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Midterm Exam II October 28, 2:10 – 3:25 pm, HW714 Guide to study: answer the questions from the Concept Check (CC) boxes in textbook: ¾ Chapters 4 (4.13 – 4.18), 5, 6 and part of 7 ¾ 60 multiple choice questions ¾ this exam constitutes 22% (only) of your total (overall) grade Remember to bring pencils!!! (No. 2) and to follow the instructions about writing your names on both exam and answer sheets, as well as to ‘bubble’ your names (no IDs!) on the appropriate place of the answer sheet (on the back). Chapter 4: 13, 14,17, 19 and 20. Chapter 5: 1, 2, 3, 4, 7 through 12, 13, 16 through 21. Chapter 6: 1, 2, 3, 4, 5 through 11, 16, 17, 18, 19, 27, 28, and 29. Chapter 7: 1, 2, 3, 4, 6, 6, 8, 9, 10. 1 Chapter 4 – Ocean Basins 2 Basins Æ Features of the Sea floor sections of the abyssal plain separated by continental margins, ridges, and rises. Oceanic Ridges Hydrothermal Vents Abyssal Plains and Abyssal Hills Seamounts and Guyots Trenches and Island Arcs Seafloor: Seafloor: 4000 – 6000 m water depth, 30% of the Earth’ Earth’s surface Abyssal Plain: vast, flat plain extending from the base of the continental slope. Ocean Basins: sections of the abyssal plain separated by continental margins, ridges, and rises. 3 4 1 Sea floor features FlatFlat-topped seamounts eroded by wave action are called guyots. guyots. Seamounts are volcanic projections from the ocean floor that do not rise above sea level. FlatFlat-topped seamounts eroded by wave action are called guyots Abyssal hills are small, extinct volcanoes or rock intrusions near the oceanic ridges. 5 Abyssal hills are flat areas of sedimentsediment-covered ocean floor found between the continental margins and oceanic ridges. Abyssal hills are small, extinct volcanoes or rock intrusions near the oceanic ridges. ridges. 6 MidMid-Ocean Ridges and Rises Hydrothermal vents are sites where superheated water containing dissolved minerals and gases escapes through fissures, or vents. Cool water (blue arrows) is heated as it descends toward the hot magma magma chamber, leaching sulfur, iron, copper, zinc, and other materials materials from the surrounding rocks. The heated water (red arrows) returning to to the surface carries these elements upward, discharging them at hydrothermal springs on the seafloor. An oceanic ridge is a mountainous chain of young, basaltic rock at an active spreading center of an ocean. 7 8 2 Major ocean trenches Island Arcs There are two ways in which a group of islands can form. 1) As a lithospheric slab is being subducted, the slab melts when the edges reach a depth which is sufficiently hot. Hot, remelted material from the subducting slab rises and leaks into the crust, forming a series of volcanoes. These volcanoes can make a chain of islands called an "island arc". Examples of island arcs are the Japanese islands, the Kuril Islands, and the Aleutian Islands of Alaska, shown here. Trenches are arcarc-shaped depressions in the ocean floor caused by the subduction of a converging ocean plate. Most trenches are around the edges of the active Pacific. Trenches Trenches are the deepest places in Earth’ Earth’s crust, 3 to 6 kilometers (1.9 to 3.7 miles) deeper than the adjacent basin floor. The ocean’ ocean’s greatest depth is the Mariana Trench where the depth reaches 11,022 meters (36,163 miles) below sea level. 9 level. 2) The second way in which islands are formed is via plumes or hot spots in the lithosphere. The Hawaiian Islands are an example of this type of island formation. In this case, there is no associated subducting slab. Island Arcs are formed on the opposing edge of a subducted slab. For each case, there is an associated subducting slab and a trench. 10 Chapter 4 - Summary • Seafloor features result from a combination of tectonic activity and the processes of erosion and deposition. • The submerged outer edge of a continent is called the continental margin. The deepdeep-sea floor beyond the continental margin is called the ocean basin • Features of the deepdeep-ocean basins include oceanic ridges, hydrothermal vents, abyssal plains and hills, seamounts, guyots, guyots, trenches, and island arcs. Formation of a volcanic island chain as an oceanic plate moves over a stationary mantle plume and hot spot. In this example, showing the 11 formation of the Hawai’ian Islands, Loihi is such a newly forming island. 