BG Biogeosciences BG Biogeosciences 1726-4189 Copernicus Publications Göttingen, Germany 10.5194/bg-11-1273-2014 Icehouse–greenhouse variations in marine denitrification Algeo T. J. 1 Meyers P. A. 2 Robinson R. S. 3 Rowe H. https://orcid.org/0000-0002-1665-6261 4 Jiang G. Q. https://orcid.org/0000-0002-6627-2848 5 Department of Geology, University of Cincinnati, Cincinnati, OH 45221-0013, USA Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48109-1063, USA Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA Department of Earth and Environmental Sciences, University of Texas at Arlington, Arlington, TX 76019, USA Department of Geoscience, University of Nevada Las Vegas, Las Vegas, Nevada, USA 27 02 2014 11 4 1273 1295 Copyright: © 2014 T. J. Algeo et al. 2014 This work is licensed under the Creative Commons Attribution 3.0 Unported License. To view a copy of this licence, visit https://creativecommons.org/licenses/by/3.0/ This article is available from https://bg.copernicus.org/articles/11/1273/2014/bg-11-1273-2014.html The full text article is available as a PDF file from https://bg.copernicus.org/articles/11/1273/2014/bg-11-1273-2014.pdf

Long-term secular variation in the isotopic composition of seawater fixed nitrogen (N) is poorly known. Here, we document variation in the N-isotopic composition of marine sediments (δ<sup>15</sup>N<sub>sed</sub>) since 660 Ma (million years ago) in order to understand major changes in the marine N cycle through time and their relationship to first-order climate variation. During the Phanerozoic, greenhouse climate modes were characterized by low δ<sup>15</sup>N<sub>sed</sub> (&sim;−2 to +2&permil;) and icehouse climate modes by high δ<sup>15</sup>N<sub>sed</sub> (&sim;+4 to +8&permil;). Shifts toward higher δ<sup>15</sup>N<sub>sed</sub> occurred rapidly during the early stages of icehouse modes, prior to the development of major continental glaciation, suggesting a potentially important role for the marine N cycle in long-term climate change. Reservoir box modeling of the marine N cycle demonstrates that secular variation in δ<sup>15</sup>N<sub>sed</sub> was likely due to changes in the dominant locus of denitrification, with a shift in favor of sedimentary denitrification during greenhouse modes owing to higher eustatic (global sea-level) elevations and greater on-shelf burial of organic matter, and a shift in favor of water-column denitrification during icehouse modes owing to lower eustatic elevations, enhanced organic carbon sinking fluxes, and expanded oceanic oxygen-minimum zones. The results of this study provide new insights into operation of the marine N cycle, its relationship to the global carbon cycle, and its potential role in modulating climate change at multimillion-year timescales.

 References Algeo, T. J. and Meyers, P. A.: Icehouse-greenhouse climate impacts on the Phanerozoic marine nitrogen cycle, Geol. Soc. Am. Abstr. Progr., 44, p. 458, 2009. Algeo, T. J., Rowe, H., Hower, J. C., Schwark, L., Hermann, A. and Heckel, P. H.: Oceanic denitrification during Late Carboniferous glacial-interglacial cycles, Nat. Geosci., 1, 709–714, 2008. Algeo, T. J., Henderson, C. M., Ellwood, B., Rowe, H., Elswick, E., Bates, S., Lyons, T., Hower, J. C., Smith, C., Maynard, J. B., Hays, L. E., Summons, R. E., Fulton, J., and Freeman, K. H.: Evidence for a diachronous Late Permian marine crisis from the Canadian Arctic region, Geol. Soc. Am. Bull., 124, 1424–1448, 2012. Altabet, M. A.: Variations in nitrogen isotopic composition between sinking and suspended particles: Implications for nitrogen cycling and particle transformation in the open ocean, Deep-Sea Res. I, 35, 535–554, 1988. Altabet, M. A.: Nitrogen isotopic evidence for