Marine_Science_100_Midterm_Review

Welcome to Marine Science 100 mid term review. We are going to review one through twelve as outlined in your introduction to Marine Science 100 Student Telecourse Handbook. All right. Getting started, we look at the world around us and we find that the reality is that we live on a water planet. Over 70 percent of the earth’s surface is covered with water. That leaves a very small chunk of the area that is land. It hopes if we go back to the beginning. The beginning for us is when the universe began and what we think was a big bang. We believe that for whatever reason all the matter in the universe was compressed in a single deminsionalist dot that for whatever reason exploded about thirteen to fourteen billion years ago. The cataclismic event is termed the Big Bang. About a million years after the big bang the universe cooled enough for atoms of hydrogen the most abundant type of atom in the universe to form. About one billion years after that collapsing masses hydrogen started forming the first stars. Our own star, which we call the sun, formed about 5.5 billion years as clouds of hydrogen condensed upon each other pulled together by gravitational attraction. As the hydrogen shrunk it heated to enormous temperatures triggering nuclear fission. During this thermal nuclear reaction the sun’s hydrogen atoms combined forming the larger helium atoms and releasing a steady stream of energy. The formation of the planets themselves began about five billion years ago. The heavier elements that make up the planets, moons and comets are produced in the nuclear fusion and explosive gas of other stars. The earth and the oceans upon it are the direct result of a super nova explosion. About five billion years ago the solar nebula was rotating in about 75 percent hydrogen and 23 percent helium and about two percent other materials. Solar nebula spun faster and faster, material concentrated near the center became the proto sun and much of the outer material eventually became planets. The smaller bodies that were over the star and do not shine by their own light but new planets formed in the disc of dust and debris surrounding the young sun through a process accretion, the clumping of small particles into large masses. Perhaps about 30 to 50 millions years. The proto sun became the star our sun. It was formed by the accretion of cold particles of those probably homogenous throughout. Then during the accretion phase the earth’s surface was heated by the impact of asteroids, comets and other falling debris. This heat combined with gravitational compression and heat from the decay of radioactive elements accumulating within the newly assembled planet caused earth to partially melt. Gravity pulled most of the iron and nickel inward to form the planets core. The sinking iron released huge amounts of gravitational energy, which through friction heated earth even more. At the same time a slush of lighter minerals rose towards the surface forming earth’s crust. This important process called density stratification lasted about 100 million years. Earth began to cool and this process formed its first surface, which we think occurred about 4.6 billion years ago. It did not remain undisturbed for long. A planetary body somewhat larger than Mars smashed into the young earth and broke apart. The metallic core fell into earth’s core and joined with it while the rocky mantel was ejected to form a ring of debris around earth. The debris began condensing soon after and became our moon. Earth’s first atmosphere was stripped away by the energetic young sun. However gases that had been trapped inside the forming planet came to the surface to form the second atmosphere. This is called out gassing. As the hot vapor rose they condensed into clouds in the cool upper atmosphere. Most of earth’s water was present in the solar nebula during the accretion phase. We believe now that earth may also have had its water contributed to by the accumulating mass of comets colliding with the earth. Earth’s surface was so hot that no water could collect there and it basically after millions of years the upper clouds cooled enough for some of the out-gassed water to form droplets. Hot rains fell towards the earth only to boil back into the clouds again. These heavy rains may have lasted about 20 million years. Large amounts of water vapor and other gases continued to escape through volcanic vents during this time and for millions of years there after. The ocean grew deeper. Evidence suggests that earth’s crust grew thicker as well. Perhaps in part from chemical reaction with oceanic compounds. Composition of the earth’s atmosphere was much different than today. Geochemists believe it may have been rich in carbon dioxide, nitrogen water vapor with traces of ammonia and methane. Beginning about 3.5 billion years ago this mixture began a gradual alteration to its present composition, which is mostly nitrogen and oxygen. Basically about 80 percent nitrogen and about 20 percent oxygen. About 1.5 billion years later the ancestors of today’s green plants produced