12 3 Study of Sediments is important to oceanography because: Chapter 5 - Sediments Distribution of sediments on the sea floor Seabed Resources 1. Sediments and volcanism are the most important agents of physical change on the deep-ocean floor Sediments are particles of organic or inorganic matter 2. Study o sediments is important to ocean’s chemistry, morphology and history as well as to Earth’s climate (paleoclimate) that accumulate in a loose, unconsolidated form. Record of geologic/oceanographic history The position and nature of sediments provide important clues to Earth's recent history, and valuable resources can sometimes be recovered from them. Types (Classification) Location or distribution of sediments Rates of Deposits/Accumulation 13 14 Sediment Classification The Sediment Cycle. Over geological time, mountains rise as lithospheric (crustal) plates collide, fuse, and subduct. Water and wind erode the mountains and transport resulting sediment to the sea. The sediments are deposited on the seafloor, where they travel with the plate and are either uplifted or subducted. Thus, the material is eventually made into mountains again. 15 * according to particle size Large (L) Medium (M) Small (S) How far sediments go horizontally and how long it takes to get to bottom of sea depends on size. Shape is also important to how sediments go around and settle in the bottom. 16 4 Sediment Classification * according to location – where sediment is found Neritic: near continental margins & islands – contains mainly terrigenous sediments Pelagic: deep sea floor – can contain a larger amount of biogenous sediments. * according to source and chemistry Type Terrigenous (Lithogenous) Æ Biogenous Æ Hydrogenous Æ Cosmogenous Æ Source pre-existing rock (land derived material) living organisms precipitation from sea water space Review information in these two tables 17 18 Compare: Rates of Sedimentation Continental Margin: rapid, neritic sediments Major Rivers: Bays: Ganges, Yangtse, Yangtse, Yellow, Brahmaputra 8 m/yr ¼ of all land derived sediment • 1. Rivers 800,000 cm/1000 years 2. Bays 500 cm/1000 years 3. Shelf 40 cm/1000 years 500 cm/ 1000 years (0.5 cm/yr) Shelf/Slope: Neritic Sediments 10 – 40 cm/ 1000 years Ocean Basins: slow, pelagic sediments 0.5 – 1.0 cm/ 1000 years Average Accumulation 500 – 600 m (during geological history, in about 100 my) Thickness depends on age Oldest sea floor is 200 million years 19 • Pelagic Sediments 1 cm/1000 years! 20 5 Lithogenous Biogenous From rocks, wood, waste sludge, volcanic stuff Oozes – sediment containing at least 30% biogenous material. Dominant on deep-ocean floor, 2 types of oozes: Results from erosion by air & water Transported by winds, water, ice and gravity. Also by glaciers and icebergs Neritic or pelagic – dominates the neritic sediments because it is the largest source for these Pelagic lithogenous sediments Æ abyssal clay (about 75% of clay), very slow accumulation, rich in Fe Æ red clay * Calcareous (CaCo3) oozes formed by organisms which contain calcium carbonate in their shells or skeletons – dominant pelagic sediment (cocolithophorids, pteropods, foraminifera) * Siliceous (SiO2) oozes formed by organisms that contain silica in their shells. Diatoms are one type of organism whose remains contribute to siliceous oozes. The ocean is under-saturated with respect to Si, so it can dissolve everywhere. (large contribution from photosynthetic organisms) 21 22 Hydrogenous Calcareous Oozes Originate from chemical reactions with water that occur in the existing sediment. Hydrogenous sediments are often found in the form of nodules containing manganese and iron oxides. Hydrogenous sediments can be: CCD (~4500 meters) depth where rate of dissolution of calcium carbonate is equals to its rate of accumulation Carbonates Æ direct deposition Phosphorites Æ abundant in continental shelf Salts Æ by evaporation Evaporites - salts that precipitate as evaporation occurs. Evaporites include many salts with economic importance. Evaporites currently form in the Gulf of California, the Red Sea, and the Persian Gulf Manganese nodules Æ Mn, Fe, Cu, Ni, Co. These are found in abyssal seafloor and continental margins, around ocean ridges and seamounts (but at higher concentrations than those found on land). The Co (cobalt) content is of strategic importance to US (used in aircraft’s manufacture). The line shows the calcium carbonate (CaCO3) compensation depth (CCD). At this depth, usually about 4,500 meters (14,800 feet – about the height of some of the peaks in the Colorado Rocky Mountains, known as ‘the fourteeners’ ), the rate at which calcareous sediments accumulate equals the rate at which those sediments dissolve. 