NOAA/WDS Paleoclimatology - Cueva de la Fábrica, Colombia Speleothem Stable Isotope Record 3,000 to 4,000 years BP

The Colombian Andes has a hydroclimate with multiple proposed drivers of interannual, sub-decadal and multidecadal variability, including the meridional movement of the Inter Tropical Convergence Zone, El Niño Southern Oscillation (ENSO), and Pacific Decadal/Atlantic Multidecadal Oscillation. Globally, the late Holocene (3-4 kyrs B.P.) is of interest as multiple proxy studies suggest modern multi-decadal variability developed during this period. Limited high-resolution proxy studies assess changes in rainfall during the late Holocene from the Tropical Andes. We present a record of stable isotopes (d18O and d13C) from two speleothems, C2A-1 and C8A that grew during the late Holocene in the Eastern Cordillera of the Colombian Andes from Cueva de la Fábrica. Hendy Tests on both stalagmites were consistent with isotopic equilibrium at the time of calcite deposition, suggesting d18O values reflect climate variability. Frequency analyses revealed statistically significant oscillations at the sub-decadal and multidecadal scale in the faster-growing portion of C2A-1. We isolated the sub-decadal d18O variability through a band-pass filter, calculated the amount of rainfall for C2A-1, and compared the distribution against modern (1979-2016 C.E.) rainfall. The unimodal distribution of band-pass filtered speleothem d18O data suggests a response to an internal mode of climate variability, such as ENSO. A regional speleothem proxy comparison over 3-4 kyrs B.P. suggest a bimodal expression of rainfall at the multidecadal timescale with drier central Amazonia and wetter coastal and high-Andes mean rainfall states. This complex regional picture of multidecadal hydroclimate is likely attributed to internal climate forcings between the Pacific and Atlantic Oceans.