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

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

Focus on the Nordic Seas

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GS

LB

NBIP

Interplay of boundary currents and gyres in the interior

4

Interplay of boundary currents and gyres in the interior

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Extrem heat lossduring winter

Interplay of boundary currents and gyres in the interior

4

Induces vertical mixing

Interplay of boundary currents and gyres in the interior

4

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?

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

What kind of measurements are available to observe the transformation?

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CTD measurementsNISE data setSummer bias

What kind of measurements are available to observe the transformation?

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Underway-CTD surveysummer 2012Polarfront

What kind of measurements are available to observe the transformation?

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Since 2001Argo float measurementsin the Nordic Seas

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

Large-scale hydrography - temperature

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temperature time series

GS LB

IP NB

Θ

Θ Arctic domain Atlantic domain °C

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

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

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

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

Thank you for your attention!

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