Case study 2: Southern Ocean Marine Research

Tracking what is happening in the ocean is the key to understanding climate change—and few places are more sensitive to change than the fragile environment of the Southern Ocean.

A major research expedition of nearly 40 Australian and international scientists set off on the Aurora Australis in January 2011 to continue measurements in the region, first begun in 1991.

As part of the Australian Antarctic Science program, the team were targeting the 140°E longitude (called the SR3 transect, Fig. 1).

Fig 1. SR3 transect showing the location of all sampling stations, together with stations sampled in the Mertz region during the 2010–11 marine science voyage (Dr Steve Rintoul, CSIRO/ACECRC).

Because this transect has been revisited several times over the past two decades, the measurements form one of the most complete records of change in the Southern Ocean.

The variations in temperature, salinity, oxygen and carbon dioxide concentration can help scientists to track how rapidly climate is changing.

Change in the region could now be more dramatic because in February 2010 the Mertz Glacier tongue, a chunk of ice 78 km by 39 km in size, located near the end of the SR3 transect, broke free after it was hit by a massive 97 km long iceberg (Figs. 2 and 3).

Fig 2. Iceberg B9B approaches the Merz Glacier tongue, 7 Jan 2010.

 

Fig 3. The glacier tongue breaks free, 20 February 2010.

This region is renowned as one of the few areas in the ocean where very dense, cold, salty water forms at the surface and then sinks four or five kilometres to the sea floor.

It is a key part of the global network of ocean currents known as the overturning, or thermohaline, circulation.

Overturning circulation is very important in the world’s oceans because it largely determines how much heat and carbon the ocean can store, and thereby influences the rate of climate change.

After measuring changes in the formation of dense water in response to the loss of the Mertz Glacier tongue, the research team is beginning to understand more about the sensitivity of this part of the ocean to change. This information will be used to test and improve climate models.

The loss of the glacier tongue also allowed researchers to reach parts of the continental shelf that had previously been inaccessible. As they undertook oceanographic measurements, the team used a camera system to observe the benthic (sea floor) communities at 75 sites over the Antarctic continental shelf and slope.

According to AAD scientist, Dr Martin Riddle, the area around the glacier is one of the ‘biological hotspots’ of the Antarctic and Southern Ocean ecosystem.

The photos revealed a variety of benthic habitats and a great diversity of organisms (Fig. 4).

Fig 4. Sea floor images near the Mertz Glacier taken by the underwater camera. (Australian Antarctic Division)

The expedition has been hailed as highly productive and a great success, with oceanographic measurements taken at 149 sites and a wide range of physical, chemical and biological analyses completed. A media team from the ABC led by Karen Barlow accompanied the project, providing excellent coverage of the entire research voyage.