Ocean Currents Paper. Lauren Murray SME 301, Section 3

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1 Ocean Currents Paper Lauren Murray SME 301, Section 3 Background The topic of ocean currents is part of the earth science content area. Earth science is the study of forces on and inside the Earth and includes topics such as weather and climate, geology, dynamics of water, and the Earth in space. Ocean currents fit into this category because they are caused by many of these Earth forces including the Earth s rotation, prevailing winds, uneven heating of the Earth, and composition of water. Ocean currents also play a large role in influencing global climate and weather patterns. Activity Materials: Directions: Two glass baby food jars Warm water Cold water Red and blue food coloring Salt water Laminated index card Differences in Temperature 1) Fill one jar with warm water and place a drop of red food coloring in this water. Fill the other jar with cold water and place a drop of blue food coloring in this water. 2) Place the index card on top of the jar of cold water. Quickly invert the jar on top of the index card. 3) Place the jar and index card on top of the jar of warm water. Carefully remove the index card until the two jars are on top of one another. Observe the results. 4) Repeat the same process, however this time place the index card on top of the jar of warm water and invert it on top of the jar of cold water. Observe the results. Differences in Salinity 1) Fill one jar with very concentrated salt water. Fill the other jar with a small amount of salt water and the rest with fresh water. Place a drop of food coloring in this jar. 2) Place the index card on top of the jar of very salty water. Quickly invert the jar on top of the index card. 3) Place the jar and index card on top of the jar of less salty water. Carefully remove the index card until the two jars are on top of one another. Observe the results. 4) Repeat the same process, however this time place the index card on top of the jar of less salty water and invert it on top of the jar of more salty water. Observe the results. Results: o When the cold water is placed on top of the warm water the water in the two jars will mix and the cold water will sink to the bottom.

2 o o o When the warm water is placed on top of the cold water the warm water will sit on top of the cold water and no mixing will occur. When the higher concentration salt water is placed on top of the lower concentration salt water the water in the two jars will mix and the saltier water will sink to the bottom. When the lower concentration salt water is placed on top of the higher concentration salt water the less salty water will sit on top of the more salty water and no mixing will occur. Explanation of Results: When the jar of cold water is turned upside down on the jar of warm water, the water will mix because the cold water is more dense than the warm water. The molecules in the jar of cold water are much more highly concentrated than the molecules in the jar of warm water, meaning there are more water molecules packed into the space of this jar than in the jar of warm water. The greater number of molecules in the cold water makes this water heavier than the warm water so it will sink into the bottom jar, mixing with the warmer water. After this mixing occurs the higher density water is sitting in the bottom jar and the lower density water has risen to the top. However, some of the heat energy in the warm water will be transferred to molecules of cold water so the water in both jars will become mixed to a certain extent and the colors of blue and red will mix. When the warm water is placed on top of the cold water, the denser water is already on the bottom so the less dense warm water will just sit on top of the more dense water. The jar of red water will stay red and the jar of blue water will stay blue. The same results will occur using the high concentration salt water and the low concentration salt water. The more salt in the water the greater its density will be because there are more molecules packed into a given area. The higher concentration salt water will be heavier than the salt water of lower concentration so when higher concentration salt water is placed on top of lower concentration salt water the two will mix and the saltier water will sink to the bottom. When lower concentration salt water is placed on top of higher concentration salt water the higher density water is already on the bottom and is held there by gravity so no mixing occurs. The colored water will stay on top of the non-colored water. This activity illustrates Big Idea #2 by showing the movement of water based on two influences on ocean currents differences in temperature and salinity, particularly in the deep ocean. Deep currents are caused by a process of cold water and very salty water sinking deeper through the water column due to its higher density. This water then moves horizontally to form currents as it travels from an area of high concentration to an area of low concentration towards water that is less warm or less salty. This water increases in salinity through evaporation or decreases in temperature by traveling farther north and the process begins all over again. Credit: SME 301 list of approved activities for this topic Big Idea #1- Ocean currents are the movement of ocean waters in repeated patterns, both at the surface and in the ocean depths. Ocean currents are the movement of ocean waters in constantly circulating patterns influenced by the prevailing winds, the rotation of the Earth, gravity, and the continents surrounding them. There are two main types of ocean currents surface currents and deep