micronutrient control of fractional NO<sub>3</sub><sup>-</sup> utilization in the equatorial Pacific, Limnol. Oceanogr., 46, 368–380, 2001. Altabet, M. A. and François, R.: Sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization, Glob. Biogeochem. Cy., 8, 103–116, 1994. Altabet, M. A., Francois, R., Murray, D. W., and Prell, W. L.: Climate-related variations in denitrification in the Arabian Sea from sediment <sup>15</sup>N / <sup>14</sup>N ratios, Nature, 373, 506–509, 1995. Bakker, C. C. E., Bange, H. W., Borges, A. V., Delille, B., Gruber, N., Johannessen, T., Löscher, C., Naqvi, S. W. A., Omar, A. M., Santana-Casiano, J. M., and Upstill-Goddard, R. C.: Air-sea interactions of natural long-lived greenhouse gases (CO<sub>2</sub>, N<sub>2</sub>O, CH<sub>4</sub>) in a changing climate, in: Ocean-Atmosphere Interactions of Gases and Particles, edited by: Liss, P. S. and Johnson, M. T., Springer, Berlin, 113–169, 2014. Barford, C. C., Montoya, J. P., Altabet, M. A., and Mitchell, R.: Steady-state nitrogen isotope effects of N<sub>2</sub> and N<sub>2</sub>O production in <i>Paracoccus denitrificans</i>, Appl. Env. Microbiol., 65, 989–994, 1999. Barrera, E., Savin, S. M., Thomas, E., and Jones, C. E.: Evidence for thermohaline-circulation reversals controlled by sea level change in the latest Cretaceous, Geology, 25, 715–718, 1997. Beauchamp, B. and Baud, A.: Growth and demise of Permian biogenic chert along northwest Pangea: evidence for end-Permian collapse of thermohaline circulation, Palaeogeogr. Palaeoclimatol. Palaeoecol., 184, 37–63, 2002. Berner, R. A.: GEOCARBSULF: A combined model for Phanerozoic atmospheric O<sub>2</sub> and CO<sub>2</sub>, Geochim. Cosmochim. Acta, 70, 5653–5664, 2006a. Berner, R. A: Geological nitrogen cycle and atmospheric N<sub>2</sub> over Phanerozoic time, Geology, 34, 413–415, 2006b. Brandes, J. A. and Devol, A. H.: Isotopic fractionation of oxygen and nitrogen in coastal marine sediments, Geochim. Cosmochim. Acta, 61, 1793–1801, 1997. Brandes, J. A. and Devol, A. H.: A global marine-fixed nitrogen isotopic budget: implications for Holocene nitrogen cycling, Glob. Biogeochem. Cy., 16, 1120, <a href="http://dx.doi.org/10.1029/2001GB001856">https://doi.org/10.1029/2001GB001856</a>, 1–14, 2002. Broecker, W. S. and Henderson, G. M.: The sequence of events surrounding Termination II and their implications for the cause of glacial-interglacial CO<sub>2</sub> changes, Paleoceanography, 13, 352–364, 1998. Busigny, V., Cartigny, P., Philippot, P., Ader, M., and Javoy, M.: Massive recycling of nitrogen and other fluid-mobile elements (K, Rb, Cs, H) in a cold slab environment: evidence from HP to UHP oceanic metasediments of the Schistes Lustrés nappe (western Alps, Europe), Earth Planet. Sci. Lett., 215, 27–42, 2003. Carpenter, E. J., Harvey, H. R., Fry, B., and Capone, D. G.: Biogeochemical tracers of the marine cyanobacterium Trichodesmium, Deep-Sea Res. I, 44, 27–38, 1997. Cleveland, W. S., Grosse, E., and Shyu, W. M.: Local regression models, in: Statistical Models in S, edited by: Chambers, J. M. and Hastie, T., Chapman Hall, Boca Raton, Florida, 309–376, 1992. Codispoti, L.: Is the ocean losing nitrate?, Nature, 376, 724, 1995. Codispoti, L. A.: An oceanic fixed nitrogen sink exceeding 400 Tg N <sup>a-1</sup> vs the concept of homeostasis in the fixed-nitrogen inventory, Biogeosciences, 4, 233–253, <a href="http://dx.doi.org/10.5194/bg-4-233-2007">https://doi.org/10.5194/bg-4-233-2007</a>, 2007. Deutsch, C., Sigman, D. M., Thunell, R. C., Meckler, N., and Haug, G. H.: Isotopic constraints on the glacial/interglacial oceanic nitrogen budget, Glob. Biogeochem. Cy., 18, 1–22, 2004. Deutsch, C., Sarmiento, J. L., Sigman, D. M., Gruber, N., and