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Title: Barrow Observatory: Investigating Oceanographic Junctions


1
Barrow Observatory Investigating Oceanographic
Junctions Thomas Weingartner Institute of
Marine Science University of Alaska Fairbanks, AK
99775
2
Barrow Canyon
3
  • The Junctions
  • Chukchi and Beaufort Shelves
  • Shelf/Slope
  • Atmosphere-Ice-Ocean-Land
  • Pacific and Atlantic Oceans

4
Mean Flow Field
Northward on average, parallels bathymetry,
major migratory corridors for organisms
(zooplankton whales)
5
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)
6
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)
7
Complex ice deformation field
Mean Flow
Barrow
Coastal polynya
Dense water formation
8
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?
9
Implications for Ventilation of Arctic Ocean
Polynya present
Polynya absent
(Weingartner et al., in revision)
10
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)
11
Relatively little mixing occurs on the northern
shelf
basin
shelf
west
east
Winter Water
AIW
12
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))
13
Eddies are ubiquitous features of the Canada
Basin missed in most models Observations are
spotty
r10km
14
But it takes a lot of fuel an expensive ship to
sample them!
15
Shelf flow Highly variable and seasonal
16
Beaufort Undercurrent (slope) highly variable
but NOT Seasonal! Why?? How much
does it transport vs. eddies?
17
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.
18
Landfast ice covers 20 of the Arctics shelf area
19
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)
20
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)
21
TIDAL SEA LEVEL??
FORCING??
(Weingartner et al., in prep.)
22
What controls flow beneath the landfast ice? How
are pressure gradients initiated?
23
90 of annual runoff occurs in 2 weeks and
beneath the landfast ice.
24
Resuspension into ice matrix
25
Ri 350 Mixing is very difficult.
Do mid-latitude plume dynamics apply to arctic
shelves?
26
Plumes affect dispersal of terrestrial materials,
shape inner shelf ecosystem.
27
Mesoscale Variability connects inner shelf to the
slope
Sep. 5, 2002
FW plume
Prudhoe Bay
Kaktovik
100 km
(SeaWIFS M. Schmidt)
28
  • 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

29
Common to other high-latitude (not only Arctic)
slopes and shelves, Contrasts/comparisons with
mid-latitude settings
30
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31
500 km
80 km
Kuparuk River
Canning River
Bathymetrically smooth Except over the
slope River outflows localized central and
eastern Beaufort
32
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)
33
Eastern Beaufort (Kaktovik) Freshwater
source(s) North Slope Rivers, Mackenzie,
ice-melt Is there an along-shelf gradient in
stratification?
(Aagaard, 1984)
34
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???
35
Current magnitudes??
36
(Weingartner et al., 1999)
37
(No Transcript)
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