Deep-Sea Researchers Probe Mystery of Record Ocean Heat

As red-hot oceans amplify deadly heat waves, storms and floods on land, exactly what's going on beneath the waves remains a big unknown. Over 80% of these bodies of water remain unmapped, unobserved and unexplored.

While a small army of underwater robots, sonars on the sea surface and satellites in space have in recent years allowed researchers to better understand how greenhouse gas emissions are impacting ocean dynamics, they've barely scratched the surface. "We don't really know the why and the how of some very interesting things happening in the deep ocean," said Nathalie Zilberman, an oceanographer at the University of California San Diego. "We don't know because there's no data."

Among the biggest mysteries is why there's an Argentina-sized chunk missing from the sea ice on the Antarctic ocean, which reached by far its lowest level for any June on record last month. Sea ice there has shrunk 2.6 million square kilometers (1 million square miles) below the average between 1981 and 2010, according to the US National Snow and Ice Data Center.

Trying to explain what's behind the vanishing Antarctic sea ice and extreme marine heat has prompted lively discussion in the scientific community. Experts have pointed to higher atmospheric temperatures, a weakening of winds that reduced the amount of Saharan dust over the Atlantic Ocean, a decrease in sulfur dioxide emissions from ships - a pollutant that blocks solar radiation and can cool the planet - and rising El Nino conditions on the Pacific Ocean. 

Things are more certain on land. Climate scientists and meteorologists managed to accurately forecast the local heat waves that brought record-high temperatures from Japan to Texas and Sardinia. Yet even more extreme events in the oceans have caught them by surprise. 

Forecasters knew something was off back in April when readings started to show sea surface temperatures in parts of the North Atlantic rising to levels not seen since satellite records started in 1979. The anomalies were so severe that scientists were forced to extend the y-axis on charts to accommodate the never-before-seen heat records. 

Finally, lets look at the North Atlantic which has been quite literally off the charts in July - in the sense that we've had to extent the y-axis of our charts to appropriately show the data.

"The temperatures in the North Atlantic are unprecedented and of great concern - much higher than anything the models predicted," Michael Sparrow, head of the World Meteorological Organization's climate research department, said earlier this month. "This will have a knock-on effect on ecosystems and fisheries and on our weather."

Another warning came from a different group of scientists, who this week released a paper in Nature Communications that concluded a system which circulates water within the Atlantic ocean could collapse between 2025 and 2095 if greenhouse gas emissions continue at present levels. The current, known as the Atlantic Meridional Overturning Circulation (AMOC), is a major tipping element in the global climate system and its shutdown would have severe impacts on the North Atlantic region, scientists said.

Beneath it all is the fact that since 1955 oceans have absorbed 90% of the additional heat due to growing greenhouse gas emissions. That means they've acted as a sponge that has prevented the atmosphere from warming up even more. Humanity's understanding of how that heat is stored and the impact it has on ocean currents and sea level rise is relatively young and incomplete. 

That gap is mainly due to the difficulties of gathering reliable and frequent ocean data. While hundreds of thousands of weather stations scattered across the planet on land gather millions of data points every day, harsh conditions in the water make this difficult to replicate. Equipment deteriorates faster and it's more expensive to maintain. And monitoring the surface isn't enough - the depths matter too. 

In an effort to solve that problem, a small group of oceanographers created the Argo program in 1999. They developed 2 meter-long robots, called "Argo floats." that freely drift on ocean currents. Every 10 days, they travel 2,000 meters underwater to gather data on sea temperatures and salinity. That data is transmitted by satellite and available for free to scientists everywhere, with a 24-hour delay. 

Over 10,000 of these marine robots have been deployed since and about 3,900 are active today. The breakthrough they provided in terms of data has been likened to the start of the satellite era. Over the past two decades, over 4,000 scientific publications have used Argo data, according to the scientists runing the program.

Their next mission is the deep seas. 

"Everything in the deep ocean is more dramatic," said Zilberman, who is also the co-chair of the Deep Argo program. "The pressure is significantly higher, conditions are harsher and it's much colder."

In 2015, scientists started to modify Argo floats to allow them to go deeper. The first attempts failed, with robots imploding at depths below 2,600 meters due to the high pressure. Little by little, the design and materials improved. The researchers made tweaks to the the original robot, switching from a cylinder shape to spheres, and from steel and titanium to glass. For the new robots - called Deep Argo floats - spending one year at 6,000-meter depths is equivalent to four years of wear in shallower waters.

Zilberman was among the scientists to sail 300 miles off the coast of New Zealand into the Pacific Ocean to launch the first two Deep Argo floats in 2015. A young researcher back then, she remembers feeling like the astronauts who sent rovers to Mars. As the floats fell overboard, she waved at them and said goodbye.

"It was nerve-wracking," she said. "You're sending a robot that will dive 6,000 meters deep every 10 days, what could go wrong?"

Deep Argo is still in pilot mode, but some robots have transmitted data that recently allowed scientists to reach a better understanding of the deep waters in the Australia-Antarctic basin, one of the planet's less-explored corners. Other missions have detected a broad warming in the Southern Ocean and a cooling trend in some parts of the North Atlantic depths. But with only 200 active robots, it's hard to get a full picture of what these trends mean globally.

"You need more Deep Argo floats deployed, about 1,200," Zilberman said. "But it's a matter of funding - Deep Argo floats cost two to three times more than regular ones."

While Deep Argo robots are expensive, deploying them is still cheaper than vessels carrying out equipment to make similar measurements. These ship-based observations, which have been conducted since the 1980s, can cost as much as $35,000 per day. 

The urgency for more research into the deep sea has grown as the extent of the climate crisis has become apparent. But for Zilberman there was always a draw. She decided to become an oceanographer focusing on the deep seas after watching Jacques Cousteau documentaries as a child. "There's a challenge associated to it which makes it more exciting," she said. 

(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)