UW OCEAN 520 - Ocean Carbonate Chemistry

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Slide 1Slide 2Slide 3Influences on pCO2Slide 5Air-Sea CO2 DisequilibriumSlide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Lecture 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 onlyInfluence of Nitrogen Uptake/Remineralization on AlkalinityNO3- assimilation by phytoplankton106 CO2 + 138 H2O + 16 NO3- → (CH2O)106(NH3)16 + 16 OH- + 138 O2NH3 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 CultureAir-Sea CO2 DisequilibriumEmerson and Hedges Plate 8-2-1012341985 1990 1995 2000 E N S O I N D E X ( M E I )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 fluxesCombining pCO2 fields with k: F = k s (pCO2w- pCO2a) On first order fux and pCO∆2 maps do not look that differentDo different parameterizations between gas exchange and wind matter?Global uptakes Liss and Merlivat-83: 1 Pg C yr-1Wanninkhof-92: 1.85 Pg C yr-1Wanninkhof&McGillis-98: 2.33 Pg C yr-1Zemmelink-03: 2.45 Pg C yr-1Yes!CO2 Fluxes: StatusGlobal average k (=21.4 cm/hr): 2.3 Pg C yr-1We might not know exact parameterization with forcing but forcing is clearly importantCompare with net flux of 1.3 PgCy-1 (1.9 - 0.6)in Sarmiento and Gruber (2002), Figure 1What happens to the CO2 that dissolves in water?CO2 is taken up by ocean biology to produce a flux of organic mater to the deep sea (BorgC)CO2 + H2O = CH2O + O2Some carbon is taken up to make a particulate flux of CaCO3 (BCaCO3)Ca2+ + 2HCO3- = CaCO3(s) + CO2 + H2OThe biologically driven flux is called the “Biological Pump”.The sediment record of BorgC and BCaCO3 are used to unravel paleoproductivity.The flux of BorgC to sediments drives an extensive set of oxidation-reduction reactions that are part of sediment diagenesis.Carbonate chemistry controls the pH of seawater which is a masterVariable for many geochemical processes.Ocean Distributions – versus depth, versus oceanAtlanticPacificPoints:1. Uniform surface concentrations2. Surface depletion - Deep enrichment3. DIC < Alk DIC > AlkSee Key et al (2004)GBCQ?The main features are:1. uniform surface values2. increase with depth3. Deep ocean values increase from the Atlantic to the Pacific4. DIC < Alk DIC > Alk5. 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 1.950 242 8.30North Atlantic 2.350 2.190 109 8.03 Deep WaterAntarctic 2.390 2.280 84 7.89 Deep WaterNorth Pacific 2.420 2.370 57 7.71 Deep waterDeep Atlantic to Deep PacificAlk = 0.070DIC = 0.180SoAlk/DIC = 0.40CO32- decreases fromsurface to deep Atlanticto deep Pacific. These CO32- are from CO2Sys.Can Approximate as CO32- ≈ Alk - DICQ? CO2SysControls 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 Photosynthesis/respiration (shown as apparent oxygen utilization or AOU = O2,sat – O2,obs) and CaCO3 dissolution/precipitation vectors (from Park, 1969)CH2O + O2 → CO2 + H2O as O2↓ AOU ↑ CO2 ↑Composition of Sinking Particles and Predicted ChangesOcean Alkalinity versus Total CO2 in the Ocean(Broecker and Peng, 1982)Emerson and Hedges Color PlateDIC/Alk ≈ 1.5/1Work BackwardsAlk / DIC ≈ 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 = 0.4 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 ~ 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.,


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