by photosynthesis enough oxygen to oxidize minerals dissolved in the ocean and surface sedimentations. Oxygen began to accumulate in the atmosphere. This monumental event in earth’s history is called the Oxygen Revolution. During the Oxygen Revolution the amount of oxygen in the atmosphere went from about one percent to about 20 percent. That occurred between two billion and 400 million years ago. The growing abundance of free oxygen made aerobic respiration practical speeding the dissembly of food molecules early animals obtained by eating autotrouf or something derived from this. Oxygen blocked most of the sun’s dangerous ultraviolet radiation from reaching the earth’s surface permitting life to survive at the surface of the ocean and later on land. So animals therefore grew in complexity as they became more abundant instead of drifting apart after reproduction. Life began from this mixture of carbon, hydrogen, oxygen and nitrogen and massive amounts of salty water and energy in the form of lighting volcanic heat and ultraviolet radiation. The evolution of life arose from the simple chemicals present on primitive earth. We call this process biosynthesis, which was first suggested in the early 20th century. Stanley Miller in 1953 constructed an apparatus that simulated the conditions of the early ocean and atmosphere. Through this he put an electric current, which produced several amino acids, the building blocks of proteins and a variety of simple carbohydrates, the other organic compounds necessary for the construction of the complex molecules of life. A wide variety of hypothesis about the origin of life had been proposed since 1953. Some argued that life began in shallow tide pools. Some say it began in the deep ocean near hydrothermal vents. Others argued that it formed on beds of clay or under ice. All the hypothesizes have some merit. No one has yet created life in a laboratory but it is certain that the type of chemicals needed can be produced under conditions modeling earth four billion years ago. It is also true that organic materials can land on earth with meteorites posing the possibility that the chemicals that spawn life on earth arrived from elsewhere. If that is true it simply displaces the question of how life started to emerge to some other world. Earth is the planet of water and life. Its dominant feature is the ocean. The study of the ocean and its numerous disciplines is conducted by oceanographers and marine sciences. Physical oceanographers study the waves, heat, tides and other physical features of the ocean while chemical oceanographers study the chemistry of seawater. Biological oceanographers study the ocean’s life and geological oceanographers study its geology. Scientific data then suggests that the age of the sun is about five billion years old. Scientific data suggests that the age of the earth then is about 4.6 billion years old so not long after the sun formed. The earth’s earliest fossilized life form is three and a half billion years old. In the first few years after the big bang the universe was very hot, had no atoms and was opaque. Scientists currently believe that the earth’s primitive atmosphere was mostly composed of carbon dioxide, methane and ammonia. Today earth’s atmosphere is composed of approximately 20 percent oxygen, 80 percent nitrogen. Prior to 3.8 billion years ago the primitive earth had a continuous bombardment by asteroids, meteors and comets. Hydrothermal events are places in the deep ocean where life may have originated. Oceans began probably about 900 to 700 BC when the Greeks first ventured through the Straits of Gibraltar and out into the Atlantic from the Mediterranean. We have records of the Phinitians in 200 B.C. leaving the Mediterranean through the Straits of Gibraltar to the shores of Britain. By the Third Century B.C. many of these records and charts were archived in the library of Alexandria in Egypt, which is often called the first university. Indonesians cultures collectively called oceanians explored about 10,000 islands across ten million square miles of ocean. In the so-called Dark Ages in Europe, Scandinavian Vikings swept the European coast raiding and pillaging. They were skilled at navigation. The Chinese also voyaged during this time and perfected their navigation techniques and ship building skills. During the age of Discovery in the Renascence, marine science continued to progress and fortunately so did record keeping. Prince Henry the Navigator sponsored much of the exploration during the mid 1400’s but because he established a center for the study of marine science and navigation he is remembered for that. Master mariner Christopher Columbus discovered the new world while searching for trade routes to India and Japan. He discovery got more credit than was due because Columbus was also a great storyteller and returned with many tales and trinkets from the new lands. The ideas of scientific oceanography are generally acknowledged to have begun with the 1768 voyage of the British ship Endeavor captained by James Cook. Cook was sent by the British royal