The largest iceberg on the planet is about to meet its destiny — it will melt and be water again (apologies to Bruce Lee). An unnamed astronaut aboard the International Space Station photographed this close-up view of the iceberg named A-23A.
This is a huge piece of ice, with an area of 3,900 km2 (1,500 miles2) and an average thickness of 280 m (920 ft). See my post: https://sky-lights.org/2024/01/15/camping-on-an-iceberg/ to get a grasp of just how big it is. Or take a look at this video and image of A-23A taken by RRS Sir David Attenborough.
The blue colors you see in that photo are ponds of meltwater forming as A-23A moves into warmer climes. The meltwater seeps into cracks in the iceberg where it re-freezes, expands, and enlarges the cracks. When the crack reaches the bottom, the iceberg calves and a section of ice breaks free. Smaller pieces of ice have a higher surface to volume ratio, so they melt more quickly. Soon, A-23A will be nothing more than a localized concentration of cold fresh water, gradually mixing with the surrounding salt-water ocean under the action of winds, waves, and currents.
Ever since it broke off from Antarctica’s Filchner Ice Shelf back in 1986, it’s been showering nutrients and minerals into the sea. While it was a glacier making its way down the mountain (over centuries), the bottom surface scoured away at the rock, embedding organic and inorganic compounds. As it melts these compounds are returned to the biosphere and provide sustenance for phytoplankton at the bottom of the food chain. In fact, marine biologists have seen phytoplankton blooms in the wake of large icebergs.
You can track A-23A using data from the U.S. National Ice Center, or any other major iceberg you might be interested in. If you then enter the latitude and longitude into Google Earth you’ll get something like this. Alas, it won’t show A-23A, but you’ve already seen what it looks like:
It’s pretty much headed north now, into even warmer waters, so it may have only weeks to months before it’s gone for good. Here’s a timeline and map of its long journey. A-23A spent its first 34 years just sitting on the continental shelf of Antarctica. Because of melting on it’s lower surface, which is in contact with seawater, it finally floated free in 2020:
Scientists now have good numbers to describe the true scale of A-23A. Satellite measurements show the frozen block has an average thickness of just over 280 m. Combined with its known area of 3,900 km2, this gives a volume of roughly 1,100 km3 and a mass around a trillion tons. That’s 1000 Gt (gigatons).
361.8 Gt of ice will raise global sea levels by 1 mm. 361.8 Gt of ice is equivalent to 394.67 km3 ice. So the melting of A-23A will raise sea levels by around 2.8 mm. When you allow for water evaporating from the iceberg into the atmosphere, that number could decrease to around 2 mm. But it’s all gonna come down as rain eventually. Evaporation might delay, but will not avoid, the ultimate rise of 2.8 mm.
2.8 mm (the thickness of a stack of three dimes) might not sound like much in the grand scheme of things. Problem is, this is not the last ice sheet to break off Antarctica, or Greenland for that matter. This is an ongoing problem that has led to a sea level rise of 210–240 mm (8–9 inches) since the start of the Industrial Revolution in 1880. Large as it is, A-23A is the proverbial “drop in the bucket.”
Next Week in Sky Lights ⇒ The Color of Pure Water