T. James Noyes, El Camino College The Ocean Environment Unit II (Topic 2A-2) – page 1 Name: The Ocean Environment Unit II: Pressure and Light (3.5 pts) Section: Sound Light goes through water, but light is slowly absorbed by water until no more light is left. This is why the ocean gets darker and darker as one goes deeper into the ocean. On land, an animal can see another animal in the distance long before it can hear the other animal. (Unless the animal is intentionally being loud.) In the ocean, animals will hear other animals coming long before they can see them. Since light does not travel as well through water as it does through air, eyesight is less valuable in the ocean and good hearing is more important. Sound is transmitted much faster and better by solid objects. In other words, sound is absorbed less quickly by solids, so it goes farther before it is absorbed. Water is more “solid” than air, so sound travels faster and better in ocean water, making hearing more useful in the ocean than on land. For example, whale songs can travel thousands of miles in the ocean, allowing whales to communicate over vast distances. (There are certain depths in the ocean where the water carries sound better, and the whales use these layers to their advantage.) Sound can also be used to “see” underwater. Dolphins emit high-pitched noises, and then listen for the echoes that bounce off objects. This is called echolocation, and is how our SONAR technology works. Dolphins listen for where the sound comes back from (its direction) and how long it takes for the sound to return (the farther away the object is, the longer it will take for the sound to return). Dolphins can not only determine the position of an object, but also tell what the object looks like, its shape. 1. Does sound travel better (farther, faster) through air or water? T. James Noyes, El Camino College The Ocean Environment Unit II (Topic 2A-2) – page 2 The Cause of Atmospheric Pressure and Hydrostatic Pressure Pressure is, of course, caused when something presses or pushes against something else. In this class, we will primarily discuss atmospheric pressure and hydrostatic ocean pressure which are caused by the weight of the air and ocean water above an object. The basic rule is this: the more stuff (air or water) there is above, the higher the pressure on things below it. More stuff is heavier than less stuff. More air is heavier than less air. When we are up in the mountains, there is less air above us, so the weight of the air is less and therefore the air pressure is lower. When at sea level, there is more air above us, so the weight of the air above us is greater and air pressure is higher. The atmosphere goes up pretty high. There is about 30 miles of air above our heads. We hardly notice the effects of the air pressure exerted by the atmosphere, because our bodies are built to tolerate it; it is “normal” for us. Water, of course, is much heavier than air. Every 10 meters (33 feet) of water that is above your head is equivalent to the weight of the entire atmosphere. You really start to feel the water pressure, especially in your ears, when you dive towards the bottom of a pool, because there is more water above your head, so there is more weight pushing down, trying to push your ear drums into your skull. Note: Sound waves are vibrations – fluctuations – in pressure. Sound waves slightly increase or decrease the pressure caused by the weight of the air and water above ocean organisms. Many ocean animals can feel these vibrations all along their bodies, not just in their ears or similar organs, and use the information to find food and avoid predators. 2. What causes pressure experienced by an object, the density of the air and water above, or the weight of the air and water above? 3. Where is there more air above your head, at the top of a mountain or at the beach (at sea level)? 4. Where is the air pressure higher, at the top of a mountain or at the beach (at sea level)? 5. Where is there more water above your head, inches below the surface of the water in a swimming pool or at the bottom of the pool? 6. Where is the water pressure higher, inches below the surface of the water in a swimming pool or at the bottom of the pool? T. James Noyes, El Camino College The Ocean Environment Unit II (Topic 2A-2) – page 3 The Effect of the Ocean’s Hydrostatic Pressure on Living Things To keep from being crushed by the pressure in the deep ocean, ocean animals fill their bodies with water and other liquids which cannot be squeezed easily (unlike air). High pressure on your body squeezes nitrogen gas (from the air in your lungs) into your blood. If you swim to the surface too quickly – that is, if the pressure outside you decreases quickly – then the nitrogen in your blood changes, forms bubbles, inside your body; there is no time for it to be squeezed back out of your body and into your lungs. This may cause nitrogen narcosis (“rapture of the deep”) in which the nitrogen gas seems to act something like nitrous oxide (“laughing gas”) and thus makes the diver feel good and impairs their reasoning. The good feelings are followed by decompression sickness (“the bends”) in which nitrogen gas joins together to form bubbles in cavities like those in your joints and pinches nerves when you try to move. Humans can safely spend about 30 minutes at a depth of about 100 feet (30 meters) using SCUBA gear. The deeper you go, the higher the pressure and the quicker nitrogen is squeezed into your body, so you cannot safely spend as much time there. Deep-diving marine mammals have lungs like you and me, so they can also suffer from these effects, though they typically have adaptations to make them less harmful. For example, whales will squeeze air out of their lungs before diving. Your Body on Coke If you experience the bends or decompression sickness, then your body is behaving like a carbonated beverage, for example a can of soda like Coca-Cola. Carbon dioxide was pushed into the liquid under high pressure back at the Coca-Cola factory. This is what happens to the gases in your lungs when you dive; a gas is pushed into your body. When you open a can of soda, you are reducing the pressure on the liquid, allowing the gas to leave the liquid and form bubbles of gas within the liquid. The major difference is that the gas cannot escape your body, whereas bubbles rise up and out of the top of a can of soda. The more gas that escapes the can, the “flatter” the beverage gets. This is what also needs to happen inside your body for you to feel better: the gas has to escape, to go from your body back into your lung. Atmospheric Pressure and Storm Surge Atmospheric pressure can have a big impact on sea-level. Changes in the weight of the air above the ocean can raise sea level by over 3 feet beneath storms. The winds of storms can push this mound of water onto land, piling it up until it is over 20 feet above sea level and flooding miles of the coast. This is called storm surge and is how Hurricane Katrina overtopped the levees, pouring water into New Orleans, and how Superstorm Sandy did so much damage to New York and New Jersey. T. James Noyes, El Camino College The Ocean Environment Unit II (Topic 2A-2) – page 4 The ocean is pushed down strongly beneath the higher air pressure outside the storm, so the ocean rises where the downward push is weaker: The water that is pushed down has to go somewhere. This is somewhat like a “see saw” or “teeter-totter”: if one end goes down, the other must come up. Examine the diagram showing the child, adult, and see saw. The adult weighs more than the child, so they exert greater pressure on their side of the see saw. The child’s side rises even though the child is exerting downward pressure too. The child weighs less, so they exert less pressure on their side. Storm systems are associated with low atmospheric pressure, because the air in a storm system is warm, rising air. Warm air expands (gets “bigger”), so there is less air above each location (it has spread off to the side), and therefore less weight above each spot and thus less pressure above each spot within the storm. Examine the picture on the right. The dotted line surrounds the air of the storm. Each black dot represents an air molecule. The arrows represent the air pressure at each location. 7. Is the air within the storm spreading out or being compressed together? 8. Does the expansion of the air within the storm increase or decrease the weight of the air above each spot within the storm? Where is the air pressure higher, below the storm or outside the storm? 9. Where will the ocean be pushed down more strongly, in a region of high atmospheric pressure or a region of low atmospheric pressure? 10. Does water get pushed from a place with high atmospheric pressure to a place with low atmospheric pressure, or does water get pushed from a place with low atmospheric pressure to a place with high atmospheric pressure? 11.