Volcanoes are generally not preserved in the geologic rock record because they are usually eroded away. However, the various materials erupted from volcanoes are often found preserved in the rock record. From what you have learned about the different prin

ES 1010, Earth Science 1 Cou rse Learning Outcomes for Unit V Upon completion of this unit, students should be able to: 7. Compare the geography, composition, circulation, and temporal cycles of the oceans. Reading Assignment Chapter 9: Oceans: The Last Frontier Chapter 10: The Restless Ocean Watch the following video: Williams, C. [IDT -CSU]. (2015, August 7). Coastal processes [Video file]. Retrieved from https://youtu.be/ZO07SgCFKW s Click here to access a transcript of the video. NASA Goddard. (2008, October 24). In the zone . Retrieved from https://youtu.be/lB1FADETAyg Unit Lesson It is easy to see why Earth is referred to as the “Blue Planet” — 71% of the Earth’s surface is covered by oceans and seas. However, less than 5% of our oceans have been explored (National Oceanic and Atmospheric Administration [NOAA] 2014). So essentially, most of our Earth is still unexplored and largely unknow n. W e do know that oceans contain the highest mountains, the deepest trenches, and the longest mountain ranges. On average, the ocean depth is about four times the average elevation of continents. In fact, Lutgens & Tarbuck (2014) state that if the Earth’s continents were perfectly flat, they would be completely submerged under more than 2,000 meters of seawater! Oceanography is the branch of science that studies the world’s oceans. It includes geology, chemistry, physics, and biology (Lutgens & Tarbuck, 2014). Oceanographers started mapping the oceans floors as early as 1872 by dropping weighted lines down to the ocean bottom at random points. The use of sound navigation and ranging (sonar) began during W orld War I to detect enemy submarines, and was late r improved during World War II. Sonar uses the echo of sound waves to plot the profile of the ocean floor. Satellite radar technology has also contributed to mapping the ocean floor. Today, we have a fairly good picture of the ocean floor topography. As w e study the ocean floor, we notice three major features: continental margins, basin floors , and mid - oceanic ridge . The continental margins can be classified as active or passive. Active margins are where the UNIT V STUDY GUIDE Oceans An iceberg captured on camera during a 30 -day mission in 2012 to map areas of the Arctic aboard the NOAA Ship Fairweather (NOAA, 2013). ES 1010, Earth Science UNIT x STUDY GUIDE Title ocean lithosphere is subducted beneath the conti nental crust (recall what you learned in Units III and IV). These are mainly found around the Pacific Ocean. Passive margins are those that are not experiencing plate tectonic activity and have more stable topography. Basin floors make up about 30% of the Earth’s surface (Lutgens & Tarbuck, 2014). These areas are between the margins and the mid -ocean ridges and include deep trenches, underwater volcanoes, and large flat areas known as abyssal plains. The mid -ocean ridges are where new oceanic lithosphere is being continuously formed. The new lithosphere is hot and is not as dense as the rest of the ocean floor. This makes it elevated above the basin floor. It takes approximately 80 million years of cooling for it to become part of the basin floor (Lutgens & Tarbuck, 2014)! The mid -ocean ridge is the largest topographic feature on Earth — both in height and in length (over 70,000 km long). The major difference between oceans and freshwater is salinity. Seawater salinity is approximately 3.5% salts — mainly sodium chloride (NaCl), but also other dissolved salts (see Fig 9.3, p. 298). Where do these salts come from? The two main sources of salts are from chemical weathering of rock, and volcanic out - gassing. With constant weathering we would expect oceans to get saltier with time. However, seawater salinity remains relatively constant. Why? Ocean organisms use many of these salts and chemicals while others drop out as sediment. Ocean salinity does, however, vary in different regions of the world. As ocean water ev aporates it leaves a higher concentration of salts. Also, sea ice forms from pure water, leaving the salts in solution; therefore, in polar regions salinity will increase in the winter months and decrease in summer months. How would you expect salinity to vary between hot, dry regions and cool, rainy regions? Other variations in seawater, such as temperature and density, vary with depth. In tropical regions (low latitudes) water temperature is warmer near the surface and decreases with depth. This is large ly due to thermal radiation (sunlight) and the mixing of water by waves on the surface. Where sunlight can no longer penetrate, temperatures decrease rapidly. This change in water temperature is called the thermocline and can limit where sea life lives. In polar regions (high latitudes) the water stays fairly cool at the surface, so there generally will not be a thermocline. Where water is warmest, density will be lowest (warmer water expands) so you will see a similar change in water density with depth in tropical areas. Water density is also affected by salinity. In inland seas, where salinity is extremely high, density will be high, allowing you to easily float on the surface. However in the open ocean, temperature has a greater influence on density than salinity does. Water is most dense in cold, deep waters. We have learned much about the history of the Earth through the study of the oceans. In Unit III, recall that we learned it was not until scientists started to study the ocean floor that the theory of plate tectonics was developed. The oceans have also given us insight into the rates of erosion that takes place on continents.

