MSL Exam 2

When two waves meet, ____.

they continue past or through each other without changing

Scientists use oxygen isotopes to ____.

. understand past climate conditions b. understand water temperature

In general, wind-driven currents are confined to the upper ____ m of the ocean surface.

100

The surface layer of the ocean, or mixed layer, is approximately ____ meters thick.

100

Sediments on the ocean floor hold a record of Earth's environmental conditions back to about ____.

170 million years ago

The large-scale ocean circulation gyres mirror Earth's long-term average planetary-scale winds with the subtropical gyres centered at approximately ____ latitude.

30

The water that makes up the deep layer of the ocean accounts for about ____ of the ocean volume.

90%

a) Explain how a cobble beach could form.

A cobble beach could form due to its location in an area that sees intense storm waves that erode the smaller particles away, leaving larger sediments.

b) What is the effect of barrier islands on waves, and what consequence does this have for the mainland coast?

Barrier islands intercept waves before they reach the coast. This protects the coast from erosion and deposition from wave sediments and creates a safe lagoon between the mainland and barrier island. As waves hit against the barrier islands they deposit sediments and erode the barrier islands instead of the mainland coast.

a) Why are biogenous sediments described as the "hard parts" of marine organisms? Where did the soft parts go?

Biogenous sediments are described as the hard parts of marine organisms because they are composed of what is left behind when an animal decomposes. Soft parts such as the animals organs and flesh decompose leaving behind their shells and skeletal systems or hard parts to be broken and recycled into biogenous sediment. Similarly, when large animals feed on small photosynthetic organisms, they digest the soft parts and excrete the hard parts which fall to the ocean floor to create biogenous sediment.

b) Why are iceberg sediments different from other ocean sediments? What is it about icebergs that causes this?

Debris from icebergs are coarse and unsorted and can often be traced back to their origin based on the rock's composition. This contrasts the fine-grained particles that make up much of the deep-ocean. Iceberg sediment is this way because when the ice formed on land, the sediments froze in it. The sediment stayed trapped in the ice, unweathered until the ice calved from its source and floated out to sea to melt, depositing the sediments along the fine-grained ocean floor.

) Name the main process that generates "deep water waves", and name two (2) ways that "shallow water waves" can form. BONUS if you can name 3 ways.

Deep water waves are formed by wind on the open ocean that approach the coastline and interact with shallow waters. When the waves enter waters shallower than the wave-base, the waves cause friction on the ocean floor and no longer act like free waves in the open ocean. When the waves get into shallower water their wave period remains the same but the wavelength shortens and the wave height increases. Shallow water waves are caused by tides where the length of the waves created are greater than the depth of the ocean, tsunamis which create rapidly propagating shallow-water waves after a disturbance, and waves generated by wind.

a) What is the difference between the formal oceanographic terms "deep water wave" and "shallow water wave"?

Deep water waves are waves that are in water deeper than half of their wave base which is half the wavelength. The orbits of the water particles are circular. Shallow water waves are in water shallower than 1/20th of the wavelength and the orbit of the water particles flatten in increasing depth

A large component of the trade winds blow from east to west along the equator. Considering both sides of the equator, the trades winds cause ____ .

Ekman transport away from the equator generating upwelling

The Great Pacific Garbage Patch is a huge patch (or patches) of trash floating in the surface layer of the North Pacific Gyre, as shown in this NOAA map (right click and open in a new tab). The currents and gyres of the North Pacific are shown in this map. Based on how the subtropical gyres work, explain how Ekman transport(1) keeps garbage in the North Pacific Gyre but Selected Answer:

Ekman transport keeps garbage in the North Pacific Gyre by constantly pushing it back towards the center. When surface winds move surface water in the ocean, the water below moves in a domino effect. Because of the coriolis effect, this water starts to domino in a circular pattern. Water in the North Pacific Gyre is pushed by surface currents and is carried to the right by the coriolis effect. The water starts to converge inward toward the center of the gyre and as more and more water is transported, a mound forms in the middle. As the mound becomes steeper, water flows from high pressure areas to low pressure, downhill of the mound. The coriolis effect causes this water to spiral around the gyre and eventually move parallel to the mound and continuously repeat this process. This causes garbage in these waters to be carried back into the gyre again and again.

Subpolar gyres are characterized by ____ .

Ekman transport moving water away from the center of the gyre

b) Suggest what oceanographers can learn from mapping the grain sizes of sediment that has settled onto the seafloor.

