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Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
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OCR for page 67
4
PHYS'CAL ~V'~O~M^T
I~T~ODUCT10~
This chapter briefly reviews the meteorological, oceanic, and cryological
(ice) characteristics of the environment in three (OCS) lease-sale areas in
Alaska: the area in the Navaho Basin portion of the Bering Sea and the two
in the Chukchi and Beautort seas (see Figure I-. (Although this report
focuses much more on the Chukchi and Beaulort lease areas Han it does on
the Navann Basin, He Bering Sea is important because it interacts with the
Chukchi Sea and, to a lesser extent, with the Beaufort Sea.) The adequacy
and applicability of existing studies are discussed as they apply to environ-
mental characterization from the point of view of offshore oil and gas
development. Specific recommendations about investigations Hat would
contribute useful information about each of regions are given in Chapter 7.
The high-latitude locations of the Tree lease-sale areas make Hem
fundamentally different from most lower latitude regions. Their environ-
ment is quite inhospitable for temperate-zone people for much of the year
because of extreme cold, strong winds, darkness, and sea ice. However,
the environment is strongly seasonal. The Navarin Basin can be ice-
covered in winter but is more temperate in summer, when all the sea ice
usually melts. Some portions of the Chukchi and Beaufort seas are affected
by sea ice all year, containing both seasonal first-year ice and Licker
multiyear Arctic pack ice. The possibility of cross-boundary (or cross-
border) impacts on Canadian and Siberian waters always exists. However,
there is a stronger possibility of transport into U.S. waters from Siberian
67
OCR for page 68
68 OCS DECISIONS: ALASKA
(Bering Sea and Chukchi Sea) and Canadian (Beaufort Sea) coastal shelf
waters because of the mean flow patterns.
All three lease areas are remote. Although there are many people and
much equipment on the North Slope, offshore locations can be hundreds of
miles from help, as are some onshore locations. Even if help is available
close by on land or on an island, the harsh environment can prevent
transportation to remote drilling or pumping sites or to a ruptured of! line
or disabled tanker. Furthermore, the United States has only two open-
ocean, polar-class, ice-breaking ships, the Coast Guard's Polar Sea and
Polar Star. It is possible, at any given time, for one or both of these ships
to be deployed in the Antarctic or in the Atlantic sector of the Arctic and to
be unavailable for help in the Alaskan OCS. A possible tempering consid-
eration is that the United States and Russia have an agreement for mutual
aid in case of an of} spill; the Soviet Union offered assistance after Me
Exxon Vaklez spill in Prince William Sound.
The background that follows could give the impression that there is an
abundance of data about the physical environment of the Bering, Chukchi,
and Beaufort lease-sale sites. In reality, the region is enormous, and the
data are probably barely adequate to correctly predict which way the air,
ice, or ocean win move at any one time or place, say, in the event of an of}
spin. The background on ice is found in Chapter 7. For recent reviews of
these regions, see Carmack (1990) and Niebauer and Schell (1993~.
We note that although the arctic environment is hostile, Alaska Natives
have lived there for at least hundreds of years and continue to do so. A
great deal of Heir food and materials comes from ice-infested ocean waters.
Their knowledge of the physical and biological environment is critical to
Weir survival. Under certain circumstances and in specific places, a good
hunter might better predict a spill trajectory than a general circulation mode}
(GCM). Although most Alaska Natives' knowledge is not written down
and is therefore not accessible in a data base, traditional knowledge is an
mpor~nt counterpart to Western science and should be taken into account
seriously.
L~VI~O~M[~TAL STUDIES
Physical oceanographic studies (including field studies and modeling in
oceanography and meteorology) provide a basis for predicting of! spill
transport in OCS regions. The starting point is typically output from an
OCR for page 69
PHYSICAL ENVIRONMENT 69
ocean circulation model, forced by observations or mode} data on meteorol-
ogy that are used to compute possible oil spill trajectories from selected
points. In conjunction with the probability of an oil spill for selected launch
sites, an oil spill risk analysis (OSRA) mode! is used by the Branch of
Environmental Operations and Analysis (BEOA) of MMS to estimate the
subsequent probability of the oil's arriving in sensitive areas or on the
shoreline within a given time. It is the compilation and distillation of these
probabilities that find their way into an Environmental Impact Statement
(EIS). OSRA calculates only the movement of the center of mass of each
hypothetical spill. Separate estimates are made of the surface area actually
covered by of! from a spill of a particular size and of the much larger area
over which the of} wood be discontinuously spread. The details of of}
transport models are provided in the EISs and references in them.
ARCTIC OCI^~I
Arctic Ocean water and ice circulation are largely contained and
restricted from contact with the temperate oceans by the continents and
islands that surround it. The center of the Arctic Ocean is permanently ice-
covered; the periphery is seasonally ice-free. It is the seasonally ice-
covered periphery that includes the lease-sale sites in the Chukchi and
Beautort seas. Should a spill occur, the ice, as well as the currents in the
region of these sites, will carry spilled oil.
The Chukchi and Beaufort seas are off the north coast of Alaska in the
Arctic Ocean proper; the Bering Sea is subarctic, located between Siberia
and Alaska soup of the Bering Strait and north of the Aleutian Island chain.
The Bering Strait is the only direct connection to the Arctic Ocean from the
Pacific Ocean; it is about 50 m deep and 85 hen wide. The net flow Trough
the strait is northward and accounts for about 15% of the inflow to the
Arctic Ocean (Aagaard and Greisman, 1975~.