Also, recall In Unit I, we learned that a main component of the rock cycle is erosion and transport of sediments. A major depo sitory of those sediments is the ocean. These sediments, eroded from land, are known as terrigenous sediments . The oceans also act as a repository for remains of sea life over the millennia. As microscopic algae and sea life die, their skeletons accumula te on the sea floor. Since the sea floor is relatively free from disturbance, these biogenous sediments will create layers of sediment. Scientists can extract cores of seafloor sediment that go back for millions of years and determine which species once li ved in the surface waters of the ocean. These organisms have different climate requirements, so these cores can give clues as to the past climates of different regions of the ocean. A third type of sediment are those that precipitate from the ocean water i tself or hydrogenous sediments . These could be salts or chemicals produced at hydrothermal vents. Since the Earth is mainly water, the oceans play a major role in the Earth’s climates and moderating temperatures. The oceans are in constant motion, both al ong the surface and through deep -ocean currents. These currents transfer both heat and nutrients around the world. The movement of water is not random, but forms predictable patterns, or currents . These currents are created both by winds and the rotation o f the Earth (the Coriolis E ffect). Major ocean currents form in a roughly circular motion called gyres . In the Northern Hemisphere, gyres move in a clockwise direction. In the Southern Hemisphere gyres move counterclockwise.

This holds true for all water — try flushing the toilet in both hemispheres and notice that the water follows this same pattern. You can see these major gyres in Fig 10.2 (p. 323 ) of your textbook. Notice how warm water from the equatorial region flow northward, bringing warmer tempera tures north. Colder water flows southward. This flow of water spreads solar energy to colder regions and moderates the warmer temperatures near the equator. Oceans also experience up -welling, or the vertical movement of water, when cold water surfaces fro m the deep ocean. Near the coast, this occurs when winds drive warm water away from the coast and deeper ES 1010, Earth Science UNIT x STUDY GUIDE Title waters come to the surface to take their place. These waters are nutrient -rich and create areas of high productivity (Fig 10.5, p. 326 ). This also e xplains why the waters of the Pacific coast are so much cooler than waters along the Atlantic coast. A similar up -welling occurs during the winter months in polar regions, but for a very different reason. As explained above, when sea -ice forms in the winte r months the remaining salts make the water much saltier. This added salinity creates very dense water. Because the water is more dense that the water below, it sinks and is replaced by surfacing water. Oceans make our planet habitable, not only by modera ting climates, but also through the production of oxygen. Much of the Earth’s oxygen is produced by microscopic organisms called phytoplankton . Like plants, these organisms produce oxygen through photosynthesis. They also provide the food base for many ocean species. These phytoplankton depend on ocean nutrients for growth and reproduction. This NASA video (NASA Goddard, 2008) shows how, in recent decades, humans have impacted populations of phytoplankton. Through increased runoff from agriculture and human waste, rivers contribute a huge nutrient load to the oceans. During summer months , these added nutrients will create what is referred to as algal blooms . As these blooms die off, the wastes collect along the ocean floor and decompose, using all available oxygen and releasing carbon dioxide. This creates what is known as a dead zone in many large bay areas where organisms cannot survive the low oxygen levels. This is just one way in which human activities have impacted our oceans. Can