PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Lecture 19 The Ocean Nitrogen CycleDenitrification Reactions DistributionsNitrogen Fixation Reactions DistributionsMain Ocean Source of NNitrogen FixationEnzyme catalyzed reduction of N2N2 + 8H+ + 8e- + 16 ATP → 2NH3 + H2 + 16 ADP + 16PiMediated by a two protein (Fe and Fe-Mo) complex called nitrogenaseInactivated when exposed to O2Main Ocean Sink of NFixed Nitrogen (NO3-, NO2-, NH4+) is converted to N2 in low oxygen zones of the oceanTwo PathwaysDenitrification ( <2 to 10 M O2): 2 NO3- + organic matter → N2Anammox (<2 M O2) NH4+ + NO2- → N2 + H2OSchematic of Ocean Nitrogen CycleGruber (2005) Nature 436, 786Global distribution of O2 at the depth of the oxygen minimumGruber and Sarmiento, 1997Coupling of N sources and sinks (Deutsch et al, 2007, Nature, 445, 163)Capone and Knapp (2007) Nature, 445, 159PO4 versus Nitrate (GEOSECS data)Insert shows the effect of nitrification, photosynthesis, N2 fixationand denitrification.The solid line shows thelinear equationP = 1/16 N + 0.345(equivalent to N* = 0)Values to the right havepositive N*, to the left have negative N*What is N*?N* is defined asN* = [NO3] – 16 x [PO4] +2.9N* is defined asN* = [NO3] – 16 x [PO4] +2.9N* at 200m in the Pacific (Gruber and Sarmiento, 1997)Kuypers (2003) Nature 422: 608-611.Nitrogen Cycle w/ anammoxWhy is this important for chemical oceanography?What controls ocean C, N, P?g ≈ 1.0Mass Balance for whole ocean:C/ t = VRCR – f BCS = 0; CD = CDVU = VD = VMIXNegative Feedback Control:if VMIX ↑VUCD ↑B ↑f B ↑ (assumes f will be constant!)assume VRCR then CD ↓ (because total ocean balanceVUCD ↓ has changed; sink > source)B ↓CSCDif VMIX = m y-1 and C = mol m-3flux = mol m-2 y-1The nutrient concentration of the deep ocean will adjust so thatthe fraction of B preserved in thesediments equals river input!Nitrogen species:NO3- ; NO2- ; N2O; N2 ; NH4+ (V) (III) (I) (0) (-III)Nitrogen Isotopes:14N 99.634%15N 0.366%Isotopic Composition:15 1514 14tan15 31514tan( ) ( )10( )[ ]sample s dards dardN NN NNNNd-= �‰ The standard is atmospheric N2Fractionation factors , where is the isotopic enrichment factor1000 1a e= �+FractionationHeavier stable isotope forms stronger bond. Microbial Enzymes break light isotope bonds more easily.Reactants become heavier (enriched) (e.g. NO3- → N2)Products become lighter (depleted)Partial versus total reaction (products have same values as reactants)The Global Nitrogen Budget-one example(Brandes et al, 2002)% of Export Production (as N) at HOT derived from N2 Fixation(N-P mass balance model of Karl et al (1997) Nature 388, p. 533)The Global Nitrogen Budget-one example(Brandes et al, 2002)Spatial coupling of N2 fixation and denitrification (Deutsch et al, 2007)Deutsch et al, 2004)Downcore records of 15N-orgN from several sitesHigh values of 15N-OrgN suggest more extensive denitrificationDeutsch et al,
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