Oceanography MCQs for UPPSC (UP) Exam

Neither of the statements is correct.

1. The first statement is incorrect. During annual or sporadic floods, it is not the hard materials that are spread over the low-lying adjacent areas, but rather a mixture of sediment, silt, and other organic material carried by the floodwaters. These materials are usually fine-grained and easily transported by the flow of water. As the floodwaters recede, they deposit this sediment, gradually building up layers of sediment over time. Levees, on the other hand, are natural or man-made embankments that are formed along the sides of a river to prevent flooding. They are not formed by the deposition of hard materials during floods.

2. The second statement is also incorrect. A floodplain is a flat or gently sloping area adjacent to a river that is periodically flooded. It is not formed by the accumulation of deposits in the riverbed or the dropping of material on the sides. Instead, a floodplain is formed over a long period of time as the river naturally meanders and changes its course. As the river meanders, it erodes its banks and deposits sediment on the floodplain, creating a flat and fertile area. The accumulation of sediment in the riverbed does not result in the formation of a floodplain.

To summarize, neither statement is correct. Floodplains are formed by the natural meandering of rivers and the deposition of sediment over time, not by the accumulation of deposits in the riverbed or the spreading of hard materials during floods. Levees, on the other hand, are embankments formed along the sides of a river to prevent flooding and are not formed by the deposition of materials during floods.

A positive movement occurs when there is a depression of land or a sea level rise. This will submerge the lands along the coast, drown' the valleys, and weaken the river's erosive power. The flow is checked, and large quantities of sediment will be dropped.

The correct answer is option 'C' - Both of them.

Explanation:

Statement 1: The flood plains of large rivers with their thick mantles of fine silt are some of the richest agricultural areas of the world.
The flood plains of large rivers are typically formed by the deposition of sediments such as silt, clay, and sand during floods. These sediments are rich in nutrients and make the soil very fertile. The fine silt in particular is known for its high fertility and ability to retain moisture. As a result, the flood plains of large rivers are highly suitable for agriculture and are considered some of the richest agricultural areas in the world. Farmers in these areas can grow a wide range of crops, including rice, wheat, maize, and vegetables. The fertility of the soil allows for high crop yields, making these areas economically important for food production.

Statement 2: They may support very dense populations and a chain of large cities may be strung along their banks.
The rich agricultural resources provided by the flood plains of large rivers often lead to the development of dense human settlements and the growth of cities. The fertile soil supports intensive agriculture, which in turn can support larger populations. The availability of food and water resources from the rivers facilitates the growth of settlements along their banks. These settlements may start as small villages, but as the population grows and agricultural production increases, they can evolve into larger towns and cities. Examples of large cities that have developed along the flood plains of rivers include Cairo along the Nile River, Dhaka along the Brahmaputra River, and Bangkok along the Chao Phraya River.

Conclusion:
Both statements 1 and 2 are correct. The flood plains of large rivers are indeed some of the richest agricultural areas in the world due to their fertile soil, and they often support dense populations and the growth of cities along their banks.

Guyots are underwater mountains in the sea. They are flat-topped seamounts that were once volcanic islands but have since sunk beneath the ocean surface. Guyots are formed through a process known as subsidence, where the seafloor gradually sinks due to various geological processes.

Underwater mountains:
- Guyots are underwater mountains that were once above the ocean surface but have sunk over time. They are typically found in the deeper parts of the ocean and have a distinct flat top, which is often covered in sediment and coral reefs.

Formation:
- Guyots are formed through a series of geological processes. Initially, they start as volcanic islands that are formed by volcanic activity. Over time, due to various factors such as tectonic plate movement, the seafloor beneath the volcanic islands begins to sink.

Sinking process:
- As the seafloor sinks, the volcanic island gradually submerges beneath the ocean surface. The sinking process can take millions of years. During this time, erosion and sedimentation occur, resulting in the flat top and gradual filling of the central depression of the guyot.

Characteristics:
- Guyots typically have a flat top, which is believed to be the remnants of the once-exposed land surface. The flat top is often covered in sediment, shells, and coral reefs. The central depression of the guyot may contain remnants of coral reefs or be filled with sediment.

Comparison to Grand Canyon:
- Option B, which states that guyots are deep valleys comparable to the Grand Canyon of Colorado, is incorrect. The Grand Canyon is a terrestrial feature formed by the erosion of the Colorado River over millions of years. Guyots, on the other hand, are underwater mountains formed through volcanic activity and subsequent subsidence.

