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By Matt Marrison 3 May 2021 4 min read

Come and science with me. And I will take you on a trip. Far across the sea.

The vast oceans surrounding Australia are wild, rich in resources, and largely unexplored. In places, they transfer heat and gases like carbon dioxide from the atmosphere to the deep sea. In other places, they return nutrients back to the surface to sustain ocean life and ecosystems.

To protect and manage our oceans, we need to understand them and their interactions with the atmosphere. These interactions can range in scale from day-night cycles to larger ocean-wide oscillations over decades. And, with impacts from climate change increasing, understanding these interactions has never been more important than it is now.

Monitoring changes to the physics, chemistry and biology of the ocean requires sustained collection of data over long time periods.

So, each year, our Research Vessel (RV) Investigator leaves port on important missions for the Integrated Marine Observing System (IMOS).

Join us as we follow their journey south to maintain massive ocean infrastructure vital for monitoring our surrounding ocean and climate.

Automated ocean sentinels

Spread offshore around our coastline are arrays of giant automated moorings that maintain watch over our oceans.

These are the IMOS deep-water mooring arrays. They form part of the national observing system that makes up IMOS, some of which has been in operation since the 1940s.

During this past April, a team of 21 researchers and 20 crew on-board RV Investigator set sail from Hobart to maintain one of these deep-water arrays.

Wild at any time, those on-board travelled to a particularly energetic area of the Southern Ocean near 47˚south. Their destination was the Southern Ocean Time Series (SOTS) site – a location where ocean-atmosphere interactions are at their extreme.

At the SOTS site, an interaction between warm and cold bodies of water results in heat being carried far into the deep ocean. It's a process that also supplies oxygen for deep ocean ecosystems.

As the team departed Hobart, the skies grew dark, the sea grew rough.

And the ship sailed on and on... and on and on and on and on.

Steadfastly standing watch

If the weather is kind, it's two days sailing to reach the SOTS site. At this location are two four-kilometre tall moorings anchored to the ocean floor.

These are massive automated scientific sentinels bristling with sensors and instrumentation. They collect an impressive range of marine data every hour, of every day of the year, for the entire time they stand in place.

Usually, this is about 12 months. But COVID-19 delayed the preceding year’s recovery, meaning nearly 16 months passed before the team on board could collect the moorings and their important data.

The two moorings at this site each collect different data. Meet the SOFS and SAZ moorings:

  • SOFS: air-sea flux surface mooring with subsurface biogeochemical sensors. This mooring collects a wide range of ocean and weather data, and measures CO2 levels in the ocean.
  • SAZ: deep ocean sediment trap mooring. This mooring captures sediments sinking in the water column to study the transfer of carbon to the deep ocean.

During the voyage, the team on-board deploys new SOFS and SAZ moorings. After that, they recover the old ones along with the important data their instruments contain.

Each operation can take a full day or longer. As part of it, over four kilometres of wire and attached instruments are carefully deployed or brought back on-board RV Investigator.

This is when you don’t want things to get rough.

The Southern Ocean isn’t always your friend, and the operations can be highly challenging, even in the most benign conditions.

Bringing it home

With the old moorings safely recovered and stowed, and new ones in their place, the ship sets a course for home. This is when the process of downloading and analysing the data begins.

The SOTS mooring array is part of Australia’s contribution to the international OceanSITES global network of time series observatories. It is one of the few comprehensive Southern Ocean sites globally.

Deployments on this voyage continue the longest continuous collection of deep-ocean data in the Southern Ocean by any nation.

The data collected is significant.

The Southern Ocean (ocean south of 30°S) is responsible for about 40 per cent of the total global ocean uptake of human-induced CO2 emissions. And 75 per cent of the additional heat these emissions have trapped on Earth.

Data collected by these and other arrays around our coastline helps map ocean currents and monitor changes in key biological drivers of ocean ecosystems and fisheries. Government, industry and others who work and play in the vast oceans around the Australian continent use this information to inform their planning and decision making.

To our enduring ocean sentinels left to monitor these stormy seas, we say thanks. We’ll see you in 12 months.

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