EGU2020-5638
https://doi.org/10.5194/egusphere-egu2020-5638
EGU General Assembly 2020
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

N2O changes during Heinrich Stadials - Isotopic source deconvolution over HS0, HS1 and HS4 and its implication for the marine and terrestrial nitrogen cycle

Hubertus Fischer1, Jochen Schmitt1, Michael Bock1, Barbara Seth1, Fortunat Joos1, Renato Spahni1, Gianna Battaglia1, Benjamin Stocker1,2,3, Sebastian Lienert1, Colin Prentice3, Bette Otto-Bliesner4, Zhengyu Liu5, Adrian Schilt1,6, and Ed Brook6
Hubertus Fischer et al.
  • 1University of Bern, Physics Institute, Climate and Environmental Physics, Bern, Switzerland (hubertus.fischer@climate.unibe.ch)
  • 2ETH Zürich, LFW C 55.3, Universitätstrasse 2, 8092 Zürich, Switzerland
  • 3AXA Chair of Biosphere and Climate Impacts, Department of Life Sciences, Imperial College London, Silwood Park Campus, Buckhurst Road, Ascot SL5 7PY, UK
  • 4Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO 80307-3000, USA
  • 5Atmospheric Science Program, Department of Geography, Ohio State University, OH 43210, USA
  • 6College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA

Using high precision and centennial resolution ice core information on atmospheric nitrous oxide concentrations and its stable nitrogen and oxygen isotopic composition enables us to quantitatively reconstruct changes in the terrestrial and marine N2O emissions over the last 21,000 years as well as over Heinrich Stadial (HS) 4.

We show that over the deglaciation N2O emissions from land and ocean increased in parallel by 1.8 ± 0.3 TgN yr-1 and 0.7 ± 0.3 TgN yr-1, respectively. However, close to 50% of the terrestrial increase is accomplished within less than 200 years at the end of HS1 starting essentially in parallel with the co-occurring CH4 increase. A similarly rapid but smaller increase is observed at the end of HS0 and suggested at the end of HS4, showing that terrestrial N2O emissions respond strongly and rapidly to the northward shift in the Intertropical Convergence Zone connected to the resumption of the Atlantic Meridional Overturning Circulation (AMOC). However, little change in terrestrial N2O emissions is observed during the onsets of Heinrich Stadials. Assuming that N2O loss from terrestrial ecosystems is directly connected to nitrogen turnover in soils, the fast increase at the end of Heinrich Stadials suggests that terrestrial ecosystems did not become nitrogen-limited on this relatively short time scales, as also supported by model runs in our LPX-Bern dynamic vegetation/biogeochemical model. However, changes in number of moles of N2O lost to the atmosphere per mole nitrogen turned over in soils (yield factor) may also contribute to the atmospheric N2O changes.

Marine N2O emissions also respond to Heinrich events and AMOC changes, however more gradually and less strongly compared to terrestrial emissions both in our data-based reconstruction and the Bern3D coupled ocean/biogeochemistry model. In fact, reconstructed marine emissions start to slowly increase many centuries before the rapid warmings, connected to a re-equilibration of subsurface oxygen concentrations in response to previous AMOC changes. At the onset of HS1 marine emissions decreased by about 0.5 TgN yr-1, concomitantly with changes in atmospheric CO2 and δ13C(CO2), and started to re-increase after about 1500 years, when also rapid CO2 and CH4 jumps occurred, pointing to Southern Ocean and low-latitude circulation changes. A similar decrease as at the start of HS1 is found after the onset of HS0, but little N2O emission change is suggested by N2O concentrations and their isotopic signature at 39.5 kyr before present when Heinrich Event 4 presumably occurred, as suggested by a co-occurring intermittent CH4 peak and a sudden increase in CO2.

How to cite: Fischer, H., Schmitt, J., Bock, M., Seth, B., Joos, F., Spahni, R., Battaglia, G., Stocker, B., Lienert, S., Prentice, C., Otto-Bliesner, B., Liu, Z., Schilt, A., and Brook, E.: N2O changes during Heinrich Stadials - Isotopic source deconvolution over HS0, HS1 and HS4 and its implication for the marine and terrestrial nitrogen cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5638, https://doi.org/10.5194/egusphere-egu2020-5638, 2020

This abstract will not be presented.