23 24 6 Distribution of sediments is determined by climate (temperature), environmental factors (nutrients, possible chemical reactions, activity of physical environment), supply, size and rate of accumulation. Map of distribution of sediment Recall (from Chapter 4) that turbidity currents can deposit Turbidites – Where would you expect to find turbidites? • Terrigenous sediments are deposited along the coastal boundaries • 75% of marine sediments are from land – coarser sediments closer to coasts and finer sediments at farther distances offshore • Higher latitudes – coarser sediments; lower latitudes – finer sediments • At higher latitudes rafting by glaciers and ice contribute significant amounts of sediments from land (coarse) • Red clay (fine, pelagic lithogenous) found where there is not much of anything else – deep ocean basins • Calcareous are not found in deep-sea areas below 4500 m or where ocean primary productivity is low. Fund in warm, tropical latitudes, shallow areas (Caribbean), elevated ridges and seamounts The general pattern of sediments on the ocean floor. Note the dominance of diatom oozes at high latitudes. What differences in the type and distribution of sediments do you note between the Atlantic Ocean and the Pacific Ocean? • Siliceous (photosynthesis) found below areas of very high biological productivity - abound in areas of N. Pacific and Antarctic Ocean: cold but nutrients and sun light good for photosynthesis. 25 26 Chapter 5 – Sediments - Summary Resources Sediment is particles of organic or inorganic matter that accumulate in a loose, unconsolidated form. Sediment may be classified by grain size of by the origin of the majority of the particles. Sand and Gravel Æ construction Phosphorite Æ fertilizers Sulfur Æ sulfuric acid for industry Coal Æ energy Oil and Gas Æ energy, transportation (20(20-25% of US production comes from offshore areas) Maganese Nodules Æ Mn, Mn, Fe, Co, Cu, Ni Gas Hydrates Æ energy in the future? Marine sediments are broadly classified by origin into four categories: (a)Terrigenous sediments are materials that originate from rocks on land and arise on the continents or islands near them; they are the most abundant. (b) Biogenous sediments are of biological origin. (c) Hydrogenous sediments are formed directly from seawater. (d) Of less importance are cosmogenous sediments, which come from space. Though there are exceptions, the sediments of continental margins tend to be mostly terrigenous, whereas the generally finer sediments of the deep-ocean floor contain a larger proportion of biogenous material. Deep sea oozes (calcareous and siliceous) form of biogenous sediment: remains of some of the ocean's most abundant and important organisms. 27 Sediment deposited on a quiet seabed can provide a sequential record of events in the water column above. In a sense sediments act as the recent memory of the ocean. The memory does not extend past about 200 million years because seabeds are relatively young and recycled into Earth at 28 subduction zones. 7 A molecule is a group of atoms held together by chemical bonds. Water is a polar molecule, having a positive and a negative side. Chapter 6 Water and Ocean Structure H2O Some basic concepts: • Covalent bonds: shared pairs of electrons • Hydrogen bonds: bonds between water molecules due to polar structure Compounds – substances that contain two or more different elements in fixed proportions Element – a substance composed of identical particles that cannot be chemically broken down into simpler substances Atoms – the particles that make up elements 29 30 Temperature, Heat, Heat Capacity, Calories Hydrogen Bonds Temperature Measure of av. kinetic energy (motion) of molecules (KE=1/2mv2) unit is degrees C, F or K (Kelvin) Hydrogen bonds form when the positive end of one water molecule bonds to the negative end of another water molecule. Heat Measure of the total kinetic energy of the molecules in a substance Unit is the calorie Two important properties of water molecules: * Heat Capacity = is a measure of the heat required to raise the temperature of 1g of a substance by 1°C. Cohesion – the ability of water molecules to stick to each other, creating surface tension. * Calorie = amount of heat to raise temperature of 1 gram of pure water by 1°C (from 14.5 °C to 15.5 °C) Adhesion – the tendency of water molecules to stick to other substances * Latent Heat 31 Water has a very high heat capacity, which means it resists changing temperature when heat is added or removed Æ 32 large thermal inertia 8 States of matter The relationship of density and temperature for pure water. Note that points C and D both represent 0°C (32°F) but different densities and thus different states of water. Ice floats because the density of ice is lower than the density of liquid water. The three common states of matter – solid, liquid, and gas. On Earth, water can occur in all three states: gas, liquid, and solid. • A gas is a substance that can expand to fill any empty container. • A liquid is a substance that flows freely in response to unbalanced forces but has a free upper surface in container it does not fill. Liquids compress only slightly under pressure. • Gases and liquids are classed as fluids because both substances flow easily. • A solid is a substance that resists changes of shape or volume. A solid can typically withstand stresses without yielding permanently. A solid usually breaks suddenly. Temperature affects water’s density 33 Water Becomes Less Dense When It Freezes The space taken by 24 water molecules in the solid lattice could be occupied by 27 water molecules in liquid state, so water expands about 9% as the crystal forms. Because molecules of liquid water are packed less efficiently, ice is less dense than liquid water and floats. 35 34 Changes of State-due to addition or loss of heat (breaks H bonds) The amount of energy required to break the bonds is termed the latent heat of vaporization. Water has the highest latent heat of vaporization of any 36 known substance. 9 Things to remember: * melting/evaporation requires addition of heat: 80 and 540 calories, respectively. For 1 gram of H2O * condensation/freezing release heat to the environment: 540 and 80 calories, respectively. Review information on Table 6.2 1. Can have liquid water at 0°C and below (supercooled water) 2. Can change directly solid to gas - sublimation 3. Can boil water at temperature below 100°C (if pressure decreases as when at the top of a high mountain) 4. Evaporation removes heat from Earth’s surface (it is a cooling mechanism) 5. Condensation in atmosphere releases heat that will drive Earth’s weather cycle 37 38 Density density = mass per unit volume measured in grams per cubic centimeters density of pure water = 1 g/cm3 (determined at ~ 4° 4°C) density increases as temperature drops to 4°C and then decreases as temperature goes to 0° 0°C ice is less dense than water Adding salt to pure water Æ Seawater 96.5% of pure water and 3.5% dissolved material Æ Seawater salt increases water’ water’s density density of sea water > density of pure water ~ 1.03 g/cm3 at 4° 4°C 39 40 10 I. add salt to water and observe 1. decrease freezing point (increase boiling point) 2. not much change in heat capacity & latent heats 3. increase surface tension (cohesion) 4. increase (of course) in density II. increase temperature and observe 1. decrease in seawater density (very sensitive to T) 2. decrease in surface tension III. but changes in pressure are mostly ignored by physical properties of water - seawater is nearly incompressible 41 The Ocean Is Stratified by Density 42 Table 6-3, p. 166 The Ocean Is Stratified into Three Density Zones by Temperature and Salinity two samples of water can have the same density at different combinations of temperature and salinity! a.The surface zone or surface layer or mixed layer b.The pycnocline, or thermocline or halocline c.The deep ocean (~ 80% of the ocean is below the surface zone 43 Fig. 6-17, p. 169 44 11 Sound and light in Seawater • Sound and light both travel in waves • Refraction is the bending of waves, which occurs when waves travel from one medium to another • Refraction Can Bend the Paths of Light and Sound through Water • Light may be absorbed, scattered, reflected, refracted and attenuated (decrease in intensity over distance) • Sunlight does not travel well in the ocean. Scattering and absorption weaken light 45 Sound Travels Much Farther Than Light in the Ocean Light Refraction: bending of light due to change in density between air and water Form of electromagnetic radiation Seawater transmits visible portion of the electromagnetic spectrum (water transmits blue light more efficiently than red) 60% is absorbed by 1 m depth 80% absorbed by 10 m depth No light penetration below 1000 m Shorter wavelengths (blues) are transmitted to deeper depths 46 The