Offshore wind is expected to move further and further from shore as demand for renewable energy increases and new floating turbine technology makes expansion into deep water possible. However, for the first time large areas of the UK continental shelf now open to development are ‘seasonally stratified’. David Attenborough described these seasonal seas as among the most biologically productive on the planet. While they only cover 7% of the ocean, they are estimated to be somewhere between 10% and 30% of life at the bottom of the food chain.
According to new searcha byproduct of offshore wind is that the foundations of these floating turbines could help reverse the damaging effects of climate change on these seas.
In seasonally stratified seas, the water is completely mixed during the winter but separates into layers in the spring with warm sunlit water forming above the colder water below. The formation of this “layering” in the spring triggers a massive explosion of marine life as phytoplankton (microscopic algae) bloom in the warm surface waters, forming the basis of a food chain that ultimately supports fish, birds, sea and whales.
However, nutrients in the sunlit surface layer are quickly depleted by plankton blooms. After this point, growth depends on nutrients being lifted from deep waters by turbulence associated with tides, winds and waves.
This turbulence not only stirs the nutrients, but also oxygen down in the dark and deep layers where dead plants and animals sink and rot. Since oxygen is needed for things to break down, this mixture helps this “sea snow” to rot, turning it back into useful nutrients.
Climate change could starve our continental seas
Our changing climate means that stratification is start earlier in the year and the plankton blooms earlier in the spring, out of step with the life cycles of large animals. In summer, stratification is should increasea change already well documented in the open ocean.
Increased stratification will reduce the ability of natural turbulence to stir vital nutrients from the depths to the warm water surface layer and thus decrease their ability to sustain marine ecosystems.
As the ocean warms, it is also less able to hold oxygen, which can lead to poor water quality.
So where do wind farms come from? Introducing wind turbines into deeper waters, where the ocean is stratified, will provide a new artificial source of turbulence. Water flowing past the turbines’ floating foundations will generate wakes, causing the hot and cold layers to mix. In fact, we recently published research show the foundation wake at least doubles the natural turbulent mixing in the region of an offshore wind farm.
This increased turbulence could potentially offset the impacts of climate change on stratification and increase the supply of nutrients to the surface layer and oxygen to deep waters. something similar is already happening around underwater banks, which is why very productive fisheries are often found in places like the Dogger Bank in the North Sea or the Grand Banks of Newfoundland – shallow points where different layers of the ocean meet are mixed.
It appears offshore wind could help seasonally stratified seas become more productive, richer in biodiversity and home to more fish. Careful wind turbine design and wind farm planning could therefore be an important tool in the battle to save these important ecosystems from the worst impacts of climate change.