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The East Greenland Polar Front as a Mediator of Climate‐Ocean‐Ecosystem Variability Along Southeast Greenland.

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Title: The East Greenland Polar Front as a Mediator of Climate‐Ocean‐Ecosystem Variability Along Southeast Greenland.
Authors: Gjelstrup, C. V. B.1,2 (AUTHOR) cvbgj@aqua.dtu.dk, Boje, J.1,3 (AUTHOR), MacKenzie, B. R.1 (AUTHOR), Post, S.3 (AUTHOR), Werner, K. M.4 (AUTHOR), Visser, A. W.1 (AUTHOR), Stedmon, C. A.1 (AUTHOR)
Source: Journal of Geophysical Research. Oceans. Oct2025, Vol. 130 Issue 10, p1-18. 18p.
Subject Terms: *Marine ecology, *Oceanography, *Biological productivity, *Climate change, Ocean gyres, Chlorophyll in water, Fronts (Meteorology)
Geographic Terms: Greenland, Arctic regions, Atlantic Ocean
Abstract: The southeast Greenland region features a confluence of Arctic‐ and Atlantic origin waters along the continental shelf‐break, forming the East Greenland Polar Front (EGPF). Here we examine the role of the EGPF in mediating climate‐ocean‐ecosystem variability. We observe systematic temporal variability in frontal intensity related to regional subpolar gyre (SPG) dynamics via gyre spin‐up. By combining sea surface temperature derived frontal metrics with sea surface height, sea‐ice concentration, surface chlorophyll‐a concentration, and fisheries survey data, we demonstrate how gyre‐induced oceanic variability is reflected in the shelf ecosystem. Elevated chlorophyll‐a concentrations along the continental slope correspond to periods when the SPG is in a negative phase, the Irminger Gyre is spun‐up and the EGPF is strong. This response in chlorophyll‐a is likely due to a combination of aggregation of phytoplankton at the frontal zone and enhanced new production fueled by increased nutrient availability. In addition to the temporal variability, the EGPF exhibits spatial variability on seasonal and interannual timescales across the wide Ammassalik shelf. As such, the EGPF has migrated 90 km shoreward in tandem with sea‐ice retreat since the early 2010s. This migration led to increased chlorophyll‐a concentrations over shallow banks and decreased chlorophyll‐a concentrations over the outer shelf and slope areas. Our findings underscore the critical role of the EGPF in mediating interactions between the physical and biological components of the southeast Greenland ecosystem. Plain Language Summary: The East Greenland region can be characterized as a transition zone between cold, fresh waters of Arctic origin and comparatively warm and salty waters of Atlantic origin. A strong hydrographic front, known as the East Greenland Polar Front (EGPF), separates the two domains. Frontal regions are commonly associated with elevated levels of biological productivity. This is also the case for East Greenland, where fishing efforts have historically been concentrated along the slope coincident with the EGPF. Here, we investigate the role of fluctuations in the position and intensity of the EGPF in shaping oceanographic conditions, and consequently biological productivity. We find the intensity of EGPF is related to open‐ocean gyre circulation. Sustained periods with strong gyre circulation favor a strong EGPF and enhanced surface chlorophyll concentrations along the southeast Greenland slope. In addition, we find that the EGPF migrates over the widest part of the shelf on seasonal and interannual timescales in tandem with the sea‐ice cover. This migration led to a redistribution of surface chlorophyll concentrations, with increased concentrations over shallow banks and decreased concentrations over the outer shelf and slope. This work highlights the central role of EGPF in mediating climate‐ocean‐ecosystem variability in southeast Greenland. Key Points: We present a climatology of East Greenland Polar Front intensity produced from daily sea surface temperature fields from 1993 to 2021The subpolar gyre drives variability in frontal intensity and impacts chlorophyll‐a patterns with a contracted gyre boosting concentrationsSea‐ice retreat coincides with a shoreward shift of the main front, altering the distribution of chlorophyll‐a over the Ammassalik shelf [ABSTRACT FROM AUTHOR]
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Abstract:The southeast Greenland region features a confluence of Arctic‐ and Atlantic origin waters along the continental shelf‐break, forming the East Greenland Polar Front (EGPF). Here we examine the role of the EGPF in mediating climate‐ocean‐ecosystem variability. We observe systematic temporal variability in frontal intensity related to regional subpolar gyre (SPG) dynamics via gyre spin‐up. By combining sea surface temperature derived frontal metrics with sea surface height, sea‐ice concentration, surface chlorophyll‐a concentration, and fisheries survey data, we demonstrate how gyre‐induced oceanic variability is reflected in the shelf ecosystem. Elevated chlorophyll‐a concentrations along the continental slope correspond to periods when the SPG is in a negative phase, the Irminger Gyre is spun‐up and the EGPF is strong. This response in chlorophyll‐a is likely due to a combination of aggregation of phytoplankton at the frontal zone and enhanced new production fueled by increased nutrient availability. In addition to the temporal variability, the EGPF exhibits spatial variability on seasonal and interannual timescales across the wide Ammassalik shelf. As such, the EGPF has migrated 90 km shoreward in tandem with sea‐ice retreat since the early 2010s. This migration led to increased chlorophyll‐a concentrations over shallow banks and decreased chlorophyll‐a concentrations over the outer shelf and slope areas. Our findings underscore the critical role of the EGPF in mediating interactions between the physical and biological components of the southeast Greenland ecosystem. Plain Language Summary: The East Greenland region can be characterized as a transition zone between cold, fresh waters of Arctic origin and comparatively warm and salty waters of Atlantic origin. A strong hydrographic front, known as the East Greenland Polar Front (EGPF), separates the two domains. Frontal regions are commonly associated with elevated levels of biological productivity. This is also the case for East Greenland, where fishing efforts have historically been concentrated along the slope coincident with the EGPF. Here, we investigate the role of fluctuations in the position and intensity of the EGPF in shaping oceanographic conditions, and consequently biological productivity. We find the intensity of EGPF is related to open‐ocean gyre circulation. Sustained periods with strong gyre circulation favor a strong EGPF and enhanced surface chlorophyll concentrations along the southeast Greenland slope. In addition, we find that the EGPF migrates over the widest part of the shelf on seasonal and interannual timescales in tandem with the sea‐ice cover. This migration led to a redistribution of surface chlorophyll concentrations, with increased concentrations over shallow banks and decreased concentrations over the outer shelf and slope. This work highlights the central role of EGPF in mediating climate‐ocean‐ecosystem variability in southeast Greenland. Key Points: We present a climatology of East Greenland Polar Front intensity produced from daily sea surface temperature fields from 1993 to 2021The subpolar gyre drives variability in frontal intensity and impacts chlorophyll‐a patterns with a contracted gyre boosting concentrationsSea‐ice retreat coincides with a shoreward shift of the main front, altering the distribution of chlorophyll‐a over the Ammassalik shelf [ABSTRACT FROM AUTHOR]
ISSN:21699275
DOI:10.1029/2025JC022669