Oceanography: Seamounts and Continental Shelves
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Questions and Answers

What are the key characteristics of seamounts?

  • They form exclusively at ocean ridges.
  • They are active volcanoes found only in the Atlantic Ocean.
  • They are primarily flat-topped underwater formations.
  • They are mostly extinct underwater volcanoes, mainly in the Pacific Ocean. (correct)

What distinguishes guyots from regular seamounts?

  • Guyots are formed by tectonic plate movements.
  • Guyots remain above water unlike seamounts.
  • Guyots are flat-topped due to wave action wear over time. (correct)
  • Guyots are actively forming volcanoes.

Which method allows for the detection of large seamounts today?

  • Manual surveying by oceanographers.
  • Measurement of sea surface height by satellite technology. (correct)
  • Underwater exploration submersibles.
  • Sonar mapping of ocean floors.

Loihi is significant because it is indicated to become what?

<p>The next Hawaiian island in about 100,000 years. (D)</p> Signup and view all the answers

What is primarily noted about ocean trenches?

<p>They are the most mysterious and least understood parts of the ocean. (B)</p> Signup and view all the answers

What term describes the sharp drop that begins beyond the continental edge?

<p>Shelf break (B)</p> Signup and view all the answers

How wide can the continental shelf vary around the world?

<p>Less than 1 km to 1500 km (D)</p> Signup and view all the answers

Which region is noted for having a broad continental shelf?

<p>The British Isles (D)</p> Signup and view all the answers

What is one of the primary economic activities associated with continental shelf areas?

<p>Fisheries (D)</p> Signup and view all the answers

What contributes to the formation of the continental shelf?

<p>Wave erosion and river-borne silt (B)</p> Signup and view all the answers

Which of the following places has a notable shelf area alongside its coast?

<p>Hudson Bay (D)</p> Signup and view all the answers

What type of organisms can form underwater barriers that contribute to the shelf areas?

<p>Coral reef builders (A)</p> Signup and view all the answers

What is a common characteristic of northern hemisphere temperate and sub-polar continental shelves?

<p>High economic importance for fisheries (B)</p> Signup and view all the answers

Which trench has the greatest measured depth according to the provided data?

<p>Calypso Deep (A)</p> Signup and view all the answers

What does the GEBCO World Map provide information about?

<p>Major topographical features of the ocean floor (D)</p> Signup and view all the answers

What is the depth of the Central trough in the Red Sea?

<p>2500 meters (A)</p> Signup and view all the answers

Which of the following seas has an area of 450,000 square kilometers?

<p>Red Sea (D)</p> Signup and view all the answers

Which of the following is NOT mentioned as a source of ocean data?

<p>Private maritime exploration companies (B)</p> Signup and view all the answers

How is the information on major topographical features of the ocean gathered?

<p>Using soundings and sonar (A)</p> Signup and view all the answers

What is a significant characteristic of ocean floor mapping mentioned in the content?

<p>New features are continuously being discovered. (C)</p> Signup and view all the answers

Which sea specified has an area of 3,700,000 square kilometers?

<p>South China Sea (A)</p> Signup and view all the answers

What is the Fleet known for in the context of ecosystems in the United Kingdom?

<p>It is the most important saline lagoon ecosystem. (B)</p> Signup and view all the answers

What primarily contributes to the sorting action of beach material?

<p>The difference in energy of swash and backwash. (B)</p> Signup and view all the answers

Which of the following best describes the characteristic of swash?

<p>It has the full force of the wave behind it. (D)</p> Signup and view all the answers

What causes larger stones to accumulate at the back of the beach?

<p>The difference in power between swash and backwash. (C)</p> Signup and view all the answers

What process forms a deep oceanic trench along the edges of colliding tectonic plates?

<p>Subduction (B)</p> Signup and view all the answers

What is the main purpose of erecting groynes on a beach?

<p>To inhibit longshore drift. (B)</p> Signup and view all the answers

Which feature is primarily formed by the volcanic extrusions of igneous rock onto the sea floor?

<p>Oceanic Ridges (B)</p> Signup and view all the answers

What can be a consequence of beach protection methods like groynes and sea walls?

