BERING STRAIT BASICS
Bering Strait Basic Facts
- WHY
is the Bering Strait throughflow important?
- WHAT are
we doing?
- WHAT are
we learning?
A Decade in the Bering Strait
Bering Strait Ice Flux
Other
Publications
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RECENT
PAPERS
Interannual
changes
in the Bering Strait Fluxes of Volume, Heat and Freshwater between 1991
and 2004 Woodgate, et al, GRL,
2006
Some Controls on Flow and
Salinity in Bering Strait Aagaard, et al, GRL,
2006
Monthly Temperature,
Salinity and Transport Variability of the Bering Strait Throughflow. Woodgate,
et al, GRL, 2005
Revising the Bering Strait Freshwater Flux to
the Arctic Ocean. Woodgate &
Aagaard, GRL, 2005
Technical Report - Using
A3 as a climate station for the Bering Strait Throughflow,
Woodgate et al, August 2007
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BERING STRAIT BASICS
- The only ocean gateway between the Pacific and Arctic,
and ~85km wide, ~55m deep
- Divided into 2 channels by the two Diomede Islands
- Covered by sea-ice from ~January to April
- ANNUAL mean flow northward, but can flow southward for a week or
more
- Water speeds highly variable, from ~2.5 knots (120 cm/s) northward to
~1 knot (50 cm/s) southward depending on local wind
- flow driven (supposedly) by a pressure gradient between the Pacific
and the Arctic oceans, opposed by the local winds
- Water surface temperature freezing in winter, max around 12 deg C in
summer
- Annual mean flow ~0.8 Sv (800,000m3/s)
(Right is a
schematic of the flows in the region from Danielson and Weingartner,
click on the image to enlarge it)
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WHY IS THE BERING STRAIT THROUGHFLOW IMPORTANT?
For the Chukchi Sea
- primary source of nutrients for the Chukchi (one of the most biologically productive regions of the
world oceans)
- dominates the water properties of the Chukchi
For the Arctic
- primary source
of nutrients for Arctic ecosystems
- melts back sea-ice in summer,
- provides cold waters in winter to stabilize the upper Arctic
ocean
(thus influencing ice thickness and upper ocean mixing)
- provides ~40% of the freshwater input to the Arctic
- water properties determine ventilation depth of the Arctic
For the World Ocean
- an important part of the global freshwater cycle
- believed to influence the Atlantic overturning circulation
Pacific waters can be traced through the Arctic and out
through Fram Strait and the Canadian Archipelago
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Sea-surface
temperature for 26th August 2004
in the Bering Strait region. In the east, red
indicates the warm Alaskan Coastal Current in the east. Black
dots mark our mooring sites, A1, A2, A3 and A3'
(black dots). White areas
indicate
clouds.
(MODIS/Aqua level 1 image
courtesy of Ocean Color
Data Processing Archive, NASA/Goddard Space Flight Center.)
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WHAT ARE WE DOING?
- measuring the long-term variability of volume and water properties
in the Bering Strait region
We measure temperature,
salinity, water velocity and sometimes ice thickness and
motion, nutrients, fluorescence,
transmissivity
with subsurface oceanographic moorings (similar to the picture on the left)
In
summer/autumn, we take oceanographic sections in the Strait and the
southern Chukchi Sea (see cruise reports)
Since 1990,
moorings have been deployed with only a 1 year break.
We place
moorings to monitor flow through the western (A1) and eastern (A2)
channels of Bering Strait. The western channel is in the
Russian EEZ, an area to which we have only had occasional access.
In
other years the western channel has been monitored by a proxy site
at A3.
Left:
Schematic of a typical mooring.
ULS =
Upward-looking sonar to measure ice thickness
Steel Float
and Trifloat = for buoyancy
RCM9=Aanderaa
Acoustic Current meter to measure water velocity and
temperature
SBE=Seabird
sensor measuring temperature, salinity, fluorescence,
transmissivity NAS=nutrient measuring instrument
RT=Acoustic
releases for recovering mooring
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WHAT
ARE WE LEARNING?
That
Bering Strait flows vary from year to year .. and that the 2004 heat
flux is the highest recorded since 1990.
Changes
in the Bering Strait Fluxes of Volume, Heat and Freshwater between 1991
and 2004 Woodgate, et al, submitted GRL,
2006
That
Bering Strait provides ~40% of the freshwater input to the Arctic
Ocean.
Revising
the Bering Strait Freshwater Flux to the Arctic Ocean. Woodgate
&
Aagaard, GRL, 2005
Quantifying
the seasonal variability of the Bering Strait throughflow, with
implications for significant seasonal variation in how the Pacific
waters ventilate the Arctic.
