Oceanography 251 Exam 1

How does seawater salinity vary at the surface and with depth?

-At low latitudes, surface salinity is high and decreases with depth. -At high latitudes, surface salinity is low and increases with depth. -Deep ocean salinity remains relatively constant.

Most lithospheric plates contain both oceanic and continental type crust. Use plate boundaries to explain why this is true.

-Because boundaries of plates do not always follow coastlines which causes nearly all plates to contain both oceanic and continental crust.

Why does a map of worldwide Earthquakes closely match the locations of worldwide plate boundaries?

-Because most large earthquakes occur at subduction zones -Earthquake activity mirrors tectonic plate boundaries

Describe the origin, composition, and distribution of biogenous sediment.

-Composition: Two most common are calcium carbonate, and silica. -Origin: Begins as the hard part of organisms (shells, teeth, bones), and when the organism dies, its body parts accumulate on the ocean floor. -Distribution: By 3 processes. 1) Productivity: number of organisms present 2) Destruction: when remains dissolve before hitting the ocean floor 3) Dilution: When deposition of other sediments decrease the % of biogenous sediment found in marine deposits.

What factors affect seawater density?

-Density increases with decreasing temperature. (greatest influence) -Density increases with increasing salinity. -Density increases with increasing pressure (doesn't affect surface waters)

What features occur at plate boundaries?

-Divergent: Plates move away from each other, found along ocean ridges where new lithosphere is added -Convergent: Plates move towards each other, one plate subducts under the other -Transform: Plates slowly slide past one another.

Describe the difference in earthquake magnitudes that occur between the three types of plate boundaries, and include why these differences occur.

-Divergent: Shall focus earthquakes, thin crust, the faster the sea floor spreads the less energy in Earthquake -Convergent: Deep focus earthquakes, converging and thick plates that build up pressure (biggest earthquakes) -Transform-Boundary: Shallow but strong earthquakes, continental crust much thicker = larger earthquakes

What Evidence supports Plate Tectonics?

-Earths magnetic field and Paleomagnetism -Earth has magnetic polarity -North and South polarities -Magnetic polarity recorded in igneous rocks -location of North pole has changed over time -apparent polar wandering

Describe Sea Floor Spreading and why it was an important piece of evidence in support of plate tectonics.

-Harry Hess developed the idea in "History of the Ocean Basins" -Definition: New ocean crust created at ridges, split apart, moved away from ridges, and disappeared back into the trenches. -Mantle convection cells were driving mechanism -The pattern of alternating reversals of Earth's magnetic field became the most supportive evidence of sea floor spreading and plate tectonics.

What are the differences between a mid-ocean ridge and a hotspot?

-Hotspot volcanism is caused by the presence of mantle plumes, and hot magma comes up through the mantle. -At mid ocean ridges, two plates move away from each other and the magma fills the empty space.

List and describe the characteristics of the four basic types of marine sediment.

-Lithogenous: land derived, eroded rock fragments -Biogenous: derived from organisms, calcium carbonate or silica -Hydrogenous: derived from water, mineral precipitate directly from seawater -Cosmogenous: derived from outer space, meteor debris

Why is lithogenous sediment the most common neritic deposit? Why are biogenous oozes the most common pelagic deposits?

-Neritic means "near shore" deposits which makes lithogenous the most common neritic deposit because it is derived from land. -Pelagic means "deep water" deposits which makes biogenous oozes the most common pelagic deposits because they are found beneath relatively shallow deep-ocean areas along the mid ocean ridge.

Describe the origin, composition, and distribution of hydrogenous sediment.

-Origin: Chemical reactions within seawater cause certain minerals to come out of solution, or precipitate (changed from dissolved to solid) -Distribution: a variety of diverse environments such as the deep south Pacific ocean floor and Death Valley, CA. -Composition: manganese nodules, phosphates, carbonates, and metal sulfides.

Describe the origin, composition, texture, and distribution of Lithogenous sediment.

-Origin: rocks on continents/islands that were weathered and eroded into small particles -Texture: Grain size, which is proportional to energy of transportation and deposition. -Composition: Naturally occurring compounds called minerals, most abundant is Quartz. -Distribution: Neritic: shallow water deposits. Pelagic: deep water deposits. (Both are carried to ocean by streams, winds, etc)

Describe the origin, composition, and distribution of cosmogenous sediment.

-Origin: small molten pieces of crust (tektites) rains down on Earth constantly as a component of space dust -Composition: microscopic spherules and macroscopic meteor debris (silicate rock material or iron and nickel) -Distribution: meteor impact, extraterrestrial impacts on other planets that eject particles into space and rain down.

What types of past environmental conditions can be inferred by studying cores of sediment?

-Sea surface temperature -Nutrient supply -Abundance of marine life -Atmospheric winds -Ocean Current patterns -Volcanic eruptions -Major extinction events -Changes in Earth's climate -Movement of tectonic plates

List the two major chemical compounds of which most biogenous sediment is composed and examples of the organisms that produce them.

-Silica: Microscopic algae called Diatoms and protozoans called Radiolarians. -Calcium Carbonate: biogenous ooze called foraminifers, and microscopic algae called coccolithophores.

Describe the ways in which dissolved components are added and removed from seawater.

-Stream runoff dissolve ions from continental rocks and carry them to sea. -Volcanic eruptions both on the land and sea floor, constantly adds ions to ocean water -Other ocean sediments contained within the shells of dead organisms can be removed when seas dry up.

What evidence supports Continental drift?

