Barrow Observatory: Investigating Oceanographic Junctions

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Barrow Observatory Investigating Oceanographic
Junctions Thomas Weingartner Institute of
Marine Science University of Alaska Fairbanks, AK
99775
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Barrow Canyon
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• The Junctions
• Chukchi and Beaufort Shelves
• Shelf/Slope
• Atmosphere-Ice-Ocean-Land
• Pacific and Atlantic Oceans

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Mean Flow Field
Northward on average, parallels bathymetry,
major migratory corridors for organisms
(zooplankton whales)
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Variability is Largely wind-driven Decorrelation
scales NE Chukchi gt300 km The flow field is
simple and well-depicted by models.
(Weingartner et al., in revision)
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Water Properties Essentially Bering Strait
properties advected northward. Barrow
Canyon AIW upwelled slope water (Atlantic
origin) Dense Water (DW) NE Chukchi Sea
polynyas Nutrient/bio. cycles not well known
AIW DW
Barrow Canyon
(Woodgate et al., in press Weingartner et al.,
in revision)
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Complex ice deformation field
Mean Flow
Barrow
Coastal polynya
Dense water formation
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Annual T/S diagrams for Bering Strait Chukchi
waters
Polynya present
Polynya absent
How frequently do these differences occur? How
much dense water is formed?
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Implications for Ventilation of Arctic Ocean
Polynya present
Polynya absent
(Weingartner et al., in revision)
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r r
Winter T/S properties are likely predictable from
models given Bering Strait (BC) inflow
properties Met. Data Ice extent/cover (maybe)
Verify by Barrow Canyon measurements Applications
to Antarctica, Sea of Okhotsk, open ocean
convection(?)
(Winsor and Chapman, 2001)
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Relatively little mixing occurs on the northern
shelf
basin
shelf
west
east
Winter Water
AIW
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Complicated adjustments/mixing occurs at the
slope within Barrow Canyon Eddy formation
(propagate into the basin) Halocline renewal by
Pacific waters (seds., nutrients,
carbon) Mechanisms/rates are unknown. Plume
dynamics, instabilities.
(Pickart et al., in revision))
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Eddies are ubiquitous features of the Canada
Basin missed in most models Observations are
spotty
r10km
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But it takes a lot of fuel an expensive ship to
sample them!
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Shelf flow Highly variable and seasonal
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Beaufort Undercurrent (slope) highly variable
but NOT Seasonal! Why?? How much
does it transport vs. eddies?
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SCICEX99 Alongslope T/S 112m (USSN Hawkbill,
April 1999)
N. Chukchi
E. Beaufort
dS/dx gt 0
An alongslope density gradient (with embedded
eddies) could support a steady Beaufort Slope
Current.
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Landfast ice covers 20 of the Arctics shelf area
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ICE ZONATION

• Effects
• No wind stress on inner shelf
• Large curl at offshore boundary
• a bumpy bottom (friction affects under-ice
  flow )
• geomorphological agent
• biological habitats

L 10 40 km H 20 40 m
t 0
t 0
(Reimnitz et al., 1978)
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900 700 500 300 100 0
Lonely- Western
Ridging (keels) Intensity varies seasonally and
spatially. Under-ice friction should also. Ice
Dynamics on shelves is poorly understood!!
1100 900 700 500 300 100 0
Kaktovik - Eastern
Ridging Intensity (m2)
Prudhoe Bay - Central
(Tucker et al., 1979)
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TIDAL SEA LEVEL??
FORCING??
(Weingartner et al., in prep.)
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What controls flow beneath the landfast ice? How
are pressure gradients initiated?
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90 of annual runoff occurs in 2 weeks and
beneath the landfast ice.
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Resuspension into ice matrix
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Ri 350 Mixing is very difficult.
Do mid-latitude plume dynamics apply to arctic
shelves?
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Plumes affect dispersal of terrestrial materials,
shape inner shelf ecosystem.
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Mesoscale Variability connects inner shelf to the
slope
Sep. 5, 2002
FW plume
Prudhoe Bay
Kaktovik
100 km
(SeaWIFS M. Schmidt)
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• What Science could the Barrow Observatory
  address
• Chukchi Shelf Dense water formation and
  plume/canyon dynamics.
• Annual cycles Geochemical (nutrients, tracers,
  sediments)
• biological (zooplankton, phytoplankton rates)
• Chukchi/Beaufort Slope mixing, eddy formation in
  a low internal wave, but strong flow environment.
• Beaufort Undercurrent Dynamics
• Downstream variations in Atlantic Water
  properties
• Beaufort Shelf Underice ocean and river plume
  dynamics
• Landfast/shelf ice dynamics
• Ice as a geomorphological/sediment
  transport agent

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Common to other high-latitude (not only Arctic)
slopes and shelves, Contrasts/comparisons with
mid-latitude settings
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500 km
80 km
Kuparuk River
Canning River
Bathymetrically smooth Except over the
slope River outflows localized central and
eastern Beaufort
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16 July 1998 AVHRR
Mackenzie Plume detectable in northern
Chukchi Sea Ak. Beaufort Shelf? Yes, but A
corridor for arctic cisco
Mackenzie R.
(Engle and Weingartner, 2001)
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Eastern Beaufort (Kaktovik) Freshwater
source(s) North Slope Rivers, Mackenzie,
ice-melt Is there an along-shelf gradient in
stratification?
(Aagaard, 1984)
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Offshore Spreading of Nearshore Water
Aug. 25, 2002 Preceding 7-days winds East West
5 10 m-s-1 (Prudhoe Bay)
Plumes?
Plumes?
Plumes?
Colville
Sag
(SeaWIFS M. Schmidt)
l 25 km, Crest trough 30 km Plume Depth???
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Current magnitudes??
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(Weingartner et al., 1999)
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