The acceleration of oceanic denitrification during deglacial warming


Eric D. Galbraith, Université McGill
Markus Kienast, Dalhousie University
Ana Luiza Luiza Albuquerque, Universidade Federal do Rio de Janeiro
Mark A. Altabet, School for Marine Science and Technology
Fabian Batista, University of California, Santa Cruz
Daniele Bianchi, Université McGill
Stephen E. Calvert, University of British Columbia
Sergio Contreras, University of Minnesota Duluth
Xavier Crosta, Université de Bordeaux
Ricardo De Pol-Holz, Universidad de Concepcion
Nathalie Dubois, Woods Hole Oceanographic Institution
Johan Etourneau, Laboratoire d'Océanographie et du Climat : Expérimentations et Approches Numériques
Roger Francois, University of British Columbia
Ting Chang Hsu, Academia Sinica, Research Center for Environmental Changes
Tara Ivanochko, University of British Columbia
Samuel J. Jaccard, Geologisches Institut
Shuh Ji Kao, Academia Sinica, Research Center for Environmental Changes
Thorsten Kiefer, PAGES International Project Office
Stephanie Kienast, Dalhousie University
Moritz F. Lehmann, Universitat Basel
Philippe Martinez, Université de Bordeaux
Matthew McCarthy, University of California, Santa Cruz
Anna Nele Meckler, Geologisches Institut
Alan Mix, Oregon State University
Jürgen Möbius, Universität Hamburg
Tom F. Pedersen, University of Victoria
Laetitia Pichevin, University of Edinburgh
Tracy M. Quan, Oklahoma State University
Rebecca S. Robinson, University of Rhode Island
Evgeniya Ryabenko, GEOMAR - Helmholtz-Zentrum für Ozeanforschung Kiel
Andreas Schmittner, Oregon State University
Ralph Schneider, Christian-Albrechts-Universität zu Kiel
Aya Schneider-Mor, Stanford University
Masahito Shigemitsu, Hokkaido University
Dan Sinclair, Rutgers University–New Brunswick
Christopher Somes, Universidade Federal do Rio de Janeiro

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Over much of the ocean's surface, productivity and growth are limited by a scarcity of bioavailable nitrogen. Sedimentary δ 15 N records spanning the last deglaciation suggest marked shifts in the nitrogen cycle during this time, but the quantification of these changes has been hindered by the complexity of nitrogen isotope cycling. Here we present a database of δ 15 N in sediments throughout the world's oceans, including 2,329 modern seafloor samples, and 76 timeseries spanning the past 30,000 years. We show that the δ 15 N values of modern seafloor sediments are consistent with values predicted by our knowledge of nitrogen cycling in the water column. Despite many local deglacial changes, the globally averaged δ 15 N values of sinking organic matter were similar during the Last Glacial Maximum and Early Holocene. Considering the global isotopic mass balance, we explain these observations with the following deglacial history of nitrogen inventory processes. During the Last Glacial Maximum, the nitrogen cycle was near steady state. During the deglaciation, denitrification in the pelagic water column accelerated. The flooding of continental shelves subsequently increased denitrification at the seafloor, and denitrification reached near steady-state conditions again in the Early Holocene. We use a recent parameterization of seafloor denitrification to estimate a 30-120% increase in benthic denitrification between 15,000 and 8,000 years ago. Based on the similarity of globally averaged δ 15 N values during the Last Glacial Maximum and Early Holocene, we infer that pelagic denitrification must have increased by a similar amount between the two steady states. © 2013 Macmillan Publishers Limited. All rights reserved.

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Nature Geoscience