Dunne, J. P.: Spatial coupling of nitrogen inputs and losses in the ocean, Nature, 445, 163–167, 2007. DeVries, T., Deutsch, C., Primeau, F., Chang, B., and Devol, A.: Global rates of water-column denitrification derived from nitrogen gas measurements, Nat. Geosci., 5, 547–550, 2012. DeVries, T., Deutsch, C., Rafter, P. A., and Primeau, F.: Marine denitrification rates determined from a global 3-D inverse model, Biogeosciences, 10, 2481–2496, <a href="http://dx.doi.org/10.5194/bg-10-2481-2013">https://doi.org/10.5194/bg-10-2481-2013</a>, 2013. Ertel, J. R. and Hedges, J. I.: Sources of sedimentary humic substances: vascular plant debris, Geochim. Cosmochim. Acta, 49, 2097–2107, 1985. Espitalié, J., Laporte, J. L., Madec, M., Marquis, F., Leplat, P., Paulet, J., and Boutefeu, A.: Méthode rapide de caractérisation des roches mères de leur potentiel pétrolier et de leur degré d'évolution, Rev. Instit. Franç. Pétrole, 32, 23–42, 1977. Espitalié, J., Deroo, G., and Marquis, F.: Rock Eval pyrolysis and its applications, Rev. Instit. Franç. Pétrole, Part I: 32, 653–578; Part II: 40, 755–784; Part III: 41, 73–89, 1985. Eugster, O. and Gruber, N.: A probabilistic estimate of global marine N-fixation and denitrification, Glob. Biogeochem. Cy., 26, GC4013, <a href="http://dx.doi.org/10.1029/2012GB004300">https://doi.org/10.1029/2012GB004300</a>, 2012. Falkowski, P., Scholes, R. J., Boyle, E., Canadell, J., Canfield, D., Elser, J., Gruber, N., Hibbard, K., Högberg, P., Linder, S., Mackenzie, F. G., Moore, B., III, Pedersen, T., Rosenthal, Y., Seitzinger, S. Smetacek, V., and Steffen, W.: The global carbon cycle: A test of our knowledge of Earth as a system, Science, 290, 291–296, 2000. François, R., Altabet, M. A., and Burckle, L. H.: Glacial to interglacial changes in surface nitrate utilization in the Indian section of the Southern Ocean as recorded by sediment δ<sup>15</sup>N, Paleoceanography, 7, 589–606, 1992. Frank, T. D. and Arthur, M. A.: Tectonic forcings of Maastrichtian ocean-climate evolution. Paleoceanography, 14, 103–117, 1999. Frimmel, A., Oschmann, W., and Schwark, L.: Chemostratigraphy of the Posidonia Black Shale, SW-Germany: I – Influence of sea level variation on organic facies evolution, Chem. Geol., 206, 199–230, 2004. Galbraith, E. D., Kienast, M., Pedersen, T. F., and Calvert, S. E.: Glacial-interglacial modulation of the marine nitrogen cycle by high-latitude O<sub>2</sub> supply to the global thermocline, Paleoceanography, 19, 1–12, 2004. Galbraith, E. D., Sigman, D. M., Robinson, R. S., and Pedersen, T. F.: Nitrogen in past marine environments, in: Nitrogen in the Marine Environment, 2nd ed., edited by: Capone, D. G., Bronk, D. A., Mulholland, M. R., and Carpenter, E. J., Elsevier, Amsterdam, 1497–1535, 2008. Galloway, J. N., Dentener, F. J., Capone, D. G., Boyer, E. W., Howarth, R. W., Seitzinger, S. P., Asner, G. P., Cleveland, C. C., Green, P. A., Holland, E. A., Karl, D. M., Michaels, A. F., Porter, J. H., Townsend, A. R., and Vörösmarty, C. J.: Nitrogen cycles: past, present, and future, Biogeochemistry, 70, 153–226, 2004. Ganeshram, R. S., Pedersen, T. F., Calvert, S. E., and Murray, J. W.: Large changes in oceanic nutrient inventories from glacial to interglacial periods, Nature, 376, 755–758, 1995. Gaye-Haake, B., Lahajnar, N., Emeis, K.