ocean final 1st half
Where would you expect to find the following types of sediment and why? Red clay, Siliceous ooze, Carbonate ooze, Coarse-grained sand, Mn nodules
Red clay: aeolian dusts are terrigenous sediments carried from deserts by the wind, sometimes 1000s of km out to sea. So they are found in ocean interiors, away from margins, and in deeper waters (in the abyssal plains), where there are isn't much sediment dilution by other kinds of sediments. Red clays accumulate very slowly, so if other sediments are present, those others dilute out the red clays easily. Siliceous ooze: found especially around Antarctica, along Pacific coast of America, along equator, in Southern Ocean (lots of divergence or upwelling, and productivity) where diatoms with their silica frustules (shells) occur. Carbonate ooze: found along high locations in the oceans like spreading zones, because calcium carbonate dissolves more with increased pressure and decreased temperature (deeper waters); and because deep waters have more CO2, are more acidic, and so tend to dissolve calcium carbonate below the lysocline. Coarse-grained sand: nearer the coastlines, usually on continental shelves (terrigenous, neritic sediment) where riverine inputs to the oceans occur, and where wind, glaciers, and coastal erosion take these sediments off the coast. Coarse grained sediments remain close to their sources because they have high sedimentation rates (accumulate quickly on the sea floor). Mn nodules: a hydrogenous sediment formed by precipitation of the minerals directly from seawater often onto bones, shark teeth, or other particles. They are found in the deep ocean, where accumulation of sediments is slow, sometimes mixed with red clays.
Would a nutrient-type element have a higher concentration in the surface ocean or the deep ocean? Why? Now, think about the circulation of the deep ocean. Would nutrient-type elements have higher concentrations in bottom water found in the North Atlantic or the North Pacific Ocean? Why?
A nutrient-type element would have a higher concentration in deep ocean. Now, many may think that it would be in shallower water, because that is where all of the deposit(s) ends up. However, there is more nutrient type water in the deep ocean because of the circulation of the ocean; and the fact that there are numerous phytoplanktons that surface the shallow parts of the ocean and deplete it of all nutrients. Meaning that the layover or the rest of those deposits fall to the seafloor once the phytoplanktons and other animals have finished. Therefore, it is more likely that the North Atlantic would have higher concentrations of nutrient-type elements, because in the North Pacific Ocean you are dealing with a slow warm water current that flows from east to west and it considered to be a subtropical gyre. Now, if there is anything I have learned it is that gyres equal down-welling, which results in a lower concentration level of nutrients.
What is a trophic cascade? Give an example of a marine trophic cascade and note what the keystone species is.
A trophic cascade is a phenomena triggered by the addition or removal of a top predator. In the kelp forest, the sea otter is the keystone species where as if it was removed, populations of sea urchins would rapidly increase causing kelp abundance to severely decrease because the sea urchins feed on kelp.
Explain why water masses sink and how you could alter the water masses to change the rate at which they sink.
A water mass is a body of water identified by its temperature and salinity from the surface of the water down to great depths. The main driving force of water masses is its density, which is the result of the water's temperature and salinity, referred to as thermohaline circulation. Water with increased density will sink, and with lower density will rise to the surface. Colder water is more dense than warmer water, and salty water is more dense than fresh water. It's important, however, to also keep in mind that frozen water (ice) is less dense than liquid water, which is why ice floats. The forming of ice near the poles can lead to something called brine rejection. Brine rejection is when the sea water freezes and the salt is forced out of the forming ice, which creates saltier, more dense water, which sinks to the bottom. Near the equator, the water is much warmer, which leads to evaporation. But only the fresh water is evaporated, and when this occurs, it leaves behind saltier, more dense water (which also sinks). On the other hand, in places where there is a lot of precipitation, the salty water is diluted and therefore less dense. The differences in densities of water masses creates these deep currents that are constantly on the move. Think of it as a huge conveyor belt that connects all of the oceans. And if you want the water masses to sink faster or more often, add more salt, decrease the temperature (but don't freeze it), or evaporate some of the fresh water out.