you think of other ways? Most of what we understand about the oceans comes from our own observations n ear the coastline. Coastlines are the interface of the oceans and land, which makes them very diverse areas. It is at the coastline where waves created by wind energy that can travel for hundreds of miles finally release their energy as they crash into lan d. The energy from these waves can carve away cliffs or other features. Coastlines are also where rivers, carrying the erosional sediments collected from huge areas, finally deposit their load. This deposition of sediments creates beaches, which are consta ntly being modified by wave energy. Sediments are carried away where wave energy is high and redeposited where energy is low. The overall process of shoreline erosion and deposition will lead to a straighter shoreline over time. We can see these changes as we visit the same areas year and year. We can also see changes in shoreline from hour to hour as a result of tides. Tides, the changes in elevation of the ocean, are caused by the gravitational pull on water by both the moon and the sun as the Earth rota tes. This gravitation pull causes tidal bulges in the water, which create a high tide. The absence of these bulges results in low tide. The gravitational pull by the moon is stronger than that of the sun because we are closer to the moon. Most days, the pu ll of the sun will be perpendicular to that of the moon. However, during times when the moon lines up with the sun (full moon or new moon), these tides will be extra high (Lutgens & Tarbuck, 2014). Coastlines have always attracted settlement. Oceans offer both food and a mode of transportation for the trading of goods. In fact, about half of the world’s population lives within 100 kilometers of a coast (Lutgens & Tarbuck, 2014). However, the transient nature of the coast makes permanent developments diffic ult. As we have seen, it only takes one large storm to completely wipe out roads, buildings, and ports. In the long run, the constant forces of wave erosion and deposition will always dominate the shoreline. References National Oceanic and Atmospheric Administration. (2013). An iceberg captured on camera [Photograph]. Retrieved from http://response.restoration.noaa.gov/about/media/international -council -agrees - cooperate -marine -oil -pollution -issues -arctic.html National Oc eanic and Atmospheric Administration. (2014). How much of the ocean have we explored? Retrieved from http://oceanservice.noaa.gov/facts/ exploration.html Lutgens, F. K., & Tarbuck, E. J. (2014). Foundations of Earth Science (7th ed.). Upper Saddle River, NJ: Pearson. NASA Goddard. (2008, October 24). In the zone . Retrieved from https://youtu.be/lB1FADETAyg ES 1010, Earth Science UNIT x STUDY GUIDE Title Suggested Reading The links below will direct you to both a PowerPoint and PDF view of the Chapter 9 and 10 Presentations.

This will summarize and reinforce the information from these chapters in your textbook. Click here to access the Chapter 9 PowerPoint Presenta tion. (Click here to access a PDF version of the presentation.) Click here to access the Chapter 10 PowerPoint Presentation. (Click here to access a PDF version of the presentation.) These web resources will further your understanding of the oceans and help you learn about exciting discoveries from ocean exploration — underwater rivers and waterfalls, new species, erupting volcanoes, etc. Ted -ed. (2012). Deep ocean mysteries and wonders —David Gallo [Video file]. Retrieved from https://www.youtube.com/watch?v=Uqly8ERIkHM. Learn about the most recent seafloor expedition to the deepest part of the ocean, the Mariana Trench. National Geographic: Deep Sea Challenge http://deepseachallenge.com/ See the ocean currents in perpetual motion: Perpetual ocean http://svs.gsfc.nasa.gov/cgi -bin/details.cgi?aid=3827 See time -lapse of coastal changes off the coast of C ape Cod http://earthobservatory.nasa.gov/Features/W orldOfChange/cape_cod.php