Correct Response: A. Oceanic upwellings bring many nutrients that have fallen to the ocean floor back up to the surface, providing an area where ocean life thrives. The fact that fisheries over areas of regular upwellings are more productive suggests that the availability of nutrients may be a limiting factor in an open-ocean system. Light intensity (B), salinity levels (C), and water temperatures (D) may vary throughout the ocean, including at the location of upwellings, so the productivity of fisheries over oceanic upwellings does not provide specific evidence that these factors are limiting.
