FLOW REVERSAL IN THE CENTRAL AMERICAN SEAWAY DURING OR AFTER THE OLIGOCENE MIOCENE TRANSITION

The Oligocene Miocene Transition (OMT) has an unclear driving mechanism. The Central American Seaway (CAS) was an important ocean gateway; its closure during the Pliocene set up the modern salinity contrast between the Pacific and Atlantic Oceans. A reversal in flow direction through the CAS would have changed the temperature in the Caribbean Sea due to the influx of cooler Pacific Ocean water. A decrease in temperature is a leading explanation for the extinction of Caribbean coral species during the OMT. Eastward flow through the CAS is important for global climate because it has the potential to limit or cause the collapse of North Atlantic Deep Water formation. A mismatch in the timing of the Atlantic v. Pacific Ocean first appearances of the tropical planktic foraminifer Paragloborotalia kugleri provides evidence for a flow reversal at the OMT. Given the restricted environment, the timing of dispersal, and results from previous modeling efforts, CAS flow reversal is the most parsimonious explanation. After originating in the tropical Pacific, P. kugleri was blocked from dispersal into the Atlantic Ocean by the westward (Atlantic to Pacific) surface circulation through the CAS during the latest Oligocene. During or after the OMT, circulation reversed and Pacific Ocean surface water flowed through the CAS into the Atlantic Ocean, allowing P. kugleri to disperse into the Atlantic.

There is a fundamental need in modern biostratigraphy to establish a better methodology for constructing calibrated ages, and to quantify the precision with which we can employ marker taxa. The first appearance ages for P. kugleri based on thirteen scientific ocean drilling sites in our compendium vary from ~23.2-23.1 Ma in the Pacific to ~23.0-22.7 Ma in the Atlantic Ocean. Key requirements for including a site in the compilation are: 1) sampling resolution, 2) independent non-biostratigraphic chronology, 3) a preference for non-shipboard biostratigraphic analyses, and 4) multiple sites.