Most icebergs in the Arctic bear traces of their origin: When large glaciers calve, not only are huge blocks of ice released, but also debris and sediments that have been carried along in the ice for years. As a result, rock fragments become embedded in the icebergs—visible as dark patches and veins on the surface and along their sides.
But what researchers observed on several icebergs in the Fram Strait in 2021 surprised even experienced expedition participants. Dr. Melanie Bergmann, a biologist at the Alfred Wegener Institute Helmholtz Centre for Polar and Marine Research (AWI), spotted the icebergs from a helicopter aboard the Polarstern research icebreaker: “Some of the icebergs were carrying unusually large amounts of debris and looked almost black from above.” In order to investigate this unusual finding, the expedition team documented the rock distribution and collected samples. Melanie Bergmann reports: “We immediately realized that tonnes of rock were drifting through the Arctic Ocean, hundreds of kilometers away from any glacier.”
The researchers found clues as to the origin of the icebergs around 2,500 meters below—on pictures taken with the long-term observatory “AWI-Hausgarten“: The stones that rained down from the melting icebergs had already left a clear trail on the deep-sea floor. Dr. Kirstin Meyer-Kaiser, a scientist at the Woods Hole Oceanographic Institution (WHOI) in the USA, has analyzed deep-sea photos from the region taken on expeditions in recent years: “Where previously there were only isolated stones of various sizes, we are now finding much larger accumulations, frequently in small groups. And with each new stone, a permanent settlement is created on the seabed. Sponges, anemones and other animals that favor hard substrates can settle there. As a result, biodiversity in the deep sea is increasing.” A comparison of the observations from the iceberg and the deep sea proved that the stones on the seabed actually originate from the icebergs. Kirstin Meyer-Kaiser: “The stones show a clear match in both size and mineralogical composition.”
But is this a regionally limited phenomenon or a consequence of climate change, which is causing glaciers to melt ever faster and increasing the number of icebergs and their stony cargo? Melanie Bergmann emphasizes: “Such puzzles can only be solved in an interdisciplinary manner. That’s why we biologists have joined forces with experts from glaciology, oceanography, geology, deep-sea and atmospheric research and have been exchanging ideas over the years.”
Dr. Thomas Krumpen, sea ice physicist at the AWI and lead author of the study together with Kirstin Meyer-Kaiser, describes the central challenge: “In order to prove that climate change is intensifying the process, we had to show that the frequency of icebergs in the region has changed.” This is not trivial, however, “because smaller icebergs and their fragments in the pack ice can hardly be recognized by satellite. That’s why no one has been able to say whether there are more icebergs today than in the past.”
In order to close this gap, the team finally analyzed a special treasure: the synoptic observations that have been carried out from the bridge of the Polarstern for around 40 years. Among many other factors, the observations document whether and how many icebergs can be seen in the vicinity of the ship. “This data set is actually a by-product of the regular weather records, but it turned out to be crucial for this issue,” said Thomas Krumpen. The analysis clearly showed: Since the early 2000s, more and more icebergs have been passing through the Fram Strait and increasingly in larger groups—an indication that the deposit of stones follows a systematic, climate-related pattern.
But where do all these icebergs come from? By way of a satellite-based method for reconstructing the movement of ice in the ocean, the researchers were able to trace some of the observed icebergs back to their place of origin: Many come from two large glaciers in north-east Greenland as well as from parts of the Russian Arctic. The glaciers in north-east Greenland in particular have lost stability since the early 2000s and are now calving much faster. The timing of this destabilization closely matches the observed increase in the frequency of icebergs further south in the Fram Strait and is a consequence of global warming. The researchers used a sea ice-ocean model to investigate the extent to which the rapidly melting Arctic sea ice could have contributed to the accumulation. The simulations show that icebergs in increasingly dynamic and retreating pack ice are transported faster and more efficiently towards the Arctic outflow and have more contact with open water overall, which in turn accelerates their melting.
The results underscore how closely processes on land and in the deep sea are intertwined—and how sensitive and far-reaching this Arctic system is in its response to progressive warming. These findings, however, are not only relevant for climate and biodiversity research, but also hold direct significance for maritime safety and planning. “An increasing presence of icebergs in certain regions of the Arctic harbors considerable risks, for example for cruise ships and cargo ships, which are traveling in ever greater numbers in the ice or near the ice edge, as well as for exploration activities for oil and gas,” said Thomas Krumpen. “As fishing moves further north, newly deposited stones in shallower areas could also become a risk for bottom trawling in the future.”
The growing need for reliable information on ice and iceberg distribution led to the establishment of the company Drift+Noise Polar Services at the AWI and hived off a few years ago, which supports ships in ice-covered regions with the corresponding position information. This study now provides an important scientific foundation for better assessing iceberg hazards in the future and further developing products for route planning in polar sea regions.
To read the paper, visit: 10.1038/s41586-026-10630-4
