Mapping the inflow and impact of warm Atlantic water
to the Barents Sea and Arctic Ocean
Ocean currents transport heat by carrying warm water into colder areas of the globe.
Warm and salty Atlantic Water enters the Arctic Ocean through Fram Strait north of Svalbard and the Barents Sea.
Therefore, the amount and temperature of Atlantic water affects the heat balance and ice cover of the Arctic Ocean.
In this storymap, you can follow the Atlantic water flow to the Arctic Ocean disclosed by the newest scientific discoveries by the Nansen Legacy project .
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Ocean heat transport to the Arctic Ocean has increased during recent decades, driven by an increase in Atlantic water temperatures.
These changes are especially large at the Barents Sea entrance where the water has warmed about 1˚C.
The ocean heat transport by Atlantic Water has varied on different time scales in the past and will do so in the future. In the long-run, heat transport by Atlantic water will increase further due to warmer water temperatures, while the amount of Atlantic water will decrease.
Variations in the Atlantic water heat transport are mainly linked to changes in the wind systems in the Nordic Seas as well as variations in heat exchanges between the atmosphere and ocean.
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The figure on the right side shows time series of simulated (black lines) and observed (thin magenta lines) anomalies of annual mean Atlantic Water temperatures in the Barents Sea opening and Fram Strait.
Find out more: Muilwijk et al. 2018 ; Årthun et al. 2019
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Atlantic Water is cooled less in the Barents Sea now than earlier, leading to warmer water masses being exported to the Arctic Ocean.
The reason for the less efficient cooling mechanisms is a weaker atmospheric cooling and vertical mixing of the Atlantic water in the Barents Sea. This results in warmer Atlantic water reaching farther north, coinciding with the northwards retreat of the ice edge.
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The figure on the right side shows changes in the climate system of the Barents Sea. The upper panel shows the water temperatures near the bottom of the Barents Sea in the periods 1985-1999 (left) and 2004-2018 (right). The thick grey lines indicate the mean sea-ice edge (15% concentration) in March for the two periods. The lower panel conceptualizes the changes of the Barents Sea cooling machine during 1985-1999 (left) and 2004-2018 (right).
Find out more: Skagseth et al. 2020
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What controls the inflow of warm Atlantic water to the Arctic Ocean north of Svalbard?
More stratified waters and stronger currents, together increase the potential vorticity in the outer part of the West Spitsbergen Current.
Stronger vorticity – the rotation tendency of the currents - guides more of the flow north of Spitsbergen to go into the Arctic Ocean, and decreases the southward divergence of the current through the Greenland Sea.
Hence, an increase in Atlantic Water temperature may proliferate the oceanic heat transport into the Arctic Ocean in two ways – through increased water temperatures as well as increased inflow of Atlantic Water into the Arctic Ocean north of Spitsbergen.
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The figure on the right side shows the average potential vorticity of the water masses between 150 and 500 m. The potential vorticity offshore of the West Spitsbergen Current was higher during increased pulses of inflow to the Arctic Ocean (right panel).
Find out more: Crews et al. 2018
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Inflow of warm Atlantic water keeps the ocean north of Svalbard ice free well into winter, as sea ice drifting into the region is efficiently melted away.
The open waters allow for episodically substantial loss of ocean heat to the atmosphere, cooling the Atlantic water flowing eastwards into the Arctic Ocean.
The area north of Svalbard first turns ice-covered when the melting of sea ice has led to the formation of a cold and fresh water layer at the surface of the sea, insulating imported sea ice from the warm Atlantic water.
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The figure on the right side illustrates the main processes leading to Atlantic Water cooling north of Svalbard during two periods; autumn to early winter and spring to early summer.
Find out more: Renner et al. 2018
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Ocean heat transport by Atlantic water is a good predictor of winter sea ice extent in the Barents Sea.
The impact of Atlantic water will, however, weaken in the future when sea ice retreats beyond the Barents Sea and into regions less influenced by Atlantic water.
Periods with increasing sea ice cover in the Barents Sea are still possible also in the future due to variations in the strength and character of the Atlantic flow.
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The figure on the right side shows the extent of Atlantic water (defined as where the water at 200m has >1C) and the winter sea ice edge (defined as 50% sea ice cover) for different decades.
Find out more: Årthun et al. 2019
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As Arctic regions become seasonally ice free, future ice loss will increasingly take place during winter.
This is already evident in the Barents Sea, which has lost its summer ice cover and which now is experience extensive sea ice loss also during winter.
Projections indicate that the Kara Sea will be the first currently perennial ice-covered sea to become ice free in September.
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The figure on the right side shows the monthly trends in sea ice extent for different Arctic seas in the period 1979 to 2016. Months are ordered from March to March, and centered around September.
Find out more: Onarheim et al. 2018