Bacteria use extracellular enzymes to cut large organic matter to sizes small enough for uptake. We compared the enzymatic response of surface, mid-water, and deep-ocean bacteria to complex natural substrates. Bacteria in surface and mid-depth waters produced a much wider range of enzymes than those in the deep ocean and may therefore consume a broader range of organic matter. The extent to which organic matter is recycled by bacteria depends in part on its residence time at different depths.