Monthly Temperature, Salinity and Transport
Variability of the Bering Strait Throughflow. Woodgate,
Aagaard, Weingartner, GRL, 2005 |
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A DECADE IN THE BERING STRAIT
(for data to
2003,
click here)
Monthly mean
temperature and
salinity in Bering Strait during 1990-2000. The western
channel of the strait (mooring A1)
lies in the Russian EEZ and has often not been accessible. The
northern site (mooring A3), which
lies just east of the Russia-U.S. convention line, is influenced by the
flows through both channels. It therefore can serve as a partial
surrogate for the western channel site. Note the pronounced
annual cycle in
both temperature and salinity. The average peak-to-peak amplitude
of the salinity variation is about 1.5 psu and is driven by freezing,
which
expels salt into the water. In addition to the annual cycle of
temperature
and salinity, there are important longer-term variations. In
particular,
the record of salinity through the past decade shows that the Bering
Strait
inflow to the Arctic freshened about 1 psu during 1991-92 and then
remained
relatively fresh until 1999-2000, when about one-half of the earlier
freshening
effect was reversed. The temperature of the inflow has also
changed
significantly during the past decade, with a dramatic long-term warming
that peaked during 1996-97. This was followed by rapid cooling,
so that water as cold as observed in summer 2000 was last seen in
1990-91.
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A combination of ice
thickness data (e.g. from Upward Looking Sonars) and ice motion (e.g.
from Acoustic Doppler Current Meters) can yield estimates of ice flux.
For 1990 to
1991, these data suggest a mean annual northward ice flux, even though
the ice flux at the start of the season is southward.
a) Time series
of the northward velocity of water at 25m depth (red) and ice (blue)
show a very strong correlation between the ice and the water motion.
b) Timeseries
of ice
thickness (assuming thickness = 1.13 x keel depth) shows
- the thickening of ice
over the
winter
- that in the early winter
(i.e.
before day 352) northflowing water carries no ice.
c) From this,
we can
estimate the northward transport of water (red)
in 106 m3/s and ice (blue)
in 105 m3/s, (assuming the strait has a width of
65km and a triangular cross-section of maximum depth 55m).
d) Cumulative
transports
of water
(red) in 2x1012 m3
and ice (blue) in 1011 m3
show that the cumulative ice transport is southward for the first part
of the winter, even though the cumulative water transport is
always
northward.
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CRUISE REPORTS
Bering Strait 2000 - RV
Alpha Helix - HX235
Bering Strait 2001 - RV
Alpha Helix - HX250
Bering Strait 2002 - RV
Alpha Helix - HX260
Bering Strait 2003 -
RV Alpha Helix - HX274
Bering
Strait 2004 - RV Alpha Helix - HX290
Bering Strait 2005
- CCGS Sir Wilfrid Laurier
- SWL2005
REFEREED PUBLICATIONS (back to top)
Woodgate, R.A., K. Aagaard, and T.J. Weingartner, Monthly
temperature, salinity, and transport variability of the Bering Strait
throughflow. Geophys. Res. Lett., Vol. 32, No. 4, L04601
10.1029/2004GL021880, 2005
Woodgate, R. A.,
and K.
Aagaard, Revising the Bering Strait freshwater flux into the Arctic
Ocean, Geophys. Res. Lett., 32, L02602, doi:10.1029/2004GL021747, 2005
Walsh, J.J., D.A. Dieterle, F.E. Muller-Karger, K. Aagaard, A.T. Roach,
T.E. Whitledge, and D. Stockwell, CO2 cycling in the coastal
ocean. II. Seasonal organic loading of the Arctic Ocean from source
waters in the Bering Sea, Continental Shelf Res., 17,1-36, 1997.
Roach, A.T., K.
Aagaard, C. H. Pease, S.A. Salo, T. Weingartner, V. Pavlov, and M.
Kulakov, Direct measurements of transport and water properties
through Bering Strait, J. Geophys. Res., 100, 18,443-18,457, 1995.
Coachman, L.K., and
K. Aagaard, Transports through Bering Strait: Annual and interannual
variability, J. Geophys. Res., 93, 15535-15539, 1988.
Aagaard, K., A.T.
Roach, and J.D. Schumacher, On the wind-driven variability of the flow
through Bering Strait, J. Geophys. Res., 90, 7213-7221, 1985.
Schumacher, J.D.,
K. Aagaard,
C.H. Pease, and R.B. Tripp, Effects of a shelf polynya on flow
and water properties in the northern Bering Sea, J. Geophys. Res.,
88, 2723-2732, 1983.
Coachman, L.K., and
K. Aagaard, Re-evaluation of water transports in the vicinity of Bering
Strait, in The Eastern Bering Sea Shelf: Oceanography and Resources,
vol. 1, edited by D.W. Hood and J.A. Calder, pp. 95-110, National
Oceanic and Atmospheric Administration, Washington, D.C., 1981.
Coachman, L.K., K.
Aagaard, and R.B. Tripp, Bering Strait: The Regional Physical
Oceanography, 172 pp., University of Washington Press, Seattle, 1975.
Coachman, L.K., and
K. Aagaard, On the water exchange through Bering Strait, Limnol.
Oceanogr., 11, 44-59, 1966.
For
use
of any of these figures, please contact Rebecca
Woodgate (woodgate@apl.washington.edu)
©
Polar Science Center, University of Washington, 2004
We gratefully
acknowledge financial support for this work from the Office of
Naval Research (ONR), High
Latitude Dynamics program,
the National Science Foundation (NSF),
and the National Oceanic and Atmospheric Administration (NOAA).
Back to High Latitude Dynamics Homepage
Little Diomede
Island, middle of the Bering Strait
