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Regional Oceanography and Evaluation of the Regional Studies Programs and Washington Office Generic Studies Programs IN~ODUCrlON Primary responsibility for planning, organizing and synthesizing data from site-specific ESP studies has rested with the four regional offices of the ESP. These offices cover the four main regions of the U.S. OCS (see Fig. 2~: the Alaskan coast, the Pacific coast, the Gulf of Mexico, and the Atlantic coast, and are coordinated by BES in Washington, D.C. The ESP's internal division of responsibility alone justifies separate consideration of each regional program in this review. There are also, however, good geological and oceanographic reasons for considering the four U.S. margins independently. Geologically, the separation of the various U.S. margins is founded on primary differences in the crustal structure of the earth. The basic processes of orate tectonics create . . . . . . . ~ severe' cnarac~er~st~c conunenta' margin forms, which can be simplified into (1) broad shelf- slope-rise with large continental drainages, formed by passive spreading, and (2) narrow shelf- steep slope-marginal trough with steep local drainages, formed by active convergence. The Gulf Coast and Atiantic coast are variants of the passive form, whereas the Pacific coast is a convergent active form with two or three variations. The Bering Sea and Arctic Ocean margins are of the broad type, but glacial effects also have played a major role in modifying the inner portions of the continental shelf. Since the morphologies of the coastline and seafloor have a major influence on circulation in the coastal ocean, these geological differences lead directly to oceanographic differences. In addition, the U.S. margins differ significantly in their mass budgets of terrigenous sediment input and removal. Oceanographic and climatological differences further distinguish the waters of the U.S. continental margins. For example, the first-order circulation of the surface ocean differs on the western and eastern sides of oceans, and ice clearly is more important in Alaskan waters than it is on the other U.S. margins. The net result of these geological, oceanographic, and climatological differences was stated succinctly by Allen et al. (1983~: "In general, observations from geographically distinct continental shelves have shown that the nature of the flow may vary considerably from region to region. Although some characteristics, such as the response of currents to wind forcing, are common to many continental shelves, the relative importance of various physical processes in influencing the shelf flow field frequently is different." This chapter briefly reviews the important physical oceanographic characteristics of each of the four major U.S. continental margins the Alaska, Pacific, Gulf of Mexico, and Atlantic regions and evaluates the adequacy and applicability of the ESP physical oceanographic studies carried out uncier the auspices of each regional office. In Alaska, much of the research was carried out by NOAA's Outer Continental Shelf Environmental Assessment Program under an interagency agreement with MMS. The WO is also evaluated. The panel's criteria for evaluating a study's adequacy are described at the end of Chapter 1. 53