From mapping grain sizes of sediment, oceanographers can learn how much energy was in the waves or currents of specific areas. The speed of the water can be determined by looking at the grain sizes. If the sediment has mostly large grain sizes then the current was moving quickly. Conversely, if there are mostly small sediment particles the water was moving slowly, possibly at a river delta where rivers slow and deposit fine sediment such as clay and silt.

(2) not in the smaller Alaska subpolar gyre. (Hint: size of the gyre is not the reason.)

Garbage does not become stuck in the subpolar Alaska gyre because Ekman transport causes the water with its subsequent garbage to spiral away from the center of the gyre. It then connects and spirals into the North Pacific Gyre. This is driven by the counterclockwise surface winds from the Aleutian low pressure system.

In the United States, ____ is(are) most at risk from tsunamis.

Hawaii and Alaska

b) Suppose a local landowner was worried about erosion of a sandy beach, so he got up one morning and spread a layer of cobbles on top of it. Would this be an effective way to prevent the beach from eroding? Explain your reasoning.`

I do not believe that puting cobbles on a sandy beach will prevent the beach from eroding. Cobblestone beaches are formed because the cobbles are what is left behind after the sand has been taken away from the beach due to many intense storms. The cobbles the landowner put out will not stop the waves from continuing to take the finer sediment from the beaches.

b) What happens in the North Atlantic and the Southern Ocean (around Antarctica) that is important for deep thermohaline circulation?

In the North Atlantic and Southern Ocean, water cools and begins to freeze, causing a decrease in temperature and increase in salinity to create denser water. This dense water sinks and is carried south in the North Atlantic and North in the Southern hemisphere to be heated and rise to continue circulation.These are the only two locations in the global ocean where new deep-water masses form. The North Atlantic water is already salty from evaporation in the tropical Atlantic, and the Southern Ocean water becomes very salty when sea ice freezes.

Which feature of the Antarctic Circumpolar Current distinguishes it from other ocean-surface currents?

It circles the globe.

a) Under what conditions do longshore currents form?

Longshore currents form because when waves break, they are not usually parallel to the shoreline. Instead, they meet the shoreline at an angle and the water resuspends sand grains. The backwash of the waves flows directly backward with gravity down the beach slope which causes the sediments and waves to move down the beach in a zigzag pattern.

a) Explain what the nodes are, and why they are out in the open ocean (not near coasts).

Nodes are sections of water that waves oscillate around in a basin. At this place, the water level does not change as the wave crests and troughs alternate back and forth. Nodes are in the open and ocean and not the coast because the waves coming into the shore are at their crest or trough. Nodes cannot be on the shore because there is no water on one side to oscillate with. Waves need a basin to oscillate back and forth in where the node is at the center of the basin. When a wave hits shore its energy is dispersed and not sent back to oscillate around the node in the basin.

Why are the world's most productive fisheries located in areas of coastal upwelling?

Nutrient-rich waters from the deep ocean are transported into the photic zone.

b) Describe 2 ways in which rip currents are different from longshore currents. Do not simply give definitions of each one. Instead, explain how they are different.

One way a rip current is different from a longshore current is that it stays in one place and does not cause a current to migrate down the beach. This is because the water is taking the path of least resistance back out to the ocean between sandbars and other obstacles. Also, riptides have an absence of waves. They only occur after the waves have broken on land and are caused by the backwash flowing back into the ocean on the path of least resistance. Rip currents are narrow; longshore currents are broad. Rip currents are shorter and more local; longshore currents can run for kilometers along the coastline. Rip currents are faster and much more dangerous.`

a) What do scientists see or measure in the Heinrich layers that is unusual, compared with the rest of the sediment in the cores?

Scientists measure the coarse grained sediment in the Heinrich layers from the North Atlantic Ocean. This is odd because sediment cores so far from land are usually fine grained, blanketing the deep-ocean floor.

a) How does swell form at sea?

Swells form when waves move outside of an area with strong storm winds and turn into rounded free waves where the only thing acting on them is gravity

b) Explain why swell is observed to have regular wave periods and wavelengths, despite forming in a chaotic way. You can see regularly spaced swell approaching an Australian beach in this photo (rip currents are also visible).

Swells still have regular wavelengths and periods because waves with longer wavelengths and periods travel faster in deep water than shorter waves. This means that longer waves out distance shorter waves and sort themselves into regular and even waves

Describe three (3) important differences between beaches and tidal wetlands (not ordinary wetlands).