The Chukchi Sea is underlain by a broad shelf, nearly 900 km from the
Bering Strait north to He Pelf break. In comparison, Be Beautort Sea has
a relatively narrow shelf. Proceeding east from Point Barrow, considered
the boundary between Be Chukchi and Beaufort seas, the continental shelf
narrows to about 70 km. The shelf widens again farmer east near Mac-
kenz~e Bay to about 160 km and extends eastward into Be Amundsen Gulf.
The marine and submarine topography of this Arctic Ocean shelf region
includes Wrange} Island, at die approximate western boundary between Be
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70 OCS DECISIONS: ALASKA
Chukchi and East Siberian seas, and Herald and Hanna shoals in the
Chukchi Sea shelf north of Bering Strait. Submarine canyons include He
Herald and Hanna canyons in the Chukchi Sea, and the Barrow Canyon at
the boundary between the Chukchi and Beautort seas. There are also
numerous barrier islands along the north and Chukchi coasts of Alaska.
Approximately the northeast half of the Bering Sea (which contains the
Navann Basin) overlies the widest continental shelf in the world outside the
Arctic; the southwest half overlies an abyssal plain with depths of about 4
km. The eastern Bering Sea shelf is about 500 km wide, but it is shallow
(approx~nately 170 m at the shelf break). This shelf borders most of Alas-
ka as well as the coast of Russia north of Cape Navarin. Southwest of Cape
Navar~n, the shelf narrows by an order of magnitude. The continental slope
is indented by several undersea canyons. King, St. Lawrence, St. Matthew,
Nun~vak, and the Pribilof islands are in the eastern Bering Sea shelf. The
climate and weather of this high-latitude region are strongly related to the
presence arm fluctuations of sea ice (Overland, 1981), which are related to
the large seasonal variation in insolation. The Arctic is surrounded by the
large weather systems of the northern hemisphere. In summer, when He
North Pacific high, the Asian continental low, and the North Atlantic high
expand to the north, the weather in the Arctic is relatively moderate. In
winter, the patterns change drastically so Hat the Asian continent is
dominated by high pressure, and He North Pacific and North Atlantic are
dominated by He Aleutian and Icelandic low-pressure systems, respectively.
Because of the weather pattern change, including the intensification of He
Aleutian low, winter is harsh in this part of the Arctic. The mean position
Of the Aleutian low is actually a statistical artifact; He low is the average
position through which most of He migrating cyclones pass. Three to five
storms each month pass along He Aleutians into the Gulf of Alaska or into
the Bering Sea-Bristo} Bay region. In comparison, fewer Han two storms
a month pass across He northern Bering (Overland, 1981~. Relatively few
storms occur norm of Bering Strait. Brower et al. (1977a,b) showed an
average of fewer Han one each year for any given monk for He region
from Wrange! Island eastward to east of Mackenzie Bay. Although
infrequent, the storms that do occur In this region can result in storm surges
and severe wave action along He norm coast of Alaska, especially during
the late summer and early fall. Intense storm surges occur about once each
year (Brower et al., 1977b). To the norm of Alaska, He interaction of
different weather systems surrounding the Arctic generates a poorly defined
OCR for page 71
PHYSICAL ENVIRONMENT 71
relative high-pressure system with clockwise circulation over the Beaufort
Gyre, which drives the clockwise flow of the near-surface ocean and ice in
the Beautort Gyre. The major rivers that enter the region of interest in-
clude the Yukon River in the northern Bering Sea/Norton Sound, the
Colville River in the U.S. Beaufort Sea, and the Mackenzie River in Be
Canadian Beautort Sea. There are a number of smaller rivers such as Be
Kobuk and Noatak that empty into the Chukchi and Beautort seas.
As pointed out by Carmack (19903, there has not yet been a synthesis of
arctic shelf waters, although he listed many individual studies. Carmack
pointed out that annually the shelf waters go through a much larger variation
in salinity (-2-4 parts per thousand (ppt)) than do the surface waters (~0.5
ppt) of the Arctic. The shelf waters are less saline in summer due to river
inflow and ice melt but are more saline in winter due to river freeze-up and
brine rejection from ice formation. In addition, in winter, upwelling may
cause higher salinities on the shelves, reaching 34.5 ppt or greater (Aagaard
et al., 1981; Melting and Lewis, 1982~. During the summer, Be shelves
show net offshore flow at the surface similar to an estuary while in the
winter, there is net inflow of more dense water at kept (Macdonald et al.
1989; Carmack et al., 1989; Carmack, 1990~.
Thus, Be Arctic Ocean surface layers are freshened by river and glacial
input, which are strongly seasonal in nature (Carmack, 1990~. The two
major freshwater inputs to Be regions of interest here are the Mackenzie
River (340 km3/yr or 0.01 Sverdrup (Sv; ~ Sv = lo6 m3/s), which flows
into the Beaufort Sea, and Be Yukon River (214 km3/yr or 0.0068 Sv),
which flows into the eastern Bering Sea. The seasonal variability for Be
Mackenzie River is about 5-fold and it is about 12-fold for the Yukon
River. In comparison, about 1,500-2,000 km3/year (~0.05 Sv) of fresh
water enters Be Arctic Ocean as a component of Be inflow Trough Be
Bering Strait, which includes some of Be Yukon River.