As you move away from a methane seep the benthic organisms change. Describe how they change and explain why.
At the methane seep there is a high flux of methane through the sediments. As methane moves through the sediments it interacts with sulfate and sulfide is produced. Sulfide is extremely toxic to living organisms. In areas of high methane flux sulfide is not completely broken down by sulfide oxidizing bacterias leaving sulfide present in the surface. These anaerobic environments are highly toxic and only sulfide oxidizing bacteria can survive here. As we move away from the see the flux of methane begins to decrease to where sulfide is not present in the surface waters. Epifaunal organisms are able to survive, often in a symbiosis with sulfide and methane oxidizing chemotrophic bacterias. As we move farther from the seep the level of anaerobic oxidation of CH4 creeps downward allowing for infaunal organisms to take hold as sulfide is completely oxidized lower in the sediments. Clams and mussels begin to take hold. The environments of low methane flux, farthest from the seep, are aerobic environments and can support a larger variety and diversity of life. Overall, the rate of methane flux from the seep determines the distribution of the biology around the seep.
Since 2002 periods of coastal hypoxia have occurred off Oregon in most summers. What is coastal hypoxia, why does it occur, and how does it impact the marine biology?
Coastal hypoxia occurs when the water oxygen levels along the coast drop below about 2 mg/l. When this happens, there is not enough oxygen in the water to sustain life and the water becomes a "dead zone" where no organisms can survive. There has been a pattern of coastal hypoxia off Oregon during summers ultimately due to the north originating winds of the California current. These winds blow along the Oregon coast from north to south, which causes Ekman transport to pull surface water away from the Oregon coast. This causes upwelling along the coast as deep sea water comes to the surface in order to replace the lost surface water. This deep sea water also brings nutrients to the surface. The increased availability of nutrients, drives increased primary production through photosynthesis. As more organic matter is created, the more respiration takes place and the more oxygen is used up from the water. At some point, the rate of respiration exceeds the rate at which oxygen can be replenished and the zone's oxygen is used up. This creates a hypoxic zone. Costal hypoxia effects marine biology as it essentially creates a toxic zone. As the oxygen levels start to drop below 5 mg/l larger organisms, such as fish, have trouble breathing and leave the area. As the hypoxic zone grows and oxygen levels continue t decrease, organisms either escape the area or suffocate due to lack of oxygen. Below 2 mg/l, no organisms can survive. Hypoxia therefore destroys the ecosystem of an area and can keep it from rebuilding for months. It very negatively effects the marine biology off the Oregon coast.
What is coral bleaching, how is it caused and is it fatal to the coral?
Coral bleaching is when the symbiotic zooxanthellae that provide coral with photosynthetic energy (and color) become stressed, usually as a result of increasing temperature, and are expelled from the coral polyp. The vibrant color of reef building corals comes from the zooxanthellae, so when they are expelled the coral appears white, thus the term "bleaching". This can be fatal to coral if the environmental conditions remain unfavorable, but if they return to a condition habitable to the zooxanthellae in time, the symbiont may resume symbiosis, allowing the coral to survive.
Why does more carbonate sediment accumulate in the Atlantic Ocean versus the Pacific Ocean? Explain your answer in detail.
I believe that more carbonate sediment accumulates in the Atlantic Ocean versus the Pacific Ocean because the Atlantic Ocean has a deeper carbonate compensation depth than the Pacific Ocean. One of the main reasons that the Atlantic Ocean has a deeper Carbonate Compensation Depth is because the Atlantic Ocean is less acidic than the Pacific Ocean. Carbonate Sediment is more sensitive to acidity and is dissolved faster by a more acidic environment. Also because of Primary Productivity activity in the coastal areas of the North Pacific when there is phytoplankton die off in the fall, the production of carbon is higher at that time. While this does not occur in the coastal areas of the North Atlantic, the carbon levels are lower. So along with lower carbon levels and lower acidity in the North Atlantic, the carbonate sediment levels accumulate deeper in the North Atlantic Ocean, than in the North Pacific.
