Horizontal and Vertical currents move huge volumes of water around the world PDF

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Running head: OCEAN CURRENTS

1 Ocean Currents

Principles of Ocean Science (MBIO 215)

Ocean currents are defined as the vertical or horizontal movements of both surface and deep water throughout the world’s oceans. They move in a specific direction and aid significantly in the circulation of the earth’s moisture, weather and water pollution (Briney, 2018). The major causes of ocean currents are generated by wind friction, water density differences (due to variations in temperature and salinity), ocean bottom topography and Coriolis effect (Edmunds, 2018). The wind is generated by differential heating of the atmospheric air masses. When the wind passes over surface waters, energy is released into the ocean due to frictional stress. This frictional stress causes the flow of wind to pull surface waters along with it thus, creating ocean currents. For example, trade winds. Trade winds blow from 30o NE to SW and 30o SE to NW. This generates currents that flow to the west in tropical latitudes (Morrall, 2018a). Density differences affect the formation of ocean currents. Variations in density are caused by variations in water salinity and temperature. Water salinity and density are proportional. If the salinity of the water increases, the density also increases. However, density and temperature are inversely proportional. Colder water is denser than warmer water. In the polar regions, cold surface waters sink to the ocean bottom. This happens as a result of ice formation in the polar region. When sea ice forms, it leaves the salt of the seawater behind. This causes an increase in salinity. As stated previously, increase salinity increases the density of water. The dense cold waters create a slow, deep water current that runs from the pole towards the equator. Warmer surface waters at the equator remains on the surface and will create a current flowing from the equator toward the poles to replace the sinking dense surface waters. This creates a thermohaline circulation (Morrall, 2018b). Thermohaline circulation is driven by a global conveyer belt. It plays an important role in supplying heat to the polar regions and influencing the rate of ice formation near the poles (UCAR, n.d.).

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Ocean bottom topography also influences ocean currents formation. If the ocean bottom consists of valleys or trenches, there will be a downward movement of water. However, if it contains mountains or ridges, the water movement will be forced upward. This upward and downward movement of water creates ocean currents (Edmunds, 2018). The Coriolis effect is a consequence of movements taking place on a revolving, spherical body that is the Earth (Morrall, 2018d). The earth’s rotation creates two currents: one in the northern hemisphere and the other, in the southern hemisphere. In the northern hemisphere, there is a clockwise movement of water, and in the southern hemisphere, the movement of water is anti-clockwise. When these currents are deflected by landmasses, they create huge ocean current called gyres (Edmunds, 2018). Gyres are mainly driven by the major wind belts. Each gyre contains four main currents which flow into each other. Energy from the wind is transferred into the water column of the ocean and, due to the Coriolis effect, each layer within the water column is deflected with respect to the one immediately above it. This resulted in the formation of Ekman Spiral. The net water movement within the Ekman spiral is called the Ekman Transport, which is at 900 to the wind direction (Morrall, 2018c). For example, Diagram 1 is showing a southerly wind blowing pass the east coast of Grenada, each layer of water within the water column is deflected to the right at 450, creating Ekman spiral. The net movement of water is Southerly deflected 900 to the right to the direction of theWind wind forming, Ekman Transport, which result in an offshore movement of surface water. Southerly Wind Ekman’s Transport (900) Ekman’s Spiral (450) East Coast Water moving seaward Diagram 1. Illustrating Coriolis effect-Ekman Spiral and Ekman Transport- AC; (Image of water from freepik). Ocean currents have multiple impacts on marine life. Not only does ocean currents move plants and animals around the ocean, they also distribute heat, oxygen, and nutrients to various organisms through processes of upwelling and downwelling.

