Oceanography Exam 2 PDF

Lecture 10: Tides (Webb Chapter 7) What Causes Tides: ○ Tides are caused by the gravitational pull of the moon and the sun on Earth's oceans, combined with the centrifugal force due to Earth's rotation. ○ The moon has a stronger influence on tides than the sun because it...

Lecture 10: Tides (Webb Chapter 7) What Causes Tides: ○ Tides are caused by the gravitational pull of the moon and the sun on Earth's oceans, combined with the centrifugal force due to Earth's rotation. ○ The moon has a stronger influence on tides than the sun because it’s much closer to Earth, even though the sun is far larger. Types of Tides: ○ Diurnal Tides: One high tide and one low tide each day. ○ Semidiurnal Tides: Two high tides and two low tides each day, roughly equal in height. ○ Mixed Tides: Two high and two low tides each day, but with unequal heights. Spring and Neap Tides: ○ Spring Tides: Occur during the full and new moons when the Earth, moon, and sun are aligned. These tides have the highest high tides and the lowest low tides. ○ Neap Tides: Occur during the first and third quarters of the moon when the Earth, moon, and sun form a right angle. These tides have the least tidal range, with lower high tides and higher low tides. Tidal Range and Influencing Factors: ○ Tidal Range: The difference in height between high tide and low tide. It varies depending on location and time. ○ Influencing factors include the shape of the coastline, the depth of the ocean, and local geography. For example, narrow bays may amplify tidal effects. Lecture 11: Estuaries and Coastal Environments (Webb Chapter 10) What is an Estuary: ○ An estuary is a partially enclosed coastal body of water where freshwater from rivers and streams mixes with salty ocean water. Estuaries are important for their biodiversity and serve as nurseries for many marine species. Types of Estuaries: ○ Drowned River Valleys (Coastal Plain Estuaries): Formed when rising sea levels flood river valleys (e.g., Chesapeake Bay). ○ Fjords: Deep, glacially carved estuaries with steep sides (e.g., Norwegian fjords). ○ Bar-Built Estuaries: Formed when sandbars or barrier islands build up, trapping freshwater behind them (e.g., Outer Banks). ○ Tectonic Estuaries: Formed by the sinking of land due to tectonic activity, allowing seawater to flood the area (e.g., San Francisco Bay). Salinity Gradients:  ○ Salinity in estuaries varies from freshwater near the river’s mouth to more saline water near the ocean. Salt wedges form where denser saltwater intrudes beneath the lighter freshwater, creating complex mixing zones. Human Impact on Estuaries: ○ Urbanization, pollution, overfishing, and dam construction significantly affect estuaries, disrupting their ecological balance and reducing biodiversity. Lecture 12: Coastal Processes and Erosion (Webb Chapter 10) Wave Action on Coasts: ○ Erosional Coasts: Waves erode the coastline, forming cliffs, sea arches, and sea stacks. Over time, wave energy shapes these landscapes, breaking down hard rock. ○ Depositional Coasts: Waves and currents transport and deposit sediments, creating features like beaches, barrier islands, and sandbars. Longshore Drift: ○ Waves often hit the shore at an angle, causing longshore currents that move sand and sediment along the coast. This process contributes to the formation of spits, bars, and other coastal landforms. Human Influence on Coastal Erosion: ○ Coastal development, seawalls, and jetties can accelerate erosion. Structures that disrupt natural sediment movement can lead to increased erosion downstream of the obstruction. Lecture 13: Physical Oceanography (Webb Chapter 6) Light in the Ocean: ○ Photic Zone: The upper layer of the ocean where sunlight penetrates, generally to a depth of about 200 meters. This is where most marine photosynthesis occurs, supporting a large portion of oceanic life. ○ Twilight Zone: Between 200 to 1000 meters, light diminishes but is still faintly present. Organisms here often have special adaptations, like bioluminescence, to survive in low-light conditions. ○ Midnight Zone: Below 1000 meters, no sunlight reaches this layer, leaving it in complete darkness. Life here relies on food falling from above or on chemosynthetic processes near hydrothermal vents. ○ Color Penetration: Different wavelengths of light penetrate water to different depths. Blue light reaches the furthest, which is why the ocean appears blue. Red light is absorbed quickly, which is why deep-sea creatures often appear red to avoid detection. Thermocline and Heat Distribution:  ○ Thermocline: The thermocline is a distinct layer in the ocean where the temperature changes rapidly with depth. Above the thermocline, surface water is warm, heated by solar energy. Below it, temperatures drop dramatically, and the water becomes much colder. ○ Seasonal Thermocline: In temperate regions, the thermocline is strongest during the summer and weakens or disappears during winter due to surface water mixing caused by storms and cooler air temperatures. ○ Heat Distribution: Oceans absorb and redistribute heat around the planet. Surface currents move warm water from the equator toward the poles, while deep ocean currents carry cold water from the poles back to the equator. Lecture 14: Ocean Currents and Circulation (Webb Chapter 9) Surface Ocean Currents: ○ These are