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

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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
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Hydrographic station locations (blue dots) in the
1950s and 1960s
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Hydrographic station locations (blue dots) in the
1970s and 1980s
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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
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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.
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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
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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
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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
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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)

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• 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

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• 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).

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• 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
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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