How does increasing atmospheric CO2 concentrations lead to the warming of the planet? What is this called?
Increased atmospheric CO2 leads to a warming of the planet because of the way that it traps solar radiation. CO2 in the atmosphere is transparent to the short-wave radiation coming in from the sun, but is able to absorb the long-wave radiation coming back from Earth's surface. This process is known as the greenhouse effect and results in climate change by global warming. CO2 concentrations have spiked since the industrial revolution and humans are the leading cause. The burning of fossil fuels and deforestation greatly add to this, but there are also natural causes, such as volcanic eruptions.
What is Meridional Overturning Circulation? Knowing this, where do you find the oldest ocean waters?
Meriodional.png The Meridional Overturning Circulation is the global current that moves cold, dense, nutrient-rich water from the deep in high latitudes to low latitudes. The formation of this deep water occurs in the North Atlantic (in the area of the upper red circles) and the Weddell Sea (the area of the lower red circle). This circulation also transfers heat from the low latitudes to the high latitudes via the warm, surface water current. One full circulation takes about 1,000 years. This would mean the oldest ocean waters are found in the Pacific Ocean. *The reason I added the screenshot of the circulation pattern is because when I tried to describe it on the quiz it was slightly confusing.
What are methane hydrates, where are they typically found, and what controls their formation?
Methane Hydrates are ice-like solids with gas that are surrounded by water. Low temperature, high pressure, and methane are required for one to form. They are typically found along continental margins, or on plate boundaries. Their formation is controlled by the trapping of methane molecules by frozen water. Methane hydrates form when microorganisms that live deep in the sediment slowly convert organic substances to methane.
What is the difference between ontogenetic vertical migration and diel vertical migration (DVM)? Why do some organisms carry out DVM?
Ontogenetic vertical migration is the movement through the water column throughout different life stages. For example a crab larvae growing in the pelagic water column and eventually settling on the ocean floor. Diel Vertical migration is a migration by fishes, usually in concert with the setting and rising of the sun, up and down in the water column. Most common is migrating up as the sun sets to feed at night then migrating back down as the sun comes up to stay hidden. The purpose of DVM is mostly simple. It is a way for fish to feed under the safety of darkness during the night at or near the surface and then avoid predators during the day by migrating back down.
What are the most important nutrients (i.e., macronutrients) required by phytoplankton? If you are a diatom what other nutrient do you need? Name one important micronutrient.
Phosphate and nitrogen, usually in ion form (PO43- and NO3-) are the two macronutrients vital to all phytoplankton. In addition to these, diatoms also need silica, usually in silicate ion form (SiO44-) in order to form their silica frustules. Iron is an important micronutrient that can be limiting in some areas, such as high nutrient low chlorophyll (HNLC) areas.
What are phytoplankton? Name four common types of phytoplankton and give one unique characteristic for each.
Phytoplankton are single-celled organisms that are autotrophic, meaning they produce their own food supply. They are able to due this through the process of photosynthesis, meaning they can gather inorganic materials and sunlight to produce glucose. They capture sunlight in their variety of different pigments, such as chlorophyll a which is the most common. They are the defining factor in the primary production of a region because they produce the biomass needed to measure it. Phytoplankton have four common types with distinctive features to distinguish between them. Cyanobacteria are photosynthetic bacteria that created the atmosphere we have on earth today. They are one of the earliest forms of life on the planet and today they are most abundant in the open ocean, where nutrients are low. To compensate for this, some species can "fix" nitrogen to give them the nutrition they need to survive. Another type of phytoplankton are the coccolithophorids. These organisms contain cell walls which contain calcium carbonate. The calcium carbonate form plates surrounding the organism called coccoliths. As the organism dies, their skeletons can form what's called a carbonate ooze. This typically happens after a large bloom occurs when conditions are right for them, such as right amount of sunlight and perfect water temperature mixed with plenty of nutrients. Another phytoplankton species are the dinoflagellates. They are similar to coccolithophorids because they also contain a cell wall, however their walls are made of cellulose. They also contain two flagella, one around their middle like a belt, the other out of their bottom, which aid them in movement. These organisms are the most likely out of all of the phytoplankton to contain bioluminescence or to form a dangerous harmful algal bloom (or an HAB). Lastly, diatoms are another form of phytoplankton. These organisms also contain a rigid cell wall, called a frustule, made of silica. It consists of two parts that fit together like a pill box. These organisms can either reproduce sexually or asexually. When the latter occurs, the organism splits into its two halves and connect to the other halves of other organisms, forming two new members. This does, however, cause the overall size of the organisms to diminish over time. They are also photosynthetic and form chains when doing so. When conditions are not favorable for photosynthesis, the organism will form what is called a resting spore and sink to the sea floor until conditions improve.
