Massive nitrous oxide emissions from the tropical South Pacific Ocean

Abstract

Nitrous oxide is a potent greenhouse gas1 and a key compound in stratospheric ozone depletion2. In the ocean, nitrous oxide is produced at intermediate depths through nitrification and denitrification, in particular at low oxygen concentrations3. Although a third of natural emissions of nitrous oxide to the atmosphere originate from the ocean1, considerable uncertainties in the distribution and magnitude of the emissions still exist4. Here we present high-resolution surface measurements and vertical profiles of nitrous oxide that include the highest reported nitrous oxide concentrations in marine surface waters, suggesting that there is a hotspot of nitrous oxide emissions in high-productivity upwelling ecosystems along the Peruvian coast. We estimate that off Peru, the extremely high nitrous oxide supersaturations we observed drive a massive efflux of 0.2–0.9 Tg of nitrogen emitted as nitrous oxide per year, equivalent to 5–22% of previous estimates of global marine nitrous oxide emissions. Nutrient and gene abundance data suggest that coupled nitrification–denitrification in the upper oxygen minimum zone and transport of resulting nitrous oxide to the surface by upwelling lead to the high nitrous oxide concentrations. Our estimate of nitrous oxide emissions from the Peruvian coast surpasses values from similar, highly productive areas.

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Figure 1: Sampling locations investigated in the ETSP.
Figure 2: Surface distribution of N2O, SST and O2 in the ETSP.
Figure 3: Comparison of N2O emissions from highly productive regions.

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Acknowledgements

We thank the Peruvian authorities for allowing us to conduct the study in their territorial waters. Likewise we would like to thank our Peruvian colleagues M. Graco, A. Bernal, G. Flores and V. León for their logistical support to our work. We thank the captains and crew of the RV Meteor for their assistance during the cruises M90, M91 and M93. We also thank L. Stramma and G. Lavik for their support during the M90 and M93 cruises, as well as B. Provencal (Los Gatos Research Inc.) and T. Steinhoff (GEOMAR) for providing technical support in setting up the systems. Moreover, we thank T. Baustian, A. Bernal, J. Craig, G. Eirund, G. Flores, V. León, M. Lohmann, N. Martogli and K. Nachtigall for their contribution in the collection and analysis of discrete samples of O2, nutrients, Chla and N2O, as well as G. Krahmann for providing processed CTD data. The work presented here was made possible by the Future Ocean Excellence Cluster at Kiel University (project CP0910), the DFG-supported project SFB754 (http://www.sfb754.de), the BMBF joint project SOPRAN II and III (FKZ 03F0611A and FKZ 03F662A), and the EU FP7 project InGOS (Grant Agreement # 284274).

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H.W.B., A.K. and D.L.A-M. designed the study; D.L.A-M. set up the continuous and discrete measuring systems for N2O on board the RV Meteor and carried out the continuous measurements during the cruises. A.K. participated in the fieldwork and carried out the discrete measurements of N2O together with D.L.A-M. Data processing, reduction and calibration routines for underway data were done by D.L.A-M., and A.K. processed and calibrated depth profile N2O data. C.R.L. collected and processed the molecular data. D.L.A-M. wrote the manuscript with contributions from H.W.B., A.K., C.R.L. and R.A.S.

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Correspondence to D. L. Arévalo-Martínez.

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Arévalo-Martínez, D., Kock, A., Löscher, C. et al. Massive nitrous oxide emissions from the tropical South Pacific Ocean. Nature Geosci 8, 530–533 (2015). https://doi.org/10.1038/ngeo2469

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