Chlorophyll is a measure of the biomass (abundance) of phytoplankton, the suspended microscopic algae that are the largest living component in San Francisco Bay. Here are two examples of vertical chlorophyll profiles. The data was collected with a fluorometer, which measures chlorophyll continuously as it is lowered through the water column. Fluorometer data can also be used to analyze long term chlorophyll temporal variability.

Plot Description:
1. This profile was measured near the San Mateo Bridge on September 21, 1995. It is an example of low phytoplankton biomass and uniform distribution from top to bottom in the water column.

2. This profile was measured near the San Mateo Bridge on April 11, 1995. It illustrates a condition in which phytoplankton biomass was high, especially in the surface layer.
   This profile was made during the spring bloom, a period of rapid phytoplankton population growth. Spring blooms occur when the water becomes stratified by salinity gradients which slow the rate of vertical mixing.