-C., Unger, D., Rixen, T., Suthhof, A., Ramaswamy, V., Schulz, H., Paropkari, A. L., Guptha, M. V. S. and Ittekkot, V.: Stable nitrogen isotopic ratios of sinking particles and sediments from the northern Indian Ocean, Mar. Chem., 96, 243–255, 2005. Gradstein, F. M., Ogg, J. G., Schmitz, M. D., and Ogg, G. M. (Eds.): The Geologic Time Scale 2012, 2 vols., Elsevier, Amsterdam, 1144 pp., 2012. Granger, J., Sigman, D. M., Rohde, M. M., Maldonado, M. T., and Tortell, P. D.: N and O isotope effects during nitrate assimilation by unicellular prokaryotic and eukaryotic plankton cultures, Geochim. Cosmochim. Acta, 74, 1030–1040, 2010. Grice, K., Cao, C., Love, G. D., Böttcher, M. E., Twitchett, R. J., Grosjean, E., Summons, R. E., Turgeon, S. C., Dunning, W., and Jin, Y.: Photic zone euxinia during the Permian-Triassic superanoxic event, Science, 307, 706–709, 2005. Grosskopf, T., Mohr, W., Baustian, T., Schunck, H., Gill, D., Kuypers, M. M. M., Lavik, G., Schmitz, R. A., Wallace, D. W. R., and LaRoche, J.: Doubling of marine dinitrogen-fixation rates based on direct measurements, Nature, 488, 361–364, 2012. Gruber, N. G.: The dynamics of the marine nitrogen cycle and its influence on atmospheric CO<sub>2</sub> variations, in: The Ocean Carbon Cycle and Climate, edietd by: Follows, M. and Oguz, T., Kluwer, Dordrecht, 97–148, 2004. Gruber, N. G.: The marine nitrogen cycle: overview and challenges, in: Nitrogen in the Marine Environment, 2nd Edn., edited by: Capone, D. G., Bronk, D. A., Mulholland, M. R., and Carpenter, E. J., Elsevier, Amsterdam, 1–50, 2008. Gruber, N. G. and Galloway, J. N.: An Earth-system perspective of the global nitrogen cycle, Nature, 451, 293–296, 2008. Gruber, N. and Sarmiento, J.: Global patterns of marine nitrogen fixation and denitrification, Glob. Biogeochem. Cy., 11, 235–266, 1997. Haq, B. U. and Al-Qahtani, A. M.: Phanerozoic cycles of sea-level change on the Arabian Platform, GeoArabia, 10, 127–160, 2005. Haq, B. U. and Schutter, S. R.: A chronology of Paleozoic sea-level changes, Science, 322, 64–68, 2008. Hartnett, H. E., Keil, R. G., Hedges, J. I., and Devol, A. H.: Influence of oxygen exposure time on organic carbon preservation in continental margin sediments, Nature, 391, 572–574, 1998. Haug, G. H., Pedersen, T. F., Sigman, D. M., Calvert, S. E., Nielsen, B., and Peterson, L. C.: Glacial/interglacial variations in production and nitrogen fixation in the Cariaco Basin during the last 580 kyr, Paleoceanography, 13, 427–432, 1998. Hedges, J. I., Keil, R. G., and Benner, R.: What happens to terrestrial organic matter in the ocean?, Org. Geochem., 27, 195–212, 1997. Higgins, M. B., Robinson, R. S., Carter, S. J., and Pearson, A.: Evidence from chlorin nitrogen isotopes for alternating nutrient regimes in the Eastern Mediterranean Sea, Earth Planet. Sci. Lett., 290, 102–107, 2010. Higgins, M. D., Robinson, R. S., Husson, J. M., Carter, S. J., and Pearson, A.: Dominant eukaryotic export production during ocean anoxic events reflects the importance of recycled NH<sub>4</sub><sup>+</sup>, Proc. Nat. Acad. Sci. (USA), 109, 2269–2274, 2012. Hoch, M. P., Fogel, M. L., and Kirchman, D. L.: Isotope fractionation during ammonium uptake by marine microbial assemblages, Geomicrobiol. J., 12, 113–127, 1994. Holloway, J. M. and Dahlgren, R. A.: Geologic nitrogen in terrestrial biogeochemical cycling, Geology, 27, 567–570, 1999. Holloway, J. M., Dahlgren, R. A., Hansen, B., and Casey, W. H.: Contribution of bedrock nitrogen to high nitrate concentrations in stream water, Nature, 395, 785–788, 1998. Holmes, M. E., Eichner, C., Struck, U., and Wefer, G.: Reconstruction of surface ocean nitrate utilization using stable nitrogen isotopes in sinking particles and sediments, in: Fischer, G. and Wefer, G. (Eds.), Use of Proxies in Paleoceanography: Examples from the South Atlantic, Springer, Berlin, 447–468, 1999. Huang, W. Y. and Meinschein, W. G.: Sterols as ecological indicators, Geochim. Cocmochim. Acta, 43, 739–745, 1979. Hutton, A. C.: Petrographic classification of oil shales, Internat. J. Coal Geol., 8, 203–231, 1987. Imbus, S. W., Macko, S. A., Elmore, R. D., and Engel, M. H.: