The transport of freshwater through the Fram Strait

Closeup of a northern fulmar in flight over the open ocean.
Photo: Stein Ø. Nilsen / Norwegian Polar Institute

The transport of freshwater in the East Greenland Current through the Fram Strait is monitored because it can affect the regional climate in northern Europe. This is one of the places where the inner dynamics of the Arctic Ocean can be measured in water masses flowing out of the Polar basin. Freshwater affects the formation of deep water. This in turn influences ocean currents, which can affect the climate in northern Europe.

What is being monitored?

Freshwater flux

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The top figure shows the average monthly southward flow of freshwater in the East Greenland Current in the Fram Strait. The freshwater transport is calculated relative to a reference salinity of 34.9. There are three different time series for 2 different measurement locations and different lateral extents:
1. flux at 79°N between 1°W and 6.5°W (1997-2002)
2: flux at 78°50'N between 1°W and 6.5°W (2002-2015)
3: flux at 78°50'N between 1°W and 8°W (2003-2015)
Comparing these time series, one can see that it matters at which latitude one measures, and how far west on the shelf one measures. Time series #3 78°50'N between 1°W and 8°W (2003-2015) is at present, the best possible year-round estimate.
The bottom figure shows the average flow of freshwater in September in the East Greenland Current in the Fram Strait. The data is obtained from a combination of CTD from the annual Fram Strait Cruise and mooring data during September.  These values are easier to update.

 

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The figure shows the average flow of freshwater in September in the East Greenland Current in the Fram Strait. The data is obtained from CTD data from the annual Fram Strait Cruise in August/September. September values based on CTD data referenced to mooring data is presented here because updates of the monthly mean time series up to 2016 are work in progress. 

Status and trend

The top figure shows there are considerable variations during the year and throughout the monitoring period. It is important to consider the three time series separately since they are from different locations and different width of the East Greenland Current. The amount of freshwater leaving the Arctic does not show a longterm trend but there was a period with larger than normal freshwater flux from 2010 to 2012 and in 2013. This freshwater anomaly was mostly due to increased southward flow (2010-2011) and secondly due to low salinity (2012-2013).

Results to date based on time series at 78°50'N between 1°W and 8°W (2003-2015) show that the East Greenland Current on average transports approximately 2217km3 of freshwater out each year. In addition, a certain amount of fresh water flows over the Greenland shelf west of 8°W. This amount is uncertain since there are no year-round measurements there. In addition, freshwater also comes as sea ice, amounting to around 2600km3 per year. All told, this gives at least ~4800km3 of freshwater export a year.

Causal factors

The increased freshwater flux in 2010-2012 and 2013 was associated with a temporal release of freshwater from the western and central Arctic. The accumulation of freshwater in the Canadian Basin which occurred in the 2000s, stagnated in 2009. The amount of freshwater within the Arctic Ocean is, however, still very large coming from increasing discharge from rivers, more inflow from the Pacific Ocean and ice melting in the Arctic Ocean. The clockwise atmospheric circulation makes that freshwater is stored in the Canadian Basin. A release of freshwater from the Arctic Ocean may happen in the near future if the atmospheric circulation becomes anti-clockwise as was the case in the early 1990s.

The monitoring of the freshwater flux in the Fram Strait would reveal this.

Consequences

The measurements reveal great variability from month to month, with a significant variation from year to year. What is important in the context of the climate, however, is if there is a sustained development over time.

The surface water in the Greenland Sea, the Irminger Sea and the Labrador Sea (situated east of Greenland and Canada, respectively) is exposed to strong cooling. In addition, salt is precipitated when sea ice forms.

The cooling down and the supply of salt cause the surface water to become heavier and to sink, thus forming deep water. The sinking water is replaced by warmer water from the south along with water driven northward by the wind. This so-called overturning circulation is the main cause of the relatively mild climate in large parts of northern Europe, including Norway.

The supply of freshwater counteracts the formation of deep water by making the surface water lighter. If sufficient freshwater is supplied over time, it can slow down the supply of warm water from the south, thus affecting the climate in northern Europe.

Large quantities of freshwater are collected in the Arctic. This water comes from precipitation, rivers and melting ice. Some also comes from Pacific Ocean water, which is less saline than Atlantic Ocean water. A significant proportion of this freshwater leaves the Arctic Ocean via the East Greenland Current in the Fram Strait and ends up in the Greenland Sea and the Labrador Sea, where it may affect the formation of deep water, as described above.

This freshwater flux increase from 2010-2013 has contributed to freshening of the North Atlantic but it is at present unclear what the effect was on dense water formation.

About the monitoring

The Norwegian Polar Institute has been monitoring this flow of freshwater since 1997 using permanently deployed instruments and annual cruises across the Fram Strait The data underlying the freshwater flux estimates come from this monitoring.

This monitoring provides a better understanding of the system, since the time series can be compared to other time series from other parts of the climate system.

Places and areas

Relations to other monitoring

Monitoring programme
International environmental agreements
Voluntary international cooperation
Related monitoring