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PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF
seasonal sea-level cycles at various tide stations as the circulation responds to the seasonal wind
stress.
The absence of the strong cyclonic wind field in summer permits relaxation of onshore
Ekman transport and cessation of coastal downwelling. This allows the onshore intrusion of
denser water over the continental shelf bottom. Renewal of bottom water in the fjords along the
coast takes place by late summer (Muench and Heggie, 1978~. This type of deep-water renewal is
indicated by seabed drifter studies near Kodiak Island, where some drifters released near the
shelf break have been found within local bays (Allen et al., 1983~.
Measurements of currents in the northeastern Gulf of Alaska indicate that the flow tends
to follow the shelf topography in the nearshore (Allen et al., 1983~. With increasing distance
offshore, the eddy kinetic energy increases as the Alaska Current is approached at the shelf
break. However, in the western gulf, as the Alaska Stream is approached seaward, the mean
energy of the current increases so that the relative eddy kinetic energy decreases. This suggests
that eddies play a more important role in the northeastern gulf shelf-break region than in the
northwestern part. The eddies embedded in the Alaska Stream and the Alaska Current appear to
be transient. However, there is at least one permanent eddy in the downstream flow to the west
of Kayak Island (Galt, 1976~. This islanc! plays an important role in deflecting part of the
relatively fresh coastal current that recirculates behinc! Kayak Island and forms the permanent
Kayak Island Eddy.
Satellite-tracked drifters released east of Kayak Island in 1976 meandered over the outer
and midshelf regions before they slowly headed inshore and were caught up in the coastal current
(Allen et al., 1983~. They were then kicked back out onto the shelf by Kayak Island and made
circuits in the Kayak Island Eddy. After the drifters exited the eddy, they entered Prince
William Sound through Hinchinbrook Entrance (where tankers bring the Alaska Pipeline oil out
for shipment elsewhere) and became stranded inside Prince William Sound. The flow continues
out of Prince William Sound and around through Montague Strait to the west.
The circulation in Cook Inlet is strongly tidal, with a great deal of local variability due to
coastal and topographic complexity. Cook Inlet is the only part of the Gulf of Alaska that is
substantially affected by sea ice, although elsewhere floating ice near glaciers can be a
navigational hazard, as the recent Exxon Halides accident illustrates.
Interannual Variability
ENSO signals can be seen in the Gulf of Alaska in sea temperatures off Seward, especially
deeper in the water column (Xiong and Royer, 1984~. Strong interannual variability also occurs
in the position and intensity of the Aleutian low, both as a result of interaction with ENSO and
with the Pacific-North American weather pattern (Niebauer, 1988~. Although the effects of
these changes in the Aleutian low can clearly be seen in the Bering Sea, especially in ice cover,
they are not as obvious in the Gulf of Alaska.
Bering Sea
The Bering Sea continental shelf is one of the widest in the world outside of the Arctic
Ocean. It is 1200 km long and 500 km wide but is fairly shallow, with a shelf break at 170 m.
Several large canyons indent the continental slope. Bristol Bay is located to the southeast, and
Norton Sound is to the northeast. The Kuskokwim and Yukon rivers empty onto the eastern
shelf. The Bering Sea shelf connects with the Arctic Ocean through the Bering Strait with about
1 sverclrup (Sv) flow toward the north (Allen et al., 1983~. However, there are reversals in the
flow that can last at least 1 week and are often associated with weather patterns. Unimak Pass is
the only large pass from the Pacific onto the shelf, with transport of only about 0.15 Sv into the
Bering Sea. Much of the remaining water required to balance the outflow through the Bering
Strait comes through the deep water Aleutian passes west of the shelf and flows across the
northern shelf south of Cape Navarin.
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REGIONAL OCEANOGRAPHYAND EVALUATION OF STUDIES PROGRAMS
Meteorology
59
The Bering Sea shelf is characterized by strong variability, including interannual
variability, due to its high latitude and to the great variability in weather. Insolation ranges from
nearly continuous darkness in winter to nearly continuous light in summer. The wind torque
varies by an order of magnitude from summer to winter. The shelf region is ice covered in
winter, but the entire Bering Sea is ice free in summer.
Circulation
Tidal currents dominate the southeastern shelf region, varying from 60% of the horizontal
kinetic energy in the outer shelf to 90°h in the coastal domains (Kinder and Schumacher, 1981~.
About 80% of the tidal energy is semidiurnal. Farther north, the tides are less energetic. The M2
constituents vary from 0.35 m/s along the Alaska Peninsula to about 0.03 m/s or less in Norton
Sound. Mean flow over the shelf is described qualitatively by the dynamic topography, with
some low-frequency pulses driven by weather systems.
From more than 20 record-years of direct current measurements on the southeast Bering
Sea shelf, three mean and low-frequency current regimes have been identified. These regimes
are nearly coincident with the previously described hydrographic domains. In the coastal domain
coastal water from the Gulf of Alaska flows through Unimak Pass and then northeastward along
the Alaska Peninsula. The flow is counterclockwise in Bristol Bay and follows the 50-m isobath
northward. Currents are strongest near the inner front and parallel the front at 0.01 to 0.06 m/s
with the highest speeds in winter. Although about 969`o of fluctuating kinetic energy is
dominated by tides, there are wind-driven events. However, the combination of baroclinic
geostrophic currents with residual flow produced by the interaction of the tides with the bottom
topography seems to account for the observed mean flow.
In the middle-shelf regime or domain that lies between the inner and middle fronts, there
is little mean flow (~0.01 m/s) except near the fronts. There are wind-ciriven pulses
corresponding to meteorological forcing at periods of 2 to 10 days that are similar in magnitude
to those in the coastal domain. Due to the width of the shelf, no coasts are within a Rossby
radius of deformation, so there is no coastal upwelling or downwelling, or any associated
currents, in this regime. This lack of mean flow, along with the strong seasonal pycnocline,
allows the retention of the cold bottom layer throughout the summer.
In the outer-shelf regime or domain, there is significant mean flow. The flow along the
isobaths toward the northwest is 0.01 to 0.1 m/s and across the isobaths onshore toward the
northeast is 0.01 to 0.05 m/s. Because the cross-shelf flow does not usually extend into the
middle-shelf regime, the middle front is often a region of surface convergence, and advection is
as important as diffusion in cross-shelf fluxes. This outer-shelf current regime has more kinetic
energy at periods greater than 10 days than do the two inshore regimes, due probably to
propagation of energy from the Bering Slope Current and associated eddies, although no eddies
have been found up on the shelf.
