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UK GEOTRACES: Characterizing nitrate isotopes in South Atlantic water masses (40°S). UK GEOTRACES: Characterizing nitrate isotopes in South Atlantic water.

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Presentation on theme: "UK GEOTRACES: Characterizing nitrate isotopes in South Atlantic water masses (40°S). UK GEOTRACES: Characterizing nitrate isotopes in South Atlantic water."— Presentation transcript:

1 UK GEOTRACES: Characterizing nitrate isotopes in South Atlantic water masses (40°S). UK GEOTRACES: Characterizing nitrate isotopes in South Atlantic water masses (40°S). Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward. Oxford 10 th -11 th September 2012

2 Marine Nitrogen cycle N Limits on biological production Sigman et al., 2000; Difiore et al.,2008 Trace N fluxes Brandes and Devol, 2002; Codispoti et al., 2001 Changing productivity patterns Duce et al., 2008; Falkowski et al., 1998 Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

3 Study area D357, RRS Discovery JC068, RRS James Cook NADW AAIW AABW SACW Agulhas Brazil Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

4 Stable isotope biogeochemistry Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward. Spatially and temporally integrated value! Sigman et al., 2009

5 N2N2 PP Nitrate isotope cycling 1. 3. 4. 2.2. ε ~ 25 ‰ ε ~5 ‰ ~ -1 ‰ ε ~≤ 3 ‰ 1. N 2 fixation 2. Remineralization 3. Nitrate utilization 4. Denitrification 4. ε ~0 ‰ NO 3 - 5‰ Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

6 SURFACE Characterizing water masses Nitrate utilization, indicator of productivity Tracer for N 2 fixation, denitrification and partially utilized nitrate Isotope fractionation Spatial pattern of δ 15 N NO3 and δ 18 O NO3 DEEP Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

7 Denitrifier method (Sigman et al., 2001, Casciotti et al., 2002) NO 3 - converted to N 2 O Isotope ratio mass spectrometry Methods Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

8 Deep water masses Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward. Station 3 Station 6 Station 10 δ 15 N 0.2 ‰ δ 18 O 0.5 ‰

9 Deep water masses Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

10 Deep water masses NADW AAIW AABW NADW AAIW AABW4.9 ± 0.1 ‰ NADW4.5 ± 0.2 ‰ AAIW5.4 ± 0.4 ‰ Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

11 Deep water masses AAIW Incorporation of NO 3 - that has been partially consumed in Antarctic surface waters AABW Formed on shelf, Weddell sea and entrainment of CDW (~ 4.8 ‰, Sigman 1999) NADW Release of lighter N through sinking particles? Depleted source values? Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

12 Surface water masses Nitrate utilization enriches δ 15 N up to 13 ‰ at surface Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward. SAMW

13 Surface water masses Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward. D357

14 Surface water masses Mixing dilutes δ 15 N values: Agulhas 6-8 ‰ SACW 5-7‰ Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

15 Nitrate Utilization 1 2 716 19 5 µM 12 ‰ 30 µM 5 ‰ 17.5 µM 6 ‰ Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

16 Mixing δ15Nnr: Indicates deviations from expected enrichment related to NO 3 - concentrations Agulhas SACW Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

17 Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward. Surface water masses Δ15,18 = (δ 15 N -δ 15 N m ) -( 15 ε/ 18 ε)x(δ 18 O-δ 18 O m ) Sigman et al., (2005) Deviations from δ 15 N:δ 18 O stoichiometry

18 Conclusions Deep AAIW: partially utilized NO 3 - in surface waters NADW: Lighter values may indicate sinking of newly fixed OM Surface Water mass mixing dilutes δ 15 N enrichment in surface waters Future work Finish analysis of surface and Western basin samples Finish particulate analyses Arctic and Southern Ocean samples Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward. High resolution deep ocean transect δ 15 N and δ 18 O measurements of NO 3 - give an integrated signal of N cycling processes over space and time δ 13 C and δ 15 N of particulates can further constrain N cycling

19 Collaborations Aerosol data - Rosie Chance and Alex Baker Mixing fluxes Biological productivity in surface waters

20 Acknowledgements Sample collection UK GEOTRACES team, Crew of the RRS Discovery and RRS James Cook, Sue Reynolds, Amandine Sabadel Method development Sian Henley, Jan Kaiser, Laura Campisi, Karen Casciotti, Matt McIlvin R.Schlitzer, Ocean Data View, http://www.awi-bremerhaven.de/GEO/ODV, 2012 http://www.awi-bremerhaven.de/GEO/ODV

21 Particulates Below 500 m Station 3 δ 15 PN increases to ~ 5 ‰ below 1000 m δ 15 NO 3 - source waters ~ 6 ‰ Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

22 Particulates… Surface Station 9 or 1.5 Enrichment in C-13 and N-15 at POC max Enrichment with depth Characterizing nitrate isotopes in South Atlantic water masses (40°S ) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward. Particulates

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