SOUTH~STI ~ BATING S"
The physical environment of the Bering Sea shelf is characterized by
strong variability in Be air, ice, and ocean climate regimes. This includes
periods of days to years, including a pronounced interannual variability
(Niebauer, 1988~. Daylight is nearly nonexistent in winter and nearly
continuous in summer. The wind stress over He sea also varies by an order
OCR for page 72
72 OCS DECISIONS: ALASKA
of magnitude from summer to winter. The shelf region is ice-covered in
winter, although the entire Bering Sea is ice- free in summer.
Tidal currents dominate the entire OCS; they contribute 60% of the
horizontal kinetic energy in the outer shelf (from water depths of approxi-
mately 100 m to the shelf break) to 90% along the coast (Kinder and
Schumacher, 1981a).
Because the southeastern Bering Sea shelf is so broad, the various
sources of energy, such as tides, winds, and freshwater input, are applied
over a large area. Over the southeastern shelf, the mean current flow is
low, 0.01~.05 m/s, and moves toward the northwest. Seaward of Be shelf
break, the Bering Slope current flows at speeds of approximately 0. ~ m/s
with numerous eddies (Kinder and Schumacher, 198Ib). Because of Be
slow mean flow, the hydrographic structure on the shelf tends to be locally
formed by the input from insolation, cooling, melting ice, freezing, and
river runoff, as well as lateral exchange with bordering oceanic water
masses (Kinder and Schumacher, 198Ib; Coachman, 1986~.
The Bering Sea has four distinct hydrographic domains, each with
associated current patterns, defined by water depths and boundary fronts
that are generally parallel to the isobaths (Kinder and Schumacher, 198la,b;
Coachman, 1986~. They are the coastal, middle shelf, outer shelf, and
· e
oceamc c Domains.
MOTH BASING Sly AND I I I Id STRAIT
The Bering Strait is narrow (85 kin) and shallow (50 m). Flow averages
about 0.25 m/s and about ~ Sv in summer, and I-~.5 Sv in winter (Coach-
man and Aagaard, 1988). The northward flow results because the sea
surface tilts downward toward He norm. There are strong currents and
current shears across the strait. The strongest currents in the upper layers
of the east side can be more Han 2 m/s. The flow in the western side can
be 0.5-0.6 m/s with little vertical shear. However, reversals in flow of at
least a week's duration, especially in winter, are related to atmospheric
pressure gradients over this region (Bloom, 1964; Coachman and Aagaard,
1981~. Winds tend to be channeled norm or soup Trough He strait.
In the northern Bering Sea (approximately norm of 62° N including
Norton Sound), there are three identifiable water masses and related fronts.
The water masses are related but not identical to He water masses in the
soudleastern Bering Sea (Coachman, 1986; Hansell et al., 1989~.
Fronts between these water masses are identified (Paquette and Bourke,
OCR for page 73
PHYSICAL ENVIRONMENT 73
1974; Wiseman and Rouse, 1980; Muench, 1990) as associated with the
boundaries between the water that flows from the Bering Sea through the
Bering Strait into the Chukchi and Beautort seas and the Arctic Ocean,
driven by the sea-level difference between the Pacific and Arctic oceans.
These waters make their way eastward along the Alaskan arctic coast as
outlined below in the individual regions.
CHU~CHI So
The Chukchi Sea widens north of the Bering Strait with Kotzebue Sound
immediately to the northeast of the strait. The shelf is relatively shallow
(20~0 m). Herald Shoal, about 200 km due north of the strait, is 20-30 m
deep. Many of the capes and headlands in the region on the Alaskan side
of the Bering Sea are high mountains, which tend to cause "corner-effect"
accelerations in winds along the coast, analogous to the high winds caused
in cities by tall buildings (Kozo, 1984~.
The three water masses that flow northward through Bering Strait cross
the Chukchi. Paquette and Bourke (1981) showed Mat flow trajectories
crossing Be Chukchi are steered Trough Be troughs and canyons. These
flows result in melting Mat causes embayments in Be sea-ice cover (see
Chapter 7~. Norm of He strait, He Anadyr and Bering water tend to
combine and flow northward and slightly eastward at 0.15~.20 m/s,
bifurcating in the region between the Point Hope-Cape Lisburne headlands
and Herald Shoal. Some of this water goes Trough the Herald Canyon into
He Arctic Ocean to He west of Herald Shoal, and some turns eastward as
Bering Sea water that flows eastward along the outer shelf of the Beaufort
Sea (Coachman et al., 1975; Aagaard, 1984~. In the eastern Chukchi Sea,
Alaska coastal water also flows along He Alaska coast, gaining fresher,
cooler water from He large rivers that empty into Kotzebue Sound. The
Alaska coastal water flows at speeds of 0.25-0.30 m/s past Point Hope,
Cape Lisburne, and Icy Cape toward the Beaufort Sea beyond. Water also
"drains" from the Chukchi Sea through He Barrow Canyon off Point
Barrow into He Arctic Ocean (Aagaard, 1984~.
The maximum amplitude of tides in He Chukchi and Beautort seas is
only 5-20 cm, which is less Han ~ % of He total variancein local sea level;
ddal speeds are about 5 cm/s, which is 1-2% of He total variance (Kowalik,
1984; Aagaard et al., 1989~. In He coastal lagoons, tidal variation can be
up to 2 m (Kowalik and Matthews, 1982~.
