课6溶解气体海洋化学

Click to edit Master title style,Click to edit Master text styles,Second Level,Third Level,Fourth Level,Fifth Level,*,*,第五章 海水中的气体,海水中除含有大量的无机物和有机物以外，还溶解一些气体，如,O,2,，,CO,2,，,N,2,等。研究这些溶解气体的来源和分布对了解海洋中各种物理和化学过程起着重要作用。,1,氧是海洋学中研究得最早、最广泛的一种气体，它在深海中的分布与海水运动有关，通过氧的分布特征可以了解海水的物理过程，如水团的划分和年龄以及运动速度等。,海水中溶解氧的含量与海洋生物的活动有关，海洋植物的光合作用放出氧气，呼吸作用消耗氧气。,“保守气体”或非活性气体：不参与海水的化学和生物反应，如氮、氢和其他惰性气体。有助于深入了解空,海界面的物理过程，以及深入了解氦经由海底的放射核素输入的过程。,微量气体，如甲烷和一氧化碳等，气体的全球性循环过程。,放射性气体，如,3,H,222,Rn,3,He,，可用来研究海,空界面的气体交换，同时也是海水运动中有用的气体指示剂。,2,海水中所溶解的气体主要来自大气、海底火山活动、海水中发生的化学反应和其他过程（例如生物过程特别是光合作用和呼吸作用、有机物的分解和放射性蜕变，以及地球化学过程等）。,水循环、风化作用、光合作用、生物的腐败分解、波浪和海流等很多海洋学和海洋化学过程都与大气有关。,大气与海洋相比有相似之处，例如两者都是流体，它们的大多数成分的逗留时间比地球寿命短等。,3,Dissolved Gases Other than CO,2,Composition of the Atmosphere,Dissolution of Gases in Seawater,Air-Sea Exchange,Nonreactive Gases in Seawater,Oxygen in the Oceans,Other Nonconservative Gases,Chemical,Oceanography,4,Sources of Gases to the Oceans,1.,Atmosphere,(N,2, O,2,),2.,Volcanic Activity,(H,2,S),3.,Chemical Processes,Biological Activity,(NO,3,N,2,O),Radioactive Decay,(,226,Ra,222,Rn),Chemical,Oceanography,5,Composition of the Atmosphere,N,2,0.7808,O,2,0.2095,Ar0.00934,CO,2,0.00033,Ne1.8 x 10,-5,He5.2 x 10,-6,Kr1.1 x 10,-6,Xe8.7 x 10,-8,Pollutants(O,3,SO,2,NO,2,CH,4,CO),Chemical,Oceanography,GasMole Fraction,6,大气中的温室气体,7,Measurement Methods,1. Equilibrating or stripping with an inert gas and measure by G.C. , M.S.,or I.R.(N,2, CH,4, CO,2, Ar, etc.).,2. Direct measurement in solution (O,2,by Winkler Method).,Mn,2+,+ 2 OH,-,Mn(OH),2,Mn(OH),2,+ O,2,MnO(OH),2,MnO(OH),2,+ 4H,+,+ 3I,-,Mn,2+,+ I,3,-,+ 3H,2,O,I,3,-,+ 2S,2,O,3,2-,2 I- + S,4,O,6,2-,Chemical,Oceanography,8,Basic Concepts,Daltons Law,P,T,= P,N2,+ P,O2,+ P,Ar,+ P,H2O,Ideal Gas Law,P,G,= n,G,RT/V,G,R = 82.05,cm,3,atm mol,-1,deg,-1,Henrys Law,P,G,= K,G,GG = P,G,/K,G,P,G,(soln) = P,G,(air),Chemical,Oceanography,9,10,Solubility of Gases in Seawater,G = k P,G,= (1/K,G,) P,G,P,G,(atm) = P,G,(solution),ln G = a,0,+ a,1,S,ln G = b,0,+ b,1,/T + b,2,ln T,ln G = A,1,+A,2,(100/T)+A,3,ln(T/100) + SB,1,+ B,2,(T/100) +B,3,(T/100)2,Chemical,Oceanography,11,Effect of Salinity on Solubility,GasWater Seawater,He2.2 nM 1.8 nM,Ne10 7.9,Kr5.8 4.0,Xe0.9 0.2,N,2,823,M616,M,O,2,456349,Ar 22 17,CO,2,23 20,Chemical,Oceanography,12,Effect of Temperature on Solubility,Gas0,o,C 25,o,C,He1.8 nM1.7 nM,Ne7.96.6,Kr4.02.3,Xe0.60.4,N,2,616,M383,M,O,2,349206,Ar1710,CO,2,20 9,Chemical,Oceanography,13,Effect of Temperature,Chemical,Oceanography,14,15,16,Causes of Deviations from Expected Solubility,1. Departures from Standard Atmosphere,2. Dissolution of Air Bubbles,3. Air Injection,4. Differential(,微分的，微分,) Heat and Gas Exchange,5. Mixing of Waters of Different Temperatures,6. Radiogenic,（放射性的，无线电广播的）,or Primordial,（原始的）,Addition,Chemical,Oceanography,17,Role of Bubbles,Chemical,Oceanography,18,Effect of Mixing Water of Different Temperature,Chemical,Oceanography,19,Gas Saturation Anomalies,Chemical,Oceanography,20,Helium in Deep Waters,Chemical,Oceanography,21,He from Hydrothermal Vents,Chemical,Oceanography,22,Helium in Deep Waters,Chemical,Oceanography,23,Flux,（流量，通量）,of Gas Across the Air-Sea Interface,Chemical,Oceanography,24,Double Layer Gas Flux Model,Chemical,Oceanography,25,Flux of Gas Across the Air-Sea Interface,Flux = dC/dt = D (dC/dz),Flux = (D/K,) P,G,(air) - P,G,(soln),Flux = k P,G,(air) - P,G,(soln) = k,P,G,k is exit coefficient, is boundary layer thickness,K is Henrys Law constant,D is diffusion coefficient,Chemical,Oceanography,26,影响气体交换的因素,温度,气体溶解度,风速,季节等,27,温度的影响,大气与海洋间的气体交换主要决定于气体在两相中的分压差。当海水温度升高或降低都会使水体中气体的分压发生变化，因而引起气体在两相间的交换。,Downing,等人,(1955),发现：,CO2,的交换速率随温度的升高而直线增加，,25,海水的交换速率大约是,5,的两倍。,28,气体溶解度的影响,不同气体在海水中的溶解度各不相同。因此，对于某一恒定的分压差，各种气体进人海洋的扩散通量相差悬殊，例如,O,2, CO,2,和,N,2,的通量比率是,2,：,70,：,1,。,29,风速的影响,Downing,等人,(1955),研究了空气和水之间的交换速率。他们指出：风速在,0-3ms,-1,时，交换速率几乎保持恒定（在液体表面上方,5 cm,处测量的）。