3/14/2005 1/32

Coastal Processes and Arctic Climate Change

Are they resolved? Do they matter?

How do they scale?

Andreas MünchowCollege of Marine Studies

University of Delaware

Collaborators:Drs. Falkner, Garvine, Melling, Weingartner

3/14/2005 2/32

Hypotheses/Conclusions•Large, abrupt pulses of freshwater discharges do not disturb the thermohaline circulation substantially;

•Freshwater driven flows scale with the internal deformation radius L~10-km (“eddy” scale);

•Scaling implies small across-shore (~10-km) and long along-shore (~1000-km) correlation scales;

•“Measured” (and modeled) freshwater fluxes do not resolve relevant scales;

•Nares Strait mooring array designed to resolve the internal deformation radius, freshwater fluxes, and dynamics.

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Coastal Processes and Arctic Climate Change:

1. Insulation of the Arctic ice-cover from warm

Atlantic water at depth, i.e., “maintenance of the

Arctic halocline”

2. Arctic freshwater and the global thermohaline

circulation (nonlinear, multiple equilibria)

How to move water across sloping topography?

global

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Hypotheses/Conclusions•Large, abrupt pulses of freshwater discharges do not disturb the thermohaline circulation substantially;

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Today’sclimate

Greenland Ice Core Data oxygen isotopes 18O ~ T temperature

Figure from Alley et al. (2001)

Climate of last 10,000 years appears most anomalous.

18O

COLD

WARM

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Hysteresis Loop of Climate ChangeO

vert

urni

ng C

ircu

lati

on 100 mSv

Rahmstorf (2000)

Nonlinear response of thermohaline circulation to freshwater pertubations

Caveats:

•Location of current climate?•100-500 year duration•Distance to convection sites

Stommel (1961)

COLD

WARM

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Hysteresis Loop of Climate ChangeO

vert

urni

ng C

ircu

lati

on 100 mSv

Rahmstorf (2000)

Stommel (1961)

COLD

WARM

Freshwater FluxAlley (2001)

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Freshwater Flux: ∫ u(s-s0)/s0 dA

0.1 Sv = 0.1106 m3/s = 100 mSv = 3,150 km3/year

Arctic RiversBering StraitDavis Strait

Lena RiverAmazon RiverLake Ontario

Arctic Ice Volume

Lake Agassiz*

110 mSv70 mSv

100 mSv

17 mSv200 mSv

9 mSv

>1,000 mSv

3,800 km3/y2,200 km3/y3,000 km3/y

510 km3/y6,300 km3/y

270 km3/y

30,000 km3

>30,000 km3/y(*) glacial lake dammed by Laurentian ice sheet burst ~8200 BP (Barber et al., 1999, Nature)

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Today’sclimate

YoungerDryas

Greenland Ice Core Data oxygen isotopes 18O ~ T temperature

Adapted from Alley et al. (2001)

Climate of last 10,000 years appears most anomalous.

18O

COLD

WARM

LakeAgassizdischarge

3/14/2005 10/32

Hypotheses/Conclusions

•Large, abrupt pulses of freshwater discharges do not disturb the thermohaline circulation substantially;

•Freshwater driven flows scale with the internal deformation radius L (“eddy” scale);

√∆/0 g D / f ~ 10 km

+∆

D

f is Coriolis “force”

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“derived” velocity

Nares Strait Hydrography, Aug.-2003

Pics-AprilPics-August

Density

Temp.

Salinity

Canada Greenland

LL

D

view from Greenland across Nares Strait

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David Huntley (UDel) with “sonar” in Aug. 2003

Velocity:Radars + Sonars

Radars send and receiveelectromagnetic waves (radio, police)

Sonars send and receives acoustic waves (sound, whales)

Same physics.

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•

•

t0

t0+16 hrs

east west

Barrow Canyon Velocity Section:

Synoptic velocity observation in Barrow Canyon, Alaska(view is to the south):

The flow scales with the internal deformation radius, about 5-km.

The flow is also unsteady.

Münchow and Carmack (1996)

D

D

L

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I

II

III

Eddies in the ArcticSept.-22, 2004

I II III

USCGC Healy 75-kHz ADCP

L

D

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Interaction of wind- and buoyancy forced motions

Salinity

Fresh riverine water turnsright at the coast.