<p>Erosion occurring at other locations along the coast. (B)</p> Signup and view all the answers

What depth is considered the maximum for the continental shelf?

<p>200 m. (D)</p> Signup and view all the answers

What is the rate of seafloor spreading along the Mid-Atlantic Ridge?

<p>2 cm per year (A)</p> Signup and view all the answers

Approximately what percentage of the total ocean floor is made up of the continental shelf?

<p>8%. (B)</p> Signup and view all the answers

Which ocean is considered younger due to its formation after the breakup of Pangea?

<p>Atlantic Ocean (A)</p> Signup and view all the answers

What can result when two oceanic plates collide?

<p>Volcanic island arc development (A)</p> Signup and view all the answers

The Mariana Trench is formed by which tectonic interaction?

<p>Subduction of oceanic plate beneath another oceanic plate (A)</p> Signup and view all the answers

What is a consequence of the subduction process along the Pacific Ocean's western rim?

<p>Creation of deep oceanic trenches and volcanic islands (C)</p> Signup and view all the answers

What may ultimately cause the Atlantic Ocean to shrink?

<p>Formation of a new subduction zone (D)</p> Signup and view all the answers

What does sonar stand for?

<p>Sound Navigation and Ranging (A)</p> Signup and view all the answers

Which method was traditionally used to measure sea depth before sonic methods?

<p>Sounding weights and lines (B)</p> Signup and view all the answers

What frequency range do modern echo sounders typically operate in?

<p>15 - 50 kHz (C)</p> Signup and view all the answers

What is one advantage of using ultrasonic frequencies in echo sounders?

<p>They can be focused into narrow beams for precise echoes. (A)</p> Signup and view all the answers

What is primarily developed from echo-sounding measurements?

<p>Nautical charts (A)</p> Signup and view all the answers

What limitation did early sounding weight methods have?

<p>They were ineffective in determining sediment composition. (A)</p> Signup and view all the answers

What component is essential in the function of an echo sounder?

<p>An acoustic transducer (B)</p> Signup and view all the answers

What aspect of echo sounders allows them to provide detailed profiles of the seabed?

<p>Narrow directional beams (B)</p> Signup and view all the answers

Flashcards

Ocean Area Variation

Ocean area measurements differ based on the source and the precise boundaries used for calculation.

Ocean Depth Data

Ocean depths are measured by various sources, with some data being less precise than others.

Calypso Deep

A deep part of the ocean, specifically measuring 1480 meters deep

Cayman Trench Depth

A deep section measuring 7685 meters deep, a part of the Cayman Trench

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Central Trough Depth

A deep part of the ocean, specifically measuring 2500 meters deep

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GEBCO World Map

A map showing ocean floor topography, including trenches, ridges, and other features.

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Ocean Floor Topography

The varied landscape of the ocean floor, featuring plains, mountains, trenches, and shelves.

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Topographical Features Mapping

Mapping ocean floor features like ridges, basins, and trenches has improved over time.

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Seamounts

Extinct underwater volcanoes, mostly found in the Pacific Ocean. They are formed by volcanic activity and can sometimes rise above the sea level, creating islands.

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Guyots

Flat-topped seamounts that were once volcanic islands, but have been eroded by wave action over millions of years. They are submerged beneath hundreds of meters of water.

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Ocean Trenches

Deep, narrow depressions in the ocean floor formed by the collision of tectonic plates. They are often associated with volcanic activity.

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What causes some Pacific Islands to form?

Many Pacific Islands, such as the Islas Marías Archipelago, are formed by peaks of the East Pacific Rise. However, more commonly they are formed by geologic 'hot spots' in the underlying mantle of oceanic tectonic plates.

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How are seamounts detected?

Modern satellite technology can detect seamounts that are 1.5 km or more in height by measuring sea surface height. This is due to the gravitational force exerted by the seabed and seamounts.

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Shingle Storm Ridge

A natural barrier formed by waves over time, often creating a saline lagoon behind it.

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Saline Lagoon

A body of water separated from the open sea, with a high salt content.

