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| Great Salinity Anomaly | |
|---|---|
| Name | Great Salinity Anomaly |
| Location | North Atlantic Ocean, Nordic Seas |
| Period | 1968–1980s (major events); recurring episodes thereafter |
Great Salinity Anomaly is a term used to describe large-scale, anomalous decreases in surface and intermediate salinity observed in the North Atlantic Ocean and Nordic Seas during the late 1960s through the 1980s and in subsequent episodic events. The phenomenon was notable for propagating as low-salinity water masses across the Irminger Sea, Labrador Sea, Greenland Sea, and into the Subpolar Gyre, affecting circulation linked to the Atlantic Meridional Overturning Circulation and interacting with climate variability modes such as the North Atlantic Oscillation and the Atlantic Multidecadal Oscillation.
The anomaly manifested as multi-year, basin-scale depressions in salinity that altered thermohaline structure in the North Atlantic Ocean and Nordic Seas, influencing exchanges between the Arctic Ocean and mid-latitude basins. Observational campaigns by institutes like the Woods Hole Oceanographic Institution, National Oceanic and Atmospheric Administration, and Institute of Ocean Sciences documented propagation pathways through the Irminger Current, East Greenland Current, and along the margins of the Labrador Current. The episodes coincided with changes in sea ice export near Fram Strait and freshwater input from the St. Lawrence River and Greenland Ice Sheet runoff.
Primary drivers implicated include anomalous freshwater release from the Arctic Ocean via enhanced sea ice export through Fram Strait and increased river discharge from catchments such as the Yenisey River and Mackenzie River. Atmospheric forcing from persistent phases of the North Atlantic Oscillation and synoptic patterns associated with the Jet stream altered wind-driven advection in the Subpolar Gyre and modulated the strength of boundary currents like the Labrador Current and East Greenland Current. Sea ice dynamics linked to the Greenland Ice Sheet melt and freshwater pulses from the Barents Sea region combined with eddy-driven mixing and mesoscale variability observed near the Charlie-Gibbs Fracture Zone to change stratification and the formation of intermediate water masses such as Labrador Sea Water.
The first well-documented event began in 1968, propagated during the 1970s, and peaked in the early 1980s with salinity anomalies tracked by hydrographic surveys conducted by the Sverdrup Institute, Scott Polar Research Institute, and national oceanographic programs including NASA-supported missions. Subsequent episodes occurred in the late 1980s and the 1990s, with renewed low-salinity pulses in the 2010s documented by the International Council for the Exploration of the Sea and Argo float arrays. Historical analysis has connected specific episodes to major climate events such as the 1976–77 climate shift and variations in the North Atlantic Oscillation index recorded at Isle of Wight Observatory and reanalysis datasets from European Centre for Medium-Range Weather Forecasts.
Salinity reductions altered buoyancy forcing, which perturbed deep convection in the Labrador Sea and the Greenland Sea, affecting the formation of North Atlantic Deep Water and potentially modulating the strength of the Atlantic Meridional Overturning Circulation. These changes translated into regional sea surface temperature anomalies influencing atmospheric circulation patterns tied to the North Atlantic Oscillation and teleconnections to the European climate and Arctic amplification processes. Long-term hydrographic shifts were recorded alongside shifts in mode waters and intermediate salinity maxima in sections monitored by programs such as WOCE and the Global Ocean Observing System.
Freshening episodes impacted stratification, light penetration, and nutrient recycling, altering ecosystems from plankton assemblages in the Irminger Sea to benthic communities on the Grand Banks. Phytoplankton dynamics, including shifts between diatom-dominated and flagellate-dominated communities, were observed by researchers at the Alfred Wegener Institute and Scottish Association for Marine Science, with downstream effects on zooplankton such as Calanus finmarchicus and fisheries targeting species like Atlantic cod, capelin, and herring. Biogeochemical cycles, including carbon sequestration via the biological pump and oxygen distribution in intermediate waters, were affected, with implications for processes studied by the International Geosphere-Biosphere Programme and regional monitoring by the Marine Strategy Framework Directive.
Detection relied on a mix of hydrographic sections, expendable bathythermograph surveys, moored instruments from programs like OSNAP and the Long-Term Ecological Research, satellite altimetry and gravimetry from TOPEX/Poseidon and GRACE, and in situ profiles from the Argo network. Numerical modeling efforts using coupled ocean–atmosphere models developed at institutions such as the Met Office Hadley Centre, NOAA Geophysical Fluid Dynamics Laboratory, and the Max Planck Institute for Meteorology have reproduced anomaly propagation and tested sensitivities to freshwater forcing, sea ice export, and wind stress variability associated with the North Atlantic Oscillation.
Changes in salinity and associated circulation impacted commercial fisheries managed by bodies like the International Council for the Exploration of the Sea and coastal communities in Iceland, Greenland, Canada, and Norway. Shipping routes, ice conditions, and search-and-rescue operations administered by agencies such as the United States Coast Guard and Royal National Lifeboat Institution faced altered hazards from sea ice export and stratification-driven storm track changes. Policy responses included adjustments in fisheries quotas by the North Atlantic Fisheries Organization and transnational scientific cooperation through initiatives like the Joint Norwegian–Russian Fisheries Commission and multinational programs under the United Nations Convention on the Law of the Sea.
Category:Oceanography Category:North Atlantic Ocean Category:Climate phenomena