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Unformatted text preview: Review of Some Important Concepts CHAPTER 6 WATER (even more!) more!) Water is a polar molecule with the ability to dissolve more substances than any other natural solvent. Salinity is the measure of dissolved inorganic solids in water. Salinity can expressed as a percent (%), but is more commonly expressed as "parts per thousand" (). Average ocean water thousand" ( salinity is about 3.5%, which equals 35 . The most abundant ions dissolved in seawater are chloride, sodium, and sulfate. The proportions of dissolved ions in seawater is nearly the same everywhere. The most abundant dissolved gases in sea water are nitrogen, oxygen, and carbon dioxide. Oxygen and carbon dioxide levels are controlled mostly by the photosynthesis and/or respiration by marine organisms. Carbonate buffering keeps ocean pH ! 8 (slightly alkaline). Outline
1. 2. 3. 4. 5. 6. 7. What's in seawater? What' Salinity and solutions Salinity factors Dissolved gasses & the concept of pH Residence time Variations in surface seawater S, T, P, and ! ("the clines") (" clines" 1 Hydrologic Cycle 5. Residence Time* Time
= Average length of time a substance spends (remains dissolved) in seawater
Residence Time = Amount of element in the ocean The rate at which the element is added to or removed from the ocean
. Long r.t. = Unreactive
" Higher concentration in seawater Short r.t. = Reactive
" Smaller concentration in seawater Hydrologic Cycle Describes (Re)cycling of Water (Etc!) *Residence time of water = Average length of time a water molecule
remains in a particular reservoir -- e.g., ocean, atmosphere, etc. Residence Time
(Cl) (Na+) (Mg2+) (K+) (SO42) (Ca2+) (CO32) (Si) (H2O) (Mn) (Al) (Fe) Conservative & Nonconservative Constituents Conservative constituents Long residence times Concentrations change slowly through time Occur in constant proportions Are the most abundant dissolved materials (major ions) in the ocean Nonconservative constituents Short residence times Concentrations change quickly through time Usually seasonal, biological, or short geological or chemical cycles Gases in seawater 2 Steady State
Is the salinity of the ocean changing over time? No, the ocean appears to be in chemical equilibrium The proportion and amounts of dissolved solids remain constant over time This concept is known as the "steady-state ocean" steady-state ocean Ions are added to and removed from the ocean at about the same rates, so salinity stays about the same 6. Variations in Surface Salinity Horizontal Variations of Salinity
Dry air descends Abundant precipitation Dry air descends Polar regions (high latitudes) Salinity is lower, lots of rain/snow and runoff Mid-latitudes Salinity is high, high rate of evaporation Near equator (low latitude) Salinity is lower, lots of rain Salinity at the surface of the ocean varies primarily with latitude 3 7. S, T, P, and ! ("the clines") (" clines"
How are salinity, temperature, pressure, and density related? How do they affect each other in ocean water? "The clines" = Rapid change of ___ with depth: Pycnocline (!) Thermocline (T) = T- and S-controlled pycnoclines Halocline (S) Seawater Density Seawater is 2%-3% denser than freshwater Density of pure water Density of seawater 1.000 g/cm3 1.020 to 1.030 g/cm3 The density is mainly a function of T and S Cold, salty water denser than warm, less-salty water Can have 2 samples with same ! by different combinations of S & T Temperature, Salinity, Density
The graph shows us that water becomes denser when: T goes down and/or S goes up In other words, cold water is denser than warm water, and saltier water is denser than less-salty water Remember, denser stuff sinks # Ocean is layered by density De ns ity inc rea sin g Fig. 6.18, p. 135 4 Density Structure of the Ocean
1. Surface zone (mixed layer) Contains the least-dense water. T & S are mixed by Surface waves and currents. In contact with atmosphere and exposed to sunlight. On average, extends to ~150 meters depth. 2. Pycnocline Density increases dramatically with depth here. Extends to ~1000 meters depth. Acts as barrier to mixing between surface zone and deep zone. 3. Deep zone Little change in density throughout this layer. Deep Thermocline
Since temperature is the primary control on ocean density, the pycnocline generally corresponds to a thermocline = a zone of rapid decrease in water temperature with depth. Note that a thermocline exists in the temperate and tropical ocean areas, but not in polar oceans, which are cold from top to bottom. Fig. 6.19a, p. 136 Fig. 6.20, p. 136 ! T 5 Halocline Surface ocean salinity is variable (by latitude, river inputs, etc) Deeper ocean salinity is quite uniform (polar source regions for deeper ocean water) Halocline between them Polar ocean is isothermal (all about the same T...cold!) # Salinity is the greatest influence on density in polar oceans Fig. 6.19, p. 136 6 " 5-Minute Write "
Summarize the main points of today's lecture. today' List 3 to 5 questions you have, based on today's lecture. today' What did you find most interesting about today's lecture? today' How was the lecture relevant to you? Increased salinity decreases the temperature of maximum density 7 ...
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- Winter '12