Thomas Krumpen

The polar regions play a central role in the Earth system through their influence on ocean circulation, ice sheets, sea level, carbon cycling, and climate variability. Rapid anthropogenic warming is transforming these regions, highlighting the need to understand the processes, feedbacks, and thresholds that govern ocean–cryosphere interactions across a wide range of timescales. Here we synthesize major scientific advances achieved at the Alfred Wegener Institute during 2021–2025 within the Helmholtz research program Changing Earth – Sustaining Our Future. Combining paleoclimate archives, sustained observations, process studies, and Earth-system modeling, these studies provide new insights into the sensitivity of the climate system under past, present, and future climate conditions. Key findings include new constraints on Antarctic Ice Sheet evolution during past greenhouse climates, improved understanding of links between Southern Ocean circulation and climate–carbon feedbacks, advances in reconstructing Northern Hemisphere ice-sheet dynamics and deglaciation processes, and evidence that regional climate variability is stronger and more persistent than represented in many current climate models. Observations and simulations further reveal accelerating changes in Greenland outlet glaciers, important couplings between cryospheric change and the carbon cycle, and a growing role of mesoscale ocean dynamics in shaping future Arctic and global climate change. Together, these results demonstrate the value of integrating observations, paleoclimate evidence, and high-resolution modeling to constrain Earth-system sensitivity, identify critical feedbacks, and improve projections of future climate change in a warming world.

The East Greenland Current (EGC) is the main conveyor of cold, fresh Polar Water and sea ice from the Arctic Ocean through Fram Strait to the subpolar North Atlantic. Seven years of continuous mooring observations on the East Greenland continental slope at 79° N (2018–2025) reveal that whilst the EGC typically maintains a southward flow year-round, it is punctuated by periodic northward flow events on the upper continental slope. The majority are short-lived local events (lasting fewer than 5 days), consistent with mesoscale eddy activity. However, two prolonged deep-reaching events — in April–May 2019 (29 days) and May–June 2025 (at least 35 days) — were anomalous in their duration, intensity (i.e. exceeding the climatological mean by 2–3 standard deviations), and vertical coherence (down to at least 500 m depth). During both events, hydrographic observations show anomalous warm Atlantic-origin waters at depths typically occupied by cooler Arctic Atlantic Water, weakened vertical stratification, and temperature-salinity properties consistent with recent West Spitsbergen Current recirculation across Fram Strait. An extended mooring record at 78°50' N (2003–2019) identified a further 7 deep-reaching northward flow events, demonstrating that episodic northward flow is a recurring intrinsic feature of the EGC system rather than a recent phenomenon. A persistent sea-level pressure dipole with anomalous northward winds along the East Greenland margin is identified all strong deep northward flow events. It is proposed that this forcing drives a lateral reorganisation of the boundary current where anomalous eastward Ekman transport displaces the EGC core offshore whilst geostrophically adjusted flow on the inner slope produces a net northward current inshore. The anomalously warm AW at depth thus arises through northward advection of recirculating AW and upwelling over the slope. These anomalous flow events establish an episodic northward pathway for warm Atlantic-origin water with a potential advective reach of perhaps hundreds of kilometres beyond the mooring location — a previously unidentified pathway of Atlantic heat transport into the Arctic interior. The co-occurrence of the 2025 event with a record low sea-ice area in July in the northeast Greenland region suggests that these oceanic events influence regional sea ice variability through dynamic atmospheric export and ocean-ice interactions, though a direct causal link remains to be established. Whether these events represent rare features of a naturally variable boundary current system or early signals of ongoing change in the Arctic-Atlantic exchange remains an open question.

