Formation and pathways of dense water in the Nordic Seas based on a regional inversion

Brakstad, Ailin; Gebbie, Geoffrey; Våge, Kjetil; Jeansson, Emil; Ólafsdóttir, Sólveig Rósa

doi:10.1016/j.pocean.2023.102981

Cited by 14 publications

(19 citation statements)

References 94 publications

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In the Nordic Seas, warm waters of Gulf Stream origin releases its heat to the atmosphere and returns south to the North Atlantic as a cold, dense current at depth (Brakstad et al, 2023;Chafik & Rossby, 2019;Eldevik & Nilsen, 2013;Smedsrud et al, 2022) (Figure 1a). This dense overflow water feeds the lower limb of the Atlantic Meridional Overturning Circulation (AMOC) (Dickson & Brown, 1994;Swift et al, 1980) and is therefore an important component of the global ocean circulation.

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confidence: 99%

Surface‐Forced Variability in the Nordic Seas Overturning Circulation and Overflows

Årthun

2023

Geophysical Research Letters

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Water mass transformation in the Nordic Seas and the associated overflow of dense waters across the Greenland‐Scotland Ridge (GSR) acts to maintain the lower limb of the Atlantic meridional overturning circulation. Here, we use ocean and atmospheric reanalysis to assess the temporal variability in the Nordic Seas overturning circulation between 1950 and 2020 and its relation to surface buoyancy forcing. We find that variable surface‐forced transformation of Atlantic waters in the eastern Nordic Seas can explain variations in overflow transport across the GSR. The production of dense water masses in the Greenland and Iceland Seas is of minor importance to overflow variability. The Nordic Seas overturning circulation shows pronounced multidecadal variability that is in phase with the Atlantic Multidecadal Variability (AMV) index, but no long‐term trend. As the AMV is currently transitioning into its negative phase, the next decades could see a decreased overflow from the Nordic Seas.

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confidence: 99%

Surface‐Forced Variability in the Nordic Seas Overturning Circulation and Overflows

Årthun

2023

Geophysical Research Letters

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“…Additionally, pointwise observations could be used instead of relying on already gridded products that might transfer their own biases to the TMI. With enough observations, a higher resolution TMI could be constrained, which would also improve the pathways (Brakstad et al., 2023). In addition, the TMI is a steady‐state approach and the findings presented here should be taken as such, that is, no variability or feedbacks are accounted for.…”

Section: Discussionmentioning

confidence: 99%

“…In our case, Ω is each of the OMZs considered (see Section 2.3), so that we are only tracing the volume of the OMZs back to surface and masking the rest of the ocean. The values in v tot corresponding to the interior ocean, match the amount of volume at Ω that crosses each interior grid cell i (Brakstad et al., 2023; Gebbie & Huybers, 2011).…”

Section: Methodsmentioning

confidence: 99%

On the Origins of Open Ocean Oxygen Minimum Zones

et al. 2023

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Recent work suggests that Oxygen Minimum Zones (OMZs) are sustained by the supply of oxygen‐poor waters rather than the export of organic matter from the local surface layer and its subsequent remineralization inside OMZs. However, the mechanisms that form and maintain OMZs are not well constrained, such as the origin of the oxygen that oxygenates OMZs, and the locations where oxygen consumption occurs. Here we use an observation‐based transport matrix to determine the origins of open ocean OMZs in terms of 1) OMZ volume, 2) oxygen that survives remineralization and oxygenates OMZs, and 3) oxygen utilization in the interior ocean that contributes to the oxygen‐deficit of OMZs. We also determine where the utilization of oxygen occurs along the pathways that ventilate the OMZs. Our results show that about half of the volume of OMZ waters originate in high‐latitude regions, but most of their oxygen is utilized for remineralization before they reach OMZs. Instead, OMZs are mostly oxygenated by tropical, subtropical and intermediate waters formed in nearby regions. More than half of the utilization of oxygen occurs in the tropics and subtropics, while less than a third occurs within the OMZs themselves. We therefore suggest that, in steady‐state, OMZs are primarily set by ocean circulation pathways that high‐latitude deep and old water upwards, with relatively low oxygen content.

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“…It is also the deepest passage between those two basins as it reaches 2,200 m (Østerhus & Gammelsrød, 1999). The Norwegian Sea Deep Water (NSDW), formed from a mixture of deep waters from the Greenland Sea (GSDW) and the Arctic Ocean, enters the Norwegian basin through a complex multi‐passage outflow system, which consists of the JMCh and other numerous pathways and gaps in the mid‐ocean ridge (Brakstad et al., 2023; Swift & Koltermann, 1988; Wang et al., 2021). However, the knowledge about these pathways allowing deep and intermediate Greenland waters to be exported to the Norwegian Sea is still incomplete despite its importance.…”

Section: Introductionmentioning

confidence: 99%

“…In the Nordic Seas, the surface circulation is mostly cyclonic, with the eastern part dominated by the Norwegian Atlantic Current carrying Atlantic-origin warm and salty water northward, while the western part is dominated by the East Greenland Current (EGC) carrying Polar-origin cold and fresher water southward (Jakobsen et al, 2003; Figure 1). consists of the JMCh and other numerous pathways and gaps in the mid-ocean ridge (Brakstad et al, 2023;Swift & Koltermann, 1988;Wang et al, 2021). However, the knowledge about these pathways allowing deep and intermediate Greenland waters to be exported to the Norwegian Sea is still incomplete despite its importance.…”

Section: Introductionmentioning

confidence: 99%

Structure and Variability of the Jan Mayen Current in the Greenland Sea Gyre From a Yearlong Mooring Array

Pellichero,

Lique,

Kolodziejczyk

et al. 2023

JGR Oceans

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The Jan Mayen Channel is located North of the Jan Mayen Island in the Nordic Seas, and is an important gateway for the exchanges of volume, heat and freshwater between the Greenland and the Norwegian basins via the Jan Mayen Current. Based on observations from moored instruments deployed on the shelf and the continental slope of the Jan Mayen Island from August 2017 to August 2018, we document the mean state and the variability of the currents, temperature and salinity and their associated vertical structure. We found that the main feature of circulation is an intense and permanent south‐eastward jet‐like current centered at 150 m depth, located on the 400 m depth slope, with a maximum mean magnitude of 7 cm·s−1. While the velocities recorded on the shelf are largely constant in speed and direction, without any strong seasonal cycle, the moorings located offshore are capturing larger anomalies on short time scales that are likely the signature of eddies passing across the mooring array. Overall, the variability of the transport across the section is correlated with the large‐scale wind pattern over the Nordic Seas, highlighting that the Jan Mayen Current is part of a complex system of currents that operates at larger scale in the region.

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Formation and pathways of dense water in the Nordic Seas based on a regional inversion

Cited by 14 publications

References 94 publications

Surface‐Forced Variability in the Nordic Seas Overturning Circulation and Overflows

Surface‐Forced Variability in the Nordic Seas Overturning Circulation and Overflows

On the Origins of Open Ocean Oxygen Minimum Zones

Structure and Variability of the Jan Mayen Current in the Greenland Sea Gyre From a Yearlong Mooring Array

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