What types of cells are found in the Open Ocean at these various depths? One technique that we used to answer this question is called a FACScan. We used the FACScan to plot cell size and fluorescence on a graph. Because we know about the size and fluorescence of certain types of cells, we are able to use this information to identify them.

FACScan DATA: At right, a plot of "Fluorescence versus Size" shows cell types from one depth. Some samples had Prochlorococcus ("P") and/or Synechococcus ("S") cells. These tiny (0.6 to 1.0 micrometers) cells, undiscovered until the 1970's, are responsible for much of the photosynthesis in the world’s oceans. Some samples also had small eukaryotic cells ("E").