The differences between beaches and tidal wetlands are that tidal wetlands are covered and exposed by shallow water depending on the tide. They also are in areas that are protected from wave action. This wave action disrupts the sediment on beaches but not the protected tidal wetlands. Compared to beaches, tidal wetlands also usually have a lot of emergent plants because they are not disrupted by the waves. This makes them a valuable place for sealife to gather.

Extra credit: What is the name for ocean sediments that come from icebergs?

The name for sediments that come from icebergs are ice-rafted debris Response Feedback: Good. Extra credit. Another name is "dropstones".

a) What is the relationship between (1) the size of sediment grains carried by ocean water and (2) the energy of the water?

The relationship between the size of sediment grains carried by ocean water and the energy of water is the higher the energy in the environment the larger the grain size of the deposited rock and the lower the energy the smaller the grain size. This is because as sediment travels long distances from its source, it is sorted according to grain size.

b) Does the same thing happen with deep-water waves as they approach a shoreline? Why or why not?

The same process does not happen to deep-water waves because the definition of a deep water wave is a wave that is in deeper water than its wave base. As deep water waves move towards the coastline, they begin to slow but the waves enter waters that are shallower than the wave base and transition into shallow-water waves.

b) What is the tidal range at a node?

The tidal range at a node is zero.

b) There are two main types of biogenous "hard parts" sediment in the ocean. What materials are these two types made of (chemical composition)?

The two types of hard parts are made up of calcium carbonate (CaCO3) from calcareous organisms and silica (SiO2) from siliceous organisms.

c) Name one water mass and describe where it forms.

The water mass in the North Atlantic is called the North Atlantic Deep Water and is the layer above the Antarctic Bottom Water and below the Antarctic Intermediate Water formed in the Atlantic ocean. It flows south, spreading into the Indian and Pacific Oceans and gradually mixing with the Antarctic Bottom Water flowing northward.

What drives thermohaline circulation? Name the two ocean water properties that are involved.

Thermohaline circulation are deep ocean currents that are driven by changes in water density due to variations in salinity and temperature.

a) Consider turbidity currents that occur on continental margins. What physical features or factors are needed to create a turbidity current? Think about what is in it, what triggers it, what drives it.

To create a turbidity current there needs to be a slope such as the edge of the continental shelf or the continental slope itself that has accumulated unstable sediments and an occurrence that breaks the sediment loose such as an earthquake or a large discharge of sediment by a river as well as a slope that the sediment can continue to move down.

Wind blowing across the surface of the North Pacific Ocean moves the ocean water ____.

To the right of the wind direction

Because deep-water wave celerity (speed) depends upon wavelength, longer waves ____ than shorter waves.

Travel faster

b) Referring to your answer in (a), where on continental margins are they more likely to occur? (There are several good answers to this.)

Turbidity currents may be likely to occur on continental shelves near plate boundaries. Plate boundaries usually include lots of earthquakes that can then trigger the avalanche of sediment needed to produce the turbidity current.

a) Explain what water masses are.

Water masses are large sections of water that sink and rise depending on their density due to differences in temperature and salinity.water masses are also defined by their temperature and salinity. We cannot say they have a uniform temperature and salinity (not strictly true) so instead the definition points to a narrow range that characterizes them: a "characteristic temperature and salinity".

a) What effects do waves have on the size and location of barrier islands?

Waves from the longshore current create spits of land that are high enough to cause a barrier island between the mainland and the rest of the ocean. Waves from strong storms raise the sea level which erodes sand from the beach which is then carried by the waves to the barrier island. Waves contribute to the location of the islands by eroding easily eroded coasts and carrying the sediment to the barrier to increase its size.

Beaches typically extend ___ in winter, compared with summer.

a shorter distance out to sea (narrower beach)

Which ocean basin contains Circumpolar Deep Water (CDW)?

a. Atlantic b. Indian c. Pacific d. all of the above

A lagoon is ____.

a. a sheltered area between a barrier island and the mainland b. a sheltered area enclosed by coral reefs c. a habitat for the young of some marine species

Upwelling occurs in which of the following?

a. along the equator b. where surface waters are moving away from the coast c. along the eastern sides of ocean basins d. all of the above

Coastal wetlands are important because they ____.

a. are nurseries for coastal and estuarine organisms b. support salt tolerant grasses c. absorb energy from storms

Once winds set the surface water in motion, the forces and features acting on the water to change its speed and direction is(are) ____ .

a. basins and coasts b. friction c. the Coriolis Effect d. all of the above

Wind blown dust ____.