OCR for page 74
74 OCS DECISIONS: ALASKA
B"UFO~T S"
There are several subscale (kilometers to tens of kilometers) wind
phenomena that are important to the shelf circulation of the Beautort Sea
(Kozo, 19844. Monsoonlike winds occur during the summer, caused by a
semipermanent arctic atmospheric front that results from horizontal thermal
contrasts along the coast. Heating of the land causes a deficit in atmo-
spheric pressure, leading to onshore winds, which are turned to the right
(toward the west) along the coast as a result of Coriolis acceleration.
Related to Be monsoon is a breeze (Kozo, 1984~. Along the Beautort Sea
coast, sea breezes are characterize by large diurnal sea-to-land temperature
contrasts, clockwise rotation of surface winds, and surface upends that
oppose offshore gradient winds. At least 25 % of the time the surface-w~nd
direction is dominated by the sea breeze. One effect of these winds is the
maintenance of coastal currents (0-20 km wider toward the west, causing
lagoon flushing. Sea breezes cause a general masking (about 25% of the
time, as mentioned above) of synoptic wind conditions in this first 20 km
from the coast. During summer, sea breezes along this coast are not
folBowed by land breezes because the land stays warmer than the water (the
summer sun does not set at this latitude).
OroUra
The Brooks Range of mountains, which has a mean height of I.5 kin, is
some 240 km inland of and parallel to Be general trend of the arctic coast
of Alaska. This major mountain range affects winds over much of Be
Beaufort Sea coast (Kozo, 1984~. For example, near Barter Island,
orographic modification of the winds can cause wind speeds 50% greater
than that of the geostrophic wind (the wind resulting from a balance
between horizontal pressure gradients and the Earth's rotation) because of
the corner effect of the mountains, which are close to the sea. This effect
can be felt as much as 350 hen away, and it can influence Be circulation of
ice and water in the Beaufort Sea.
In addition, mountain barrier baroclinicity (a condition in which surfaces
of equal pressure are inclined to surfaces of equal density) occurs when
stable air moves toward and up a mountain without heating from below.
This causes Be isobaric (equal pressure) and isothermal (equal temperature)
OCR for page 75
PHYSICAL ENVIRONMENT 75
surfaces to tilt away from Be mountain range, resulting in geostrophic
winds parallel to the axis of the mountain range. This is mainly a winter
phenomenon and is a major reason for wintertime winds from Be west-
sou~west between Prubhoe Bay and Barter Island. This phenomenon re-
sults in a nearly Degree difference in wind direction when compared
with the winds predominantly from He northeast at Barrow. Because
mountain barrier baroclinicity depends on high surface albedo (the fraction
of incident electromagnetic radiation reflected by a surface), it disappears
in summer, when there is no snow. This effect has a horizontal extent of
approximately 120 km and occurs about 25% of Be time in Be coastal zone
from Crusoe Bay to east of Barter Island.
Finally, wintertime atmospheric temperature inversions are common in
the Arctic. They cause strong atmospheric surface stability that leads to
diminished vertical turbulent exchange and hence to reduced wind stress on
Be surface to drive ice and ocean circulation.
Current
Along the Beaufort Sea coast, in Be event of a spill, Be ice pack will
trap and carry Be oil in addition to He currents. There are also river
plumes from He Colville River (and He Mackenzie River to He east in
Canada), as well as the smaller rivers along the Beautort coast, that affect
the coasts and shelf flow of the He Beaulort Sea. The fresh water flowing
out over He salt water causes buoyancy-driven circulation. In He winter,
river flow often does not completely stop so there is freshwater flow out
onto the open shelf under the land-fast ice. Variable weaker patterns can
cause these buoyancy flows to interact with winds, causing transient current
jets along He coast, especially in summer when ice may not shield the ocean
surface from wind stress. Shoreward of the 50-m isobath, local winds do-
minate the shelf flow of He ocean currents and drive Hem mostly toward
the west under He generally prevailing easterly winds. However, Here are
periods, occasionally prolonged in some summers, when west winds cause
easterly flow. Thus, the circulation at the coast is strongly wind~riven, but
variable and highly seasonal; it is less energetic in winter because of the ice
cover. The result is that significant coastal flow in this shallow inshore re-
gion appears to be primarily a summer phenomenon (Aagaard, 1984~.
Kowalik and Matthews (1983) showed evidence that salt rejection from
OCR for page 76
76 OCSDECISlONS: ALASKA
growing sea ice in a shallow coastal lagoon induces a two-layer water
system. The higher-salinity, higher~ensity, and, hence deeper water moves
offshore at a rate of approximately I-2 km/day (~-2 cm/s); the less-saline,
less~ense upper layer moves onshore. Drifter studies cited by Kowalik and
Matthews (1983) showed shoreward movement for drifters released under
the sea ice as far as 10 On seaward of the barrier islands. Tidal and surge
currents account for most of the variation in the currents, but these are
superimposed on the mean brine-induced currents.
Offshore, seaward of 50 m over the OCS and continental slope, there is
an organized band of flow toward the east, called the Beaufort Undercurrent
(Aagaard, 1984), which is topographically steered but apparently not driven
by local wind stress. It is estimated that less Wan 25% of flow variability
below 60 m is caused by wind (Aagaard et al., 1989~. The dynamics of the
undercurrent are not yet filthy understood, but it is characterized by a
temperature maximum associated with eastward flow originating in We
Bering Sea. The Bering Sea water can be traced at least as far east as Bar-
ter Island. This flow seems to be trapped along the OCS and slope between
the Am (~40 On offshore) and Be 2,500-m isobaths (~120 km offshore).
