Upwelling and nutrient availability in the upwelled waters are two different aspects of oceanographic conditions. Coastal upwelling is only one of a number of different mechanisms that bring deeper waters to the surface. High-latitude convective motions upwell and downwell large volumes of water rapidly, so that only part of the nutrients can be utilized by phytoplankton. Equatorial upwelling produces high productivity over the ocean basins but rarely impinges on continental margins. Other upwelling modes in the open ocean, such as that associated with ice margins, currents, thermocline domes, cyclonic eddies, and Ekman pumping, may have been significant in the past, but little is known about their geologic record. Wind-driven and Kelvin wave-driven coastal upwelling occurs on the eastern margins of the ocean basins in the tropics and subtropics, but the upwelled water is not everywhere nutrient rich. The upwelling is locally enhanced by favorable bathymetry offshore or orographic conditions on land. 

In considering how the ocean may have operated in the past, it is necessary to consider how the structure of the ocean may have differed in the past. Other processes, such as caballing, the sinking of denser water produced by mixing waters of equal density but of different temperatures and salinities,