A new joint study of the Arctic Ocean administered by Yale and the Woods Hole Oceanographic Institution provides more evidence for global warming and its ominous consequences.
For three decades, researchers in Yale’s Department of Geology and Geophysics, as well as those in the Woods Hole Department of Physical Oceanography, measured the temperature and salt content of the Beaufort Gyre, a region north of Canada known for its fresh water and heat absorption. What they found was startling: Not only did the heat content of the region almost double, but the amount of heat that the surface waters absorbed also quintupled between 1987 and 2017. They concluded that decreasing amounts of sea ice in the Arctic caused this effect. The study was published in the journal Science Advances on Aug. 29.
“That heat isn’t going to go away on its own,” said Woods Hole, researcher and study co-author John Toole. “Once you lose the ice, there’s no additional fresh water to add because it’s gone.”
According to Geology and Geophysics Director of Undergraduate Studies Mary-Louise Timmermans, the Beaufort Gyre is a large weather circulation just above Alaska that swirls year-round with fast winds, trapping freshwater and sea ice. Under normal circumstances, the ice would reflect solar rays, keeping the freshwater directly underneath cool and the denser, saltier water further down even cooler.
Nowadays, however, this careful balance between hot and cold is put in jeopardy. Decreasing amounts of sea ice around the edges of the Beaufort Gyre means more solar heat for the water to absorb, Timmermans said. When combined with a higher salt content, warm water sinks hundreds of meters under the surface, where it cannot release its heat as easily. These deep sea waters continue to grow hotter and hotter every year, melting more and more ice in the process, she continued.
Timmermans and her colleagues sail regularly to the gyre and drill weighted tethers through the ice sheet and into the deep waters to capture temperature and salt content. Three decades’ worth of data were aggregated and analyzed for the study. Sensors attached to the tethers move up and down the line as the ice sheet swirls around the gyre and measure temperature and salt content researchers concluded that the upward trend of both temperature and salinity directly increased the amount of sea ice that melted each year.
“What we’re seeing in the Arctic is this complicated physical process that means that the summertime warming isn’t just limited to summer, but it manifests year-round,” said Timmermans, who made his first expedition to the Arctic was in 1995. “Short of some really clever geoengineering effort, at this point, [reversing this trend] is probably not in the near future. There’s no doubt that ocean temperatures will continue to get warmer and we will continue to see increases in sea ice losses.”
Yale oceanic and atmospheric sciences professor Alexey Fedorov said the team’s findings were well supported.
“It is a state-of-the-art observational study, so I don’t think any improvements are needed,” he said.
Since the study was published, Woods Hole Oceanographic Institution researcher Richard Krishfield has traveled to the Arctic Ocean to collect more data and maintain existing sensors. Krishfield and his colleagues are part of the Arctic Observing Network, an international group of scientists focused on measuring the effects of climate change on the Beaufort Gyre and its surrounding waters.
Polar bears depend on surface ice in the Beaufort Gyre to live, hunt and sleep on; warming of Arctic Ocean temperatures may endanger the survival of the species. Nearby indigenous populations that rely on a stable climate for subsistence farming will most likely suffer a similar fate should the trends outlined in the study continue, Timmermans said.
But while it is clear the vanishing ice does not bode well for the Gyre’s immediate inhabitants, Timmermans said that the further-reaching implications of the warming remain hazy.
“The details of a warmer planet, whether it means more or fewer hurricanes, or bigger hurricanes, or where the sea level is going to rise the most, or how quickly the sea ice will melt, how soon we won’t have sea ice left in the summertime — these are all questions that we’re continually trying to answer by doing these types of studies that tell us better how the climate system works,” she said.
The amount of Arctic sea ice in September is declining at a rate of 13.2 percent per decade, according to the National Aeronautics and Space Administration.
Matthew Kristoffersen | matthew.kristoffersen@yale.edu
Correction, Sep. 11: A previous version of this article mistakenly stated the full name of the Woods Hole Oceanographic Institution.