BATS Data: Ocean Rates
Adopt a Link! for more information.) Primary Production
During photosynthesis, phytoplankton take up carbon dioxide that is dissolved in sea water. These tiny marine organisms thus provide the entry point for carbon into the marine food chain, Knowing how fast phytoplankton grow gives oceanographers an idea of how much carbon they take up, and how rapidly.
To measure the rate of plant photosynthesis at the BATS site, BATS technicians collect water samples just before sunrise at various depths in the top 140 meters of the ocean. (Below this depth there is generally not enough light for photosynthesis.) They then pour these water samples into transparent bottles and add a tiny amount of radioactive tracer. Attaching the bottles to a line, they release them overboard at the depth from which the water in the bottle was originally collected. At sunset, they retrieve this floating array of bottles, and filter the water to collect any small phytoplankton. They then use a scintillation counter to measure the amount of radioactive tracer that the phytoplankton cells have incorporated during the day. The quantity of radioactive tracer in the cells divided by the number of hours that the bottles were deployed gives the rate of photosynthesis. (Return to top) Bacteria Growth Rates
Bacteria are extremely important in the sea. They play a part in every nutrient cycle in the ocean, and, like the fungi on land, are the primary decomposers. Thus oceanographers are interested in bacteria abundance and in how fast they grow and reproduce.
Bacteria growth is measured using a radioactive tracer. A minute amount of radioactive material is added to water samples containing bacteria. These samples are allowed to incubate for a set period, during which the bacteria incorporate the tracer into their DNA. The samples are then filtered, and the amount of radioactive material incorporated into the bacteria is measured on a scintillation counter. (Return to top) Particle Flux
The sea holds large amounts of detritus. Detritus in the sea is made up of many different things. This includes dead phytoplankton and zooplankton, the feces of zooplankton and fish, mucus and other material produced by zooplankton or bacteria, sediment particles carried in by rivers, and many other different kinds of particles. This material, often termed marine snow because of its appearance, is an important food source for organisms that live in the deep sea, and also provides a mechanism for transporting material from the surface waters to the deep sea where it is eventually decomposed by bacteria. Only a fraction of the sinking detritus in the sea makes it to the bottom of the ocean. There it forms the oceans' sediments.
Particle flux in the ocean is measured by sediment traps. These are cone-shaped or cylindrical collectors that catch the detritus that rains down from the surface ocean to the deep sea. The sediment traps are attached to a line with floats on the surface and a weight at the bottom to keep it vertical. Some sediment traps have subsurface floats and a bottom weight that actually rests on the sea floor. After several days or weeks, oceanographers recover the traps, weigh the particulate material therein, and analyze the material's chemistry. The quantity of material divided by time the traps were deployed gives the particle flux.(Return to top)
Zooplankton Biomass and Species Composition
Zooplankton, small drifting animals in the sea, are the next step up in the marine food chain from phytoplankton. They are important because they consume plants (and each other), and are food for many fish, seabirds, and some marine mammals. By eating marine plants, the zooplankton incorporate some of the carbon and nutrients that these phytoplankton took up during photosynthesis and growth. By excreting wastes and producing sinking feces, zooplankton can transport these carbon and nutrients to the deep sea, where they may not return to the atmosphere for hundreds or even thousands of years. Thus these tiny marine animals play an important role in nutrient cycling and particle flux in the sea. The abundance and species composition of the zooplankton can affect the structure of the food web, and how nutrients are cycled. Thus it is important for oceanographers to know the numbers and types of zooplankton that are present.
Researchers usually catch zooplankton with plankton nets. The nets are of a much finer mesh than fish nets, as the mesh openings must be small enough to concentrate the plankton while still allowing water through. Zooplankton nets have meshes with openings of about one 1/3 to 1/2 of a mm. The nets are attached to the hydrowire and towed behind the ship. Plankton tows can be done at any depth or time of day, and can be used with opening/ closing mechanisms to enable them to collect at a desired depth interval. In many cases, part of the catch is preserved to determine species composition, and part is dried and weighed to determine the biomass.(Return to top)