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

UK GEOTRACES: Characterizing nitrate i sotopes in South Atlantic water masses (40°S). . Oxford 10 th -11 th September 2012. Robyn Tuerena , Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward. Marine Nitrogen cycle. N Limits on biological production

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

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

  2. Marine Nitrogen cycle • N Limits on biological production • Sigman et al., 2000; Difiore et al.,2008 • Trace N fluxes • Brandesand 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 SACW Agulhas Brazil AAIW NADW AABW 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 δ15N (‰ vs. air) = x 1000 Spatially and temporally integrated value! Sigman et al., 2009 Characterizing nitrate isotopes in South Atlantic water masses (40°S) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

  5. Nitrate isotope cycling 1. N2 fixation 2. Remineralization 3. Nitrate utilization 4. Denitrification N2 ~ -1 ‰ ε ~ 25 ‰ 1. 4. NO3- ε ~5 ‰ 3. PP 5‰ 2. ε ~≤ 3 ‰ 4. ε ~0 ‰ Characterizing nitrate isotopes in South Atlantic water masses (40°S) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

  6. Characterizing water masses Isotope fractionation SURFACE Nitrate utilization, indicator of productivity Spatial pattern of δ15NNO3and δ18ONO3 DEEP Tracer for N2 fixation, denitrification and partially utilized nitrate Characterizing nitrate isotopes in South Atlantic water masses (40°S) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

  7. Methods Denitrifier method (Sigman et al., 2001, Casciotti et al., 2002) NO3- converted to N2O Isotope ratio mass spectrometry 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 Station 3 Station 6 Station 10 δ15N 0.2 ‰ δ18O 0.5 ‰ Characterizing nitrate isotopes in South Atlantic water masses (40°S) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

  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 AAIW AABW 4.9 ± 0.1 ‰ AABW NADW 4.5 ± 0.2 ‰ NADW AAIW 5.4 ± 0.4 ‰ AAIW NADW AABW 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 NO3- that has been partially consumed in Antarctic surface waters NADW Release of lighter N through sinking particles? Depleted source values? AABW Formed on shelf, Weddell sea and entrainment of CDW (~ 4.8 ‰, Sigman 1999) 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 SAMW Nitrate utilization enriches δ15N 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.

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

  14. Surface water masses Mixing dilutes δ15N 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 2 1 19 16 7 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 Agulhas SACW δ15Nnr: Indicates deviations from expected enrichment related to NO3- concentrations Characterizing nitrate isotopes in South Atlantic water masses (40°S) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

  17. Surface water masses Δ15,18 = (δ15N -δ15Nm) -(15ε/18ε)x(δ18O-δ18Om) Sigman et al., (2005) Deviations from δ15N:δ18O stoichiometry Characterizing nitrate isotopes in South Atlantic water masses (40°S) Robyn Tuerena, Raja Ganeshram, Anthony Fallick, Andrew Tait, Julie Dougans, Malcolm Woodward.

  18. Conclusions Deep AAIW: partially utilized NO3- in surface waters NADW: Lighter values may indicate sinking of newly fixed OM Surface Water mass mixing dilutes δ15N enrichment in surface waters High resolution deep ocean transect δ15N and δ18O measurements of NO3- give an integrated signal of N cycling processes over space and time δ13C and δ15N of particulates can further constrain N cycling 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.

  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

  21. Particulates Below 500 m Station 3 δ15PN increases to ~ 5 ‰ below 1000 m δ15NO3- 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 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.

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