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Nutrient fluxes in the eastern North Atlantic

Nutrient fluxes in the eastern North 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. Subpolar North Atlantic. Extended Ellett Line 1997 onwards

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Nutrient fluxes in the eastern North Atlantic

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  1. Nutrient fluxes in the eastern North 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

  2. Subpolar North Atlantic • Extended Ellett Line • 1997 onwards • Annual hydrographic section Iceland Nordic Seas Greenland 63 N 72 N 60 N Iceland Basin 64 N UK 57 N UK Rockall Trough 54 N North Atlantic 56 N 51 N 48 N 15 W 10 W 5 W 25 W 20 W 0° 40 N 15 W 0 30 W 45 W

  3. Mean geostrophic transports (1997-2012) ≈ total transports (difference between geostrophic-derived surface velocities and altimeter-derived surface velocities minimised) Holliday et al., accepted, JGR, early view.

  4. Nutrient data quality assessment Mean ± stdev 1997 -2011 (no QC) Sherwin et al., 2012, ICES Journal of Marine Science, 69,751-757. [SiO3] (µM) NO3 PO4 SiO3 Black: all data 1997-2013 Red: data from 1 cruise Decision: ‘good’ data mode ± 1 stdev Johnson et al., 2013, DSR, 82, 95-107 [NO3] (µM)

  5. Example nutrient sections Iceland Rockall Scotland NO2+3 (µM) PO4 (µM) (µM) SiO3

  6. Calculation 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 Holliday et al., accepted, JGR, early view. Nutrient (µM)

  7. Volume and nutrient transports 0.5 ± 0.5 3.9 ± 1.9 2.3 ± 1.3 Volume (Sv) UW +6.7 OW -2.1 Total +2.5 -2.1 ± 0.9 44.0 5.1 23.1 NO2+3 (kmol s-1) UW +72.2 OW -25.8 Total +46.4 -25.8

  8. Volume and nutrient transports 2.8 0.3 1.3 PO4 (kmol s-1) UW +4.4 OW -1.9 Total +2.3 -1.9 17.0 1.9 7.4 SiO3 (kmol s-1) UW +26.3 OW -14.7 Total +11.6 -14.7

  9. Summary • 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). Future work • More sophisticated nutrient transport calculation. • Calculation of variability around mean transports. • Produce time-series of volume and nutrient transports between 1997 and present.

  10. 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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