A productivity decline in the late Pliocene may have been caused by some combination of causes at three geographic scales: (1) globally - marine productivity may have fallen due to changes in continental weathering; (2) regionally - North Atlantic productivity may have fallen as a result of initiation of North Atlantic Deep Water formation (possibly a consequence of formation of the Central American Isthmus, CAI) and resulting net transfer of nutrients to the Pacific; (3) locally - productivity may have fallen only in the eastern Gulf, due to circulation changes assisted with the formation of the CAI, and an accompanying decline in upwelling.