primarily driven by the wind and affected by the Earth's rotation (Coriolis effect). Wind friction on the water’s surface creates currents, which are deflected to the right in the Northern Hemisphere and to the left in the Southern Hemisphere. ○ Gyres: Large, circular surface current systems dominate the major ocean basins. These include the North Atlantic, South Atlantic, North Pacific, South Pacific, and Indian Ocean gyres. Gyres help redistribute heat globally, moving warm water toward the poles and cold water toward the equator. Ekman Spiral and Transport: ○ Due to the Coriolis effect, surface water is deflected 45° from the wind direction. With increasing depth, each subsequent layer of water is further deflected, resulting in the "Ekman Spiral." ○ Ekman Transport: The net movement of water through the entire spiral is at a 90° angle to the wind direction. This effect contributes to phenomena such as upwelling, where deeper, nutrient-rich water rises to the surface, fueling marine productivity. Geostrophic Flow: ○ In a gyre, the balance between the pressure gradient (water piling up in the center due to wind) and the Coriolis force results in geostrophic flow. This creates the circular motion of currents around the gyre. Western Boundary Currents: ○ Strong, fast currents along the western edges of ocean basins, like the Gulf Stream in the North Atlantic. These currents are vital for transferring heat from the tropics toward higher latitudes and influencing climate patterns. Lecture 15: Deep Water Formation and Conveyor Belt  Deep Water Formation: ○ Deep water forms in the polar regions (e.g., the North Atlantic and near Antarctica) where cold temperatures and high salinity cause seawater to become dense and sink. This process is a key driver of thermohaline circulation. ○ Thermohaline Circulation: Also known as the "global conveyor belt," this deep-ocean current system moves water around the globe. Cold, dense water sinks in high-latitude regions and spreads throughout the ocean basins. It then slowly rises back to the surface (upwelling) in other areas, completing the circuit. North Atlantic Deep Water (NADW): ○ Formed in the North Atlantic when cold winds chill surface waters, which then sink due to increased density from high salinity. NADW flows southward along the ocean floor and is a critical component of the conveyor belt. Antarctic Bottom Water (AABW): ○ The densest water in the ocean, formed around Antarctica. It spreads into the deepest parts of the world’s oceans, displacing older water masses and contributing to global deep-water circulation. Importance of Thermohaline Circulation: ○ This circulation is essential for regulating Earth’s climate. It distributes heat, moves nutrients across the oceans, and plays a key role in carbon cycling by transporting dissolved gases like CO2 to deep waters. Lecture 16: Waves and Tsunamis Wave Formation: ○ Waves are generated by wind blowing over the surface of the water. The size of the waves depends on wind speed, the distance over which the wind blows (fetch), and the duration of the wind. ○ Wave Anatomy: Waves are described by their wavelength (distance between two crests), wave height(vertical distance from trough to crest), and period (time it takes for one wave to pass a point). Deep Water Waves vs. Shallow Water Waves: ○ Deep Water Waves: In deep water, the movement of water particles is circular and confined to the upper layers of the ocean. The deeper you go, the less movement there is. ○ Shallow Water Waves: When waves approach the shore and enter shallower water, their orbits become flattened and elongated. The waves slow down, and their height increases, causing them to break. Types of Breaking Waves: ○ Spilling Waves: These occur on gently sloping shorelines, where the wave gradually spills forward. ○ Plunging Waves: These form when the seabed is steeper, causing the wave crest to curl and plunge forward dramatically.  ○ Surging Waves: These happen on very steep shorelines where the wave does not break, but instead surges up the beach. Lecture 17: Tsunamis and Rogue Waves Tsunami Formation: ○ Tsunamis are large waves generated primarily by seismic activity, such as underwater earthquakes, volcanic eruptions, or landslides. The displacement of a large volume of water sends powerful waves radiating outward. ○ Wave Behavior: In the deep ocean, tsunamis have long wavelengths (hundreds of kilometers) but low heights, making them difficult to detect. As they approach the shore, they slow down and grow in height dramatically, leading to devastating coastal impacts. Tsunami Impact: ○ When a tsunami reaches shallow water near the coast, the wave height can increase to tens of meters, causing massive flooding and destruction. The immense energy carried by a tsunami can devastate coastal communities and lead to significant loss of life and property damage. Rogue Waves: ○ Rogue Waves are unexpectedly large, solitary waves that can appear seemingly out of nowhere. They are thought to result from constructive interference, where multiple smaller waves combine to form a larger wave. ○ These waves can be two to three times the height of surrounding waves and are dangerous to ships and offshore structures because of their suddenness and size. Although rare, they are now recognized as a real and significant ocean hazard.