Ocean Climate

Sea temperatures around Scotland are affected by local climatic conditions (heat flux with atmosphere) and the heat transferred to the shores of Scotland by ocean currents (advective effects). Sea surface temperatures vary with an annual cycle, lagging behind the cycle of atmospheric temperature by around one month.

Average sea temperatures around Scotland reflect the influence of heat transported from oceanic waters. On average, winter temperatures on the west coast of Scotland are higher than those on the east coast. In summer this situation is reversed as waters in the shallower North Sea warm up more quickly, and so summer temperatures on the east coast are higher than on the west coast. The influence of the North Atlantic Current and climate system can also be observed in the long term variability of sea surface temperatures.

In deeper waters, the circulation patterns have a strong influence on temperatures. Cold Arctic waters fill the deep basins below about 800 m and intermediate waters lie between these and the warmer Atlantic waters above.

Salinity in the open sea is controlled by the balance between evaporation (fresh water out) and precipitation or run-off from land (fresh water in). In coastal waters, the direct input of fresh water from land run-off and rivers dominates the changes in salinity and the salinity of many shelf areas is reduced as a result. Areas where fresh water inputs have high influence are the large estuaries and adjacent coastal waters of the Clyde, Solway Firth, Moray Firth, Firth of Tay and Firth of Forth as well as coastal areas on the west coast that receive a lot of fresh water from land runoff and numerous small rivers.

Many west coast Scottish sea lochs have restricted water exchange with the surrounding seas, particularly those with a sill at the mouth of the loch, and this means they can have salinities that differ considerably from those of the open sea.

Salinity can be an important factor determining the ecology of coastal communities. Moreover, depending upon flow rates in adjacent rivers, there will be large variations in salinity in some coastal regions. Since fresh water tends to sit on top of the denser salty water of the open sea, this variation can take place through the water column as well as geographically.