THE SHOALING OF THE CENTRAL AMERICAN SEAWAY AND ASSOCIATED IMPACTS: A PALEOCEANOGRAPHIC PERSPECTIVE

Until recently, the literature (focused on biogeographic and evolutionary evidence) placed the rise of the Isthmus of Panama and closure of the Central American Seaway (CAS) between ~9 and 2 Ma. However, new studies of Panama’s volcanic and tectonic history suggest that the isthmus rose several Ma earlier than previous estimates. This calls into question our understanding of the ‘Panama Hypothesis’ under which decreased flow between the Pacific and Atlantic during closure of the CAS from 13 - 2.6 Ma led to stronger thermohaline circulation, the production of North Atlantic Deep Water, and increased North Atlantic temperatures, evaporation, and precipitation at high latitudes, thus resulting in Northern Hemisphere glaciation. Despite the potential significance of these connections, comparatively few paleoceanographic studies have directly examined the timing and climatic impacts of closure.

Research on marine species divergence resulting from CAS closure has been ongoing since the ‘70s. These and other paleoceanographic studies suggest gradual shoaling over ≥12 Ma caused a stepwise shutdown of deep, intermediate, and ultimately shallow water flow through the CAS. It is argued that these restrictions had considerable impacts on surface currents and global ocean circulation at depth, thereby influencing both regional and global climate; however, the exact linkages and timing are not well defined. The Nd isotopic composition of fish teeth from Pacific and Caribbean sediments act as sensitive recorders of local water masses and can be used to better constrain the timing and effects of closure. Notable changes in this isotopic signature have been documented in the Neogene Caribbean and interpreted as a record of CAS shoaling. In order to investigate earlier evidence of restricted flow through the seaway related to sill formation or pulsed exhumation events, the Nd isotope records from Ocean Drilling Program Sites 998 and 999 will be extended to 50 Ma. The acquired data will be combined with global climate and Nd models to determine teleconnections between this region and major global changes seen in the Neogene. Also, novel paleoceanographic proxies will be explored and the terrestrial and marine literature integrated to create a comprehensive history of the shoaling of the CAS and rise of the Isthmus of Panama.