JC36: Geology & biology of the Whittard Canyon


Cruise diary

23 June 2009
Location: NE Atlantic

Will writes:

On 23rd June 2009 ISIS dive 101 took place. Experiments were placed onto the canyon seafloor at 3500m to study ecosystem function. This is achieved by testing how the groups of animals and microbes in the seafloor ecosystem respond to organic matter (food) deposition. The deep-sea contains no plants, and so life in this region relies on food sinking from shallower waters. Therefore if we are to understand how deep-sea ecosystems fit into the global carbon cycle, we must understand how they process this food falling from above.

The experimental equipment features two types of computerised chamber, AROBIC (Aberdeen ROV Operated Benthic Incubation Chamber) and TOCS (Total Oxygen Consumption System). Both of which enclose a known area of the seabed and the overlying water. Both chambers take measurements of the amount of oxygen in enclosed water, and we use this information to calculate how much oxygen the sea floor consumes as the animals and microbes within respire (breathe). The AROBIC chambers also feature a device to release algae into the enclosed area. This allow us to release algae labelled with a stable (non-radioactive) form of carbon, carbon-13. The algae settles on the sediment and we can observe how the oxygen consumption changes as the organisms eat the algae. In contrast the TOCS chamber is a simpler device, basically a tube with a lid attached. The lid contains a electric stirrer and oxygen optode, to measure oxygen levels inside the chamber every hour. The experiments will be left on the seafloor for three days, during which oxygen consumption is measured. After these three days the AROBIC chambers have a roller shutter door which digs under the sediment and closes around it, allowing us to bring the enclosed sediment back to the surface. Back on the surface  the sediment collected is processed  to analyse how much of the algae has been eaten, and by which organisms. This is done in the laboratory using a machine called a stable-isotope mass-spectrometer, which can measure the amount of carbon-13 present in samples of animals, microbes and even mud.

The AROBIC and TOCS Chamber systems being
deployed from the ship on an elevator

The chambers, dwarfed by a giant fish.

An AROBIC chamber.

A TOCS chamber

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