Conclusion:
- In summary, guyots are underwater mountains in the sea that were once volcanic islands but have sunk beneath the ocean surface over time. They have a distinct flat top and are formed through the process of subsidence. Unlike deep valleys like the Grand Canyon, guyots are submerged features found in the deeper parts of the ocean.

The discovery of some modem hydrothermal systems in the deep oceanic realm along the mid-ocean ridges has kindled a lot of interest primarily on account of the high concentration of base metals (Cu and Zn) and many noble metals (Au, Ag, Pd, Pt) in them.

Understanding the Assertion and Reason
The question presents an assertion and a reason regarding sea levels and ocean connectivity. Let's break down both statements.
Assertion (A): The level of the sea remains almost the same everywhere.
- This statement is generally considered correct in the context of large-scale ocean levels.
- While there can be local variations due to tides, weather, or geographical features, the overall average sea level tends to be consistent across vast areas of the ocean.
Reason (R): All the oceans of the world are interconnected with each other.
- This statement is also correct. The world's oceans are indeed interconnected through various channels and currents.
- This connectivity contributes to the uniformity of sea levels, as water is able to flow and redistribute itself across different ocean basins.
Analysis of the Relationship Between A and R
- Although both statements are correct, the reason does not directly explain the assertion.
- Sea levels can vary locally due to various factors, but the interconnectedness of oceans contributes to a more stable average level across the globe rather than making them uniformly equal everywhere.
Conclusion
Given the above analysis, the correct option is:
- A is correct but R is incorrect.
This means that while the assertion holds true on a broader scale, the reason does not serve as a valid explanation for the assertion. The correct answer is actually c), not a) as initially stated.

Ocean Temperatures

Highest Temperature in Open Seas

- This statement is incorrect as the highest ocean temperature is observed in coastal areas, where the Sun’s rays heat the water near the surface.

Ocean Temperature Decreases with Depth

- This statement is correct as the temperature of ocean water decreases with increasing depth due to several factors like pressure, density, and salinity.

Temperature of Oceans Reduces Near Polar Regions

- This statement is correct as the polar regions receive less sunlight and experience colder temperatures, leading to a reduction in ocean temperatures.

Conclusion

- Option A is the correct answer as statements 1 and 3 are incorrect while statement 2 is correct.

The wind not only produces currents, it creates waves.

Understanding Ocean as a Carbon Sink
The ocean plays a crucial role in regulating the Earth’s climate by acting as a significant carbon sink. This phenomenon is attributed to several interrelated factors:
Large Geographical Coverage
- The ocean covers about 71% of the Earth's surface.
- This vast expanse allows it to absorb a substantial amount of carbon dioxide (CO2) from the atmosphere.
Rich Population of Phytoplankton and Seagrass
- Phytoplankton, the microscopic plants in the ocean, undergo photosynthesis, absorbing CO2 and releasing oxygen.
- Seagrasses, found in shallow marine waters, also contribute by sequestering carbon through their root systems.
- Together, these organisms play a critical role in the biological carbon pump, enhancing carbon storage in the ocean.
Difference in Partial Pressure of Carbon Dioxide
- The partial pressure of CO2 in the atmosphere is typically higher than in seawater.
- This difference drives the diffusion of CO2 from the atmosphere into the ocean, where it can be utilized by marine organisms or stored in various forms.
- The solubility of CO2 in seawater further facilitates its absorption.
Conclusion
- All these factors combined—large geographical coverage, rich biological communities, and the dynamics of CO2 partial pressures—make the ocean a highly effective carbon sink.
- Thus, the correct answer is indeed option D: All of the above. The ocean’s ability to absorb and store carbon is vital for mitigating climate change and maintaining ecological balance.

Explanation:
The correct answer is option 'C' i.e., 1 and 3 only. Let's understand why the other statements are correct and why these two statements are incorrect.

Statement 1: In mountainous coasts, continental shelves are broad.
This statement is correct. The width of the continental shelf varies depending on the topography of the coastline. In mountainous coasts, the continental shelves tend to be broader because the mountains extend underwater, resulting in a wider shelf.

Statement 2: The continental shelf is an underwater landmass which extends from a continent.
This statement is correct. The continental shelf is the shallow submerged extension of a continent. It is part of the continental crust and is located between the shoreline and the continental slope. It gradually slopes down from the shoreline to the deeper ocean floor.

