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Coastal Processes and Arctic Climate Change. Are they resolved? Do they matter? How do they scale?. Andreas Münchow College of Marine Studies University of Delaware. Collaborators: Drs. Falkner, Garvine, Melling, Weingartner. Hypotheses/Conclusions.

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Coastal processes and arctic climate change

Coastal Processes and Arctic Climate Change

Are they resolved? Do they matter? How do they scale?

Andreas Münchow

College of Marine Studies

University of Delaware

Collaborators:

Drs. Falkner, Garvine, Melling, Weingartner


Hypotheses conclusions

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.


Coastal processes and arctic climate change1

global

Coastal Processes and Arctic Climate Change:

  • Insulation of the Arctic ice-cover from warm Atlantic water at depth, i.e., “maintenance of the Arctic halocline”

  • Arctic freshwater and the global thermohaline circulation (nonlinear, multiple equilibria)

How to move water across sloping topography?


Hypotheses conclusions1

Hypotheses/Conclusions

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


Coastal processes and arctic climate change

Greenland Ice Core Data

oxygen isotopes 18O ~ T temperature

Today’s

climate

WARM

18O

COLD

Climate of last 10,000 years appears most anomalous.

Figure from Alley et al. (2001)


Hysteresis loop of climate change

100 mSv

Overturning Circulation

Hysteresis Loop of Climate Change

Stommel (1961)

Nonlinear response of thermohaline circulation to freshwater pertubations

WARM

Caveats:

  • Location of current climate?

  • 100-500 year duration

  • Distance to convection sites

COLD

Rahmstorf (2000)


Hysteresis loop of climate change1

100 mSv

Overturning Circulation

Freshwater Flux

Alley (2001)

Hysteresis Loop of Climate Change

Stommel (1961)

WARM

COLD

Rahmstorf (2000)


Freshwater flux u s s 0 s 0 da
Freshwater Flux: ∫ u(s-s0)/s0 dA

Arctic Rivers

Bering Strait

Davis Strait

Lena River

Amazon River

Lake Ontario

Arctic Ice Volume

Lake Agassiz*

110 mSv

70 mSv

100 mSv

17 mSv

200 mSv

9 mSv

>1,000 mSv

3,800 km3/y

2,200 km3/y

3,000 km3/y

510 km3/y

6,300 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)

0.1 Sv = 0.1106 m3/s

= 100 mSv

= 3,150 km3/year


Coastal processes and arctic climate change

Greenland Ice Core Data

oxygen isotopes 18O ~ T temperature

Today’s

climate

WARM

18O

Lake

Agassiz

discharge

COLD

Younger

Dryas

Climate of last 10,000 years appears most anomalous.

Adapted from Alley et al. (2001)


Hypotheses conclusions2

√∆/0 g D / f

~ 10 km

D

+∆

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);

f is Coriolis “force”


Coastal processes and arctic climate change

L

D

Nares Strait Hydrography, Aug.-2003

L

Density

“derived” velocity

view from Greenland across Nares Strait

Temp.

Salinity

Canada

Greenland

Pics-August

Pics-April


Velocity radars sonars
Velocity:Radars + Sonars

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

Radars send and receive

electromagnetic waves (radio, police)

Sonars send and receives acoustic waves (sound, whales)

Same physics.


Barrow canyon velocity section

L

D

D

east

west

t0

t0+16 hrs

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)


Eddies in the arctic sept 22 2004

I

II

III

Eddies in the ArcticSept.-22, 2004

I

II

III

D

L

USCGC Healy 75-kHz ADCP


Coastal processes and arctic climate change

Interaction of wind- and buoyancy forced motions

L

D

Salinity

Fresh riverine water turns

right at the coast.

Münchow and Garvine (1993)


Hypotheses conclusions3

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


Ward hunt ice shelf
Ward Hunt Ice Shelf

Arctic Ocean

Ice shelf

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

Ellesmere

Island

Mueller et al. (2003)

Disraeli Fjord

crack


Coastal processes and arctic climate change

1964

1962

Ward Hunt

Ice Shelf

1963

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


Labrador shelf

Hudson Strait

LABRADOR

NASA

Labrador Shelf

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

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


Coastal processes and arctic climate change

North

(cm/s)

East

(cm/s)

Labrador Sea

Labrador

Crossing the Labrador Current, July-23, 2003

eastward

Velocity

Velocity

southward

shelf

Depth

basin

cold

cool

warm

Temp.

fresh

salty

Sal.

Time (hours)


Hypotheses conclusions4

??

???

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 by

Khatiwala et al. (1999)


Davis strait 3 year mean 1987 1990
Davis Strait 3-year Mean1987-1990

~150-m

~300-m

with

95% confidence levels

for speed and direction

~500-m

“Ross” data

(Tan et al., 2005)


Coastal processes and arctic climate change

Velocity normal to Davis Strait mooring section:

Volume flux: 1.5 ± 0.8 Sv

Freshwater flux: 75 ± 38 mSv

2.3Sv

3-year mean velocity

plus 95% confidence

Baffin Island Current

West Greenland Current

3-year mean velocity

minus 95% confidence

0.7Sv

3-year mean velocity (contours)

over 1987-1990 salinity (color)

1.5Sv

EOF Analyses


Coastal processes and arctic climate change

Davis Strait Northward Flow

@ 150-m (“surface”)

Annual harmonic

+ Semi-annual harmonic

+ record mean

Baffin Island Current

West Greenland Current


Retreat of jakobshavn isbr

Greenland Ice Sheet

5-km

NASA/USGS

Baffin

Bay

Retreat of Jakobshavn Isbræ

West-Greenland


Hypotheses conclusions5

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


Canadian archipelago throughflow study cats

Arctic Ocean

Greenland

NASA 2002/223

Petermann Glacier

Humbold Glacier

Canadian Archipelago Throughflow Study (CATS):


Coastal processes and arctic climate change

L

L



S

Canada

Greenland

Kennedy Channel Hydrography, Aug.-2003

Geostrophic current

D

view from Greenland across Nares Strait

D

Pics-August

Pics-April


Coastal processes and arctic climate change

Nares Strait South (Kennedy Channel)

Salinity s

Velocity

∫ u dA

Freshwater

Flux/unit area

∫ u(s-s0)/s0 dA


Coastal processes and arctic climate change

Wind

Across-channel flow

Along-channel flow

.html

Pics-April

Pics-August

*

Currents

@ 100-m


Hypotheses conclusions6

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.