Community composition and intertidal zonation is dictated by what factors? Give examples of how each influence the type of organisms that are found.
The Intertidal zone is located on the shoreline between high and low tide. Communities can be very diverse within the intertidal zone. Depending on where they are located, organisms are subject to threats such as drying out, predation, sunlight and waves. In this area, organisms have adapted to be able to live there. In the upper area, sunlight is a big threat. To prevent drying out, barnacles have a calcium carbonate exoskeleton that keeps them safe while not submerged. Organisms such as sea urchins and anemone prefer to stay wet, and are found deeper. Mussels clump together to help deal with wave activity, because waves also influence zonation. Predation is also a serious threat to marine life. When tides recede, birds can prey on sea life that is exposed. Also, sea stars are predators that generally live in the lower littoral zone. They come up and snack on urchins and shellfish. Zonation depends on what type of stresses are placed on that shoreline. The organisms adapt to harsh conditions in order to survive there.
What is the Pacific Decadal Oscillation and how does it influence marine productivity along the west coast of North America?
The Pacific Decadal Oscillation (PDO) refers to a fluctuation of eastern North Pacific sea surface temperatures operating on cycles of 20 to 30 years. Periods with above normal mean temperatures are known as positive phases while periods exhibiting cooler temperatures are referred to as negative phases. The primary determinant of these phases is the strength and position of a low pressure system in the Gulf of Alaska known as the Aleutian Low. A stronger Aleutian Low is associated with a positive / warmer PDO and results in more water being directed north into the Alaskan Current and less water flowing south into the California current. Due to the diminished California current during positive phases, coastal upwelling along the west coast of the US is reduced, leading to lower nutrients in surface waters. As a consequence of this occurrence, productivity along the west coast is lower than normal. However, positive PDO phases result in open ocean upwelling in the Gulf of Alaska, leading to an abundance in nutrients and higher primary productivity in this location. During positive PDO phases, salmon are more abundant in the waters near Alaska but decrease in numbers off the west coast, while sardines increase in population off the California coast. A negative / cool phase PDO is associated with a weaker Aleutian Low. During these periods, more water is directed into the California current and sea surface temperatures in the eastern Pacific decrease. As a result of a stronger California current, coastal upwelling increases along the west coast. This occurrence leads to higher levels of productivity along the west coast as well as an abundance of salmon in the region. Additionally, the waters off the California coast also experience higher levels of anchovies.
What is the Wilson Cycle? Now explain why the Atlantic Ocean is getting bigger and the Pacific Ocean is getting smaller. Reply
The Wilson Cycle is a series of 6 stages that defines how an ocean basin is formed and then eventually destroyed by plate tectonics. The first stage is the embryonic stage in which the mantle pushes up on the crust, causing it to thin and split apart. The juvenile stage sees ocean crust forming as the 2 land masses (plates) slowly separate and water fills in the rift area. During the mature stage, the ocean basin is large and growing larger as new oceanic crust is continuously made at the rift. This is the stage that the Atlantic Ocean is currently in. The declining stage occurs when the ocean basin becomes smaller due to the plate with oceanic crust subducting under the more buoyant continental plate. The destruction of the Pacific Plate as it is subducted under the North American plate is causing the Pacific Ocean to slowly shrink in size. Eventually, the continents on the west side of the Pacific Ocean will grow closer to the Americas. As the ocean crust becomes fully subducted and the continents begin to collide, the ocean basin will disappear. This is the terminal stage of the Wilson Cycle. The suturing stage takes place as the two continents smash against each other and form large mountain ranges.
