Altabet and Francois, 1994 Voss et al., 2001 Nakatsuka et al., 1995 CO Bacastow and Maier-Reimer 1990 Yamanaka et al., Altabet and Fr

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1 Chikyukagaku Geochemistry Marine nitrogen cycle studies byusingnitrogen isotopes and material cycle simulation model Chisato YOSHIKAWA Interdisciplinary Graduate School of Science and Engineering, Tokyo Institute of Technology Nagatsuta-cho 4259, Midori-ku, Yokohama, Kanagawa , Japan The marine nitrogen cycle is known to often control biological activity in the ocean, because nitrogen is an indispensable nutrient for phytoplankton. Understanding the marine nitrogen cycleis very important with respect to marine biological activity. In this study, nitrogen isotopic ratios ( 15 N) and marine material cycle models are used tounderstand the marine nitrogen cycle. Here, our previous studies of nitrogen cycle in the western and central equatorial Pacific and in the Sea of Okhotsk are introduced. In the equatorial Pacific, the distributions of 15 Nvalues of nitraterevealed that surface nutrient sources are atmospheric and/or terrestrial nitrogen in the western and marine nitrogen in the central. Moreover, the time variations of 15 Nvalues in sinking particles reconstructedthe transition of surface nutrient sources with transport of the fresh pool. In the Sea of Okhotsk, a marine nitrogen cycle model including nitrogen isotopes wasnewly developed in order to quantitatively understand the observed feature of winter high 15 Nvaluesofsinking particles relative to the spring values. The model suggested that the nitrification with large isotopic effects causes the winter high 15 Nvaluesofsinking particles. Finally, my future prospects of the nitrogen isotopic modeling are discussed. Key words: Marine nitrogen cycle, Nitrogen isotope ratios, Material cycle model, Equatorial Pacific, Sea of Okhotsk G1 17 Yamanaka et al., 2004 Miyake and Wada 1967

2 Altabet and Francois, 1994 Voss et al., 2001 Nakatsuka et al., 1995 CO Bacastow and Maier-Reimer 1990 Yamanaka et al., Altabet and Francois 1994 Nakatsuka et al Miyake and Wada 1967 N Sigman et al Sigman et al Yoshikawa et al. 2005a EA-IRMS Yoshikawa et al., 2005a; Yoshikawa et al., 2006a MR

3 Fig. 1 EA-IRMS EA-IRMS Fig. 2 St N fresh pool SSS 35 St fresh pool Fig. 3 fresh pool 4 Fig. 3a b 8 Fig. 1 Map of the western and central equatorial Pacific and locations of hydro cast and mooring stations (St. 1, 2, 3, and 9) during the cruise MR99-K07 in December (from Yoshikawa et al.(2006a)) Fig. 2 Vertical profiles of nitrate concentrations and those of 15 Nvalues. 15 N shows values greater than 2.5 moll 1 due to the analytical limit. (from Yoshikawa et al.(2006a))

4 Fig. 3d fresh pool St. 3 St Fig. 3c Fig. 4 St. 3 TRITON St fresh pool Fig. 3 Seasonal changes in the 15 Nvaluesofsettling particles (a: St. 1, b: St. 2, c:st.3,d:st.9) and nitrogen fluxes (e: St. 1, f: 2, g: St. 3, h: St. 9) from January to November Closed and open circles indicate the values at the upper and lower traps, respectively. (from Yoshikawa et al.(2005a)) Fig. 4 Seasonal changes in the 15 Nvaluesofsettling particles at the upper (closed circle) and lower (open circle) traps at St. 3 from December 1998 to November 1999 together with the salinity (solid line) and temperature (dotted line) variations at 100 m for 0 N, 147 E. Data for salinity and temperature are derived from the TRITON project. Data before February 1999 were not available. We adjusted the delay on the 15 Ndataforsettling particles in the upper and lower trapsby half a month and one and half month, respectively. (from Yoshikawa et al.(2005a))

EA-IRMS fresh pool Nakatsuka et al. 1995 Fig. 5 2 6 12 Fig. 5 Map of the Sea of Okhotsk and locations of the sediment trap mooring M4 and M6.

5 EA-IRMS fresh pool Nakatsuka et al Fig Fig. 5 Map of the Sea of Okhotsk and locations of the sediment trap mooring M4 and M6. Arrows show a pattern of the surface current. The square off the east coast of Sakhalin shows the region where our model is applied. (from Yoshikawa et al.(2005b))

6 3 N 5 6 Yoshikawa et al., 2006b Yoshikawa et al., 2005b 6 15 N 0 20 m m 2 Fig. 6 Fig. 6 Schematic view of interactions among the six model compartments in the upper (0-20 m deep) and lower ( m deep) layers. The symbol NO3 indicates nitrate concentration, NH4 ammonium, PHY phytoplankton, ZOO zooplankton, PON particulate organic nitrogen, and DON dissolved organic nitrogen. Dashed and solid arrows indicate nitrogen flows with and without isotope fractionation, respectively. (from Yoshikawa et al. (2005b))

7 WOA 94 NCEP Kawamiya et al Fig. 7 Fig. 7 Comparison of 15 Nofsinkingparticles among experiments changing the isotopic fractionation effects within the range measured in previous studies: (a) nitrate assimilation by phytoplankton of the small case of 0, thecontrol case of 5 and the large case of 10,(b)ammonium assimilation by phytoplankton of 5, 10 and 15, (c)nitrification of 9, 4, 19 and the non-fractionation case (thin line), (d) excretion by zooplankton of 2, 5 and 8, (e)egestion by zooplankton of 0, 2 and 4 and (f) decompositions of 0, 1 and 2. Dashed,thickanddotted lines and open circles are small, control and large cases and observed values, respectively. Open circles and triangles indicate observed vales of sinking particles from August 1998 to August 1999 and from September 1999 to June 2000, respectively. (from Yoshikawa et al.(2005b))

