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Title: Oceanography of the Beaufort Gyre: state and problems


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  • Oceanography of the Beaufort Gyre state and
    problems
  • A. Proshutinsky, Woods Hole Oceanographic
    Institution
  • Oceanographic conditions of the Beaufort
    Gyre (BG) are regulated by the BG system
    (atmosphere, sea ice, and ocean) mechanisms and
    interactions and will be discussed in the context
    of the entire Beaufort Gyre system variability.
  • The major goal of this talk is to show how
    a long-term observational program specifically
    designed for the Barrow Cabled Observatory (BCO)
    will contribute to our understanding and
    prediction of state and variability of the
    Beaufort Gyre (BG) system, its regulating
    mechanisms, and impact on Arctic climate.

Science and Education Opportunities for an Arctic
Cabled Seafloor Observatory An NSF-Supported
Community Meeting, Barrow, Alaska 7 8 February,
2005
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Beaufort Gyre region
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BG in the Arctic climate system
Aagaard and Carmack, 1994.
BG
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Arctic Ocean vertical stratification
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2
Kara Sea
Laptev Sea
Siberia
1 Beaufort Gyre 2 Transpolar Drift 3 West
Greenland current
Barents Sea
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Greenland
Barrow and Barrow Canyon
  • Alaska

Baffin Bay
Toporkov, 1970.
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Coupling Diagram of the Beaufort Gyre System
Each component of the system stores and exchanges
mass and energy differently during different
climate regimes. Quantifying and describing the
state and variability of these components and
their coupling is essential to understand the
state and fate of present day Arctic climate.
Atmosphere
Sea Ice
Ocean Mixed Layer
Pacific Halocline
Atlantic Layer
Deep Waters
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  • SOURCES OF INFORMATION
  • Environmental Working Group (EWG) Atlas of the
    Arctic Ocean, 1997,1998 (water temperature and
    salinity for 1950s, 1960s, 1970s, 1980s)
  • 1990-present hydrographic surveys in the Beaufort
    Sea (submarines, icebreakers, buoys, airborne
    expeditions, drifting stations)
  • International Arctic Buoy Program (IABP) (sea
    level pressure, 2-m air temperature, ice drift
    vectors for 1979-present)
  • NCAR/NCEP reanalysis project (6-hourly SLP and
    SAT, 1948 - present)
  • Satellite based sea ice concentration, drift,
    surface temperature and other products
    (1978-present)
  • Atlases and reference books

8
Characteristics of the Beaufort Gyre Climate
System
  • Atmospheric system
  • Atmospheric system of the BG is regulated by the
    Arctic Oscillation processes. The origin of these
    processes is debatable and is beyond our
    discussion here. In normal oscillating arctic
    climate conditions the atmospheric part of the BG
    is responsible for
  • Forcing dynamics of anticyclonic and cyclonic
    circulation regimes (dynamics of AO).
  • Establishing positive anomalies of air
    temperature during high AO and negative anomalies
    during low AO.
  • Producing positive anomalies of precipitation
    during high AO and negative during low AO.
  • Variability of other atmospheric parameters
    (cloudiness, solar radiation, humidity, wind
    speed) that change from regime to regime
    accordingly.