What is the surface zone with enough light for photosynthesis called. Would you expect this zone to be deeper in coastal regions or in the open ocean? Why?
The surface zone with enough light for photosynthesis is called the Euphotic zone. The high density of suspended particulate matter in the coastal regions forms a euphotic base that is much higher in the water column (only 15 m to 20 m in some areas). However, in the deep ocean where there are less particles to obscure the light, the Euphotic zone can reach up to 200 m.
What three factors controls how large waves get? Knowing this, would you expect larger waves in the Pacific Ocean or the Mediterranean Sea? Why?
The three factors that control the size of the waves are the duration of the wind, the fetch (or distance across the water that the wind blows in one direction), and the strength or speed of the wind. Any of these can restrict the size of the waves, regardless of how much the other two factors may promote a larger wave size. If the wind is very strong, but only blows for a short time, then the waves will still be smaller. Even if the wind blows for a long time across a small fetch, the waves will not be large. Between the two, the Pacific Ocean has a much larger surface area than the Mediterranean Sea, allowing for a significantly larger fetch on the Ocean. If both the duration of the wind and the wind speed were equal, it would be expected that the waves produced on the Pacific Ocean would be larger than those on the Mediterranean, as the shorter distance or fetch would limit the size of the waves on the Sea.
Describe the three types of plate boundaries. Give an example of each.
The three types of plate boundaries are divergent, convergent, and transform boundaries. At divergent boundaries, two lithospheric plates move away from each other. Mantle upwelling occurs at these boundaries, which creates new crust at a rate of between under 1 cm to 18 cm a year. Divergent boundaries on the seafloor form new oceanic crust as mantle upwelling occurs, forming mid-ocean ridge basalt, or MORB. On continents, this forms rifts and rift valleys. An example of this form of plate boundary is the Mid-Atlantic Ridge. Convergent plate boundaries are where lithospheric plates collide into each other. These are split into three types: ocean-ocean convergence, ocean-continent convergence, and continent-continent convergence. At ocean-ocean convergent boundaries, the plate that is colder, older, and denser subducts under the other. These boundaries are associated with the formation of island arcs, like Japan, and the deepest trenches in the ocean. At ocean-continent convergent boundaries, the oceanic plate subducts below the continental plate since the former is denser than the latter. This forms oceanic trenches and is associated with mountain-forming, volcanoes, and Earth's strongest earthquakes. The Cascade Mountain Range is one geographic feature that arose from an ocean-continent convergence. At continent-continent convergent boundaries, the two meeting plates are compressed together, folded, and lifted, forming mountains like the Himalayas. The last form of plate boundaries, transform boundaries, occur where two plates move in opposite directions past each other. These can occur on continents or in oceans where they connect regions of seafloor spreading. At these boundaries, Earth crust is not destroyed or formed as the plates are not colliding into or diverging from one another. Transform boundaries are associated with shallow and severe earthquakes that occur relatively frequently. One notable example of this boundary type is the San Andreas Fault.
Describe the ways we can map the bathymetry of the ocean.
There are three ways we can map the bathymetry of the ocean: 1) Use of hand line with a weight; 2) Use of sound through an echo sounder and/or multibeam/side-scan sonar; or 3) Via satellites. The first method is antiquated and no longer used. With sound, generated by an echo sounder or multibeam or side-scan sonar, depth is a function of the time it takes a pulse of sound to travel from the surface to the seafloor and back. Multibeam sonar gives us a picture of the seafloor much faster than an echo sounder, as it uses multiple beams of sound. (We can also identify what's below the seafloor with sub-bottom profiling, which uses more powerful sources of sound.) We can also map features of the seafloor with satellites. Via satellite we can measure the height of the sea surface. This lets us know what's on the seafloor because large features pull water towards them, due to their increased gravity.
