Satellite sensors such as SeaWiFS can provide us with up-to-the minute quantified chlorophyll abundance data on both the local and global scales and also give us a means to assess spatial and temporal variations as never before. The images below represent mean global chlorophyll distributions during the boreal spring, as revealed by SeaWiFS data. It would be impossible to gain such a snapshot of the world's chlorophyll without satellites!

A SeaWiFS view of the world, prepared using NASA's SeaWiFS Globe Design Tool

Clearly, though, the chlorophyll present in the ocean cannot all represent upwelling. So, while the presence of high levels of chlorophyll could indicate a phytoplankton bloom in response to upwelling, other clues are necessary to identify true upwelling events.