Presentation on the ocean's carbon and nitrogen cycle during the last glacial maximum constrained by isotopes given at the IPODS workshop "The overturning circulation and carbon cycle" Aug. 27, 2016, in Utrecht, Netherlands.
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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.
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
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)
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)
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