8 Fig. 8 Seasonal variations: (a) Chlorophyll-a concentrations, (b) ZOO concentrations, (c) NO3 concentrations, (d) NH4 concentrations, (e) Sinking PON fluxes, (f) 15 NvaluesofDON, (g) 15 NvaluesofPHY, (h), 15 NvaluesofZOO, (i) 15 NvaluesofNO3, (j) 15 NvaluesofNH4, (k) 15 Nvaluesofsinking PON and (l) 15 NvaluesofDON. Solid and dashed lines and symbols are the simulated upper and lower values and observed values, respectively. The bottled data are collected by three cruises, which were conducted in June 2000, from July to August 1998 and in September 1999, in the region where our model is applied. The moored data are collected from August 1998 to August 1999 (open circle) and from September 1999 to June 2000 (open triangle). (Modified from Yoshikawa et al.(2005b))

9 Fig. 8 a 2 Fig. 8 Fig Fig. 9 (a) simulated ratio among components of sinking particles which originated from dead bodies of phytoplankton (short-dashed line), dead bodies of zooplankton (solid line) and fecal pellet (long-dashed line), and (d) simulated 15 Nvaluesofdeadbodies of phytoplankton (short-dashed line), dead bodies of zooplankton (solid line), fecal pellet (longdashed line), and sinking particles (thick line). (Modified from Yoshikawa et al. (2005 b))

10 Minagawa and Wada, 1984 Miyake and Wada Isoscapes Graham et al., 2010 Raleigh Hood Victoria Coles COE Altabet, M. A. and Francois, R. (1994) Sedimentary nitrogen isotopic ratio as a recorder for surface ocean nitrate utilization. Global Biogeochemical Cycle, 8, Bacastow, R. and Maier-Reimer, E. (1990) Ocean-circulation model of the carbon cycle. Climate Dynamics, 4, Graham, B. S., Koch, P. L., Newsome, S. D., McMahon, K. W. and Aurioles, D. (2010) Using Isoscapes to Trace the Movements and Foraging Behavior of Top Predators in Oceanic Ecosystems. In: Isoscapes: Understanding Movement, Pattern, and Process on Earth Through Isotope Mapping (eds. J. B. West, G. J. Bowen, T. E. Dawson and K. P. Tu), Springer Science Business Media B. V., pp , doi / _14. Kawamiya, M., Kishi, M. J., Yamanaka, Y. and Suginohara, N. (1997) Obtaining reasonable results in different oceanic regimes with the same ecological-physical coupled model. Journal of Oceanography, 53, Minagawa, M. and Wada, E. (1984) Stepwise enrichment of 15 Nalongfood chains: Further evidence and the relation between 15 N and animal age. Geochimica et Cosmochimica Acta, 48, Miyake, Y. and Wada, E. (1967) The abundance ratio of 15 N/ 14 Ninmarineenvironments. Records of Oceanographic Works in Japan, 9, Nakatsuka, T., Harada, N., Matsumoto, E., Handa, N., Oba, T., Ikehara, M., Matsuoka, H. and Kimoto, K. (1995) Glacial-interglacial migration of an upwelling field in the western equatorial Pacific recorded by sediment 15 N/ 14 N. Geophysical Research Letters, 22, Sigman, D. M., Altabet, M. A., Michener, R., McCorkle, D. C., Fry, B. and Holmes, R. M. (1997) Natural abundancelevel measurement of the nitrogen isotopic composition of oceanic nitrate: an adaptation of the ammonia diffusion method. Marine Chemistry, 57, Sigman, D. M., Casciotti, K. L., Andreani, M., Barford, C., Galanter, M. and Böhlke, J. K. (2001) A bacterial method

11 for the nitrogen isotopic analysis of nitrate in seawater and freshwater. Analytical Chemistry, 73, Voss, M., Joachim, W. D. and Joseph, P. M. (2001) Nitrogen isotope patterns in the oxygen-deficient waters of the Eastern Tropical North Pacific Ocean. Deep-Sea Research I, 48, Yamanaka, Y., Yoshie, N., Fujii, M., Aita, M. N. and Kishi, M. J. (2004) An ecosystem model coupled with nitrogensilicon-carbon cycles applied to Station A7 in the Northwestern Pacific. Journal of Oceanography, 60, Yoshikawa, C., Nakatsuka, T. and Kawahata, H. (2005a) Transition of low-salinity water in the Western Pacific Warm Pool recorded in the nitrogen isotopic ratios of settling particles. Geophysical Research Letters, 32, doi: /2005 GL Yoshikawa, C., Yamanaka, Y. and Nakatsuka, T. (2005b) An ecosystem model including nitrogen isotopes: perspectives on a study of the marine nitrogen cycle. Journal of Oceanography, 61(5), Yoshikawa, C., Yamanaka, Y. and Nakatsuka, T. (2006a) Nitrogen isotopic patterns of nitrate in surface waters of the western and central equatorial Pacific. Journal of Oceanography, 62, Yoshikawa, C., Nakatsuka, T. and Wakatsuchi, M. (2006b) Distribution of N in the Sea of Okhotsk and its use as a biogeochemical tracer of the Okhotsk Sea Intermediate Water formation process. Journal of Marine Systems, 63,

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untitled 48 B 17 4 Annuals of Disas. Prev. Res. Inst., Kyoto Univ., No. 48 B, 2005 (CO 2 ) (2003) Sim-CYCLE(Ito and Oikawa, 2000) CO 2 CO 2 Figure 1 CO 2 0 (Denning et al., 1995) CO 2 (2004) Sim-CYCLE CO 2 CO 2