PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5The Ocean ConveyorMeridional Overturning Sinking and Remineralization: Atlantic SectionSlide 8Surface isopycnal outcrops - PacificSlide 10Slide 11Slide 12Slide 13Slide 14Slide 15Changing atmospheric gasesExample: Deep horizontal flow: 14CSlide 18Example: Thermocline ventilation: TritiumSlide 20Slide 21Slide 22Slide 23Slide 24Composite cruise trackOxygen DistributionApparent Oxygen UtilizationSlide 28Slide 29Surface fingerprints: ventilationSurface fingerprints: exportSlide 32Slide 33Slide 34Example: Thermocline ventilation: CFCsSlide 36Deep Ocean RespirationSlide 38Lecture 17: Respiration Oxygen distributions and ocean ventilationThermocline Ventilation and Deep Water FormationOxygen Utilization ratesAerobic 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))Apparent 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 (100% saturated) when they sink to become the deep ocean water. O2 is the dissolved oxygen actually measured in the same water sample.Nutrients 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!Winter Outcrops of Isopycnal Surfaces - AtlanticWaters will move mostly along surfaces of constant density.Surface isopycnal outcrops - PacificMeridionalDensity Sections3H penetration depth during GEOSECSAtlanticPacificIndianP = [PO4] - [PO4] = RPO4/O2 x AOU N = [NO3] - [NO3] = RNO3/O2 x AOUon  = 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 + as H2O (or HTO)Changing atmospheric gasesComparison of atmospheric history of tritium and 14CExample: Deep horizontal flow: 14CTritium 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, 15,817Winter Outcrops of Isopycnal SurfacesExample:Oxygen Utilization Rate calculated from AOU versus ageExample for onedensity surfaceθ = 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 depthComparison with O2 Flux approachOUR  New ProductionConvert the integrated O2 consumption to the POC flux requiredUse Takahashi et al (1985) stoichiometric ratio to convert C to O2Integrated OUR x conversion = Integrated C oxidized5.7 mol O2 m-2 y-1 x 106C/172O2 = 3.51 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/172O2)= 3.1 mol C m-2 y-1Two independent estimates – remarkably close agreement!Composite cruise trackOxygen DistributionApparent Oxygen UtilizationHow and why do we define the quantity called AOU?Is 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 ventilation will cause changes in air-sea fluxes of both O2 and CO2 coincident with the ventilation change…Surface fingerprints: exportthermoclineMixed layerAtm.thermoclineMixed layerAtm.Increase export fluxExport fluxAir-sea O2 fluxΔAOUoutcroptimesubtropicsSimilar AOU anomalies may be caused by increased export flux, with very different signatures of O2/CO2 gas exchange.Tritium 3H: 1/2 = 12.5 y3H  3He + as H20 (or HTO)3H = A conservative, radioactive tracerIn rain in IrelandLocate and define the outcrop of this isopycnal (constant density) surfaceExample: Thermocline ventilation: CFCsTritium is a conservative tracer for water (as HTO) – thermocline penetrationMeridional Section in the PacificEqOUR = AOU age Oxygen Utilization Rate:Deep Ocean RespirationSurface O2