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The Fleet

A prominent example of a saline lagoon ecosystem in the United Kingdom.

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Beach Material Sorting

Waves deposit different sizes of beach material at different levels, due to wave energy.

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Swash and Backwash

The swash is the incoming wave, while the backwash is the receding water.

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Continental Shelf

The shallow, sloping seafloor near the shore, extending to about 200 meters deep.

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Groynes

Structures built to prevent beach erosion by trapping sand and pebbles.

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Longshore Drift

The movement of sediment along the coast, driven by waves and currents.

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Continental Edge

The boundary where the shallow continental shelf abruptly drops into the deep ocean.

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Shelf Break

Another name for the Continental Edge, marking the transition from shallow shelf to steep slope.

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Continental Slope

The steep descent from the Continental Shelf into the deep ocean floor.

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Continental Shelf Width

The distance from the coastline to the Shelf Break, varying greatly across the globe.

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North-Western European Shelf

A broad continental shelf encompassing the British Isles, Irish Sea, and North Sea.

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Shelf Formation

Continental shelves form through a combination of wave erosion, coastal sediment deposition, and underwater barriers.

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Economic Importance of Shelves

Continental shelves are crucial for fishing and oil/gas extraction due to their abundant resources.

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Fishery Concentration

Over 90% of ocean-derived fish and food resources are found in the relatively shallow continental shelf regions.

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Seafloor Spreading

Process where new oceanic crust is formed at mid-ocean ridges and pushes existing crust away, causing the ocean floor to expand.

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Subduction Zones

Areas where one tectonic plate slides beneath another, often forming trenches and volcanic activity.

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Mid-Ocean Ridges

Underwater mountain ranges formed by volcanic activity as new oceanic crust is created.

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Volcanic Island Arcs

Chains of volcanic islands formed when oceanic plates subduct beneath another oceanic plate.

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Ring of Fire

A zone of intense volcanic and earthquake activity surrounding the Pacific Ocean, caused by subduction zones.

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Pangea

The supercontinent that existed millions of years ago before breaking apart into the continents we know today.

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Atlantic Ocean Formation

The Atlantic Ocean is believed to have formed when the supercontinent Pangea broke apart, and its floor continues to expand through seafloor spreading.

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Seabed Depth Measurement

The process of determining the depth of the ocean floor, historically using sounding weights and lines, but now predominantly relying on sonar technology.

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Echo Sounders

Devices that emit sound waves and measure the time it takes for the echoes to return, providing depth measurements and seabed profiling.

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Sonar

Acronym for 'Sound Navigation and Ranging,' a method of detecting objects underwater using sound waves, crucial for seabed mapping and object location.

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Sonic Scattering Layers

Layers within the ocean where sound waves are heavily scattered, often caused by fish and other marine organisms, discovered using echo sounders.

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Ultrasonic Frequencies

Sound frequencies higher than the human hearing range, used in echo sounders to achieve targeted beams, detailed imaging, and reduced interference.

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Nautical Charts

Maps of the ocean floor, created using data from echo sounders, showing seabed features like trenches, ridges, and other relevant information.

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Seabed Profiling

The process of creating detailed images of the ocean floor topography using echo sounders, revealing the shape and features of the seabed.

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Tallow

Animal fat used in the past to help bring up bottom sediment when using sounding weights and lines.

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Study Notes

Chapter 1: Physical Structure of Oceans

  • This chapter introduces the physical features and zones of the ocean.
  • Understanding the physical environment is crucial for comprehending marine communities and organisms' distribution and ecology.
  • Major oceans and seas are interconnected (Figure 1.1).
  • Average ocean depth is approximately 3700 m, with some areas exceeding 10,000 m (Table 1.1).
  • Marine life is unevenly distributed but found throughout the ocean's three-dimensional environment.

Figure 1.1: Major Oceans and Seas of the World

  • Labels locations of various seas and oceans.

Figure 1.2: Major Topographical Features of the Ocean

  • Provides a map showing locations of trenches, ridges, basins, and other features.
  • Locations of features like Aleutian Trench, Northeast Pacific Basin, Hawaiian Ridge, Central Pacific Basin, etc are labelled in the figure.