Aagaard (1984) suggested Cat Be Beautort Undercurrent extends the full
length of the Beaufort shelf and slope. The mean currents are approx'-
mately 0.~ m/s toward Be east. Aagaard (1984) also reported frequent
cross-shelf flow (mostly offshore flow of up to 5 cm/s for as long as 3
days), which links the nearshore region to the undercurrent. The ocean
driving of this circulation includes shelf waves and eddies (Aagaard et al.,
19893. Upwelling appears to be connected wig eastward-traveling wavelike
disturbances in Be velocity records wig vertical displacements of about
150m.
Condoning farther offshore of He Beaufort Undercurrent into Be Arctic
Ocean, Be surface current and ice flow are characterized by a mean west-
ward movement of ice and water at Be outer edge of Be anticyclonic Arctic
Ocean gyre.
S" ICE
The presence of ice in tile arctic OCS is arguably Be most significant
physical condition to be dealt wig in developing OCS oil and gas resources
(see Chapter 7~.
OCR for page 77
PHYSICAL ENVIRONMENT 77
Sea ice in the area shows great seasonal and interannual variability as
well as some predictable mesoscale features (Burns et al., 1981~. For
example, the seasonal sea ice advance and retreat in the Bering Sea is the
largest of any found in the Arctic or in subarctic regions, averaging about
1,700 km (Walsh arm Johnson, 1979~. Interannual variability in the position
of the average ice edge in the Bering Sea is as great as 400 An (Niebauer,
1983~. Farther north, the oceanic flow that fans out in the Chukchi Sea
after going through Bering Strait causes significant mesoscale embayments
in the Chukchi ice cover (Paquette and Bourke, 1981), which are predict-
able from summer to summer. Finally, winter conditions in the Chukchi
and Beautort seas produce fast ice along Be coast that interacts with the off-
shore open Arctic Ocean current and wind-driven free-floating sea ice to
cause an extensive, somewhat predictable, system of flaw leads and polyn-
yas off the Chukchi and Beautort coasts eastward to Be Canadian Archipel-
ago.
Maximum sea-ice cover occurs in March or early April, lagging
minimum insolation in late December by 3 months because of the heat
capacity of the ocean and the cold atmosphere. At this time, essentially all
of the Arctic is ice-covered, as is about one-third to one-half of the Bering
Sea. The mean ice edge in the Bering Sea is about 900 km south of Bering
Strait, and it varies from 700 km to about 1,100 hen south of Bering Strait,
a range of 400 fan, or more than 40% of the seasonal ice cycle (Niebauer,
1983).
Maximum retreat of Be sea ice occurs in September, again lagging
maximum insoladon by about 3 monks. In Be mean, Be ice edge retreats
about 1,600 km between March and September, moving into Be Chukchi
Sea (~e Bering Sea becomes ice-free). By September, in normal years, Be
ice pulls away from Be Arctic coasts of Canada, Alaska, and Siberia,
except for an approximately 300-lan-long section of Be Siberian coast;
leaving a nearly continuous, relatively ice-free corridor around Be perma-
nent ice pack. In most years, this corridor varies in wide from about 300
km at the western end of Be East Siberian Sea to less Man 50 hen off
Pru~hoe Bay. The deviations around these locations are large. In warm
years, Be ice is 600 km off Be coast of Be East Siberian Sea and 300 km
off Be Beautort Sea coast at Prubhoe Bay. In cold years, Be ice sometimes
does not pull away from Be coast, although Here is invariably open water
In some of He bays along He norm coast of Russia in He Chukchi and East
Siberian seas. However, individual storms can cause large changes in ice
OCR for page 78
78 OCS DECISIONS: ALASKA
cover in a short time. For example, off Barrow, northwesterly and nor-
~erly winds can cause compaction of drifting ice, closure of open coastal
water, and extensive runup and pileup of ice onto Me coast Leeks and
Weller, 1984~. Such events trapped and destroyed many whaling ships in
He northeastern Chukchi Sea during Be late nineteenth century.
In September, when there is a minimum of ice, Be dis~ibudon of ice and
open water reflect space ocean flow patterns into Be Chukchi Sea. Open
water generally reaches Trough Be strait into Be Chukchi and Beaufort
seas, paralleling the coast of Alaska norm to Point Barrow and Ben
extending eastward all Be way to Be Canadian Archipelago. This is a
region of extensive nearshore leads and recurrent polynyas, which form as
a result of Be ~nteracdon of the fast ice and land with drifting ice driven by
ocean currents and winds. To Be west, Be ice sometimes does not pull
away from Be Chukchi coast south of Wrangel Island. During years of
unusually heavy ice cover the ice margin in September can be as far south
as about 66° N on the Siberian side but only 70° N on the Alaskan side.
This is the result of warm currents that flow through Bering Strait, hugging
the Alaskan coast to Point Barrow and then curving off to the east (Paquette
and Bourke, 1981~. Paquette and Bourke (1981) depicted current flow
crossing the Chukchi as being steered by the bottom troughs and canyons.
This flow of warmer water from Bering Strait results in the melting of sea
ice and causes recurring embayments in the ice (Paquette and Bourke,
1981~. In spring, along the northwestern coast of Alaska from Point Hope
to Point Barrow, there is a region of leads and polynyas offshore of He
land-fast ice (Stringer et al., 1982~.
