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Moored Current Observationsfrom Nares Strait:

Andreas MünchowCollege of Marine and Earth Studies

University of Delaware

Collaborators:Drs. Melling (Canada) and Samelson (Oregon)

1. Relevance/context2. The descriptive view3. The statistical view4. The “missing” view

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Dilution of the northern North Atlantic Ocean in recent decadesRuth Curry and Cecilie Mauritzen (2005, Science):

How much fresh water causes salinity change?

How fast does fresh water enter the sub-Arctic circulation?

Where is the fresh water stored?

“Excessive amounts of fresh water could alter the ocean density contrasts that drive the

northernmost extension of the Atlantic MOC, diminish its northward heat transport, and

substantially cool some regions …” “Great Salinity Anomaly”

0.03 Sv

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from National Sea Ice Data Centerhttp://nsidc.org/data/seaice_index/

Sea Ice Extent

March (max. extent)

September (min. extent)

2006

2006

2007

2007

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Ice Area Extent: Deviation from 1979-2007 mean

from http://www.arctic.noaa.gov/reportcard/seaice.html

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QuickTime™ and aCinepak decompressor

are needed to see this picture.

AMSR-E imagery (89 GHz): Sept.-2004 through May-2005

Agnew,Canadian Met. Service

Dr. Holt ofNASA/JPL

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1. Descriptive View

ADCP mooring recovery, Northern Greenland, Aug.-16, 2006

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David Huntley (UDel) with “sonar

Velocity:Sonars

Sonars send and receives acoustic waves

Measured Dopper shift proportional velocity

Kennedy Channel,August 2003

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Nares Strait Freshwater Flux Experiment

Velocity Snapshot (4-days)

cm/s

LD

Greenland

from Münchow et al. (2007)

Volume Flux:

Fresh Water Flux:

100-m

Longitude West

Lat

itud

e N

orth

0.77±0.10 106 m3/s

28 ±4 106 m3/s

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July/August 2003 ADCP Survey Volume Flux Summary

-0.77 Sv

-0.92 Sv

-0.91 Sv

-1.03 Sv

+4.3 Sv

-4.8 Sv

Greenland

0.90.10 Sv

1 Sv=106 m3/s ~5 Amazon ~1000 Delaware

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Nares Strait Hydrography,Aug.-2003

Density

Temp.

Salinity

Canada Greenland

LD

D

LD = (∆/0 g D)1/2 / f ~ 10 km

+∆ D

from Münchow et al. (2006)

Internal Rossby radius of deformation

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XXX XX ADCP

CT/CTD

All recovered instruments have clean 3-year records

X X X

X

XX

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Nares Strait Freshwater Flux Experiment

km-03,Canada

km-24

km-30

Greenland,km-34

Time2003 2006

30

-30

Along-Channel Currents, cm/s

Velocity Time Series (3-years)

cm/s

Greenland

~300

-km

Arctic Ocean

Aug. 5, 2005

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April-29, 2005

EllesmereIsland

Greenland

Land-fast ice cover

Mooring line

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3. Statistical Views

Ellesmere Island, Aug.-16, 2006: CT/CTD string recovery

15 of 27Time (days), April 2005

Sea level

Atmospheric pressure

Filtered sea level

Adjusted sea level

Alert, northern Ellesmere IslandTides and Filters

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High-resolution Power-spectra of Depth-averaged Flow at KS10

All frequencies

Diurnal band

Semi-diurnal band

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Kennedy Channel Tidal Ellipsesof depth-averaged flow

12.42 hrs, the M2 semi-diurnal tide

23.93 hrs, the K1 diurnal tide

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Degrees of freedom: T/TD

KS02 red (Canada)KS10 blueKS12 greenKS14 black (Greenland)

TD ~ 4-5 days

TD ~ 1 days

TD decorrelation timeT record length

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Wind from Samelson et al (2006)

KS14 (Greenland)

KS10

KS02 (Canada)

KS12

•Note the southward flow and wind (significant at 95% confidence);

•Trends are in red (significant at 95% confidence)

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Record-Mean (3-year) Flow

44% 35% 13% 8% weightsKS02 KS10 KS12 KS14 mooring

0.59±0.09 106 m3/s

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April-292005

August-122005

2004 2005

northward flow(coastal Greenland)

southward flow(channel)

Mean + SeasonalSignal

Sa solar annual

Ssa solar semi-annual

Flux

Flow

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Principal Axes of variability after mean, trend, and seasonalvariability has been removed (standard deviation)

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y, North

Gre

enla

nd

Can

ada

= (x1,y2,t)

u=u(x,y1,z,t)= (x,y1,z,t)

p=p(x,y0,zb,t) 2 bottom pressure series

4 locations with ~30 current series6 locations 4 density series

Alert sea level and atmospheric pressure

x, East

= (x2,y-1,z,t) Thule sea level and atmospheric pressure

The “missing” view-1: Dynamics

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3-year Mean FlowsKennedy Channel

Channel center,KS10

300m

0m

Dep

th (

m)

0 20(cm/s) -180 90Deg.

Speed Direction

The “missing” view-2: Vertical variability

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Conclusions:•Array design and processing methodology sufficient to resolve scales of variability of the depth-averaged flow;

•Record-mean volume flux is 0.59±0.09 Sv southward;

•Seasonal variability has an amplitude of 0.15 Sv, thus does not reverse the mean flux;

•Linear trend indicates a steady increase in southward volume flux of 0.05±0.09 Sv/year which corresponds to a 25% increase from 2003 through 2006;

•Vertical variations and dynamics require attention desperately

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Going home …

Navy Board Inlet, Aug.-2006

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MaslowskiNPS

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Across-channel integralof f/g times V0(x)

V0(x)=Vg-VADCP

Vg = relative geostrophicVADCP = observed velocity

Canada Greenland

Estimating Absolute Geostrophic Transport:

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