- cannot form Halocline (Aagaard,...

Arctic Change 2009 - Woodgate

How to form halocline water?

Adapted from Steele and Boyd, 1998

Atlantic water

Surface Water

- cannot form Halocline water simply by mixing

(Aagaard, 1981)


Temp Fresh Salty

ADD COLD, SALTY

Aagaard et al, 1981

Rudels et al, 1996Temp Salty

Con

vect

ADD COLD, FRESH

~ 50m

~ 100m

~ 50m

~ 100m

ADVECTIVE HC

CONVECTIVE HC

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)


Halocline formation

Woodgate etal, 2001

ConvectiveAdvective


Basin/Shelf FSBW/BSBW

origin

Rudels et al, 2004, Polar Research

Black= FSBWBlue = BSBW

Red = AWGreen = Rivers

Orange = Pacific inflow

.. but what about change??


Retreat of the Cold Halocline

(Steele and Boyd, 1998)

In 1995, only Makarovhas a cold halocline

Use salinity in 40-60m band as an indicator

Hi S = NO CHLLo S = CHL


Retreat of the Cold Halocline (Steele and Boyd, 1998)

Injection point of freshwater (Russian Rivers) has changedBacked up by chemical data,

Ekwurzel et al., 2001

PREVIOUS – RW into Eurasian Basin – CHL in Eurasian Basin1995 – RW along shelf instead – no CHL in Eurasian Basin


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


“Levitus” for the Arctic 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


Western versus Eastern Arctic Halocline

EASTERN ARCTIC (ATLANTIC) HALOCLINE- less salinity range- saltier at surface

- sharper bend in TS space

Adapted from Steele and Boyd 1998

BSW – Bering Sea WaterUHW – Upper Halocline WaterLHW – Lower Halocline Water

AW – Atlantic WaterDW – Deep Water

WESTERN ARCTIC(PACIFIC) HALOCLINE- greater salinity range

- fresher at surface- general Tmax above Tmin

- very varied- (rich in nutrients)


Western versus Eastern Arctic HaloclineImage from Steele and Boyd 1998

BSW – Bering Sea WaterUHW – Upper Halocline WaterLHW – Lower Halocline Water

AW – Atlantic WaterDW – Deep Water

European Speak: e.g. Manley et al, 1992Polar Water T: < 0 deg C and S: <34.4 psuArctic Surface Water T: < 0 deg C and S: 34.4-34.9 psuAtlantic Intermediate Water T: 0-3 deg C and S: 34.4-34.9 psuAtlantic Water T: > 3 deg C and S: > 34.9 psu

Polar Water

ArcticSurfaceWater

Arctic IntermediateWater

Atla

ntic

Wat

er


Shift of Pacific/Atlantic Front

- use TS and chemistry to show Pacific Atlantic Front retreated from Lomo Ridge

to Mendeleev Ridge by 1993

JGR, 1996 JGR, 2005

Historic Russian Data- silicate profiles in central Makarov- Si max disappears in late 1980s


Bering Strait and the Chukchi SeaNutrient-rich

Anadyr waters

Bering Shelf waters

Alaskan Coastal Current

(warm, fresh, seasonal)

Siberian Coastal Current

(cold, fresh, seasonal)

Stagnation Zones over Herald and

Hanna Shoals

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

COLDERSALTIER

RICHER IN NUTRIENTS

WARMERFRESHER

LOWER IN NUTRIENTS


JGR, 2004

ACW=Alaskan Coastal WatersBSW = summer Bering Sea Water


Generic Pacific Water circulation

Steele et al, 2004

BUT- doesn’t always match Fram Strait outflow – is there a better tracer

- how get the Pacific Water off from the Chukchi

- change in pathway with change in Atmospheric state- shift of Pacific/Atlantic boundary from Lomonosov Ridge


=Four main outflows1. Barrow Canyon 2. Central Gap3. Herald Canyon 4. Long Strait??= Most nutrients in West= Outflows move east & north= Seasonal & interannual variabilityin TS (thus density and equilibrium depth) and also in volume

= TOPOGRAPHIC CONSTRAINTS(Potential Vorticity Conservation)- Taylor columns in Chukchi

- flow ~ along isobaths eastwardBUT WE SEE PW GETS AWAY

FROM TOPOGRAPHY

= FRICTION (TOP or BOTTOM)

= DENSITY DIFFERENCES- dense water outflows

= WIND EFFECTS- upwelling and downwelling- undercurrents

= EDDIES

= INERTIAL and TIDAL OSCILLATIONS AND MIXING

LongStrait

Chukchi Sea Outflow


Dense Water Outflow– e.g. from coastal polynyas

(e.g. Martin et al, 2004)

ICETemperature

ICEThickness

WindX Ice

S flux as new ice

Dense water on shelf

Dense water flows down shelf as a

descending plume,entraining water.

(i.e. down, but not OUT)


2002, JGR

- can get the salinities,but volume is small

~0.06Sv


Wind effects

WindX WindX

Upwelling of deeper water- can come up canyon

onto the shelf- cf Chukchi slope

canyons, Barrow Canyon, and many others

If initial stratification enough,can get undercurrent opposite to the wind

(Yoshida Undercurrent)- cf Beaufort slope

isopycnal


3rd October

5th October

Results of a strong westward wind

Ship’s ADCP of the Beaufort slope current system

(red= towards you)

(Andreas Muncheow, UDel)


Chukchi slope velocity 2002-2003red=73 20N blue=73 37N


Chukchi Slope 2002-2003TS-properties

73 20N- red 60m/70m water73 37N- cyan 60m/110m water- navy 100m/110m water

Temperature Maximum is

December – March, i.e. advective from the

south

Intrusions of Atlantic Water in Autumn


Upwelling versus polynyas??

Use Silicate to track Pacific Water in the Chukchi Borderland


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 StraitTS 1990-1991

Woodgate et al, 2005


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)


The Eddy Band-wagon


Eddies in the Beaufort Seae.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


Eddy Census 1 eddy =

(10 km radius, 50m)

~ 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

- XBT lines


Eddies in the non-Beaufort

Arctic(Woodgate et al, 2001)

TWO EDDY TYPESCold (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

LM1

LM2 LM3


PW - Low Oxygen

NPEO

SWYD

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 Pacific W

ater

Falkner et al, 2005 DSR

AW

PW


PW - Hi NutrientsSILICATE, NITRATE, PHOSPHATE

- High from source in PacificBUT – not conservative

Try to create a “tracer” that is conservative “Quasi-conservative Tracer”

“NO” and “PO” – Broecker, 1974- cope with growth and decay

NO = 9 NO3 + O2PO = 135 PO4 + O2

N:P ratiosNO: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]

(CH20)106(NH)16(H3PO4) + 138 O2 = 106 CO2 + 122 H2O + 16 HNO3 + H3PO4

Biogenic matter + oxygen = Carbon Dioxide + Water + NUTRIENTS

Fixing of nutrients and Carbon to make biogenic matter

Decay of biogenic matter using up Oxygen, forming nutrients

Redfield-Ketchum-Richards Model (Redfield et al, 1963)


PW versus AW in N:P spaceNITRATE:PHOSPHATE RELATIONSHIP

different in AW and PW= For a Nitrate value, PW have more Phosphate

= Slope set by Redfield

= Exact lines may changeNO3(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

AW

% PW in upper 30m

Jones, Anderson and Swift, GRL, 1998Distribution of Atlantic and Pacific waters in the upper Arctic Ocean: Implications for circulation

- cannot form Halocline (Aagaard,...

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