1. Exit Choose to view chapter section with a click on the section heading. The Physics of Water How Water Physics Affect Marine Life Chapter Topic Menu

2. MenuPreviousNext 7 - 2 The Physics of Water Heat and Heat Capacity nHeat is the kinetic energy in the random movement, or vibration, of individual atoms and molecules in a substance. The faster molecules move, the more heat there is. Total heat energy is measured based on both the quantity and speed of vibrating molecules. nTemperature measures only how fast the molecules vibrate. The two most common temperature systems are Fahrenheit and Celsius. Celsius is most used in science because it is based on waters physical properties. Seawaters chemical properties affect how life functions in the oceans. Waters physical properties not only affect life processes of marine organisms, but of human beings in the water. The Physics of Water Chapter 7 Pages 7-3 to 7-5

3. MenuPreviousNext 7 - 3 Heat and Heat Capacity (continued) nHeat capacity of a substance is the amount of heat energy required to raise a given amount of a substance by a given temperature. Scientists express heat capacity in terms of the amount of heat energy it takes to change one gram of a substance by 1°C. Its expressed as the number of calories required. It takes more heat energy to raise waters temperature than that of most substances. nTherefore water can absorb or release a lot of heat with little temperature change. Waters heat capacity affects the worlds climate and weather. nHeat is carried to areas that would otherwise be cooler, and heat is absorbed in areas that would otherwise be hotter. The Physics of Water Chapter 7 Page 7-6

4. MenuPreviousNext 7 - 4 Water Temperature and Density nAs water cools it becomes denser. At 3.98°C (39.16°F) it reaches maximum density. Below this point, it crystallizes into ice. As water moves into a solid state* it becomes less dense. nIce does not form all at once at the freezing point of 0°C (32°F), but crystallizes continuously until all liquid turns solid. Temperature does not drop any further until all the liquid water freezes, even though heat continues to leave. This produces non-sensible heat – a change in heat energy that cannot be sensed with a thermometer. The non-sensible heat lost when water goes from liquid to solid state is called the latent heat of fusion. Sensible heat is that which you can sense with a thermometer. * State is an expression of a substances form as it changes from solid, to liquid, to gas with the addition of heat. Latent Heat of Vaporization nLatent heat of vaporization is the heat required to vaporize a substance. It takes more latent heat to vaporize water than to freeze it because when water freezes only some of the hydrogen bonds break. When it vaporizes, all the hydrogen bonds must break, which requires more energy. The Physics of Water Chapter 7 Pages 7-7 to 7-11

5. MenuPreviousNext 7 - 5 Thermal Inertia nThe tendency of water to resist temperature change is called thermal inertia. nThermal equilibrium means water cools at about the same rate as it heats. nThese concepts are important to life and Earths climate because: Seawater acts as a global thermostat, preventing broad temperature swings. nTemperature changes would be drastic between night and day and between summer and winter. nWithout the thermal inertia, many – perhaps most – of the organisms on Earth could not survive the drastic temperature changes that would occur each night. The Physics of Water Chapter 7 Pages 7-11 & 7-12

6. MenuPreviousNext 7 - 6 Ocean Water Density nSeawater density varies with salinity and temperature. This causes seawater to stratify, or form layers. nDense water is heavy and sinks below less dense layers. The three commonly found density layers are: 1. Surface zone – varies in places from absent to 500 meters (1,640 feet). In general it extends from the top to about 100 meters (328 feet). This zone accounts for about only 2% of the oceans volume. 2. Thermocline – separates the surface zone from the deep zone. It only needs a temperature or salinity difference to exist. This zone makes up about 18% of the oceans volume. 3. Deep zone – lies below the thermocline. It is a very stable region of cold water beginning deeper than 1,000 meters (3,280 feet) in the middle latitudes, but is shallower in the polar regions. The deep zone makes up about 80% of the oceans volume. The Physics of Water Chapter 7 Pages 7-13 & 7-14

7. MenuPreviousNext 7 - 7 Light nWater scatters and absorbs light. When light reaches the waters surface, some light penetrates, but, depending on the suns angle, much may simply reflect back out of the water. Within the water, light reflects off light-colored suspended particles. Dark colored suspended particles and algae absorb some of the light. Water molecules absorb the energy, converting light into heat. Water absorbs colors at the red end of the spectrum more easily than at the blue end. nTwo zones exist with respect to light penetration: 1. Photic Zone – where light reaches (can be as deep as 200 meters (656 feet). The photic zone has two subzones. nEuphotic Zone – the upper shallow portion where most biological production occurs – comprises about 1% of the oceans. nDysphotic Zone – where light reaches, but not enough for photosynthetic life. 2. Aphotic Zone – it makes up the vast majority of the oceans. Where light does not reach and only a fraction of marine organisms live. How Water Physics Affect Marine Life Chapter 7 Pages 7-16 to 7-20

