Timing of the Oceanographic and Biological Isolation of the Caribbean Sea from the Tropical Eastern Pacific Ocean

Geological uplift along the Central American Arc began in the Eocene with extensive development of emergent terrains by the early Miocene. Nevertheless, three independent lines of evidence are consistent with abundant seawater exchange between the oceans until about 4.7–3 Ma. (1) Isotopic and sedimentary data from ocean cores demonstrate that divergence in surface salinity and deep-sea carbonate accumulation between the Caribbean and eastern Pacific did not occur until 4.7–4.2 Ma. Moreover, strong upwelling comparable to the Pacific today persisted in Caribbean shelf environments until 4.5–3.5 Ma. (2) North and South American terrestrial mammals and tropical forest bird faunas remained overwhelmingly isolated until about 3 Ma. Some birds flew across the seaway and numerous small amphibians and plants began mixing millions of years earlier as expected due to their high probability of rafting. The rarity and ambiguity of reported exceptions to these result after a century of intensive sampling strengthen the general pattern. (3) Bathyal foraminifera first separated across the developing Isthmus approximately 13 Ma but numerous mollusks and cheilostomes are known from both oceans until the Middle Pliocene. Some species now restricted to the Pacific persisted in the Caribbean until the Pleistocene, but no species known to have originated after the Early Pliocene occurs in both oceans except for dispersal by shorebirds or human introductions. Molecular clock estimates for the timing of divergence of taxa strongly support these patterns. Isolation of the Caribbean from the Pacific about 3 Ma provides a robust model system for the study of vicariance in the oceans.