How to form halocline water?
Atlantic water
- cannot form Halocline
water simply by mixing
(Aagaard, 1981)
Surface Water
Adapted from Steele and Boyd, 1998
Arctic Change 2009 - Woodgate
ADVECTIVE HC
Temp
Fresh
Aagaard et al, 1981
Salty
~ 50m
ADD
COLD, SALTY
~ 100m
~ 50m
Salty
Convect
Temp
CONVECTIVE HC
Rudels et al, 1996
ADD
COLD, FRESH
~ 100m
Steele and Boyd, 1998 – source of halocline water differs (advective or convective)
Woodgate et al, 2001 – temperature of halocline water differs
(convective must be at freezing temperature, advective may or may not be at freezing)
Arctic Change 2009 - Woodgate
Halocline formation
Co
nv
ec
tiv
e
Ad
ve
cti
ve
Woodgate etal, 2001
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Basin/Shelf
FSBW/BSBW
origin
Black= FSBW
Blue = BSBW
Red = AW
Green = Rivers
Orange = Pacific inflow
.. but what about
change??
Rudels et al, 2004, Polar Research
Arctic Change 2009 - Woodgate
Retreat of the Cold
Halocline
(Steele and Boyd, 1998)
In 1995, only Makarov
has a cold halocline
Use salinity in 40-60m
band as an indicator
Hi S = NO CHL
Lo S = CHL
Arctic Change 2009 - Woodgate
Retreat of the Cold Halocline
(Steele and Boyd, 1998)
Injection point of freshwater
(Russian Rivers) has changed
Backed up by chemical data,
Ekwurzel et al., 2001
PREVIOUS – RW into Eurasian Basin – CHL in Eurasian Basin
1995
– RW along shelf instead – no CHL in Eurasian Basin
Arctic Change 2009 - Woodgate
Decadal averages of Russian Data
1950s to 1980s
http://nsidc.org/data/g01961.html
(see also Swift et al, 2005 annual averages in boxes 1948-1993
- ftp:://odf.ucsd.edu/pub/jswift/arctic_aari_method_B
Arctic Change 2009 - Woodgate
“Levitus” for the Arctic
Arctic Change 2009 - Woodgate
http://psc.apl,washington.edu/Climatology.html
The (partial) return of
the Cold Halocline
(Boyd et al, 2002)
Consider (upper 80m) S over Lomo Ridge
- 1995 ~ 34 psu – no CHL
- 1997 ~ 33.55 psu
- 1999 ~ 33 psu
- 2000 ~ 33.3 psu – CHL returning
What could be causing this??
So far, this is EASTERN Arctic story,
what about the Western Arctic
Arctic Change 2009 - Woodgate
Western versus Eastern Arctic Halocline
WESTERN ARCTIC
(PACIFIC) HALOCLINE
- greater salinity range
- fresher at surface
- general Tmax above Tmin
- very varied
- (rich in nutrients)
BSW – Bering Sea Water
UHW – Upper Halocline Water
LHW – Lower Halocline Water
AW – Atlantic Water
DW – Deep Water
Adapted from Steele and Boyd 1998
EASTERN ARCTIC (ATLANTIC) HALOCLINE
- less salinity range
- saltier at surface
- sharper bend in TS space
Arctic Change 2009 - Woodgate
Atlantic Water
Arctic Intermediate
Water
Western versus Eastern Arctic Halocline
Image from Steele and Boyd 1998
Polar Water
Arctic
Surface
Water
European Speak: e.g. Manley et al, 1992
Polar Water
T: < 0 deg C and
Arctic Surface Water
T: < 0 deg C and
Atlantic Intermediate Water T: 0-3 deg C and
Atlantic Water
T: > 3 deg C and
Arctic Change 2009 - Woodgate
BSW – Bering Sea Water
UHW – Upper Halocline Water
S: <34.4 psu
S: 34.4-34.9 psu LHW – Lower Halocline Water
S: 34.4-34.9 psu
AW – Atlantic Water
S: > 34.9 psu
DW – Deep Water
Shift of Pacific/Atlantic Front
JGR, 1996
