the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 13 Feb 2026
Rapid Communication: Two-phase Arctic cryosphere patterns associated with delayed Norwegian Sea warming peak during the Last Interglacial
Abstract. The Last Interglacial (LIG; ~129–117 ka), when global temperatures were comparable to today, provides a valuable testbed for understanding how Arctic cryosphere–ocean interactions may shape regional climate responses. By synthesizing multiproxy records from the Norwegian Sea, North Atlantic, and Southern Ocean, we identify two previously unrecognized phases of delayed Norwegian Sea warming during the early LIG. Phase I (~129–128 ka) was marked by widespread winter sea ice and freshwater input from the retreating Eurasian ice sheets, and was likely associated with large-scale reorganizations of the Atlantic Meridional Overturning Circulation (AMOC). Phase II (during 128–124 ka) featured a localized delay in Norwegian Sea warming peak, likely associated with enhanced Arctic sea-ice melt and freshwater export rather than residual deglacial meltwater. This two-phase framework suggests that sea ice-driven feedbacks, rather than lingering Eurasian ice sheets, were linked to the Phase II delay. Importantly, Phase II does not necessarily imply a synchronous central Arctic cooling, and may instead reflect a localized “warming hole” in the Norwegian Sea. These findings refine the context for the 127 ka Coupled Model Intercomparison Project (CMIP) paleoclimate simulations and further highlight the potential role of Arctic sea ice dynamics in modulating the AMOC and subpolar climate anomalies.
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Status: final response (author comments only)
- RC1: 'Comment on egusphere-2026-732', Anonymous Referee #1, 07 Apr 2026
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RC2: 'Comment on egusphere-2026-732', Anonymous Referee #2, 07 Apr 2026
Ezat and Bakker come up with a notion that the post-glacial oceanographic evolution in the Norwegian Sea during the last interglacial was affected by a 2-phase “Arctic cryosphere pattern” which led to a delayed warm peak in the Norwegian Sea facilitated by a so-called “warming hole”. They refer to 3 nearby sediments cores located at the Iceland-Faroe-Ridge.
The paper is a summary of some results from the last interglacial of the Nordic seas, but basically only looking at the surface water changes of a rather constraint small area in the southernmost Norwegian Sea. The paper ignores almost completely the substantial data that is available from the wide ranges of important parts of the Nordic Seas and in particular along the pathway of Atlantic-derived waters towards the Arctic Ocean through Fram Strait. Especially published cores from farther north, for example on and around the Voring Plateau area, give clear evidence of the various phases during 5e. Regardless of the actually published age models – age models beyond radiocarbon are indeed subject to change anyway – but many published core records could be easily compared on the basis of existing proxy records with those from the IFR.
The one and only claim of the paper is actually that the late delay of the 5e-development is due to enhanced Arctic sea-ice melt contradicting previously proposed long-lasting deglacial effects as prime cause. The authors now claim to have identified a 2-phase development. Apart from the fact that there are more than just 2, in general, it is nothing really new as others have already shown and discussed such phases in detail, too.
In addition, the authors somehow misinterpret the main finding of others: For one, it has already been stated previously by others that the “delay” was caused by residing meltwater after the main deglaciation was concluded – ie. disappearance of iceberg IRD. But icebergs only indicate calving activity on land-ocean margins not how long the abounding western Eurasian continental areas (eg, Norway and Arctic archipelagos farther north) were still glaciated long after the icebergs had vanished from the ocean. And second, the main thing of the previous findings on the delay is that meltwater in vast areas of the Nordic Seas suppressed the inflowing Atlantic water at the very surface, forcing it to flow at greater depth for a considerable time. Only after that meltwater had ceded to exist, did the warm Atlantic water affect the actual ocean surface thus causing the “delay”.
The authors now suggest that enhanced melting of Arctic sea ice is the lone cause for the delay. I wonder how does that work in an overly warm interglacial that apparently had hardly any sea-ice left in the summer and thus could not build up substantial amounts of thick-enough sea-ice during ensuing winters? Work in the Fram Strait clearly show that the delay is found there too, and seemingly much more drastic than further south (see previous work by Zhuravleva et al. from the eastern side, and 2025 by Zehnich et al. for the western Fram Strait); there is also a new work on the last interglacial by Sicard et al. which might be useful.
As mentioned, all data shown now were already published, very few by others, but all relevant ones by Ezat (mostly in the 2024 publication). That being said, however, is no proof that all the proxies employed previously are justified tools. Using, for instance, Ba/Ca in Np as indicator of sea-ice meltwater, contrary to iceberg meltwater, is a far shot from having been properly validated.
This paper is not a study which provides anything new in terms of data. Just the opposite, it is more of a contemplation that muses about a “potential” subject of interest to some. I don’t see the merit of this manuscript for the wider paleoclimate community. As a “rapid communication” it should be rejected.
Few further notes (there could be many more):
Because the relevant cores are from the shallow and rather restricted entrance gateway into the Nordic Seas, they undoubtedly are related to the surface waters in the southern Norwegian Sea. But these cores alone have little to say about the entire Nordic Seas, and certainly even much less about Arctic proper which is even farther north.
Phase 1 is described as 1 ky long (129-128ka), in main figure 1 it starts much earlier and clearly is nothing but part of deglacial Termination 2.
