Scientists have created the most accurate map ever made of the mountains, canyons and plains that make up the ocean floor around Antarctica.
Covering 48 million square kilometers, this graph details for the first time a new deepest point — a depression at 7,432 meters deep called the Factorian Deep.
Knowledge of the shape of the ocean floor is essential for safe navigation, marine conservation, and understanding of the Earth’s climate and geological history.
But there is still a lot to learn. Vast tracts of land have never been properly observed.
The International Bathymetric Chart of the Southern Ocean (IBCSO) project took five years to create the first attempt at a comprehensive map, published in 2013.
The IBCSO and other similar projects around the world are gradually filling in the gaps in our scarce knowledge of the world’s ocean floor.
Ships and boats are being encouraged to routinely turn on their sonar devices to take depth measurements. Governments, corporations and institutions are being urged to share data and put as much of it into the public domain as possible. And this is bearing fruit.
The new map covers the area from the bottom of the Southern Ocean to 50 degrees south. If you divide the 48 million square kilometers into squares of 500 m grids, 23% of those cells have passed at least one modern depth measurement. That’s a big improvement over nine years ago.
Previously, the IBCSO started at 60 degrees south, with less than 17% of the grids having modern measurement.
“You have to understand exactly what the change from 60 to 50 degrees means; we have more than doubled the area of the graph,” says Boris Dorschel of the Alfred Wegener Institute in Germany.
“So we’ve increased the coverage of the area, but we’ve also increased the data density, because at the same time we keep acquiring new data,” he told BBC News.
Much of the information in the chart comes from icebreakers supporting scientific efforts in Antarctica, including the UK’s former polar ship, the RRS James Clark Ross. (In the future, this British contribution will come from his successor, RRS Sir David Attenborough, affectionately known as Boaty McBoatface.)
On trips between the White Continent and countries such as Chile, South Africa and Tasmania, its echo sounders survey the submerged terrain below.
And this activity is increasingly coordinated, with research organizations from different nations working together to slightly modify the routes followed by their icebreakers.
More detailed maps of the sea floor are needed for several reasons.
They are essential for safe navigation, but also for the management and conservation of fisheries, because it is around the seamounts that marine fauna tends to gather. Each seamount is a core of biodiversity.
In addition, the rugged seafloor influences the behavior of ocean currents and the vertical mixing of water. This is information needed to improve models that predict future climate change — because it is the oceans that play a key role in moving heat around the planet.
“We can also study how the Antarctic ice sheet has changed over thousands of years just by looking at the sea floor,” explains Rob Larter of the British Antarctic Survey.
“There is a record of where the ice flowed and where its grounding zones (places in contact with the seafloor) extended. This is beautifully preserved in the form of the seafloor.”
The new map was made possible by funding from the Nippon Foundation of Japan and support from SeaBed2030, the international effort to map Earth’s ocean floor by the end of the decade.
At the moment, our knowledge of four-fifths of the planet’s underwater terrain comes only from low-resolution satellite measurements that inferred the presence of seamounts and deep valleys from the gravitational influence these features have on the sea surface. The water accumulates over the mass of a large seamount and sinks slightly where there is a trench.
An important discovery between the first and second versions of the IBCSO is the recognition of the deepest point in the Southern Ocean. This is a depression called the Factorian Deep at the southern end of the South Sandwich Trench. It lies at a depth of 7,432 m. This was measured and visited by Texan adventurer Victor Vescovo with his Limiting Factor submarine in 2019.
The remote and often inhospitable nature of the Southern Ocean makes it difficult to map substantial sections of the bed. There is great hope that an emerging class of robotic craft can fulfill this task in the years to come.
The Southern Ocean International Bathymetric Chart was published in Scientific Data.