The East Greenland Current (EGC) is the main conveyor of cold, fresh Polar Water and sea ice from the Arctic Ocean through Fram Strait to the subpolar North Atlantic. Seven years of continuous mooring observations on the East Greenland continental slope at 79° N (2018–2025) reveal that whilst the EGC typically maintains a southward flow year-round, it is punctuated by periodic northward flow events on the upper continental slope. The majority are short-lived local events (lasting fewer than 5 days), consistent with mesoscale eddy activity. However, two prolonged deep-reaching events — in April–May 2019 (29 days) and May–June 2025 (at least 35 days) — were anomalous in their duration, intensity (i.e. exceeding the climatological mean by 2–3 standard deviations), and vertical coherence (down to at least 500 m depth). During both events, hydrographic observations show anomalous warm Atlantic-origin waters at depths typically occupied by cooler Arctic Atlantic Water, weakened vertical stratification, and temperature-salinity properties consistent with recent West Spitsbergen Current recirculation across Fram Strait. An extended mooring record at 78°50' N (2003–2019) identified a further 7 deep-reaching northward flow events, demonstrating that episodic northward flow is a recurring intrinsic feature of the EGC system rather than a recent phenomenon. A persistent sea-level pressure dipole with anomalous northward winds along the East Greenland margin is identified all strong deep northward flow events. It is proposed that this forcing drives a lateral reorganisation of the boundary current where anomalous eastward Ekman transport displaces the EGC core offshore whilst geostrophically adjusted flow on the inner slope produces a net northward current inshore. The anomalously warm AW at depth thus arises through northward advection of recirculating AW and upwelling over the slope. These anomalous flow events establish an episodic northward pathway for warm Atlantic-origin water with a potential advective reach of perhaps hundreds of kilometres beyond the mooring location — a previously unidentified pathway of Atlantic heat transport into the Arctic interior. The co-occurrence of the 2025 event with a record low sea-ice area in July in the northeast Greenland region suggests that these oceanic events influence regional sea ice variability through dynamic atmospheric export and ocean-ice interactions, though a direct causal link remains to be established. Whether these events represent rare features of a naturally variable boundary current system or early signals of ongoing change in the Arctic-Atlantic exchange remains an open question.

The East Greenland Current (EGC) is the main conveyor of cold, fresh Polar Water and sea ice from the Arctic Ocean through Fram Strait to the subpolar North Atlantic. Seven years of continuous mooring observations on the East Greenland continental slope at 79° N (2018–2025) reveal that whilst the EGC typically maintains a southward flow year-round, it is punctuated by periodic northward flow events on the upper continental slope. The majority are short-lived local events (lasting fewer than 5 days), consistent with mesoscale eddy activity. However, two prolonged deep-reaching events — in April–May 2019 (29 days) and May–June 2025 (at least 35 days) — were anomalous in their duration, intensity (i.e. exceeding the climatological mean by 2–3 standard deviations), and vertical coherence (down to at least 500 m depth). During both events, hydrographic observations show anomalous warm Atlantic-origin waters at depths typically occupied by cooler Arctic Atlantic Water, weakened vertical stratification, and temperature-salinity properties consistent with recent West Spitsbergen Current recirculation across Fram Strait. An extended mooring record at 78°50' N (2003–2019) identified a further 7 deep-reaching northward flow events, demonstrating that episodic northward flow is a recurring intrinsic feature of the EGC system rather than a recent phenomenon. A persistent sea-level pressure dipole with anomalous northward winds along the East Greenland margin is identified all strong deep northward flow events. It is proposed that this forcing drives a lateral reorganisation of the boundary current where anomalous eastward Ekman transport displaces the EGC core offshore whilst geostrophically adjusted flow on the inner slope produces a net northward current inshore. The anomalously warm AW at depth thus arises through northward advection of recirculating AW and upwelling over the slope. These anomalous flow events establish an episodic northward pathway for warm Atlantic-origin water with a potential advective reach of perhaps hundreds of kilometres beyond the mooring location — a previously unidentified pathway of Atlantic heat transport into the Arctic interior. The co-occurrence of the 2025 event with a record low sea-ice area in July in the northeast Greenland region suggests that these oceanic events influence regional sea ice variability through dynamic atmospheric export and ocean-ice interactions, though a direct causal link remains to be established. Whether these events represent rare features of a naturally variable boundary current system or early signals of ongoing change in the Arctic-Atlantic exchange remains an open question.