The increasing re-occurrence of polar Np after 124 ka (making up almost entirely the high carbonate content; thus, this proxy reflects shell abundance not warmth as stated(!) which is quite typical for the Nordic Seas in general and rather specific near the end of 5e. Together with increasing IRD means melting icebergs, and hence a surface salinity drop and potentially winter sea-ice. That BPIP25-Ip25 etc. does not show up is likely due to decreased sedimentation rates, causing massive degradation of organic matter, the principal bearer of biomarkers. This might indeed indicate a limitation of this so-called sea-ice proxy and associated biomarkers.
Fig. 1: f and c have faulty y-scales
Fig B1: it misses the “i” label
Note to the Editor:
This so-called paper strikes me as being a bit odd considering both its intention and what’s in it for the paleo-community in terms of novelty.
1- The latter certainly is hardly there – data-wise it’s just a reiteration of Ezat’s own recent publication (2024 in Nat comm) – for a Rapid Communication I would expect something surprisingly new. Instead what I see is a negligence of other peoples’ work and interpretations who actually have generated data on the very subject in the Nordic Seas too.
2- And the former relates to the co-author Bakker, by record mainly a modeler. His contribution is basically zero, at least nothing in the manuscript relates to any of his work, according to the references listed. That makes me wonder if the authors use the rapid communication platform as a pretext, hoping for a quickly citable reference for something that is already in their pipeline, namely a LIG-CMIP simulation using their suggested “warming hole” as the principle novel idea? Of course, I may be wrong...just a thought.
Citation: https://doi.org/10.5194/egusphere-2026-732-RC2 -
RC3: 'Comment on egusphere-2026-732', Anonymous Referee #3, 11 Apr 2026
Ezat et al. synthesize existing records from the Norwegian Sea, North Atlantic, and one Southern Ocean site to propose a two-phase pattern of Norwegian Sea surface warming during the Last Interglacial (LIG): (1) an early phase associated with increased IRD and a weakened AMOC, and (2) a delayed warming of the Norwegian Sea relative to North Atlantic SSTs during ~128–124 ka. The authors attribute this pattern to enhanced southward export of Arctic sea ice meltwater.
I agree with the other posted reviews that the manuscript does not present sufficiently novel insights. Both the hypothesis and much of the dataset have already been published or synthesized in Ezat et al. (2024, Nature Communications), and the current study does not substantially advance beyond that work.
I also find the proposed mechanism linking increased Arctic meltwater export to suppressed convection in the Norwegian Sea to be speculative. If the Arctic experienced warming and reduced sea-ice extent during the LIG, it is counterintuitive and against my experience why meltwater export to lower latitudes would increase. Moreover, since the authors cite Guarino et al. (2020)'s modeling work as support for higher SSTs and reduced sea ice during Phase II, the associated changes in freshwater export should be testable. Analysis of this model or similar LIG simulations from PMIP4 would strengthen the argument but is currently missing.
Finally, the use of the tephra layer as a key criterion for excluding certain records requires further clarification. More detail is needed about what this tephra layer is. Also, it is unclear why the same criterion is not applied to the North Atlantic records. If the goal is to compare records chronologically, consistent selection criteria should be used across regions.
A figure showing the core locations, at least those ones from the North Atlantic and Norwegian Sea would be helpful.
Citation: https://doi.org/10.5194/egusphere-2026-732-RC3
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As far as I can see, the present manuscript does not present any new data or information than that already appearing in Ezat et al. (2024). The only difference is that now the start of the Last Interglacial has been moved from 128 to 129 ka and thus the so-called Phase I (129-128 ka) now includes the impact of the last part of glacial meltwater originating from remnants of the Fennoscandian Ice Sheet (FIS) and shows winter sea ice extending in the southern Nordic Seas. Phase II (128-124 ka), is associated with enhanced Arctic sea-ice melt and freshwater export, as suggested by Ezat et al. (2024).
The evidence for the switch from glacial meltwater to Arctic sea-ice meltwater remains difficult to assess. The terminal Heinrich stadial HS11 would have led to extreme cooling in the North Atlantic and downstream Europe and may have arrested melting of the FIS. The absence of IRD from 128 ka merely shows that FIS had retreated from the coastline. The decline in Ba/Ca values in N. pachyderma does indeed provide evidence of decreased glacial runoff, though it is not clear (at least to me) whether the distance from the Norwegian coast to the southern Norwegian Sea sites could allow for continued runoff from a small residual ice sheet that remained undetected by the Ba/Ca proxy at 19PC core. The increase in d18O values of N. pachyderma is used as further evidence for a cessation of glacial meltwater influx, presumably because the ice sheet d18O is typically lighter than sea ice d18O. Missing however from the data in the present MS (and in Ezat et al. (2024)) is a discussion of the temperature component of the d18O of meltwater originating from residual FIS and from sea ice; a deconvolved record of SST and d18O of seawater may have been of assistance here.
Finally, the main premise of the study based on inferred melting of Arctic sea ice rests on contentious evidence, as the authors also concede here (e.g. Stein et al., 2017; Vermassen et al., 2023). In the absence of any new material to address these issues, I am afraid I have no choice but to recommend rejection.
PS I have to say that the quality of Fig. 1 and Fig. B1 is not up to standard. The x-axes are too short and the lines too thick to discern details. The use of dark blue, black and brown colors for the three marine sites in Fig. B1 are ill-chosen as it becomes near-impossible to distinguish them.