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Great Australian Bight Deepwater Survey

By: Dr Penny Berents, Category: AMRI, Date: 07 Apr 2017

The science of the Great Australian Bight (GAB) is poorly known but the CSIRO GAB Deepwater Marine Program is hoping to change that.

AMRI's Penny Berents on the Rem Etive

AMRI's Penny Berents on the Rem Etive
Photographer: Deborah Osterhage © CSIRO

A team of scientists from Australia and New Zealand has been surveying in waters from 1000 - 3000 m deep for the last few weeks on the Fugro vessel the Rem Etive. The boat is a 93 m, 4200 Te vessel equipped with two Remote Operated Vehicles (ROV) and a Sea Floor Drilling rig (SFD).

The Great Australian Bight (GAB) is of interest scientifically as it is an area of unique passive margin geology ( a boundary between continental and oceanic crust which is not tectonically active) approximately16 km of sediments were deposited in the area by paleo rivers after the rifting of Australia from Antarctica, late stage volcanism is present, and there are significant knowledge gaps about possible hydrocarbon systems and subsurface processes. The deep sea biological communities on the margin, in waters over 1500 m, are virtually unsampled.

The aim of the deepwater survey is to explore seamounts, canyons and possible seeps on the seafloor at sites which have been selected based on an initial survey conducted by CSIRO in 2015. CSIRO has drawn together a team of 26 geologists, chemists and biologists from CSIRO, Australian museums and NIWA (National Institute of Water and Atmospheric Research in New Zealand) and I was very lucky to represent the Australian Museum on this voyage.

At each site the ROVs are used to map the fauna and geology of a 400 x 400 m grid with live video feed to the ROV Inspection Room on the ship. The live video feed is fascinating to watch as squid, swimming holothurians, fish, squat lobsters and prawns can be seen in the bright ROV lights as well as the sessile bottom fauna which is mapped. At the completion of reconnaissance the ROVs are then directed back to particular specimens for collection. The robotic arm of the ROV is skillfully maneuvered by the ROV pilots to collect rocks and animals such as corals, anemones, starfish, sea urchins, sea lilies, sponges, brittle stars and sea pens. Push cores are taken in soft sediment to examine sediment, geochemistry and infauna. The ROVs are also equipped with Niskin bottles to collect water samples and sensors to measure water properties such as hydrocarbons, chlorophyll, turbidity, particle size, methane and dissolved oxygen. The advantage of sampling with ROVs compared with more traditional deep sea sampling methods such as trawls and dredges, is that fragile specimens such as corals, anemones and sea urchins are collected without damage. Video mapping will allow quantitative assessment of the density and abundance of deep sea bottom dwelling animals.

The ROVs are also used to help position the subsea drill which drills shallow cores which will be transported back to Perth for further study by the geologists. The cores are used to study stratigraphy and to calculate the age of volcanic flows. Drilling operations were conducted for 45 hours at the deepest site of 3050 metres and a core of 45.6 m retrieved. The SFD also provided the opportunity to place a baited amphipod trap in 3050 m to collect scavenging amphipods (small crustaceans).

One of the highlights of the voyage was the sighting of Magnapinna sp. (Big-finned Squid) at 3000m. This species has never been seen in Australian waters.

The voyage is only the beginning of the work for this study and the biological collections will be deposited at the Australian Museum, Museum Victoria, South Australian Museum and CSIRO where taxonomists will identify the animals and prepare reports. The Australian Museum will be the repository for crustaceans and some polychaete families.

 

Penny Berents, Senior Fellow, AMRI


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