Geological Society of America

224 Paleoclimatology/Paleoceanography

Wednesday, 12 October 2011
8:00 AM - 12:00 PM
Room 200FG

A PUERTO RICO SPELEOTHEM AND INFERRED DRYING OF THE EASTERN CARIBBEAN CLIMATE IN THE PAST 800 YEARS

Paper number: 224-14
Program: Technical Sessions
Time: 11:15 AM – 11:30 AM

Authors

Thomas E. Miller Presenting Author
University of Puerto Rico, Mayaguez, PR
R. Lawrence Edwards
University of Minnesota, Minneapolis, MN
A. Winter
University of Puerto Rico, Mayagüez, Mayagüez, PR
Lowell Stott
Univ of southern california, Los Angeles, CA
Yochanan Kushnir
Lamont-Doherty Earth Observatory of Columbia University, Palisades, NY
Ashish Sinha
California State University, Dominguez Hills, Carson, CA
Axel Timmermann
University of Hawaii, Honolulu, HI
Mark Jury
University of Puerto Rico, Mayagüez, Mayagüez, PR
C. Gallup
University of Minnesota Duluth, Duluth, MN
Hai Cheng
University of Minnesota, Minneapolis, MN

Abstract

The active stalagmite PDR-1 from a Puerto Rico cave has provided the first reconstruction of rainfall variability for the past 800 years of the western tropical Atlantic. The δ¹⁸O of speleothem calcite was analyzed at annual resolution from 1850 to the collection in June, 2006, and every five years from AD 1200-1850. The δ¹⁸O of Puerto Rico primarily varies with changes in the amount of summer rain (85% of the annual total), and suggests an overall trend of declining rainfall and warmer temperatures for the past eight centuries in the eastern Caribbean. The speleothem data set can be subdivided into three segments (the period from 1850 to the present which tracks the Atlantic Multidecadal Oscillation (AMO), the middle segment co-varies well with the tree-ring based extension of the AMO back to 1597, and lastly, the independent speleothem data of AD 1200-1600). Given the first two correlations, we suggest that the speleothem δ¹⁸O-based rainfall record from Puerto Rico extends the history of the AMO to the 12th century.

The collection was from a large cave (Cueva Perdida, 18.3°N, 350 m a.s.l.), in an isolated chamber >360 m from an entrance; subsequent to removal, a data logger onsite recorded very stable temperatures of 22⁰C and 100% relative humidity during the period of monitoring. The 15 cm stalagmite was cut along its vertical growth axis, polished, and samples of the upper 3 cm were collected for ²³⁰Th dating. Using a magnetic sector ICPMS, seven dates were obtained in stratigraphic order. An eighth date of ~10.5 kaBP was determined for the base. Samples for δ¹⁸O analysis were milled at intervals of 0.05mm along the axis.

These δ¹⁸O_(VPDB) values varied between -1.5 to -3.5 ‰ , steadily rising from AD 1200-1600, dropping abruptly from then to 1700, rising again to 1850, and oscillating since then. During this same period, at the other end of the Caribbean rainfall also appears to have decreased in Belize, but stayed more or unless unchanged in the dry Yucatan to the north.