Paper No. 10
Presentation Time: 11:10 AM


MILLER, Thomas E., Department of Geology, University of Puerto Rico, Mayaguez, PR 00681, BREITENBACH, Sebastian, Climate Geology, (ETHZ) Geologisches Institut, NO G 47, Sonneggstrasse 5, Zuerich, CH-8092, Switzerland, WINTER, Amos, Department of Marine Sciences, University of Puerto Rico, Mayagüez, Mayagüez, PR 00681 and KELLY, Megan, Department of Earth Sciences, University of Minnesota, Minneapolis, MN 55455,

High-resolution stable isotope records of dated speleothem have been published in the Americas sufficient to provide proxy precipitation snapshots of the recent millennium. The speleothem can be precisely dated with MC-ICPMS 230Th/U-methods, and precipitation proxies are recovered as a result of the negative correlation of rainfall with δ18O. The period centered on 1500 A.D. is of interest in that it may represent the interval with the most intense (century-long) and widespread drought of the Neotropics of the past 1000 years and also coincides with the first historical descriptions of El Niño. The fourteen stalagmite records chosen outline a sharp boundary between the regime of the tropical humid Caribbean and that of the Gulf of Mexico.

Peruvian stalagmite collections at the fringes of Amazonia record dry periods that persisted a century in the 1500’s. Andean glaciers also stopped growing then, until about 1600. Far south-east of Peru at the Brazilian coast, speleothem responses were moderate, and mixed (wet and dry). From Peru north, speleothem collections do not cover the past millennium well until Belize, Guatemala and the Yucatan. The southernmost three sites are in tropical rainforest and simultaneously record lengthy droughts exceeding a century in the decades immediately after 1500. Near the far eastern end of the Caribbean, a stalagmite from Puerto Rico also recorded a sharp drop in rainfall for this period (lasting a century), as did another suggesting a smaller arid episode for Venezuela. δ18O values during these excursions ranged about 0.7-1.3 ‰. Other evidence for this same widespread drought is from Cariaco Basin titanium concentrations, and lake sediments of the Dominican Republic.

The Gulf of Mexico reacted oppositely, with increased precipitation recorded in speleothem tracking from west-central Mexico to the Yucatan, to the west end of Cuba to Florida. Although speleothems covering this period at the northern end of the Gulf are lacking, tree-ring records support wet conditions existing in the Texas-Chihuahua areas of northern Mexico and the U.S.

This evidence of widespread drying environments in terrestrial locations of the north tropics- both the circum-Caribbean and northern South America- further supports the idea of southerly ITCZ migration during the Little Ice Age, and its global impact.