For the first time in history, scientists managed to take measurements directly near the giant iceberg A-68a and look under it. This made it possible to more deeply investigate the impact of meltwater on the Southern Ocean and its ecosystem, informs Nature Geoscience.
“We believe this is the first time measurements have been made so close to an iceberg, so it’s a real breakthrough in science!” – noted the author of the study, Natasha Lucas.
A team of scientists from the British Antarctic Survey (BAS) and the National Oceanographic Center (NOC) embarked on an expedition aboard the RRS James Cook. Two remotely controlled underwater gliders were launched at a distance of 23 km from A-68a, one of the largest icebergs in the world, drifting off South Georgia Island.
Obtaining data in the immediate vicinity of icebergs is extremely difficult, because despite the possibility of satellite observation, ships usually do not approach due to the dangerous dynamics of the ice. This time, the gliders collected unique indicators of temperature, salinity, chlorophyll content (an indicator of productivity) and suspended particles in the water (optical backscattering).
The results of the study showed that the basal (bottom) melting of the iceberg destroys the seasonal layer of “winter water” that forms in the austral summer and prevents the vertical exchange between the surface and the depths of the ocean. The disappearance of this natural boundary allows nutrients such as iron and silica to rise to the upper layers, stimulating the growth of phytoplankton, a key element of the food chain in the Southern Ocean.
“The number of giant icebergs is increasing due to climate change, so it is very important to understand the physical and biological processes that occur when an iceberg of this size melts – often far from its place of formation.
When an iceberg mixes the oceanic layers, which are normally very stable in the Antarctic summer, the water’s temperature, salinity and nutrient content change. All of this ultimately affects how much heat and carbon is exchanged between the ocean and the atmosphere.” Natasha Lucas stressed.
Despite difficult conditions, including the loss of one of the gliders and several “stucks” under the ice, the second vehicle successfully completed the 17-day mission and provided valuable data on the melting processes.
It will be recalled that the A-68a iceberg broke off from the Larsen Ice Shelf in July 2017. Its area then was about 5,800 km² — twice the size of the territory of Luxembourg. Eventually, the iceberg broke into smaller pieces.
Photo: bas.ac.uk
