| 25 Feb 2026
Greenland tip jet and deep convection in the Irminger Sea: disentangling the roles of heat loss and wind stress
Abstract. The strength of the Atlantic Meridional Overturning Circulation (AMOC) depends on deep-water formation in the Subpolar Gyre, particularly in the Irminger Sea, where convection is strongly modulated by short-lived but intense Greenland tip jet. These mesoscale westerlies induce substantial surface heat loss and impose wind stress on the ocean, jointly influencing convective intensity. Using the high-resolution Parallel Ocean Program (POP) within the Community Earth System Model (CESM), we disentangle the thermal and mechanical effects of tip jet on mixed layer deepening through three ensemble experiments: full-forcing (heat loss + wind stress anomalies), heat-only, and wind-only, each compared to a climatological control run. All forced cases show a significant December–April deepening of the mixed layer relative to the control. The heat-only and full-forcing experiments produce similar mixed layer depth (MLD) increases (+1200 m; reaching ~1800 m), confirming that surface heat loss is the primary driver of deep convection. The wind-only case shows a smaller but still significant increase (+400 m; MLD ~1000 m), associated with enhanced early-winter mixing and wind-driven salinity increases in the upper ocean. This wind stress forcing erodes the fresh surface layer, reduces buoyancy, and promotes shear-driven mixing in December so that climatological winter heat loss can deepen the mixed layer more efficiently. Because wind stress is not projected to weaken under future warming, its mechanical influence may help delay or modulate the decline of convection in the Irminger Sea as surface heat loss decreases.
The manuscript presents a detailed and well-structured analysis of the role of Greenland tip jets in driving mixed layer deepening and deep convection in the Irminger Sea. The authors employ a set of ensemble ocean model simulations to separate the contributions of surface heat loss and wind stress. They compare heat-only, wind-only, and full-forcing experiments against a climatological control. While the manuscript is clearly written and the analysis is comprehensive, I have a few comments regarding the limitations of the experimental framework and the associated results sensitivity. This is not a criticism, as limitations are inherent to modeling works. I don’t recommend running additional simulations that would be a significant amount of work, but I suggest better acknowledging these limitations. Overall, the manuscript is of good quality and addresses an important question in subpolar ocean dynamics. I look forward to reading a revised version.
Major Comments
1. The authors attribute the observed changes in mixed layer depth and convection specifically to tip jets. However, from my understanding, since the control run is forced with a smoothed climatological annual cycle that contains no high-frequency variability, the experiments as designed cannot distinguish the effect of tip jets specifically from the effect of any intense episodic atmospheric forcing event. Could the results simply reflect the ocean's response to high-frequency wind and heat flux variability in general, rather than to the particular spatial and temporal structure of tip jets? The authors could explain what makes tip jet forcing dynamically distinct from other intense weather events in the region, such as reversed tip-jets, or acknowledge more explicitly that their results may generalize beyond tip jets to high-frequency atmospheric forcing.
2. The study relies on a composite representation of tip jets, based on the strongest 10% of westerly wind events. However, recent studies (DuVivier and Cassano 2015, Coquereau et al., 2024) have demonstrated that tip jets exist in various forms, with distinct spatial structures, intensities, and frequencies. Some of these forms are more prevalent than the canonical type examined in this study. For instance, Coquereau et al. (2024) found that tip-jet-like events occur in an average of 12% of the time, which is approximately twice as frequent as the peak frequency of canonical events during the 2014-2015 period. This frequency increases to 42% in DuVivier and Cassano (2015), because more events are associated to tip-jets. It remains uncertain how the results would change if a more realistic distribution of wind events in general (and tip-jets specifically) considered.
I appreciated the effort made to quantify the uncertainty presented at the end of the discussion (around l. 399-400). The authors should also discuss how the idealized composite forcing may limit the generalizability of their conclusions, and how the importance of heat loss compared to wind stress could vary across the entire spectrum of tip jets. This could potentially lead to less extreme canonical events compared to the 2014-2015 period but an increase in the occurrence of other types of tip jets.
3. In the introduction, the authors state that “variations in wind stress can drive […] Ekman-driven freshwater export from the Greenland shelf near Cape Farewell.” In the literature, tip jets are indeed suspected to have an impact on this shelfwater export to the gyre (Duyck et al. 2022, Coquereau et al. 2024 …). However, in the modeling framework, the applied tip-jet pattern does not extend to the shelf and is confined to the deep ocean (Fig 1). This raises questions about how the results shown, where tip jets predominantly drive a salinification of the Irminger Sea, reconcile with these previous results. Does the modeling framework underestimate the shelf water export, or is this process negligible compared to the enhanced vertical mixing of the surface ocean induced by tip-jets?
4. The wind stress anomaly is applied within a confined region and gradually decreases to zero over a buffer zone. However, any lateral gradient in wind stress will cause Ekman divergence or convergence at the forcing boundary, potentially leading to spurious upwelling or downwelling that could affect the results. Have you checked for any systematic vertical velocity or MLD signal around your forcing area? Do you think this could impact your results?
Minor Comments
References
A. K. DuVivier, J. J. Cassano, Exploration of turbulent heat fluxes and wind stress curl in WRF and ERA- interim during wintertime mesoscale wind events around southeastern Greenland. J. Geophys. Res. 120, 3593–3609 (2015).
Duyck, E., Gelderloos, R., and de Jong, M. F.: Wind‐Driven Freshwater Export at Cape Farewell, J. Geophys. Res. Oceans, 127, https://doi.org/10.1029/2021JC018309, 2022.
Arthur Coquereau et al. ,Extreme wind events responsible for an outsized role in shelf-basin exchange around the southern tip of Greenland. Sci Adv 10,eadp9266(2024).DOI:10.1126/sciadv.adp9266