Gulf of Maine stratification and windturbines

• Offshore wind farms can impact hydrodynamics
in the surrounding ocean in two principal ways:

 1) through an atmospheric wake effect that reduces
wind speeds behind wid turbines that can
reach the ocean surface, reducing surface wind
stress and wind-induced currents, and

 2) through subsurface mixing induced by the presence 

of the turbine substructure within the water column.

• Hydrodynamics and wind wake effects around
offshore wind turbines are driven by physical
ocean processes including tides, stratification,
water depth, and wind-driven currents; and atmospheric
processes such as turbulence and stability,
all of which have significant natural variation.

• Changes in surface currents and sea surface
temperatures caused by turbines in European
windfarms (e.g., North Sea) are small enough that
they can be difficult to isolate from other sources
of natural variability.

• Although studies from the North Sea suggest that
wind turbines could cause mixing and disrupt
the tratification of ocean waters, wind turbines
in the Mid-Atlantic Bight are unlikely to have
much influence on summer stratification, which
is significantly stronger than the weakly stratified
waters of the North Sea.

• Due to the distinct oceanographic differences
between the North Sea and the Western North
Atlantic Ocean (and among regions therein),
impacts of wind turbines in one region are not
necessarily directly transferrable to other regions.

• Increased turbulent mixing caused by wind
turbines may enhance nutrient mixing and
stimulate primary production, in turn enhancing
zooplankton abundance, including copepods.

However, if turbulence levels are significant and
cause sediment resuspension, primary production
may decrease due to reduced light penetration.

• Hydrodynamic impacts are highly dependent on
wind farm layout and wind turbine parameters,
including turbine size (hub height and power
capacity), type of foundation, turbine spacing
within the wind farm, and the spacing between
adjacent wind farms.

• Extensive build-out of offshore wind farms is likely
necessary for these structures to have a significant
hydrodynamic impact.

• Larger, more widely spaced turbines, such as
those being planned for U.S. windfarms, are likely
to have less hydrodynamic influence than the
smaller, more closely spaced turbines currently in
operation in Europe and other parts of the world.

Oceanographic Effects