Upwelling along the Pacific coast of Central America today occurs where the land drops to less than 500m. Low land allows the trade winds to blow across and push surface waters out to open ocean causing strong coastal upwelling.
In this paper we estimate the strength of upwelling in the Plio-Pleistocene of eastern Costa Rica and western Panama; today a mountainous region with no upwelling.
When finding evidence that strong upwelling persisted until as recently as 0.5-0.3Ma we deduce that the elevation of the Isthmus in eastern Costa Rica-western Panama must have been less than 500m until the mid-Pleistocene.
Click on the image for the pdf for the paper published this year.