Unit 8

Data Collection and Analysis Oceanography is the scientific study of Earth’s oceans Technologies such as sonar, floats, satellites, submersibles, and computers have become central to the continuing exploration of the ocean.

Data Collection and Analysis At the Surface Sonar, which stands for sound navigation and ranging, is used by oceanographers to learn more about the topography of the ocean floor Large portions of the seafloor have been mapped using side-scan sonar, a technique that directs sound waves at an angle to the seafloor, so that the sides of underwater hills can be mapped.

Data Collection and Analysis In the deep sea Submersibles, underwater vessels which can be remotely operated or carry people to the deepest area of the ocean, have allowed scientists to explore.

Origin of the Oceans Where did the water come from? Scientists hypothesize that Earth’s water originated from either a remote source or a local source, or both Comets and meteorites are two remote sources that could have contributed to the accumulation of water on Earth.

Origin of the Oceans Volcanism In addition to comets, water for Earth’s early oceans might have come from volcanic eruptions. An intense period of volcanism occurred shortly after the planet formed. An episode of volcanism released large quantities of water vapor and other gases into the atmosphere. The water vapor eventually condensed into oceans.

Distribution of Earth’s Water The oceans contains 97% of the water found on Earth. Another 3% is freshwater located in the frozen ice caps and in rivers, lakes, and underground sources. Approximately 71% of Earth’s surface is covered by oceans.

Distribution of Earth’s Water Sea Level Global sea level, which is the level of the oceans’ surfaces, has risen and fallen by hundreds of meters in response to melting ice during warm and cold periods. Sea level is also affected by tectonic forces that lift or lower portions of Earth’s crust.

Distribution of Earth’s Water Major Oceans There are three major oceans: The Pacific The Atlantic The Indian Polar Oceans The artic and Southern oceans are covered by vast expanses of sea ice, particularly during the winter.

Chemical Properties of Seawater Ocean water contains dissolved gases including oxygen and carbon dioxide, and dissolved nutrients such as nitrates and phosphates.

Chemical Properties of Seawater The measure of the amount of dissolved salts in seawater is salinity. Oceanographers express salinity as grams of salt per kilogram of water, or parts per thousand (ppt) The average salinity of the oceans is 35 ppt The lowest salinity often occurs where large rivers empty into the oceans, creating areas of water called estuaries

Chemical Properties of Seawater Sources of Sea Salt Geologic evidence indicates that the salinity of ancient seas was not much different from that of today’s oceans. Sources of sea salts have also stayed the same over time. Sulfur dioxide and chlorine gas released by volcanoes form sulfate and chlorine ions. Most other ions in seawater, including sodium and calcium, come from weathering rocks.

Chemical Properties of Seawater Removal of Sea Salts In arid coastal regions, water evaporates from seawater and leaves solid salt behind. Marine organisms remove ions from seawater to build shells, bones, and teeth. Winds can pick up salty droplets from breaking waves and deposits the slat further inland.

Physical Properties of Seawater Density Salt ions add to overall mass of water, they increase the density of water. Seawater is therefore more dense than freshwater. Temperature also affects density – cold water is more dense than warm water. Variations in salinity also cause the freezing point of seawater (-2 degrees Celsius) to be somewhat lower than that that of freshwater (O degrees Celsius)

Ocean Layering Temperature Profiles, which plot changing water temperatures against depth. Such profiles vary, depending on location and season. Ocean layering is caused by density differences.

Ocean Layering The thermocline is the transitional ocean layer that lies between the relatively warm, sunlit surface layer and the colder, dark, dense bottom layer. It is characterized by temperatures that decrease rapidly with depth.

Three water masses account for most of the deepwater masses in the oceans Antarctic Bottom Water North Atlantic Deep Water Antarctic Intermediate Water

Water Masses Antarctic Bottom Water is the densest and coldest deepwater mass. It is overridden by the slightly warmer and less dense North Atlantic Deep Water. Antartic Intermediate Water is warmer and less dense, and thus it overrides the other two deepwater masses.

Waves A wave is a rhythmic movement that carries energy through space or matter. Ocean waves are generated mainly by wind blowing over the water’s surface. Highest point of a wave: crest Lowest point of a wave: trough Vertical distance between crest and through: wave height Horizontal distance crest to crest: wavelength

Waves Wave height depends on three factors: fetch, wind duration, and wind speed. Fetch refers to the expanse of water that the wind blows across.

Waves Collapsing waves are called breakers. A breaker forms when wavelength decreases and wave height increases as the wave nears the shore. Tides are the periodic rise and fall of sea level. The highest level to which water regularly rises is known as high tide, and lowest level is called low tide.

Tides The Moon Influence The Moon and Earth experience unbalanced gravitational forces. These forces cause tidal bulges on opposite sides of Earth.

Tides The Sun’s Influence The gravitational attraction of the Sun and Earth’s orbital motion around the Sun influences tides. Lunar tides are more than twice as high as those caused by the Sun because the Moon is much closer to Earth.

Tides During a full moon, the Sun, the Moon, and Earth are all aligned. This causes solar tides to enhance lunar tides, causing high tides to be higher than normal and low tides to be lower than normal. These types of tides are called spring tides. A neap tide occurs during a first-or third-quarter moon, when the Sun, the Moon, and Earth form a right angle. When this occurs, solar tides diminish lunar tides, causing high tides to be lower and low tides to be higher than normal.

Currents Surface currents are wind-driven movements of ocean water that primarily affect the upper few hundred meters of the ocean. Surface currents follow predictable patterns are driven by Earth’s global wind systems.

Currents Continents deflect ocean currents to the north and south so that closed circular current systems, called gyres, develop. There are five majors gyres: North Pacific North Atlantic South Pacific South Atlantic Indian Ocean

Currents The upward motion of ocean water is called upwelling. Upwelling occurs when surface water is moved offshore and deep, colder water rises to the surface to replace it. A density current is the movement of ocean water that occurs in depths too great to be affected by surface winds and is generated by differences in water temperature and salinity.

A beach is the area in which sediment is deposited along the shore. The size of sediment depends on the energy of the waves striking the coast and on the source of the sediment.

Longshore Currents The longshore bar is a sand bar that forms in front of most beaches. As water from incoming breakers spills over the longshore bar, a current flowing parallel to the shore, called the longshore current

–Barrier islands are long ridges of sand or other sediment, deposited or shaped by the longshore current, that are separated from the mainland.

Protective Structures In many coastal areas, protective structures are built in an attempt to prevent beach erosion and destruction of oceanfront properties. Seawall Groin Jetty Breakwater

–Groins walls built into the water perpendicular to the shoreline for the purpose of trapping beach sand. – Seawalls reflect the energy large storm waves back towards the beach. –Jetties are walls of concrete built to protect a harbor entrance from drifting sand. Breakwater –Breakwaters are built in the water parallel to straight shorelines to provide anchorages for small boats. Groin Jetty Seawall

Seafloor Features Continental Margin – area where edges of continents meet the ocean Continental Shelf – the shallowest part of a continental margin extending seaward from the shore Continental Slope – found beyond continental shelves, the seafloor drops away quickly

Deep-Ocean Basins Abyssal Plain: flattest parts of the ocean floor Deep-Sea Trench: deepest parts of the ocean basin, elongated sometimes arc-shaped depressions in the seafloor Mid-ocean ridges: underwater mountains, sites where volcanic activity is often found

Hydrothermal Vent: a hole in the seafloor through which fluid heated by magma erupts Seamounts: submerged basaltic volcanoes more than 1 km high Guyots: large, extinct, basaltic volcanoes with flat, submerged tops