The Bering Slope Current flows northwestward seaward of the shelf-break front at along-
slope speeds of 0.05 to 0.15 m/s. This current parallels the shelf break, flowing from Unimak
Pass to near Cape Navarin at a speed of 0.1 m/s with a transport of about 5 Sv. The slope
current is characterized by mesoscale eddies that appear to be formed and/or trapped by bottom
topography, especially in the undersea canyons that are present in the slope. Eddies have been
found not to propagate up onto the shelf.
Currents on the northern shelf are dominated by the northward flow into the Arctic, with
temporary reversals caused by storms, particularly in winter (Kinder and Schumacher, 1981~.
The mean flow seems generally to parallel the isobaths, with currents moving at speeds of 0.1 to
0.25 m/s in the Bering Strait and east and west of St. Lawrence Island. In Norton Sound the flow
is generally weak, although instantaneous wind-driven currents flowing at up to 1 m/s have been
measured.
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60
Interannual Variability
PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF
In the Bering Sea, in addition to the strong annual variability, extraordinary multiyear or
interannual variability in ice cover, air and sea temperatures, and winds over the eastern Bering
Sea shelf have been observed (see, e.g., Niebauer, 1988~. For example, sea-surface temperature
(SST) was 2 to 3°C below normal and winter ice-cover about 20% above normal in 1976. By
1979, SST was 2°C above normal and ice cover about 35% below normal. This resulted in an
interannual ice-cover retreat of about 400 km, or about 40% of the ice extent in the Bering Sea.
These observations have led to a conceptual model in which variability in the winter atmospheric
circulation, primarily the Aleutian low, appears to be the primary driving force behind the
interannual variability in the eastern Bering Sea oceanic environment. This model implies that
the interannual signal is not driven by the Bering Sea ocean circulation because of the sluggish
mean flow on the shelf and because of the restricted flow through the Aleutian passes. In
addition, the flow through the Bering Strait is mainly northward out of the Bering Sea. The
variability in the Bering Sea occurs primarily in winter because of the interannual variability in
the mean winter atmospheric circulation and because the Aleutian low essentially disappears in
summer. Recently, this interannual variability has been linked to ENSO variability (Niebauer,
1988).
Hydrography
The immense width of the shelf tends to spread the various sources of energy (e.g., tides,
wind, and fresh water) over a large area. Over the southeastern shelf the mean flow is low, of
the order of 0.1 to 0.2 m/s toward the northwest. Most of the horizontal kinetic energy is tidal.
Seaward of the shelf break, the Bering Slope Current flows at speeds of approximately 0.1 m/s,
with frequent mesoscale eddies. The hydrographic structure on the shelf, which seems little
influenced by the slow mean flow, tends to be formed by the boundary inputs from insolation,
cooling, melting ice, freezing, and river runoff, as well as lateral exchange with bordering
oceanic water masses.
Three distinct shelf hydrographic domains and an oceanic domain can be defined,
delineated by water depths and separated by fronts that generally parallel the isobaths (see, e.g.,
Coachman, 1986~:
1. The coastal domain, inshore of the 50-m isobath, is vertically homogeneous due to
bottom tidal shear and surface wind shear overcoming the buoyancy input and mixing the water
column from top to bottom. The coastal domain is separated from the middle domain or middle
shelf by a narrow (10-km) front, called the inner front, where the tidally mixed bottom layer is
separated from the wind-mixed surface layer as depth increases.
2. The middle domain or middle shelf, between the 50- and 100-m isobaths, tends to be
strongly stratified and has a two-layered structure in summer due to the vertical separation of the
tidal and wind mixing and due to seasonal buoyancy input (insolation and/or ice melt). In winter
this region tends to be homogeneous due to strong winter storms and lack of buoyancy input.
There is no significant advection, so heat content is determined by air-sea interaction. The salt
flux required to maintain the relatively constant mean salinity is due to cross-shelf, tidally-driven
diffusion. The middle shelf is separated from the adjacent outer domain or shelf by a weak
front, called the middle front, located over the 100-m isobath.
3. The outer domain, located between the 100-m isobath and the shelf break, has surface
(wind-mixed) and bottom (tidally mixed) layers above and below a stratified interior. Oceanic
water tends to intrude landward along the bottom, whereas middle-shelf water extends seaward
in the surface layers so that in the water column of the outer domain, vertical fluxes are
enhanced. This interior region of enhanced vertical flux has pronounced fine structure due to
the interleaving of sheets of warmer, but more saline, oceanic water intruding shoreward and
cooler, less-saline water moving seaward. The interleaving occurs at vertical scales of 1 to 25 m.
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REGIONAL OCEANOGRAPHY AND EVALUATION OF STUDIES PROGRAMS
The shelf-break front, which is manifested mainly in enhanced salinity gradients,
separates the outer shelf from the Bering Slope Current water. This water is a mixture of Alaska
Stream and Bering Sea water. The Alaska Stream water has its source in the Aleutian passes.
. _ ~ _ _ ~
On the northern Bering shell (approximately north of OZ-N), 1ncludlng Norton bound,
there are three identifiable water masses (Coachman et al., 1975~. The Gulf of Anadyr water is
the most saline and lies west of St. Lawrence Island and on the west side of the Bering Strait.
Alaskan coastal water lies along the Alaskan coast to the east. In between lies Bering Sea shelf
water of intermediate salinity.
The Arctic Chukchi Sea and Bering Strait
61
The Bering Strait-northern Bering Sea-Chukchi Sea system water-mass characteristics and
currents are dominated by the general northward flow (Coachman et al., 1975~. The Bering Strait
is only 85 km wide and is 30 to 50 m deep. Winds tend to be channeled north or south through
the strait. The mean northward flow is due to the sea surface tilting downward toward the north
and averages about 1 Sv. Reversals of about 1-week duration have been observed and are
significantly correlated with atmospheric pressure gradients over this region.
Three water masses are squeezed through the strait from the Bering Sea. Definition of the
water masses is based mainly on salinity. Water from the Gulf of Anadyr (actually 20% from the
Gulf of Anadyr and 809/0 from the Bering Sea), which is the most saline (32.S to 33.2 parts per
thousand (ppt)), occurs on the west side. Bering shelf water, which comes around both sides of
St. Lawrence Island and occupies the center of the strait, has salinities of 32.4 to 32.S pot.
