Anomaly The Great Salinity Anomalies of the 1970’s and 1980’s were well-documented decadal-scale events, where minima in salinity (and temperature) were observed successively in different basins around the northern North Atlantic Ocean. The fact that the anomaly was observed in different basins after each other indicates that this was an advective event, accounted for by the movement of a fresh (and cold) anomaly along main ocean currents. For the 1970s GSA, the propagation was traceable around the Atlantic sub-polar gyre from its origins in the northeast of Iceland in the mid to late 1960s until its return to the Greenland Sea in 1981-82. The 1980s GSA began with the anomaly being advected by the West Greenland Current In 1982 and ending up back in north Icelandic waters in 1989-90. Salinity is a measure of how ‘salty’ water is, or the amount of dissolved matter within seawater. This is measured by passing seawater through a very fine filter to remove particulate matter , historically, this was measured using a glass fibre filter with a nominal pore size of 0.45 , but more recently, smaller and smaller pores have been used. Salinity is difficult to directly measure , as dissolved matter in seawater is a complicated mixture of virtually every known element and it is impossible to measure to complete composition of every water sample. Originally, chlorinity  was measured and converted to salinity using a simple linear function. Since the early 1980s, the value calculated as salinity is actually the Practical Salinity, which is a proxy for the true salinity. The new seawater standard TEOS-10 defined a better measure of salinity used since 2010, named Absolute Salinity. This is measured by first measuring the electrical conductivity, temperature, and pressure of a water parcel.  400px|A schematic showing the causes of the GSA of the 1970s  The Great Salinity Anomalies observed could have different driving causes. For the anomaly in the late 1960's and early 1970's , the main cause of the anomaly was by a freshwater and sea ice pulse which came from the Arctic Ocean via the Fram Strait. Studies show an indirect cause of this pulse to be abnormally strong northern winds over the Greenland Sea, which brought more cold and fresh polar water to Iceland, which was in turn caused by a high pressure anomaly cell over Greenland in the 1960s. This is known as a remote cause of GSA's. However, local conditions  are also important for the preservation of a GSA, in order to stop the anomaly being mixed out and allowing it to propagate as the GSA of the 1970's did.   Recent Anomalies From the years of 2012-2016, the largest and most rapid change in salinity since the GSA has been observed. However, this ‘freshening signal’ is limited to the Icelandic basin, the Rockall Trough, and downstream into the southern Norwegian Sea – there is no similar signal in the Labrador Sea, as with previous GSA's. Further Research Recent studies (2017) suggest potential subpolar North Atlantic (SPG) convection collapse, resulting in rapid North Atlantic cooling, and assess AMOC slow or shutdown .
Salinity Anomaly Occurences The Great Salinity Anomalies of the 1970s and 1980s were well-documented decadal-scale events, where minima in salinity (and temperature) were observed successively in different basins around the northern North Atlantic Ocean. The fact that the anomaly was observed in different basins after each other indicates that this was an advective event, accounted for by the movement of a fresh (and cold) anomaly along main ocean currents. For the 1970s GSA, the propagation was traceable around the Atlantic sub-polar gyre from its origins in the northeast of Iceland in the mid- to late- 1960s until its return to the Greenland Sea in 1981-82. The 1980s GSA began with the anomaly being advected by the West Greenland Current In 1982 and ending up back in north Icelandic waters in 1989-90. Salinity is a measure of how ‘salty’ water is, or the amount of dissolved matter within seawater. This is measured by passing seawater through a very fine filter to remove particulate matter . Historically, this was measured using a glass fibre filter with a nominal pore size of 0.45 . More recently, though, smaller and smaller pores have been used. Salinity is difficult to measure directly as dissolved matter in seawater is a complicated mixture of virtually every known element and it is impossible to measure to complete composition of every water sample. Originally, chlorinity (the measure of the chloride content, by mass, of seawater) was measured and converted to salinity using a simple linear function. Since the early 1980s, the value calculated as salinity is actually the Practical Salinity, which is a proxy for the true salinity. The new seawater standard TEOS-10 defined a better measure of salinity used since 2010, named Absolute Salinity. This is measured by first measuring the electrical conductivity, temperature, and pressure of a water parcel. The electrical conductivity of a water sample is influenced by the concentration and composition of dissolved salts, as salts increase the ability of a solution to conduct an electrical current. 400px|A schematic showing the causes of the GSA of the 1970s . The thinner line indicates a weaker cause than a thicker line. The GSA's observed could have different driving causes. For the anomaly in the late 1960s and early 1970s , the main cause of the anomaly was by a freshwater and sea ice pulse which came from the Arctic Ocean via the Fram Strait. Studies show an indirect cause of this pulse to be abnormally strong northern winds over the Greenland Sea, which brought more cold and fresh polar water to Iceland, which was in turn caused by a high pressure anomaly cell over Greenland in the 1960s. This is known as a remote cause of GSA's. However, local conditions such as cold weather are also important for the preservation of a GSA, in order to stop the anomaly being mixed out and allowing it to propagate as the GSA of the 1970s did. Further Research Recent studies (2017) suggest a potential subpolar North Atlantic (SPG) convection collapse, resulting in rapid North Atlantic cooling, and assess the AMOC slowing or shutdown. Recent Anomalies From the years of 2012-2016, the largest and most rapid change in salinity since the GSA has been observed. However, this ‘freshening signal’ is limited to the Icelandic basin, the Rockall Trough, and downstream into the southern Norwegian Sea – there is no similar signal in the Labrador Sea, as with previous GSA's. This is because the earlier GSA's were due to the addition of freshwater through the Fram Strait, with the wind pattern spreading this freshwater over the Labrador Sea. For this recent anomaly, the processes driving it were different .
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Anomaly
Salinity Anomaly Occurences
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1970’s and 1980’s
1970s and 1980s
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mid to late
mid- to late-
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, historically,
. Historically,
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, but more recently,
. More recently, though,
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directly measure ,
measure directly
A
(the measure of the chloride content, by mass, of seawater)
A
The electrical conductivity of a water sample is influenced by the concentration and composition of dissolved salts, as salts increase the ability of a solution to conduct an electrical current.
A
. The thinner line indicates a weaker cause than a thicker line.
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Great Salinity Anomalies
GSA's
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1960's and early 1970's
1960s and early 1970s
A
such as cold weather
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1970's
1970s
A
Further Research
A
Recent studies (2017) suggest a potential subpolar North Atlantic (SPG) convection collapse, resulting in rapid North Atlantic cooling, and assess the AMOC slowing or shutdown.
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Further Research Recent studies (2017) suggest potential subpolar North Atlantic (SPG) convection collapse, resulting in rapid North Atlantic cooling, and assess AMOC slow or shutdown
This is because the earlier GSA's were due to the addition of freshwater through the Fram Strait, with the wind pattern spreading this freshwater over the Labrador Sea. For this recent anomaly, the processes driving it were different