Nitrate and Phosphate are two essential nutrients for plant growth in the sea. At BATS, concentrations of these two nutrients are generally low. Plants take up nutrients in the surface waters, so that they are almost undetectable. However, in winter, storms mix deep, cold, nutrient-rich water into the surface waters. This can be seen well in the nitrate graph.
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. This spring bloom is also reflected in the amount of Chlorophyll a pigments in the water. Many bacteria use dissolved organic material to grow. Much of this is produced by phytoplankton in the surface waters. Thus we tend to get higher numbers of bacteria where there are more plants.