Alaskan coastal water occupies the eastern strait and has a salinity of 32 opt. Temperatures are
strongly seasonal but are typically cooler to the west (more oceanic water) and warmer to the east
(more coastal water and freshwater runoff from the Yukon River).
There are strong current shears across the Bering Strait. The strongest currents are in the
upper layers of the east side and can have speeds of more than 2 m/s. Currents at lower-level
speeds are half as strong. The flow on the western side is of the order of 0.5 to 0.6 m/s with
little vertical shear.
The Chukchi Sea area widens quickly north of the Bering Strait, with Kotzebue Sound
immediately to the east of the strait. The shelf is shallow (20 to 60 m), with Herald Shoal (20 to
30 m) about 200 km due north of the strait. Many of the capes and headlands in the region on
the U.S. side are high mountains that tend to cause "corner effect" accelerations in winds along
the coast (Kozo, 1984~.
The three water masses that flow northward through the Bering Strait cross the Chukchi
Sea enroute to the Arctic (Coachman et al., 1975~. North of the strait, the Gulf of Anadyr water
and Bering Sea water tend to combine and flow northward at 0.15 to 0.2 m/s, splitting around
Herald Shoal so that some water goes straight into the Arctic Ocean through Hope Canyon and
some turns eastward along the outer shelf of the Beaufort Sea. The Alaskan coastal water also
flows along the Alaskan coast, gaining fresher, cooler water from Kotzebue Sound and flowing at
speeds of 0.25 to 0.30 m/s along Point Hope, Cape Lisburne, and Icy Cape toward Barrow and
the Beaufort Sea beyond. Water also "drains" from the Chukchi Sea through the Barrow Canyon
into a layer 50 to 200 m deep in the Arctic Ocean.
Me Arctic Beautort Sea
Meteorology
Winds are a major factor in the timing of ice freezing and ice breakup as well as storm
and ice surges along the Arctic coast. They also create nearshore currents. However, along this
coast there are subscale (subsynoptic surface-pressure grid) phenomena that are important to the
shelf oceanography. Monsoon-type winds occur during the summer, caused by a semipermanent
arctic front due to the thermal contrast along the coast (Kozo, 1984~. Heating of the land causes
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PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF
a pressure deficit, leading to easterly coastal winds that are in quasi-geostrophic balance with the
pressure gradient (Kozo, 1984~.
The sea breeze is related to the monsoon. Along the Beaufort coast, sea breezes are
characterized by large diurnal sea-land temperature contrasts, clockwise rotation of surface
winds, and surface winds opposing offshore gradient winds (Kozo, 1984~. At least 25°h of the
time, surface wind direction is dominated by sea breeze. The effects of these winds are the
maintaining of coastal (up to 20 km from shore) currents toward the west that cause lagoon
flushing, and a general masking of synoptic wind conditions in this first 20 km. In addition, sea
breezes along the Beaufort coast are not followed by land breezes, because the land stays warmer
than the water, in part because the sun does not set in summer.
Circulation
The offshore portion of the Beaufort Sea is characterized by a mean westward flow of ice
and water at the outer edge of the anticyclonic Beaufort gyre (Aagaard, 1984~. Over the slope
and shelf seaward of the 50-m isobath, the flow is eastward. This is called the Beaufort
Undercurrent (Aagaard, l9X4~. The Beaufort Undercurrent is characterized by a temperature
maximum associated with eastward flow originating in the Bering Sea. This flow seems to be
trapped along the outer continental shelf and slope and centered at a depth of 40 to 50 m. Bering
Sea water can be traced at least as far as Barter Island. Closer to the coast, local winds appear to
dominate the ocean flow and drive it toward the west. This coastal flow appears to be primarily
a summer phenomenon.
Different circulation regimes occur on the inner and outer shelf, and the 50-m isobath
seems to be a boundary. The inner circulation is strongly wind-driven but is also highly seasonal
and less energetic in winter. Outside the 50-m isobath, the circulation is consistent (about 0.1
m/s) throughout the year, topographically steered toward the east and not, apparently, locally
driven. Near the inshore side of the Beaufort Undercurrent, frequent cross-shelf transport events
are possible, with time scales of about 3 days.
Although currents and tides along the Arctic coast are relatively small, storm surges due
to strong winds can cause considerable flooding (up to 1 km onshore).
Orography
The Brooks Range, some 250 km inland but parallel to the coast anti with a mean height
of 1.5 km, has an effect on the winds over much of the Beaufort coast. Near Barter Island,
orographic modification of the winds can cause wind speeds 50% greater than that of the
geostrophic wind due to the "corner effect" (Kozo, 1984~. This effect can be felt as much as 350
km away.
Mountain-barrier baroclinicity occurs when stable air moves toward and up a mountain
without heating from below. This causes the isobaric and isothermal surfaces to tilt away from
the mountain range, resulting in winds parallel to the axis of the mountain range. This is mainly
a winter phenomenon and is a major reason for wintertime west-southwest winds between Barter
Island and Prudhoe Bay. This results in a nearly 180° difference in wind direction when
compared to the easterly winds at Barrow. Mountain-barrier baroclinicity depends on high
surface albedo and so disappears in summer. This effect has a horizontal extent of 120 km and
occurs about 25% of the time in the coastal zone from east of Barter Island to Pru~hoe Bay.
In winter, temperature inversions are common in the Arctic. This results in strong
surface stability, leading to diminished vertical turbulent exchange and hence to reduced wind
stress on the surface.
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REGIONAL OCEANOGRAPHYAND EVALUATION OF STUDIES PROGRAMS
Sea Ice In Alaskan Waters
Ice along the Alaskan coasts shows large seasonal and interannual variability (Niebauer,
1988~. The seasonal cycle of ice cover in Alaskan waters is the largest of any of the arctic
regions, averaging about 1,700 km in the north-south direction. Interannual variability in the
Bering Sea is as high as 400 km.
63
In general, the greatest northerly retreat of the ice occurs in September to October, when
there is no ice in the Bering Sea and the ice has pulled away from the Arctic coast. At this time
the ice can be as much as 250 km off Barrow. Under conditions of northerly winds, extensive
pileup and run-up of ice onto the Arctic coast can occur (Weeks and Weller, 1984~.
