State of the Arctic - Arctic oceanography
- 11:00 Rapid climate shift in Arctic warming hotspot driven by declining sea-ice import and freshwater loss
Authors: Sigrid Lind ( Institute of Marine Research ); Randi Ingvaldsen ( Institute of Marine Research ); Tore Furevik ( Bjerknes Centre for Climate Research )
The Arctic experiences the strongest warming on the planet, with recent decades’ loss of sea-ice unprecedented in observations. The Arctic warming is not uniform, but stronger in the eastern Arctic Ocean and further amplified in the northern Barents and Kara Seas—the Arctic warming hotspot—experiencing the most rapid surface warming and strongest decline in winter sea-ice concentration in the entire Arctic. Here, the warming extends into the lower atmosphere and throughout the water column, which is stratified with warm and saline Atlantic Water submerged below a fresher and colder Arctic layer, as in the interior Arctic Ocean. Interannual variability in the Arctic layer salinity determines the strength of the stratification and the amount of vertical mixing between the layers, and a fresher Arctic layer efficiently hinders large upward fluxes of heat from the deep. Large-scale changes in freshwater storage and transport have been documented for the Arctic Ocean, but the link to warming hotspots has not previously been established. Using an extensive set of hydrographic observations in the northern Barents Sea from 1970 to 2016, we document a sharp increase in ocean temperature and salinity after the mid-2000s. We further show that sea-ice import to the Barents Sea impacts the sea ice cover directly by adding ice but also indirectly through being the major freshwater source: A recent decline in the sea-ice import and a corresponding loss in freshwater has led to weakened ocean stratification, enhanced vertical mixing and increased upward fluxes of heat and salt from the deep Atlantic layer. The additional heat in the Arctic layer may explain the reduced sea-ice formation and increased heat loss to the atmosphere in winter, making this region the hotspot of Arctic warming. The associated salt flux involves a positive feedback that reduces the stratification and further enhances the vertical mixing. Unless the freshwater input should recover, the northern Barents Sea may soon complete the transition from a cold and stratified Arctic to a warm and well-mixed Atlantic climate regime. Such rapid climate shifts have previously only been documented indirectly from paleoclimate records, but is here extraordinary well documented and shown to be driven by freshwater loss, likely as a consequence of global warming. This implies that ocean stratification is a key to understand, model and predict the development into a new eastern Arctic that becomes warmer, weakly-stratified and seasonally ice-covered, with considerable upward fluxes of heat from the deep Atlantic layer.
- 11:30 Statistical position of the oceanic polar front in the Barents Sea
Authors: Ingrid H. Onarheim ( Equinor ); Sigurd H. Teigen ( Equinor ); Kenneth J. Eik ( Equinor )
The Barents Sea is a highly productive Arctic shelf sea and a transition zone between the temperate Nordic Seas and the cold Arctic Ocean. The polar front is a dominant oceanographic feature in the Barents Sea that separates warm, saline Atlantic water in the south from cold, fresh Arctic water in the north. As the polar front is associated with high biological production and is typically the southern border for sea ice, a good understanding of the position of the front is needed. In the western Barents Sea, the polar front is tied to the bathymetry, whereas the front is typically less distinct and less studied further east. The numerical ocean model hindcast archive SVIM is here used to assess the position and variability of the polar front throughout the Barents Sea between 1960 and 2016 at 50-100 m and 0-20 m depth. Based on probability density functions of temperature and salinity, we find that the polar front largely follows the bathymetry and that its position shows limited seasonal and interannual variations throughout the Barents Sea, except for near the Novaya Zemlya Bank. Although the position of the front appears stationary, the front is typically 2°C warmer in summer than winter, and the characteristic frontal temperature has increased by 1°C since 1960. West of 30°E, the position of the front agrees well with the front outlined in the management plan by the Ministry of Climate and Environment in 2011. Further east, however, we find that the topographic control persists, contrasting the front in the management plan. The climatological position of the polar front based on the SVIM archive is supported by results from the Nordic Seas Atlas.
- 11:45 Temporal and spatial variations in the frontal zone north of Spitsbergen
near synoptic measurements compared with an operational numerical ocean model
Authors: Petter Østenstad ( Norwegian Defence Research Establishment (FFI) )
Increased melting of the Arctic sea ice reveals new areas of open water within the Norwegian Economic Zone. This leads to an increased interest in the properties of the ocean environment in such areas, including oceanographic features such as fronts and eddies. Information about the average oceanographic situation is important, but equally important is knowledge of spatial and temporal variations. Temporal variation in this context is from hours to weeks. Both measurements and numerical ocean models can be used to increase this knowledge.
To gather new in situ data and information on oceanographic conditions in the seasonally ice-free waters north of Svalbard, the Norwegian Defence Research Establishment (FFI) in September, 2017 conducted an oceanographic survey north of Spitsbergen. Using the FFI research vessel R/V H U SVERDRUP II, a data set consisting of 73 vertical temperature and salinity profiles along 7 transect (each of length up to 60 km) from the continental shelf break north of Spitsbergen to the prevailing ice edge (to 81 20’ N) was collected. An ODIM Moving Vessel Profiler (MVP) was used and collected consecutive profiles along each transect. These near-synoptic measurements took only a few hours per transect.
In this paper we present the measurements and compare these with output from the ROMS 4km numerical ocean model run operationally by Norwegian Meteorological Institute. The measured transects covered the frontal zone between the Atlantic Water inflow (the Svalbard Branch of the West Spitsbergen Current) along the shelf and the colder Polar water masses. The possible detection of a cold core eddy will be described. The ocean model provided a reasonably good description of the main observed oceanographic structures. However, model-measurement discrepancies were found in vertical and horizontal temperature and salinity gradients, and the eddy was not predicted by the ocean model, probably due to coarse model resolution.
Wednesday 23rd January 2019
11:00 - 12:00