OCN 100L Midterm Study Guide Fall 2024 PDF

OCN 100L Midterm Study Guide This study guide is for the purpose of preparing for your first midterm. The midterm will consist of material covered so far this semester in labs 1-6. Unlike lecture, you must be able to apply each topic (e.g., interpret isobaths, read a refractometer, measure bearings,...

OCN 100L Midterm Study Guide This study guide is for the purpose of preparing for your first midterm. The midterm will consist of material covered so far this semester in labs 1-6. Unlike lecture, you must be able to apply each topic (e.g., interpret isobaths, read a refractometer, measure bearings, know how to identify plate boundary features on a map, etc.). This guide covers all the major topics, there won’t be any topics on the midterm that aren’t in the guide, though not every detail is listed here so you will still want to review your labs and notes as well. Lab 1: Error, Precision, and Rounding Precision: When we take measurements, our instruments have a limit to their precision and thus our answers are rounded to the smallest graduation of measurement. We call the smallest graduation of measurement for an instrument its PRECISION. Since all measuring devices have a limit to their precision, there will always be a range (or error) to our measurements, depending on that precision. Error: All measured numbers (units attached) should come with an error. If none is given, then you assume the error to be +/-1/2 the measurement of the next number or decimal place. Note: If the error is greater than the precision of the instrument, the above rule does not apply. Instead provide an error based on human measurement and not more precise than the instrument allows. For example, you measure temperature with a thermometer and read a value of 30.6°C and provide an error of +/- 0.05°C. However, the thermometer is only precise to the tenths place. Therefore, a more appreopriate error is +/- 0.1°C or 0.2°C since your measurement error will always be greater than the minimum error of the instrument (+/- 0.05). Rounding: Basic rule: if your calculation involves any measured numbers (recognizable because they come with a unit!), and those numbers all have the same unit, and your result also has the same unit, then round your answer so it is as precise as the least precise of any of your starting measurements. Lab 1: Unit Conversion Whenever you want to convert units from one into another, follow this simple technique that ALWAYS works: 1. Turn your original number into a fraction over 1. 2. Multiply this fraction by another fraction, one that equals 1: the conversion factor. Put the number with the units you want to cancel out on the bottom and the number with the units you want to end with on the top. (So the original unit cancels, and the new unit remains). For example, to convert 3605 cm to inches: 3605 cm x = ? in → 3605 cm x in = ? in → 3605 cm x 1 in = 3605 in = 1419 in 1 1 cm 1 2.54 cm 2.54 How do we round our answer? If your calculation involves any measured numbers (recognizable because they come with a unit!), those numbers all have the same unit, and your result also has the same unit, then round your answer so it is as precise as the least precise of your starting measurements. You can’t be more precise than your least precise measurement. E.g., 12.6 cm + 3 cm = 15.6 cm, rounds to 16 cm (precision has to match 3, rounded to the ones place). Lab 1: Reading a Refractometer: Refractometer measures the refractive index of liquids/solutions. Gives density in g/mL and salinity in ppt (‰) 1 g/mL is equivalent to 1 g/cm3 Once liquid is placed on device, read the line measurement and record density and salinity Salinity has a precision of 1 ‰, minimum error of +/- 0.5 ‰ Density has a precision of.001 g/mL, minimum error of +/- 0.0005 g/mL Lab 1: Angles & Compasses A circle encompasses 360° of arc. Starting with 0° at the top of the circle facing North (N), and moving clockwise, the first ¼ of the circle, facing East (E) is 90°, the second ¼, facing South (S) is 180°, the third ¼ facing West (W) is 270°, and the final ¼, facing back North (N) or all the way back to the beginning is 360°. The easiest way to draw and/or measure angles is using a protractor. Make sure to practice using one! Note: An oceanographer measures the angle always as a number from 0 to 360°, measured clockwise from north. As always, make sure to attach an error (+/- 2° is an acceptable error). Lab 2: Latitude and Longitude Latitude and longitude are simply an angular coordinate system we use to uniquely locate a point on Earth's