The maximum extent of ice in the Bering Sea generally occurs in April. Most of this ice
is open pack ice that is driven by current and wind. Fast ice occurs in the Bering Sea in
protected bays. In the Beaufort Sea, fast ice is more extensive due to the barrier islands and
grounded pileups of sea ice.
Winter ice characteristics in the Bering Sea can be described by a "conveyor belt" analogy.
Ice growth is primarily along south-facing coasts, where polynyas are created as the
predominantly northerly winds advect the ice southward away from these ice-generation sites.
The ice is pushed southward until it hits its thermodynamic limit and melts. The sea ice limit
thus advances southward as melt water cools the upper layer, but probably moves no farther than
the deep water at the shelf break.
Ice-drift rates are variable, with the Bering Sea rates being on the order of 20 to 50 km/d.
In the Bering Strait speeds as high as 50 km/d have been observed. Although the direction of
this flow is generally southward, strong northerly events have been observed, with ice passing
northward through the Bering Strait before turning around and flowing back southward. In the
Chukchi Sea, drift rates are lower (on the order of 0.4 to 4.S km/ for mean annual drift, but
rates as high as 7.4 km/d have been observed (Weeks and Weller, 1984~.
In the Beaufort and Chukchi seas, offshore ice circulation generally follows the east to
west anticyclonic ocean circulation, which is essentially parallel to the coast. Near the coast, fast
ice does not move much, perhaps less than 1 km/yr (Weeks and Weller, 1984~.
The thickness of undeformed sea ice increases toward the north, ranging from about 0.5
to 1 m in the open Bering Sea, to 1 m in Bristol Bay, to 2 m off the Arctic coast (Weeks and
Weller, 1984~. The Bering Sea ice is almost entirely first-year ice, whereas north of the Bering
Strait, the ice is 25-75% second-year or older ice. The older ice is thicker, perhaps with a mean
thickness of 4 m. However, deformed ice in pressure ridges has been observed with maximum
keels of 50 m and sails of 13 m. These keels can cause appreciable gouging of the shelf when
they become grounded. The ice over the arctic shelf is highly deformed, with up to 10 ridges per
km due to shearing. Farther offshore, 2-3 ridges per km is more typical. There are fewer ridges
in Bering Sea ice due to the free-floating nature of this ice.
Although relatively rare, ice islands composed of freshwater glacial ice are also found in
the Arctic. They are tabular icebergs with typical thicknesses of tens of meters and lateral
dimensions of up to 10 km (Weeks and Weller, 1984~.
Interannual variability of ice cover can be quite large (Niebauer, 1988~. In 1976 in the
Bering Sea, ice cover was about 15-20% above normal. By 1979, the ice cover was about 15-20%
below normal. The edge of the sea ice had retreated about 400 km over this period. Some of this
variability has been related to E1 Nino events as well as to atmospheric variability in the North
Pacific.
Evaluation of MMS-funded Research in the Alaska Region
Synopsis
Gulf of Alaska
From the mid-1970s into the 1980s, data from nearly 130 current-meter moorings were
collected on the Gulf of Alaska continental shelf supported by hundreds of current, temperature,
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PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF
activities occur over the continental shelf in water shallower than 150 m, the lack of focus on
shelf circulation is disturbing. Little attention has been paid to the Texas-Louisiana shelf, where
oil exploration and drilling activities are the most intense. However, projects are being started in
this area.
The Texas-Louisiana shelf region is occasionally influenced by warm-core rings of Loop
Current origin, but these rings are not the major oceanographic process governing the circulation
on the shelf, ant! the frequency of occurrence of rings in the western gulf is not high. Thus,
although MMS has been supporting a physical oceanographic observational program that was
adequate to describe some aspects of the general circulation of the Gulf of Mexico, the focus of
this program was on circulation features that are of minor importance to the needs of programs
designed to perform oil-spill risk-analysis assessments. In summary, the MMS physical
oceanography program was designed to look at space and time scales that are too large to be of
use for oil-spill risk-assessment analysis.
Modeling Studies
The MMS-supported modeling studies of circulation in the Gulf of Mexico consisted of
the development of models to predict the seasonal water circulation over the southwest Florida
shelf, the geostrophic circulation on the Texas-Louisiana shelf, and the basin-wide circulation of
the Gulf of Mexico. Brief descriptions of these models are given below. Details of the models
can be found in the reports based on the contracts listen! in Appendix C.
Southwest Florida Shelf Dodge!
The model developed for the southwest Florida shelf (Cooper, 1982) was a linear
hydrodynamic model that included vertical and lateral friction effects and a free surface. The
model allowed for forcing due to surface-wind stress, atmospheric-pressure gradients, and
bottom stress. The vertical structure of the flow was represented by a series of functions that
allowed for vertical variation in the velocity fields. The model used a time-invariant density
field that was specified from seasonally averaged hydrographic observations made on the west
Florida shelf. Model boundaries were specified as land boundaries (inshore) and as either closed
or open along the north, south, and offshore boundaries. Model output consisted of distributions
of the horizontal velocity components (u and v) on a grid with a 30-km resolution. Steady-state
and time-varying velocity distributions were computed with the model. The maximum depth
allowed in the model was 200 m.
The effect of the Loop Current was included in the model by specifying a velocity
distribution along the outer (offshore) boundary of the model. This flow was specified as a
constant velocity along the boundary or as a velocity that linearly increased or decreased along
the outer boundary of the model. This approach assumes that the Loop Current is essentially
barotropic and does not allow for any baroclinic structure or adjustments of the flow.
The use of a time-invariant density field places a severe restriction on the usefulness and
reliability of the simulated circulation distributions. The assumption made in this approach is
that the wind field does not interact with the density structure of the shelf waters. This is
contrary to understanding of coastal circulation processes. In general, the calculation of seasonal
circulation patterns is questionable.
Texas-Louisiana Shelf Mode'
The circulation distributions used to perform oil-spill risk-assessment analyses for the
Texas-Louisiana continental shelf region were derived from geostrophic velocity calculations.
The geostrophic velocity fields were obtained using seasonally averaged density fields for the
shelf waters. Consequently, the circulation fields, at best, can only be representative of seasonal
circulation patterns. Such circulation patterns are not appropriate for determining the trajectories
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REGIONAL OCEANOGRAPHY AND EVALUATION OF STUDIES PROGRAMS
85
that may be followed by an oil spill. Oil-spill trajectories are determined by the prevailing
circulation, which may not be represented in a seasonally averaged circulation pattern. For
example, wind forcing can produce currents that flow in a direction opposite to that suggested by
a long time-averaged circulation.