而风速在,3-13,米秒时，交换速率迅速增加。,30,季节的影响,进入或逸出海洋表层气体的体积随季节性的变化是相当大的。,Redfield(1948),曾估计，在秋季和冬季平均约有,3010,4,cm,3,O,2,进入美国缅因湾的海洋表层，在春季和夏季却以相应的体积从海洋表面逸出。其中大约,2/5,是光合作用产生的氧，其余的是由于在温暖的水中氧的溶解度降低而逸出的。,31,Diffusion Coefficients (10,5,cm,2,s,-1,),GasMW0,o,C24,o,C,He42.04.0,Ne201.42.8,N,2,281.12.1,O,2,321.22.3,Ar400.81.5,CO,2,441.01.9,N,2,O441.02.0,Kr840.71.4,Xe1310.71.4,Rn2220.71.4,Chemical,Oceanography,32,Boundry Layer Thickness,Chemical,Oceanography,33,Exit Coefficient as Function of Wind Speed,Chemical,Oceanography,34,35,nitrogen,: most common dissolved gas in seawater (accounts for 50% of the dissolved gas in water),major source is diffusion from the atmosphere,is extremely important for protein and amino acid,（氨基酸）,production by organisms, but is only available when fixed (oxidized) into a form like ammonia,（氨基，氨水）,- then it can be converted into nitrate,（硝酸盐,硝酸钾）,The principal gases dissolved in seawater are oxygen and nitrogen.,Nitrogen is conservative (like the 11 major elements; concentration changes by mixing only),36,Oxygen in the Oceans,Chemical,Oceanography,37,Oxygen in Surface Waters,Chemical,Oceanography,38,Effect of Photosynthesis on O,2,Chemical,Oceanography,39,40,Effect of Upwelling on O,2,Chemical,Oceanography,41,Oxygen in Atlantic Ocean Waters,Chemical,Oceanography,42,Oxygen Distribution - Atlantic,43,Oxygen in Pacific Ocean Waters,Chemical,Oceanography,44,Oxygen in Indian Ocean Waters,Chemical,Oceanography,45,Apparent Oxygen Utilization,Chemical,Oceanography,AOU = O,2,Calc - O,2,Meas,AOU 0 O,2,is being used,AOU 0 O,2,is being produced,46,AOU in Deep Ocean Waters,Chemical,Oceanography,47,AOU in Pacific Waters,Chemical,Oceanography,48,Modeling O,2,Profiles,Chemical,Oceanography,49,Oxygen Utilization Rates,Chemical,Oceanography,50,oxygen,:,major source,of dissolved oxygen,is the photosynthetic activity,of plants living in the surface layer of the ocean,seawater can hold only a small fraction of the oxygen that is produced, so,excess oxygen is diffused into the atmosphere,(ocean provides 50% of the atmospheres oxygen content),the,amount of dissolved oxygen can be increased by turbulence,(water movement) caused by waves and surface winds,dissolved oxygen declines rapidly as depth increases,because the rate of photosynthesis is slowed by decreasing light intensity,thermoclines can also decrease the level of oxygen,due to the high level of bacterial respiration at this depth, but below the thermocline, the amount of dissolved oxygen may increase again since oxygen solubility is increased by colder waters and there are fewer organisms living in deep waters (and most have lower metabolic rates),51,Carbon Monoxide Saturation,Chemical,Oceanography,52,Hydrogen in the Oceans,Chemical,Oceanography,53,Methane in the Oceans,Chemical,Oceanography,54,Methane in Coastal Waters,Chemical,Oceanography,55,N,2,O and O,2,in Arabian Sea,Chemical,Oceanography,56,Carbon Monoxide,Chemical,Oceanography,57,carbon dioxide,: can enter seawater in two ways:,from the atmosphere (oceans contain 60 times more carbon dioxide than the atmosphere because it is extremely soluble in seawater),from the breakdown of organic materials (is a common constituent of shells and sediments),is present as dissolved carbon dioxide, bicarbonate,（重碳酸盐）, and carbonate,（碳酸盐）,dissolved CO,2,reacts with water form carbonic acid (H,2,CO,3,) which then dissociates to form bicarbonate and carbonate - this dissociation forms a buffering system which maintains seawaters pH at about 8.00.5; CO,2,can also react with carbonate to for bicarbonate,CO,2,concentrations increase with depth because it is used during photosynthesis and released during respiration and because its solubility in water increases with pressure,the concentration of carbon dioxide in seawater is relatively constant; this provides seawaters buffering,（,减震,阻尼,隔离,）,capacity,58,