Sebastien Moreau

Antarctic krill, Euphausia superba , is an important species in the Southern Ocean and is vulnerable to climate change. We studied the carbon sources for krill—specifically pelagic and ice‐associated (sympagic) particulate organic matter (POM), representing phytoplankton and sea‐ice algae, respectively—during March 2019 across three distinct areas of the Kong Håkon VII Sea (KHS) in the eastern Weddell Gyre. Analyses of δ ¹³ C and δ ¹⁵ N composition revealed large geographic differences in pelagic POM that were reflected in krill across life stages. At Astrid Ridge (the eastern study area), elevated pelagic POM δ ¹³ C suggested that sea‐ice algae seeding influenced phytoplankton development, in line with the more extensive sea‐ice cover in this area and with the dominance of typically ice‐associated pennate diatoms. This was also reflected in the elevated krill δ ¹³ C compositions at Astrid Ridge as compared to the other two areas. In contrast, in the western areas (Maud Rise and 6° East), lower δ ¹³ C values in both pelagic POM and krill suggested limited influence of sea‐ice algae on phytoplankton communities and krill feeding. Moreover, no significant difference in the δ ¹³ C and δ ¹⁵ N compositions was found among krill genders and life stages throughout the study area. These geographical, rather than ontogenetic, differences suggest that krill of all life stages feed opportunistically on the most available algal sources in early autumn in the KHS. Considering the ongoing reduction in the seasonal sea‐ice cover, continued research on the dietary plasticity of krill is essential to understand the resilience and health of krill stocks in a changing Southern Ocean.

In ocean carbon budget assessments, sea ice is still treated as an impermeable barrier, rather than a dynamic interface mediating CO₂ exchange between ocean and atmosphere. We compiled more than 6000 chamber-based air–ice CO₂ flux measurements from the Arctic and Southern Oceans between 2003 and 2021, spanning diverse ice, snow, and seasonal conditions. These data show that sea ice releases CO₂ in winter and absorbs it in summer, with summer uptake offsetting winter emissions. On an annual basis, sea ice represents a small net CO₂ source of +4 Tg C yr⁻¹ in the Arctic and +2 Tg C yr⁻¹ in the Southern Ocean, challenging earlier views of a major sink. Although these fluxes are negligible at basin scales relative to open-ocean uptake, sea ice exchanges gases even in cold winter conditions, with implications for small-scale processes and other trace gases, underscoring the need for sustained, process-resolving observations.

2025 marks iC3’s third year as a Research Council of Norway Centre of Excellence. Since its start-up in 2023, the Centre has grown into a dynamic and collaborative hub for polar cryospheric research, supporting groundbreaking science and fostering a stimulating research environment. iC3 scientists continue to contribute vital scientific knowledge on ice sheets, carbon cycles and ocean ecosystems through interdisciplinary collaboration across the entire ice-to-ocean continuum, via both field campaigns in Svalbard, Greenland, mainland Norway and Antarctica, and integration of observational science and modelling. Early career researchers remain central to iC3’s strategic vision and play a key role through their active commitment to both science and communication. Furthermore, iC3’s research infrastructure is expanding, with the PolarMAGIC lab now fully operational, and the PlasmaLab successfully funded and under development. Over the coming year, iC3 will continue its pursuit of high-impact science driven by important collaborations between UiT The Arctic University of Norway, the Norwegian Polar Institute, and NORCE, and supported by its vibrant research culture.

In Earth system models and ocean carbon budget assessments, sea-ice is still treated as an impermeable barrier rather than a dynamic interface mediating CO₂ exchange between the ocean and atmosphere. To quantify its contribution to the polar ocean carbon budget, we compiled over 6000 chamber-based air–ice CO2 flux collected across the Arctic and Southern Ocean between 2003 and 2021. This unprecedented database spans diverse sea-ice, snow, and seasonal conditions. Despite spatiotemporal limitations, this database enables a comprehensive reassessment of sea-ice’s role in the carbon budgets of polar oceans. Sea ice acts as a CO₂ source in winter and a sink in summer, as summer drawdowns offset most winter emissions. On an annual basis, sea-ice represents a small net CO₂ source of +4 Tg C yr⁻¹ in the Arctic and +2 Tg C yr⁻¹ in the Southern Ocean, refuting previous hypotheses of a major sea-ice carbon sink. Although these net fluxes remain negligible at basin scales relative to concurrent open-ocean uptake, our results highlight that sea-ice exchanges gases even in cold winter conditions. These exchanges may have critical implications for short-term, small-scale processes and for other trace gases, underscoring the need for continuous, process-resolving flux observations.