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ATMOSPHERE and ICE DRIFT
A. Winter SLP and wind B. Summer
SLP and wind
Over the Beaufort Gyre, large-scale atmospheric
circulation changes from season to season and
alternates between cyclonic (summer) and
anticyclonic circulation (winter conditions).
High atmospheric pressure prevails over the
Beaufort Gyre in winter and low pressure
dominates in summer
C. Winter buoy drift D.
Summer buoy drift
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Seasonal variability of SLP Solid Anticyclonic
circulation regime Dotted Cyclonic circulation
regime
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Seasonal variability of surface winds Solid
Anticyclonic circulation regime Dotted Cyclonic
circulation regime
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ATMOSPHERE and ICE DRIFT
A. Winter SLP and wind B. Summer
SLP and wind
Figure shows that the sea ice drifts
anticyclonically in both winter and summer. This
is because sea ice is driven by winds and ocean
currents and in the annual ice drift, the ocean
currents dominate wind-driven circulation.
C. Winter buoy drift D.
Summer buoy drift
13
Hydrographic station locations (blue dots) in the
1950s and 1960s
14
Hydrographic station locations (blue dots) in the
1970s and 1980s
15
WATER TEMPERATURE 5 meters
1950s
1960s
1970s
1980s
Source EWG, 1997,1998
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WATER TEMPERATURE 250M
1950s
1960s
1970s
1980s
Source EWG, 1997,1998
17
WATER TEMPERATURE 500M
1950s
1960s
Atlantic water with temperatures higher than 0 C
occupies water layer from 300-400 to
1,000-1,500m in the Canadian Basin
1970s
1980s
Source EWG Atlas, 1997,1998.
18
WATER SALINITY 5 M
1950s
1960s
Arctic surface waters occupy 30-50 meter layer
with water temperatures at freezing point and
relatively low salinities
1970s
1980s
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WATER SALINITY 150 M
20
Salinity distribution in the upper 200-meter
layer
Alaska
Chukchi Sea
East-Siberian Sea
Beaufort Sea
Beaufort Gyre
Laptev Sea
Kara Sea
Greenland
Barents Sea
21
Top Left water salinity (S) at 10 m Right
Salinity section Bottom Left water salinity (S)
at 100 m Right Dynamic topography Data source
EWG Atlas, 1997, 1998
22
Beaufort Gyre mechanism of fresh water
accumulation and release
Ice and water convergence, Fresh water
accumulation due to Ekman pumping and sea ice
accumulation due to ridging and cooling
Beaufort Gyre
Downwelling in the center and upwelling along
continental slope
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From Proshutinsky and Johnson, 1997
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  • Interpretation of observed and simulated
    anomalies of environmental parameters for
  • ACCR -Anticyclonic Circulation Regime, and
  • CCR - Cyclonic Circulation Regime in the
    Canadian Basin and the Beaufort Gyre.
  • N negative anomaly
  • P positive anomaly
  • A anticyclonic (clockwise)
  • C cyclonic (counterclockwise)

56
  • Oceanic system
  • The oceanic portion of the Beaufort Gyre climate
    system
  • Stabilizes the anticyclonic circulation of sea
    ice and upper ocean
  • Accumulates and releases liquid fresh water and
    sea ice from the BG
  • Governs the ventilation of the ocean in coastal
    polynyas and openings along shelf-break
  • Regulates the circulation and fractional
    redistribution of the summer and winter Pacific
    waters
  • Determines the pathways of fresh water export
    from the Arctic to the North Atlantic
  • WE ASSUME THAT BARROW CANYON CAN BE USED TO
    DETECT CHANGES IN THE BG SYSTEN BECAUSE IT
    AMPLIFIES DYNAMYCS OF THE OCEANIC PORTION OF THE
    BG

57
  • Sea Ice System
  • Sea ice is an intermediate link between
    the atmosphere and ocean and is a product of
    interactions between the two. The sea ice system
    in the BG system is responsible for
  • Regulating momentum and heat transfer between the
    atmosphere and ocean.
  • Accumulating and releasing fresh water or salt
    during melting-freezing cycle.
  • Redistributing fresh water sources by
    incorporating first year ice from the marginal
    seas into the convergent BG circulation, holding
    it there and transforming it into ridged and
    thick multi-year ice.
  • Memorizing the previous years conditions,
    buffering variations and reducing abrupt changes.
  • Protecting the ocean from overcooling or
    overheating (the latter is extremely important
    for polar biology).
  • Sea ice plays an important role in the storage
    and redistribution of energy in arctic climate
    (Overland and Turet, 1994).