- use TS and chemistry to show Pacific
Atlantic Front retreated from Lomo Ridge
to Mendeleev Ridge by 1993
Arctic Change 2009 - Woodgate
JGR, 2005
Historic Russian Data
- silicate profiles in central Makarov
- Si max disappears in late 1980s
Bering Strait and the Chukchi Sea
Nutrient-rich
Anadyr waters
COLDER
SALTIER
RICHER IN NUTRIENTS
Bering Shelf
waters
Alaskan
Coastal Current
(warm, fresh,
seasonal)
Siberian
Coastal Current
(cold, fresh,
seasonal)
Stagnation
Zones over
Herald and
Hanna Shoals
Arctic Change 2009 - Woodgate
WARMER
FRESHER
LOWER IN NUTRIENTS
To first order,
except for
- cooling
- input from
coastal
polynyas,
Chukchi
dominated by
input through
Bering Strait
Export to Arctic
~
Input through
Bering Strait
Woodgate et al, DSR, 2005, http://psc.apl.washington.edu/Chukchi.html
JGR, 2004
ACW=Alaskan Coastal Water
sBSW = summer Bering Sea Water
Arctic Change 2009 - Woodgate
Generic Pacific Water
circulation
Steele et al, 2004
- change in pathway with change in Atmospheric state
- shift of Pacific/Atlantic boundary from Lomonosov Ridge
BUT
- doesn’t always match Fram Strait outflow – is there a better tracer
- how get the Pacific Water off from the Chukchi
Arctic Change 2009 - Woodgate
Chukchi Sea
Outflow
Long
Strait
= TOPOGRAPHIC CONSTRAINTS
(Potential Vorticity Conservation)
- Taylor columns in Chukchi
- flow ~ along isobaths eastward
BUT WE SEE PW GETS AWAY
FROM TOPOGRAPHY
= FRICTION (TOP or BOTTOM)
= DENSITY DIFFERENCES
- dense water outflows
=Four main outflows
1. Barrow Canyon 2. Central Gap
3. Herald Canyon 4. Long Strait??
= Most nutrients in West
= Outflows move east & north
= Seasonal & interannual variability
in TS (thus density and equilibrium
depth) and also in volume
Arctic Change 2009 - Woodgate
= WIND EFFECTS
- upwelling and downwelling
- undercurrents
= EDDIES
= INERTIAL and TIDAL
OSCILLATIONS AND MIXING
Dense Water Outflow
– e.g. from coastal polynyas
(e.g. Martin et al, 2004)
X
Wind
Ice
S flux as new ice
ICE
Temperature
ICE
Thickness
Dense water on shelf
Dense water flows
down shelf as a
descending plume,
entraining water.
(i.e. down, but not OUT)
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2002, JGR
~0.06Sv
- can get the salinities,
but volume is small
Arctic Change 2009 - Woodgate
Wind effects
X
Wind
X
Wind
isopycnal
Upwelling of deeper water
- can come up canyon
onto the shelf
- cf Chukchi slope
canyons, Barrow Canyon,
and many others
Arctic Change 2009 - Woodgate
If initial stratification enough,
can get undercurrent
opposite to the wind
(Yoshida Undercurrent)
- cf Beaufort slope
Results of a strong westward wind
3rd October
5th October
Ship’s ADCP of the Beaufort
slope current system
(red= towards you)
(Andreas Muncheow, UDel)
Arctic Change 2009 - Woodgate
Chukchi slope velocity 2002-2003
red=73 20N blue=73 37N
Arctic Change 2009 - Woodgate
Chukchi Slope 2002-2003
TS-properties
Temperature
Maximum is
December – March,
i.e. advective from the
south
Intrusions of Atlantic
Water in Autumn
73 20N
- red 60m/70m water
73 37N
- cyan 60m/110m water
- navy 100m/110m water
Arctic Change 2009 - Woodgate
Upwelling versus polynyas??