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Upwelling is a process whereby deep cold waters rise towards the surface to replace warm surface waters that had been pushed away by the wind. Another way upwelling can occur is illustrated in Diagram 1. The offshore movement of surface water (due to Coriolis effect) causes the deep water to rise to the surface and replace the water that was pushed away. Upwelling carries nutrient-rich waters towards the surface, thus increasing the biological productivity of surface waters. In areas around Antarctica, strong currents pump nitrogen and phosphate from the deep waters to fertilize phytoplankton and seaweed, who, provide energy for consumers higher in the food chain such as fishes, humans and marine animals such as Krill, who benefit mostly by upwelling nutrients. The major upwelling region is located along the Eastern Boundary Currents (National Oceanic and Atmospheric Administration (NOAA), n.d.a). We can gain alternative form of energy from ocean currents. Since cold water is dense, they carry a lot of energy, which can be captured by water turbines (Briney, 2018). Downwelling results from wind driven surface waters that build up along coastlines. Increase pressure of the piled-up water causes it to sink towards the bottom. Downwelling can also occur, when the seawater becomes denser and saltier. Although warm downwelling is uncommon, it does occur. Warm waters can sink to the bottom where they are cold water only if, the cold water has lower salinity. As a result, downwelling causes oxygen-rich waters to travel down through the water column and provide oxygen for benthic animals. A cease in thermohaline circulation can cause a cease in downwelling. A lack of downwelling can cause mass extinction of marine organisms. Dissolved oxygen in the bottom of the ocean will be quickly used up by decayed organic matter, resulting in anaerobic bacteria to take over the decomposition, causes an increase in hydrogen sulfide with can create toxic environments for the benthic animals (NOAA, n.d.a) Ocean currents play a significant role in the reproductive process of marine animals. It distributes larvae and reproductive cells of marine organisms. Catchpole (2005) stated, “Many marine organisms use the current as a conveyor belt, spending their larval and adult lives in vastly different parts of the ocean because of the rotating motion of the current” (para. 4). Many other major currents affect marine and terrestrial ecosystem. For example, Gulf Stream Current has numerous effects on Climate. This current, also called North Atlantic Drift, originates from the Gulf of Mexico to the tip of Florida further along the eastern coastlines of the

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United States into the Atlantic Ocean. The climate in Northwestern Europe is more mild than the climate across the Atlantic in Canada and the Northeastern of the United States. Gulf Stream Current is responsible for the temperature difference between those areas since it locks the ice in the Atlantic Ocean near Canada during winter (UCSB, n.d.). As stated previously, the global conveyor belt drives the thermohaline circulation, which is responsible for redistributing heat on the Earth’s surface. However, it is can be easily disrupted. Any disruptions can affect the climate and living conditions for plants and animals, both marine and on land. For example, Global warming. Global warming can disrupt the process of thermohaline circulation by melting ices in polar regions. This can result in an increase in freshwater input in polar regions. Fresh water is less dense than seawater so it remains on the surface and prevent the dense cold waters to sink to the bottom (which is necessary to drive the thermohaline circulation), therefore causing a cease in circulation. When this happens, places located in higher latitudes, for example, England, will become colder since there are no warm surface waters from the equator to be brought up to the polar region. The equatorial region will also be affected, it will become warmer because there is no dense cold water in the polar regions to be replaced (USCB, 2005). The Humboldt Current, also called the Peru current, is another example of a current that affects climate. It is a cold current that runs from the southern tip of Chile to northern Peru. During its presence, it keeps the coast of Chile and Peru cool and northern Chile arid. However, when it becomes disrupted, the Chile’s climate is altered (Briney, 2018). Gyres also influences the climate. As previously explained gyres are huge ocean currents that consist of four main currents that helps spread energy from the sun. The sun waters at the equator and the gyre transport water and heat to higher latitudes. An example is El Niño. El Niño is the periodic warming of water in the Pacific Ocean every few years. During El Niño years, the equatorial current intensifies the Pacific Ocean. When this occurs, more energy is available to induce a storm. El Niño also affect changes in weather (by affect wind shear and amount of rain). Wind shear is when air current at lower altitude blow in different directions from the winds higher in the atmosphere. This makes the formation of hurricanes more difficult. El Niño weakens this wind shear in the Pacific and causes wind shear in the Atlantic to strengthen. El Niño was responsible for 24 tropical storms and 15 hurricanes from the Pacific Ocean; namely, one of the strongest hurricane ever measured with winds 200 mph (325 km/h), hurricane Patricia;

