Evidence for 800years 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.