so(sound)f(fixing)a(and)r(ranging) zone The sofar layer, in which sound waves travel at minimum speed. On average: ss in Air = 334 m/s ss in Water = 1500 m/s Sound transmission is particularly efficient - that is, sounds can be heard for great distances - because refraction tends to keep sound waves within the layer. ss increases as temperature and pressure increase: sound travels faster in warm surface waters and then again in deep (cold) waters where pressures are higher 47 48 12 Chapter 6 – Summary The shadow zone Water is a polar chemical compound composed of two hydrogen atoms and one oxygen atom. Its remarkable thermal properties result from the large number and relatively great strength of hydrogen bonds between water molecules. Heat and temperature are not the same thing. Heat is energy produced by the random vibration of atoms or molecules. Heat is a measure of how many molecules are vibrating and how rapidly they are vibrating. Sound velocity (m/sec) 0 0 Sound bends up Maximum 80 sound velocity 120 200 300 400 Depth (ft) Depth (m) 40 Without water's unique thermal properties, temperatures on Earth's surface would change dramatically with only minor changes in atmospheric transparency or solar output. Water acts as a "global thermostat.” 100 Shadow zone Sound bends down Water density is greatly influenced by changes in temperature and salinity. Water masses are usually layered by density, with the densest (coldest and saltiest) water on or near the ocean floor. Differences in the density of water masses power deep ocean circulation. Submarine Light and sound are affected by the physical properties of water, with refraction and absorption effects playing important roles 49 Fig. 6-25, p. 178 50 Ocean Salinity Chapter 7 Ocean Chemistry Salinity is the total quantity of dissolved inorganic solids in water. 3.5% salt on average measured in g/kg (ppt (ppt = parts per thousand) About solutions and mixtures A solution is made of two components, with uniform (meaning ‘the same everywhere’ everywhere’) molecular properties: Ocean salinities vary in space The solvent, which is usually a liquid, and is the more abundant component. Processes that affect salinity: evaporation, precipitation, runoff, freezing, and thawing The solute, often a solid or gas, is the less abundant component. And recall that: The heat capacity of water decreases with increasing salinity As salinity increases, freezing point decreases As salinity increases, evaporation slows (boiling point increases) increases) A mixture is different from a solution. In a mixture the components retain separate identities, so it is NOT uniform throughout. 51 52 13 A few ions (charged particles) account for most of the salinity of the oceans. • Dissolved salts Major constituents and trace elements Conservative/nonconservative constituents Major Constituents = [] > 1 part per million Na+ Cl SO4 Mg2+ Ca2+ K+ Sodium Chloride Sulfate Magnesium Calcium Potassium 86 % 99 % Trace Elements = [] < 1 part per million See Table 7.2 for minor and trace elements in seawater 53 Surface Salinity Northern Hemisphere Summer 54 • Dissolved salts Major constituents and trace elements Conservative/nonconservative constituents Major Constituents = [] > 1 part per million Na+ Cl SO4 Mg2+ Ca2+ K+ High = high evaporation Low = coastal regions and high precipitation regions 55 Sodium Chloride Sulfate Magnesium Calcium Potassium 86 % Trace Elements = [] < 1 part per million 99 % 56 14 A few ions (charged particles) account for most of the salinity of the oceans. Seawater’ Seawater’s constituents may be conservative or nonconservative Conservative = concentration changes only as a result of mixing, diffusion, and advection NonNon-conservative = concentration changes as a result of biological or chemical processes as well as mixing, diffusion, and advection See Table 7.2 for minor and trace elements in seawater 57 58 Chapter 7 - Summary The polar nature of the water molecule is responsible for water's water's remarkable ability to dissolve more substances than any other natural solvent. The most abundant ions dissolved in seawater are chloride, sodium, sulfate. The quantity of dissolved inorganic solids in water is its salinity. salinity. Constituents of seawater can be major constituents or trace constituents. Seawater’ Seawater’s constituents may be conservative or nonconservative Ocean salinities vary in space. Processes that affect salinity: evaporation, precipitation, runoff, runoff, freezing, and thawing. 59 15