The use of geostrophic calculations for determining circulation patterns in
continental-shelf waters is questionable, particularly in shallow waters. Furthermore, the
accuracy of the density fields that go into the geostrophic calculation will determine the
reliability of the derived circulation. Also, the shelf circulation models might not account for
such climatological variations as timing in the maximum river runoff and changes in wind
patterns, which can vary from year to year. In summary, the Texas-Louisiana Shelf Model is not
adequate to meet the stated objectives of oil-spill risk-assessment modeling studies.
Basin-wide Circulation Mode!
The circulation model used by MMS for the basin-wide Gulf of Mexico modeling studies
is a modification of an existing model developed by Hurlburt and Thompson (Wallcraft, 1986~.
The Hurlburt and Thompson (1980) model is a two-layer, nonlinear, hydrodynamic, free-surface,
primitive equation model on a beta plane, with a realistic coastline geometry and full-scale
bottom topography confined to the lower layer. This mode! provides velocity distributions on a
grid with a resolution of 0.2 degrees. The model is forced by inflow through the Yucatan Strait
and compensated by outflow through the Straits of Florida. Wind forcing was not treated in the
Hulburt and Thompson model but was included in some experiments with the modified model.
MMS sunnorted a modeling effort that had the overall objectives of modifvina the
. _ _ ~ ~ ~ ,, ,, -,
Hurlburt and Thompson model so that it had a toner spatial resolution tU.1 degrees) and Included
an additional layer (3 versus 2 layers), so that the circulation results could be coupled with a
mixed-layer model, specifically the Navy's operational mixed-layer forecast model. It should be
pointed out that these are all modifications to an existing model; initial model development was
not necessary.
A major problem with a layer model is that the model becomes unstable when the layer
surfaces intersect the bottom topography, or the surface. Much of the effort in modifying the
Hurlburt and Thompson model has been directed at correcting this problem. This is a particular
problem for the objectives of the MMS modeling program, because it means that the model is not
valid for shallow depths. Indeed, the basin-wide circulation model produced for MMS does not
provide usable velocity distributions in regions of the gulf with depths of less than about 500 m.
Evaluation of Modeling Studies
The circulation models developed for the southwest Florida shelf, the Texas-Louisiana
shelf, and the Gulf of Mexico (the basin-wide model) are inappropriate for the objectives of the
MMS modeling program. In particular, the first two models are not designed to provide more
than a best guess at the circulation pattern.
The basin-wide circulation model is interesting from a scientific standpoint, but is of
little practical use in meeting the goals of the MMS modeling program. Given the inability of
this model to produce realistic flows in the shelf/slope regions, it is not clear what MMS has
gained by funding the modifications to the Hurlburt and Thompson model. Furthermore, this
modified model is complex, and understanding the simulated circulations produced with the
model would require considerable effort. It is not clear that MMS would (or perhaps should)
fund such an analysis. It is doubtful that the basin-wide mode! would be of much use in oil-spill
risk-assessment analysis. It should be noted that few of the results obtained with the modified
Hurlburt and Thompson model have been published in the refereed scientific literature. One
interpretation of this is that the modified model does not represent any significant advance over
what was learned from the Hurlburt and Thompson studies. However, the MMS Gulf of Mexico
modeling effort has attempted to incorporate flux-corrected transport techniques that will remedy
some of the problems encountered in layer models when interfaces intersect the surface or bottom
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PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF
topography. If this effort is successful, it will represent an advance over the Gulf of Mexico
model done by Hurlburt and Thompson.
In summary, the MMS modeling program has not been successful. It appears that
inappropriate decisions as to what models would be used were made in the early stages of the
program. Instead of those decisions being reevaluated at the mid-point of the study, for
example, the models were continued, even when it should have been obvious that they were
inappropriate. The results of the Gulf of Mexico circulation modeling program have not yet been
used by BEM in oil-spill-risk assessments because the work is not complete, and the results have
not been verified (personal communication, T. Paluszkiewicz, April IS, 19893.
On the positive side, the data obtained from the physical oceanography observational
program are adequate to form the basis of circulation modeling studies in some specific regions
and for some specific oceanographic features. However, there seems to have been insufficient
interaction between the observational and modeling programs. This is not a new problem and
should be avoided in future MMS studies.
THE ATLANTIC REGION
The Atlantic region can be divided into two parts. The region south of Cape Hatteras is
known as the South Atlantic Bight, and that north of Cape Hatteras is known as the Mid-
Atlantic Bight. In the South Atlantic Bight, the mid- and outer-shelf region is dominated by the
Gulf Stream flow, with eddies at the shelf edge providing very strong variability in the currents.
The shelf is about 100 km wide. The shelf widens over the Mid-Atlantic Bight, with the Gulf
Stream further offshore. There are strong southwestward currents in the slope water and the
shelf with, again, strong variability associated with winds, tides, and offshore meandering of the
Gulf Stream, mesoscale eddies, and Gulf Stream rings. For MMS planning purposes the Atlantic
region is divided into the north Atlantic, mid-Atlantic, and south Atlantic subregions (Figs. 15,
16,and 17~.
Meteorology
Meteorology and Circulation
The meteorological conditions differ in the northern and southern parts of the Atlantic
region. Seasonal winds in the South Atlantic Bight stem from circulations around either the
Azores-Bermuda high-pressure center (tropical, maritime air) or a high-pressure region in the
Ohio Valley (colder and drier air). In the spring, the Azores-Bermuda high dominates, and the
flow is to the west over south Florida, turning to the north and northeast over the Blake Plateau.
Monthly averaged velocities are 1 to 2 m/s. In summer, the northward flow strengthens. In
autumn, there is a transition to southwestward flow as the Ohio Valley pressure center becomes
dominant. Warm northward flowing air persists only over the Blake Plateau and offshore. The
winter regime is dominated by southeastward winds of about 1 to 2 m/s. However, to a large
degree, this mean is the average of numerous weather systems passing through the area.
In the Mid-Atlantic Bight, the seasonally averaged winds show strong southeastward flows
in the winter, due to the Icelandic low and the weak North American high, but become less
organized in spring. Northward to northeastward winds develop in summer (Azores-Bermuda
high), shifting to southwestward winds in fall (Canadian high). In the Georges Bank region
further north, this pattern persists: the mean winds are eastward to southeastward during the fall
to spring months, averaging 3 to 6 m/s, and are weaker and northeastward in the summer.
