The Polar Retrospective – Competition for krill, new influence Arctic sea ice formation and messages in ice

The Polar Retrospective looks at recent stories from around the world’s polar regions. This week we take a look at competition for krill between animals and trawlers, and bubble messages trapped in ice.

The Polar Retrospective is a collaborative effort by the editorial team of polarjournal.net. Each writer chooses a topic they found interesting and important in the past week. The initials at the end of each section indicate the author. We hope you enjoy it.

Humans and animals overlap to harvest krill

To what extent does industrial krill fishing encroach on the feeding grounds of whales, penguins, and seals? Published on June 16 in PNAS, a German-Norwegian study analyzes for the first time 30,000 hours of sonar data recorded aboard several krill-fishing vessels, including the Antarctic Endurance. The goal: to assess the intensity of competition between human fishing activity and the natural predators of this key species in the Southern Ocean ecosystem. Five main trends emerge:

1. Fishing vessels regularly encounter seals and penguins year-round, particularly in the South Orkney Islands and South Georgia.
2. In Antarctica, protective measures established around penguin breeding colonies – notably a 30 km buffer zone – are pushing fishing efforts toward other areas, such as the South Orkneys.
3. The South Orkney Islands are becoming a new hotspot of interactions, but there is no active ecological monitoring of penguin colonies in this archipelago.
4. Another issue arises during the austral autumn, when the peak market demand for krill coincides with the humpback whales’ need to build up fat reserves before migration, leading to increased overlap with fishing activity along the Antarctic Peninsula.
5. The 2025 fishing season began in December 2024 in the Gerlache Strait, less than 30 km from the coast, in contradiction with current recommendations. The fleet usually operates in the South Orkneys during this season, but the schedule was disrupted by sea ice.

While some fishing companies collaborate with scientists, all regulatory decisions fall under the authority of the CCAMLR. The study highlights the urgency of reaching consensus: sustainability depends not only on catch volumes, but also on a detailed spatial understanding of how marine areas are used. C.L

Previously unknown current influences winter sea ice in the Arctic

A recent study by the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) has revealed the significant impact of a previously little-investigated ocean current on the winter sea ice formation in the Barents Sea. The findings, published in the journal Nature Communications, shed new light on the complex processes that govern the shrinking of Arctic sea ice.

For decades, scientists have observed a retreat of Arctic sea ice, a trend that persists even during the winter months. A primary driver of this phenomenon is the inflow of warm Atlantic water into the Arctic Ocean. However, the recent AWI study highlights a crucial, previously overlooked factor: not all of this warm water directly interacts with the sea ice. “The amount of Atlantic water that flows into the Barents Sea but immediately leaves again through recirculation can have a significant impact on how sea ice forms from year to year, but also in the long term”, says Dr. Finn Heukamp, lead author of the study.

The German-US research team discovered that a substantial portion of the Atlantic water entering the Barents Sea recirculates and flows back into the European North Sea. This “recirculation” has a significant and previously underestimated influence on the amount of sea ice that forms in the Barents Sea during the winter. This recirculation normally acts as a barrier, limiting the amount of heat that continues north towards the sea-ice edge. “When the return flow is weaker, less Atlantic water is immediately transported back out. Instead of leaving the Barents Sea, this Atlantic water flows through it and warms it up. The result is that less new sea ice forms during these years and existing ice melts more quickly”, explains Dr. Heukamp.

Using a series of advanced ocean model simulations, the AWI scientists were able to precisely analyze this system and uncover a critical change. Their models showed that since the late 1990s, the strength of this recirculating current has significantly diminished. With the inflow of Atlantic water remaining relatively constant, this weakening of the return flow means a larger volume of warm water is now able to penetrate further north and east. This previously unaccounted-for heat influx directly contributes to the reduction of winter sea ice in the Barents Sea, providing a vital new insight into the rapid changes occurring in the Arctic. M.W.

You have one bubble message

Chinese researchers, inspired by air bubbles trapped in ice for millennia, have developed a novel method to encode messages within ice. Published on June 18 in the journal Cell Reports Physical Science, their study describes how information can be transmitted by altering the size, shape, and distribution of air bubbles in ice.

Using a precisely controlled cold plate, the team succeeded in creating readable patterns in Morse or binary code. Egg-shaped or needle-like bubbles, arranged in successive layers, become characters in a frozen language. Once photographed, these patterns are interpreted by an algorithm that deciphers the original message. According to the authors, this discreet and durable process could prove useful in extreme environments like the Arctic or Antarctic, where conventional data storage is limited.

Beyond this message application, the researchers also envision industrial uses: creating structural weak points in ice, or better understanding how bubbles form in certain metals such as aluminum. Far from being silent, the ice still has many stories to tell. M.B.