1、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O2，CO2，N2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。,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，
2、气体的全球性循环过程。 放射性气体，如3H,222Rn,3He，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。,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。,Dissolved Gases Other than CO2,Composition of the Atmospher
3、eDissolution of Gases in SeawaterAir-Sea ExchangeNonreactive Gases in SeawaterOxygen in the OceansOther Nonconservative Gases,Chemical Oceanography,Sources of Gases to the Oceans,1. Atmosphere (N2, O2) 2. Volcanic Activity (H2S) 3. Chemical ProcessesBiological Activity(NO3 N2O)Radioactive Decay (226
4、Ra 222Rn),Chemical Oceanography,Composition of the Atmosphere,N2 0.7808O2 0.2095Ar 0.00934CO2 0.00033Ne 1.8 x 10-5He 5.2 x 10-6Kr 1.1 x 10-6Xe 8.7 x 10-8Pollutants (O3,SO2,NO2,CH4,CO),Chemical Oceanography,Gas Mole Fraction,大气中的温室气体,Measurement Methods,1. Equilibrating or stripping with an inert gas
5、 and measure by G.C. , M.S. or I.R.(N2, CH4, CO2, Ar, etc.). 2. Direct measurement in solution (O2 by Winkler Method).Mn2+ + 2 OH- Mn(OH)2Mn(OH)2 + O2 MnO(OH)2MnO(OH)2 + 4H+ + 3I- Mn2+ + I3- + 3H2OI3- + 2S2O32- 2 I- + S4O62-,Chemical Oceanography,Basic Concepts,Daltons LawPT = PN2 + PO2 + PAr + PH2O
6、Ideal Gas LawPG = nGRT/VG R = 82.05 cm3atm mol-1deg-1Henrys LawPG = KG G G = PG/KGPG(soln) = PG(air),Chemical Oceanography,Solubility of Gases in Seawater,G = k PG = (1/KG) PGPG(atm) = PG(solution)ln G = a0 + a1 Sln G = b0 + b1/T + b2 ln Tln G = A1+A2(100/T)+A3ln(T/100) + SB1+ B2(T/100) +B3(T/100)2,
7、Chemical Oceanography,Effect of Salinity on Solubility,Gas Water Seawater He 2.2 nM 1.8 nM Ne 10 7.9 Kr 5.8 4.0 Xe 0.9 0.2 N2 823 M 616 M O2 456 349 Ar 22 17 CO2 23 20,Chemical Oceanography,Effect of Temperature on Solubility,Gas 0oC 25oC He 1.8 nM 1.7 nM Ne 7.9 6.6 Kr 4.0 2.3 Xe 0.6 0.4 N2 616 M 38
8、3M O2 349 206 Ar 17 10 CO2 20 9,Chemical Oceanography,Effect of Temperature,Chemical Oceanography,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 D
9、ifferent Temperatures 6. Radiogenic（放射性的，无线电广播的） or Primordial （原始的）Addition,Chemical Oceanography,Role of Bubbles,Chemical Oceanography,Effect of Mixing Water of Different Temperature,Chemical Oceanography,Gas Saturation Anomalies,Chemical Oceanography,Helium in Deep Waters,Chemical Oceanography,He
10、 from Hydrothermal Vents,Chemical Oceanography,Helium in Deep Waters,Chemical Oceanography,Flux （流量，通量）of Gas Across the Air-Sea Interface,Chemical Oceanography,Double Layer Gas Flux Model,Chemical Oceanography,Flux of Gas Across the Air-Sea Interface,Flux = dC/dt = D (dC/dz)Flux = (D/K) PG(air) - P
11、G(soln)Flux = k PG(air) - PG(soln) = k PGk is exit coefficient is boundary layer thicknessK is Henrys Law constantD is diffusion coefficient,Chemical Oceanography,影响气体交换的因素,温度 气体溶解度 风速 季节等,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，2
12、5海水的交换速率大约是5的两倍。,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O2 , CO2和N2的通量比率是2：70：1。,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。,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30104cm 3 O2进入美国缅因湾的海洋表层，在春季和夏季却以相应的
13、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。,Diffusion Coefficients (105 cm2 s-1),Gas MW 0oC 24oC He 4 2.0 4.0 Ne 20 1.4 2.8 N2 28 1.1 2.1 O2 32 1.2 2.3 Ar 40 0.8 1.5 CO2 44 1.0 1.9 N2O 44 1.0 2.0 Kr 84 0.7 1.4Xe 131 0.7 1.4Rn 222 0.7 1.4,Chemical Oceanography,Boundry Layer Thickness,Chemical
14、 Oceanography,Exit Coefficient as Function of Wind Speed,Chemical Oceanography,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
15、, 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),Oxygen in the
16、Oceans,Chemical Oceanography,Oxygen in Surface Waters,Chemical Oceanography,Effect of Photosynthesis on O2,Chemical Oceanography,Effect of Upwelling on O2,Chemical Oceanography,Oxygen in Atlantic Ocean Waters,Chemical Oceanography,Oxygen Distribution - Atlantic,Oxygen in Pacific Ocean Waters,Chemica
17、l Oceanography,Oxygen in Indian Ocean Waters,Chemical Oceanography,Apparent Oxygen Utilization,Chemical Oceanography,AOU = O2Calc - O2MeasAOU 0 O2 is being usedAOU 0 O2 is being produced,AOU in Deep Ocean Waters,Chemical Oceanography,AOU in Pacific Waters,Chemical Oceanography,Modeling O2 Profiles,C
18、hemical Oceanography,Oxygen Utilization Rates,Chemical Oceanography,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
19、 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 in
20、tensity 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 wat
21、ers (and most have lower metabolic rates),Carbon Monoxide Saturation,Chemical Oceanography,Hydrogen in the Oceans,Chemical Oceanography,Methane in the Oceans,Chemical Oceanography,Methane in Coastal Waters,Chemical Oceanography,N2O and O2 in Arabian Sea,Chemical Oceanography,Carbon Monoxide,Chemical
22、 Oceanography,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 diss
23、olved carbon dioxide, bicarbonate（重碳酸盐）, and carbonate （碳酸盐） dissolved CO2 reacts with water form carbonic acid (H2CO3) which then dissociates to form bicarbonate and carbonate - this dissociation forms a buffering system which maintains seawaters pH at about 8.00.5; CO2 can also react with carbonat
24、e to for bicarbonate CO2 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,