Stable isotope (C, S, N) and molecular studies on the Precambrian Nonesuch Shale (Wisconsin-Michigan, USA): evidence for differential preservation rates, depositional environment and hydrothermal influence, Chem. Geol., 101, 255–281, 1992. Jaminski, J., Algeo, T. J., Maynard, J. B., and Hower, J. C.: Climatic origin of dm-scale compositional cyclicity in the Cleveland Member of the Ohio Shale (Upper Devonian), Central Appalachian Basin, USA, in: Shales and Mudstones, v. 1, Schieber, J., Zimmerle, W., and Sethi, P. S., Schweizerbart'sche, Stuttgart, 217–242, 1998. Jenkyns, H. C., Gröcke, D. R., and Hesselbo, S. P.: Nitrogen isotope evidence for water mass denitrification during the early Toarcian (Jurassic) oceanic anoxic event, Paleoceanography, 16, 593–603, 2001. Jenkyns, H. C., Matthews, A., Tsikos, H., and Erel, Y.: Nitrate reduction, sulfate reduction, and sedimentary iron isotope evolution during the Cenomanian-Turonian oceanic anoxic event, Paleoceanography, 22, 1–17, 2007. Jia, Y. and Kerrich, R.: Nitrogen 15-enriched Precambrian kerogen and hydrothermal systems, Geochem. Geophys. Geosyst., 5, 1–21, 2004. Junium, C. K. and Arthur, M. A.: Nitrogen cycling during the Cretaceous, Cenomanian-Turonian Oceanic Anoxic Event II, Geochem. Geophys. Geosyst., 8, 1–18, 2007. Kenrick, P. and Crane, P. R.: The origin and early evolution of plants on land, Nature, 389, 33–39, 1997. Knapp, A. N., DiFiore, P. J., Deutsch, C., Sigman, D. M., and Lipschultz, F.: Nitrate isotopic composition between Bermuda and Puerto Rico: implications for N<sub>2</sub> fixation in the Atlantic Ocean, Glob. Biogeochem. Cy., 22, 1–14, 2008. Kritee, K., Sigman, D. M., Granger, J., Ward, B. B., Jayakumar, A., and Deutsch, C.: Reduced isotope fractionation by denitrification under conditions relevant to the ocean, Geochim. Cosmochim. Acta, 92, 243–259, 2012. Kuypers, M. M. M., Lavik, G., Woebken, D., Schmid, M., Fuchs, B. M., Amann, R., Jorgensen, B. B., and Jetten, M. S. M.: Massive nitrogen loss from the Benguela upwelling system through anaerobic ammonium oxidation, Proc. Natl. Acad. Sci. (USA), 102, 6478–6483, 2005. Lehmann, M. F., Sigman, D. M., and Berelson, W. M.: Coupling the N-15/N-14 and O-18/O-16 of nitrate as a constraint on benthic nitrogen cycling, Mar. Chem., 88, 1–20, 2004. Lehmann, M. F., Sigman, D. M., McCorkle, D. C., Granger, J., Hoffmann, S., Cane, G., and Brunelle, B. G.: The distribution of nitrate <sup>15</sup>N/<sup>14</sup>N in marine sediments and the impact of benthic nitrogen loss on the isotopic composition of oceanic nitrate, Geochim. Cosmochim. Acta, 71, 5384–5404, 2007. Libes, S. M. and Deuser, W. G.: The isotopic geochemistry of particulate nitrogen in the Peru Upwelling Area and the Gulf of Maine, Deep-Sea Res. I, 35, 517–533, 1988. Liu, Z., Altabet, M. A., and Herbert, T. D.: Glacial-interglacial modulation of eastern tropical North Pacific denitrification over the last 1.8-Myr, Geophys. Res. Lett., 32, 1–4, 2005. Liu, Z., Altabet, M. A., and Herbert, T. D.: Plio-Pleistocene denitrification in the eastern tropical North Pacific: intensification at 2.1 Ma, Geochem. Geophys. Geosyst., 9, 1–14, 2008. Lourey, M. J., Trull, T. W. and Sigman, D. M.: Sensitivity of δ<sup>15</sup>N of nitrate, surface suspended and deep sinking particulate nitrogen to seasonal nitrate depletion in the Southern Ocean, Glob. Biogeochem. Cy., 17, 1–18, 2003. Lücke, A. and Brauer, A.: Biogeochemical and micro-facial fingerprints of ecosystem response to rapid Late Glacial climatic changes in varved sediments of Meerfelder Maar (Germany), Palaeogeogr. Palaeoclimatal. Palaeoecol., 211, 139–155, 2004. Luo, G., Wang, Y., Kump, L. R., Bai, X., Algeo, T. J., Yang, H., and Xie, S.: Enhanced nitrogen fixation