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Nitrogen Isotope Measurements-in the context of 40ºS GEOTRACES Transect Raja S. Ganeshram.

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1 Nitrogen Isotope Measurements-in the context of 40ºS GEOTRACES Transect
Raja S. Ganeshram

2 N isotopes proxy nutrient utilisation Denitrification N-fixation
OM Regeneration Water mass tracer

3 Difiore et al, JGR, 2006

4 Knapp et al., GBC, 2008

5

6 Sigman et al., GBC, 2006

7 Isotope fractionation during sedimentation
Settling particles tends to get heavy on transit 3‰ difference between diatom-bound and bulk sediments Such differences are variable no effect in margin sediments Effect of sediment?

8

9 Tracing northern & southern sourced waters -foram & diatom bound N-isotope signatures N-fixation budgets in the Atlantic -Large uncertainties Role of riverine OM & DIN on N-isotopes & C isotopes signatures Role of margin sediments -sediment denitrification

10 Nitrate Isotopes Water requirement: ml most sites ml in surface/oligotrophic sites/underway system Sampling resolution: -12 8 to 10 stations + 10 margins stations Other: Need good nitrate/nitrite concentration. Costs: 500 samples X £20 = 10,000 consumable + Mass spec time (no salary) 2 berths Postdoc or tech. + PhD student


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