a. can reach any part of the ocean b. is supplied by desert regions of the world c. is found as deep-sea red and brown mud far from land d. is found in a narrow range of grain size

Manganese nodules are marine sediments that are ____.

a. chemically precipitated from ocean water b. found on the ocean floor far from shore, away from influx of lithogenous sediments c. found under relatively unproductive ocean surface regions so biogenous sedimentation is low

Longshore drift can be interrupted by ____.

a. coastal armoring structures such as groins b. submarine canyons c. headlands d. rocky shores

Water movement sorts sediment grain sizes by ____.

a. depositing the larger sediment grains when water flow slows down b. resuspending (picking up) smaller sediment grains from the seafloor when water flows faster

North Atlantic Deep Water (NADW) ____ .

a. forms mainly in the Greenland and Labrador Seas b. is the most abundant deep ocean water mass c. sinks in the North Atlantic but rises around Antarctica d. mixes with CDW

Turbidity currents ____.

a. have been known to cut telegraph cables on the ocean floor b. can flow relatively long distances (hundreds of km) c. are sufficiently powerful to erode submarine canyons on the continental slope d. can travel up to 70 km per hr

Ekman transport is ____.

a. movement of surface water in response to wind b. toward the right in the northern hemisphere and toward the left in the southern hemisphere c. a result of the Coriolis Effect d. all of the above

Deep-sea clays are most common ____.

a. on the abyssal plains b. where nothing else accumulates c. below the CCD

Particles may reach the ocean floor faster by ____.

a. physically or chemically aggregating into larger particles b. being ingested by zooplankton and repackaged as faster sinking fecal pellets

Non-astronomical factors affecting ocean tides include(s) ____.

a. presence of continents b. Coriolis Effect c. coastal configuration

A common problem with harbors built on straight coastlines is ____.

a. sand buildup inside the harbor from longshore drift b. a sand spit growing across the entrance from longshore drift c. shoreline erosion next to the harbor from longshore drift

Coral reefs may die due to ____.

a. sea level rising faster than the coral can grow upward b. sinking seafloor that carries the coral too deep for photosynthesis c. turbid water that filters sunlight

Water masses are classified based on ____ .

a. source region c. relative depth in the ocean where they reach equilibrium with their surroundings

Surface circulation tends to be stronger, more variable, and energetic because of ____ .

a. surface winds

Below the "carbonate compensation depth" (CCD), ____.

all of the carbonate sediment that reaches the seafloor is dissolved

Coastal upwelling is caused by wind blowing ____.

along the coast line

During evaporation of seawater, the dissolved salts ____.

are left behind in the surface waters

Most deep-ocean water masses form ____ .

at high latitudes

Internal waves form ____.

at the interface between layers of water where there is an abrupt change in gradient at the base of the pycnocline or mixed layer

In an undisturbed sequence of ocean sediment, the youngest sediment is ____.

at the top of the sequence

When wave trains move into shoaling water and come ashore along a coast or island, the wave condition is known as ____.

breakers and surf

Most biogenous sediments are made up of ____.

calcium carbonate or silica

Viewed from above, subtropical gyres rotate ____ in the Northern Hemisphere and ____ in the Southern Hemisphere.

clockwise....counterclockwise ...

Today, sedimentation rates are highest ____.

close to land

Coastal upwelling produces ____ sea surface temperatures.

cooler

Because of ocean chemistry, including the solubility of carbon dioxide in seawater, calcareous oozes ____.

cover the tops of undersea mountains

Beach sediment in a protected bay is expected to be ____ than beach sediment on a headland.

finer grained

In general, the size of sediment grains ____.

decreases from the shoreline to the deep ocean and is smaller in the deep ocean

If a wave on the ocean has a wavelength of 200 m, the wave is a deep-water wave only if the water is ____.

deeper than 100 m

In general, rivers that flow into estuaries ____ transport much sediment to the ocean.

do not

Deep water ____ form in the Pacific Ocean basin.

does not

Waves traveling across an ocean basin cause movement of _____ over long distances.

energy

Surface currents on the western side of the subtropical gyres are ____ than their eastern counterparts.

faster

An onshore wind blows _____.

from the ocean toward the shore

The restoring force that works on larger waves to return the ocean to a flat surface is ____.

gravity

When winds strengthen, waves become ____.

higher with faster speeds and longer wavelengths

Particles that precipitate from seawater, such as evaporites, are known as ____ sediments.

hydrogenous

Most siliceous oozes are found ____.