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54 PHYSICAL OCEANOGRAPHY OF THE U.S. OUTER CONTINENTAL SHELF THE ALASKA REGION The continental shelf off the coast of Alaska can be divided into three distinct subregions defined by the topography and bathymetry of the Alaskan coast. Approached from the southern coast clockwise around the Alaska Peninsula, these subregions are the Gulf of Alaska (Fig. 7), the Bering Sea (Fig. S), and the Chukchi ant! Beaufort Sea in the Arctic (Fig. 9), which are further subdivided into planning areas (see Fig. 3~. The meteorology and circulation of each of the subregions are discussed below, followed by a discussion of sea ice in Alaskan waters. Meteorology and Circulation Gulf of Alaska The shelf in the Gulf of Alaska is in general broad, up to 200 km, and contains several deep troughs. Cook Inlet extends inland from the northern apex of the gulf. The northeastern shelf has two major islands (Kayak and Middleton), and to the west, Kodiak Island is midshelf. To the west of Kodiak Island, the Aleutian Islands form a leaky boundary between the North Pacific and the Bering Sea. The shelf is quite deep, with depths in excess of 200 m within several kilometers of the mountainous coastline. Approximately 20% of the coastal region east of Cook Inlet is covered with glaciers. The only major river to empty onto the shelf is the Copper River, although the total freshwater input to the shelf waters is appreciable (Allen et al., 1983), equivalent to the flow of the Mississippi River. Meteorology The weather over the Gulf of Alaska has large seasonal variations in temperature, wind, pressure, and precipitation, all of which affect the ocean. Winter winds over the gulf result from strong cyclonic systems that tend to be trapped in the gulf. This leads to alongshore winds, onshore Ekman transport, and coastal downwelling. A weak high-pressure system replaces the Aleutian low in summer, which results in relaxation of the coastal winds and cessation of coastal downwelling (Royer, 1975~. Adiabatic ascent of moist marine air over the coastal mountains due to trapped storms results in high precipitation rates and runoff in the coastal drainage areas. As much as ~ m/yr falls in the coastal mountains. Although its significance has generally been disregarded, this runoff is equivalent to the flow of the Mississippi River, with a peak in fall and a weak secondary peak in spring. Circulation Off the shelf on the east side of the Gulf of Alaska is the Alaska Current, which is wide (greater than 100 km) and flows at about 0.3 m/s. This current becomes the Alaska Stream as it turns toward the west-southwest off Kodiak Island. Here it narrows to less than 60 km, with speeds of l m/s (Royer, 1981~. High-frequency variability is not typical of this system, although eddies have been observed, and the consequent flux of momentum into coastal waters has not yet been established. The shelf circulation system, which is generally separated from the Alaska Stream and the Alaska Current by a midshelf "doldrum," is strongly influenced by freshwater input from the coast (Allen et al., 1983~. Along the Kenai Peninsula, this flow is a distinct narrow coastal current flowing westward with typical speeds of 0.2 m/s. However, currents can reach speeds as high as 1.5 m/s in the fall due to maximum freshwater discharge in September to October, resulting in surface salinities as low as 25 parts per thousand at the coast. This maximum current precedes the maximum winter winds by several months. An important role of the alongshore winds, which cause coastal downwelling, is to trap the fresh water along the coast even after being transported hundreds of kilometers from the source. These features are clearly seen in

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58 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 90h 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 3C below normal and winter ice-cover about 20% above normal in 1976. By 1979, SST was 2C 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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62 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 25h 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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84 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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86 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 _ S NEW ~ _.\ HA~PSHIRF i-~ : -45- :-.:/ :.~ .. ~ "&I OF . ~ .~e ';~1 .:-' :' '.' is, .' - ~ +.; ~ r -41 _39. O tS ~T' loo STATUTE HODS 0 20 50 re 100 K1~0~5 ski., is. tq g \ ) ~J - Jay -Act NORTH Be_ ) ~ATLANTIC ,r~-~ CANAD^ 1 1 (, ~ ~ In.._ ~ UNITED {'~ em-. STATES N\\ ~ \ ATLANTIC (a 'a ~REGIO N 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 . . , . . , . ~. . , 7C- 75- rue / r5e 72. 71-: rot .~. I ' .2'/ AsSACHU5ETT8 .~- . :.: - S _~.. ~is._ _~. PE HN SYLVANIA .> -40- a; ~. a. 0 's so re loo STATUTE MILES L ' L it: , I . t) 26 ~75 1~ KILOMETERS ;r ~ ~ L. ~ ~ i, .~ ~NEW YORE | CONNECTICUT 1 1~ I ~ T! ~ ATLANTIC UHITE0 $~ <~ ~ ATLANTIC lo\\ \' ~REGION FIGURE 16 Mid-Atlantic planning area of the Atlantic region. Source: MMS.

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REGIONAL OCE~4NOGRAPHYAND EVALUATION OF STUDIES PROGRAMS - -54- ~ ~ J SOUTH \ ~C ~ R O L I N A \ _ 53- "N A'.. 11. . ~. rso ~78- . NOR T ~, - C A R O L I N \ -\` \ ,". \ SOUTHPORti][ ...;.'~1 ../ _~! ~ CHARLESTON _' BUMP ~ ~ ~5 I" STATUTE ~lLtSi if- I - } L O /25 50 as loo KIL~ETER~ : AS //j // / ,/// / - ~CAN4n ~ TIC ) ~ J ATLANTIC N;-r-. . ~ 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 32N), 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 33.5N) 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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92 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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94 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 41.5N and west of 69.5W. 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. - ~