3 currents. The surface currents are the movement of water in the top 10% of the ocean, from the very surface to about 400 meters down. Deep currents refer to the movement of water in the bottom 90% of the ocean which circulates in a continuous pattern across the globe, known as the Global Conveyor Belt. Surface currents take the form of circulatory patterns known as gyres and there are five major gyres and several smaller ones located across the globe. There is a gyre in the northern Atlantic, southern Atlantic, northern Pacific, southern Pacific, and the Indian Oceans and these gyres rotate clockwise in the northern hemisphere and counter-clockwise in the southern hemisphere. Most major currents in the world are part of these larger circulating gyres that are propelled by prevailing winds and given shape by the orientation of continents. For example, the Gulf Stream is a current contained within the North Atlantic gyre, originating near Florida and flowing first northward and then east in the clockwise turning of this gyre. Real World Example: Christopher Columbus s journey. Christopher Columbus did not use the same route to travel both to and from the North American continent. Following the circular rotation of the North Atlantic gyre, when Columbus left Spain he first followed the Canary Current south along the coast of Africa and then turned west near the northern Tropics, blown by the Trade Winds. To return from the Americas he continued to follow the clockwise rotation of the gyre, following the Gulf Stream north and then continuing east propelled by the Westerlies. E4.2A Describe the major causes for the ocean s surface and deep water currents, including the prevailing winds, the Coriolis effect, unequal heating of the earth, changes in water temperature and salinity in high latitudes, and basin shape. Big Idea #2- The movement of ocean currents are influenced by a variety of factors. The continuous rotation of gyres and the surface currents within them is largely influenced by the Earth s prevailing winds. The sun s uneven heating of the Earth based on the tilt of the Earth s axis and the different angles of the sun to the Earth at different latitudes causes differences in air pressure that lead to the prevailing winds. In the northern hemisphere the Trade Winds, or Easterlies, carry the ocean waters from east to west in the latitudes just north of the Tropic of Cancer and the Westerlies carry waters from west to east in the mid latitudes. As the prevailing winds blow across the surface of the ocean the friction of the wind against the water pulls the water along with it, effecting the topmost 400 meters of so of the ocean, with the effect of wind becoming weaker the deeper in the ocean you go. Both prevailing winds and the ocean waters themselves are effected by the Coriolis effect, a phenomenon related to the Earth s rotation. Due to the fact that the Earth is wider at its equator than it is at its poles, the rotational speed of the Earth will be faster at the equator than at the poles. If you think about it the Earth must rotate faster at the equator in order for a point to return to its original position in 24 hours than it would on the Arctic Circle, for example. Winds and ocean currents veer slightly as they move away from the equator because of this change in rotational speed, veering right in the northern hemisphere and left in the southern hemisphere. However, when an eastward or westward moving current meets a continent it will be redirected either north or south. This causing the circular motion of gyres, which are given their pattern by a combination of prevailing winds, Earth s rotation, and the placement of continents.

