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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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slide1
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

slide2
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

slide3
Revised circulation scheme north of the Denmark Strait

- overturning circulation schemes

  • Transformation within boundary current loop (Mauritzen, 1996)
slide4
Revised circulation scheme north of the Denmark Strait

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

from Jónsson and Valdimarsson (2004)

slide5
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
slide7
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)

slide8
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

slide9
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

slide10
Inflow into the Denmark Strait

- revised circulation scheme

East Greenland Current (EGC)

North Icelandic Jet (NIJ)

slide11
Mean properties at the Kögur transect

EGC: East Greenland Current

NIJ: North Icelandic Jet

PSW: Polar Surface Water

AW: Atlantic Water

slide12
Transport estimates

- Freshwater

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

Reference salinity = 34.8

slide13
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

slide14
Historical hydrography

- Upper ocean circulation

Dynamic height of sea surface relative to 500 db

EGC

shelf break EGC

Iceland Sea gyre

separated EGC

slide15
Historical hydrography

- Near-surface layer

Potential temperature

Salinity

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

slide16
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
slide17
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
slide18
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
slide19
Numerical simulations

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

slide20
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
slide27
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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