Scientists don’t doubt that climate change is bringing catastrophic changes to Antarctica. Surprisingly, however, researchers didn’t have enough ocean data to issue a firm verdict on certain warming trends. Well, the data they needed just hit the tables, and the signs are clearer than ever.
According to a 20-year-long survey of ocean measurements, a warm mass of circumpolar deepwater continues to inch closer to Antarctica’s ice shelves. This shift in deep-ocean heat showed up in climate model predictions, but the latest findings, published today in Communications Earth & Environment, provide empirical confirmation that warm deep-ocean water is moving closer to Antarctica’s ice shelves.
“This isn’t just a possible future scenario suggested by models,” Joshua Lanham, the study’s lead author and an earth scientist at Cambridge University in the U.K., said in a statement. “It’s something that is happening now, bringing wider implications for how carbon, nutrients, and heat are cycled through the global ocean.”
Our natural regulators
Deep ocean currents play a vital role in regulating the Earth’s climate system, as well as the ocean nutrients and carbon dioxide cycles, according to the U.S. National Oceanic and Atmospheric Administration. These currents are driven by differences in water density caused by variations in temperature and salinity.
Around the poles, extremely cold temperatures cause frigid, dense water to sink deep underwater, bringing with it heat, carbon, and nutrients. This process is also critical to the Atlantic Meridional Overturning Circulation, which redistributes heat from the tropics to the Arctic, regulating Earth’s climate.
Circumpolar deep water (CDW), on the other hand, refers to the water mass formed by the mixing of different water masses in the Pacific and Indian Oceans. Circumpolar deep water can grow as warm as 32 degrees Fahrenheit (0 degrees Celsius) near the Antarctic shelf break, making it a major source of oceanic heat in the region, the researchers explained in the paper.
Ominous shifts
The latest findings present alarming evidence of increased CDW volume near Antarctica “across almost all longitudes,” the study noted. For the analysis, the team combined measurements collected by Argo floats—small robotic floating devices released in bulk in the Southern Ocean—with public data from other autonomous floats in the upper ocean.
Then, the researchers used machine learning to consolidate this data with long-term patterns collected by research expeditions. The team offers some potential reasons for this expansion, such as unidentified changes in other water masses or the strengthening of westerly winds around the Southern Ocean. Confirming this will require further investigations, the researchers said in the study.
The terrible hot bath
In any case, we now have more evidence that Antarctica is in hot water. According to Sarah Purkey, the study’s senior author and an oceanographer at the Scripps Institution of Oceanography, the Southern Ocean absorbs most of the anthropogenic heat stored in the ocean, which holds more than 90% of excess heat created by global warming.
“In the past, the ice sheets were protected by a bath of cold water, preventing them from melting,” Purkey said. “Now it looks like the ocean’s circulation has changed, and it’s almost like someone turned on the hot tap and now the bath is getting warmer!”
If this unwanted “hot bath” persists and the ice shelves unravel, the consequences aren’t great. Antarctica’s ice shelves keep the region’s ice sheets and glaciers intact, which hold enough freshwater to raise global mean sea levels by 190 feet (58 meters), according to NASA. Of particular concern, the study concluded, is how the expansion of CDW will affect the Antarctic Circumpolar Current, an irreplaceable part of Earth’s natural carbon sink.
Typically, when a study ends like this, it’s usually the case that we’ll have to wait for independent verification or other natural developments to confirm anything. But with everything that’s at stake, waiting patiently might be the worst option.
