Influence of the Amazon River development and constriction of the Central American Seaway on Middle/Late Miocene oceanic conditions at the Ceara Rise

At about 11.2 Ma the first appearance of Leonella granifera indicates river influence at the sample site. This first indication of river influence in the western equatorial Atlantic can be linked to the developing Amazon River. The cyst association changes at about 11.2 Ma from almost monospecific to highly diverse and the permanent presence and increased abundance of L. granifera suggest that river waters were able to reach the study site by now, probably as a result of the southward flowing North Brazil Current. After 10.5 Ma the cyst association indicates a decrease in Amazon influence at Site 926A. This change can be correlated to a reducing inflow of Pacific waters through the Central American Seaway leading to a reverse of the North Brazil Current to its modern northwards flow pattern.