

State and trends of the Southern Ocean
State and trends of the Southern Ocean
Ocean temperature
This assessment summary component has changed from 2011.
- In 2011 only the sea surface temperature was assessed, whereas the 2016 assessment includes the entire water column
The original 2011 summary, grade, trend and confidence levels have been replicated here to assist comparison of changes between reporting cycles.
The Southern Ocean has warmed in recent decades; warming is strongest in the upper ocean
Since 1950, the upper kilometre of the water column and densest part of Antarctic bottom water in the Weddell Sea warmed by 0.2°C at 700-1000 metres between 35°S and 65°S.
Polar pH levels are changing twice as fast as tropical ones. Pre-industrial acidity has dropped from pH 8.2 to pH 8.1
Polar pH levels are changing twice as fast as tropical ones; pre-industrial pH 8.2 dropped to pH 8.1, indicating increased acidity
The salinity of the Southern Ocean has reduced in recent decades
The coastal waters between the Ross Sea and the southern Indian Ocean are fresher now than 50 years ago, making the Antarctic bottom water that forms here less saline
Changes in wind forcing caused by human activities (ozone depletion and increased greenhouse gases) have driven a polewards shift of Southern Ocean currents, contributing to warming. Antarctic bottom water has warmed, freshened and decreased in volume, and this has likely influenced large-scale circulation. Changes in patterns in sea ice formation and melting may influence shallow overturning near the continent
Increase in wind strength is expected to affect the ACC and upwelling of circumpolar deep water, formation of different water masses and gyre activity
Global sea levels are rising because of uptake of heat by the oceans and run-off from ice caps and glaciers. The rate of sea level change shows regional and global variation with time because of particular aspects of climate variability
In December 2009, data were obtained from about 135 locations from 250 tide gauges, but large gaps still exist in datasets
Sea level changes are not expected to be uniform across Earth. Sea level rise in the Southern Ocean south of the ACC is predicted to be less than in the Arctic
ACC = Antarctic Circumpolar Current
Assessment Summary Key
Grades
Very good
There are no significant changes in physical and/or chemical processes as a result of human activities
Good
There are some significant changes in physical and/or chemical processes as a result of human activities
Poor
There are substantial changes in physical and/or chemical processes as a result of human activities that significantly affect ecosystem functions in some areas
Very poor
There are substantial changes in physical and/or chemical processes as a result of human activities that significantly affect ecosystem functions in much of the region
Recent Trends
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Improving
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Stable
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Deteriorating
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Unclear
Confidence
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Adequate: Adequate high-quality evidence and high level of consensus
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Somewhat adequate: Adequate high-quality evidence or high level of consensus
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Limited: Limited evidence or limited consensus
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Very limited: Limited evidence and limited consensus
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Low: Evidence and consensus too low to make an assessment
Comparability
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Comparable: Grade and trend are comparable to the previous assessment
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Somewhat comparable: Grade and trend are somewhat comparable to the previous assessment
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Not comparable: Grade and trend are not comparable to the previous assessment
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Not previously assessed
Comments
Assessment remains the same as in 2011.