58
  • Surface Water
  • Along with sea ice, the surface water is the most
    active oceanic part of the BG. It is assumed that
    the surface water follows sea ice drift however
    its circulation patterns have not been measured
    directly.
  • It is important to investigate the processes and
    mechanisms of heat transformation and variability
    of FW in the upper layer for a better
    understanding of the FW role in stabilizing the
    BG system.
  • Recent changes in surface water structure were
    reported by Macdonald et al. (2002). The
    unusually fresh surface layer and thin ice
    observed in the Canada Basin interior appear to
    be manifestations of a complex interaction
    between wind fields, runoff and ice.

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Pacific Water - The circulation of
Pacific water may be coherent with the surface
currents but its pathways are not known from
direct observations. Recently the vertical
structure of this layer and its properties have
been revised by Shimada et al., (2001) and Steele
et al., (2004) where the presence of two types
of summer Pacific halocline water and one type of
winter Pacific halocline water in the BG were
reported. - According to EWG analysis,
the total thickness of the Pacific layer in the
BG is approximately 150 m. This thickness is
subject to temporal variability (McLaughlin et
al., 2003) depending on wind stresses and
circulation modes (Proshutinsky et al., 2002).
- It is important to investigate the
variability of the different Pacific-origin water
components, their circulation patterns and their
role in stabilizing or destabilizing the BG
climatic flywheel.
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  • Atlantic Water
  • The circulation pattern of this water is probably
    better known, but the role that atmospheric
    forcing plays in the propagation and
    transformation of Atlantic-origin waters is
    poorly understood.
  • The cyclonic pattern of this water propagation
    along the continental slope, proposed by Rudels
    et al. (1994) is supported by some numerical
    models (Holland, Karcher, Holloway, AOMIP, pers.
    com.). However other models (Häkkinen, Maslowski,
    Zhang, AOMIP, pers. com.) show anticyclonic
    rotation of this wheel.

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Models with cyclonic circulation of Atlantic water
MOM high resolution
POM
MOM low resolution
Global, OPA
MOM
64
Models with anticyclonic circulation of Atlantic
layer
MOM high resolution
Finite elements
MOM
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  • Atlantic Water
  • McLauglin et al., (2004) showed that Atlantic
    water as much as 0.5C warmer than the historical
    record were observed in the eastern Canada
    Basin.These observations signaled that
    warm-anomaly Fram Strait waters, first observed
    upstream in the Nansen Basin in 1990, had arrived
    in the Canada Basin and BG and confirm the
    cyclonic circulation scheme.
  • The collected data show that the Atlantic Waters
    are in transition and less dense than in previous
    decades. The impetus for such change requires
    further investigation.

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  • Deep Water
  • There are several hypotheses for the origin of
    the deep water in the Canada Basin (Timmermans et
    al., 2003).
  • One hypothesis is that deep-water renewal is
    episodic. Another hypothesis is that the deep
    water is derived from continuous renewal by shelf
    water. It has been suggested that brine release
    on Arctic continental shelves is partly
    responsible for the formation of water that
    ventilates the cold Arctic halocline in the upper
    200 m. Further, if the salinity of the shelf
    water in the Arctic increases, then water that
    presently maintains the halocline can become
    sufficiently dense to sink into the deep basins.
  • Presumably these processes were not important in
    the past but under new climatic conditions their
    role could be enhanced. This is because the
    reduction of sea ice extent and the enhanced
    formation of sea ice in winter as a result may
    lead to a larger volume of dense water
    formation (c.f. McLaughlin et al., 2003), under
    warmer climate conditions.

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BGOS and BSFCO
The Beaufort Gyre Observing System (BGOS) is
operational since August 2003. The BGOS project
is supported by NSF and current support covers
2005-2008 (including International Polar Year
2007/2008). White starts CTD stations Yellow
circles moorings red triangles Ice-tethered
profilers (drifting buoys)
Mooring equipped with MMP profiler, ULS, ADCP,
sediment trap, and bottom pressure recorder
(bottom tide gauge)
Beaufort Sea floor cable observatory (BGFO)
location
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Freshwater content (meters) and station locations
in 1950s and 1960s
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Freshwater content (meters) and station locations
in 1970s and 1980s
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