society to study the transect of Venus across the sun thus attempting to verify the gravitational theories of Isaac Newton and Edmond Haley as they applied to cometary’s movement. On completion of that task he was authorized to do some exploring before returning home. Cook explored and charted around the Great Barrier Reef in Australia and New Zealand and was probably one of the first to accurately determine and record the locations of his findings. It was easy to find one’s latitude at sea but to determine longitude, east; west positions required a very accurate timepiece that could withstand conditions at sea. In 1760 John Harrison perfected such a timepiece the chronometer, redefining the concept of accuracy in navigation. Cook made several voyages accompanied by various scientists, collected specimens and used some of the first crude devices for obtaining samples from the sea floor. Cook was a giant in the history of marine science but it would be nearly 100 years before the first expedition totally devoted to science would be launched. Voyages of note are Charles Darwin’s on board the Bego in the 1830’s. Charles Darwin is known for his theory of biological evolution. He made his historic four and one half year journey gathering natural history and oceanographic samples and data. The first famous and important expedition undertaken to this day is the British Challenger expedition. The four-year journey began in 1872 and the first sailing expedition totally dedicated to marine science. The Challenger Report, a fifty-volume set of text and hand colored illustration stands as a monument in the field of oceanography. Reviewing some of the information, scientific theories are supported by a great deal of evidence and widely accepted. Scientific theory has withstood the test of time, the evidence gathered has supported it and it is widely accepted among marine scientists. The scientific method comes about by observation of the potential problem or some intriguing aspect of a line of work that someone is interested in and wants to find out why what they are seeing the observation is occurring. Generally with the hypothesis that you then design experiments to test your hypothesis. Again a scientific theory then is supported by a good deal of evidence and widely accepted. A test of a hypothesis is called an experiment. Records show that around 900 B.C. the Greeks began traveling outside the Mediterranean and into the Atlantic. Early in the history of voyage and it became standard to use the equator for determining latitude. The term oceanography was coined by Wyville Thomson and John Murray on the first voyage of the Challenger. While not considered to be a marine scientist Matthew Murray was perhaps the first person for whom oceanography was a full time profession. The first sailing expedition devoted to exclusively marine science was that of the Challenger. Central ideas to the study of oceanography are that of plate tectonics. What is interesting about plate tectonics is that it only became an accepted theory in the last fifty years. Prior to that scientists for the most part could not quite figure out what the mechanism could be that could make continents move apart so any idea to the contrary that they could move apart was soundly rejected by all. In about 1912 Alfred Wegener proposed the idea of continental drift based on the jigsaw puzzle fit of certain continental edges and the existence of the same variety of plant and animal fossils on different continents. And geological features that matched, strikingly matched on both sides of the ocean. However as he was never able to quite come up with a mechanism that could accurately explain how these continents could have moved apart based on the understanding of the day, his ideas were not widely accepted. In 1835 Kiyoo Wadati suggested that volcanoes and earthquakes around Japan are associated with continental drift. In 1940 Hugo Benioff mapped the deep earthquakes in the Pacific region clearly displaying the Pacific Ring of Fire. This evidenced the border of a large and active Pacific plate. When World War II came it became increasingly important for the military to determine what the topography of the ocean floors were so they began mini advances in echo sounding and finding out just what the composition of the sea floor. By so doing this they propelled science into the investigation of sea floor spreading. Details of ethmotry the mid ocean ridge system; trenches, seamounts and continental shelves were examined and cataloged. Using these and other data Harry Heis and Charles Deitz purposed the idea of sea floor spreading. This was in the early 60’s. They suggested that the world wide system of undersea mountains called mid ocean ridges is where new ocean floor is created as plates move apart. As they diverge they move a large crust of plates along with the continents that sit a top them. Charting the magnetic features of the ocean crust revealed a distinct pattern of symmetry spreading out from the mid ocean ridges demonstrated most clearly in the Atlantic Ocean. Molten crusts