Münchow and Garvine (1993)

L

D

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Hypotheses/Conclusions•Large, abrupt pulses of freshwater discharges do not disturb the thermohaline circulation substantially;

•Freshwater driven flows scale with the internal deformation radius L~10-km (“eddy” scale);

•Scaling implies short across- (~10-km) and long along-shore (~1000-km) correlation scales

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Ward Hunt Ice Shelf

~ 4 km3 fresh water and unique ecosystem lost from dammed epishelf lake in Disraeli Fjord 1999-2002

Mueller et al. (2003)

crack

Ice shelf

EllesmereIsland

Disraeli Fjord

Arctic Ocean

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Ward HuntIce Shelf

1962

1963

1964

Nutt (1966): The drift of ice island WH-5

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Labrador Shelf

Moving ice on the Labrador shelf indicates trapping of fresh water and ice on the shelf

Hudson Strait

LABRADOR

NA

SA

deep convection site winter 1997 (Pickart et al., 2002)

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North(cm/s)

East(cm/s)

Labrador

Labrador Sea

Time (hours)

basinshelf

fresh salty

Velocity

Velocity

Depth

Sal.

Temp.warmcoolcold

Crossing the Labrador Current, July-23, 2003

southward

eastward

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Hypotheses/Conclusions

•Large, abrupt pulses of freshwater discharges do not disturb the thermohaline circulation substantially;

•Freshwater driven flows scale with the internal deformation radius L~10-km (“eddy” scale);

•Scaling implies small across-shore (~10-km) and long along-shore (~1000-km) correlation scales;

•“Measured” (and modeled) freshwater fluxes do not resolve relevant scales

???

??

Chapman and Beardsley (1989) adapted byKhatiwala et al. (1999)

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Davis Strait 3-year Mean1987-1990

~150-m

~300-m

~500-m

with95% confidence levelsfor speed and direction

“Ross” data(Tan et al., 2005)

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Baffin Island Current

West Greenland Current

1.5Sv

0.7Sv

2.3Sv

Velocity normal to Davis Strait mooring section:

3-year mean velocity (contours)over 1987-1990 salinity (color)

3-year mean velocityminus 95% confidence

3-year mean velocityplus 95% confidence

Volume flux: 1.5 ± 0.8 SvFreshwater flux: 75 ± 38 mSv

EOF Analyses

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Davis Strait Northward Flow@ 150-m (“surface”)

Annual harmonic+ Semi-annual harmonic+ record mean

Baffin Island Current

West Greenland Current

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Retreat of Jakobshavn IsbræWest-Greenland

NA

SA

/US

GS

Greenland Ice Sheet

BaffinBay

5-km

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Hypotheses/Conclusions

•Large, abrupt pulses of freshwater discharges do not disturb the thermohaline circulation substantially;

•Freshwater driven flows scale with the internal deformation radius L~10 km (“eddy” scale);

•Scaling implies short across-shore (~10-km) and long along-shore (~1000-km) correlation scales;

•“Measured” (and modeled) freshwater fluxes do not resolve relevant scales;

•Nares Strait mooring array designed to resolve the internal deformation radius, freshwater fluxes, and dynamics

3/14/2005 27/32

Canadian Archipelago Throughflow Study (CATS):

NA

SA

200

2/22

3

Petermann Glacier

Humbold Glacier

Arctic Ocean

Greenland

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Geostrophic current

Kennedy Channel Hydrography, Aug.-2003

Pics-AprilPics-August

S

Canada Greenland

LL

D

D

view from Greenland across Nares Strait

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Salinity s

Velocity

FreshwaterFlux/unit area

Nares Strait South (Kennedy Channel)

∫ u(s-s0)/s0 dA

∫ u dA

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Across-channel flow

Along-channel flow

Currents@ 100-m

*

Pics-April

Pics-August

.html

Wind

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Hypotheses/Conclusions•Large, abrupt pulses of freshwater discharges do not disturb the thermohaline circulation substantially;

•Freshwater driven flows scale with the internal deformation radius L~10-km (“eddy” scale);

•Scaling implies small across-shore (~10-km) and long along-shore (~1000-km) correlation scales;

•“Measured” (and modeled) freshwater fluxes do not resolve relevant scales;

•Nares Strait mooring array designed to resolve the internal deformation radius, freshwater fluxes, and dynamics.