Oxygen in the Ocean. 1/28

Transcription

1 Oxygen in the Ocean 1/28

2 2/28 Oxygen in the Oceans 1000 O2 (µm) O 2 (µm) OMZ oxygen minimum zone photosynthesis respiration DEPTH (m) North Pacific North Atlantic respiration and mixing

3 Dissolved oxygen determinations 1. Equilibrating or stripping with an inert gas and measure by G.C., M.S. or I.R. To gas chromatograph, Mass spectrometer or I.R. spectrometer Sample introduction N 2 septum Signal O 2 CO 2 frit He Elution time 3/28

4 Dissolved oxygen determinations 2. Diffusion of oxygen through a Teflon membrane and polarographic determination. Oxygen Seabird SBE-43 O 2 probe Dissolved oxygen is reduced to hydroxide at the cathode, while the silver anode is oxidised: O 2 + 2H 2 O + 4ē 4OH - 4Ag o + 4Cl - 4AgCl + 4ē and the resulting current is proportional to the concentration of oxygen. 4/28

5 5/28 Dissolved oxygen determinations 3. Quenching of a fluorescent dye trapped within a sensing foil (optode).

6 6/28 4. Direct measurement in solution (O 2 by Winkler Method). Mn 2+ Dissolved oxygen determinations + 2 OH - Mn(OH) 2 (Winkler reagent) Mn(OH) O 2 MnO(OH) 2 2 Mn(OH) O 2 2 Mn(OH) 3 MnO(OH) 2 + 4H + + 3I - Mn 2+ + I H 2 O 2Mn(OH) 3 + 6H + + 3I - 2Mn 2+ + I H 2 O I S 2 O I- + S 4 O 6 2- The thiosulfate titrant is standardized daily with KIO 3 : IO H + + 8I - 3I H 2 O I S 2 O I- + S 4 O 6 2-

7 7/28 Dissolved oxygen determinations NS 2 O 3 2- = NIO3 - VIO 3 - /(VS2 O Vblank) Vblank = volume of titrant needed to titrate the reagent blank (KI + NaOH, H 2 SO 4 ) [O 2 ] = (VS 2 O Vblank) NS 2 O Vreagent [O 2 ]reagent (Vbottle Vreagent) [O 2 ]reagent = oxygen concentration in the combined reagents

8 Dissolved oxygen determinations 8/28

9 Dissolved oxygen determinations Reagent blank Probe calibration Dissolved oxygen (microm) y = x R² = Titrant volume (ml) Probe DO (microm) y = 0.927x R² = n = Measured/Winkler DO (microm) 9/28

10 Oxygen solubility = f (temperature & salinity) ln C = x 10 5 /T x 10 7 /T x /T x /T 4 S p ( /T /T 2 ) From: Benson and Krause (1984) Limnol. Oceanogr. 29: /28

11 Oxygen in the Oceans 1000 O2 (µm) O 2 (µm) OMZ oxygen minimum zone photosynthesis respiration DEPTH (m) North Pacific North Atlantic respiration and mixing /28

12 Oxygen in surface waters 12/28

13 Oxygen supersaturation in the surface ocean TEMPERATURE ( o C) O 2 (µm) O 2 SATURATION DEPTH (m) /28

14 Oxygen in surface waters Oxygen saturation (%) = 100 [G]/[G ] = 100 [G]/(P G /K G ) 14/28

15 Bubble injection 1. N 2 time N 2 O 2 Due to Greater Solubility of O 2 2. Diffusion Coefficients are Approximately Double in Bubbles 3. Bubbles are Pushed to Depths of 50 m 4. Air Injection- the total dissolution of the Air in a Bubble due to Hydrostatic Pressure Gas N 2 O 2 Ar CO 2 Ne He Kr δ Air % From the total dissolution of a bubble (1cm 3 ) of air at STP (15 o C and S =35) δ Air (%) = (([G] meas /[G] equil )-1) /28

16 Gas supersaturation in the Ocean 16/28

17 Contribution of productivity/photosynthesis to oxygen supersaturation in the surface ocean Inert gases correct biological oxygen production for physical processes Ar has very similar physical properties to O 2 O 2 :Ar ratios are a qualitative measure of biological oxygen production Need to account for physical processes using inert gases 17/28

18 Oxygen distribution in the oceans 18/28

19 Effect of upwelling on surface ocean oxygen concentrations 10 [O 2 ] MEAS - [O 2 ] CALC (µmol kg -1 ) Surface Waters 5 o S 0 5 o N LATITUDE 19/28

20 Apparent Oxygen Utilization C 106 H 263 O 110 N 16 P O CO NO 3- + HPO H 2 O + 18 H + + (trace elements) AOU = amount of dissolved oxygen used for respiration = [O 2 ] sat n [O 2 ] meas where [O 2 ] sat n = PO 2 (atm)/ko 2, with KO 2 being a function of T and S 20/28

21 Effect of upwelling on surfaceocean oxygen concentrations 10 [O 2 ] MEAS - [O 2 ] CALC (µmol kg -1 ) Surface Waters 5 o S 0 5 o N LATITUDE 21/28

22 Apparent Oxygen Utilization and water age 22/28

23 Dissolved oxygen and Apparent Oxygen Utilization 23/28

24 Apparent Oxygen Utilization AOU = measure of the amount of dissolved oxygen used for respiration = [O 2 ] sat n [O 2 ] meas C 106 H 263 O 110 N 16 P O CO NO 3- + HPO H 2 O + 18 H + + (trace elements) [NO 3- ] o.o. = AOU * 16/138; [SRP] o.o. = AOU/138 Redfield called the nitrate and phosphate produced in this way as nutrients of oxidative origin, as opposed to the preformed nutrients present in the body of water before it left the surface. [NO 3- ] meas = [NO 3- ] preformed + [NO 3- ] o.o. = [NO 3- ] preformed + AOU*16/138 [SRP] meas = [SRP] preformed + [SRP] o.o. = [SRP] preformed + AOU/138 24/28

25 Preformed and oxidative nitrate [NO 3- ] meas = [NO 3- ] preformed + [NO 3- ] o.o. = [NO 3- ] preformed + AOU*16/138 25/28

26 Organic matter respiration C 106 H 263 O 110 N 16 P O CO NO 3- + HPO H 2 O + 18 H + + (trace elements) Hence, when phytodetritus is oxidized, 1.3 moles of oxygen are required to remineralize an amount of organic material containing one mole of carbon. Whereas this ratio applies to the average organic matter formed in surface water, it does not necessarily apply to the organic matter falling to the deep sea. This material is partially decomposed, some is encapsulated in feacal pellets, and it does not necessarily have the same composition as the plant material synthesized in the euphotic zone. Furthermore, in some regions of the deep sea, where oxygen becomes severely depleted, organisms use nitrate as an oxidant instead of O 2. 26/28

27 From: Broecker and Peng (1982) Tracers in the Sea, Eldigio Press 27/28

28 Stoichiometry of organic matter respiration (4) ΔCaCO 3 = 0.5 (ΔAlk + ΔNO 3- ) = contribution of ΣCO 2 from CaCO 3 dissolution ΔOrg = ΔΣCO 2 - ΔCaCO 3 = change in ΣCO 2 from organic matter oxidation 28/28