An underwater observatory keeping the pulse of the Southern Ocean for nearly 30 years yields fresh results

In a world affected by climate change, the Southern Ocean plays an outsized role. It absorbs up to 40% of the human-caused emissions taken up by the oceans while also being home to some of the world’s most vulnerable ecosystems.

Understanding these ecosystems and how they’re changing is crucial – but challenging. Patterns and trends in this remote, chaotic ocean are often obscured by short-term variation.

The only way to see through the noise is to make sustained measurements, year after year, for decades.

In the heart of the Southern Ocean there is a car-sized yellow and blue structure floating on the surface. It may not look like much, but this is the tip of a vast underwater observatory that has monitored the pulse of this region for nearly three decades.

Known as the Southern Ocean Time Series (SOTS), this observatory endures cyclone-strength winds and waves up to 18 metres high. The knowledge it provides has been collected in several recent studies, including one just published in Ocean Science.

From the surface to the seafloor

Established in 1997 by CSIRO researcher Tom Trull, the observatory consists of two automated deep-water moorings about 500 kilometres southwest of Tasmania.

Anchored to the seafloor 4,500 metres below, these moorings are maintained by annual voyages of the CSIRO research vessel Investigator from Hobart.

Together, they observe the entire water column, from the wave-lashed surface to the deep. Now in its 28th year, the SOTS program is the longest-running observation program in the open Southern Ocean.

The only actual sign of the observatory is the yellow mooring on the surface, known as the Southern Ocean Flux Station. It has an array of 30 different atmospheric and weather sensors. These transmit near-real time weather data used in Bureau of Meteorology forecasts.

Below the surface is an automated water sampler and some 40 sensors mounted along the 4,500m mooring lines down to the deep sea. Joining the floating laboratory is another mooring made of three large funnels that intercept sinking marine particles on their journey to the seafloor.

What data has the observatory provided?

The newly published study uses the observatory’s data from 1997 to 2022 to quantify how heat and carbon enter the ocean, and how ecosystem structure changes over seasons.

These results show just how important are the tiny marine plants known as phytoplankton.

They control the amount of atmospheric carbon dioxide entering the ocean. This can be directly linked to how much carbon actually makes it to the deep ocean and is locked away for long periods of time – this process is known as the “biological pump”.

At the same time, we’ve been figuring out what controls phytoplankton populations and their ability to help this part of the ocean absorb more carbon. Other research from the SOTS site published earlier this year shows exactly how marine life in this region is inextricably linked to an essential yet sparse trace metal in seawater – iron.

Read more: Marine CO₂ removal technologies could depend on the appetite of the ocean's tiniest animals

The SOTS program has also been helping scientists detect changes in the chemistry of the Southern Ocean, such as ocean acidification from rising atmospheric carbon dioxide.

It also allows for measurements of how carbon is absorbed by the sea, how marine ecosystems help store that carbon at depth, and how high-energy winds help supply vital nutrients to fuel these ecosystems.

The observatory has even been the site of discovery of a new marine species.

The key to success

All these results are only possible thanks to the longevity and sustained funding of the SOTS program. It yields sufficient data far enough back in time, and fills gaps that can’t be provided by satellites.

Without dedicated, long-term monitoring, we would have no baseline to track climate change and a poor understanding of the weather systems and ecosystems in this important part of the world. It also contributes to our ability to forecast daily weather in Australia and long-term climate.

But the value of SOTS reaches far beyond the Southern Ocean. Our national monitoring program contributes to global networks in an international, coordinated effort to observe, understand and predict weather and climate. It helps us prepare for extreme events that are set to become more frequent.

This example is timely. Funding cuts to the US National Oceanic and Atmospheric Administration (NOAA) have resulted in staff layoffs, with 17% of NOAA’s workforce to be cut next year and the risk of extreme weather monitoring stations shutting down.

NOAA is responsible for several ocean monitoring sites. It is also responsible for meteorological satellites and the Argo robotic float program – both globally important monitoring platforms.

As ocean and climate monitoring systems abroad face the fallout from potential loss of observing systems, Australia’s Southern Ocean Time Series continues on – and its importance is only increasing.

Funding for the SOTS program comes via the Integrated Marine Observing System, the Australian Antarctic Program Partnership, and through collaboration between CSIRO and the Bureau of Meteorology.