Annual average abundance of heterotrophic bacteria and Synechococcus in surface ocean waters

Global abundance of marine bacteria was investigated at the annual climatological scale. In surface waters of diverse marine habitats, the annual average abundances of heterotrophic bacteria and the photosynthetic cyanobacterium Synechococcus are directly related to annual average temperature below 14 degrees C. Notably, average nitrate concentrations at the surface are never high where the temperature is above 14 degrees C. These results suggest that, over the course of a year, temperature is the dominant factor affecting bacterial growth and loss in colder waters. Other factors, such as substrate supply, may be important in warmer waters.