An Antarctic silk-and-plankton sandwich

An expeditioner lowers a plankton sampling device into the Southern Ocean from the trawl deck of the Aurora Australis.
Another Continuous Plankton Recorder is released from the trawl deck of the Aurora Australis. It is towed 100 metres behind the ship at about 10 metres depth, for approximately 450 nautical miles at a time. (Photo: Lloyd Symons)
View of silk mesh under electron microscope, with a trapped diatom.Silk mesh caked in filamentous diatoms, as seen under electron microscope.An amphipodAn amphipoda ctenophoreA map of continuous plankton recording tows in the Southern Ocean 1991–2016Hands unwinding the silk roll from inside the continuous plankton recorder

Australia’s icebreaker RSV Aurora Australis is steaming south to Antarctica and over the last week has been towing an ingenious plankton sampling device.

The Continuous Plankton Recorder (CPR) traps plankton swimming in the ocean between moving sheets of silk.

The silk-and-plankton sandwich is wound up in a removable cassette, driven by the passing water turning a propeller, at a constant rate of 1cm for each nautical mile travelled.

Each tow lasts about 450 nautical miles, and also records ocean and climate data at the same time.

CPR surveys have been run by the Australian Antarctic Program in the Southern Ocean since 1991, involving ships from several nations.

A staggering amount of data has been amassed — around 47,000 samples analysed from more than 1000 CPR tows for a total of approximately 240,000 nautical miles.

This long-term monitoring (supported by the Scientific Committee on Antarctic Research) is crucial to map the shifting patterns of plankton biodiversity in the Southern Ocean, and provide early warning signs of its changing health.