Indirect estimate of fluxes between boundary current and deep basins in the Nordic Seas:
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Indirect estimate of fluxes between boundary current and deep basins in the Nordic Seas:
heat and freshwater budgets
Katrin Latarius1 and Detlef Quadfasel2
1Alfred-Wegener-Institut Bremerhaven, Germany
2Institut für Meereskunde, University Hamburg, Germany
Contributions from: Jan Backhaus, Bert Rudels, Johannes Karstensen, Bogi Hansen,
Manuela Köllner, Antje Müller-Michaelis, Kerstin Jochumsen, Gereon Budéus
This work is financed by national funding from the DFG (SFB 512 E2)
and BMBF (NA) and European funding (MERSEA, THOR, NACLIM).
Ocean Science meeting February 2014 Honolulu
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Circulation and ice coverage
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Sea Ice coverage in the Arctic Mediterraneanblue-max, red-min Rudels et al., 2012
McCartney et al., 1997
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Focus on the Nordic Seas
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GS
LB
NBIP
Interplay of boundary currents and gyres in the interior
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Interplay of boundary currents and gyres in the interior
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Extrem heat lossduring winter
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Interplay of boundary currents and gyres in the interior
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Induces vertical mixing
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Interplay of boundary currents and gyres in the interior
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Eddy exchange between boundary currentand interior basins
How important are the basins for the transformation from inflowing Atlantic Water to Overflow Water?i.e. how large is the heat/frehswater exchange between boundary current and interior basins?
What kind of observations do we have to answer this question?
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What kind of measurements are available to observe the transformation?
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Inflow of Atlantic Water~ 9 °C, 35.33, 8 SvHansen et al., 2010, Berx et al., 2012
Overflow~ 0.2°C, 34.9, 6 SvHansen & Østerhus, 2007; Jochumsen et al., 2012
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What kind of measurements are available to observe the transformation?
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CTD measurementsNISE data setSummer bias
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What kind of measurements are available to observe the transformation?
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Underway-CTD surveysummer 2012Polarfront
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What kind of measurements are available to observe the transformation?
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Since 2001Argo float measurementsin the Nordic Seas
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The dataset
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Measurements are concentrated on the deep basins of the Nordic Seas
Greenland Sea
IcelandicPlateau
Lofoten Basin
Norwegian Basin
Argo-Float-Profiles2001-2012total: 6000 (4000)mean: 3-4 floats per basin
and month
2001 2003 2005 2007 2009 2011
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Large-scale hydrography - temperature
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temperature time series
GS LB
IP NB
Θ
Θ Arctic domain Atlantic domain °C
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Heat and freshwater budgets - concept
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the development of the heat and freshwater content in the basins is determined from the float data (mean annual cycle)
with a number of assumptions lateral exchange and vertical mixing are separeted from each other
the seasonal cycle of heat and freshwater fluxes is given by NCEP with corrections according to Renfrew et al. (2002)
residuum: lateral exchange and vertical mixing
lateral exchange – contribution to the water mass transformation
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Heat and freshwater budgets
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annual heatbudget[W/m²]
annualfreshwaterbudget[mm/month]
GS
Heat loss to the atmosphere introduces the destabilization of the water columnand thus vertical mixing and redistribution of properties in the water column.
Lateral exchange 50-800m: contribution of the basins to the water mass transformation from Atlantic water into overflow water.
This contribution is understimated when taken only fluxes between ocean and atmosphere into account.
1:2 100:1
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deep basins of the Nordic Seas
∆T=1.4 K 17%∆S=0.03 7%
although only 4% of total area
from Atlantic water inflow (9°C, 35.33)to overflow (0.2°C, 34.9)
∆T=8.8 K∆S=0.43
Contribution of the deep basins to the total water mass transformation
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Importance of the individual basins
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west:important for salinity characteristic
Greenland Sea∆ T:-0.45°C -> 31% ∆ S: -0.015 -> 49%
Lofoten Basin∆ T: - 0.42°C -> 29%∆ S: -0.004 -> 12%Icelandic-Plateau
∆ T: -0.07°C -> 5%∆ S: +0.002 -> 1%
Norwegian Basin∆ T: -0.5°C -> 35%∆ S: -0.012 -> 39%
∆ T: 36%∆ S: 49% ∆ T: 64%
∆ S: 51%
east:for densification
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Conclusions
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From heat and freshwater budgets for the deep basins of the Nordic Seas the lateral exchange between basins and boundary current is estimated,i.e. the contribution of the basins to the water mass transformation
The basins contribute 17% (temperature) and 7% (salinity) to the total transformation in the Arctic Mediterranean although they account for only 4% of the total area
More than 50% of the transformation takes place in the eastern Nordic Seas
Additional input of freshwater at first reaches the western Nordic Seasand thus influences less than half of the transformation
Transformation is underestimated when taking only atmospheric fluxes into accountHeat loss to the atmosphere introduces the destabilization of the water column in the basins
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Thank you for your attention!
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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