PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Temperature and Salinity along the BosporusSlide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Lecture 18 Redox Environments in the OceansDiagenesis in SedimentsAnoxic BasinsGlobal Carbon Cycle – Fate of organic matter in sedimentsRedox Half Reactions written as reductantsin terms of 1 e-Organic Matter Degradation (using Redfield stoichiometry)“OM” = (CH2O)106(NH3)16(H3PO4)Photosynthesis106CO2 + 16 NO3- + HPO42- + 18H+ 122 H2O → “OM” + 138 O2RespirationAerobic Respiration138 O2 + “OM” + 18 HCO3- → 124 CO2 + 16 NO3- + HPO42- + 140 H2ODenitrification94.4 NO3- + “OM” → 13.6 CO2 + 92.4 HCO3- + 55.3 N2 + 84.8 H2O + HPO42-Manganese Oxide Reduction236 MnO2 + “OM” + 364 CO2 + 104 H2O → 470 HCO3- + 8N2 + 236 Mn2+ + HPO42-Iron Oxide Reduction212 Fe2O3 + “OM” + 742 CO2 + 318 H2O → 848 HCO3- + 16 NH3 + 424 Fe2+ + HPO42-Sulfate Reduction53 SO42- + “OM” → 39 CO2 + 67 HCO3- + 16 NH4+ + 53 HS- + 39 H2O + HPO42-Methane Fermentation“OM” → 53 CO2 + 53 CH4 + 16 NH3 + HPO42- + 2H+Indicator species are circledDrilling Platform Blowout 2010 in the Deep Gulf of Mexico.J D Kessler et al. Science 2011;331:312-315The integrated dissolved oxygen anomaly was about3.0 x 1010 moles O2. If this O2 anomaly was due to CH4 oxidation, how much CH4 wouldit account for?Sampling stationsContours of O2 anomaly¼ O2(g) + H+ + e- = ½ H2O log K = 20.751/8 CO2(g) + H+ + e- = 1/8 CH4 (g) + ¼ H2O log K = 2.87Reverse 2nd reaction1/8 CH4(g) + 1/4H2O = 1/8 CO2(g) + H+ + e- log K = -2.87Add to first reaction1/4O2(g) + 1/8 CH4(g) = 1/8 CO2(g) + ¼ H2O log K = 17.88Multiply by x82O2(g) + CH4(g) = CO2(g) + 2 H2O log K = 143.04So: 3.0 x 1010 mol O2 = 1.5 x 1010 mol CH4 (upper limit due to C2H6, C3H8)Multi-colored sediments!What’s going on here???Rarely see all reactions easily at the same siteAerobic Respiration in Red Clay SedimentsDenitrification and MnO2 reduction – Hemipelagic SedimentsEmerson et alGuatemala Basin, North PacificIron reduction – Hemipelagic SedimentsEmerson et alEast Pacific Rise – North PacificSulfate ReductionMethane ProductionAnaerobic Methane ConsumptionSaanich Inlet, BCSedimentsKuivila and Murray (1990)The Black SeaWhy 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.The 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 Bosporus•Some CIW advected into strait in upper half of interface•T minimum in deep water erased over South SillGregg et al (1999)Bosporus Inflow and Entrainment of CIL CIL(from NW Shelfin winter)from Ozsoy et al.,(1993)Bosporus InflowCIL/BI ≈ 4 for deep Black Seafrom 50m to 2000mThe Suboxic Zone: Oxygen – Sulfide Depth versus DensityTotal depth = 2200m0 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 e Example of NO3-, NO2- and NH4+ for R/V Knorr 2003 suboxic zoneCILData suggests anammoxFirst seen during 1988 ExpeditionResults from Knorr 1988 Cruise(w/ Pump Profiling System)Oxygenated surface layer over a sulfide rich deep layerwith a suboxic zone at the interfaceO2H2SNO3Suboxic ZoneNO2Murray et al