Interannual variability in the monthly mean wind speeds is substantial, partly because the
transitions from one regime to the other occur at differing times. Representations of the
windfield need to appropriately account for the long-term distribution of speeds and directions in
the monthly averages.
For simulations of currents and oil-spill motion, the synoptic variability in the wind field
is as important as the mean, especially in the more northerly regions. Major wind systems in the
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REGIONAL OCEANOGRAPHYAND EVALUATION OF STUDIES PROGRAMS
71° rot
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FIGURE 15 North Atlantic planning area of the Atlantic region. Source: MMS.
87
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88
PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF
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FIGURE 16 Mid-Atlantic planning area of the Atlantic region. Source: MMS.
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REGIONAL OCE~4NOGRAPHYAND EVALUATION OF STUDIES PROGRAMS
-
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FIGURE 17 South Atlantic planning area of the Atlantic region. Source: MMS.
89
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9o
PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF
South Atlantic Bight have 2- to 14-day periodicities, with shorter diurnal periods also appearing
near the coast. These sea-breeze cycles can also be seen near shore, peaking during the
summertime. The major frontal events move offshore nearly parallel to the coast, setting up
large-scale, alongcoast current patterns. In addition, the varying wind strengths are important in
establishing the amount of vertical mixing and the depth and strength of the seasonal pycnocline.
The variability in winds in the winter is caused by the fairly regular passage of cyclonic
disturbances along a storm track lying in the Mid-Atlantic Bight. In addition, some cyclogenesis
occurs off Cape Hatteras, and some storms do come up from the Gulf of Mexico. Fewer cyclones
occur in summer, with the storm tracks lying further north. Anticyclonic events are less
frequent, but again the storms follow storm tracks lying in the Mid-Atlantic Bight north of Cape
Hatteras. In an average year, 5 (Florida) to 20 (New England) cyclone events occur. The
synoptic scale variance shows a strong anticyclonic component to the rotary spectrum over the
Blake Plateau, especially in winter.
Nor'easters, large (1,000-2,500 km), severe low-pressure systems moving from the west or
southwest with winds at speeds up to 35 m/s from the northeast, are frequent in the wintertime.
Over 10% of the observations in December through March at Georges Shoal show wind speeds
higher than 17 m/s; most of these high-wind periods are associated with these nor'easter events.
They also contribute significantly to the observed higher average wind speeds. Because the winds
generally have a long fetch, the associated waves are on the order of 3 m in height, occasionally
reaching 12 m on Georges Bank. Precipitation, consisting of rain or snow, is also heavy.
Tropical cyclones and hurricanes may strike many of the offshore sites along the Atlantic
coast. Wind speeds of 50 m/s may occur, along with heavy rain.
For the purpose of simulating oil motion, winds in nearshore regions have two effects.
They can directly produce surface currents by creating a turbulent Ekman layer with surface
drifts to the right of the winds. Secondly, the winds in the presence of a lateral boundary may
also cause setup of the ocean surface. Currents, driven by the resulting pressure gradients and
retarded by bottom friction, can have a magnitude comparable to or larger than the directly
driven flows. These flows depend in a complicated way on the direction' strength, and history of
the wind stress, as well as on the topography.
Wind measurements are most readily available from shore stations. However, the
atmospheric boundary layer changes character significantly over water as moisture and heat are
exchanged with the sea surface, so that the wind field measured on land is quite different from
that taken from stations 20 to 50 km offshore. Schwing and Blanton (1984) found that the ocean
stations had more energy by a factor of 4 in the synoptic time scales; the directions were also
significantly different. The shore-normal component, in particular, was not well predicted by
even an appropriately magnified form of the winds measured on land. Thus, the estimated wind
stress based on data from shore stations may easily be too low by a factor of 2 to 5 and may be
off by 40 degrees in direction.
Circulation
The South Atiantic Bight
The oceanography of the South Atlantic Bight region is very well summarized in Atkinson
et al. (1983~. This region is characterized by a relatively narrow shelf (50 to 120 km) with a
water depth of about 50 m, bounded by the coast on one side and the Gulf Stream on the other.
South of the topographic feature known as the Charleston Bump (at 32°N), the Gulf Stream flows
in about 400 to 600 m of water, with currents of 1 m/s. The stream is deflected eastward by the
bump and then returns to the shelf edge near Wilmington (at 33.5°N) and continues slightly
farther offshore to Cape Hatteras. In the midshelf region (water depths of 15 to 400 m), the
currents are, on the average, in the same direction as the Gulf Stream, although reverse flows can
often be found around the low-pressure center formed by the offshore meander. In the
shallowest part of the shelf, there is often a baroclinic southward current associated with the
1aye3r of fresh river runoff water. The rivers in the South Atlantic Bight provide from 3 to 7.7
km of fresh water per month, distributed fairly evenly along the shelf. This can significantly
alter the flow and stratification near the shore.
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REGIONAL OCEANOGRAPHY AND EVALUATION OF STUDIES PROGRAMS
91
Currents are highly variable; tides, wind-driven motions, and mesoscale eddies all cause
significant fluctuations on the shelf. The tides (predominantly M') have a range of 1 to 3 m
along the coast, with tidal excursions of 4 to 20 km in the inner shelf region. Currents may reach
0.4 m/s nearshore. In the midshelf areas, the tides account for 80 to 90% of the cross-shelf
variability and 20 to 40% of the alongshelf current fluctuations. Over the outer shelf, tides
become less significant, accounting for less than 30% of the variability.
Wind-driven currents lead to strong motions-at 5- to 10-day periods as well as mean
northward drift. These are significantly correlated with the coastal sea-surface pressure and the
alongshelf component of the winds, but are not very coherent spatially. Fluctuations of 0.1 to 0.3
m/s are common. Modeling work by Lee et al. (1984) suggested that displacements of 70 km
over ~ days were characteristic of the midshelf region; of this, about half was caused by
wind-driven currents. It should be noted that the winds in this region show strong variability
from synoptic systems moving through the area. The winds over the ocean are consistently
stronger by a factor of 2 than those measured even at nearby onshore stations. Furthermore, the
directions may be off by as much as 40 degrees during periods of changing winds. The
alongshore winds are usually well represented (except for strength) by the coastal stations, but the
onshore or offshore winds may be quite different. Sea breeze contributes significantly to
currents near shore.
Mesoscale variability is primarily produced by the frontal waves and eddies of the Gulf
Stream at the outer edge of the shelf. These disturbances, with wavelengths of 100 to 300 km,
displace the shelf break front by 10 to 100 km across the shelf. Cyclonic circulations develop in
the troughs corresponding to reverse flow near shore. About once a week' the disturbances grow
_ 4, , ~ ,~
~ . . . . ~ .. . . ~ . ~ ,
and fold backwards to term a cold pool and a Pattern ot- northeast-southwest- northeast currents.
. · .
~. . . . . . .
Upwelling at a rate of about 10~ m/s occurs in the cold pool; this may significantly influence the
biological and chemical distributions. Transient upwelling also occurs over topographic features.
The current fluctuations are about 0.S m/s and are coherent for about 100 km along the Gulf
Stream. The average propagation rate for these waves or eddies is 0.5 m/s, dominated by the
advection by the strong currents of the Gulf Stream.
The waters on the shelf of the South Atlantic Bight are vertically well mixed during the
winter, with a strong horizontal temperature gradient occurring across the shelf into the Gulf
Stream. During the summer, the shelf area is stratified, and the surface thermal gradient is quite
small. Some estimates of horizontal mixing and flushing times exist for this region. Bumpus
(1973) has estimated a residence time of about 3 months based on the transport and volume of the
shelf waters.
The Mid-Atiantic Bight and Georges Bank
North of Cape Hatteras, the physical oceanography changes significantly: the shelf is
wider (150 km), and the Gulf Stream moves further offshore (200 to 300 km from the shelf
break). Georges Bank lies off Cape Cod, separating the Gulf of Maine from the slope water,
with most of the water exchange occurring through the Great South Channel and Northeast
Channel. There are fairly strong temperature-salinity contrasts across the shelf, with the
shelf-slope front along the 100-m isobath in winter separating the two water masses. The front
leans outward by about 30 km as it extends to the surface. The density contrast is relatively
weak, so that, although the currents along the front are fairly strong, there is not a large
baroclinic component. In the summer, a strong seasonal thermocline develops, and a cold pool of
water cuts off along the 100-m isobath; there is still a moderate salinity gradient.
Mean currents in the Mid-Atiantic Bight are generally along-isobath, with flow along the
bottom into estuaries and strong currents in canyons. There is a complicated circulation around
Georges Bank, with flow into the Gulf of Maine near Nova Scotia, cyclonic circulation around
the gulf, and a strong jet (0.3 m/s) around the northeast side of Georges Bank, which turns to the
southwest along the 70-m isobath. Some of this flow appears to recirculate around the bank
through the Great South Channel, while some proceeds to the west and south into the
Mid-Atlantic Bight. In addition, some of the Gulf of Maine circulation passes through the Great
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PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF
South Channel and joins the general alongshelf drift. Further offshore, in the slope water, the
mean circulation also has a southwestward flow at about 0.7 m/s at the surface.
Tidal currents are strong in the northern region; tidal range varies from 0.5 to 4 m, and
current speects can reach 1 m/s in the Northeast Channel, with tidal excursions on the order of 20
km. In shallow areas, these currents are sufficient to vertically mix the water even during the
summer and to cause substantial sediment transport. Rectification of tidal fluctuations is thought
to be an important driving mechanism for mean flows.
Low-frequency motions on the shelf of the Mid-Atlantic Bight are dominated by the
wind, which drives energetic alongshelf fluctuations of 2 to 3 times the mean flow velocity, with
periods on the order of 5 days. The onshore-offshore flows are at least twice as weak.
Alongshelf currents are fairly coherent all along the shelf, but the cross-shelf flows are
incoherent over distances of 50 km and across the shelf.
Another source of variability on the shelf is forcing from the slope water mesoscale eddy
field, the Gulf Stream rings passing down the coast, and the large meanders of the Gulf Stream
(and the waves associated with these). Warm-core rings bring strong currents to the edge of the
shelf and can force slope water or Gulf Stream water into shallower regions and entrain material
off the shelf. Several of these pass by Georges Bank each year. They significantly reduce the
residence time for water on the bank and increase the mixing of waters on the bank.
Summaries of drogue experiments and model estimates indicate that water is resident on
Georges Bank for 40 to 80 days, with the nearly closed circulation being responsible for the long
period. Further south in the Mid-AtIantic Bight, the flushing time- is shorter, about 30 days.
Mixing is strong on the shelf, both because of the tides, which disperse material over a scale of
the tidal excursion in one period, and because of energetic fluctuations driven by winds and by
eddy and meander events.
Evaluation of MMS-funded Research in the Atlantic Region
History of MMS-fundec! Research in the Atlantic Region
MMS has funded a number of large physical oceanographic studies in the Atlantic region.
Among these are the Blake Plateau Current Measurement study (October 1982 to September
1986), the Florida Atlantic Coast Transport Study, or FACTS (January 1984 to February 1986),
the South Atlantic Bight numerical modeling study, and the Mid-Atiantic Slope and Rise study,
or MASAR, two of which are discussed below. Appendix C contains a full list of MMS-funded
studies in the Atlantic region.
Evaluation of Observational Studies
These studies have generally consisted of gathering current, hycirographic, and surface
imagery data. In most cases, the studies were carefully done and provided good data on the mean
and variable circulations in the various areas. The mooring programs have been quite ambitious:
the FACTS program began with 41 current meters deployed on 10 moorings, one line of 7
spanning the Gulf Stream and 3 more located along the continental slope upstream. The Blake
Plateau study maintained three lines of moorings across the stream at Onslow Bay, Long Bay, and
the Charleston Bump for over 2 years. However, the programs all suffered from instrument
failures and losses, partly because of the difficulty of mooring work in strong, highly sheared
currents and probably also in part from fishing activity.
The FACTS program also involved drifting-buoy and drift-card releases. Buoys launched
about 50 km offshore of Melbourne Beach stayed within the stream, whereas those launched
nearer inshore or in the Straits of Florida tended to move into the coastal waters. Drift-card
returns indicated more significant onshore motion, perhaps associated with increased wind
influence. No attempts were made to relate either directly to oil motion.