Use Silicate to track
Pacific Water in the
Chukchi Borderland
Arctic Change 2009 - Woodgate
Can we get this
TS from Bering
Strait??
NO ... salinities are only near 34 psu in extreme winters,
and then the waters are at freezing, not warmer
Bering Strait
TS 1990-1991
Woodgate et al, 2005
Arctic Change 2009 - Woodgate
Influence of shelf waters??
Along the Chukchi
Shelf, upwelling and
diapycnal mixing of
lower halocline waters
and Pacific waters
(Note ventilation by
polynya waters
couldn’t give this T-S
structure)
(Woodgate et al, 2005)
Arctic Change 2009 - Woodgate
The Eddy Band-wagon
Arctic Change 2009 - Woodgate
Eddies in the Beaufort Sea
e.g.,Hunkins and Manley, Plueddemann and MANY others
http://www.whoi.edu/science/PO/arcticgroup/projects/eddies.html
halocline depth
Arctic Rossby Radius
Predominantly Anticyclonic
Arctic Change 2009 - Woodgate
Eddy Census
1 eddy =
(10 km radius, 50m)
- XBT lines
~ 2 x 1010 m3
Flux through Bering
Strait ~ 1 Sv
~ 3 x 1013 m3 per yr
If all eddies, makes
~1000 eddies a
year.
Do we see 1000
eddies??? - no
Arctic Change 2009 - Woodgate
Eddies in the
non-Beaufort
Arctic
(Woodgate et al, 2001)
LM2
LM3
LM1
TWO EDDY TYPES
Cold (Tf), Fresh, near surface, AC,
- likely from shelf polynyas
Warm, Salty, ~ 1000m deep, AC
- instabilities on upstream front
(e.g. St Anna)
40 cm/s; ~ 10km radius, but volume flux ~ 0.1 Sv or less
Arctic Change 2009 - Woodgate
PW - Low Oxygen
Pacific Water
DISSOLVED OXYGEN
- High at surface (ventilated from atmosphere)
- Low = OLD water (long time since at surface)
or
= Evidence of high biological activity
THUS – Pacific Water has LOW Dissolved Oxygen
NPEO
SWYD
AW
PW
Falkner
et al, 2009
2005
DSR
Arctic Change
- Woodgate
SILICATE, NITRATE, PHOSPHATE
- High from source in Pacific
BUT – not conservative
PW - Hi Nutrients
Redfield-Ketchum-Richards Model (Redfield et al, 1963)
(CH20)106(NH)16(H3PO4) + 138 O2 = 106 CO2 + 122 H2O + 16 HNO3 + H3PO4
Biogenic matter
+ oxygen
= Carbon Dioxide + Water + NUTRIENTS
Decay of biogenic matter
using up Oxygen, forming nutrients
Fixing of nutrients and Carbon
to make biogenic matter
Try to create a “tracer” that is conservative “Quasi-conservative Tracer”
“NO” and “PO” – Broecker, 1974
- cope with growth and decay
NO = 9 NO3 + O2
PO = 135 PO4 + O2
N:P ratios
NO:PO ratios
N* (N star) – Gruber and Sarmiento, 1997
- indicates nitrogen fixation and denitrification
N* = 0.87 [N – 16 P + 2.9 µmol kg-1]
Arctic Change 2009 - Woodgate
NITRATE:PHOSPHATE
RELATIONSHIP
different in AW and PW
PW versus AW in N:P space
= For a Nitrate value, PW have more Phosphate
AW
= Slope set by Redfield
= Exact lines may change
NO3(pw) = 14.828 x PO4(pw) – 12.16 (Falck, 2001)
BUT work out % influence of PW and AW
(..but certainly no better than 10%
.... assumes ice melt, P and runoff same as AW
.... denitrification .. and other such processes)
PW
% PW in upper 30m
Jones, Anderson and Swift, GRL, 1998
Distribution of Atlantic and Pacific waters in the
upper Arctic Ocean: Implications for circulation
Arctic Change 2009 - Woodgate