Freshening of the Southern OceanOver the second half of the twentieth century, the salinity in the S
Freshening of the Southern OceanOver the second half of the twentieth century, the salinity in the Southern Ocean has witnessed significant freshening in the surface waters long the coast, open ocean, and the water masses formed from them. This observed drop in salinity is the most pronounced among the global oceans. The reason for the changes in salinity can be explained by changes in the northward transport of sea-ice by stronger southerly winds. The sea-ice conveyor belt around Antarctica extracts freshwater from the coastal regions around Antarctica (region where sea ice forms) and releases at the northern extent of the sea-ice (region where the sea ice melts – 60 degree south latitude).Strong southerlies especially over the Weddell and Ross seas have the strength to push the sea-ice northwards. These winds have strengthened considerably over the recent decades due to a combination of factors such as changes in greenhouse concentrations, stratospheric ozone depletion, and natural variability.When sea ice forms in the coastal regions, salt is rejected into the ocean making the ocean increase its salinity. However, this is counteracted with an increase in glacial meltwater from the adjacent ice shelves. 40% of the ice formed in the coastal regions of Antarctica are transported 1,000 km along the conveyor belt northwards where it releases the freshwater back into the oceans as they melt during the spring season.Implications of recent changes in sea-ice transport not only affects the salinity of the Southern Ocean, but also its stratification. Observations show that there are large stratified layers in the upper Southern Ocean. Fresh water is lighter than salty water and so it tends to float making it hard for saltier/heavy water to rise. Furthermore, stratification determines how the oceans interact with the atmosphere to take up heat and carbon-dioxide. Increased stratification hinders the mixing of warm, deep, carbon-rich waters into the surface layer. This could potentially increase the uptake of carbon-dioxide by the Southern Ocean – affecting the carbon cycle and eventually affecting global climateNateImage Credit: Sea-ice Formation - Hubert, Scripps Institution of Oceanography/NSFhttp://bit.ly/2dlTd17Source (Original Paper) - http://go.nature.com/2bVMv1f -- source link
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