surface. Longitude -- Lines of equal length that run from north pole to south pole and are used to measure angular distance away from the Prime Meridian. Also known as Meridians. Memory aid: length of the planet from pole to pole. Example: the longitude of San Francisco is 122° West of the Prime Meridian. Latitude -- Lines of varying length that run parallel to the equator and measure angular distance north or south of the equator. Memory aid: like a lateral throw (sideways) in Football or Rugby. Example: the latitude of San Francisco is 38° North of the Equator. Prime Meridian -- The Y-axis of our world coordinate system – (imaginary line connecting the poles and intersecting Greenwich, England) International Date Line or Antimeridian -- The longitude line that is opposite the Prime Meridian: 180° of a circle around the planet. Equator -- The X-axis of our world coordinate system – (imaginary line running around the center of Earth) Latitude/Longitude formats: Example: 24.6° N, 56.2° W +/- 0.2° (always include N for S for north or south latitude, W or E for west or east longitude) Lab 2: Plate Boundaries The edges or boundaries of lithospheric plates are where the vast majority of earthquakes, volcanic eruptions, and tsunamis are generated, where mountain ranges form, and where new seafloor forms at mid-ocean ridges. Make sure you know how to identify the plate boundary types on a map based on earthquakes, volcanoes, and the direction of plate motion. Divergent boundaries (a.k.a. spreading centers, mid-ocean ridges): plates move away from the boundary, new seafloor forms along the boundary, along with earthquakes (typically shallow and weak), volcanic seamounts, and lava flows. Often starts as rifting within a continent, where the pre-existing material is broken up and thinned. Convergent boundaries: plates move toward each other, creating either a subduction zone or a continental collision zone. If two oceanic plates or an oceanic and a continental plate converge, the denser oceanic plate sinks into the mantle, creating a subduction zone and a deep trench along the boundary where the plate sinks into the mantle. If two continental plates collide, neither can subduct since they are too low density, so a tall mountain range with thick crust is formed (e.g., Himalayas). Convergent boundaries have the most abundant, largest, and deepest earthquakes, and the most explosive volcanic eruptions. Transform boundaries: plates slide past each other along the boundary, forming earthquakes but no volcanoes, trenches, new seafloor, or mountain ranges. Earthquakes are stronger and more abundant compared to divergent boundaries, but weaker and less abundant than at convergent boundaries. Transform boundaries usually connect two offset segments of a mid-ocean ridge, linking the two in a step-like shape since the ridge can’t curve. Lab 3: Bathymetric Maps & Isobaths Bathymetric charts show depth to the ocean floor. Isobaths connect points of the same depth. Because the sea surface is (nearly) horizontal, isobaths are shorelines that would exist if sea level dropped and exposed increasing amounts of seafloor. The isobath interval is the difference in depth between one isobath and the next. A common chart interval is 40 feet, but it can be more or less, depending on scale and terrain steepness. Isobath interval: The vertical distance between two isobaths. This value is set for all isobaths on any given map (unless indicated otherwise, which happens generally only if the map shows both land and seafloor under water -- then it might have one interval for land and the other for the seafloor). Isobath intervals are always written on a map, usually at the bottom and are consistent throughout the map. Example: 20-feet isobath interval means that all isobath lines are separated by 20 vertical feet.  Index isobath: A darker, thicker isobath line with the depth written on it and occurring at regular intervals that are usually 4 or 5 times as big as the regular isobath interval. Example: in a map with an isobath interval of 100 ft, index isobaths will be every 5th isobath or every 500 feet. By darkening these lines and labeling them, it makes them easier to see. So you'd find dark, labeled lines for 500 ft, 1000 ft, 1500 ft, etc. Index isobath interval: The interval or vertical distance between two index isobaths. For the example above, that would be 500 ft. Isobath Interpretation Reminders: Depths between isobaths should NOT be interpolated. All isobaths close somewhere, although the closure point may not appear on a map sheet. Isobaths never divide or split, although