Abstract
The northward flow of warm and saline Atlantic Water through the eastern Nordic Seas sustains a spring-bloom ecosystem that hosts some of the world’s largest commercial fish stocks. Abrupt climatic changes, or changes beyond species-specific thresholds, may have severe effects on species abundance and distribution. Here, we utilize a numerical ocean model hindcast to explore the similarities and differences between large-scale anomalies, such as great salinity anomalies, and along-shelf hydrographic anomalies of regional origin, which represent abrupt changes at subannual time scales. The large-scale anomalies enter the Nordic Seas to the south and propagate northward at a speed one order of magnitude less than the Atlantic Water current speed. On the contrary, wind-generated along-shelf anomalies appear simultaneously along the Norwegian continental shelf and propagate northward at speeds associated with topographically trapped Kelvin waves. This process involves changes in the vertical extent of the Atlantic Water along the continental slope. Such a dynamic oceanic response both affects thermal habitats and has the potential to ventilate shelf waters by modifying the cross-shelf transport of nutrients and key prey items for early stages of fish.
Highlights
The heat content and water mass characteristics of the Nordic Seas are controlled by the inflow of warm and saline Atlantic Water (AW) in the southeast (e.g., Hansen and Østerhus 2000) and cold and less saline Arctic-influenced water masses in the northwest (e.g., Rabe et al 2013)
Pronounced minima are observed during the mid-1960s, late 1970s, late 1980s, and mid1990s, which is consistent with the chain of both positive and negative Great Salinity Anomalies (GSAs) reported by Sundby and Drinkwater (2007)
The model exaggerates the salinity anomaly associated with the GSA of the 1990s, the modeled temperature is close to the observed temperature during this period (Fig. 2)
Summary
The heat content and water mass characteristics of the Nordic Seas are controlled by the inflow of warm and saline Atlantic Water (AW) in the southeast (e.g., Hansen and Østerhus 2000) and cold and less saline Arctic-influenced water masses in the northwest (e.g., Rabe et al 2013). Negative salinity anomalies, commonly termed Great Salinity Anomalies (GSAs), have been identified in the northeastern North Atlantic and downstream (northward) in the eastern Nordic Seas during the last 50 years. Assuming a constant salt diffusion, a reduced (increased) volume transport through the Faroe-Shetland Channel causes a reduction (increase) in the downstream salt transport This relationship explains why the advection speed of a GSA is much lower than the AW current speed. We argue that the short-term oceanic adjustments to transient changes in regional atmospheric circulation, less durable than the GSAs, may play an important role in the ecosystem functioning Our understanding of these processes and ability to distinguish between them in time-series analyses that relate climate signals to biological effects has great implications for our general understanding of how marine species in the Nordic Seas ecosystem may respond to expected changes in their environment
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
