The transport of freshwater through the Fram Strait
Last updated 4 October 2022
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
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 2°W and 8°W (2003-2019)
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 2°W and 8°W (2003-2019) 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 (Karpouzoglou et al., 2022).
(Cite these data: Norwegian Polar Institute (2022). Freshwater flux in the Fram Strait. Environmental monitoring of Svalbard and Jan Mayen (MOSJ). URL: https://mosj.no/en/climate/ocean/freshwater-flux-fram-strait.html)
The figure shows the average southward 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.
(Cite these data: Norwegian Polar Institute (2022). Freshwater flux in the Fram strait in September. Environmental monitoring of Svalbard and Jan Mayen (MOSJ). URL: https://mosj.no/en/climate/ocean/freshwater-flux-fram-strait.html)
Details on these data
| Last updated | 4 October 2022 |
| Update interval | Two year |
| Next update | September 2024 |
| Commissioning organization | Ministry of Climate and Environment |
| Executive organization | Norwegian Polar Institute |
| Contact person | Laura de Steur |
Method
The monthly mean time series of freshwater transport is based on year-round oceanographic mooring data and CTD data collected on a section across Fram Strait at at 79·N (from 1997 to 2002) and later on at 78°50’N (from 2002 to present). The moorings from the East Greenland Current in Fram Strait are recovered once per year during the annual Fram Strait cruise by the Norwegian Polar Institute. The cruise typically takes place in August–September when the sea ice concentration and extent is at its minimum.
The mooring data delivers high-resolution salinity and velocities from instrumentation at fixed depths varying between 50 m and 2500 m. SBE37 Microcats provide salinity each 15 minutes, while current meters (Aanderaa RCM8, RCM9, RCM11, Seaguards, or RDI 300kHz ADCPs) provide velocity data typically each hour. Further details, for example on how data gaps in velocity and salinity have been dealt with, are available in de Steur et al., 2018. The CTD data is included in the calculation in order to obtain realistic stratification in the vertical between mooring instruments. The freshwater transport is determined relative to a reference salinity of 34.9 and is integrated between the surface and the 34.9 isohaline. In the study by Karpouzoglou et al. in 2022, the method is improved by including continuous data between 2014-2019 from instruments at approximately 25-30 m below the surface in the western Framstrait. This data has also been used to optimize estimates from before 2015.
The transport is determined across the East Greenland Current between 6.5°W and 0°W between 1997 and 2003, and between 8°W and 2°W from 2003 onward. Expanding the array up to 8°W allowed for a much better coverage of the outflow and delivers the best possible estimate at present. It still implies, however, that we do not cover all of the broad east Greenland shelf (west of the 8°W) and hence the freshwater transport may be underestimated. For example, CTD data in September show that there may be extra fresh water transport on the shelf – between 400 to 1000 km3 per year. At present, we are looking for opportunities to add more instrumentation and novel technology to the Fram Strait mooring array to fill those data gaps.
September values based on CTD data referenced to velocities from the moorings is presented here because updates of the monthly mean time series up to 2019 is work in progress. The September mean freshwater transports are presented as obtained from the CTD data from the cruise in August/September. The absolute geostrophic velocity is obtained from calculating the geostrophic velocity from the hydrographic section data which is then referenced to the vertically averaged monthly mean velocity from mooring data in September. The freshwater transport is determined again relative to 34.9 and is integrated between 8°W and 0°W. The standard deviation is 583 km3/year.
Quality
The WOCE protocol documents and Sea-Bird Electronics application note provide detailed descriptions of the procedures for collecting and calibrating hydrographic data which are followed during annual Fram Strait cruises. CTD data collected during annual cruises are used to check the quality of data collected by moored instruments. The Sea-Bird SBE37 Microcats from the ocean moorings are send to Sea-Bird each year for calibration.
Hydrographic and measurement techniques closely follow WOCE protocols with additional calibration following the procedure described in Sea Bird Electronics Application note 31:
- C. Stalcup: Salinity measurements, In: US WOCE Hydrographic Program Report WHPO 91-1,WOCE Report No.68/91,1991.
- I. Gordon, J. C. Jennings, A. A. Ross and J. M. Krest: A suggested protocol for continuous flow automated analysis of seawater nutrients (phosphate, nitrate, nitrite and silicic acid) in the WOCE Hydrographic Program and the Joint Global Ocean Fluxes Study, WOCE Hydrographic Program Office, Methods Manual WHPO 91-1,1993.
- Sea-Bird Electronics: Computing Temperature and Conductivity Slope and Offset Correction Coefficients from Laboratory Calibrations and Salinity Bottle Samples. Application note 31.
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. The decrease in freshwater flux after 2015 can be explained by a reduction in the expansion of polar water in the East Greenland Current, an increase in Atlantic water and a reduction in current speed thorough the Fram Strait.
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
- None
Voluntary international cooperation
- None
Related monitoring
- None
Further reading
Publications
- de Steur, L., Hansen, E., Gerdes, R., Karcher, M., Fahrbach, E., & Holfort, J. (2009). Freshwater fluxes in the East Greenland Current: A decade of observations. Geophysical Research Letters 36(23). https://doi.org/10.1029/2009GL041278.
- de Steur, L., Peralta‐Ferriz, C., & Pavlova, O. 2018. Freshwater export in the East Greenland Current freshens the North Atlantic. Geophysical Research Letters 45(24). https://doi.org/10.1029/2018GL080207.
- Haine, T. W., Curry, B., Gerdes, R., Hansen, E., Karcher, M., Lee, C., … & Woodgate, R. (2015). Arctic freshwater export: Status, mechanisms, and prospects. Global and Planetary Change, 125, 13-35. https://doi.org/10.1016/j.gloplacha.2014.11.013.
- Holfort, J., & Hansen, E. (2005). Timeseries of Polar Water properties in Fram Strait. Geophysical Research Letters 32(19). https://doi.org/:10.1029/2005GL022957.
- Jahn, A., Aksenov, Y., de Cuevas, B. A., De Steur, L., Häkkinen, S., Hansen, E., … & Zhang, J. (2012). Arctic Ocean freshwater: How robust are model simulations?. Journal of Geophysical Research: Oceans, 117(C8). https://doi.org/10.1029/2012JC007907.
- Karpouzoglou, T., de Steur, L., Smedsrud, L.H., & Sumata, H. (2022). Observed Changes in the Arctic Freshwater Outflow in Fram Strait. Journal of Geophysical Research: Oceans 127(3), e2021JC018122. https://doi.org/10.1029/2021JC018122.
- Proshutinsky, A., Dukhovskoy, D., Timmermans, M.-L., Krishfield, R., & Bamber, J.L. (2015). Arctic circulation regimes. Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 373(2052), 20140160. https://doi.org/10.1098/rsta.2014.0160.
- Tsubouchi, T., Bacon, S., Aksenov, Y., Garabato, A. C. N., Beszczynska-Möller, A., Hansen, E., … & Lee, C. M. (2018). The Arctic Ocean seasonal cycles of heat and freshwater fluxes: Observation-based inverse estimates. Journal of Physical Oceanography, 48(9), 2029-2055. https://doi.org/10.1175/JPO-D-17-0239.1.
