Scientists have some solid numbers revealing how massive the world’s largest iceberg, A23a, really is. When we look at it from space, it turns out this frozen giant has an average thickness of a little more than 920 feet (280 meters).
If we combine this with its known area of 1,500 square miles (3,900 square kilometers), we get a mind-blowing volume of around 263 cubic miles and a weight just shy of a trillion tons. This iceberg formed at the Antarctic coast in 1986.
A23a’s measurements
The data regarding A23a’s measurements has been obtained by the European Space Agency’s CryoSat-2 mission. This seasoned spacecraft is equipped with a radar altimeter that can determine how much of the iceberg is sticking out above water. By knowing the density of ice, scientists can then calculate how much of the iceberg is underwater.
Dr. Anne Braakmann-Folgmann from the University of Tromsø – The Arctic University of Norway, explained to BBC News how satellites like CryoSat-2 work. She said, “Altimetry satellites like CryoSat-2, which measure the distance to the iceberg surface and to the sea surface, allow us to monitor iceberg thickness from space.”
She added that “they also enable us to watch the iceberg thinning as it gets exposed to warmer ocean waters…And together with knowledge of the sea-floor topography, we know where an iceberg will ground or when it has thinned enough to be released again.”
Formation of A23a
A23a, the world’s largest iceberg, formed during a mass breakout of icebergs from the Filchner Ice Shelf in the southern Weddell Sea and got stuck in the shallows. It then turned into an “ice island” for over three decades.
Unlike a solid block of ice, A23a is a bit uneven. Some parts are thicker than others. According to CryoSat, there is a specific section with a remarkably deep keel. In 2018, this keel reached a depth of almost 350 meters below the water surface, acting like an anchor and keeping A23a in place.
Satellite images reveal cracks right above this deep keel. Professor Andrew Shepherd from Northumbria University and the Natural Environment Research Council Centre for Polar Observation and Modelling (CPOM) explains, “This is likely the surface expression of the damage that was caused when A23a hit the seabed.”
In the years that passed, A23a slowly shed its mass, eventually breaking free. It was then set in motion. Dr. Andy Ridout, a senior research fellow from University College London, explained that over the past ten years, they have seen a steady annual decrease in thickness of about 2.5 meters. This aligns with what we’d anticipate considering the water temperatures in the Weddell Sea.
Journey of this colossal iceberg
Scientists are keeping a close eye on A23a’s journey because colossal icebergs such as this one play a significant role in shaping their surroundings.
Currently, A23a has made its way to the tip of the Antarctic Peninsula, where different fast-moving water streams converge, flowing in a clockwise direction around the continent. How A23a interacts with these currents and the prevailing westerly winds in that region will determine its next path.
Experts predict it will likely follow a route known as “iceberg alley,” pointing towards the British overseas territory of South Georgia.
This morning we arrived at A23a, which you will remember from yesterday’s lecture is the biggest and oldest iceberg on Earth! pic.twitter.com/vpdMG2w3rO
— Gretchen Winter, MD 🌼 (Warning: Feral) (@gretchemaben) December 10, 2023
According to Professor Mike Meredith from the British Antarctic Survey, these large icebergs have a profound impact on the environment. As they migrate, they cause a deep mixing of seawater. This action forces essential nutrients up to the ocean’s surface resulting in the release of a considerable amount of dust.
“They churn ocean waters, bringing nutrients up to the surface, and, of course,” he said, “they also drop a lot of dust. All this will fertilize the ocean—you’ll often see phytoplankton blooms in their wake.”