Hydrographic data provided tracers of water masses, including river runoff, and indicated
the occurrence of strong wind mixing, upwelling, and injection of water onto the shelf from Gulf
Stream frontal eddies. Surface satellite imagery was also used to observe and describe eddy
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REGIONAL OCEANOGRAPHY AND EVALUATION OF STUDIES PROGRAMS
features, both to provide a context and to obtain estimates of the frequency of strong onshore
events.
93
MMS has included a fairly high proportion of investigators from universities and research
institutions in the FACTS program. The analyses of the individual data sets by the
subcontractors have been competent. However, there has been no quantitative synthesis of the
various types of data to produce a dynamically consistent description of the flow. It does not
appear that much of the information from this study (or any synthesis work) has been published
in the reviewed literature. This problem can be seen in a number of other MMS-sponsored
programs, although the work on Georges Bank has been published and some synthesis has been
presented.
In the Atlantic region, MMS has generally made good efforts to coordinate its field
programs with other ongoing projects. This has enabled the various scientists involved to gain a
broader perspective on their observations and has contributed to the other programs as well.
Evaluation of Mo~iel~ng Studies
Modeling work in the Atlantic region has progressed in two stages. The contractor
(Dynalysis of Princeton) has worked with equations for horizontal momentum, heat, salt,
turbulent energy, and turbulent length scale (as part of a second-order closure scheme).
Dynalysis first produced a characteristic tracing model CTM, which neglects advection in the
momentum and turbulent energy/length scale equations. The equations are solved by integrating
along contours of the Coriolis parameter divided by the depth (also known as f/h contours). This
diagnostic calculation produces a steady flow pattern under fixed boundary conditions. In the
second stage, the CTM is used to produce boundary information for a full primitive equation
general circulation model (GCM). The contractor uses diagnostic and prognostic forms of the
temperature and salinity equations. These models do not appear to produce significant eddying,
despite the fairly fine grid resolution. The contractor is working on incorporating more
variability into its model by varying the boundary conditions. It is not clear why instabilities do
not appear to be significant, in contrast to the calculations of Orlanski and Cox (1973) for a
· · ~
slm1 ar region.
The models use data for initialization, forcing, and boundary conditions. There appears
to be little relationship between the modeling work and the data collection. The reports do not
reference each other, and the modeling does not appear as a subcontract in the same project as
the observational work. (MASAR is an exception to this, although the modeling work in that
study does not seem to be of the directly applied numerical simulation kind.) The data used in
the models come from the historical record; verification of the models has been rather minimal.
Environmental Impact Statements
It is disappointing to note that the OSRAs produced in 1984 and 1985 continued to use
the CTM model, despite the fact that the GCM reports were available in 1981 (Blumberg and
Mellor, 1981~. MMS judged the GCM calculations to be too short and to cover too limited an
area and, therefore, chose not to incorporate this information into their risk analysis (pers.
comm., MMS, 1990~. In addition, large amounts of field data on the magnitude and importance
of the variability were available, but were not used in the risk analysis.
The EIS for the sales in the Georges Bank region (U.S. DOI, 1983a) exhibits similar
problems and is discussed in more depth here as an example of poor use of the available data
base. The document has a 15-page summary of the physical oceanography of the region. This
draws on both published and unpublished reports and is a good summary of the currents,
hydrographic structure, and wave conditions. Then, 143 pages later, risk analysis is finally
discussed, and there is a 2-page discussion of the analysis, which is based entirely on modeling as
discussed further below. There is no reference at all in the risk analysis section to the preceding
summary of oceanographic knowledge.
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PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF
Furthermore, the modeling work, reported in Appendix D (2 pages) of the EIS document,
uses the CTM south of 41.5°N and west of 69.5°W. These boundaries correspond to Rhode Island
and Cape Cod to the north and to Nantucket Shoals on the eastern edge. Thus, the numerical
model does not cover the Great South Channel or Georges Bank at all. Instead, currents based on
a "geostrophic assumption," calculated by F.A. Godshall in a NOAA unofficial report and cited in
Appendix D of the EIS, were used for the rest of the study area (U.S. DOI, 1983b). None of the
simulated trajectories are shown, so it is impossible to judge the performance of this calculation.
Again, no comparisons with the actual observations are offered.
Thus, we have a fairly elaborate and expensive field study and (perhaps unique to this
region) synthesis work in the EIS, giving a rather full picture of the circulation and mixing, all of
which was ignored when oil motion was estimated.
THE WASHINGTON OFFICE
The efforts of the WO, in contrast with the regional offices' goal of data collection,
analysis, and synthesis, are focused on supporting regional studies, addressing issues that are
common to several or more of the regions (generic studies), and summarizing or documenting
previous studies. From 1973 to 1988, physical oceanography studies funded by the WO accounted
for 4% of all MMS funding for physical oceanography.
The number of physical oceanography studies funded under the WO is extremely limited
(see Appendix C). According to the summary list of studies (FY 1973 to FY 1986, 3rd quarter)
appended to the Washington Office Regional Studies Plan for FY 198S, only seven studies have
been funded for that period, and only two since the previous NRC review (NRC, 1978~. The
major effort is an interagency agreement with NOAA for bathymetric mapping services.
Another study, proposed in the Regional Studies Plan for FY 1989, which requires study of near-
surface physical oceanographic processes, is assessing the use of satellite-tracked surface buoys in
simulating the movement of spilled oil in the marine environment.
According to the material available, the physical oceanographic studies completed under
the WO of the ESP address areas of real concern and have been completed with quality products
in a timely manner. An important question is why the WO budget is so small compared with
those of its regional counterparts. Several important generic research efforts that have been
carried out by the regional offices clearly seem appropriate for the WO. These include, among
others, efforts to characterize the transport and fate of oil in the marine environment, to develop
models of atmospheric and drill-cuttings dispersion and of coastline-oil interaction, to investigate
oil-sediment interaction, to characterize coastal wave dynamics, and to develop methodologies for
specifying wind and atmospheric forcing for circulation and trajectory models. It appears that
such studies could have been better directed and more efficiently executed, with results that
would have been more widely useful, if they had been managed by the WO. It is likely that these
investigations were not organized under the WO generic studies program because of the historical
strength of the regional offices in establishing the total ESP for MMS. The mandate to complete
these overview or generic efforts clearly belongs with the WO. The management structure and
funding allocations should clearly reflect that fact.
-
· ~
Representative terms from entire chapter:
physical oceanography
