Anthropogenic mixing in seasonally stratified shelf seas by offshore wind farm infrastructure

The offshore wind energy sector has rapidly expanded over the past two decades,
providing a renewable energy solution for coastal nations. Sector development has
been led in Europe, but is growing globally. Most developments to date have been in
well-mixed, i.e., unstratified, shallow-waters near to shore. Sector growth is, for the first
time, pushing developments to deep water, into a brand new environment: seasonally
stratified shelf seas. Seasonally stratified shelf seas, where water density varies with
depth, have a disproportionately key role in primary production, marine ecosystem and
biogeochemical cycling. Infrastructure will directly mix stratified shelf seas. The magnitude
of this mixing, additional to natural background processes, has yet to be fully quantified.
If large enough it may erode shelf sea stratification. Therefore, offshore wind growth may
destabilize and fundamentally change shelf sea systems. However, enhanced mixing may
also positively impact some marine ecosystems. This paper sets the scene for sector
development into this new environment, reviews the potential physical and environmental
benefits and impacts of large scale industrialization of seasonally stratified shelf seas
and identifies areas where research is required to best utilize, manage, and mitigate
environmental change.