Can Zooplankton make a submarine disappear?

Sham S. Misri

Small and microscopic animals, and single cell forms that are found floating on ocean waters are called zooplanktons. Masses of drifting zooplanktons can hide larger objects, even submarines.

Sonar was invented to help warships find enemy submarines. It also helped sailors to judge how far the ocean bottom was beneath their ships. Sound waves are sent out under water, and the sonar records how long it takes an  echo to bounce off an  object and back to the receiver. Using the same principal as the natural sonar of Dolphins, this instrument allows scientists to map the sea floor and fishermen  to find schools of fish.

During  the  world war two, navy ships picked up peculiar readings in the deep Atlantic and Pacific oceans . Hazy images showed upon their sonar screens that looked like the ocean bottom rising far above the ocean floor. At first scientists thought they might be the tops  of underwater mountains. Observing them carefully, the scientists realized they were not the tops of underwater mountains; but something like- ‘moving under water clouds.’

Navy scientists did not know what  created these” false bottoms ,” but they realized they could make ideal hiding places for enemy submarines. Because this sound – reflecting  layers scattered the sonar  signal returning to the  ship, this unusual ocean feature was named  the  “ Deep scattering layer” or DSL for short.

Scientists at Institution of Oceanography later discovered that these layers moved as deep as 700-2400 feet during the day and rose almost to the surface at night. Scientists found that the    DSL floated closer to the surface on cloudy days than on Sunny days. Whatever was responsible for creating these layers must be alive!

Because of their possible use  in submarine warfare , both the Japanese and the Americans kept  information about these deep scattering  layers secret  until after the war. But it took even longer to solve the mystery. Scientists dragged nets through  the water but they came up mostly empty.  It wasn’t  until  faster , deep water nets  and deep sea cameras were invented that researchers finally could prove  what was making these layers.  They found that they consist mainly of small , jellyfish like zooplankton called siphonophores , krill, and deep sea fish that probably feed on the plankton. These animals occur in such vast numbers  that their bodies reflect  back the sonar (sound ) waves- so zooplankton could actually hide a submarine.