Landing a bouy on the aft deck.

Moorings

Moorings are specialised sea laboratories that are deployed in a location and left there for one to two years. Their big advantage is that they can monitor over a long period and provide an understanding of the changes that occur. This is something a research vessel cannot do as it is in one area for a relatively short period of time.

An ocean wave crests at sunset.

An ocean wave crests at sunset.

Moorings are not a part of Investigator’s equipment but their deployment and retrieval form an important part of the work carried out by the Marine National Facility. Often the research vessel will return to the same spot over a series of years to service a mooring that remains in place to develop time-series of data.  The Investigator will work from the tropic to the Southern Ocean deploying moorings for the Australian and international science community.

Moorings differ depending on their purpose. Some have a buoy at the top which enables data to be transmitted back by satellite to a land laboratory. Others can be as deep as a kilometre below the surface. For these moorings the data and samples are collected when the mooring is retrieved.

A mooring can be long, over six kilometres high, with sensors and sample collection devices located along its length from the surface to the sea floor. Weights at the bottom of the mooring hold it in one place, while floats located along its length keep the mooring upright and allow for ease of retrieval. 

When deploying the mooring the floats and instruments are often laid out behind the vessel as it slowly steams forwards.  The weights, which are often train wheels, are the last items to be lowered off the back deck.  During recovery, a signal is sent from the surface to special acoustic releases that detach from the weights and allow the whole mooring to float to the surface.

Some of the moorings deployed by the Marine National Facility include the SAZ, SOFS and Pulse moorings which make up the Southern Ocean Time series.  This series of mooring has been serviced by the MNF since 2010.  The SAZ moorings purpose is to measure the amount of sediment that falls out of the ocean towards the sea floor.  It does this with special sediment traps suspended at points along the mooring line (Fig 1).  The Pulse mooring takes monthly water samples at a depth of 30m below the surface (Fig 2). The samples are stored and preserved to investigate the microscopic plants and animals that live in the Southern Ocean.  The SOFS mooring is the largest mooring deployed by the MNF and is a fully functional weather station, measuring wind and waves (Fig 3).  Across the moorings other sensors are also deployed to record water temperatures and currents, salinity, oxygen, turbidity and the amount of Chlorophyll from the microscopic plants or phytoplankton in the water column.

The Southern Ocean time-series is in very deep water (4500m) and more than 300 nm south of Tasmania so the weather can be very rough, with seas on average 3 metres high which can reach 15 metres during storms .  When recovering or deploying gear even a boat as big as the Investigator needs to pick the right conditions to service the moorings.

Updated: 27 November 2014