILITY IN THE CARIBBEAN

In 2000, we retrieved a 4-m core from 16.2-m of water in Lake Punta Laguna, Yucatan (Mexico), that spans the last 9,000 cal yrs B.P. Sedimentation rates range from 35 to 100 cm/10³ yrs. Holocene sediments are finely laminated and composed of alternating layers of carbonate and organic-rich strata. Lithologic variations are expressed in sediment bulk density and magnetic susceptibility that were measured at 0.5 cm increments by a GEOTEK Multi-Sensor Core Logger and by color variations that were determined from digital images captured with a GEOSCAN color line scan camera. The lake was more saline than today throughout the early Holocene (9000 to 7300 cal yr B.P.) as evidenced by the presence of the euryhaline benthic foraminifer Ammonia beccarii. Low, but rising, sea level during this period depressed water levels in the phreatic karst aquifer of northern Yucatan relative to today. Sea level has been at or near present limits for the last 6,000 years and, consequently, lake level variations during the mid-to-late Holocene were controlled primarily by changes in evaporation/precipitation. During this interval, sediment color (red 650-750 nm) variations in the Punta Laguna core are remarkably similar to the %Ti record from the Cariaco Basin (Haug et al., in press), especially in the interval between ~3800 and 2500 cal yr B.P. where both records are marked by rapid sub-centennial oscillations. A distinct decrease in variability occurs at 2500 yrs BP in both records and is followed by a 1200-year long period of relative climate stability in which the Maya civilization developed, flourished, and ultimately collapsed in the 9th century A.D. The latter event is marked by a prolonged period of dry climate in both northern Yucatan and Venezuela. The tight coupling of climate variability between these regions is best explained by latitudinal variations in the position of the Atlantic Intertropical Convergence Zone.