Unusually for any ocean, the Arctic isn’t layered based on temperature. Instead of having the colder, denser water at the bottom and the warmer, lighter water at the top, the Arctic has the saltiest water at the bottom, below the freshest water. And since the saltiest water in that region is also the warmest, heat is sinking below the sheets of Arctic ice.
This warm water gathers in moving pockets, or ‘heat bombs’. They can maintain enough stability to gush around underneath the main ice pack near the North pole for months or years, shifting it around and destabilising it. And scientists have watched them getting stronger over the last decade.
"The rate of accelerating sea ice melt in the Arctic has been hard to predict accurately"
What the scientists at SODA (Stratified Ocean Dynamics of the Arctic) set out to research was exactly how the warmer water was moving underneath the ice sheets. This is the first paper to observe and understand the process of subduction that leads to ‘heat bombs’.
Jennifer Mackinnon, chief scientist of the expedition, said to Scripps Oceanography Institute that “The rate of accelerating sea ice melt in the Arctic has been hard to predict accurately, in part because of all of the complex local feedbacks between ice, ocean and atmosphere; this work showcases the large role in warming that ocean water plays as part of those feedbacks.”
Since this phenomenon has only just been discovered, researchers have never been able to factor it into any climate change forecast models, which has led to underestimates of sea ice melt rates. Now that the process has been documented, all eyes should be on the Pacific Ocean, which is pushing increasingly large amounts of warm, salty water through the Bering Strait and into the Arctic.
The research team concluded their report, saying that the increasing Pacific summer water “should lead to a pattern of accelerating sea ice melt spreading out from the Pacific inflow, as has been observed in recent decades.”