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killed 12 persons while causing detrimental damages passing thorough Mexico to Texas (Howard, 2015). To conclude, ocean currents are driven by wind, density difference, ocean bottom topography and Coriolis effect; form specific patterns called gyres or thermohaline circulation, which distribute the energy globally from the sun. Any disruption in these can cause severe effects on climate, which can harm both marine and terrestrial ecosystems. References Briney, A. (2018, January 13th). How ocean currents work. Retrieved from https://www.thoughtco.com/ocean-currents-1435343 Catchpole, H. (2005, September 8th). Ocean Currents. Retrieved from http://www.abc.net.au/science/articles/2005/09/08/2043133.htm Edmunds, S. (2018, March 13th). Four Factors That Create Ocean Currents. Retrieved from https://sciencing.com/four-factors-create-ocean-currents-5997662.html Freepik. (n.d.). Water (photograph). Retrieved from https://www.freepik.com/free-vector/wavespattern_770524.htm#term=waves&page=1&position=16 Howard, B. (2015, November 30th). How El Niño affect weather. Retrieved from https://news.nationalgeographic.com/2015/11/151125-el-nino-hurricanes-droughtclimate-science/ May, A. (2017, August 20th). Oceanic Downwelling and our Low Surface Temperatures. Retrieved from https://wattsupwiththat.com/2017/08/20/oceanic-downwelling-and-ourlow-surface-temperatures/ Morrall, C. (2018a, January 30th). Atmospheric Ocean Circulation. Retrieved from https://mycourses.sgu.edu/access/content/group/c3bc240b-db1a-4f5d-8eca1f977f703b60/Lecture%20Material%20week%201-7/MBIO%20205%20session %205%20division%20of%20the%20oceans%20and%20atmospheric%20ocean %20circulation%20Jan%2030%202018%20for%20sakai.pdf

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Morrall, C. (2018b, February 15th). Thermohaline Circulation. Retrieved from https://mycourses.sgu.edu/access/content/group/c3bc240b-db1a-4f5d-8eca1f977f703b60/Lecture%20Material%20week%201-7/MBIO%20205%20session %209%20thermohaline%20circulation%20and%20waves%20part%20I%20Feb %2015%202018.pdf Morrall, C. (2018c, February 1st). Ocean Dynamics. Retrieved from https://mycourses.sgu.edu/access/content/group/c3bc240b-db1a-4f5d-8eca1f977f703b60/Lecture%20Material%20week%201-7/MBIO%20205%20session %206%20ocean%20surface%20circulation%20Feb%201%202018.pdf Morrall, C. (2018d, February 13th). Ocean Dynamics. Retrieved from https://mycourses.sgu.edu/access/content/group/c3bc240b-db1a-4f5d-8eca1f977f703b60/Lecture%20Material%20week%201-7/MBIO%20205%20session %208%20current%20flow%20rates%20ekman%20up%20and%20downwelling%20Feb %2013%202018.pdf National Oceanic and Atmospheric Administration (n.d.a). Currents and marine life. Retrieved from https://oceanexplorer.noaa.gov/edu/learning/8_ocean_currents/activities/currents.html National Oceanic and Atmospheric Administration. (2011, August). Ocean Currents. Retrieved from http://www.noaa.gov/resource-collections/ocean-currents National Oceanic and Atmospheric Administration (n.d.). Currents. Thermohaline circulation Retrieved from https://oceanservice.noaa.gov/education/tutorial_currents/05conveyor1.html National Oceanic and Atmospheric Administration (n.d.). Currents. Effects of climate change. Retrieved from https://oceanservice.noaa.gov/education/tutorial_currents/05conveyor3.html UCAR Center for Science Education. (n.d.). Ocean on the move: Thermohaline Circulation. Retrieved from https://scied.ucar.edu/ocean-move-thermohaline-circulation

OCEAN CURRENTS USCB. (2005 May 22nd). How do ocean currents contribute to the change in climate? Retrieved from http://scienceline.ucsb.edu/getkey.php?key=922

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