Between 2005 and 2008, the Norwegian Component of the Ecosystem Studies of Sub-Arctic Seas (NESSAS) studied atmospheric and advective forcing on the Barents Sea using retrospective analysis and modeling. Atmospheric processes such as the North Atlantic Oscillation (NAO) and seasonal cyclones affect temperature and salinity in the Barents Sea. Advection from the North Atlantic and surrounding Sub-Arctic seas also affects temperature and salinity. (Drinkwater 2011) These variables in turn determine the sea-ice extent. There is a corresponding affect on fisheries and primary production. Positive NAO, a greater number of cyclones, and advection of warmer water produce a warmer Barents Sea with less sea-ice. (Drinkwater 2011) This leads to increased primary production and greater fisheries. Additionally, in a warmer climate spawning sites will shift, fish populations will expand or retreat northward, and maturation will be faster. (Drinkwater 2011) These effects were compared to other seas at similar latitudes to the Barents Sea. Many similarities in responses to forcing and overall biological processes were observed. NESSAS recommends that further studies be carried out to better determine the effects of climate change on Sub-Arctic seas. —Katherine Recinos
Drinkwater, K., 2011. The influence of climate variability and change on the ecosystems of the Barents Sea and adjacent waters: Review and synthesis of recent studies from the NESSAS Project. Progress in Oceanography. 90, 47-61.
The NESSAS program, as previously mentioned, was the Norwegian version of the more regional Ecosystem Studies of Sub-Arctic Seas (ESSAS) program. The goals of both programs were the same; to examine how forcing, especially climate processes, effect physical oceanography, to look at how change affects marine ecosystems, and to see within those ecosystems how variability affects productivity and fish stocks. The results could be used to combat future climate change. The Norwegian program also compared the Barents Sea to other Arctic and Sub-Arctic seas.
Drinkwater begins with an overview of the NESSAS results. Researchers looked at the NAO which has both a positive and negative phase. During the positive phase, strong winds and storms blowing westward carry warm air and Atlantic water into the Barents Sea. During the negative phase, the winds are weaker; cold air and less Atlantic water are carried into the Barents Sea. The result is that positive phase NAO means higher sea temperatures in the Barents Sea and negative phase NAO means lower sea temperatures. Sea temperature affects how much ice forms and when it forms and melts which has important ecological consequences.
The NAO is associated with North Atlantic and Arctic cyclones. The NESSAS studies investigated the patterns of cyclones that affect the Barents Sea. An annual correlation was found between times of more intense Arctic cyclones and greater sea-ice cover. However, longer term sea-ice extent was determined by North Atlantic cyclones with a one to two year lag from presence of cyclones to noticeable effects on sea-ice. These effects are caused by the cyclones transporting different temperature waters into the Barents Sea.
A different type of forcing is moisture flux which controls the amount of freshwater input from rivers, runoff, and precipitation. Cyclones in northern latitudes play a role in moisture flux in Arctic and Sub-Arctic oceans and seas. Seasonal variability affects the influence of the cyclones on moisture flux; there is a greater link between moisture flux and cyclone activity in the spring, summer, and autumn. Atmospheric pressure patterns which produce cyclones and storms may also be changing. The Arctic/North Atlantic Oscillation (AO/NAO) pressure pattern used to have three centers of action but now has only two more northerly centers. This is leading to less atmospheric forcing and therefore a warmer Arctic overall.
Drinkwater then discusses the effects of advection on the Barents Sea. Not only does advection have the power to bring water of different temperature and varying salinities to the Barents Sea, it can also carry phytoplankton, zooplankton, and fish larvae to the Sea. Several studies were carried out as part of NESSAS to try and figure out what factors determine advection, and how advection specifically works on the Barents Sea and surrounding oceans. There are a series of differing salinity water masses known as the Great Salinity Anomalies (GSAs) which are either negative or positive anomalies. A gradient across the northwest to northeast Atlantic controls their movements. Due to advection, these water masses can affect Arctic waters and their respective salinities which affect, among other things, sea-ice formation. Other studies used moors to monitor the flow of water into the Barents Sea. This advection is important because it has major effects on the temperature of Barents Sea water, including heat fluxes. It is affected by cyclones, storms, seasonal variability, and the NAO.
The NESSAS study also looked at biological effects. The NORWECOM model, a coupled 3-D physical, chemical, and biological ocean model was used to examine primary production. The North Atlantic coastal waters and the waters off the coast of Norway had the highest primary production. Variability in primary production over the years was stated to be caused by the NAO. When the NAO is high, there is more mixing, a greater concentration of nutrients, and therefore greater production. When the NAO is low, the opposite is true. Researchers investigated the future of fish stocks by looking at past data on fish populations. A period of climate variability, the Atlantic Multidecadal Oscillation (AMO), produced a warming period in the 20thcentury that resulted in greater numbers of fish, northward spread of fish populations, changes in spawning areas, changes in timing of spawning, and faster growth and development for many cold-water species (ex. cod). It also caused an increase in primary production which helped increase fish abundance.
Drinkwater lists the results of comparative studies undertaken by NESSAS. The Barents Sea is experiencing similar effects from atmospheric forcing as other seas at similar latitudes and would be similarly affected by climate change. Many of the trends noted in the Barents Sea were also seen in other seas including advections affect on salinity and temperature, relationship of sea-ice to primary production, and spread of fish northward as temperatures increase.
The NESSAS study admits uncertainty where climate change is concerned. If warming continues, there could be a multitude of effects on fisheries, including increased yields. For example, one study showed that capelin (a small fish) spawning sites would move further north and east in the Barents Sea. The effects of climate change on physical properties of the Barents Sea could be mitigated by conflicting atmospheric processes such as the AMO and AMOC which could bring colder, saltier waters to the Arctic and Sub-Arctic.