in the aftermath of the latest Permian marine mass extinction, Geology, 39, 647–650, 2011. Mackenzie, F. T. and Pigott, J. D.: Tectonic controls of Phanerozoic sedimentary rock cycling, J. Geol. Soc. London, 138, 183–196, 1981. Macko, S. A. and Estep, M. L. F.: Microbial alteration of stable nitrogen and carbon isotopic compositions of organic matter, Org. Geochem., 6, 787–790, 1984. Macko, S. A., Estep, M. L. F., Engel, M. H., and Hare, P. E.: Kinetic fractionation of stable nitrogen isotopes during amino acid transamination, Geochim. Cosmochim. Acta, 50, 2143–2146, 1986. Macko, S. A., Fogel, M. L., Hare, P. E., and Hoering, T. C.: Isotopic fractionation of nitrogen and carbon in the synthesis of amino acids by microorganisms, Chem. Geol., 65, 79–92, 1987. MacLeod, K. G. and Huber, B. T.: Reorganization of deep ocean circulation accompanying a Late Cretaceous extinction event, Nature, 380, 422-425, 1996. Mariotti, A.: Natural <sup>15</sup>N abundance measurements and atmospheric nitrogen standard calibration, Nature, 311, 251–252, 1984. Meyers, P. A.: Preservation of elemental and isotopic source identification of sedimentary organic matter, Chem. Geol., 114, 289–302, 1994. Meyers, P. A.: Organic geochemical proxies of paleoceanographic, paleolimnologic, and paleoclimatic processes, Org. Geochem., 27, 213–250, 1997. Meyers, P. A., Yum, J.-G., and Wise, S. W.: Origins and maturity of organic matter in mid-Cretaceous black shales from ODP Site 1138 on the Kerguelen Plateau, Mar. Petrol. Geol., 26, 909–915, 2009a. Meyers, P. A., Bernasconi, S. M., and Yum, J.-G.: 20 My of nitrogen fixation during deposition of mid-Cretaceous black shales on the Demerara Rise, equatorial Atlantic Ocean, Org. Geochem., 40, 158–166, 2009b. Middelburg, J. J., Soetaert, K., Herman, P. M. J., and Heip, C. H. R.: Denitrification in marine sediments: a model study, Glob. Biogeochem. Cy., 10, 661–673, 1996. Mii, H.-S., Grossman, E. L., Yancey, T. E., Chuvashov, B., and Egorov, A.: Isotopic records of brachiopod shells from the Russian Platform – evidence for the onset of mid-Carboniferous glaciation, Chem. Geol., 175, 133–147, 2001. Miller, K. G., Kominz, M. A., Browning, J. V., Wright, J. D., Mountain, G. S., Katz, M. E., Sugarman, P. J., Cramer, B. S., Christie-Blick, N., and Pekar, S. F.: The Phanerozoic record of global sea-level change, Science, 310, 1293–1298, 2005. Montañez, I. P. Norris, R. D., Algeo, T. J., Chandler, M. A., Johnson, K. R., Kennedy, M. J., Kent, D. V., Kiehl, J. T., Kump, L. R., Ravelo, A. C., and Turekian, K. K.: Understanding Earth's Deep Past: Lessons for Our Climate Future, National Academy of Sciences, Washington, DC, 212 pp., 2011. Mulder, A., van de Graaf, A. A., Robertson, L. A., and Kuenen, J. G.: Anaerobic ammonium oxidation discovered in a denitrifying fluidized bed reactor, FEMS Microbiol. Ecol., 16, 177–184, 1995. Müller, P. J.: C / N ratios in Pacific deep-sea sediments: Effect of inorganic ammonium and organic nitrogen compounds sorbed by clays, Geochim. Cosmochim. Acta, 41, 765–776, 1977. Murray, J. W., Fuchsman, C., Kirkpatrick, J., Paul, B., and Konovalov, S. K.: Species and δ<sup>15</sup>N signatures of nitrogen transformations in the suboxic zone of the Black Sea, Oceanography, 18, 36–47, 2005. Naqvi, S. W. A., Yoshinari, T., Jayakumar, D. A., Altabet, M. A., Narvekar, P. V., Devol, A. H., Brandes, J. A., and Codispoti, L. A.: Budgetary and biogeochemical implications of N<sub>2</sub>O isotope signatures in the Arabian Sea, Nature, 394, 462–464, 1998. Ogrinc, N., Fontolan, G., Faganeli, J., and Covelli, S.: Carbon and nitrogen isotope compositions of organic matter in coastal marine sediments (the Gulf of Trieste, N Adriatic Sea): indicators of sources and