Most of the ice in these regions is open pack ice driven by wind and
ocean currents. The pack ice is primarily first-year ice, except in the Beau-
fort Sea, which contains some multiyear ice from the Arctic. Limited fast
ice is present in the eastern Bering Sea, found mainly in protected bays or
along shores facing the prevailing winter winds. In the Beautort Sea, fast
ice is more extensive because of protective barrier islands and because the
grounded pileups of sea ice on the shelf act like small barrier islands.
However, the fast ice in the Beaufort Sea is seasonal, usually lasting from
November through June.
Ice drift rates are highly variable in the Bering Sea, frequently with rates
of 17-22 km/day. Rates as high as 32 km/day have been reported (Shapiro
and Burns, 1975; Muench and AhInas, 1976; Weeks and Weller, 1984~. In
Bering Strait, ice movements of 50 km/day have been observed, although
there are reversals. In tile Chukchi Sea, drift rates are considerably lower,
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PHYSICAL ENVIRONMENT 79
0.~4.8 km/day for the mean annual drift, but rates as high as 7.4 km/day
have been observed (Weeks and Weller, 1984~. In the Beautort Sea, the ice
spews are 2-S ~n/day. The offshore ice generally follows the east-to-west
anticyclonic ocean circulation, essentially parallel to the coast.
Undeformed ice thickness increases toward the north from about 0.5-~.0
m in the open Bering Sea and ~ m in Bristol Bay to 2 m off the arctic coast
(Weeks and Weller 1984~. The Bering Sea ice cover is almost entirely
first-year ice; north of Bering Strait, the ice is 25-75% second-year ice or
older. The older ice is thicker, with a mean of roughly 4 m. However,
pressure ridges of heavily deformed ice have been observed with maximum
depths (keels) of 50 m and heights (sails) of 13 m. When they become
grounded, these deep keels can cause appreciable gouging of the shelf. In
near-coastal zones where grounded ridges can form, sails can be as much
as 20 m high. The pack ice over the arctic shelf is commonly highly de-
formed, with up to 10 ridgesJlan, because of shearing. Farther offshore,
beyond the shelf, 2-3 ridges/hn is more typical. There are fewer large
ridges in Be Bering Sea ice because of the less constrained nature of the ice
drift (there are fewer immovable barriers Me ice can work against to form
ridges as it drifts toward Be open sea).
PHYSICAL OC~OGQAPHIC STUDII S
Given He state of knowledge as described previously, we have come to
He following evaluations of He available data.
Models of Circulation
and Oil pill Tralectories
OSRA is He mode} used by BEOA to generate of} spill trajectories from
selected hypothetical spill points, and estimate He number of "hits" on an
environmental resource target or a shoreline segment, and the conditional
probability of some effect on He resource within a selected time. It is He
compilation and distillation of these probabilities Hat finally find Heir way
into an EIS.
The input requirements of He model include data on air and ocean
circulation in an area. These inputs typically are taken from ocean
circulation and meteorology models. Trajectories for all OCS waters except
OCR for page 80
SO OCS DECISIONS: ALASKA
those in the Alaska region are calculated by BEOA. In He Alaska region,
contractors calculate trajectories and provide them to BEOA for mode!
input. An important consideration in Alaskan modeling is the presence of
ice. The trajectories, and hence OSRA's results, have been of varying
quality over the past 17 years (NRC, 1990a [Physical Oceanography]~.
Circulation Models
The National Research Council has reviewed Me information available
for gas and of} leasing in other OCS areas (NRC, 1989a [California and
FIoridal; NRC, 1991a [Georges Bank]) and has concluded that ocean spill
trajectory estimates have relied too heavily on GCMs. The committee be-
lieves the same conclusion holds for the Tree lease areas involved here.
With the relative lack of observations, initial reliance on model predictions
is understarK able, but as stated in the previous NRC reviews (NRC, 1990a,
1993a) trajectory predictions must be tied more closely to observations Man
has been Be practice. The committee also notes dlat GCMs for Be Alaska
region have been used by several different contractors using different
models, with little effort to synthesize the various results or to reconcile Be
predictions with the limited existing observational data.
The committee believes that little progress can be expected from refining
existing GCMs for such vast areas. It would be more useful to develop
limited-area GCMs for use at sites selected for exploration and develop-
ment. These could be used to explore Be possible effects to biologically or
ecologically important areas in Be vicinity of Be production zone, to
explain how mitigation measures might work, and to predict of! movement
in Be event of an accident. It is important Mat such a modeling effort be
coordinated wig observational efforts in die same area and take advantage
of traditional knowledge.
The duration of the existing base of observations, in addition to being
geographically sparse, is insufficient to distinguish mean circulation from
fluctuations that result from annual or even seasonal processes. MMS has
Ken an important step in addressing these issues in other lease-sale areas
by deploying meteorological buoys. MMS is to be commended as well for
equipping some of these wig acoustic Doppler current profilers, which
record Be current profile beneath the buoys as a function of time. Because
harsh weather and ice preclude the deployment of similar tools in most of
OCR for page 81
PHYSICAL ENVIRONMENT 81
the lease-sale areas, the description of long-term variability is an important
issue.
