Complementary Constraints from Carbon and Nitrogen Isotopes on the Glacial Ocean's Soft-Tissue Pump and Circulation

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Published on November 16, 2016

Author: AndreasSchmittner

Source: slideshare.net

1. Complementary Constraints from Carbon and Nitrogen Isotopes on the Glacial Ocean's Soft-Tissue Pump and Circulation Andreas Schmittner and Christopher Somes College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, USA. Contact information: aschmitt@coas.oregonstate.edu Figure 1: Schematic diagram of MOBI showing prognostic tracers (biological on left and inorganic on right) and fluxes between them. Fractionation factors and typical delta values are also indicated. Methods ● Model of Ocean Biogeochemistry and Isotopes coupled to University of Victoria (UVic) model version 2.9. No sediments. ● LGM orbital parameters, atmospheric CO2 level (185 ppm) and ice sheets. Wind changes and sea level effects on benthic denitrification not considered. ● Physics not inconsistent with reconstructions: ΔSAT = -4.3K, sea ice area increased by 70%, AMOC is weaker (11 Sv) and shallower than PI (17 Sv), bottom waters are saltier, deep ocean has higher radiocarbon age Δ14 Cage(z>2 km) = +600 a. ● We evaluate the effect of idealized changes of the biological pump by varying maximum phytoplankton growth rates μmax (mimics iron fertilization). Introduction ● Was biological pump enhanced during LGM? ● If so, why? Changes in biology (e.g. iron fertilization) and in physics (e.g. ocean circulation and sea ice cover) have been implicated. ● Explore effects on ocean carbon cycle and isotope distributions. Figure 3: Zonally averaged dissolved oxygen in piCtrl (top) and changes LGM-piCtrl (bottom color scale). Results: Figure 2: Global horizontally averaged profiles. Figure 5: δ15 N changes from reconstructions (colored circles; Galbraith et al., 2013) and simulated by the models. Figure 6: LGM δ13 CDIC comparison with reconstructions (Peterson et al. 2014). Left: horizontal basin-wide averages. Right: zonal averages of best fitting model. Conclusions: ● Carbon and nitrogen isotopes provide complementary constraints on glacial ocean's biological pump. ● Carbon isotopes sensitive to circulation and Corg distribution, nitrogen isotopes sensitive to iron fertilization. ● Best fitting models (Tab. 2) indicate increased biological carbon storage of 500-700 Pg (Tab. 1). Figure 4: Zonally averaged δ13 CDIC . Conclusions: ● Carbon and nitrogen isotopes provide complementary constraints on glacial ocean's biological pump. ● Carbon isotopes sensitive to circulation and Corg distribution, nitrogen isotopes sensitive to iron fertilization. ● Best fitting models (Tab. 2) indicate increased biological carbon storage of 500-700 Pg (Tab. 1). References: ● Schmittner and Somes (2016) Paleoceanogr., doi:10.1002/2015PA002905. ● Galbraith et al. (2013) Nat. Geosci., doi:10.1038/ngeo1832 Peterson et al. (2014) Paleoceanogr., doi:10.1002/2013PA002552.

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