Late Pliocene Caribbean surface water dynamics and climatic changes based on calcareous nannofossil records

Abstract

Quantitative analyses of nannofossil assemblages from two ODP sites were performed to determine changes in the surface water structure in the Caribbean Sea and implications for climatic changes during the late Pliocene. Analysis was made by calculation of accumulation rates and division of nannofossils into ecological groups based on their depth distributions and trophic regime (oligotrophic vs eutrophic). Between 3.5 and 2.7 Ma, separate surface water masses existed in the northern and southern Caribbean. The northern surface water was strongly oligotrophic, with a deep thermocline/nutricline. Prior to 3.1 Ma, the southern Caribbean was characterized by a shallower thermocline/nutricline with minor upwelling induced by the presence of the past ITCZ (Intertropical Convergence Zone). After 3.1 Ma, the thermocline/nutricline deepened in the southern Caribbean and the upper water became oligotrophic as a result of the completion of the closure of the Isthmus. After an episodic invasion of cooler surface waters associated with high-latitude cooling at approximately 2.7 Ma, coccolith productivity in the Caribbean was at its lowest. A deep thermocline existed between 2.7 and 2.4 Ma and nutrient-depleted waters spread on the SUW (Subtropical Under Water) in the Caribbean. After 2.4 Ma, the increase of terrigenous materials from the South American continent caused an abundance of eutrophic taxa. This suggests that recent climate systems were established due to the intensification of the northern hemisphere glaciation.