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OCN520 Fall 2009 Mid-Term #2 Review

OCN520 Fall 2009 Mid-Term #2 Review. Since Mid-Term #1 Ocean Carbonate Distributions Ocean Acidification Stable Isotopes Radioactive Isotopes Nutrients and Production POC Export and Respiration O2: Ventilation versus Respiration.

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OCN520 Fall 2009 Mid-Term #2 Review

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  1. OCN520 Fall 2009 Mid-Term #2 Review Since Mid-Term #1 Ocean Carbonate Distributions Ocean Acidification Stable Isotopes Radioactive Isotopes Nutrients and Production POC Export and Respiration O2: Ventilation versus Respiration

  2. Sarmiento and Gruber (2002) Sinks for Anthropogenic Carbon Physics Today August 2002 30-36

  3. Ocean Distributions – versus depth, versus ocean Atlantic Pacific Points: 1. Uniform surface concentrations 2. Surface depletion - Deep enrichment 3. DIC < Alk 4. DDIC > DAlk See Key et al (2004) GBC Q?

  4. Ocean Distributions of, DIC, Alk, O2 and PO4 versus Depth and Ocean The main features are: 1. uniform surface values 2. increase with depth 3. Deep ocean values increase from the Atlantic to the Pacific 4. DIC < Alk DDIC > DAlk 5. Profile of pH is similar in shape to O2. 6. Profile of PCO2 (not shown) mirrors O2.

  5. Paleo Nutrient Distributions Boyle and Keigwin (1982) Science Data in benthic forams – North Atlantic

  6. Controls on Ocean Distributions A) Photosynthesis/Respiration Organic matter (approximated as CH2O for this example) is produced and consumed as follows: CH2O + O2 CO2 + H2O Then: 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/precipitation CaCO3(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

  7. DDIC/DAlk ≈ 1.5/1 Work Backwards DAlk / DDIC ≈ 0.66 = 2/3 = 2 mol Org C / 1 mol CaCO3 Emerson and Hedges Color Plate

  8. Example: Estimation of temperature in ancient ocean environments CaCO3(s) + H218O  CaC18OO2 + H2O The exchange of 18O between CaCO3 and H2O The distribution is Temperature dependent last interglacial Holocene last glacial d18O of planktonic and benthic foraminifera from piston core V28-238 (160ºE 1ºN) Planktonic and Benthic differ due to differences in water temperature where they grow. Assumptions: 1. Organism ppted CaCO3 in isotopic equilibrium with dissolved CO32- 2. The δ18O of the original water is known 3. The δ18O of the shell has remained unchanged Planktonic forams measure sea surface T Benthic forams measure benthic T

  9. δ13C in different reservoirs E & H Fig. 5.6

  10. Distillation of meteoric water – large kinetic fractionation occurs between ocean and vapor. Then rain forming in clouds is in equilibrium with vapor and is heavier that the vapor. Vapor becomes progressively lighter. dD and d18O get lower with distance from source. Water evaporation is a kinetic effect. Vapor is lighter than liquid. At 20ºC the difference is 9‰ (see Raleigh plot). The BP of H218O is higher than for H216O Air masses transported to higher latitudes where it is cooler. water lost due to rain raindrops are rich in 18O relative to cloud. Cloud gets lighter

  11. Secular equilibrium t1/2 daughter = 0.8 hr t1/2 parent =  parent daughter Activity (log scale) ! Daughter grows in with half life of the daughter! t1/2 time (hr)

  12. 222Rn Example Profile from North Atlantic Does Secular Equilibrium Apply? t1/2222Rn << t1/2 226Ra (3.8 d) (1600 yrs) YES! A226Ra = A222Rn 222Rn 226Ra Why is 222Rn activity less than 226Ra?

  13. Particle and 234Th Export Coale & Bruland 1987 Vertical zonation of 234Th removal

  14. Annual Mean Surface Nitrate

  15. The Redfield or "RKR" Equation (A Model) The mean elemental ratio of marine organic particles is given as: P : N : C = 1 : 16 : 106 The average ocean photosynthesis (forward) and aerobic ( O2 ) respiration (reverse) is written as: 106 CO2 + 16 HNO3 + H3PO4 + 122 H2O + trace elements (e.g. Fe) light (h n)  ( C106H263O110N16P ) + 138 O2 or (CH2O)106(NH3)16(H3PO4) Algal Protoplasm The actual chemical species assimilated during this reaction are: HCO3- NO3- PO43- NO2- NH4+

  16. Food Web Cartoon Follow the N! Follow the C! Follow the O2! Fe plays a role! DON Euphotic Zone (~100m) At steady state: New NO3 = O2 flux to atm = PON (and DON) export PON

  17. Atm. Mixed layer thermocline ventilation outcrop Air-sea O2 flux subtropics ΔAOU time Surface fingerprints: ventilation Atm. Mixed layer Decrease ventilation thermocline An increase in AOU due to decreased ventilation will cause changes in air-sea fluxes of both O2 and CO2 coincident with the ventilation change…

  18. outcrop Surface fingerprints: export Atm. Atm. Mixed layer Mixed layer Increase export flux thermocline thermocline Export flux Similar AOU anomalies may be caused by increased export flux, with very different signatures of O2/CO2 gas exchange. subtropics Air-sea O2 flux ΔAOU time

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