Nelson Mandela University marine biologist Prof Tommy Bornman has returned from a pioneering international expedition in the Southern Ocean which has revealed evidence of icemelt on the underside of icebergs, an ominous new signature of climate change.
Working with two autonomous undersea vehicles (AUVs) worth $10m (R141m) each, the Weddell Sea Expedition recorded salinity, temperature and other related data and photographed tell-tale rounded edges along the bottom of the massive icebergs and ice shelves in the remote zone between Chile and Antarctica, Bornman said on Friday.
“The total Antarctic ice mass appeared to be growing and yet there was massive ice calving and icebergs were breaking loose. We knew the ocean was getting warmer.
“The theory was the ice was being eroded from beneath.
“Now we’ve got evidence that this is indeed happening.”
The data recorded by the AUVs will now be overlaid with drone and satellite images of the surface ice and analysed together with a treasure chest of other geological and biologi- cal samples gathered by the team, which probed further south of the Weddell Sea’s eastern peninsula than ever before.
“It will probably take us five years, but the Weddell Sea is one of the most important sources of life on Earth so it’s vital work,” he said.
One of the reasons why the area was so important was its vast blankets of phytoplankton which, spread across the Southern Ocean, supplied 50% of the Earth’s oxygen and absorbed significant volumes of carbon dioxide from the atmosphere, Bornman said.
“Carbon dioxide is a main driver of climate change and so without the phytoplankton we would be much worse off in this regard than we are.”
The hyper-cold water in the Weddell Sea also sank to the sea floor, where it formed the thermohaline circulation which drove the global oceanic currents, distributing nutrients and oxygen, he said.
Using instruments and nets lowered over the side of the research vessel and drawn up through the 3,000m water column, Bornman identified an unusually rich diversity of phytoplankton species.
This finding highlighted the role of the phytoplankton as the anchor of the Southern Ocean food web – feeding zooplankton, which feed tiny shrimp-like krill, which in turn feed penguins, seals and whales.
The final brief of the expedition, funded by the Netherlands-based Flotilla Foundation, was to find the wreck of the Endurance, the ship of legendary British explorer Sir Earnest Shackleton which sank in the area in 1915 after being crushed by ice.
The site of the wreck was plotted at the time but half a dozen recovery expeditions through the decades failed because of fearsome conditions.
Bornman said that, aided by the ice-breaking capability of research ship SA Agulhas II, piloted by co-captains Knowledge Bhengu and Freddie Ligthelm, they had reached the 12-nautical-mile area where the wreck was thought to lie.
The Agulhas’s AUVs – from the same fleet owned by US-based company Ocean Infinity that discovered the missing Argentinian submarine in 2017 in the Atlantic Ocean in 800m of water – were pre-programmed for a grid search of the area and were being deployed for 48 hours at a time.
Discovery seemed imminent when one of the undersea vehicles went under a vast ice floe and contact was lost with the ship.
“Conditions deteriorated and with the risk of losing our ship the expedition leaders decided to abandon the search.”