Describe the physical differences between active and passive continental margins. Where would we find a passive margin and where would be find an active margin.
There are two basic types of Earth's crust: oceanic crust composed of basalt and continental crust mostly made of granite. When continental crust is found at the submerged edges of continents, this is referred to as a continental margin. Continental margins are divided into two types: active or passive. Active continental margins are found at a plate boundary. Active continental margins are "active" because subduction is occurring, where one lithospheric plate is being forced under another. When examining an ocean basin cross section, an active continental margin exhibits a narrow continental shelf, followed by a dramatic continental slope, and little or no continental rise; rather the slope may end in an oceanic trench where the subduction is occurring. Beyond the oceanic trench lies the abyssal plain, or seafloor. Passive continental margins occur not at a plate boundary. Passive continental margins are "passive" because there is no subduction taking place. Upon inspecting an oceanic basic cross section, a passive continental margin can be identified by rather flat features: a wide continental shelf, an easy continental slope, and a gradual continental rise leading to the abyssal plain. An example of where to find an active continental margin would be along the west coast of the U.S., such as Oregon, where oceanic plates are being subducted below continental plates. We would find passive continental margins along the east coast of the U.S., such as New Jersey, where there is no plate subduction occurring.
Which species (Blue fin tuna, Orange Roughy, or White Shark) do you think would form the best basis for a fishery? Why?
This question ended up being a little more difficult than I thought it would be. If I had to choose one species that would form the best basis for a fishery between Blue fin tuna, Orange Roughy and White Sharks, I would choose the Orange Roughy. The reason that I say it was difficult to choose between the three is because none of the species are classic r-selection species. Each of the species take more than 8 years to reach sexual maturity which doesn't make the best fishery basis. The reason that I chose the Orange Roughy is because even though they can't reproduce until they are 20 years old (they live for over 100 years), they are able to produce over 20,000 eggs each time they lay. The time it takes from fertilization to hatching is only around 20 days which is very quick. I think this is what makes the Orange Roughy more of an r-selection species than the Blue fin tuna and the White Shark. The Orange Roughy has high offspring rates, they can reproduce quickly after they mature, they have a short gestational period and they produce multiple young.
Compare and contrast western and eastern boundary currents? Name two western boundary currents and two eastern boundary currents.
Western and eastern boundary currents are the currents that form the western and eastern sides of the main open ocean gyres. These gyres are forms as a result of the interaction of prevailing winds (such as the trade winds) and the Coriolis effect, as well as the geostrophic flow of water from the center of the gyres outward. Because of these factors, gyres rotate, and the western and eastern boundary currents are set up. Western boundary currents carry warm water from the equator toward the polar regions, and eastern boundary currents carry cold water from the polar regions toward the equator. In addition to temperature differences, western and eastern boundary currents differ in their intensity. Because of the rotation of the earth, "western intensification" occurs, which piles up water on the western sides of gyres and causes western boundary currents to be deeper, narrower, and faster than eastern boundary currents and allows them to carry more water. By contrast, eastern boundary currents are shallower, slower, and, broader. Eastern boundary currents are often associated with seasonal coastal upwelling, bringing cold nutrient-rich water to the surface which greatly increases primary production. Examples of western boundary currents: Gulf Stream (North Atlantic Gyre) Kuroshio Current (North Pacific Gyre) Examples of eastern boundary currents: California Current in the North Pacific (our local boundary current along the west coast of the United States) Chile-Peru Current (South Pacific).
Why is the ocean capable of holding 50x more CO2 than the atmosphere? Hint - think about what happens to CO2 when it dissolves in seawater.
When CO2 reacts with sea water, it forms carbonic acid as well as bicarbonates/carbonate ions. This diffusion of gas into non-gaseous forms releases the CO2 pressure. Many marine plants (i.e. phytoplankton) require CO2 and convert it into oxygen, providing for the ecosystem.
