Nutrient fluxes in the eastern North Atlantic Clare Johnson (1), Stuart Cunningham (1), Penny...

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Nutrient fluxes in the eastern Nutrient fluxes in the eastern North AtlanticNorth Atlantic

Clare Johnson(1), Stuart Cunningham(1), Penny Holliday(2) and Stefan Gary(1)

(1) Scottish Association of Marine Science (2) National Oceanography Centre, Southampton

www.sams.ac.ukcljo@sams.ac.uk

Subpolar North AtlanticSubpolar North Atlantic

64 N

56 N

48 N

72 N

40 N 15 W30 W45 W 0

UK

North Atlantic

Nordic SeasGreenland

0°25 W 20 W 15 W 10 W 5 W

60 N

63 N

57 N

54 N

51 N

UK

Iceland

Rockall Trough

Iceland Basin

Extended Ellett Line•1997 onwards•Annual hydrographic section

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Mean geostrophic transports (1997-2012)Mean geostrophic transports (1997-2012)

Holliday et al., accepted, JGR, early view.

≈ total transports(difference between geostrophic-derived surface velocities and altimeter-derived surface velocities minimised)

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Nutrient data quality assessmentNutrient data quality assessment

Mean ± stdev 1997 -2011 (no QC)Sherwin et al., 2012, ICES Journal of Marine Science, 69,751-757.

Black: all data 1997-2013Red: data from 1 cruiseDecision: ‘good’ data mode ± 1 stdevJohnson et al., 2013, DSR, 82, 95-107

[NO3] (µM)

[SiO

3] (µ

M)

NO3 PO4 SiO3

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Example nutrient sectionsExample nutrient sections

NO2+3

PO4

SiO3

Iceland Rockall Scotland

(µM)

(µM)

(µM)

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Calculation of nutrient fluxesCalculation of nutrient fluxes

Two water masses defined by density:

(1) Upper water < 27.50 kg m-3

(2) Overflow water > 27.85 kg m-3

Nutrient (µM)

Holliday et al., accepted, JGR, early view.

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Volume and nutrient transportsVolume and nutrient transports3.9 ± 1.9 0.5 ± 0.5 2.3 ± 1.3

-2.1 ± 0.9

NO2+3 (kmol s-1)UW +72.2OW -25.8Total +46.4

-25.8

44.0 5.1 23.1

Volume (Sv)UW +6.7OW -2.1Total +2.5

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Volume and nutrient transportsVolume and nutrient transports

1.3

SiO3 (kmol s-1)UW +26.3OW -14.7Total +11.6

-14.7

17.0 1.9 7.4

PO4 (kmol s-1)UW +4.4 OW -1.9Total +2.3

0.32.8

-1.9

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• Nutrient distribution in eastern North Atlantic shows water mass structure as well as non-conservative behaviour.

• Eastern North Atlantic net source of nutrients to Nordic Seas and Arctic Ocean.

• First look mean values 1997 to 2013: NO2+3 +42.8 kmol s-1, PO4 +2.5 kmol s-1, SiO3 +11.6 kmol s-1 (likely to be slightly on high side).

SummarySummary

Future workFuture work• More sophisticated nutrient transport calculation.

• Calculation of variability around mean transports.

• Produce time-series of volume and nutrient transports between 1997 and present.

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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.308299NACLIM www.naclim.eu