MIDDLE MIOCENE UPWELLING AND THE EVOLUTION OF THE NORTH PACIFIC FAUNA

A significant component of the high-diversity temperate marine fauna along the western coast of North America appears to be a relict of a Late Miocene radiation. Molecular and paleontological data document that the timing of the radiation of a number of important marine groups coincides with peaks of upwelling on the West Coast. Upwelling along temperate western margins around the world began about 14 million years ago triggered by the cooling of Antarctica and the consequent cooling of the deep waters of the oceans. Continuity of upwelling, silica rich subthermocline waters and the relative stability of trophic structure in the region’s kelp forests helped nurture and sustain diversity in the northeastern Pacific relative to other upwelling areas around the world. Groups such as kelp, alcid birds, marine mammals, salmon, rockfish, abalone and crabs of the genus Cancer all radiate in close association with the peaks in the upwelling regime. The ecologically important groups and those with high energetic demands seem to be strongly influenced. This reconstruction of Neogene events suggests that episodes of upwelling are likely to be critical in the evolution of temperate zone diversity and trophic structure at other times in the Phanerozoic.