Skip to main content

By Johnny Hamilton

Sunlight through the Kelp Oysterhaven

Sunlight filters through the Kelp on an Oceanaddicts day out South Cork Coast

In general sea water temperatures take longer to rise and fall than temperatures over land masses. Irelands relatively warm temperate climate is primarily influenced by our surrounding seas. The Gulf Stream, evolving into the North Atlantic Drift, keeps the waters around our coasts on average 7°C to  8°C warmer than global seas at similar latitudes. Our prevailing southwesterly winds then transfer the heat from the sea to the land. As a general rule sea temperatures are higher than those of the air during the winter months with the reverse being true during the summer months.

Overall, this summer we have had glorious diving conditions with visibility averaging 8m to 10m. The sea temperatures off Kinsale have ranged from a low of 12°C to a high of 18°C. This six degrees of separation mirrors the average Irish sea temperature range of 10°C to 16°C for the months of February and August respectively. The range of temperature in the oceans as a whole is from the freezing point, which is around -1.7°C (depending on salinity) to a maximum of around 30°C in the tropical oceans with the exception being hydrothermal vents where temperatures can reach a whopping 460°C.

Thermoclines , areas of rapid change in temperature, would be familiar to most divers with the thermocline remaining fairly constant in the relatively calm summer months whereas thermoclines virtually disappear with the onset of winter due to an increase in vertical mixing processes. Around springtime, stratification becomes more apparent with a calmer sea state. Thus, thermoclines generally occur in shallower seas close to the shore when the sun heats the upper layer causing the resultant warmer less dense water to sit on top of the colder denser lower layer. As the weather cools so too does the upper layer and mixing takes place. The cycle is repeated as spring approaches with the formation of the thermocline again. This process is referred to as a physical process of the ocean, with the formation of the thermocline stimulating the biological process of primary production which in turn allows for the chemical process of inorganic nutrient regulation. The physical, biological and chemical processes of the ocean are interwoven and dependant on eachother proving to be one of natures most fascinating characteristics , for example, the silicon weathered from rocks on land forming the cell wall of microscopic phytoplankton (diatoms) in the ocean which in turn dissolve and influence the silicate content of the seawater. Such processes and cycles have formed and shaped  the oceans over millions of years and will continue to do so for many millions more.

Leave a Reply