Offshore wind turbines “consume wind”, a force which is no longer available in the West Wind Drift to flow smoothly eastwards, explained a recent post (Link 1) with reference to work by Mark Z. Jacobson. Chien Wang and Ronald G Prinn (2011) found that offshore wind turbine installations cause a surface cooling over the installed offshore regions whereby this cooling is due principally to the enhanced latent heat flux from the sea surface to lower atmosphere, driven by an increase in turbulent mixing caused by the wind turbines which was not entirely offset by the concurrent reduction of mean wind kinetic energy (Link 2).
What the two papers ignore is the impact offshore installation cause due to immense obstacles between sea surface and the sea floor. They permanently change to flow of sea current and tides, altering the temperature and salinity structure on all levels. That is presumably much more relevant as what the papers discuss.
New field observations of actual wind turbine arrays are definitely required to provide ultimate validation of potential climatic impacts.
Link 1: http://oceansgovernclimate.com/weather-blocked-by-north-sea-offshore-wind-farms-soon/
Link 2: Potential climatic impacts and reliability of large-scale offshore wind farms. Environ. Res. Lett. 6 (April-June 2011) ¸ http://iopscience.iop.org/1748-9326/6/2/025101/fulltext/