in the tropics d. in the polar regions

The carbonate compensation depth (CCD) ____.

is controlled by the amount of dissolved carbon dioxide in the water

The wave base ____.

is the depth below which a wave does not cause significant water motion

Which of the following coastal structures disrupt longshore drift (littoral drift) and the natural flow of beach sediments?

jetties

For the same wind speed, higher sea waves are generated for ____ fetch.

longer

b) Explain how and where water masses form (in general).

new" water masses form at the ocean surface in contact with the atmosphere. The climate of the region sets their temperature and salinity (by warming, cooling, evaporation, precipitation, freezing), and that is why they are often named after that source region. The temperature-salinity properties are retained if the water mass sinks below the surface, and change only very slowly by diffusion.

Upwelling occurs along the California coast when surface winds blow from the ____ .

north

The trade winds blow from the ____ in the Northern Hemisphere.

north east

Ocean tides are caused by the gravitational attraction ____.

of the Sun and the Moon on the Earth

For waves propagating through relatively deep water, the nearly circular orbits of water particles weaken with increasing depth. Waves essentially disappear at a water depth of ____ the wavelength, known as the wave-base.

one -half

Sand dunes are formed when ____ move the sand up the beach.

onshore winds

The color of red clay is due to ____.

oxidation of iron

In both the Northern Hemisphere and the Southern Hemisphere, western boundary currents transport heat toward the ____ .

poles

Barrier islands are of great importance because they provide ____.

protection for mainland coastal structures from storms and waves

Sediment commonly found in the central basin of the ocean is ____.

red clay

Today, evaporites form in the ____.

red sea

In order to balance all the water coming into a beach by breaking waves, ____ return(s) water seaward.

rip currents

The largest amount of sediment from land reaches the ocean via ____.

rivers

Lithogenous sediments are basically ____.

rocks and fragments of rock

An ocean surface consisting of a confused mass of sharp crested waves moving in many different directions is known as ____.

sea

Salinity in the ocean's surface waters can be increased by ____.

sea ice formation (freezing)

The most famous river delta in the U.S. is the Mississippi Delta. River deltas in Alaska include the Copper River Delta and the Yukon-Kuskokwim Delta. A river delta forms because ____.

sediment has filled in the river valley out to the ocean

Astronomical tides behave as ____.

shallow-water waves

When they reach a shoaling coast or island, tsunamis ____.

slow, shorten, and grow in height

Waves that continue to propagate beyond the area of strong storm winds are known as ____.

swell

Semi-diurnal and diurnal tides do not have periods of exactly 12 and 24 hrs because ____.

the Moon orbits the Earth

The majority of tsunamis are triggered by tectonic events in ____.

the Pacific Ocean "ring of fire" subduction zones

The main factor in the amount of siliceous sediment on different areas of the seafloor is ____.

the amount of siliceous organisms in the surface waters

Wind fetch is ____.

the distance the wind blows over a continuous water surface

Wave refraction is caused by _____.

the shape of the seafloor

Orbital velocity in an ocean wave refers to ____.

the speed of circular particle motion in the wave

When the crest of one wave intersects or crosses the crest of another wave, ____.

the two wave crests combine into a higher wave crest

a) When shallow-water waves approach a shoreline, how do the waves' characteristics change? Think about the overall wave shape and behavior, not particle motion inside the wave. (Figure 1 from Lab 6A might be useful)

the wave slows (friction with the seafloor) and wavelength shortens (wave is compressed into a shorter distance when it slows down) . The third major change is that the wave height increases (some of the energy goes up instead of forward). Think of a tsunami.

When deep-water waves approach shallower water and start to "feel" the bottom, _____.

their wave height grows

Ekman transport causes surface water to move ____ the center of a subtropical gyre.

toward

The prevailing surface winds over the tropical ocean are the ____.

trade winds

Coastal ____ occurs where Ekman transport moves surface water away from the coast.

upwelling

The main factor in the amount of calcareous sediment on different areas of the seafloor is ____.

variations in seawater composition that affect how fast the calcareous particles dissolve

Deep-ocean currents are driven by ____.

water density

The term thermohaline refers to the seawater properties that control water movement through ____.

water density

The speed of shallow-water waves depends upon gravity and ____.

water depth

The celerity (speed) of deep-water waves depends upon gravity and ____.

wavelength

In a large ocean gyre, the narrower, faster-moving currents are on the ____ boundary.

western

Surface currents in the ocean are driven by ____.

wind