8. MenuPreviousNext 7 - 8 Temperature nCompared to land-based climates, marine organisms live in a much less challenging environment with respect to temperature range. Ectotherm – An organism who's internal temperature changes with seawater temperature. Commonly called cold-blooded. Endotherm – Organisms that have an internal temperature that varies, but remains 9°- 16°C (48.2°- 60.8°F) warmer than the surrounding water. Homeotherm – Have an internal temperature that is relatively stable. They are called warm-blooded; marine mammals and birds are in this category. nTemperature affects metabolism – the higher the temperature within an organism the more energy-releasing chemical processes (metabolism) happen. Endotherms and homeotherms can tolerate a wide range of external temperatures. nInternal heat regulation allows endotherms an advantage. Their metabolic rate remains the same regardless of external temperature allowing them to live in a variety of habitats. How Water Physics Affect Marine Life Chapter 7 Pages 7-21 & 7-22

9. MenuPreviousNext 7 - 9 Sound nSound travels five times faster in water than in air. It travels through warm water faster than cool… but it travels faster in deep water due to pressure. Sound bounces off suspended particles, water layers, the bottom and other obstacles. Sound travels much farther through water than light does. Sound is eventually absorbed by water as heat. nBecause sound travels so well in water, marine mammals use echolocation to sense an objects size, distance, density, and position underwater. How Water Physics Affect Marine Life Chapter 7 Pages 7-22 to 7-24

10. MenuPreviousNext 7 - 10 Pressure nPressure exerted by water is called hydrostatic pressure. Its simply the weight of the water. At 10 meters (33 feet) hydrostatic pressure is equal to atmospheric pressure – 1 bar/ata. At 10 meters (33 feet) the total pressure is 2 bar – 1 bar from atmospheric pressure plus 1 bar from hydrostatic pressure. A marine organism living at 10 meters (33 feet) experiences twice the pressure present at sea level. Pressure increases 1 bar for each additional 10 meters (33 feet). nHydrostatic pressure doesnt affect marine organisms because it is the same inside the organism as outside. Living tissue is made primarily of water, which (within limits) transmits pressure evenly. Since its in balance, pressure doesnt crush or harm marine organisms. Hydrostatic pressure is primarily an issue only for organisms that have gas spaces in their bodies. How Water Physics Affect Marine Life Chapter 7 Pages 7-25 to 7-27

11. MenuPreviousNext 7 - 11 Size and Volume nUsing a sphere to substitute for a cell: The volume of a sphere increases with the cube of its radius and the surface area increases with the square of its radius. nIf a cell were to increase diameter 24 times original size, the volume would increase 64 times, but the surface area would increase only 16 times. High surface-to-volume ratio is important for cell function. The bigger the cell, the lower the surface-to-volume ratio, which means that theres less relative area through which to exchange gases, nutrients, and waste. nThis is why large organisms are multicellular rather than a giant single cell. Buoyancy nArchimedes Principle states that an object immersed in a gas or liquid is buoyed up by a force equal to the weight of the gas or liquid displaced. This means marine organisms dont have to expend much energy to offset their own weight compared to a land-based existence. nIt allows entire communities to exist simply by drifting. nIt allows organisms to grow larger than those on land. nIt allows many swimming creatures to live without ever actually coming into contact with the bottom. How Water Physics Affect Marine Life Chapter 7 Pages 7-28 to 7-31

12. MenuPreviousNext 7 - 12 Movement and Drag nMarine organisms avoid sinking by: Plumes, hairs, ribbons, spines, and other protrusions that increase their drag and help them resist sinking. Others have buoyancy adaptations that help them remain suspended in the water column. nSome marine organisms need to overcome drag as they swim. Adaptations that help them overcome drag: Moving or swimming very slowly. Excreting mucus or oil that actually lubricates them to slip through the water. The most common is to have a shape that reduces drag – streamlining. Currents nIt is speculated that drifting provides several advantages. 1. Drifting disperses organisms into new habitats, ensuring survival should something happen to the original community. 2. May take organisms into nutrient-rich areas, preventing too many offspring from competing for the same resources in the original community. How Water Physics Affect Marine Life Chapter 7 Pages 7-31 & 7-32