K-Axis voyage reaches half-way point

Pulling the Rectangular Midwater Trawl net in behind the ship
Pulling the Rectangular Midwater Trawl net in behind the ship. (Photo: Christina Schallenberg)
The cod end on the RMT net overflowing with krill.Rob King selects healthy animals from the catch to use in experiments.

17th February 2016

Krill are spawning and the ocean is teeming with life as the Aurora Australis reaches the half-way point of the Kerguelen Axis Marine Science voyage.

The ship has reached the location known as the Kerguelen Axis, known to be a highly productive region for polar plants and animals, and valuable toothfish, icefish and krill fisheries. Scientists are seeing a remarkable diversity of fauna including birds, many pods of humpback whales, minke whales, crabeater seals and Adélie penguins. Fur seals have also been spotted, likely from Heard and Kerguelen Islands, which was gratifying for scientists who had tracked them to this area in a 2004 study.

The Science Technical Support team orchestrated a historic moment for the Aurora Australis' capability, switching on live feeds from two video cameras mounted on a Rectangular Midwater Trawl (RMT) net at 200 metres depth. The video feed makes it possible for the crew to see how the net is flying through the water in real time, and the fibre optic cable also transmits conductivity, temperature and depth information as it goes. There are many applications for this technology including the ability to see if the net is functioning correctly, what’s going in and whether certain creatures are actively avoiding it.

The RMT net was deployed to sample an enormous krill swarm on one of the scientific stations. The acoustic instruments on board have detected many small swarms but the biggest observed to date left the net dripping with krill, allowing the team to collect buckets of live krill for experiments on board. Many females carrying fertilised eggs have now begun to spawn in the on-board laboratory. The eggs will be used in an experiment to test how ocean acidification affects their development.

An interesting transect took the ship from east to west on the southern foothills of the Kerguelen Plateau. In terms of scale, the submarine Kerguelen Plateau is a similar size to the Tibetan Plateau, rising from 3500 metres depth to 1000 metres depth with many canyons and ravines fracturing its margins.

Scientists saw a clear separation of the eastern and western areas, delineated by an amazing blue water strip, in which they found very little algae. Satellite data shows that the blue water seemed to be part of a 'jet' of water forging north from the Antarctic continent to the east side of the plateau.

This phenomenon was first analysed by Australian scientists in 2008 from satellite sea ice data, and it was great to see it in action. The catch from this area will be keenly analysed to see if there is a separation in the types of plants and animals found on either side of the jet.

The source of iron to areas of production is one of the important questions of the voyage, and it is thought this jet may also be an important conveyor of iron from the continental margin to the areas of algal growth and production further north. Iron is in short supply in the Southern Ocean and controls the growth and productivity of algae.

A change of focus is imminent, as preparations for the Mawson resupply ramp up. Watercraft operators, refuellers and plant operators are putting aside their newly developed skills in marine science to finalise plans for resupply. A busy schedule of cargo and refuelling operations will begin later this week when the Aurora Australis pulls up into Horseshoe Harbour.

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