  This study investigates the influence of suspended kelp farms on ocean mixed
layer hydrodynamics in the presence of currents and waves. We use the large
eddy simulation method, where the wave effect is incorporated by solving the
wave-averaged equations. Distinct Langmuir circulation patterns are generated
within various suspended farm configurations, including horizontally uniform
kelp blocks and spaced kelp rows. Intensified turbulence arises from the
farm-generated Langmuir circulation, as opposed to the standard Langmuir
turbulence observed without a farm. The creation of Langmuir circulation within
the farm is attributed to two primary factors depending on farm configuration:
(1) enhanced vertical shear due to kelp frond area density variability, and (2)
enhanced lateral shear due to canopy discontinuity at lateral edges of spaced
rows. Both enhanced vertical and lateral shear of streamwise velocity,
representing the lateral and vertical vorticity components respectively, can be
tilted into downstream vorticity to create Langmuir circulation. This vorticity
tilting is driven by the Craik- Leibovich vortex force associated with the
Stokes drift of surface gravity waves. In addition to the farm-generated
Langmuir turbulence, canopy shear layer turbulence is created at the farm
bottom edge due to drag discontinuity. The intensity of different types of
turbulence depends on both kelp frond area density and the geometric
configuration of the farm. The farm-generated turbulence has substantial
consequences for nutrient supply and kelp growth. These findings also
underscore the significance of the presence of obstacle structures in modifying
ocean mixed layer characteristics.