To maximize the ability to contain spills and protect sensitive resources
from them, a mode} must be used quickly enough to provide actual
predictions of trajectories. This is different from the requirement in the EIS
process for statistical estimates of of} spill trajectories in that it must be run
on a time scale commensurate with an actual spill. It must include envi-
ronmental data and forecasts for currents, wind, and ice conditions as
observed during the spill, although it might contain a statistical component
that would allow for uncertainties and predict the most likely or possible
paths. Several such models are available and have been useful (Giammona
et al., 1992~. Once possible development sites have been selected, one or
more of these models should be selected for use in case of an accident, and
the appropriate site-specific information required by the model (such as
local mean currents, tidal currents, mesoscale eddy energy, and ice
conditions) should be measured and made ready for mode} input.
Atmospheric Forcing of the Ocean Clrcula~on
The atmosphere is important in determining the local effect of wind stress
and heat transport and also, remotely, as conditions in distant areas are
propagated through the coastal ocean by pressure gradients. In OCS areas
off the continental United States and in the Bering Sea, MMS has estab-
lished a network of meteorological buoys to monitor the lower atmosphere
over long periods (10 years). I,here is no comparable set of observations
for the Chukchi and Beautort lease-sale areas, although the committee
believes that sufficient information is available from standard numerical
weather forecasting products and from fixed-station observations to describe
atmospheric variability on scales larger than the mesoscale (100 kind. The
absence of information related to mesoscale variability in Me lease-sale
areas is not seen as a flaw in the existing EIS, but that information will be
required once specific production areas are identified.
Studies should be designed to determine the spatial structure of Me wind
field on scales of a few ldlometers in areas of production, with emphasis on
the mechanics of the marine boundary layer and the interaction between the
layer and coastal topography. Such observational studies should involve
aircraft surveys and fixed-station observations. To take advantage of the
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82 OCS DECISIONS: ALASKA
long time series of weaker on larger scales, Here should also be studies
that define Be relationship between mesoscale variability and fluctuations
in larger scale weather.
AvallaDilitv and Sultanillt
Of the Onse~ational Base
Considerable efforts have been made by MMS and other federal
agencies, by Be state of Alaska, and by local organizations such as the
North Slope Borough to acquire observations on ocean circulation in the
areas considered here. Although these efforts have in many cases been
quite successful, the number of observations available to describe the
circulation in this vast area is much smaller than it is for other OCS areas
bordering Be continental United States. Important distinctions also exist
between the three lease areas: The Bering Sea, in which Be Navarin Basin
is located, is the area for which the richest base of observations is available;
less information is available for the Chukchi Sea, and Be greatest uncer-
tainties concern Be U.S. portion of the Beautort Sea, although Canadian
research on Be eastern portion of Be Beautort is helpful. Ironically, it is
the region with Be least data Mat is currently of most interest to Be of}
industry.
Given the size of Be regions involved and Be relative paucity of physical
observations, Be information available is marginally adequate for Be
preparation of EISs. The information base is not adequate to build any de-
tailed predictive circulation model, as would be required to effectively
manage an of} spill in Be Chukchi and Beaufort lease-sale areas.
Studies of circulation in specific sites identified for production are
recommended. This is consistent wad the strategy followed by MMS in
over OCS areas such as studies of ocean circulation on Be Texas-Lowsiana
shelf and in the Santa Barbara Channel.
Data that have been certified by investigators are available from several
federal archives (e.g., Be National Oceanographic Data Center (NODC)
and the National Snow and Ice Center). In the case of NODC, data
gathered on oceanographic cruises funded by the National Science Foun-
dation are required to be report to and eventually archived at the NODC.
Data are also available from researchers in their published results as well
as data reports. For example, MMS makes dlese research and data reports
available. An enormous amount of data is available Trough tile EISs.
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PHYSICAL ENVIRONMENT 83
PhYslcal ProoerIles of All and Water
The high viscosity of oil at low temperatures, combined wig He influ-
ence of surface waves and mesoscale eddies, will lead to spilled of} forming
a highly discontinuous pattern of patches, windrows, and sheens rawer than
a more-or-less continuous slick. Although models for this have been devel-
oped and Weir resets are reported in EISs, this topic needs to be kept under
review as new information becomes available about the physical properties
of crude of! Cat is discovered in Be region and as understanding of Me
physical oceanic conditions improves.
T~SMISS10~ OF POISE
1~ THE M~121~ ~VI~O~MI AT
The effect of noise on marine mammals especially bowhead whales is
a critical issue on the Norm Slope because Alaska Nadves depend on whales
for subsistence. Although noise transmission and attenuation in Be sea are
physical phenomena, this issue is discussed in detail in Chapter 5, where the
committee argues that additional physical information alone is unlikely to be
instrumental in resolving Be issue.
CONCLUSIONS AND 121 COMMENDATIONS
The specific conclusions and recommendations for tills chapter follow.
For Be general and overall conclusions, see Chapter 8.
Conclusion I: The oceanographic model Cat has been used is elaborate,
but inevitably inaccurate because of major uncertainties about the physical
processes and the mathematical conditions that are applied to mode}
boundaries in the water. Nevertheless, the model's output is sdI! a useful
rough guide to the path and fate of spilled oil, although a simpler mode}
might have been just as useful and credible.
Recommendation I: Improve mode! predictions based on existing
knowledge. Blend in observations of factors, such as the mean circu-
lation in an area, rather than trusting the model to generate this
information accurately (which it generally will not). There are
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84 OCS DECISIONS: ALASKA
numerous ways in which improvement of the model could come from
further research on sea ice physics, on interactions of the currents
with topographic features, and on the representation or analysis of
small-scale turbulence and mesoscale (tens of kilometers and smaller)
eddies. Ideally, there would be continuing evolution of the mode!
through comparison of its predictions with new data. More attention
should be paid to the tremendous interannual variability in oceanic and
ice conditions, and there should be more analysis of extreme events
and worst-case scenarios. Further improvements in predicting the fate
of spilled oil could come from a better understanding of its spreading
and weathering.
