Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11The Ocean ConveyorSlide 13Slide 14Density (σθ) Cross Section (Pacific Ocean)Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Example: Thermocline ventilation: TritiumSlide 26Slide 27Slide 28Slide 29Slide 30Composite cruise trackSlide 32Slide 33Surface fingerprints: ventilationSurface fingerprints: exportSlide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Oxygen DistributionApparent Oxygen UtilizationSlide 45Slide 46Example: Deep horizontal flow: 14CChanging atmospheric gasesSlide 49Slide 50Example: Thermocline ventilation: CFCsSlide 52Deep Ocean RespirationSlide 54Lecture 17: Respiration Oxygen distributions and ocean ventilationThermocline Ventilation and Deep Water FormationOxygen Utilization ratesOxygen in the AtlanticWhat controls the distribution of oxygen in the ocean?Salinity in the AtlanticAerobic respirationOxygen is consumed and nutrients are released. (CH2O)106(NH3)16(H3PO4) + 138 O2Algal Protoplasm  bacteria 106 CO2 + 16 HNO3 + H3PO4 + 122 H2O + trace elementsThe oxidation of the NH3 in organic matter to NO3 is referred to as nitrification (bacterial (AOB) or archaeal (AOA))O2 versus temperaturein surface oceansolid line equals saturationfor S = 35 at different temperaturesaverage supersaturation≈ 7 mmol/kg (~3%)Temperature controlon gas concentrationsApparent Oxygen Utilization (AOU)Apparent Oxygen Utilization or AOU. AOU is defined as:AOU = O2' - O2where: O2' = value of O2 the water would have if it was in equilibrium with the atmosphere at the temperature and salinity of the seawater. This is called saturation. This implies that all waters are in equilibrium with the atmosphere (exactly 100% saturated) when they sink to become the deep ocean water. O2 is the dissolved oxygen actually measured in the same water sample.O2 versus temperaturein surface oceansolid line equals saturationfor S = 35 at different temperaturesaverage supersaturation≈ 7 mmol/kg (~3%)Temperature controlon gas concentrationsWhat is AOU for these samples?Nutrients versus DepthExample from a verticalprofile from off theOregon coastNutrients versus AOUExample from a verticalprofile from off theOregon coastOxidative and Preformed Nutrients versus Depth1 mol O2 = 106/138 mol CO2 + 16/138 mol HNO3 + 1/138 mol H3PO4consumed = 0.77 CO2 + 0.12 HNO3 + 0.0072 H3PO4Vertical profiles are not the best way to study this problem.What are preformed nutrients?The Ocean ConveyorWhat is it conveying? (at the surface? and at depth?)Meridional Overturning Sinking and Remineralization:Atlantic SectionRemineralization keeps the biological pump pumping!B FluxDensity (σθ) Cross Section (North Atlantic)Density (σθ) Cross Section (Pacific Ocean)LatitudeNone of the deep densities in the Pacific outcrop in the PacificDensest surface water is st = 26.6Winter Outcrops of Isopycnal Surfaces – AtlanticWinter Outcrops of Isopycnal Surfaces – PacificDP = [PO4] - [PO4] = RPO4/O2 x AOU DN = [NO3] - [NO3] = RNO3/O2 x AOUon s = 27.0 to 27.2Takahashi et al, 1985Remineralization Ratios versus DepthAnderson and Sarmiento, 1994)average for 400m to 4000mP N C O21 : 16±1 : 117±14 : 170±10It is clear that more O2 (~170 moles) is actually required to respire sinking organic matter than was originally calculated from the RKR equation (138 moles). The RKR type organic matter has an oxidation state as for carbohydrate (CH2O). Real plankton have 65% protein, 19% lipid and 16% carbohydrate (from NMR studies)The higher O2 demand suggests that sinking organic matter has more of a lipid-like nature.Instead of:CH2O + O2 = CO2 + H2OMore like:CH2 + 3/2 O2 = CO2 + H2O Real plankton biomass is more like C106H177O37N17S0.4 instead of C106H260O106N16Complete oxidation requires 154 moles of O2 instead of 138Compare with Hedges ModelHow fast does ventilation occur?Time series of northern hemisphere atmospheric concentrationsand tritium in North Atlantic surface waters. When will CFCs not be a good clock?Atmospheric Record of Thermocline Ventilation TracersConservative, non-radioactive tracers (CFC-11, CFC-12, CFC-13, SF6)CFC-11PropellentStyrofoamCFC-12Air conditioningRefrigeratorsCFC-113solventSF6TransformersNike/Mercedesdown 10%down 2%Tritium 3H: t1/2 = 12.5 y3H  3He + bas H2O (or HTO)MeridionalDensity Sections3H penetration depth during GEOSECS (1970s)AtlanticPacificIndianTritium Contours(as of GEOSECS)A good tracer forthermocline ventilation¼ of surfaceWhy is Tritium concentration slightly different from Tritium/Helium Age?Example: Thermocline ventilation: TritiumTritium/Helium Age (yr)see Jenkins (1998) JGR, 103, 15,8173H = 3He + b by n = p + e-Winter Outcrops of Isopycnal Surfaces – AtlanticExample: Oxygen Utilization Rate calculated from AOU versus ageExample for onedensity surfacesθ = 26.80Jenkins (1982), Nature, 300, 246OUR versus DepthOUR decreases exponentially with depth below the euphotic zone (Z in m) according to:ln OUR = -(0.68) - (0.00295) Z OUR = 5.7 mol O2 m-2 yr-1Integrated OUR from100m to depthO2 Flux MethodBermuda - Panulirus Time Series DataJenkins and Goldman (1985) J. Marine Research 43, 465-491Density - st[O2] – [O2sat]Integrated [O2] – [O2sat] versus depthThey calculated:P – R = 5 mol O2 m-2 y-1 x 106 C/138 O2 = 3.8 molC m-2 y-1If P – R / P = 0.2 then P ≈ 19 mol C m-2 y-1 (at least 5x higher than previous measurements with 14COUR  New ProductionConvert the integrated O2 consumption to the POC flux requiredUse Redfield stoichiometric ratio to convert C to O2Integrated OUR x conversion = Integrated C oxidized5.7 mol O2 m-2 y-1 x 106C/138O2 = 4.37 mol C m-2 y-1 If we had used 106C/170O2 = 3.55 mol C m-2 y-1For comparison in the last lecture we calculated the annual newproduction of C from the O2 mass balance in the euphotic zone.From that approach the new production is (using 106C/138O2)= 3.8 mol C m-2 y-1Two independent estimates – remarkably close agreement!Composite cruise trackIs AOU Changing?Case Study from the North PacificOxygen is a tracer of both physical and biological changesApparent Oxygen UtilizationAOU = O2sat -O2ΔO2 = ΔO2sat - ΔAOU(from Deutsch et al)Surface fingerprints: ventilationthermoclineMixed layerAtm.thermoclineMixed layerAtm.Decrease ventilationventilationAir-sea O2 fluxΔAOUsubtropicstimeoutcropAn increase in AOU due to decreased