that exudes at the mid ocean ridges contains crystals of magnetite and actually magnetic mineral. These crystals align in the earth’s magnetic field leaving a permanent record of their compass position when the lava hardens. The history of the earth’s magnetic characteristic is thus preserved in the sea floor. The magnetic strength direction polarity on either side of the mid oceans ridges are symmetrical. The earth’s magnetic field has shifted numerous times in the past, on average about once every 350,000 years the North and South Pole flip flop. South pole becomes the North Pole and vice a versa. When this happens, any molten magnetic rocks on the earth’s surface take on the direction of the current polarization of the earth’s poles. As time goes by, on either side of that mid ocean ridge if you look at sediments, not sediments but if you look at sub strait of the same age you will find that the magnetic orientation is always exactly the same. It is either North and South and as you get further away, the same distance away from the mid ocean ridges you will find that even though there is a reversal in magnetic field that it is captured on both sides of it suggesting that this molten magna is in fact pushing apart equally in both directions. Plate tectonic theory is thus. The spreading centers is where crust at the mid ocean ridges is where new crust is formed. What happens to the old crust' Obviously the planet is not getting larger so as this new crust forms, the spreading plates and there are seven large tectonic plates and several small ones. The spreading plates collide with other plates. Where these plates come together we call these active margins. Where these active margins come together various things happen. If a continent, the continent collision we have both plates up lift and we have mountain chains forming much as the Himalayas are an example of a mountain-to-mountain collision there. If an ocean plate collides with a continental plate the assault of the ocean basin is much denser than that of granite, which comprises most of the continental crust. So as the granite comes in contact with an ocean crust, what happens is that the ocean subducts underneath the continent and at the same time it pushes up the continent plate to form mountains fringing the continental border. This is evidenced very well with the Andes Mountains right off of South America where you’ve got that long ridge of mountains that are about 20 to 30 miles inland that rise up to 20,000 feet high and right off shore there is a deep ocean basin, which is more than 20,000 feet deep. So in a space of just a few miles there is a difference in height of over 40 miles. This is caused by the oceanic crust subducting underneath the continental plate. Still more examples are where two continental plates slip next to each other. We call it a slip strike fault is caused something like this. It is a transformed plate boundary is an area where two plates are essentially going in the same direction and rubbing up against each other. The San Andreas Fault in California is a prime example of a transformed plate. On one side you have the Pacific continent and on the other side you have the North American continental plate. These two are basically going in the same direction so they slide up against each other. Lots of earthquakes are formed along the continent, along the San Andreas Fault and occasionally one slips up on top of the other. So it causes a lot of pressure, it causes a lot. So this is an example of a transformed fault there or a parallel slip fault. In a short period of time huge amounts of evidence was gathered that verified the existence of plate tectonics. We know that new sea floor is produced and spreads out from the mid ocean ridges. We can see if we look at the shapes of the coastline that they look like they once fitted together. When we look at the shape of the continental shelves we see a much more accurate representation of what the continents looked like. When we match the continental shelves up with different continental shelves we find an even more striking example of how well these continents fit together at one point. Intuitively you would expect to find in a basin more sediment forming in the middle of the basin. Counter intuitively what is found when we go out there and look is that there is less sediment at the middle of ocean there where the mid ocean ridges form and much more sediment as you get closer and closer to the continents themselves. What is also interesting is if we drill rocks we can’t find any rocks older than 200 million years old. On the continents themselves we can find rocks that are three and a half billion years old. So this is an example of a very, very, young ocean. What also is intriguing is as you get closer to the mid ocean ridges the age of the sub strait becomes much, much younger. Conversely as you go away from the mid ocean ridges towards the continents the sub strait becomes older and older and older until you get to the 200 million years old right off shore of the continents. The magnetic properties found in