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UW OCEAN 400 - Ocean Carbonate Chemistry

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Slide 1Slide 2Slide 3Influences on pCO2Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Air-Sea CO2 DisequilibriumSlide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Lecture 10: Ocean Carbonate Chemistry: Ocean DistributionsOcean DistributionsControls on DistributionsWhat is the distribution of CO2 added to the ocean?See Section 4.4 Emerson and HedgesSarmiento and Gruber (2002) Sinks for Anthropogenic CarbonPhysics Today August 2002 30-36CO2CO2 → H2CO3 → HCO3- → CO32-+ H2O = CH2O + O2BorgC+ Ca2+ = CaCO3BCaCO3AtmOcnBiological PumpControls:pH of oceanSediment diagenesisCO2Gas ExchangeUpwelling/MixingRiver FluxCO2 + rocks = HCO3- + claysInfluences on pCO2 Ko: Solubility of CO2K1, K2: Dissociation constantsFunction of Temperature, SalinityDepends on biologyand gas exchangeDepends on biology onlyOcean Distributions – versus depth, versus oceanAtlanticPacificPoints:1. Uniform surface concentrations2. Surface depletion - Deep enrichment3. DIC < Alk4. DDIC > DAlkSee Key et al (2004)GBCQ?Controls on Ocean DistributionsA) Photosynthesis/RespirationOrganic matter (approximated as CH2O for this example) is produced and consumed as follows:CH2O + O2  CO2 + H2OThen:CO2 + H2O  H2CO3*H2CO3*  H+ + HCO3-HCO3-  H+ + CO32-As CO2 is produced during respiration we should observe:pH  DIC  Alk  PCO2 The trends will be the opposite for photosynthesis.B) CaCO3 dissolution/precipitationCaCO3(s)  Ca2+ + CO3 2-Also written as:CaCO3(s) + CO2 + H2O  Ca2+ + 2 HCO3-As CaCO3(s) dissolves, CO32- is added to solution. We should observe:pH  DIC  Alk  PCO2 Influence of Nitrogen Uptake/Remineralization on AlkalinityNO3- assimilation by phytoplankton106 CO2 + 138 H2O + 16 NO3- → (CH2O)106(NH3)16 + 16 OH- + 138 O2NH4 assimilation by phytoplankton106 CO2 + 106 H2O + 16 NH4+ → (CH2O)106(NH3)16 + 16 H+ + 106 O2NO3- uptake is balanced by OH- productionAlk ↑NH4+ uptake leads to H+ generationAlk ↓Alk = HCO3- + 2 CO32- + OH- - H+See Brewer and Goldman (1976) L&OGoldman and Brewer (1980) L&OExperimental CultureThe main features are:1. uniform surface values2. increase with depth3. Deep ocean values increase from the Atlantic to the Pacific4. DIC < Alk DDIC > DAlk5. Profile of pH is similar in shape to O2.6. Profile of PCO2 (not shown) mirrors O2.Ocean Distributions of, DIC, Alk, O2 and PO4 versus Depth and OceanInter-Ocean ComparisonCarbonate ion (CO32-) and pH decrease from Atlantic to Pacific x 10-3 mol kg-1 x 10-6 mol kg-1Alk DIC CO32-pHSurface Water 2.300 1.950 246 8.12North Atlantic 2.350 2.190 128 7.75 Deep WaterAntarctic 2.390 2.280 101 7.63 Deep WaterNorth Pacific 2.420 2.370 72 7.46 Deep waterDeep Atlantic to Deep PacificDAlk = 0.070DDIC = 0.180SoDAlk/DDIC = 0.40CO32- decreases fromsurface to deep Atlanticto deep Pacific. These CO32- are from CO2Sys.Can Approximate as CO32- ≈ Alk - DICQ? CO2Sys/CO2CalcS = 35T = 25CComposition of Sinking Particles and Predicted ChangesOcean Alkalinity versus Total CO2 in the Ocean(Broecker and Peng, 1982)Emerson and Hedges Color PlateDDIC/DAlk ≈ 1.5/1Work BackwardsDAlk / DDIC ≈ 0.66 = 2/3= 2 mol Org C / 1 