Cenozoic cooling, Antarctic nutrient pump, and the evolution of whales

The evolution of large marine mammals and their invasion of the pelagic realm is tied to the availability of sufficient food, which in turn is linked to upwelling areas and other highly productive regions in the ocean, as has been recognized for some time. Here I propose that silicate-supported upwelling (which provides the shorter food chain and hence the higher yield for apex consumers) and deep mixing within the Southern Ocean are the crucial ingredients of the system providing the stage for the evolution of whales. The Circumpolar Current receives silicate from various sources but especially from the North Atlantic Deep Water introduced in the Atlantic sector. The silicate is largely trapped in the Ring, some in the water, and some in the sediment, and is made available to shallower waters by unusually deep mixing. From these shallower depths silica-rich waters can enter the thermocline all through the southern hemisphere, stimulating diatom growth in upwelling systems to the equator and beyond. From the link diatoms–krill–whales and diatoms–krill–small fishes, it is readily apparent that the link between the climate narrative and the narrative of whale evolution (both for mysticetes and odontocetes) is the silica cycle. Studying it will generate hypotheses about whale evolution that can be tested using fossils.