Evidence of El Niño/La Niña–Southern Oscillation Variability in the Neogene-Pleistocene of Panama Revealed by a New Bryozoan Assemblage-Based Proxy

Here we explore how fossil cheilostome bryozoans can demonstrate El Niño/La Niña–Southern Oscillation (ENSO) variability in ancient tropical environments of the tropical eastern Pacific and southwestern caribbean when used collectively to produce frequency distributions of estimates of mean annual ranges in temperature (MARTs) via zooid-size MART analysis (zs-MART). The approach is based on linking variation in the sizes of constituent zooids in bryozoan colonies with the temperature regimes in which the zooids developed. The shapes of frequency distributions of zs-MART estimates from modern environments are consistent with known upwelling and non-upwelling environments and ENSO variability. Data from fossil colonies provide evidence that ENSO variability characterized caribbean environments in what is now present-day Panama during the miocene and Pliocene (thus supporting neither a permanent El niño nor a permanent la niña in the Pliocene), but not the Pleistocene after the isthmus of Panama closed. Western atlantic data provide further evidence for ENSO variability in the Pliocene of florida but not virginia. Our study shows the potential of bryozoan assemblages to infer variation in seasonal regimes thus encouraging the further development of this proxy for inferring ENSO variability.