Revised circulation scheme north of the Denmark Strait
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Kjetil Våge, UiB Bob Pickart, WHOI Mike Spall, WHOI Kent Moore, UoT H éðinn Valdimarsson , MRI PowerPoint PPT Presentation


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Revised circulation scheme north of the Denmark Strait. Kjetil Våge, UiB Bob Pickart, WHOI Mike Spall, WHOI Kent Moore, UoT H éðinn Valdimarsson , MRI Dan Torres, WHOI Svetlana Erofeeva, OSU Jan Even Ø. Nilsen, NERSC. Blosseville coast, north of the Denmark Strait

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Kjetil Våge, UiB Bob Pickart, WHOI Mike Spall, WHOI Kent Moore, UoT H éðinn Valdimarsson , MRI

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Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait

Kjetil Våge, UiB

Bob Pickart, WHOI

Mike Spall, WHOI

Kent Moore, UoT

HéðinnValdimarsson, MRI

Dan Torres, WHOI

Svetlana Erofeeva, OSU

Jan Even Ø. Nilsen, NERSC

Blosseville coast, north of the Denmark Strait

View from R/V Knorr, October 2008


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait

- the Greenland-Scotland Ridge

1 Sv = 106 m3/s

Exchange across the ridge

  • Crucial part of climate system

  • Denmark Strait

    • Largest overflow plume

    • Arctic freshwater export

from Hansen et al.(2010)

theDenmarkStrait

- a choke point in the overturning circulation

from www.whoi.edu

from www.whoi.edu


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait

- overturning circulation schemes

  • Transformation within boundary current loop (Mauritzen, 1996)


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait

- the North Icelandic Jet – another source of overflow water?

from Jónsson and Valdimarsson (2004)


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait

- overturning circulation schemes

  • Transformation within boundary current loop (Mauritzen, 1996)

  • Transformation within interior loop (Våge et al., 2011)

  • Roughly equal contribution from either source


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Bathymetry north of the Denmark Strait

- the Blosseville Basin


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Inflow into the Denmark Strait

- present state of knowledge

East Greenland Current (EGC)

  • Two currents advecting overflow water into the Denmark Strait

North Icelandic Jet (NIJ)


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Observed circulation at the Kögur transect

- an unknown current in the interior Blosseville Basin

EGC

???

NIJ

σθ = 27.8 kg/m3

Greenland

Iceland

θ = 0oC

Mean absolute geostrophic velocity at Kögur computed from 4 realizations

EGC: East Greenland Current

NIJ: North Icelandic Jet


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Observed circulation at the Kögur transect

- the separated East Greenland Current

shelf break

EGC

separated

EGC

NIJ

σθ = 27.8 kg/m3

Greenland

Iceland

θ = 0oC

Mean absolute geostrophic velocity at Kögur computed from 4 realizations


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Inflow into the Denmark Strait

- revised circulation scheme

East Greenland Current (EGC)

North Icelandic Jet (NIJ)


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Mean properties at the Kögur transect

EGC: East Greenland Current

NIJ: North Icelandic Jet

PSW: Polar Surface Water

AW: Atlantic Water


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Transport estimates

- Freshwater

Nearly ¼ of the EGC system FW transport takes place in the interior

Reference salinity = 34.8


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Transport estimates

- Overflow water

Nearly ¼ of the EGC system FW transport takes place in the interior

Reference salinity = 34.8

The majority of the OW approaches the strait along the Iceland slope

0.8 ± 0.3 Sv

1.3 ± 0.4 Sv

1.4 ± 0.3 Sv

Total: 3.5 Sv


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Historical hydrography

- Upper ocean circulation

Dynamic height of sea surface relative to 500 db

EGC

shelf break EGC

Iceland Sea gyre

separated EGC


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Historical hydrography

- Near-surface layer

Potential temperature

Salinity

Vertically averaged between 50-100 m (potential temperature) and 10-30 m (salinity)


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Numerical simulations

- Model domain

  • MITgcm

  • Channel oriented along the east coast of Greenland

  • Southern outflow becomes northern inflow

  • Salinity restored to initial conditions in the northern end (32 at the surface on the shelf, 35 in the deep interior), temperature is constant

  • 1 km horizontal resolution, 30 vertical levels

  • Forced by steady annual mean wind stress


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Numerical simulations

- Mean sea surface salinity over final 2 years of integration

  • Sharp gradient near the shelf break at high latitudes supporting a shelf break jet

  • Offshore diversion of freshwater near y = 500 km


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Numerical simulations

- Sea surface salinity on day 770

  • Eddies and filaments dominate the Blosseville Basin

  • Freshwater diversion from the shelf break is highly time dependent


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Numerical simulations

- Temporal evolution of near-surface layer at y = 320 km


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Numerical simulations

- Eddy scenario

  • Southward flow inshore of x = 50 km

  • Offshore salinity front near x = 120 km, coincident with southward flow

  • The separated EGC arises from eddies that coalesce when encountering the Iceland slope


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait


Kjetil v ge uib bob pickart whoi mike spall whoi kent moore uot h inn valdimarsson mri

Revised circulation scheme north of the Denmark Strait

The research leading to these results has received funding from the European Union 7th Framework Programme (FP7 2007-2013), under grant agreement n.308299 NACLIM www.naclim.eu


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