The East Greenland Current (EGC) is the main conveyor of cold, fresh Polar Water and sea ice from the Arctic Ocean through Fram Strait to the subpolar North Atlantic. Seven years of continuous mooring observations on the East Greenland continental slope at 79° N (2018–2025) reveal that whilst the EGC typically maintains a southward flow year-round, it is punctuated by periodic northward flow events on the upper continental slope. The majority are short-lived local events (lasting fewer than 5 days), consistent with mesoscale eddy activity. However, two prolonged deep-reaching events — in April–May 2019 (29 days) and May–June 2025 (at least 35 days) — were anomalous in their duration, intensity (i.e. exceeding the climatological mean by 2–3 standard deviations), and vertical coherence (down to at least 500 m depth). During both events, hydrographic observations show anomalous warm Atlantic-origin waters at depths typically occupied by cooler Arctic Atlantic Water, weakened vertical stratification, and temperature-salinity properties consistent with recent West Spitsbergen Current recirculation across Fram Strait. An extended mooring record at 78°50' N (2003–2019) identified a further 7 deep-reaching northward flow events, demonstrating that episodic northward flow is a recurring intrinsic feature of the EGC system rather than a recent phenomenon. A persistent sea-level pressure dipole with anomalous northward winds along the East Greenland margin is identified all strong deep northward flow events. It is proposed that this forcing drives a lateral reorganisation of the boundary current where anomalous eastward Ekman transport displaces the EGC core offshore whilst geostrophically adjusted flow on the inner slope produces a net northward current inshore. The anomalously warm AW at depth thus arises through northward advection of recirculating AW and upwelling over the slope. These anomalous flow events establish an episodic northward pathway for warm Atlantic-origin water with a potential advective reach of perhaps hundreds of kilometres beyond the mooring location — a previously unidentified pathway of Atlantic heat transport into the Arctic interior. The co-occurrence of the 2025 event with a record low sea-ice area in July in the northeast Greenland region suggests that these oceanic events influence regional sea ice variability through dynamic atmospheric export and ocean-ice interactions, though a direct causal link remains to be established. Whether these events represent rare features of a naturally variable boundary current system or early signals of ongoing change in the Arctic-Atlantic exchange remains an open question.

The East Greenland Current (EGC) is the main conveyor of cold, fresh Polar Water and sea ice from the Arctic Ocean through Fram Strait to the subpolar North Atlantic. Seven years of continuous mooring observations on the East Greenland continental slope at 79° N (2018–2025) reveal that whilst the EGC typically maintains a southward flow year-round, it is punctuated by periodic northward flow events on the upper continental slope. The majority are short-lived local events (lasting fewer than 5 days), consistent with mesoscale eddy activity. However, two prolonged deep-reaching events — in April–May 2019 (29 days) and May–June 2025 (at least 35 days) — were anomalous in their duration, intensity (i.e. exceeding the climatological mean by 2–3 standard deviations), and vertical coherence (down to at least 500 m depth). During both events, hydrographic observations show anomalous warm Atlantic-origin waters at depths typically occupied by cooler Arctic Atlantic Water, weakened vertical stratification, and temperature-salinity properties consistent with recent West Spitsbergen Current recirculation across Fram Strait. An extended mooring record at 78°50' N (2003–2019) identified a further 7 deep-reaching northward flow events, demonstrating that episodic northward flow is a recurring intrinsic feature of the EGC system rather than a recent phenomenon. A persistent sea-level pressure dipole with anomalous northward winds along the East Greenland margin is identified all strong deep northward flow events. It is proposed that this forcing drives a lateral reorganisation of the boundary current where anomalous eastward Ekman transport displaces the EGC core offshore whilst geostrophically adjusted flow on the inner slope produces a net northward current inshore. The anomalously warm AW at depth thus arises through northward advection of recirculating AW and upwelling over the slope. These anomalous flow events establish an episodic northward pathway for warm Atlantic-origin water with a potential advective reach of perhaps hundreds of kilometres beyond the mooring location — a previously unidentified pathway of Atlantic heat transport into the Arctic interior. The co-occurrence of the 2025 event with a record low sea-ice area in July in the northeast Greenland region suggests that these oceanic events influence regional sea ice variability through dynamic atmospheric export and ocean-ice interactions, though a direct causal link remains to be established. Whether these events represent rare features of a naturally variable boundary current system or early signals of ongoing change in the Arctic-Atlantic exchange remains an open question.

