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Schmittner ipods talk Aug. 27, 2016
- 1. Complementary Constraints from Carbon and Nitrogen Isotopes on the LGM Ocean’s Biological Pump Andreas Schmittner and Christopher Somes College of Earth, Ocean, and Atmospheric Sciences Oregon State University δ13C I’ll tell you about circulation δ15N I’ll tell you about iron fertilization Δ14C I’ll tell you about ventilation Funded by NSF’s Marine Geology and Geophysics Program IPODS Workshop Aug. 27, 2016, Utrecht
- 2. Goals • Explore effects of changes in physics (e.g. circulation, sea ice) and biology (e.g. iron fertilization) on LGM distributions of δ13C, δ15N • Compare model solutions to reconstructions • Was the LGM biological pump stronger? Schmittner and Somes (2016) Paleoceanography, doi:10.1002/2015PA002905.
- 3. Detritus DIC PO4 NO3 O2 Photosynthesis Fast Recycling 13C Water Column Denitrification Sinking 15N 15N 13C Grazing Mortality Remineralization Excretion CO2O2 13C N-Fixation N2δ15NN2=0 Benthic Denitrification (Fe) εBD ! −4‰ εWCD ! −25‰ εP ! −5‰ εP εP εE = −6‰ εAS CaCO3 δ 13 C ! 2‰ 13C δ 13 CDIC ! 2‰ Phytoplankton 15N 13C δ 13 C ! −20‰ Diazotrophs 15N 13C δ 13 C ! −12‰ δ 13 C ! −20‰ Zooplankton 15N 13C δ 13 C ! −20‰ 14C Decay δ 13 CCO2 ! −6.5‰ δ 13 CDIC ! 0.5‰ DOM 15N 13C δ 13 C ! −20‰ εP ! −20‰ εNF ! −1‰ δ 15 NNO3 ! 9‰ δ 15 NNO3 ! 5.5‰ δ 15 N ! −1‰ δ 15 N ! 4‰ δ 15 N ! 7‰ δ 15 N ! 5‰ δ 15 N ! 6‰ MOBI Model of Ocean Biogeochemistry and Isotopes Somes et al. (2013, 2015) Schmittner et al. (2015)
- 4. Numerical Experiments • Pre-industrial Control (piCtrl) μmax = 0.6 d-1 • 6 idealized LGM experiments • same physics: PMIP3-like boundary conditions (ice sheets, CO2), δ13CCO2 = -6.5‰ • different maximum phytoplankton growth rates μmax = 0.6 - 1.2 d-1 to mimic iron fertilization (LGM0.6, LGM0.7, … LGM1.2)
- 5. Simplifications • No spatial differences of iron fertilization effects on growth rates • No changes in winds or tides • No sea level effects on benthic denitrification • No interactive sediments (global ALK = const, DIC will be too low)
- 6. Results (Physics) • ΔSAT = -4.3 K • Sea ice cover increased by 70% • AMOC weaker (11 Sv) and shallower than piCtrl (17 Sv) • Deep 14C-ages increased by 600 years Annan and Hargreaves (2013) Roche et al. (2012) Sarnthein et al. (2013) Skinner et al. (previous IPODS mtg) briefly: not inconsistent with reconstructions
- 8. Global Mean Vertical Profiles (horizontally averaged)
- 9. DIC = Cpre + Corg + CCaCO3 δ13CDIC = δ13Cpre + δ13Corg ︷Biological Pump Corg=RC:OAOU
- 10. “Physics” ΔCorg = 280 Pg “Iron Fertilization” ΔCorg = 400 Pg ΔCorg vs Δδ13C R=-0.89 δ13C is a proxy of ΔCorg ΔCorg vs Δδ13C R=-0.97
- 11. “Physics” shallower AMOC increases vertical gradient in Atlantic “Iron Fertilization” further increases vertical gradient in Atlantic and decreases δ13C in Indian & Pacific δ13C
- 12. Oxygen Similar to Corg “Physics” increased O2 in thermocline, smaller suboxic zones (green lines), decreased O2 in deep ocean “Iron Fertilization” decreases oxygen in lower thermocline and deep ocean, increases suboxic zones Huge suboxic zone in North Pacific inconsistent with reconstructions (Jaccard and Galbraith, 2011)
- 13. Nitrogen Cycle “Physics” decreases water- column denitrification and N- fixation, increases N inventory “Iron Fertilization” decreases surface nutrients, increases WCD and NF, decreases N inventory
- 14. “Physics” decreases δ15N “Iron Fertilization” increases δ15N δ15N
- 15. Comparison to Reconstructions • δ15N reconstructions from Nitrogen Cycle in the Ocean Past and Present (NICOPP) compilation (Galbraith et al., 2013) • δ13C reconstructions from Peterson et al. (2014)
- 16. R RMSE 0.33 2.1 0.34 1.8 0.21 2.9 0.45 1.3 0.21 2.4 0.21 3.2 R RMSE
- 17. R RMSE 0.75 1.140.63 1.48 R RMSE 0.78 0.770.78 0.76 σobs=0.52‰
- 21. Conclusions • N and C isotopes provide complementary constraints on the biological pump • Models with weaker and shallower AMOC and moderately increased iron fertilization fit observations best • ΔCorg ~ 500 - 700 Pg δ13C I’ll tell you about Corg δ15N I’ll tell you about iron fertilization
- 22. Ongoing and Future Work • Effects on CO2 (Samar Khatiwala) • Iron and Circulation (Juan Muglia) • LGM Nitrogen Cycle (Somes et al., in prep for Frontiers in Marine Sciences) • Early Deglaciation
- 23. Dank je ! 🌷