Table 1.1: Approximate Statistics for Major Oceans and Seas

  • Provides data on the area and average depth of major oceans and seas.
  • Includes data for the Mariana Trench, Puerto Rico Trench, Sunda Trench, Eurasia Basin, and Sandwich Trench as examples.

1.1 Physical features and topography

  • Full map of ocean floor not yet available, but features like ridges, trenches, shelves and other features are documented.
  • GEBCO World Map (http://www.gebco.net) shows known seafloor contours and features.
  • Major features such as ridges and basins described in subsequent sections.

1.1.1 Coastlines and Beaches

  • Diverse coastlines exist, from vertical cliffs to intertidal mudflats.
  • Coastlines are constantly shaped by erosion, wave action, river currents, and other factors.
  • Processes like erosion and deposition shape coastlines over time.

1.1.2 Continental Shelf

  • The continental shelf is a shallow, gradually sloping area near the coast.
  • Its seaward edge, the shelf break, marks a sharp drop-off to deeper ocean depths.
  • Average width is approximately 65 km.

1.1.3 Ocean Basins and Abyssal Plains

  • Beyond the continental shelf, the continental slope descends steeply to the abyssal plains.
  • Abyssal plains are flat, wide areas of the deep-sea floor covered with sediment.

1.1.4 Ocean Ridges and Seamounts

  • Ocean ridges are underwater mountain ranges where new seafloor forms.
  • Seamounts are underwater volcanic peaks that may rise above sea level to form islands.
  • Guyots are flat-topped seamounts.

1.1.5 Ocean Trenches

  • Ocean trenches are the deepest parts of the ocean, falling below 6000 m.
  • Found mainly around the rim of the Pacific Ocean.
  • Formed where one tectonic plate subducts (slides beneath) another.

1.1.6 Driving Forces: Plate Tectonics

  • Plate tectonics describes the movement of Earth's lithospheric plates.
  • Mid-ocean ridges are associated with seafloor spreading, where new crust forms.
  • Trenches are associated with subduction zones, where one plate slides beneath another.

1.3 Seabed Composition

  • Ocean floor composition varies significantly.
  • Terrigenous sediments are near land, originating from weathering and erosion.
  • Pelagic sediments are far from land, primarily composed of skeletal remains of marine organisms.

1.3.1 Terrigenous Deposits

  • Found near land, composed of various materials ranging from large boulders to fine clay.
  • Composition affected by factors such as coastline, water movement, and seabed contours.

1.3.2 Pelagic Deposits

  • Found in deep-water areas beyond the continental slope, primarily comprised of biogenic components.
  • These areas can be rich in calcareous and/or siliceous material.

1.3.3 Deepsea (Polymetallic) Nodules

  • Found on the ocean floor, mainly in deep water.
  • Consist primarily of manganese, iron and other rarer metals.

1.4 Sediment Sampling

  • Scientists use various methods including coring to study sediment.
  • Methods vary depending on water depth and location.
  • Techniques include gravity corers, piston corers, and sonar systems.

Box 1.1: Seabed 2030

  • International project to complete mapping of the ocean floor by 2030.
  • Using existing data and new technologies.

Box 1.2: The Kaikoura Canyon

  • Deep submarine canyon in New Zealand.
  • Rich in biodiversity, supporting species at depths not often explored.

Box 1.3: Visible Ridges

  • Icelandic ridge that is an example of a segment of the Mid-Atlantic Ridge where the ridge is closely located near the surface.

Box 1.4: Five Deep Expeditions

  • Expeditions used to explore the deepest points of the world's oceans.
  • Used a purpose-built submersible and instruments.

Box 1.5: GLORIA

  • Early side-scan sonar system.
  • Contributed to mapping and detailed seabed visualization.

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The Physical Structure of Oceans PDF

Description

Test your knowledge on the features and significance of seamounts and continental shelves in oceanography. This quiz covers key characteristics, economic activities, and geological formations that define these underwater structures. Ideal for students studying oceanic ecosystems and geological formations.

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