preservation, Mar. Chem., 95, 163–181, 2005. Peters, K. E.: Guidelines for evaluating petroleum source rock using programmed pyrolysis, Am. Assoc. Petrol. Geol. Bull., 70, 318–329, 1986. Peters, K. E., Walters, C. C., and Moldowan, J. M., The Biomarker Guide, 2nd Edn., 2 vols., Cambridge University Press, Cambridge, 2004. Prahl, F. G., de Lange, G. J., Scholten, S., and Cowie, G. L.: A case of post-depositional aerobic degradation of terrestrial organic matter in turbidite deposits from the Madeira abyssal plain, Org. Geochem., 27, 141–152, 1997. Prokopenko, M. G., Hammond, D. E., Berelson, W. M., Bernhard, J. M., Stott, L., and Douglas, R.: Nitrogen cycling in the sediments of Santa Barbara basin and Eastern Subtropical North Pacific: nitrogen isotopes, diagenesis and possible chemosymbiosis between two lithotrophs (Thioploca and Anammox) – "riding on a glider", Earth Planet. Sci. Lett., 242, 186–204, 2006. Rau, G. H., Arthur, M. A., and Dean, W. E.: <sup>15</sup>N/<sup>14</sup>N variations in Cretaceous Atlantic sedimentary sequences: Implication for past changes in marine nitrogen biogeochemistry, Earth Planet. Sci. Lett., 82, 269–279, 1987. Raymo, M. E. and Ruddiman, W. F.: Tectonic forcing of late Cenozoic climate, Nature, 359, 117–122, 1991. Robinson, R. S. and Meyers, P. A.: Biogeochemical changes within the Benguela Current upwelling system during the Matuyama Diatom Maximum: Nitrogen isotope evidence from Ocean Drilling Program Sites 1082 and 1084, Paleoceanography, 17, 1–10, 2002. Robinson, R. S., Sigman, D. M., DiFiore, P. J., Rohde, M. M., Mashiotta, T. A., and Lea, D. W.: Diatom-bound <sup>15</sup>N/<sup>14</sup>N: New support for enhanced nutrient consumption in the ice age subantarctic, Paleoceanography, 20, 1–14, 2005. Robinson, R. S. and 30 coauthors: A review of nitrogen isotope alteration in marine sediments, Paleoceanography, 27, 1–13, 2012. Romano, C., Goudemand, N., Vennemann, T. W., Ware, D., Schneebeli-Hermann, E., Hochuli, P. A., Brühwiler, T., Brinkmann, W., and Bucher, H.: Climatic and biotic upheavals following the end-Permian mass extinction, Nat. Geosci., 6, 57–60, 2012. Ronov, A. B.: Phanerozoic transgressions and regressions on the continents: A quantitative approach based on areas flooded by the sea and areas of marine and continental deposition, Am. J. Sci., 294, 777–801, 1984. Sachs, J. P. and Repeta, D. J.: Oligotrophy and nitrogen fixation during Eastern Mediterranean sapropel events, Science, 286, 2485–2488, 1999. Sachs, J. P., Repeta, D. J., and Goericke, R.: Nitrogen and carbon isotopic ratios of chlorophyll from marine phytoplankton, Geochim. Cosmochim. Acta, 63, 1431–1441, 1999. Saino, T.: <sup>15</sup>N and <sup>13</sup>C natural abundance in suspended particulate organic matter from a Kuroshio warm-core ring, Deep-Sea Res. I, 39, 347–362, 1992. Saltzman, M. R.: Late Paleozoic ice age: oceanic gateway or <i>p</i>CO<sub>2</sub>?, Geology, 31, 151–154, 2003. Schoepfer, S. D., Henderson, C. M., Garrison, G. H., and Ward, P. D.: Cessation of a productive coastal upwelling system in the Panthalassic Ocean at the Permian-Triassic boundary, Palaeogeogr. Palaeoclimatol. Palaeoecol., 313/314, 181–188, 2012. Schoepfer, S. D., Henderson, C. M., Garrison, G. H., Ward, P. D., Foriel, J., Selby, D., Hower, J. C., Algeo, T. J., and Shen, Y.: Termination of a continent-margin upwelling system at the Permian-Triassic boundary (Opal Creek, Alberta, Canada), Glob. Planet. Change, 105, 21–35, 2013. Sephton, M. A., Looy, C. V., Brinkhuis, H., Wignall, P. B., de Leeuw, J. W., and Visscher, H.: Catastrophic soil erosion during the end-Permian biotic crisis, Geology, 33, 941–944, 2005. Sigman, D. M., Altabet, M. A., François, R., McCorkle, D. C., and Gaillard, J.