The NASA airborne Arctic Radiation-Cloud-aerosol-Surface-Interaction Experiment (ARCSIX) collected a unique data set providing a near-simultaneous characterization of radiative fluxes, surface, cloud, and aerosol particle properties to address science questions on the surface radiation budget, the processes governing the cloud lifecycle, atmospheric composition, and the interactions between the surface and atmosphere. The overarching goal of ARCSIX was to quantify the contributions of surface, clouds, aerosol particles, and precipitation to summer sea ice melt. ARCSIX consisted of two deployments in 2024 (Spring: 2024-05-28 through 2024-06-13 and Summer: 2024-07-25 through 2024-08-15) to capture pre- and post-melt conditions. ARCSIX provided coordinated remote sensing and in situ sampling using three aircraft in a high-flyer/low-flyer configuration. The NASA G-III served as the high-flying remote sensing platform with two lower flying in situ and near-target remote sensor observing platforms, NASA P-3B and SPEC Inc. Learjet. ARCSIX data are well-suited to improve satellite remote sensing capabilities in the Arctic. ARCSIX included an array of sea ice mass balance buoys deployed in the Lincoln Sea that were regularly overflown during the campaign. ARCSIX research flights spanned the Baffin Bay, Lincoln Sea, west and north of the Canadian Archipelago, and the Greenland north and northeast coasts. During the spring deployment, 19 research flights took place covering 114 flight hours: 10 flights and 68 hours by the P-3B and nine flights and 46 hours by the G-III. During summer, 24 research flights covered 136 flight hours: nine flights and 75 hours by the P-3B, five flights and 26 hours by the G-III, and 10 flights and 35 hours by the Learjet. A total of 13 coordinated flights with 2+ aircraft were carried out. This paper describes the ARCSIX flight strategy, instrumentation, and data set access, and usage details. ARCSIX data are publicly available at https://doi.org/10.5067/SUBORBITAL/ARCSIX/DATA001.

Highly pathogenic avian influenza of subtype H5N1 (HPAIV H5N1) reached Antarctica in late 2023/2024 breeding season, but the host ecology and movement processes shaping its incursion and spread remain poorly resolved. We investigated these mechanisms by integrating viral genomics, multi-season serology, and seabird movement data at King George Island (Fildes Peninsula, South Shetland Islands), a likely gateway between South America and the Antarctic Peninsula. Across three breeding seasons (2022/23–2024/25), we collected swabs and blood serum from key scavenging and predatory seabirds (Brown skua, South Polar skua, Southern Giant petrel) and paired these data with light-level geolocator tracks (10–16 full annual tracks per species) and breeding-season GPS tracks (10–20 individuals per species). Phylogenetic analyses including three newly generated HPAIV H5N1 genomes from infected Brown skuas placed these viruses within the South Georgia–Antarctic lineage, consistent with introduction via South Georgia followed by onward spread within the region. Longitudinal serology revealed a rapid increase in cumulative exposure in scavenging species, with antibodies against influenza A virus’ nucleoprotein and hemagglutinin subtype H5 rising to high levels by 2024/25 in Brown skuas (52.2%) and Southern Giant petrels (62.5%), but remaining markedly lower in South Polar skuas (12.5%), consistent with their more pelagic and less scavenging foraging behaviour. Tracking showed that migratory connectivity was greatest during the non-breeding period but contracted rapidly during colony return and early breeding. In contrast, network simulations parameterized by high-percentile breeding-season foraging distances indicated strong peninsula-wide connectivity and non-zero potential links toward South Georgia and other sub-Antarctic stepping-stones. Together, these results provide a mechanistic, host-based framework suggesting that HPAIV H5N1 likely reached Antarctica through the South Georgia pathway, but that its regional spread was shaped primarily by foraging ecology and breeding-season movement networks rather than by long-distance migration.

The Arctic is undergoing rapid warming, resulting in retreating sea ice and glaciers ¹ , yet how cryospheric changes propagate into the deep ocean remains poorly understood ² . Here we identify a climate-driven mechanism linking accelerating glacier disintegration to an increase in deep-sea hard-bottom habitats far beyond calving fronts. Seafloor observations in Fram Strait show a localized increase in the density and patchiness of dropstones delivered by debris-laden icebergs. At the same time, four decades of shipboard records show that the occurrence of icebergs increased abruptly in the early 2000s. Backtracking links these icebergs to the main outlet glaciers in northeast Greenland and the Russian High Arctic. In northeast Greenland, the timing of glacier destabilization coincides with this rise, whereas sparse satellite coverage in the Russian sector limits temporal attribution despite indications of enhanced glacier activity. A model sensitivity study shows that, apart from intensified calving, a more dynamic sea ice cover enhances downstream transport of glacial ice. Along these pathways, increased iceberg activity could reshape deep-sea habitats through enhanced melt and associated lithogenic input, and elevate navigational hazards as maritime traffic expands in the Arctic. Although modest compared with the iceberg discharges of Pleistocene Heinrich events, this mechanism provides a modern analogue of long-range cryospheric influence on the seafloor in a warming climate.