By understanding these ocean currents, researchers hope to determine if, and when, rising temperatures will disrupt global weather conditions.
In 2011, Bob Pickart was aboard a research vessel in the Denmark Strait, facing a real scientific mystery.
While studying the waters that separate Greenland and Iceland with a team of Icelandic scientists, the data revealed the presence of a current that no one suspected existed… and it was flowing in the opposite direction.
« I wondered what it could be, » recalls Pickart, a physical oceanographer and researcher at the Woods Hole Oceanographic Institution in Massachusetts.
The scientist returned to his primary research, and the mystery of this strange current lingered in the back of his mind for over ten years, until he decided to revisit the subject this summer.
With an interdisciplinary group of researchers, Pickart tracked the current, now named the Iceland Faroe Slope Jet (IFSJ). For six weeks, amid a major storm, they followed the current’s path through the Nordic seas, heading towards the northern Arctic.
It is essential for scientists to determine the starting point of the current because they already know where it ends. The IFSJ, a dense, deep-water current, begins somewhere in the Nordic seas, flowing south and east, eventually entering the Faroe Bank Channel, a gap in the underwater ridge extending from Greenland to Scotland. From there, its waters feed the lower branch of the Atlantic Meridional Overturning Circulation (AMOC).
The AMOC, often described as an oceanic conveyor belt, is a complex system of ocean currents that redistributes heat around the planet and influences regional climate patterns.
However, climate models indicate the possibility of a slowdown, or even a collapse, of the AMOC due to global warming. In simulations, an excessive amount of warm, fresh water is injected, disrupting the process that keeps this circulation functioning. The consequences of such a collapse would be catastrophic: temperatures would drop in northern Europe, sea levels would rise even more along the US coast, and the southern hemisphere’s monsoons could change course.
The scientific community is divided on the timeline for when this phenomenon could occur. While the latest IPCC report suggests this decline is likely to happen after 2100, some scientists argue that a collapse could occur within the next few decades. Others maintain that, while the data shows warming waters, the flow has remained stable in the critical sections of the AMOC.
According to some experts, including Dipanjan Dey, assistant professor at the Indian Institute of Technology Bhubaneswar, the lack of consensus on modeled projections is due to a lack of long-term observations. Complete measurements of the AMOC only date back twenty years.
« We cannot say with certainty when the tipping point will occur… However, even if we don’t yet fully understand its scope, we should prepare for it, » says Dey, who was not involved in Pickart’s research but studies the potential impact of the AMOC on monsoons.
That is why, at the age of sixty-five, Pickart found himself holding onto rails to move through a hallway as strong winds and large waves shook the RV Neil Armstrong. The researcher hopes that discovering the starting point of the IFSJ and its link with the AMOC will help fill in the gaps in current data.
« We need to understand how the system works before we can truly predict how it will change in response to climate warming »
THE INVESTIGATION IS OPEN
To understand the role of the Iceland Faroe Slope Jet in this system and locate its origin, Pickart’s team began searching for clues.
« It leaves a trace, a certain signature of temperature, salinity, speed: we can trace it, » says Stefanie Semper, thirty-six, a physical oceanographer and scientist at the University of Bergen, Norway.
It was Semper who, in 2019, conducted the first analysis of the original IFSJ data.
« At my institute, we still call it Stefanie’s current, » she revealed with a laugh.
During this expedition, Semper collected the current’s signature using a CTD probe, an instrument designed to measure electrical conductivity (for salinity), temperature, water depth, and other tools to determine its speed. The CTDs are monitored by watchstanders, or « lookouts, » who, except for Semper, are all post-doctoral or doctoral researchers working in teams of two, day and night.
The CTD probes are mounted on rosettes made up of large metal bottles. To take these measurements, the rosettes are lifted by a hydraulic arm, transported to the side of the ship, and then lowered into the water. From the main lab, Semper directed these operations with the night team, communicating via walkie-talkie with Chris Cabell, the crew member in charge of controlling the hydraulic arm from a viewpoint two floors above. Sitting in front of twelve computer screens, she calculated the distance the CTD needed to travel to reach the ocean floor.
« And now, we’re waiting to reach 1,000 meters, » she described during the descent of the CTD into the depths. Two colored vertical lines then appeared on the graph of one of the screens, and the sensors began transmitting data.
Later, in the early morning, Semper put on a winter coat, life jacket, and safety helmet and went out to retrieve and secure the CTD so the ship could continue its journey.
Missions like this are cold and wet; earlier that night, Semper had nearly been struck by a wave that flooded the deck.
EVEN MORE QUESTIONS
In total, the watchstanders of the team made 212 CTD descents, while Pickart collected real-time data and captured a vertical snapshot of the current. Thanks to this snapshot and weather forecasts, the captain and researcher occasionally adjusted the ship’s course; the Armstrong sailed as far north as 75°N, well beyond the Arctic Circle, before turning around to head back to port.
« 75°N is the farthest north we’ve ever been aboard this ship, within one degree of latitude, I believe, » commented Captain Mike Singleton.
On land, the Armstrong’s data will be merged with that of two other vessels working in coordination with Pickart’s expedition, and all water samples not treated onboard will be analyzed. Pickart also deployed scientific moorings and a glider just north of the Faroe Islands, which will collect data for a year before being retrieved.
Overall, this represents years of additional work, but some initial observations have already been made. It was known that the Iceland Faroe Slope Jet had two branches, and scientists suspected, though they couldn’t prove it, that they originated from the Greenland Sea. According to Pickart, this research seems to confirm that one of the branches does indeed start in the Greenland Sea, which is significant because this current connects the Greenland Sea to the AMOC and transports water from a rapidly warming region.
The second branch, however, appears to come from a completely different place.
Pickart does not plan to answer the questions raised by this discovery himself. After more than thirty years at sea, the researcher intends to retire in the coming years, which is why he has entrusted these questions to a new generation of physical oceanographers. Jie Huang, a thirty-one-year-old postdoctoral researcher who worked closely with Pickart during the expedition, will lead the analysis on land with the help of Semper.
« It’s like a wonderful birthday gift, » Jie Huang admitted in an email, several weeks after the expedition. « This data is very rare. »
Pickart hopes that other young scientists will also tackle another issue raised by the expedition. Amid the measurements, data revealed the presence of an unexpected phenomenon: a water flow that, once again, no one suspected existed.
So, the current has a third branch.
« I’m not even sure about the implications of this third branch, but it transports a significant amount of water, » Pickart commented at the end of the expedition. « That’s what exploration is all about. Incredible, isn’t it? »
Source: nationalgeographic
