The scientists are lowering a sophisticated net sampling system called MOCNESS
(Multiple Opening/ Closing Net and Environmental Sampling System).
The MOCNESS is lowered into the water and towed behind the ship at a speed of about 1.5 knots. There are nine nets, each of which is controlled by a computer in the ship's lab. One at a time, the nets are opened and closed at desired depths, according to what the scientists want to measure. Instruments at the top of the frame help control the nets, and also report depth, salinity, temperature, chlorophyll fluorescence (a measure of phytoplankton in the water), and flow into the nets.
This is a sketch of a research vessel towing a 1-m MOCNESS. "1-m" refers to the projected area (one square meter) of the net opening (mouth) as it is towed. The instrument packages at the top collect information about the water (such as temperature, salinity, depth, and chlorophyll) and send it up the tow wire to computers on board. In this schematic, the eight nets at the bottom have all collected samples at various depths and are now closed; the top net is sampling the shallowest depths on its way back to the surface. The "buckets" on the ends of the nets are PVC collectors which hold the samples after the nets have filtered plankton from the water. When the MOCNESS is retrieved on board, the collectors are each handled separately for sorting and preserving.
Betsy Broughton at the computer "flies" the MOCNESS underwater by remote-control: Signals go down the conducting tow cable while data come up the cable.
Scientists help guide the MOCNESS overboard as a winch operator (not seen) lifts the equipment.
The MOCNESS equipment between uses must be tied down securely because the seas often get rough.
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