Evidence for 800 years of North Atlantic multi-decadal variability from a Puerto Rican speleothem

The long-term behavior of the tropical Atlantic ocean/atmospheric system prior to the 20th century is not well characterized due to a lack of high-resolution proxy records to extend the short instrumental record. Here we present the first reconstruction of rainfall variability for the western tropical Atlantic that spans the past 8 centuries and is derived from the δ18O of speleothem calcite. The δ18O of speleothem calcite at this Puerto Rican location varies primarily in response to changes in the amount of summer-time precipitation. The speleothem documents multi-decadal to centennial length oscillations in δ18O that point to large variations in rainfall that have not been manifest in the short instrumental period. Since AD 1850, variations in δ18O have tracked shifts in the Atlantic Multidecadal Oscillation (AMO). We tentatively suggest that the speleothem δ18O-based rainfall record from Puerto Rico extends the history of the AMO to the 12th century.