| 03 Sep 2026
Seasonal stratification controls on vertical nutrient exchange in a High Arctic fjord (Inglefield Bredning, NW Greenland)
Abstract. High Arctic fjords are changing rapidly under ongoing global warming yet remain comparatively understudied despite their sensitivity to shifts in sea ice, ocean temperature, and glacier dynamics. In northwest Greenland, Inglefield Bredning is influenced by marine-terminating glaciers and exchange with Baffin Bay and the North Water polynya, making it a representative system for assessing how physical changes in the Arctic propagate into fjord biogeochemistry. Here, we investigate how seasonal stratification develops across winter, spring, and early summer, and how it regulates vertical nutrient exchange and biological activity. A persistent Atlantic Water layer below ~220 m occupies the fjord year-round, forming a stable reservoir of heat and nutrients that defines the background hydrographic structure. However, strong vertical stratification limits exchange between this deep nutrient reservoir and the euphotic zone, where nutrient concentrations remain low throughout the year. Upper-water-column nutrient concentrations are higher in winter than in early summer, but do not indicate complete winter homogenization with deeper waters. Pronounced spatial variability along the fjord further reflects the influence of marine-terminating glaciers, with localized hydrographic modification suggesting that glacier-driven processes may intermittently enhance vertical nutrient supply. Chlorophyll concentration peak in summer, consistent with strong biological uptake under increasingly stratified conditions. Together, these results indicate that productivity in Inglefield Bredning is governed not by the magnitude of the deep nutrient reservoir itself, but by the availability if macronutrients and the physical processes controlling their transfer to the euphotic zone. As Arctic warming strengthens stratification while altering glacier dynamics and sea ice cover, future productivity in high Arctic fjords will depend critically on the evolving balance between mechanisms that restrict and promote vertical nutrient supply.
Review of Seasonal stratification controls on vertical nutrient exchange in a High Arctic fjord
By Anna Pedersen et al.
The paper presents an interesting dataset collected during four field campaigns based in Qaanaaq, Greenland. It describes the seasonal variability of the water column and nutrients and aims to identify the drivers and controls of the observed seasonality. The observations are quite unique, this fjord is in a remote location, and the seasonality that is described appears very much ‘as expected’ – but is nevertheless important to document. The data set thus provides an important addition to our current understanding of the seasonal biogeochemistry in Northwest Greenland. The paper is nicely written, and the figures are illustrative.
I only have one ‘major’ issue, and that is the lack of discussion of Glacially Modified Water (GMW). This water mass resides below the (fresher) surface layer and the denser (warmer and saltier) Atlantic layer. There are three places where this process is discussed, but the term is not used. There are simple models that can estimate the temperature and salinity of the GMW based on Subglacial Discharge and the depth of the marine terminating glacier. You need to discuss if it would be possible to calculate this water mass in your fjord. A good way to do this is described in Muilwijk et al (2022). This paper should be cited and you need to explain why such calculations are not done. It sounds like you don’t have the Subglacial Discharge volumes, but that could be estimated based on surface mass balance. Do you know the depth of the local ice fronts? Some more discussion is needed here.
I therefore suggest that the paper is accepted into Ocean Science once the one major and the few minor suggested changes below have been addressed.
Muilwijk et al (2022) Export of ice sheet meltwater from Upernavik Fjord, West Greenland, Journal of Physical Oceanography; doi: 10.1175/JPO-D-21-0084.1
Minor suggestions, corrections and comments:
Abstract – line 21: How can you know that “Arctic warming” strengthens stratification? First of all salinity matters too. Also the warming could be stronger at depth than in the polar layer close to the surface.
Line 33: longer open water seasons and reduced…. Not reduces.
Line 39: vertical mixing, not micing.
Line 83: The air temperature during the field campaigns varied from…. Not varies.
Line 225: decoupling from the winter mixed layer by the surface inflow. Not input.
Line 240: This data needs to be described in the Methods: (MicroCAT C-T sensors (SBE-37-SI) and RBRsolo4 temperature loggers), deployed at fixed depths (3, 10, 20, 30, 40, 60, 90, 120, 150, 200, 250, 300m).
Line 242: It is not correct to state “thermal stratification”, stratification depends on temperature and salinity. You should use the term “vertical temperature field”. Most Arctic fjords are stratified by salinity, and are UNSTABLE in their temperature contribution to density.
Line 244: Again is “Thermal stratification” wrong. Re-write, or quantify. There is no obvious sign of a an increased vertical temperature gradient.
Figure 6 caption, use a small sized a)
Line 268: (%saturation values!) something wrong here…
Line 288: NO_x
Figure 8: Caption and Figure. Full grey line is not visible.
Line 307: Despite surface cooling, stratification persists due to the halocline structure. So this fjord is also salt stratified. Hence – “thermal stratification” is utterly wrong.
Line 311: You need to explain how this can be true. How do you know that solar radiation penetrates the sea ice + snow layer? “With the transition to spring, increasing solar radiation initiates biological activity….”
Line 325: Fig. 5), indicating that freshwater input and glacier-driven processes
modulate mixing at sub-fjord scales. Here you need to discuss in relation to GMW as noted in the major comment.
Line 327: Do you mean: “a localized influence of glacier driven circulation on the vertical exchange” ?
Line 363: “Buoyant meltwater plumes entrain large volumes of nutrient-rich saline fjord water during their ascent (Bendtsen et al., 2015; Mortensen et al., 2011; Sciascia et al., 2013), subsequently settling beneath the low-salinity surface layer and generating subsurface cold-water anomalies.” This is GMW, you need to discuss in relation to GMW as noted in the major comment.
Line 380: “Furthermore, we see how the spring samples close to the marine-terminating glaciers are closer to the deep-water sample stoichiometry, indicating that the surface layer near the glaciers is supplied with nutrients from the deep reservoir in the AW layer.” Again – this is GMW.
Line 413: Widespread thinning and retreat of marine-terminating glaciers…
Line 417: potentially leading to reduced….
Line 421: Should be: “…. and similar High Arctic fjords and how they are governed by a balance between increasing stratification and mechanisms that enhance vertical exchange.”
Conclusion: Nice short and simple. All good here.