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Currents and Carbonate System in the Deep Black Sea

Currents and Carbonate System in the Deep Black Sea. James W. Murray School of Oceanography University of Washington Seattle, WA. Ankara Dec 5, 2006. Deep Currents using ARGO Profiling Floats (Korotaev, Oguz and Riser, 2006).

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Currents and Carbonate System in the Deep Black Sea

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  1. Currents and Carbonate System in the Deep Black Sea James W. Murray School of Oceanography University of Washington Seattle, WA Ankara Dec 5, 2006

  2. Deep Currents using ARGO Profiling Floats (Korotaev, Oguz and Riser, 2006) Three profiling floats deployed from R/V Bilim in Sept 2002 in SW Black Sea Two were at parking depth of 200m and 1550m at center of western gyre One was parked at 750m closer to the coast and the Rim Current Data transferred at the sea surface via ARGOS Accuracy of T = 0.005°C; S = 0.01; Depth = 5m Most previous research on circulation has been in the upper 500m. The Black Sea has a highly dynamic circulation above the permanent pycnocline (~100 - 200m) characterized by a basin wide cyclonic circulation called the Rim Current with anticyclonic and cyclonic eddies. Driven by wind-stress – intensifying in the winter. The deep water has been thought to be sluggish.

  3. Schematic of the main features of the surface layer circulation Cyclonic Eddies – Rim Current - Upwelling - Central Gyres Anticyclonic Eddies - Downwelling – Coastal of Rim Current Permanent Topographic Control - e.g. Sakarya Eddy Temporally and Spatially Variable - e.g. Sevastopol Eddy Sevastopol Eddy NW Shelf Rim Current Sakarya Eddy

  4. Korotaev et al., 2006 Data at http://flux.ocean.washington.edu/metu Float #634 Parked at 200m. To east at ~1cm s-1, then 5, then 10 then 15 cm s-1 Large diversion in eastern basin due to cyclonic eddy Average speed = 7 cm s-1

  5. Float #634 Velocity at 200m solid = zonal dashed = meridional

  6. Float # 631 Parked at 750m Followed coast (avg speed in Rim Current = 4 cm s-1) Deflected to north – trapped by Kerch eddy – then back to Rim Current

  7. Float #631 Velocity at 750m

  8. Float #587 Parked at 1550m Followed Rim Current – similar speed as float at 750m Eventually grounded Summary of Currents All Floats Reflect Rim Current and mesoscale eddies Deep currents are cyclonic and unidirectional Mean driving Force is wind stress The Black Sea has a highly dynamic deep circulation

  9. Float #587 Velocity at 1550m

  10. Carbonate System (Hiscock and Millero, 2006; Goyet and Brewer 1991; Dyrssen 1984) G &B – Sampled during Knorr 1988 TCO2 measured at sea. Alkalinity in the lab. H &M - Sampled during Knorr 2001 Alkalinity and pH measured at sea Total CO2 by calculation

  11. Knorr 2001 Station Locations – May 2001

  12. Alkalinity constrains the stoichiometry of suboxic reactions. Total CO2 and alkalinity increase with depth through the suboxic zone into the deep anoxic water. They reflect the net effect of all the oxidation-reduction reactions on the carbon and proton balances. In the oxic euphotic zone, total CO2 increases due to aerobic respiration while alkalinity stays approximately constant. In the anoxic, sulfide containing, waters total CO2 and alkalinity both increase due to sulfate reduction. 106 CH2O + 53 SO42+→ 106 HCO3- + 53 H2S and ammonia production 16 NH3(org) → 16 NH3 Dissolution of CaCO3 causes additional increases in total CO2 and alkalinity.

  13. Most models of oxic-anoxic interfaces assumed that sulfide is oxidized by oxygen. There are several choices for the product of sulfide oxidation and alkalinity is a sensitive tracer for. For example, the ratios of Dalk/ DHS- are different depending on whether HS- is oxidized to SO42- , SO32- , S2O32- or S°. Dalk/ DHS- 2O2 + HS- = SO42- + H+ 2 1.5 O2 + HS- = SO32- + H+ 2 O2 + HS- = 0.5 S2O32- + 0.5 H2O 1 0.5O2 + HS- + H+ = S° + H2O 0

  14. In the suboxic zone, the balance of DTCO2/Dalk also should be a sensitive constraint on the choice of reactions. The ratio of alkalinity to NO3 would be very different depending on whether NO3- is reduced by the heterotrophic pathway or by reaction with NH4+ , Mn2+ or Fe2+. This is just one reaction, and the alkalinity is influenced by many others as well, but it does illustrate this constraint. DNO3/DAlk 5{CH2O} + 4NO3- = 2N2 + 5HCO3- + H+ + 2H2O 4/-1 3NO3- + 5NH4+ = 4N2 + 9H2O + 2H+ 3/-2 2NO3- + 5Mn2+ + 4H2O = N2 + 5MnO2(s) + 8H+ 2/-8 2NO3- + 10Fe2+ + 24H2O = N2 + 10Fe(OH)3(s) + 18H+ 2/-18 2 NH4+ + 3 MnO2(s) + 4H+ = N2 + 3 Mn2+ + 6 H2O

  15. Stn 6 surface 0-75m TCO2↑ Alk ↔ pH ↓ 75-120m TCO2 ↔ Alk ↔ pH ↓ 120-2000m TCO2 ↑ Alk ↑ pH ↑ then ↓ Hiscock and Millero, 2006

  16. Stn 6 Deep TCO2 ↑ and pH ↓ due to respiration Alk ↑ due to sulfate reduction and CaCO3 dissolution TCO2 and Alk increase to very high values – 3X greater than seawater Hiscock and Millero, 2006

  17. Stn 7 Surface

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