CHAPTER 6 Water and Seawater

H 2 O molecule Two hydrogen H and one oxygen O atoms bonded by sharing electrons Two hydrogen H and one oxygen O atoms bonded by sharing electrons Both H atoms on same side of O atom Both H atoms on same side of O atom Dipolar Dipolar

Hydrogen bonding Polarity means small negative charge at O end Polarity means small negative charge at O end Small positive charge at H end Small positive charge at H end Attraction between + and – ends of water molecules to each other or other ions Attraction between + and – ends of water molecules to each other or other ions Fig. 5.3

Hydrogen bonding Hydrogen bonds are weaker than covalent bonds but still strong enough to result in Hydrogen bonds are weaker than covalent bonds but still strong enough to result in High surface tension High surface tension High solubility of chemical compounds in water High solubility of chemical compounds in water Solid, liquid, gas at Earth ’ s surface Solid, liquid, gas at Earth ’ s surface Unusual thermal properties Unusual thermal properties Unusual density Unusual density

Water molecules in different states of matter Fig. 5.5

Surface Tension A measure of the tendency of surface molecules of liquid to cling together A measure of the tendency of surface molecules of liquid to cling together Evidence of hydrogen bonding Evidence of hydrogen bonding Cohesion – strong attraction between water molecules Cohesion – strong attraction between water molecules Adhesion – water clings to many surfaces Adhesion – water clings to many surfaces Capillarity (ex. This is how plants transport water from roots to stems.) Capillarity (ex. This is how plants transport water from roots to stems.)

Viscosity A measure of the tendency of a substance to resist flow. A measure of the tendency of a substance to resist flow. Increased by hydrogen bonding in H 2 O Increased by hydrogen bonding in H 2 O Increases in water with decreasing temperature, increasing salinity, and decreasing pressure Increases in water with decreasing temperature, increasing salinity, and decreasing pressure

Light Transmission Underwater true colors can only be seen near the surface Underwater true colors can only be seen near the surface As depth increases more of the red end of the spectrum is absorbed and blue is reflected As depth increases more of the red end of the spectrum is absorbed and blue is reflected Top 10 m red wavelengths are absorbed Top 10 m red wavelengths are absorbed Within 100 m yellow is absorbed Within 100 m yellow is absorbed Blue and green to about 250 m (w/ fewer green as depth increases) Blue and green to about 250 m (w/ fewer green as depth increases) No light beyond 1000 m No light beyond 1000 m

Particles suspended in water column Particles suspended in water column Mud and sediment Mud and sediment Plankton and photosynthesis Plankton and photosynthesis More particles the less light is transmitted More particles the less light is transmitted Secchi disk – measures visible light transmission Secchi disk – measures visible light transmission Turbidity is the amount of suspended matter, is greater at shallow depths. Turbidity is the amount of suspended matter, is greater at shallow depths. Light Transmission, cont…

Sound Transmission Travels more efficiently through water than air Travels more efficiently through water than air Velocity increases as temperature, salinity, and pressure increase Velocity increases as temperature, salinity, and pressure increase SOFAR (Sound Fixing And Ranging) channel SOFAR (Sound Fixing And Ranging) channel Marine mammals may use for long-distance communication Marine mammals may use for long-distance communication Marine mammals Marine mammals

Changes of state due to adding or subtracting heat Heat is energy of moving molecules Heat is energy of moving molecules Temperature is measurement of average kinetic energy Temperature is measurement of average kinetic energy Calorie is amount of heat needed to raise the temperature of 1 gram of water by 1 o C Calorie is amount of heat needed to raise the temperature of 1 gram of water by 1 o C

Unusual thermal properties of H 2 O High boiling point (100°C) High boiling point (100°C) High freezing point (0°C) High freezing point (0°C) Most H 2 O is in the form of water (liquid) on Earth ’ s surface (good for life) Most H 2 O is in the form of water (liquid) on Earth ’ s surface (good for life) High latent (hidden) heats of High latent (hidden) heats of Vaporization/condensation Vaporization/condensation Melting/freezing Melting/freezing Evaporation Evaporation

Fig. 5.6

Unusual thermal properties of H 2 O Water high heat capacity Water high heat capacity Amount of heat required to raise the temperature of 1 gram of any substance 1 o C ( 1 calorie/gram/°C) Amount of heat required to raise the temperature of 1 gram of any substance 1 o C ( 1 calorie/gram/°C) Water can take in/lose lots of heat without changing temperature Water can take in/lose lots of heat without changing temperature Rocks low heat capacity Rocks low heat capacity Rocks quickly change temperature as they gain/lose heat Rocks quickly change temperature as they gain/lose heat

Global thermostatic effects Moderate temperature on Earth ’ s surface Moderate temperature on Earth ’ s surface Equatorial oceans (hot) don ’ t boil Equatorial oceans (hot) don ’ t boil Polar oceans (cold) don ’ t freeze solid Polar oceans (cold) don ’ t freeze solid Marine effect Marine effect Oceans moderate temperature changes day/night; different seasons Oceans moderate temperature changes day/night; different seasons Continental effect Continental effect Land areas have greater range of temperatures day/night and during different seasons Land areas have greater range of temperatures day/night and during different seasons

Density of water Density of water increases as temperature decreases Density of water increases as temperature decreases Density of ice is less than density of water Density of ice is less than density of water From 4 o C to 0 o C density of water decreases as temperature decreases From 4 o C to 0 o C density of water decreases as temperature decreases

Density of water Fig. 5.10

The Hydrologic/Water Cycle Consists of reservoirs and fluxes Consists of reservoirs and fluxes Reservoirs are locations where water is found Reservoirs are locations where water is found Fluxes are the reactions or pathways that takes water from one reservoir to another Fluxes are the reactions or pathways that takes water from one reservoir to another Closed cycle Closed cycle

Hydrologic cycle describes recycling of water near Earth ’ s surface Fig. 5.15

Residence time Average length of time a substance remains dissolved in seawater Average length of time a substance remains dissolved in seawater Ions with long residence time are in high concentration in seawater Ions with long residence time are in high concentration in seawater Ions with short residence time are in low concentration in seawater Ions with short residence time are in low concentration in seawater Steady state condition Steady state condition

Average reservoir residence times ReservoirAverage residence time Oceans2000 years Glaciers and land ice10 to 1000 years Seasonal snow cover2 to 6 months Soil moisture1 to 2 months Groundwater: shallow0.003 to 1000 years Groundwater: deep10,000 years Lakes1-3 years Rivers0.03 years Atmosphere years

Residence time and steady state Fig. 5.16

The END!!!!