About 68 percent of the ocean floor categorized along a series of magnetic profiles throughout the Gakkel Ridge is deemed amagmatic, indicating it does not possess the magnetic characteristics of volcanic crust, in contrast to 32 percent that does. This is the primary finding of [a research on the Arctic Ocean floor](https://doi.org/10.1038/s41467-026-76409-3) released in Nature Communications on 7 August 2026, and the researchers characterize the predominance of the non-volcanic seafloor as surprising. It ranks high, but not a record: the same document mentions 25 percent at the Mid-Cayman Spreading Center, at least 41 percent at the easternmost Southwest Indian Ridge, and up to 70 percent at the Australian-Antarctic Discordance.
Mid-ocean ridges are typically described as the Earth’s longest volcanic system. Along the majority of them, magma ascends into the gap between two diverging plates, solidifies into basalt, and forms new crust at a relatively consistent pace. The Gakkel Ridge, extending about 1,800 kilometers from the Lena Trough near Svalbard to the Laptev Sea near Siberia, seems to do this only sporadically. In the surveyed area, most of the classified ocean floor is instead interpreted as mantle rock brought up to fill the gap and transformed into serpentinite.
The survey was conducted half a century ago
The data are not recent. Fei Zhou, Ingo Grevemeyer, and Jérôme Dyment scrutinized 60 aeromagnetic profiles gathered by Project Magnet in 1974 and 1975, flown at an altitude of 300 meters above sea level with readings taken every 250 meters and track lines spaced 9 to 17 kilometers apart. The profiles traverse the ridge from 3 degrees west to 50 degrees east, encompassing crust ranging from zero age to about 35 million years old. Navigation, leveling, and field corrections had already been made to the archived data; the authors eliminated long-wavelength trends from it and built upon that foundation.
The age of the survey is less significant here than the challenges of conducting any survey whatsoever. As the paper states, dense sediments in the Amundsen and Nansen basins, along with the ice covering the Arctic Ocean, “complicate systematic geophysical and geological surveys beyond the ridge axis.” Ships may dredge rock from the ridge crest. Accessing the seafloor that is hidden under ice and covered by up to a kilometer of mud poses a different challenge.
The authors validated the 1974 to 1975 lines against a second, independently navigated magnetic dataset compiled in 1998 and 1999. They report that both the location and the magnitude of the anomalies align where the two surveys overlap.
The magnetic distinction between erupted basalt and exhumed mantle
The approach revolves around a difference in how two types of rock retain magnetism. Basalt that erupts at a spreading center cools in the Earth’s magnetic field at that moment and secures that polarity, so seafloor formed magmatically bears the familiar pattern of reversals. Serpentinite emerges where water interacts with exposed mantle peridotite. The authors suggest that its “uncoherent remanent magnetization” cannot accurately capture reversals, thereby resulting in weaker, more subdued anomalies.
In the model, basalt and gabbro exhibit remanent magnetizations of 20 and 2 amps per meter respectively. The serpentinite layer is assigned a low induced magnetization of 0.5 amps per meter, which, as stated in the paper, “does not register magnetic reversals.” The team created forward models for each profile and concurrently adjusted two factors: the arrangement of magmatic and non-magmatic crust and the spacing of the magnetic chrons, until the synthetic anomaly corresponded to the observed one. This involves two sets of adjustable parameters rather than one, which allows for more flexibility in interpreting any single fit. Alteration is handled as a linear decay of basalt magnetization away from the ridge axis.
The classification yielded the notable ratio and another, more intriguing finding. When comparing the two sides of the ridge for each profile, the authors categorized every segment into robust magmatism, where both sides are volcanic, intermediate magmatism, where one side is volcanic and its counterpart is not, and starved magmatism, where neither side is.
No new samples were collected
No rock was dredged for this research, no seismic line was shot, and no camera was deployed. The paper clearly states that its constraints are indirect, describing the effort as “overcoming the difficulties of systematic rock sampling in an environment where the basement is covered by thick sediments.” The dredged peridotite, basalt, and gabbro featured in the study’s first figure originate from earlier expeditions, and that sampling occurs on the ridge axis rather than in the sediment-covered crust further out.
The authors emphasize the most