volcanoes as we mentioned take on the magnetic polarity of the earth at the time. However even though we know that the North and South Pole switches they never move around on the earth but because of the spin of the earth, it is either at one axis or the other axis. However the volcanic, when we look at volcanoes millions of years ago and we go measure the polarity in different continents we will find that it is saying hey, north is to the east. That is impossible. We know that that whole continent at one point has shifted its orientation so it has moved. So it is another evidence in support of the theory of plate tectonics. Further evidence, Ernest Shackleton back in the 1900’s found coal in Antarctica. Coal comes from deciduous force that existed millions and millions of years ago but they had to exist in a temperate zone. The Antarctic is too cold for these forces ever to have existed. So it stands to reason that at one point Antarctic was not in its present location, that it was in a more favorable area that allowed the growth of large forests on its land. Evidence with our satellites now we can actually measure the rate of sea floor spreading. We can actually record the fact that we are moving apart at any where from two to six centimeters a year. That is about one to three inches per year. So the rate of drift is very, very small but it is enough that over 200 million years it separated the continents of Europe and Untied States, North America by 3,000 miles. Another line of evidence is we look at sea turtles which are very old and they have been making a trip to a small island that was probably originally just very, very close off shore of South America. Every year as it moved three or four inches further away, they would have to make a longer and longer trip. Over a period of 200 million years, that short little trip to the island just a few miles off shore has become a trip of about 1,500 miles to a tiny island out on the mid ocean ridge. Mid Atlantic ridge. This feat of navigation for these turtles to be able to swim all the way out there and find this thing is another evidence of plate tectonics. How these animals were forced to essentially develop a better system of navigation in order to be productive. Wegener’s theory of continental drift then was based primarily on maps of South America, Africa and the Atlantic Ocean. We know that the large crystal igneous rock that is characteristic of the continental crust is granite and that of the oceanic crust. The oldest rocks of the continents are over three billion years old. The oldest rocks from the sea floor are only about two hundred million years old. In the eighteenth century James Hutton formalized the idea of uniformataritism and suggested earth’s age should be measured in millions of years. The contrasting aisle of catrophism calculated earth’s age to be about 6,000 years old. The theory of sea floor spreading was proposed by Heis and Deitz. The bar-code magnetic stripping of the sea floor in considered evidence of sea floor spreading because it is symmetrical on either side of the mid ocean ridges. The place were sea floor spreading originates and where new crust is produced is in the central regions of the mid ocean ridges. Cores drove into the sea floor has shown that the youngest sea floors are in the central regions of the mid ocean ridges and the super continent of Pangaea began to break up about 200 million years ago. Subduction zones are associated with belts of deep focused earthquakes. It can be seen that plate boundaries coincide with belts of frequent earthquakes. Sea floor spreading the production of new crusts occurs at divergent boundaries. If you examine two core samples drilled from the sea floor ten miles east of and ten west miles west of the mid Atlantic ridge, you’d probably find that both are the same age and relatively young. The Himalayans are associated with conversion and collision. The Andes Mountains are associated with a subduction zone where the oceanic plate is sliding under a continental plate. Where an oceanic plate collides with a continental plate, the oceanic plate subducts. The most logical interpretation of the parent pole wandering is the North Pole has remained fixed and the continents have moved in relationship to the Poles. Where granite continental crust is manufactured is at convergent margins. Plate movement along a transform boundary causes most earthquakes in California. The Pacific plate in the region of Hawaii is presently moving to the Southwest. Active margin continental shelves tend to be formed by faulting. Formed by volcanoes and formed by tectonic deformation. So the three of those would be faulting, volcanoes and tectonic deformation. They tend to be short as opposed to passive margins, which would be for instance the east coast, which has a long continental shelf, which tend to be broad and flat. Seamounts are best described as volcanic protrusions below the sea surface. Island arcs are curving chains of islands and seamounts associated with the edges of trenches. Mid ocean ridge is found where ocean crust is