Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Temperature and Salinity along the BosporusSlide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Lecture 19 The Ocean Nitrogen CycleSinks/SourcesDenitrification Reactions DistributionsNitrogen Fixation Reactions DistributionsThe Global Oxygen CycleSource/SinksOrganic Carbon BurialWeatheringMain 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 mM O2): 2 NO3- + organic matter → N2Anammox (<2 mM 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*?How to calculateexcess or deficientNO3-N* is defined asN* = [NO3] – 16 x [PO4] +2.9N* is defined asN* = [NO3] – 16 x [PO4] +2.9Vertical distribution of N*deficitexcessN* at 200m in the Pacific (Gruber and Sarmiento, 1997)Map View of N*Kuypers (2003) Nature 422: 608-611.Nitrogen Cycle w/ anammoxWhy is N* negative - sinksNitrogen species:NO3- ; NO2- ; N2O; N2 ; NH4+ (V) (III) (I) (0) (-III)Nitrogen Isotopes:14N 99.634%15N 0.366%Isotopic Composition:‰ The standard is atmospheric N215 1514 14tan15 31514tan( ) ( )10( )[ ]sample s dards dardN NN NNNNd-= �Fractionation factors , where e is the isotopic enrichment factorFractionationHeavier 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) 1000 1a e= �+The Global Nitrogen Budget-one example(Brandes et al, 2002)Why 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!CRCR (25)N2 Fix (100-330)Denitrification sed = 200-289 wc = 75BfB (25)Fluxes in Tg N y-1Net fluxes = -200 to 0(sink > source; non-SS??)Nitrogen BalanceWalker (1974) AJSThe Global Oxygen Balancesolar UVonly non-cycliconly w/o biologyEarth is overall reducingSeparate O2; sequester reducing materialPresent is key to pastP and R in balanceSmall imbalance in P-Rmarine org C only, not terrestrial80% in hemipelagic sedimentswhere %orgC = 0.5%orgC includes H2S and Fe(II)stoichiometric so use molesLarge O2 linked to Small CAs P = R, O2 not affected by DPacceleratedweathering tC = 20yrtO2 = 4 mytC = 108 yr1) If P ceased and R continuedorg C would be consumed in 20 yrO2 would decrease by 1%2) If only sink weathering, O2 would go to 0 in 4 my. This is short geologically so controllingbalance must to strong.3) Control on O2 = org C burial vs weathering4) Feedback mechanism if atm O2 anoxic ocean org C burial atm O25) Control is with source rather than sinkSedimentary org C reservoir has not changed with timeHemipelagic sediments200m to 3000m80% of sediment orgCThe Black Sea - IstanbulRush hour on the BosphorusRumelihisarıWhy is the Black Sea Interesting to Oceanographers?1. The classic anoxic basin.Oxic layer over sulfidic layer.2.Model for modern and ancient anoxic environments.3. Well developed transitionor suboxic zone. Model forworld’s organic rich sediments.4. Suboxic reactions easy to study here because of predictable depth locations.5. An ideal location to study effect of climate forcing on ocean distributions.Climate  Physical  Chemical  BiologicalThe Bosporus Strait connects the Black Sea with the Marmara Seaand is the only source of (relatively warm) salty water.Marmara SeaBlack SeaTemperature and Salinity along the BosporusGregg et al (1999)CILMEDN. SillS. SillBosporus Inflow and Entrainment of CILresults in the Bosporus Plume CIL (~50m)(from the surfacein winter)from Ozsoy et al.(1993)Bosporus InflowAvg CIL/BI ≈ 4 to 10The Suboxic Zone: Oxygen – Sulfide Depth versus DensityTotal depth = 2200mRegional coupling of sources and sinks (Deutsch et al, 2007; Capone and Knapp, 2007)Potential for such coupling exists in the Black SeaExample of NO3-, NO2- and NH4+ for R/V Knorr 2003 suboxic zoneCILData suggests anammoxFirst seen during 1988 Expedition0 1 0 0 2 0 0 3 0 0 4 0 0O x y g e n (M )1 71 6 . 51 61 5 . 51 51 4 . 51 41 3 . 5S i g m a T h e t a0 1 0 2 0 3 0 4 0 5 0H y d r o g e n S u l f i d e (M )S t . 7 L e g 8 K n o r r 2 0 0 3O x y g e nH y d r o g e n S u l f i d e0 1 2 3 4 5N O3- M1 71 6 . 51 61 5 . 51 51 4 . 51 41 3 . 5S i g m a T h e t a0 5 1 0 1 5 2 0 2 5N H4+ M0 0 . 0 2 0 . 0 4 0 . 0 6 0 . 0 8 0 . 1N O2- MS t 7 L e g 8 K n o r r 2 0 0 3N i t r a t eA m m o n i aN i t r i t eA combined geochemical and microbiological research approach consists of four approaches.1) Determine net reactions using in situ distributions of nitrogen species and their 15N signatures 2) Measure specific rates of reactions using labeled nutrient spikes and selective inhibitors 3) Culture organisms of interest4) Use DNA sequencing to determine the distributions of attached and free living microorganisms5) Conduct mRNA analyses to determine which bacteria are functionally active.Kuypers. (2003) Nature 422: