Recent advances in the biogeochemistry of nitrogen in the ocean

Determination of total N <sub>2</sub> fixation rates in the ocean taking into account both the particulate and filtrate fractions

“…Konno (utakonno@mail.sci.hokudai.ac.jp) total fixed nitrogen is predominantly controlled by the total influx of fixed nitrogen through N 2 fixation and by the total efflux of fixed nitrogen through denitrification (Codispoti et al, 2001;Brandes and Devol, 2002;Deutsch et al, 2004). However, the estimated values of both fluxes obtained in different studies are highly variable (e.g., Wada et al, 1975;Liu, 1979;Codispoti and Christensen, 1985;Gruber and Sarmiento, 1997;Codispoti et al, 2001;Brandes and Devol, 2002;Capone and Knapp 2007;Naqvi et al, 2008). Earlier estimates have revealed the efflux of 95 ± 20 Tg N yr −1 through sedimentary denitrification (Gruber and Sarmiento, 1997) and the influx of 110 ± 40 Tg N yr −1 through oceanic N 2 fixation (Codispoti et al, 2001).…”

Ontogenetic variation of δ13C and δ15N recorded in the gladius of the jumbo squid Dosidicus gigas: geographic differences

“…For instance, denitrification (conversion of NO 3 -and NO 2 -to N 2 O by microbes) produces high isotopic values in suboxic subsurface waters such as in the Carmen and Guaymas basin of the Gulf of California (Altabet et al 1999), while undetectable changes in δ 15 N exist during N 2 fixation (Hoering & Ford 1960). Because N is an essential nutrient that can limit primary production (Naqvi et al 2008), the interoceanic and intraoceanic variation in δ 15 N from animal tissues may relate to differences in the metabolism and cycling of N, which in turn is driven by variability in the physical and biochemical properties between oceanic basins (Takai et al 2000, Wallace et al 2006. Our samples were collected in sites from various systems such as the Gulf of California, Costa Rica Dome, the eastern equatorial current, and the California Current.…”

North Pacific-wide spreading of isotopically heavy nitrogen during the last deglaciation: Evidence from the western Pacific

“…Sedimentary nitrogen isotope (δ 15 N) records from oligotrophic regions distant from zones of vigorous water column denitrification (WCD) may help in assessing past changes in the magnitude of global WCD, which along with sedimentary denitrification is the main pathway of losses of fixed N from the ocean (Brandes and Devol, 2002;Altabet, 2007;Naqvi et al, 2008). One of the unsettled issues is the intensity of WCD in the North Pacific during the last deglaciation and its effect on global oceanic N inventory.…”

“…As an essential nutrient, changes in the oceanic inventory of biologically available N (or "fixed nitrogen", which is dominated by nitrate) would be expected to impact the biological carbon pump over large regions of the ocean through glacial-interglacial cycles (Falkowski, 1997;Broecker and Henderson, 1998;Archer et al, 2000;Naqvi et al, 2008).…”