forming. Scientist propose that our existing continental shelves were greatly influenced by lower sea level. The extent of ice coverage or the height of the Ice Age occurred about 18,000 years ago. Marine sediments are typically terrigenous in nature, which means they came from the land. Sediments that originate from the continents are called terrigenous. You might see paleoceanographers and paleontologists working together to explain the sudden extinction of the dinosaurs at the end of the Cretaceous period. The two most common components of terrigenous marine sediments are quartz and clay. The term salinity refers to the total concentration of absolved inorganic solids in seawater. The property seawater used by salinometers to measure salinity is its electrical conductivity. The two most abundant elements dissolved in seawater are sodium and chloride. Pure water has its maximum density when its temperature reaches four degrees centigrade. The salty water near Greenland that becomes cold and dense and sinks originated in the Gulf Stream. About 200 billion years ago the levels of iron in the oceans declined rapidly because oxygen produced by photosynthesis caused it to precipitate in solution. Now we are getting into some of the other properties of seawater. Sounds travels fastest in warm, fresh water. It travels approximately four times faster or five times faster than it does in air. Thermal stratification is generally most pronounced and stable in temperate oceans. The hadopelagic and the abyssopelagic and the bathypelagic are perpetually dark. The epipelagic is the zone of light. In the sound channel layer sound travels slowly and refract inward by using the SOFAR channel, the density channel. Whales are known to communicate across vast stretches of the ocean over thousands of miles and that is because even though the sounds are low intensity they travel very, very slowly and they refract inward. In the ocean itself, the deep zone contains about eighty percent of the earth’s volume of water. Methods of sending a sound signal and bounces off something and by knowing the temperature of the medium we can determine how far away that object is and we can actually begin to determine the shape. Animals such as dolphins and whales have been able to do this for millions of years and they can distinguish the difference between a penny and a nickel incredibly accurate with sound. The sonar require that they bounce an image, a sound signal off of the receiving object and we here the echo. So it is often referred to as echo location. Now another aspect of sonar is what we call passive sonar, which is when you listen and try to determine what sounds are coming from a particular emitter. The speed of sound in air as we said is about five times slower than the speed of sound in water. The Euphotic zone is that area that is lit, that sunlight reaches. As we mentioned, 80 percent of the earth’s ocean are perpetually dark. The deep dark water and you have about ten percent of what we call the main thermocline which is shallower and the other 10 percent is what we essentially term the euphotic zone. In tropical seas at noon in the summer the euphotic zone extends to a maximum depth of about 600 meters, that is about 2,000 feet. Researchers are using measurements of speed of sound through the ocean to study ocean temperatures in the sofar layer, internal waves and turbulence and global warming. The afternoon effect refers to the exaggeration of the shadow zone and sound refraction as the ocean heats. The ocean appears blue to your eyes primarily because of the scattering of blue light. Upwelling systems are a means of distributing nutrients in the world’s ocean. Upwelling system exists along generally temperate areas where currents can encounter landmasses and cause upwelling of nutrients in the bottom water along the shore areas. Areas that are generally composed of upwelling ecosystems are coastal Peru, coastal Southern California, the central Atlantic between Europe and North America. There is very little upwelling that goes on in for instance the Equatorial open Pacific. One of the reasons why the poor oceans are so productive are that sunshine is available six months out of the year due to the tilt of the earth 23 and a half degrees. Polar oceans have six months of light and six months of darkness. During this period of light, primary productivity is greater than probably anywhere else on earth. One of the animals that probably far exceed the biomass of any other species on earth is the krill. The Antarctic krill is able to survive that six months of wintering by utilizing stored lipids and by having low metabolic rates. We believe that most of the off shore tropical oceans have low productivity essentially because nutrient levels are low. Low productivity means that is lower than temperate waters but we are just now beginning to find out that the tropical waters may not have as low of productivity and nutrient contents as we originally thought. So as more information comes in we are beginning to change some of the ideas there. Increasingly man’s work on the planet earth is causing wide range and effects, which affects the earth’s atmosphere and the earth’s ocean. One of the problems is ozone. The ozone layer actually protects us from the ultra violet radiation reaching the earth’s surface. Ozone itself is composed of oxygen. Scientist fear that holes in the ozone layer could potentially cause cosmic radiation, ultra violet radiation to reach the earth, which could cause serious health problems on the earth for people including cataracts. Scientists fear also that about 70 percent of earth’s coral reefs may disappear in the next fifty years. When we look at deep-water ocean masses we find that the most distinctive of all water masses is the deep water. The most important primary producers in the ocean vital plankton and bacteria or vital plankton mostly but some bacteria and we are beginning to realize that bacteria may play a much larger role in it than we thought earlier. Corals, they are members of the phylum cnidaria . Their skeletons can be used to study ancient environmental conditions and their skeletons grow in a variety of shapes including branch, dome and plate like. Getting into seasons as I mentioned earlier are caused by the tilt of earth’s axis relative to its orbital plane. Because of that 23 and a half-degree tilt of the earth as the earth orbits the sun it exposes a different portion of the earth to the full direct rays of the sun. During the wintertime the rays of the sun glance off the earth and are reflected away and during the summertime they are absorbed by the earth which increases the temperature and we have what we call summer. Because of the tilt of the earth if you look at the equator, the equator almost always is in direct sunlight so temperatures stay relatively warm at the equator. The Poles on the other hand, during one season they get essentially six months of darkness and then followed by six months of light. The Coriolis effect which is a deflection of a current or wind as it leaves the equator and hands towards the pole to the right is caused by the earth’s rotation and is most apparent at the mid latitudes. The earth rotates at approximately 1,000 miles an hour at the equator and by the time you get up to Buffalo, New York the earth is only rotating at about 700 miles an hour. How is that possible' The earth is 24,000 miles around at the equator which is the fattest part of the earth and somewhat less at say Buffalo, New York where the distance around the earth at that point would be about probably less than 20,000 miles which brings the speed; it still is completing a circuit in 24 hours so its average speed drops down to about 700 miles per hour. So an object leaving the equator at 1,000 miles per hour would apparently deflect to the right as it leaves the equator. Now if you turn around and head towards the South Pole that deflection would be apparent also. The most favorable and dependable winds for early mariners were the trade winds. We find that air circulation within each atmospheric cell is powered by uneven solar heating. An air mass is characterized by having uniform internal temperatures and humidity. The main difference between an extra tropical and tropical cyclones are that tropical cyclones form within one air mass. An important factor in determining how much light penetrates the ocean is the angle at which light strikes the sea surface turbulence and sea surface transparency. The circulation patterns in the North Atlantic and North Pacific basins are called sub tropical gyres. A western boundary current is located off the east coast of continents. Conversely an eastern boundary current is located off of the western continent coast. To illustrate a point, Mark Twain was once famously quoted, as saying the coldest winter he ever spent was a summer in San Francisco. The whole Pacific coast here is influenced by an eastern boundary current which keeps our water much, much, colder than you would see in a comparable latitude around the earth. The first recorded description of the Gulf Stream came from Benjamin Franklin. We talked about El Nino’s. El Nino events warm the water and displace the regular ocean currents. An El Nino event can cause serious problems for kelp beds offshore of California because the cold, nutrient waters are displaced off shore. The warm waters coming in are very, very low in nutrients. It also causes a problem for Peru because the upwelling stops, the anchovies move off shore because primary productivity is curtailed because of the lack of nutrients in the near shore waters. Because of that the fish move off shore after the anchovies and the Peruvian fisherman essentially starve to death. That concludes our review. Be sure you understand the theory of plate tectonics and the mechanisms by where by we verify the existence of plate tectonics. So what you need to know is lots of evidence for the existence of plate tectonics. You should know the mechanism whereby plate tectonics takes place. That pretty well concludes the review at this point and this concludes Marine Science 100 review for the midterm.