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Chapter 2: Ocean Processes
The main changes in ocean processes over the past few decades are largely due to the effects of rising sea surface temperature, rising sea levels and ocean acidity. The changes are already affecting some sensitive ecosystems and could have significant long-term impacts.
Key findings
- Sea-surface temperatures around the UK have risen by between 0.5 and 1 °C from 1870 to 2007, with much of this change having occurred since the mid-1980s. This reduces the ability of the ocean to hold oxygen and to soak up carbon dioxide (CO2); forces certain species to adapt, move or suffer detrimental consequences; and contributes to rising sea level. There is extensive coastal erosion around parts of the UK and a decrease in the intertidal area (known as ‘coastal squeeze’), caused at least in part by the presence of hard coastal defences. This in turn is causing loss of land, property and coastal habitat, particularly saltmarshes and mud flats, which are also bird feeding grounds.
- Over the 20th century, mean and extreme sea levels rose in tandem by about 14 cm. Sea level rise increases the risk of flooding, and infusion of land with salt. It also allows larger waves to approach the shore leading to more erosion, damage and risk to coastal structures.
- UK seawater is probably becoming more acidic, mirroring the global pattern. This could affect many marine species. Acidification also decreases the ability of the oceans to take up human emissions of CO2, which may affect the rate of global warming.
- The Atlantic Meridional Overturning Circulation, which is partly responsible for the temperate UK climate, is extremely variable, and it is not clear whether it has yet shown the longer term decline suggested by most climate models. It continues to contribute to the UK’s temperate climate.
Improvements in assessment methodology and future requirements
Since Charting Progress, we have made considerable progress in our ability to assess the state of ocean processes through more comprehensive datasets, and improved models and their more widespread application. Many new monitoring projects have greatly helped our assessments, notably RAPID, which monitors the Atlantic Meridional Overturning Circulation (AMOC); the deployment of FerryBox equipment; more extended observatory time-series and the recently introduced measurements of pH and dissolved CO2 concentrations. To get a more robust picture, it will be necessary to maintain existing time-series, and to improve the resolution, scope and representation of ocean processes by the models. Beyond that, we will need to reassess the location and extent of our observations, using models to determine the best coverage from the point of view of costs and benefits.
Gaps in knowledge
Gaps in knowledge associated with ocean processes are addressed under Climate Change.
Ocean Processes - Summary assessment
Click on the table row headings to go to the relevant section of the report.
Trend in variable assessed | Status in UK atmosphere and seas | Influencing factors and significance for UK seas |
|---|---|---|
Air temperature
| Rising in all regionsUK annual mean temperature has risen by about 1 °C since the beginning of the 20th century. 2006 was the warmest year in central England since records began in the 17th century | Influencing factorsGlobal climate change mostly resulting from anthropogenic greenhouse gas emissions SignificanceRaises sea temperature |
Sea temperature
| Rising in all regionsSea-surface temperature has risen by between 0.5 and 1 °C from 1870 to 2007. Warming since the mid-1980s has been more pronounced in Regions 2, 5 and 6 (Southern North Sea, Irish Sea, Minches and Western Scotland) | Influencing factorsAir temperature SignificanceReduces the ability of the oceans to take up CO2, affects certain species, e.g. forcing them to move or adapt, and contributes to rising sea level. Shifts in plankton populations on which most marine animals feed are associated with temperature rise |
Sea level
| Rising in all regionsMean sea level around the UK coast rose by about 1.4 mm per year during the 20th century | Influencing factorsTemperature (the greater effect to date) and melting land-based ice (potentially more important in future) SignificanceIntertidal habitats and groundwater regimes are affected, and the flooding risk for vulnerable coastal populations will increase, notably in Region 2 (Southern North Sea), if upward trends continue |
Carbon dioxide and ocean acidification
| Acidification in all regionsOceans are acidifying (pH decreasing) as CO2 is absorbed. In UK waters we have no baseline measurements of pH against which changes can be judged, and it will be some time before we can make accurate judgements about the rate of acidification relative to natural annual and interannual cycles of pH | Influencing factorsCO2 which is present naturally and released from anthropogenic sources (e.g. combustion of fossil fuel). Various climatic factors influence its concentration in the sea SignificanceThere are potential threats to marine species and ecosystems if acidification continues |
Circulation, suspended particulate matter, turbidity,salinity and waves
| VariableThese processes vary on daily to interannual timescales but show no significant trend over the past decade, except for a slight salinity decrease in Region 2 (Southern North Sea) and a slight increase in salinity in the northern Regions 1, 7 and 8 | Influencing factorsCirculation: tides and weather, especially winds Salinity: rainfall near the surface and near river outflows; adjacent Atlantic salinity SignificanceSuspended particles: can reduce light availability and inhibit plant growth Waves: the main cause of damage to offshore and coastal structures |
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