From the deck of a ship on the east coast of Greenland, the most majestic presence is not that of whales, icebergs or towering glacier-capped mountains.
It is a parade of icy blue water, 120 kilometers wide, which flows along the coast from the Arctic Ocean. Farther south, these currents mix with the rising tropical waters of the Gulf Stream, and together they determine ocean temperatures across the North Atlantic, like hot and cold faucets in a giant bathtub.
But today, humans are tinkering with faucets. Rapid warming caused by greenhouse gas emissions is making the Arctic wetter and melting its ice, both on land and at sea.
If too much of this excess water reaches the North Atlantic, scientists fear it could disrupt the processes that bring warm water from the tropics. The consequences for the climate would be far-reaching: colder winters in Britain, stronger hurricanes in the eastern United States and, perhaps most worrying, changes in the rain bands that feed people in Africa, South America and Asia.
To better understand this threat, a team of researchers sailed this summer from Iceland to the east coast of Greenland with a ship loaded with data collection equipment. These waters are not forgiving of delicate instruments: encounters with icebergs constitute a constant risk. Sea ice makes the area impassable for much of the year.
“There’s very little data here,” said Nick Foukal, an oceanographer at the University of Georgia who led the two-week expedition. “So all the data is going to be really, really important.”
Observing ocean currents as they evolve is crucial to allowing scientists to better understand how and when they can reach points of no return. The problem as humans alter Earth’s climate is that drastic changes may not wait until researchers feel secure in their understanding before they begin.
What makes the seas around Greenland so important to the planet? The answer is linked to an immense water cycle that winds across the world’s oceans, linking climate changes in distant places.
You might start following this cycle in the tropical Atlantic, where strong sunlight warms the sea and makes it even saltier through evaporation. This water travels up the east coast of North America until it begins to pass near Iceland and Greenland.
Hot water meets cold air and releases some of its heat, becoming colder and denser. This makes her sink to the depths. It crosses the abyss, crosses South America and goes around Antarctica, before reappearing centuries later, ready to begin its journey again.
Scientists have given this Atlantic part of the ocean conveyor belt an inelegant name: Atlantic Meridional Overturning Circulation, or Amoc (pronounced “eimoque” in English). And they fear that one day it will stop completely.
What worries them is the increasing amounts of fresh water flowing into the North Atlantic. They dilute the warm, salty currents coming from the tropics, making them flow less. But it’s this sinking that pushes the warm waters north in the first place. When one end of the treadmill slows down, the other end slows down as well. Little by little, the entire treadmill slows down until it stops at some point.
If this happened, less tropical heat would reach the North Atlantic regions, making Britain and the Nordic countries cooler. More heat could linger near the Caribbean, providing additional fuel for hurricanes and distorting atmospheric patterns that distribute precipitation on both sides of the Atlantic and beyond.
Geological evidence tells us that all of this has happened many times before, most recently about 12,800 years ago. Today, there are signs that a slowdown is underway, and scientific models predict that this slowdown will continue for decades. The hardest part is anticipating when this might lead to another shutdown. In the next century? In the next decade? Next year?
“In the real world, the tipping point seems much closer than the models suggest,” said Stefan Rahmstorf, a professor of ocean physics at the University of Potsdam in Germany. That means the risk of this happening before the end of the century is too great to ignore, Rahmstorf said.
What would help reduce uncertainty would be more sustained, long-term measurements of water change across the Atlantic, said Thomas Haine, professor of earth and planetary sciences at Johns Hopkins University.
Over the past two decades, scientists have measured Amoc along two major cross-sections in the Northern Hemisphere, one stretching from Labrador to Greenland through Scotland; the other between the Bahamas and the Canary Islands. But they have much less clarity on fresh water coming from the Arctic, Haine said.
“We think the system is going to go through this big change, and we know that in advance,” he said. “We should go out and try to see this happen.”
After leaving the Icelandic port and sailing past Snaefellsjokull – the volcano where Jules Verne’s book “Journey to the Center of the Earth” begins – Foukal and his colleagues were greeted on the coast of Greenland by bright sunshine and completely calm seas. It would be days before they saw any of these things again.
The main cargo of his expedition was an arsenal of moorings, each equipped with sonar-like instruments to measure ocean currents. Each mooring was also connected to a series of floats, buoys and smaller instruments measuring water temperature and salinity, like a chain several hundred meters long.
Five of the tethers looked like yellow lunar modules. Another looked like a flat orange torpedo and was connected to a barrel-shaped buoy designed to deflect icebergs. The buoy would remain hidden in the depths, scanning the waters above for ice, then rise to a safe depth to take measurements before diving again.
Scientists planned to place the moorings along a roughly 56 km stretch of seafloor at 71 degrees north latitude. They would leave them there until next year, allowing them to collect months of measurements of the water flowing along Greenland’s east coast.
Collecting data in this way reminds Foukal of the lobster fishing he did when he was growing up in Massachusetts: you don’t know what you’ve got until you take the cages out. “It’s like rolling dice,” he said.
But first, the scientists and crew had to safely remove the heavy tethers from the moving ship and place them overboard in exactly the right places — a highly choreographed production of winches, pulleys and ropes that James Dunn, the expedition’s assistant principal engineer, likened to a ballet.
“Everything has to come together at the same time,” said Dunn, who works for the Woods Hole Oceanographic Institute in Massachusetts.
During the first days of the voyage, clear skies and calm seas helped the scientists and crew install the moorings smoothly. But soon the wind picked up and things became more difficult.
The team’s cigar-shaped underwater robot stopped working and had to be fished out. Important scientific equipment on deck blew a fuse, and replacement equipment was flown from Iceland to the sealing village of Ittoqqortoormiit and taken on board.
To shelter from the storms, the scientists took a several-day detour into Scoresby Sound, one of the world’s largest fjords, where they collected measurements of the water flowing in and out of the deep inlet.
Then the buoy that deflects icebergs started having problems, and the scientists came up with a risky plan: They were going to go back, pull the mooring line out of the water, try to repair the buoy, and redeploy it.
The goal was that the researchers hoped to collect all the data they wanted before July of next year, when they plan to get their instruments back and start drawing conclusions about how coastal currents move and change.
On a cool, gray morning, the torpedo-shaped structure came into view. Andrew Davies, Woods Hole’s technical assistant, leaned over the starboard rail and grabbed it with a hook on a stick. Nikiforos Delatolas, an engineer, spent the afternoon and evening hunched over his laptop troubleshooting the faulty float.
It was midnight, cold and raining when all the equipment was back under the waves. For the first time in hours, the scientists smiled.
“It was fun,” Dunn said. “Let’s do it again.”
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