Oceans

OceansUnit 8Data Collection and AnalysisOceanography is the scientific study of Earths oceans

Technologies such as sonar, floats, satellites, submersibles, and computers have become central to the continuing exploration of the ocean.

Data Collection and AnalysisAt the SurfaceSonar, 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 AnalysisIn the deep seaSubmersibles, 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 OceansWhere did the water come from?Scientists hypothesize that Earths 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 OceansVolcanismIn addition to comets, water for Earths 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 Earths WaterThe 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 Earths surface is covered by oceans.Distribution of Earths WaterSea LevelGlobal 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 Earths crust.Distribution of Earths WaterMajor OceansThere are three major oceans: The PacificThe AtlanticThe Indian

Polar OceansThe artic and Southern oceans are covered by vast expanses of sea ice, particularly during the winter.

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

Chemical Properties of SeawaterThe 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 pptThe lowest salinity often occurs where large rivers empty into the oceans, creating areas of water called estuaries

Chemical Properties of SeawaterSources of Sea SaltGeologic evidence indicates that the salinity of ancient seas was not much different from that of todays 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 SeawaterRemoval of Sea SaltsIn 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 SeawaterDensitySalt 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 LayeringTemperature Profiles, which plot changing water temperatures against depth. Such profiles vary, depending on location and season.Ocean layering is caused by density differences.

Ocean LayeringThe 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 WaterNorth Atlantic Deep WaterAntarctic Intermediate Water

Water MassesAntarctic 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.WavesA wave is a rhythmic movement that carries energy through space or matter. Ocean waves are generated mainly by wind blowing over the waters surface.Highest point of a wave: crestLowest point of a wave: troughVertical distance between crest and through: wave heightHorizontal distance crest to crest: wavelength

WavesWave height depends on three factors: fetch, wind duration, and wind speed.

Fetch refers to the expanse of water that the wind blows across.

WavesCollapsing 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.

TidesThe Moon InfluenceThe Moon and Earth experience unbalanced gravitational forces. These forces cause tidal bulges on opposite sides of Earth.

TidesThe Suns InfluenceThe gravitational attraction of the Sun and Earths 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.TidesDuring 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.CurrentsSurface 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 Earths global wind systems.CurrentsContinents deflect ocean currents to the north and south so that closed circular current systems, called gyres, develop.There are five majors gyres:North PacificNorth AtlanticSouth PacificSouth AtlanticIndian OceanCurrentsThe 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 CurrentsThe 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 StructuresIn many coastal areas, protective structures are built in an attempt to prevent beach erosion and destruction of oceanfront properties.

SeawallGroinJettyBreakwater

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.

BreakwaterBreakwaters are built in the water parallel to straight shorelines to provide anchorages for small boats.

Groin

Jetty

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

Deep-Ocean BasinsAbyssal Plain: flattest parts of the ocean floorDeep-Sea Trench: deepest parts of the ocean basin, elongated sometimes arc-shaped depressions in the seafloorMid-ocean ridges: underwater mountains, sites where volcanic activity is often found

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