Sampling water from the bottom of the world’s stormiest sea is most people’s idea of hell. For scientist Ryan Cloete, it’s a career highlight.
The weather-beaten academic, part of a research team from Stellenbosch University, intentionally set off into the wintry depths of the Southern Ocean, braving 10m waves and daytime temperatures of -13°C.
The team worked in snow and howling wind for five straight weeks, with little contact with the outside world.
And what they found there might change the way we understand climate change.
• The SA Agulhas II is an ice-breaking polar supply and research ship owned by the department of environment, forestry & fisheries. The ship was built in 2012 by STX Finland Rauma shipyard in Rauma, Finland.
The vessel replaced the ageing SA Agulhas, which was retired from Antarctic service in April 2012.
- Wikipedia
— HOT SHIP FOR A COLD CLIMATE
“You get used to it,” Cloete said this week of his third trip aboard the research ship SA Agulhas II. “It’s a different kind of cold, like a dry cold, but sometimes it feels like the wind is hitting you with icicles.”
Johan Viljoen, a member of the team, explained that at one point it was so cold he could see his seawater samples beginning to freeze on contact with the icy air while being transferred to storage.
But the pain was worth the gain: four years later the team have published results of their ocean analysis, and the results are surprising.
Contrary to expectation, they found that the ocean continues to serve as a “biological carbon pump” throughout the winter months.
Water samples contained a higher than expected number of tiny phytoplankton that make up the bulk of the biomass in summer months and form the basis of the ocean food chain. (“Phyto” means plant and “plankton” means to drift, so phytoplankton are essentially tiny plants drifting in the ocean’s surface layer).
Until now, the general consensus has been that these phytoplankton were more dormant in the winter months.
Cloete explained: “Akin to trees having lost all their leaves by the winter, because of unfavourable growth conditions, the assumption was that phytoplankton would also not be active during the winter.
“One of our major findings is that phytoplankton are indeed active during winter in the Southern Ocean, although not to the levels we see in summer. Consequently, the role of the Southern Ocean in annual carbon drawdown may be stronger than previously thought.
“How phytoplankton are able to adapt to winter conditions is not well understood, and our research on trace nutrients is the first step in figuring out these adaption strategies.”
To date, scientists’ understanding of Southern Ocean conditions during winter has been limited by the challenge of sampling the water in sub-zero temperatures.
Cloete said the task was only possible thanks to the state-of-the-art SA Agulhas II, which allowed scientists relative comfort compared with research cruises of yesteryear.
To obtain their samples the team used a mechanical arm that can drop a cradle of 24l bottles into the sea and automatically open them at different depths.
“We are interested in the full water column, and as a result we take samples from the sea surface to the ocean floor — more than 5km deep in some cases,” Cloete said.
• 1603 - First recorded sighting of Antarctica
• 700 - The number of terrestrial and aquatic algal species that live on Antarctic shores
— IN NUMBERS
Carrying the sample bottles was challenging, and often humorous when the ship was rocking in bad weather. “We had some incredible storms — the worst seas I’ve ever been in,” said Cloete.
Generally, however, the ship offered scientists a unique opportunity to gather material that was analysed at the Stellenbosch laboratory.
Cloete and his colleagues are attached to Stellenbosch University’s Centre for Trace and Experimental Biogeochemistry (TracEx) in the earth sciences department.
Their project forms part of an international collaboration called the Geotraces Programme, which is aimed at “understanding the biological intricacies of the ocean”, said Cloete.
He said the Southern Ocean plays a fundamental role in regulating the Earth’s climate. “It is estimated to store about 75% of the global oceanic uptake of excess heat and 35% of the global uptake of excess carbon from the atmosphere.
“The Southern Ocean is also the only ocean that directly connects the three major ocean basins — the Pacific, Atlantic and Indian Oceans. In other words, what happens in the Southern Ocean has an impact on the global ocean,” he said.
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