Primary production is the rate of plant photosynthesis.  At BATS, primary production tends to be highest in the springtime when there are nutrients present in the surface waters from winter mixing, and increased day length and strength of sunlight.  Just as wildflowers bloom every spring in the mountains on land, there is a spring bloom of phytoplankton in the sea!  This spring bloom is also reflected in the amount of Chlorophyll a pigments in the water.