Any study of environmental impact is likely to require a mode} that
can predict the path of an of! spill, but after the initial use of such a
model it is important to identify important problems about which
uncertainty is unacceptably high and for which reduction in uncertainty
in the physical oceanographic parts of the problem would be worth-
while. The current approach is "bottom-up," where physical ocean-
ographers strive to produce the best model possible. A "top-down"
approach driven by specific environmental concerns and spill-response
operations might better focus the research. There is little evidence
that this focusing has been attempted, and until it has occurred it is
difficult to say with confidence whether the existing environmental
information and modeling are adequate.
Alterrlative: None recommended.
Conclusion 2: Trajectory estimates have relied too heavily on general
circulation models (GCMs); they have not been closely tied to observations
in the past. The committee also notes that the GCMs for the Alaska region
have been prepared by different contractors using different models, with
little effort to synthesize the various results or to reconcile the predictions
with the limited existing observational data.
Recommendation 2a: Conduct site-speci~c circulation st~ies In
areas identified for production and in "hot spots" - reedling, feeding,
arm aggregation areasidentifiedl by biologists and Alaska Natives with
long experience in debug with the physical environment. Large-scale
studies of He circulation are unlikely to be effective. (The committee
estimates that these studies will require at least 2-5 years; Key should
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PHYSICAL ENVIRONMENT 85
be subject to continued review. The time required will depend on
what the key problems turn out to be and the degree to which inter-
annual variability is a consideration.)
In particular, the committee recommends five studies:
(a) Further work on the exchange of water between shallow
lagoons and He open sea is required to develop the basic data and un-
ders~ing Mat would be necessary to protect them in the event of an
approaching oil spill and to facilitate their restoration should Key be
damaged.
(b) Boundaries between different water masses are frequently
zones of significant biological activity and accumulation, and they also
can be places where spilled of} converges. A survey of fronts in the
Beaufort and Chukchi seas and studies of their causes and variability
would be useful.
(c) Interpretation of the ice gouges on the seafloor is hindered by
a lack of information about the rate at which they are filled in by the
transport of sediment (see Chapter 7~. Determination of near-bottom
currents (on all time scales) would provide, in combination with mea-
surements of sediment properties, some guidance in interpreting the
bottom topography as observed at a specific time.
(~) Long time series of ocean currents and related physical
characteristics are required to quantify the interannual and seasonal
variability in the lease areas.
(e) Field work and modeling would clarify the extent to which
causeways from the shore that have been built or that are proposed in
support of industrial operations need to incorporate breaches to permit
Be continued alongshore flow of water and to permit fish passage.
Such studies need not delay leasing decisions.
Alternative: None recommended.
Recommendation 2b: Refine existing models for use at sites selected
for exploration Carl development ares at biological "hot spots."
Coordinate modeling with observations in the same area. Little
progress can be expected from refining existing large-scale models.
MMS should develop limited-area models for use at sites selected for
exploration and development dial could be used to explore possible
effects on biologically, ecologically, and socially important zones in
Be vicinity of He production region, to explain how mitigation mea
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86 OCS DECISIONS: ALASKA
sures might work, and to predict oil movement should an accident
occur. Trajectory models should be used to provide focus and esti-
mates of probability, but they should not be used as the sole deter-
m~nant of where biological studies wall be conducted. If Me models
are not refined for specific sites, the results will be of dubious value.
See detailed recommendations a, b, 1, and e in Recommendation 2.
Altemative: None recommended.
Conclusion 3: It is well understood that the atmosphere influences ocean
circulation in OCS areas, in part because of the local effect of wind stress
and heat transport, but also farther away as conditions in distant areas are
propagated through the coastal ocean by pressure gradients. In OCS areas
off Me continental United States and in the Bering Sea, MMS has estab-
lished a network of meteorological buoys to monitor the lower atmosphere
over periods (10 years). There is no comparable set of observations for the
Chukchi and Beautort lease-sale areas, although the committee believes that
sufficient information is available from standard numerical weaker forecast-
ing products and from fixed-station observations to describe atmospheric
variability on scales larger than the mesoscale. The absence of information
related to mesoscale variability in He lease-sale areas is not seen as a
deficiency at Me leasing stage in tile existing EIS, but we note that tills
information will be required once specific production areas are identified.
Recommendation 3: In production areas and biological "hot-spots, "
design studies of the spatial structure of the wir~fie~ on scales of a
few kilometers that emphasize marine boundary layer mechanics and
the interaction between the boundary layer And coastal topography
interaction. Such observational sh~ies should involve aircraft surveys
and fixed-station observations. To take advantage of Be long time
series of weather on larger scales, studies also will have to be
sponsored Mat define Be relation between Be mesoscale variability
and fluctuations in Be larger-scale weather. The committee under-
stands that Be Beaufort and Arctic Storms Experiment (BASE) pro-
gram of the Canadian Atmospheric Environment Service, which is
relevant to this recommendation, is planned for 1994.
See ~ in Recommendation 2.
Alternative: None recommended.
Representative terms from entire chapter:
bering strait
