water mass transformation in the iceland sea
DESCRIPTION
Water mass transformation in the Iceland Sea. Kjetil Våge Kent Moore Steingrímur Jónsson H éðinn Valdimarsson. Irminger Sea, R/V Knorr , October 2008. Water mass transformation in the Iceland Sea - the Denmark Strait Overflow Water. Denmark Strait Largest overflow plume - PowerPoint PPT PresentationTRANSCRIPT
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Water mass transformation in the Iceland Sea
Irminger Sea, R/V Knorr, October 2008
Kjetil Våge Kent Moore Steingrímur JónssonHéðinn Valdimarsson
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Water mass transformation in the Iceland Sea- the Denmark Strait Overflow Water
Denmark Strait Largest overflow plume Source of densest water to the lower limb of the AMOC
Iceland Sea Wintertime convection First definitive scenario for the source of DSOW (Swift et al., 1980)
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Water mass transformation in the Iceland Sea - overturning circulation schemes
Formed in the
Iceland Sea
(Swift et al., 1980)
Transformation
within boundary
current loop
(Mauritzen, 1996)
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Water mass transformation in the Iceland Sea - the North Icelandic Jet – another source of overflow water?
from Jónsson and Valdimarsson (2004)
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Water mass transformation in the Iceland Sea - overturning circulation schemes
Formed in the
Iceland Sea
(Swift et al., 1980)
Transformation
within boundary
current loop
(Mauritzen, 1996)
Transformation
within interior loop
(Våge et al., 2011)
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Water mass transformation in the Iceland Sea - climatological winter total turbulent heat flux
from Moore et al. (2012)
Winter (DJFM) climatological mean total turbulent heat flux from ERA-Interim
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from Jónsson (2007)
Cyclonic circulation in the
central Iceland Sea
Typical wintertime mixed
layer depths about 150-200 m
Surface densities exceeding
27.8 kg\m3 common in winter
Surface circulation
Water mass transformation in the Iceland Sea - circulation in the Iceland Sea
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Water mass transformation in the Iceland Sea - historical hydrographic measurements in the Iceland Sea
Collection of historical hydrographic measurements (1980 - present)
Determination of mixed-
layer depth and properties visual inspection of all profiles automated detection routines
employed manually determined when
those failed
→ robust data set
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Water mass transformation in the Iceland Sea - February-April mixed-layer depths
Map of mixed-layer depths
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Water mass transformation in the Iceland Sea - February-April mixed-layer depths
Map of mixed-layer depths
Contours of dynamic height
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Water mass transformation in the Iceland Sea - February-April mixed-layer densities
Map of mixed-layer potential densities
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Water mass transformation in the Iceland Sea - convection in the north-central Iceland Sea
Profiles located within the north-central Iceland Sea
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Water mass transformation in the Iceland Sea - the annual cycle
Mixed-layer depths
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Water mass transformation in the Iceland Sea - the annual cycle
Mixed-layer depths Mixed-layer potential densities
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Water mass transformation in the Iceland Sea - convective activity in the north-central Iceland Sea
Potential density in the central Iceland Sea (time vs. depth)
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Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet
σθ > 28.03 kg/m3
Potential density in the central Iceland Sea (time vs. depth)
Transport of σθ > 28.03 kg/m3 in the NIJ: 0.6 ± 0.1 Sv
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Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet
Mixed-layer depths Mixed-layer potential densities
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Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet
Mixed layers denser than σθ = 28.03 kg/m3
5 profiles from 2013
Important caveats sparse data set huge spatial and temporal variability
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Temporal evolution of potential vorticity along Argo float trajectory
Water mass transformation in the Iceland Sea - convective activity as recorded by Argo float winter 2008
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Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet
Profiles at the outer end of the Langanes section
Langanes repeat hydrographic section
Langanes 6
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Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet
Depth of the 28.03 kg/m3 isopycnal at Langanes 6
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Water mass transformation in the Iceland Sea - the densest component of the North Icelandic Jet
Difference: ~60 m
Depth of the 28.03 kg/m3 isopycnal at Langanes 6
→ Reduced production of dense water?
→ Different circulation regime?
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Water mass transformation in the Iceland Sea - atmospheric forcing
Decrease in the total turbulent heat flux, discontinuity around 1995
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Water mass transformation in the Iceland Sea - atmospheric forcing
Decrease in the total turbulent heat flux, discontinuity around 1995
Decrease in the wind stress curl, discontinuity around 1995
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Water mass transformation in the Iceland Sea - change in wintertime atmospheric circulation
1980-1995
1996-2013
Difference between the periods
1980-1995 and 1996-2013 Increased pressure Reduced northerly winds Anti-cyclonic circulation anomaly
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Water mass transformation in the Iceland Sea - change in wintertime atmospheric circulation
Difference between the periods
1980-1995 and 1996-2013 Increased pressure Reduced northerly winds Anti-cyclonic circulation anomaly
1980-1995
1996-2013 Difference between the periods
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Water mass transformation in the Iceland Sea - frequency of high heat flux events
Frequency of high heat flux events Decreasing occurrence of heat flux
events exceeding the 90th percentile value
Consistent with a weakening of the northerly winds
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Water mass transformation in the Iceland Sea - composite means of high heat flux events
Nature of high heat flux events Retreat of sea ice Northward shift of the highest
fluxes Narrowing of marginal ice zone Reduced number of events
(75 during first period, 65 during last)
1980-1989
2004-2013
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Water mass transformation in the Iceland Sea - ramifications of reduced forcing
November profiles from the Iceland Sea – initial conditions
from Moore et al. (2014)
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Water mass transformation in the Iceland Sea - ramifications of reduced forcing
1D mixed-layer model in the Iceland Sea
from Moore et al. (2014)
Ramifications of reduced forcing Gradual reduction in depth and density of
convection If this continues, it may weaken the
overturning loop that feeds the NIJ and reduce the supply of the densest water to the AMOC
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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
Water mass transformation in the Iceland Sea
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Water mass transformation in the Iceland Sea - NAO and ILD indices
North Atlantic Oscillation (NAO) index
Icelandic Lofoten Dipole (ILD) index
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Water mass transformation in the Iceland Sea - ramifications of reduced forcing
from Moore et al. (2014)
Model-data comparisons suggest that the 1D mixed-layer model is reasonable
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Water mass transformation in the Iceland Sea - Summertime stratification
Difference in potential density between 10 and 250 m
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Water mass transformation in the Iceland Sea - June-August mixed-layer densities
Map of mixed-layer potential densities
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Polar inflow
Arctic domain
Surface salinity, from Swift and Aagaard (1981)
Local modification
leads to formation of
Arctic Intermediate Water
Contributes to
overflows east and west
of Iceland
Atlantic inflow
Water mass transformation in the Iceland Sea - the Arctic domain
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•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