Antarctica InSync is a global effort to synchronise research across Antarctica and the Southern Ocean, connecting ice, ocean, land, climate, and life to protect this vital region. This roadmap paper introduces the scientific and technological motivation and action plan to build an international programme for a coordinated field season in Antarctica and its surrounding seas. It lays out the international collaboration that is required to realise an ambitious action plan and the opportunities for the science community to address important scientific themes that identify current knowledge gaps. In the spirit of the Antarctic Treaty Consultative Meeting (ATCM), the planned scientific action mandates free data exchange, facilitates international collaboration, and derives expert scientific advice together with the Scientific Committee on Antarctic Research (SCAR). Aligned with challenges of the United Nation Ocean and Cryosphere Decades, we plan a shared global effort to better understand the role of Antarctica and its surrounding ocean for our global futures, building on decades of achievements in polar and ocean science. As a milestone leading up to the next International Polar Year in 2032/33 (IPY5), the ambition is to achieve a new level of cooperation, with opportunities for the next generation of polar scientists around the world by enhancing practices in sharing of ideas, infrastructure and information.

Since 2015, Antarctic sea ice has entered a period of persistent record-low extent after decades of strong regional variability and large swings. The speed and persistence of this decline point to a system that may be changing state, with implications for the Southern Ocean, Antarctic ecosystems, and the global climate system. What is driving this shift remains insufficiently understood. Atmospheric variability plays a role, but ocean processes, including subsurface heat release and changes in stratification, are increasingly recognized as key pieces of the puzzle, alongside feedbacks involving snow, ice shelves, clouds, and freshwater input. This white paper focuses on four areas where progress is needed. First, improved understanding is needed of sea ice mass balance and dynamics: how sea ice grows, melts, moves, and deforms. Second, exchanges of heat, mass, and momentum between ocean, atmosphere, sea ice, and ice shelves need to be quantified across seasons and regions. Third, the consequences for ecosystems and biogeochemistry are likely substantial. Sea ice supports productive microbial communities and carbon and nutrient cycling, so its decline will affect polar food webs and Southern Ocean carbon storage. Finally, climate feedbacks, from albedo changes to cloud and ocean interactions, remain poorly constrained but could amplify ongoing change. A recurring limitation is the lack of coordinated, year-round observations across Antarctica. Existing data are sparse and uneven in space and time. Antarctica InSync is designed to address this by bringing together satellite observations, autonomous platforms, field campaigns, coastal observatories, harmonized data products, and modelling across pack ice, the marginal ice zone, landfast ice, and polynyas. The white paper recommends standardized observations of essential sea ice, snow, ocean, atmospheric, ecosystem, and biogeochemical variables, integrated into interoperable data products and models. Addressing these gaps is essential to improve predictability and anticipate future Antarctic sea ice change.

Phytoplankton blooms above the seamount Maud Rise in the Antarctic Ocean have been reported but their emerging mechanisms and their importance for the wider Southern Ocean are not well known. We use satellite data spanning over the last two decades and in-situ data collected from a ship, an underwater glider and Biogeochemical-Argo profiling floats to understand the processes involved in the formation of Maud Rise phytoplankton blooms. We find that the seamount generates upwelling of warm deep water that transports heat, and likely dissolved iron, to the surface via diapycnal mixing. This creates a recurring annular structure of chlorophyll concentration (or chlorophyll halo) in correspondence with the previously observed warm water and sea ice halo over Maud Rise. The in-situ observations reveal integrated chlorophyll-a concentrations of up to 100 mg·m ⁻² , which suggests exceptionally high phytoplankton biomass within the Southern Ocean, thus making the seamount a regional phytoplankton hotspot.

We document layers of incorporated platelet ice up to 0.81 m thick in broken out landfast ice for the first time in the Kong Håkon VII Hav, Southern Ocean. Sampling occurred in January 2022 when...

The Southern Ocean (south of 30°S) contributes significantly to global ocean carbon uptake through the solubility, physical and biological pumps. Many studies have estimated carbon export to the deep ocean, but very few have attempted a basin‐scale perspective, or accounted for the sea‐ice zone (SIZ). In this study, we use an extensive array of BGC‐Argo floats to improve previous estimates of carbon export across basins and frontal zones, specifically including the SIZ. Using a new method involving changes in particulate organic carbon and dissolved oxygen along the mesopelagic layer, we find that the total Southern Ocean carbon export from 2014 to 2022 is 2.69 ± 1.23 PgC y⁻¹. The polar Antarctic zone contributes the most (41%) with 1.09 ± 0.46 PgC y⁻¹. Conversely, the SIZ contributes the least (8%) with 0.21 ± 0.09 PgC y⁻¹ and displays a strong shallow respiration in the upper 200 m. However, the SIZ contribution can increase up to 14% depending on the depth range investigated. We also consider vertical turbulent fluxes, which can be neglected at depth but are important near the surface. Our work provides a complementary approach to previous studies and is relevant for work that focuses on evaluating the biogeochemical impacts of changes in Antarctic sea‐ice extent. Refining estimates of carbon export and understanding its drivers ultimately impacts our comprehension of climate variability at the global ocean scale.

Since the establishment of iC3 in July 2023, we can reflect on an exciting period marked by increasing activity within the Centre. During this time of significant growth, it has been both inspiring and motivating to see the development of a supportive and stimulating research culture among our diverse team of scientists and across iC3´s partnership of UiT The Arctic University of Norway, the Norwegian Polar Institute and NORCE.