-The way the continents fit together like a puzzle (pangea) -The way rocks and mountain formations align -Glacial evidence that has been found on continents with no current glacial activity -Organisms were found on vastly separated continents that had no way of crossing the ocean

Cite lines of Alfred Wegener. Why did scientists of his time not believe him?

-They did not believe him because they didn't think that continents could plow through oceans basins, and that the tidal gravitational attractions were too small

How are marine sediments collected and what historical events do they reveal?

-Various methods such as using a dredge, the gravity corer, and specially designed rotary drilling. -They reveal past conditions on Earth, such as sea surface temperature, abundance of marine life, volcanic eruptions, movements of plates, and much more.

Describe the manganese nodules, including what is currently known about how they form.

-rounded, hard lumps of manganese, iron, and other metals -found on the deep ocean floor at concentrations of 100 nodules per square meter -grow at a rate of 5 millimeters per million years -may be aided by bacteria that intermittently lifts and rotates them -may form in spurts due to specific conditions in the water

Convergent boundaries can be divided into three types, based on the type of crust contained on the two colliding plates. Compare and contrast the different types of convergent boundaries that result from these collisions.

1) Oceanic-Continental: The Oceanic plate is subducted, continental arcs created, as well as volcanic eruptions. 2) Oceanic-Oceanic: Denser plate is subducted, deep trenches created, volcanic island arcs created as well 3) Continental-Continental: No subduction, tall mountains uplifted

Why is it so rare to find a pure marine sediment type? Give some examples of mixtures of sediment.

Because the ocean is considered such a "messy place", lithogenous and biogenous sediment rarely occur as absolutely pure sediment that do not contain other types. As a result, most are mixtures such as: calcareous ooze containing siliceous ooze, or vice versa, clay-sized lithogenous particles incorporated into every sediment, and the many types of hydrogenous sediment.

Explain the stages of progression that result in calcareous ooze existing below the CCD.

Calcareous ooze deposits that land on top of a mid ocean ridge that peaks above the CCD will not be dissolved. Over time, seafloor spreading causes the new seafloor and calcareous sediment to move below the CCD. The sediment will then dissolve below the CCD unless it is covered by a deposit unaffected by the CCD such as siliceous ooze.

What evidence is used to support the hypothesis that ocean salinity has remained constant through time?

Evidence known as the steady state condition states that the salinity has remained constant over time because the rate at which an element leaves the ocean equals the rate at which an element enters the ocean, keeping the average amounts of various elements relatively the same.

Describe how excess heat energy absorbed by Earth's low-latitude regions is transferred to heat-deficient higher latitudes.

Huge amounts of heat energy are removed from the low-latitude oceans and are carried towards the poles and released at the higher heat-deficient latitudes through precipitation, thus moderating Earth's temperature.

Why does water have such unusual chemical properties?

Instead of water's atoms being in a straight line, both hydrogen atoms are located on the same side of the oxygen atom. This curious bend in the geometry of the molecule is the underlying cause of most of the unique properties of water.

Describe the most common types of cosmogenous sediment and give the probably source of these particles.

Microscopic iron-nickel and silicate spherules (tektites and space dust) that rain down on Earth due to an extraterrestrial event that occurred on Earth or another planet that ejected piece of crust into space.

How are seawater and pure water similar? How are the two different?

Most of their physical properties are somewhat identical, such as their color. But because of the dissolved substances in salt water, the odor and taste are changed, the pH becomes slightly alkaline, the density increases, the freezing point decreases, and the boiling point increases.

If siliceous ooze is slowly but constantly dissolving in seawater, how can deposits of siliceous ooze accumulate on the ocean floor?

One way is to accumulate the siliceous tests faster than seawater can dissolve them. Many tests sinking at the same time will cause the other tests to be buried and no longer exposed to the effects of seawater. Thus, siliceous ooze is found in places with high population of silica-secreting organisms.

Draw and describe each of the three stages of coral reef development. How does this sequence tie into the plate tectonic model?

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Using the processes that affect seawater salinity, explain why there is such a large range of salinity variation at the surface, but such a narrow range of salinity at depth.

Salinity varies widely at the surface and hardly varies with depth because all the processes that affect salinity (precipitation, runoff, melting sea ice, sea ice forming, and evaporation) occur at the surface and thus have no effect on deep water below.

How salty is seawater?

Seawater not only contains sodium chloride to give it its salty taste. It has other dissolved substances such as other salts, metals, and dissolved gases. Oceans contain enough salt to cover the entire planet in a layer of salt that is 150 meters thick.

Why does seawater salinity vary?

Seawater salinity varies from 33-38% because of three main reasons. 1) An infux of freshwater lowers salinity or creates brackish conditions 2) A greater rate of evaporation raises salinity or create hypersaline conditions. 3) Salinity may very with the seasons (dry/rain)

How is the age distribution pattern of the Hawaiian Islands-Emperor Seamount Chain explained by the position of the Hawaiian hotspot? What could have caused the curious bend in the chain?

The Hawaiian hotspot is at the very south-east end of the chain, and as the islands go up northwest, the older the islands are. The Bend could have been caused by a combination of the Pacific plate moving, as well as the hotspot moving itself.

Describe the process of how a drill ship like the JOIDES Resolution obtains core samples from the deep-ocean floor.

This ship has a tall metal drilling rig that can conduct rotary drilling. This is done by taking a drill pipe that rotates while pressed against the ocean floor to begin drilling and dig up to 2100 meters.

How does the specific heat capacity of water compare with that of other substances? Describe the effects this has on climate.

Water has an extremely high heat capacity that allows it to take in or lose a lot of heat without changing temperature. This creates a moderate temperature across Earth with continents having a greater range of temp throughout the day while oceans have smaller changes from day to night and during different seasons.