Using a high-resolution MITgcm simulation paired with Lagrangian particle tracking, a new study traces where Irminger Current waters actually go and shows they do not just hug the boundary.

Reporting by Helen Hill for MITgcm

If you picture the North Atlantic as part of Earth’s climate engine, the Irminger Sea is one of the places where that engine does some of its most important work. In winter, cold winds strip heat from the ocean surface, increasing water density and driving deep convection, an essential component of the Atlantic Meridional overturning circulation. But this process is not controlled by the atmosphere alone. A study by Fried et al. (2026) shows that ocean circulation, specifically the Irminger Current, plays a central role in shaping where this convection occurs.

The Irminger Current carries relatively warm, salty water northward along the eastern edge of the basin. At first glance, it might seem like a boundary current that simply skirts the convection region, leaving the colder interior largely disconnected. However, when the authors combine a high-resolution ocean model with a Lagrangian perspective by tracking virtual water parcels through the flow, a more complex picture emerges. A substantial fraction of the current’s waters does not remain confined to the boundary. Instead, it spreads into the basin interior along intricate, looping pathways shaped by eddies and other mesoscale variability.

In fact, the study finds that roughly 60% of the tracked water parcels leave the boundary current and enter the interior Irminger Sea within a few months. This exchange is not driven by the mean circulation, which tends to steer water along the basin’s edges. Rather, it is the ocean’s smaller-scale variability, including eddies, meanders, and transient features, that drives this cross-basin transport. These features effectively act as conveyor belts, intermittently carrying warm, salty Irminger Current water into the central basin.

From an MITgcm perspective, the work rests on a high-resolution regional configuration that resolves these processes explicitly. The model domain covers the eastern subpolar North Atlantic, including the Irminger Sea and Iceland Basin, with horizontal grid spacing of about 2 km in the region of interest, fine enough to capture mesoscale variability, and 216 vertical levels with enhanced near-surface resolution. The simulation is forced with realistic atmospheric fields and run for one year, with 6-hourly output saved for velocity, temperature, and salinity. Those fields then drive an offline Lagrangian particle tracker, with particles seeded densely across the upper 1500 m of the Irminger Current and advected forward in time. In effect, MITgcm provides the dynamically consistent, eddy-resolving flow, while the Lagrangian framework reveals pathways and connections that are largely invisible in time-mean diagnostics.

The key question is whether any of this boundary-origin water actually reaches the deep convection area. The answer is yes: about a quarter of the released parcels make their way into the convection region within six months. This represents a strong link between the boundary current and the interior. Importantly, when these waters arrive, they remain relatively buoyant compared to the colder, denser waters in the convection region of the Irminger Sea. Although they cool and freshen along the way, they do not fully equilibrate with their surroundings.

This buoyancy has a direct dynamical consequence. Deep convection depends on surface waters becoming dense enough to sink. The steady supply of lighter water from the boundary acts to stabilize the water column, limiting how deeply convection can penetrate. In the Irminger Sea, this restratification effect is strongest in the eastern basin, effectively confining the most vigorous convection to the west.

The study also highlights differences within the Irminger Current itself. The current has a two-core structure, and waters originating in the western core are more likely to enter the basin interior and reach the convection region. By the time they arrive, however, waters from both cores have similar densities, so their overall impact depends more on how much water arrives than on subtle differences in source properties.

Taken together, these results underscore the importance of lateral exchanges in setting the structure of deep convection. Similar dynamics have been identified in the Labrador Sea, where eddy-driven transport of buoyant boundary waters limits the extent of convection. In both regions, convection emerges not simply as a local response to winter cooling, but as the outcome of basin-scale interactions between circulation, eddies, and water-mass transformation.

There are also broader implications. The Irminger Current varies in both strength and properties, including during events when freshwater anomalies propagate through the North Atlantic. Because a significant portion of its waters reaches the convection region, such variability can directly influence where and how strongly convection occurs. Given the role of the Irminger Sea in the overturning circulation, and by extension in climate, understanding these pathways is an important step toward anticipating how the system may evolve in the future.

To find out more about this study, contact Nora

Story image: Schematic showing the percentages and volume transports of the particle transportation in various categories. Fried et al (2026), fig. 7 – courtesy of the researchers.

About the Researcher

Nora Fried is a postdoctoral researcher in the Biosphere–Atmosphere Interaction group at the University of Münster, Germany. She earned her Ph.D. in Physical Oceanography in 2024 from the Royal Netherlands Institute for Sea Research and Utrecht University. Her work focuses on North Atlantic ocean circulation and climate dynamics. She has been using MITgcm since 2022.

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