4 Ocean waters will also be higher in elevation when close to continents and will flow downwards toward the center of the ocean by the force of gravity, creating smaller surface currents and causing the water in the center of each gyre to be lower in elevation than the water on the edges. Also, water in the Tropics tends to be higher in elevation than water north and south of the Tropics, causing ocean waters to be pulled away from the Tropics by gravity. Like all surfaces of the Earth ocean waters absorb light energy from the sun and transform this light energy into heat energy. The more highly concentrated the sun s light is on the ocean waters the warmer these waters will be, which is the case for ocean waters in the Tropics which receive the most intense sunlight based on the fact that the sun is closest to a 90 angle in these locations. As the water is heated the molecules spread farther apart, the water expands, and the volume increases. This causes the ocean waters to bulge slightly upwards in the Tropics due to this greater volume, and the water will flow downwards from here, either north or south. This expansion will vary in size with the seasons depending on whether the sun s most intense light is concentrated on the northern Tropics or the southern Tropics. This seasonal change and the interplay of water levels and prevailing winds on the direction of currents can cause pronounced effects in some locations. In the Indian Ocean the movement of wind and ocean currents actually changes direction from summer to winter. In the summer a strong current called the Somali Current is blown toward India and Indonesia leading to heavy monsoon rains, while in the winter weather is much milder as winds blow from the land out toward the ocean. Deep currents are effected by differences in temperature and salinity of ocean waters, a process known as thermohaline circulation. The deep waters of the oceans (below 400 meters) are all connected to each other as deep currents flow between all of the oceans, kept in motion by constantly changing density of water in different locations. The highest density water in the world is found in the very cold regions of the North Atlantic (near Greenland) and around Antarctica. Large masses of ice are formed in these locations, but the salt of the oceans does not freeze with the water. The salinity of the remaining ocean water in these locations will increase and the water will become more highly concentrated with salt, denser, and heavier. This water is very dense and heavy because the lower temperature causes molecules to pull closer together and pack more tightly into a given area and the higher concentration of salt adds an even greater number of molecules. This cold, salty water that forms around these locations will sink to the bottom of the ocean and begin to spread out from its original location, south from Greenland through the Atlantic Ocean (known as North Atlantic Deep Water) and north from Antarctica into the Indian and Pacific Oceans (known as the Antarctic Circumpolar Current). This north flowing water from Antarctica is eventually warmed, the molecules of water spread out, and it becomes less dense and rises closer to the surface. High evaporation in these warmer areas will increase the salinity of water again, as water molecules spread out and rise into the atmosphere as water vapor and salt is left behind. This dense salt water will sink back down into the deep ocean and flow westward toward the Atlantic Ocean, steered by the Coriolis effect and the position of the continents. The movement of deep ocean circulation is generated by these changes in temperature and salinity that effect the density of the water and its movement. The continual rising and sinking of deep waters as they change in density keeps the deep oceans constantly in motion and flowing into one another. Real World Example: Global warming. One of the worries raised about global warming concerns the constantly circulating movement of deep ocean currents. It is believed that if global warming continues to increase more polar ice will begin to melt decreasing the amount of dense salty water sinking into the

5 deep ocean in these regions. If temperatures increase and less freezing occurs at the poles the changes in water salinity that increase density will not occur, the polar water will sit on the surface instead of sinking to the bottom of the ocean and disruptions will occur in the process of deep ocean circulation. Deep ocean waters will become less saline and dense and less separated from surface waters, likely changing some of the ocean water movement that defines the Earth s current climate patterns. Many of these effects are not certain, but deep ocean circulation is an important phenomenon that keeps all ocean waters flowing into one another so a disruption to this cycle will certainly have far reaching influences. E4.2A Describe the major causes for the ocean s surface and deep water currents, including the prevailing winds, the Coriolis effect, unequal heating of the earth, changes in water temperature and salinity in high latitudes, and basin shape. E4.2D Identify factors affecting seawater density and salinity and describe how density affects oceanic layering and currents. E4.2F Explain how the Coriolis effect controls oceanic circulation. Big Idea #3- Ocean currents have a large impact on climates and weather patterns across the globe. Interactions between ocean currents and the continents around them have many effects on weather patterns and climates across the globe. It has been discussed already that ocean waters that are pushed in one direction by prevailing winds can be steered in a different direction when encountering a continent, called boundary currents. Western boundary currents run along eastern coasts of continents and curve toward the west, carrying warm water from the Tropics toward the Poles and are very deep and fast moving. Eastern boundary currents run along western coasts of continents and curve toward the east, carrying colder water towards the equator and are slower and shallower. Western boundary currents often bring milder climates to higher latitude areas. For example, the warm water carried by the Gulf Stream is pushed eastward by the Westerlies and brings heavy rainfall and warmer temperatures to western Europe. For this reason, western Europe has a milder climate than other regions at its same latitude, such as Canada. The shallow depth of eastern boundary currents helps to promote the process of upwelling. Upwelling occurs when winds blowing parallel to the shore blow surface waters away and cold deeper water comes up to replace it. The shallower the surface water is, the more readily it is moved away from the shore by the force of the wind. This cold water is very nutrient-rich and plants and animals thrive in regions where upwelling occurs such as the west coasts of Peru, Chile, and Mexico. Fishing industries are very dominant in these locations, supported by the abundant marine life. In the South Pacific Ocean every four years an event called El Niño can occur that disrupts the normal pattern of upwelling on the west coast of South America and cause numerous other weather changes worldwide as well. Normally in this part of the world westward blowing Trade Winds push warm surface water away from South America toward Indonesia, which causes the level of surface water effected by winds to be shallower near South America than it is near Indonesia. Upwelling occurs off the coast of South America and Indonesia receives heavy rainfall as a result of this warm, moist water near its shores. However every four years or so the Trade Winds do not blow as strongly as usual and the level of surface water is evenly distributed