they may appear to do so when they represent a vertical cliff. In this case they overlap one another. Isobaths are farther apart on gentle slopes and closer together on steep slopes. Isobaths bend (or V points) upslope for valleys or canyons and cross valley or canyon floors perpendicularly, making a V pointing upslope. Every chart has the scale and the isobath interval given on the bottom or top margin. If you’re lost, look for the nearest index isobaths! Lab 4: Marine Rocks Rocks are made up of one or minerals, derived from a melt (igneous), pre-existing sediments (sedimentary), or adding a significant amount of heat and pressure to create a new rock from a previous rock (metamorphic). We looked at 3 types of rocks but focused on two: Sedimentary and Igneous Rocks. Sedimentary Rocks: form through the precipitation of minerals directly from water (example: salt flats that form when seawater evaporates) or through the lithification of sediment – small particles of rocks, minerals, and organic material, broken up, transported, and deposited in layers. Sedimentary rocks are identified by: Texture o Gravel-sized, sand-sized, mud-sized, crystalline/microcrystalline o Angular or rounded clasts Composition (lithogenous, biogenous, hydrogenous sediment components) Know the following sedimentary rocks: Sandstone Breccia Conglomerate Limestone o Fossiliferous limestone o Coquina o Micritic limestone Mudstone Manganese (Mn) Nodules Evaporites (Gypsum, Rock Salt) Chalk Diatomite Igneous Rocks: Igneous rocks form from the solidification of magmas (molten rock). Magmas form at depth when the Earth’s mantle melts. Hot, fluid magmas are lower density than the rocks within which they form. Magmas rise toward Earth’s surface, where they cool to become igneous rocks. If magmas erupt on the Earth’s surface, they cool very quickly and form crystals that are too small to see with the eye or no crystals at all (glass). We call such igneous rocks extrusive or volcanic, with an aphanitic texture. If magmas cool slowly under the surface, they can form large crystals. We call such igneous rocks intrusive or plutonic, with a phaneritic texture. All igneous rocks are either volcanic or plutonic. Igneous rocks are identified by: Texture o Phaneritic (large, visible crystals, slow cooling) o Aphanitic (tiny, mostly invisible crystals, fast cooling)) Composition o Felsic o Mafic o Ultramafic Know the following igneous rocks: Basalt Granite Peridotite Lab 5: Marine Sediments Ocean sediments can be divided into 4 main categories, generally determined by their source/composition: Lithogenous (terrigenous): Derived from pre-existing rocks, generally from continental and terrestrial rocks. Biogenous: Derived from shells of marine organisms. Hydrogenous: Derived from solid material precipitated or evaporated out of fluids. Cosmogenous: Derived from extraterrestrial material (asteroids, meteors, etc.). Sediments are also described by texture, the way each sediment grain looks: Grain-size: Gravel: Pebbles, Cobbles, Boulders (>2 mm) – Associated with high-energy water, like headlands or the base of cliffs. Sand: Coarse, medium, and fine-grained (< 2 mm, > 1/16 mm) – Associated with moderate-energy waters, like beaches or rivers. Mud: Silt, Clay ( 7, neutral = 7 (pure water) The ocean tries to remain in equilibrium through buffering (when CO2 reacts with H2O). The reaction (below) will move to the left to remove the acid and neutralize the water. The reaction will move to the right to produce more H+ to neutralize the OH-. The buffering equation for pH in water: H2O + CO2 ⇆ H2CO3 ⇆ HCO3- + H+ ⇆ CO32- + 2H+ Water + Carbon Dioxide ⇆ Carbonic Acid ⇆ Bicarbonate + Hydrogen Ion ⇆ Carbonate + 2 hydrogen ions Alkalinity: Alkalinity is a measure of the amount of ions dissolved in seawater than can combine with H+ or release H+ thereby enabling the solution to neutralize acids and bases that are added and stabilize pH (called “buffering”). In seawater, the most abundant ions available for this are carbonates (linking to the carbonate buffering system!). Ocean Acidification: The buffering equation shows that when carbon dioxide reacts with water, it creates carbonic acid. If carbon dioxide levels get too high, it exceeds the buffering ability of the Ocean, and pH decreases. This causes shells and other hard parts (like coral reefs) made of calcium carbonate to start to dissolve, harming some of the most abundant and important creatures in the Ocean. The main source of carbon dioxide in our atmosphere is the burning of fossil fuels like, oil, coal, and natural gas for energy by humans.