Ocean Basins, Relief & Marine Water Bodies

These flashcards cover key concepts related to ocean basins, marine geology, and marine ecosystems, providing an in-depth review for students preparing for an exam in World Geography.

Why does the continental shelf vary widely in width across different coasts?

Tectonic history, erosional processes, sea level changes, and depositional patterns determine shelf extent.

How do submarine canyons form despite their position far below active river channels?

They are carved by underwater landslides and turbidity currents triggered by earthquakes or storms.

Why is the abyssal plain considered the flattest area on Earth?

Continuous sediment deposition from suspended materials smooths out topographic irregularities over time.

How does the formation of mid-oceanic ridges explain sea floor spreading?

They are sites of divergent plate boundaries where magma emerges, forming new oceanic crust and pushing plates apart.

What distinguishes guyots from seamounts in origin and structure?

Guyots are flat-topped due to erosion; seamounts retain pointed volcanic peaks.

Why do ocean trenches mark the deepest zones on Earth’s surface?

They form at subduction zones where one plate bends and descends beneath another.

How does the age of oceanic crust vary with distance from mid-ocean ridges?

It increases symmetrically on both sides of the ridge due to continuous seafloor spreading.

What is the significance of transform faults along mid-ocean ridges?

They offset segments of ridges and facilitate differential plate movement, causing seismic activity.

Why do back-arc basins form behind island arcs?

Subducting slabs create extensional forces behind volcanic arcs, pulling crust apart to form basins.

How do fracture zones extend beyond active transform boundaries?

They are relics of past plate movements, showing linear bathymetric features even after seismicity ceases.

Why is pelagic sediment deposition slow compared to terrigenous sediment?

Pelagic sources settle slowly in deep oceans, while terrigenous sediments are transported rapidly by rivers.

How does the carbonate compensation depth (CCD) influence ocean floor composition?

Below CCD, calcium carbonate dissolves rapidly, limiting accumulation of calcareous sediments.

Why are manganese nodules more common on abyssal plains than continental margins?

Slow sedimentation and absence of disturbance allow hydrogenous deposits to grow undisturbed.

What explains the presence of red clay in remote oceanic areas?

It’s composed of wind-blown dust and volcanic material that settles slowly in low productivity zones.

How can marine sediment cores reveal paleoenvironmental changes?

Variations in sediment type, microfossils, and isotopic ratios record past ocean temperatures and ice volume.

Why do thermoclines inhibit vertical mixing in tropical oceans?

Sharp temperature gradients create stable stratification that prevents cold deep water from rising.

How does salinity variation influence global ocean circulation?

Differences in salinity contribute to density-driven thermohaline circulation, affecting climate.

Why is the Antarctic Bottom Water denser than North Atlantic Deep Water?

It forms from cold, salty water sinking off Antarctica.

What causes the formation of oxygen minimum zones in oceans?

High biological activity and restricted vertical mixing lead to oxygen depletion at intermediate depths.

How do water masses maintain distinct identities over long distances?

They retain unique temperature-salinity profiles that resist mixing due to density stability.

Why do atolls form circular reef structures in open oceans?

They develop from coral growth around subsiding volcanic islands, forming rings.

How do ocean ridges differ from rift valleys in plate tectonics?

Ocean ridges are constructive boundaries creating crust, while rift valleys are initial stages of continental breakup.

What causes the formation of seamount chains like the Hawaiian Islands?

They are formed by mantle plumes (hotspots) creating volcanic islands as plates move over them.

Why are hydrothermal vents important for deep sea ecosystems?

They release mineral-rich fluids that sustain chemosynthetic organisms independent of sunlight.

How do bathymetric maps differ from topographic maps?

Bathymetric maps show depth below sea level using contours, while topographic maps represent elevation above sea level.

Why are enclosed seas like the Baltic more brackish than open oceans?

Limited exchange with open oceans and high freshwater input from rivers reduce salinity.

How does the Mediterranean Sea influence adjacent climate zones?

Its warm waters moderate coastal temperatures and provide moisture for precipitation.

Why is the Bering Strait geopolitically and ecologically significant?

It connects Arctic and Pacific Oceans, influencing marine biodiversity and trade routes.

What factors contribute to the hypersalinity of the Dead Sea?

High evaporation rates and minimal freshwater inflow concentrate salts.

How does the Red Sea support coral reefs despite high temperatures and salinity?

Clear waters, limited sedimentation, and adaptive coral species enable reef survival.

Why are western boundary currents faster and narrower than eastern ones?

Earth’s rotation and conservation of angular momentum intensify currents on western ocean margins.

How does Ekman transport explain coastal upwelling?

Wind-driven surface water moves at an angle, causing deep nutrient-rich water to rise along coasts.

Why are gyres asymmetric in structure and speed?

Coriolis effect and wind belts cause stronger currents on the western edges of gyres.

What is the role of the Antarctic Circumpolar Current in global circulation?

It connects major ocean basins, distributing heat and mixing water masses around Antarctica.

Why does the El Niño phenomenon disrupt global weather patterns?

Warm Pacific waters shift convection zones, altering jet streams and weakening trade winds.

Why is the Indian Ocean considered geopolitically vital?

It hosts major trade routes, chokepoints like the Strait of Hormuz, and regional power interests.

How does the monsoon influence surface currents in the Indian Ocean?

Seasonal wind reversal causes bi-directional current shifts, unique to this ocean.

Why is the Arabian Sea more productive than the Bay of Bengal?

Strong upwelling during SW monsoon brings nutrients to the surface in Arabian Sea.

What explains the difference in sediment load between eastern and western Indian coasts?

Major rivers like Ganga-Brahmaputra deliver more sediment to the east coast.

How do marginal seas like the Andaman Sea contribute to regional marine biodiversity?

Sheltered waters, coral reefs, and nutrient-rich upwelling zones support high biodiversity.

Why is sonar mapping preferred over satellite altimetry for fine-scale ocean floor mapping?

Sonar provides direct, high-resolution depth data, while satellite estimates are coarser.

How do Argo floats contribute to ocean monitoring?

They collect real-time temperature, salinity, and depth data for modeling climate and ocean circulation.

Why are Exclusive Economic Zones (EEZs) important for marine sovereignty?

They grant nations rights over marine resources up to 200 nautical miles from the coast.

How does bathymetry influence submarine cable routing?

Cables are laid to avoid steep slopes and tectonic zones, using gentle abyssal plains and shelves.

Why are ocean currents essential for understanding marine debris dispersion?

Surface currents determine the accumulation and movement of floating plastic and waste globally.

Why is the Mariana Trench deeper than other oceanic trenches?

It lies at the convergent boundary between fast-subducting Pacific Plate and the smaller Mariana Plate.

How does the thermohaline conveyor belt influence nutrient cycling in oceans?

It facilitates the upwelling and downwelling of water masses, redistributing oxygen and nutrients.

Why are submarine fans like the Bengal Fan among the largest sedimentary features on Earth?

Massive sediment supply from Himalayan rivers and turbidity flows deposit thick layers over vast distances.

What role do ocean plateaus like the Kerguelen play in paleoceanographic studies?

They preserve thick sediment layers and ancient volcanic activity records, crucial for reconstructing ocean history.

Why is the Scotia Plate important in understanding microplate tectonics in oceans?

Its complex interactions with South American and Antarctic plates offer insights into microplate dynamics.