State and trends of the Southern Ocean

Component
Summary
Grade
Very poor Poor Good Very good
Confidence
In Grade In Trend
Comparability
To previous years

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

Year(s): 
2016
3
Deteriorating
Confidence (in grade): 
Adequate
Confidence (in trend): 
Adequate
Comparability (to previous reports): 
Comparable

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.

Year(s): 
2011
3
Deteriorating
Confidence (in grade): 
Adequate
Confidence (in trend): 
Adequate
Comparability (to previous reports): 
Not assessed

Polar pH levels are changing twice as fast as tropical ones. Pre-industrial acidity has dropped from pH 8.2 to pH 8.1

Year(s): 
2016
3
Deteriorating
Confidence (in grade): 
Adequate
Confidence (in trend): 
Adequate
Comparability (to previous reports): 
Comparable

Polar pH levels are changing twice as fast as tropical ones; pre-industrial pH 8.2 dropped to pH 8.1, indicating increased acidity

Year(s): 
2011
3
Deteriorating
Confidence (in grade): 
Adequate
Confidence (in trend): 
Adequate
Comparability (to previous reports): 
Not assessed

The salinity of the Southern Ocean has reduced in recent decades

Year(s): 
2016
3
Deteriorating
Confidence (in grade): 
Adequate
Confidence (in trend): 
Adequate
Comparability (to previous reports): 
Comparable

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

Year(s): 
2011
3
Deteriorating
Confidence (in grade): 
Adequate
Confidence (in trend): 
Adequate
Comparability (to previous reports): 
Not assessed

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

Year(s): 
2016
3
Deteriorating
Confidence (in grade): 
Adequate
Confidence (in trend): 
Adequate
Comparability (to previous reports): 
Not comparable

Increase in wind strength is expected to affect the ACC and upwelling of circumpolar deep water, formation of different water masses and gyre activity

Year(s): 
2011
0
Unclear
Confidence (in grade): 
Low
Confidence (in trend): 
Low
Comparability (to previous reports): 
Not assessed

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

Year(s): 
2016
3
Deteriorating
Confidence (in grade): 
Adequate
Confidence (in trend): 
Adequate
Comparability (to previous reports): 
Not comparable

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

Year(s): 
2011
0
Unclear
Confidence (in grade): 
Low
Confidence (in trend): 
Low
Comparability (to previous reports): 
Not assessed

ACC = Antarctic Circumpolar Current

Klekociuk A, Wienecke B (2016). Antarctic environment: State and trends of the Southern Ocean. In: Australia state of the environment 2016, Australian Government Department of the Environment and Energy, Canberra, https://soe.environment.gov.au/assessment-summary-73-state-and-trends-southern-ocean, DOI 10.4226/94/58b65b2b307c0