Statement 3: The continental shelves are poor in fish resources as they are shallow.
This statement is incorrect. Continental shelves are actually rich in fish resources. They provide a productive and diverse ecosystem for fish and other marine organisms. The shallow waters of the continental shelves are ideal for the growth of phytoplankton, which forms the base of the marine food chain. This abundance of phytoplankton attracts small fish and other organisms, which in turn attract larger fish. Therefore, continental shelves are often important fishing grounds and support commercial fisheries.

Conclusion:
Based on the above explanation, it can be concluded that statements 1 and 3 are incorrect. The correct answer is option 'C' i.e., 1 and 3 only.

Continental Shelf and Fossil Fuels:
- Continental shelves are the submerged edges of continents that extend from the shoreline to the point where the slope becomes significantly steeper, usually at the shelf break.
- These shelves are rich in sedimentary deposits because of the river sediment load they carry. The sediments are transported by rivers from the land and deposited on the continental shelf.
- Fossil fuels, such as oil and natural gas, are formed from the remains of plants and animals that lived millions of years ago. These organic materials get buried under layers of sediment and are subjected to heat and pressure over time, leading to their transformation into fossil fuels.
- The continental shelf, being a repository of sediments, provides an ideal environment for the accumulation and preservation of organic materials necessary for the formation of fossil fuels. Therefore, it can be a rich source of fossil fuels.

Oceanic Deeps and Plate Movement:
- Oceanic deeps, also known as oceanic trenches, are the deepest parts of the ocean floor. They are formed when one tectonic plate is forced beneath another in a process called subduction.
- Subduction zones, where oceanic trenches are located, are important sites for the study of plate movement. The movement of tectonic plates is responsible for various geological phenomena, such as earthquakes, volcanic eruptions, and the formation of mountain ranges.
- Oceanic trenches are associated with subduction zones and are often accompanied by active volcanoes. The subducting plate melts as it sinks into the mantle, leading to the formation of magma. This magma can rise to the surface and result in volcanic activity. Therefore, oceanic deeps are important for the study of plate movement as they provide evidence of active volcanic processes.

Conclusion:
- Both statements are correct.
- Continental shelves can indeed be rich sources of fossil fuels due to the sediment load they carry, which provides an ideal environment for the formation and preservation of organic materials.
- Oceanic deeps, on the other hand, are important for the study of plate movement as they contain several active volcanoes, which are associated with subduction zones and provide valuable insights into the processes occurring at tectonic plate boundaries.

Factors Affecting Local Sea Level Rise

Local sea level rise can vary from the global average due to several factors. These factors include:

1. Local Land Subsidence:
- Land subsidence refers to the sinking or settling of the Earth's surface. It can be caused by various factors such as groundwater extraction, natural compaction of sediments, and tectonic activity.
- When the land subsides, it effectively reduces the height of the land relative to the sea level. This can lead to an apparent increase in sea level at a specific location, making it higher than the global average.

2. Ocean Currents:
- Ocean currents play a crucial role in redistributing heat around the globe, which can affect sea level.
- Currents, such as the Gulf Stream, can transport warm water from the tropics to higher latitudes. This can result in higher sea levels in regions where the warm water accumulates.
- Conversely, currents that transport colder water away from a region can cause a decrease in sea level due to the thermal contraction of the water.

3. Variations in Land Height:
- The elevation of the land surface can also influence local sea level.
- In areas where the land is rising or uplifting, the relative sea level may appear to be falling because the land is increasing in height faster than the sea level is rising.
- Conversely, in areas where the land is sinking or subsiding, the relative sea level may appear to be rising even if the global average sea level remains constant.

Overall, a combination of these factors can lead to significant differences between local sea level and the global average. Local land subsidence, ocean currents, and variations in land height all contribute to these differences. Therefore, the correct answer is option 'D' - all of the above.

Lower or Plain Course of a River

The lower or plain course of a river is the final stage of its journey towards the sea. The following statements explain the characteristics of the lower course of a river:

Heavy with Debris: The river moving downstream across a broad, level plain is heavy with debris brought down from the upper course. This debris includes boulders, pebbles, and sand that have been eroded from the upper course of the river.

Lateral Corrasion: Vertical corrasion has almost ceased through lateral corrasion still goes on to erode its banks further. Lateral corrasion is the process by which a river erodes its banks through the sideways movement of water.

Deposition: The work of the river is mainly deposition, building up its bed and forming extensive flood plains. Deposition is the process by which a river drops the sediment it has been carrying, forming features such as sandbars, levees, and floodplains.

Conclusion

All of the above statements are correct. The lower or plain course of a river is characterized by the heavy deposition of sediment brought down from the upper course, erosion of banks through lateral corrasion, and the formation of extensive floodplains.