6 across the South Pacific. Upwelling decreases, and a process called downwelling begins in which surface water is pushed against the surface of a continent, stacks up and begins to sink deeper into the ocean, carrying nutrients down with it. During El Niño Indonesia receives less moisture and often suffers drought, heavy rains fall in the middle of the Pacific Ocean, and the decrease in upwelling off the coast of South America causes a decrease in fishing productivity. This seemingly small shift in current movement can have significant effects on weather patterns throughout the Earth as warm, moist air moves farther eastward than usual. North America usually has heavier rain and snow during these years and Asia experiences drought. The west coasts of most continents tend to also experience a characteristic moist climate in their middle latitudes due to ocean currents. This coastal climate, or maritime climate is characterized by heavy rains most of the year, winters that are not extremely cold and summers that are not extremely hot. Eastward blowing prevailing winds will bring large amounts of moist, usually warmer air off the oceans onto these coastal regions. This type of climate characterizes western Europe, the northwest United States and Canada, and southwest Australia and South America. Out of these regions, western Europe has the most mild climate since the warm Gulf Stream current is so strong and carries warmer water than any of the currents effecting these other regions. Real World Example: Japan s climate Just like the Gulf Stream carries warm tropical waters northward to western Europe, the North Pacific gyre contains a current called Kuroshio Current, located off the coast of Japan This western boundary current influences Japan s relatively mild year-round climate. The westward blowing Trade Winds carry warm tropical waters toward southeast Asia and the Asian continent deflects these waters northward in the form of the Kuroshio Current. The prevailing winds blow warm air above the Kuroshio Current towards Japan, influencing its climate. E4.2B Explain how interactions between the oceans and the atmosphere influence global and regional climate. E4.2C Explain the dynamics of the El Nino-Southern Oscillation and its effect on continental climates. E4.2E Explain the differences between maritime and continental climates with regard to oceanic currents. Classroom Resource This demonstration is meant to illustrate the circular motion of ocean gyres and some of the factors that cause these currents to move as they do. Materials: Directions: Square glass baking dish Food coloring 1) Fill the baking dish with water 3) Place a drop of food coloring in the water in the center of the dish 4) Blow the food coloring toward one side of the dish. Observe what happens when the food coloring hits the side of the dish.

7 5) Now have a partner blow the food coloring that has spread out along one side of the dish toward the opposite side. Observe what happens to the food coloring when it hits this side of the dish. Explanation: This demonstration illustrates Big Idea #1 by presenting ocean currents as movement of water and showing how prevailing winds and continents shape the circulating movement of gyres. If the water in the baking dish was imagined to be the Atlantic Ocean the air blown on the water in Step 4 would be the westward blowing Trade Winds. The moving air is a force of friction that pulls the surface of the water containing the food coloring across the baking dish. The side of the baking dish can represent the North American continent which deflects the water northward as the Gulf Stream. (In this case, along the side of the dish.) The air blown in Step 5 represents the Westerlies carrying the Atlantic Ocean waters east toward Europe. The opposite side of the dish represents the continents of Europe and Africa which deflect the water south toward the Tropics as the Canary Current. By repeating this demonstration many times, adding more food coloring as needed, it will show fairly accurate the rotation of an ocean gyre and the constant movement of water. Credit: SME 301 list of approved activities for this topic, with some of my own variation to make this activity specifically illustrate the rotational movement of a gyre Big Blue Ocean By Bill Nye Resources The Blue Planet By Brian J. Skinner, Stephen C. Porter, and Daniel B. Botkin Prentice Hall Science Explorer: Earth s Waters By Barbara Brooks Simon and Thomas R. Wellnitz National Oceanic and Atmospheric Administration: Ocean Currents Ocean Currents and Climate Water Encyclopedia: Ocean Currents (By Piers Chapman) Climate and the Ocean (By Ron Crouse) El Nino and La Nina (By Ron Crouse)