mol CaCO3From Klaas and Archer (2002) GBCData from annual sediment traps deployments5 g POC g m-2 y-1 / 12 g mol-1 = 0.42 mol C m-2 y-140 g CaCO3 g m-2 y-1 / 105 g mol-1 = 0.38 mol C m-2 y-1What is composition of sinking particles?Org C / CaCO3 ~ 1.1PIC/POC in sediment trap samplesPOC and CaCO3 Export Fluxes This Study Previous StudiesPOC (Gt a−1)Global export 9.6 ± 3.6 11.1–12.9 [Laws et al., 2000]b9.2 [Aumont et al., 2003]c8.6 [Heinze et al., 2003]c8.7–10.0 [Gnanadesikan et al., 2004]c9.6 [Schlitzer, 2004]d5.8–6.6 [Moore et al., 2004]cCaCO3 (GtC a−1)Global export 0.52 ± 0.15 0.9–1.1 [Lee, 2001]b1.8 [Heinze et al., 1999]c1.64 [Heinze et al., 2003]c0.68–0.78 [Gnanadesikan et al., 2004]c0.38 [Moore et al., 2004]c0.84 [Jin et al., 2006]c0.5–4.7 [Berelson et al., 2007]bBased on Global Model results of Sarmiento et al (2992) GBC; Dunne et al (2007) GBCPOC/CaCO3 = 9.6 / 0.52 = 18.5Revelle FactorThe Revelle buffer factor defines how much CO2 can be absorbed by homogeneous reaction with seawater. B = dPCO2/PCO2 / dDIC/ DICB = CT / PCO2 (∂PCO2/∂CT)alk = CT (∂PCO2/∂H)alk PCO2 (∂CT/∂H)alkAfter substitutionB ≈ CT / (H2CO3 + CO32-)For typical seawater with pH = 8, Alk = 10-2.7 and CT = 10-2.7H2CO3 = 10-4.7 and CO32- = 10-3.8; then B = 11.2Field data from GEOSECSSundquist et al., Science (1979)dPCO2/PCO2 = B dDIC/DICA value of 10 tells you that a change of 10%in atm CO2 is required to produce a 1% change in total CO2 content of seawater, By this mechanism the oceans can absorb about half ofthe increase in atmospheric CO2 B↑ as T↓ as CT↑CO2CO2 → H2CO3 → HCO3- → CO32-AtmOcn350ppm + 10% = 385ppm11.3 mM+1.2 (10.6%)12.51640.5 mM+27.7 (1.7%)1668.2183.7-11.1 (-6.0%)174.2Revelle Factor Numerical Example (using CO2Sys)CO2 + CO32- = HCO3-1837+17.9 (+0.97%)1854.9DICThe total increase in DIC of +17.9 mM is mostly due to a big changein HCO3- (+27.7 mM) countering a decrease in CO32- (-11.1 mM).Most of the CO2 added to the ocean reacts with CO32- to make HCO3-.The final increase in H2CO3 is a small (+1.2 mM) portion of the total.at constant alkalinityAir-Sea CO2 DisequilibriumEmerson and Hedges Plate 8-2-1012341985 1990 1995 2000 ENSO INDEX (MEI)yearEfect of El Nino on pCO∆2 fieldsHigh resolution pCO2 measurements in the Pacific since Eq. Pac-92Eq Pac-92 process studyCosca et al. in pressEl Nino IndexPCO2swAlways greater than atmosphericExpression of Air -Sea CO2 Fluxk-transfer velocityFrom Sc # & wind speedFrom CMDLCCGG networkS – SolubilityFrom SST & SalinityFrom measurements and proxies F = k s (pCO2w- pCO2a) = K pCO∆2pCO2apCO2wMagnitudeMechanismApply over larger space time domainGlobal Map of Piston Velocity (k in m yr-1) times CO2 solubility (mol m-3) = Kfrom satellite observations (Nightingale and Liss, 2004 from Boutin).Overall trends known:* Outgassing at low latitudes (e.g. equatorial)* Influx at high latitudes (e.g. circumpolar)* Spring blooms draw down pCO2 (N. Atl)* El Niños decrease efflux∆pCO2 fieldsMonthly changes in pCO2w∆pCO2 fields:Takahashi climatologyJGOFS Gas Exchange Highlight #4 -Fluxes: JGOFS- Global monthly


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UW OCEAN 400 - Ocean Carbonate Chemistry

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