June 2025 | Oceanography
PERSPECTIVE
The National Academies Consensus Study Report, Potential
Hydrodynamic Impacts of Offshore Wind Energy on Nantucket
Shoals Regional Ecology: An Evaluation from Wind to Whales
(NASEM, 2024), is important, timely, and succinct. During this
time of political and financial uncertainty regarding the devel
opment of offshore wind, this report, summarized by Hofmann
et al. (2025, in this issue), offers clear directions for the research
needed to resolve significant scientific and engineering questions
during a time of rapid change in the Northwest Atlantic Ocean.
The report highlights the difficulty of unraveling the impacts
of offshore wind development from oceanographic variabil
ity. The Northwest Atlantic is one of the most rapidly warm
ing regions in the world ocean (e.g., Pershing et al., 2015; Chen
et al., 2020; Seidov et al., 2021), resulting in a trend of increas
ing stratification in the region (Harden et al., 2020). While
there is a longer-term warming trend, in part relating to vari
ability upstream (e.g., Gonçalves Neto et al., 2021), extreme
events, such as marine heatwaves in the region, have resulted
in large temperature anomalies over time periods from days
to months. Further complicating the matter, the spatial scales
of the marine heatwaves depend on whether they result from
atmospheric forcing or ocean advection (e.g., Chen et al., 2014;
Großelindemann et al., 2022).
Another factor that makes attributing impacts in the region
complex is the manner in which Gulf Stream variability has influ
enced continental shelf stratification and water mass properties
via increases in shelf break exchange processes. Gulf Stream
meanders have increased in peak-to-trough size, and their first
downstream appearance from the Cape Hatteras destabilization
point first shifted west over an extended period of time (Andres,
2016) and then shifted eastward over the last several years
(Sánchez-Roman et al., 2024). This increased Gulf Stream vari
ability is likely related to a regime shift in the annual formation
rate of warm core rings in the year 2000 (Gangopadhyay et al.,
2019). An indication of the growing influence of Gulf Stream
rings and water masses on the continental shelf in this region
is the remarkable increase in frequency of mid-depth salinity
maximum intrusions (Gawarkiewicz et al., 2022). These intru
sions commonly occur in proximity to warm core rings (Silver
et al., 2023) and bring warm salty water tens of kilometers shore
ward of the shelf break and potentially into the offshore wind
lease areas off Nantucket Shoals. Significantly for northern right
whale prey fields, salinity profiles reveal there may be several dif
ferent intrusions at different depths in the water column over the
continental shelf, thus possibly diminishing the concentration
within an individual intrusion layer.
The flow around offshore wind turbines is affected by pre-
existing continental shelf processes and in turn alters those pro
cesses. A key contribution of the Consensus Study Report is to
clearly delineate the three major scales over which the effects
on hydrodynamics must be considered and assessed: the indi
vidual turbine scale, the wind farm scale including all turbines
in the region, and the larger regional scale over which the wind
farm scale exerts an impact via advection and changes in stratifi
cation. This delineation is important as both the computational
approaches and the observational tools differ among the differ
ent spatial scales. Prioritization is important, as is the linkage in
understanding among the scales.
A key portion of the report is the careful evaluation and sum
mary of numerical modeling studies that highlight the wide
uncertainties regarding the impacts of turbine wakes on strati
fication. Most of these studies have been directed toward infra
structure in the North Sea, which exhibits considerable dif
ferences in stratification, tidal velocities, and wind forcing
relative to the Nantucket Shoals region. Validation of mod
els with careful observations is stressed and will be crucial to
reducing uncertainties.
Several challenges inhibit progress over these three spatial
scales. Large Eddy Simulations are needed at the individual tur
bine scale to parameterize mixing and the downstream evo
lution of turbulent wakes from the turbines. On larger scales,
much of the small-scale turbulence will need to be parameter
ized. Progress in this specific area has been achieved by numer
ical modelers in Europe, and parallel efforts are needed for the
Nantucket Shoals region.
A significant gap that is not addressed directly in the report is
the manner in which internal waves and tides have been chang
ing over the past decade as stratification has changed. In addition
SETTING A COURSE
FOR RESEARCH ON OFFSHORE WIND DEVELOPMENT
IMPACTS NEAR NANTUCKET SHOALS
By Glen Gawarkiewicz