-F.: The isotopic composition of diatom-bound nitrogen in Southern Ocean sediments, Paleoceanography, 14, 118–134, 1999. Sigman, D. M., Altabet, M. A., McCorkle, D. C., François, R., and Fischer, G.: The δ<sup>15</sup>N of nitrate in the Southern Ocean: nitrogen cycling and circulation in the ocean interior, J. Geophys. Res., 105, 19599–19614, 2000. Sigman, D. M., Robinson, R., Knapp, A. N., van Geen, A., McCorkle, D. C., Brandes, J. A., and Thunell, R. C.: Distinguishing between water column and sedimentary denitrification in the Santa Barbara Basin using the stable isotopes of nitrate, Geochem. Geophys. Geosyst., 4, 1–20, 2003. Sloss, L. L.: Sequences in the cratonic interior of North America. Geol. Soc. Am. Bull., 74, 93–114, 1963. Snedden, J. W. and Liu, C. J.: A compilation of Phanerozoic sea-level change, coastal onlaps and recommended sequence designations, Am. Assoc. Petrol. Geol. Search and Discovery Article #40594, 3 pp., 2010. Somes, C. J., Schmittner, A., and Altabet, M. A.: Nitrogen isotope simulations show the importance of atmospheric iron deposition for nitrogen fixation across the Pacific Ocean, Geophys. Res. Lett., 37, 1–6, 2010. Song, H. Y., Tong, J. N., Algeo, T. J., Horacek, M., Qiu, H. O., Song, H. J., Tian, L., and Chen, Z. Q.: Large vertical δ<sup>13</sup>C gradients in Early Triassic seas of the South China craton: Implications for oceanographic changes related to Siberian Traps volcanism, Glob. Planet. Change, 105, 7–20, 2013. Sun, Y., Joachimski, M. M., Wignall, P. B., Yan, C., Chen, Y., Jiang, H., Wang, L., and Lai, X.: Lethally hot temperatures during the Early Triassic greenhouse, Science, 338, 366–370, 2012. Suthhof, A., Ittekkot, V., and Gaye-Haake, B.: Millennial-scale oscillation of denitrification intensity in the Arabian Sea during the late Quaternary and its potential influence on atmospheric N<sub>2</sub>O and global climate, Glob. Biogeochem. Cy., 15, 637–649, 2001. Tesdal, J. E., Galbraith, E. D., and Kienast, M.: The marine sedimentary nitrogen isotope record, Biogeosci. Disc., 9, 4067–4097, 2012. Thamdrup, B., Dalsgaard, T., Jensen, M. M., Ulloa, O., Farías, L., and Escribano, R.: Anaerobic ammonium oxidation in the oxygen-deficient waters off northern Chile, Limnol. Oceanogr., 51, 2145–2156, 2006. Thornton, S. F. and McManus, J.: Application of organic carbon and nitrogen stable isotopes and OC/TN ratios as source indicators of OM provenance in estuarine systems: evidence from the Tay Estuary, Scotland, Estuar. Coast. Shelf Sci., 38, 219–233, 1994. Tyrrell, T.: The relative influences of nitrogen and phosphorus on oceanic primary productivity, Nature, 400, 525–531, 1999. Voss, M., Dippner, J. W., and Montoya, J. P.: Nitrogen isotope patterns in the oxygen-deficient waters of the Eastern Tropical North Pacific Ocean, Deep-Sea Res. I, 48, 1905–1921, 2001. Wang, C. J. and Visscher, H.: Abundance anomalies of aromatic biomarkers in the Permian-Triassic boundary section at Meishan, China–-Evidence of end-Permian terrestrial ecosystem collapse, Palaeogeogr. Palaeoclimatol. Palaeoecol., 252, 291–303, 2007. Waser, N. A. D., Harrison, P. J., Nielsen, B., Calvert, S. E., and Turpin, D. H.: Nitrogen isotope fractionation during the uptake and assimilation of nitrate, nitrite, ammonium and urea by a marine diatom, Limnol. Oceanogr., 43, 215–224, 1998. Xie, S., Pancost, R. D., Huang, J., Wignall, P. B., Yu, J., Tang, X., Chen, L., Huang, X., and Lai, X.: Changes in the global carbon cycle occurred as two episodes during the Permian-Triassic crisis, Geology, 35, 1083–1086, 2007. Zachos, J., Pagani, M., Sloan, L., Thomas, E., and Billups, K.: Trends, rhythms, and aberrations in global climate 65 Ma to present, Science, 292, 686–693, 2001.