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?

The next Hawaiian island in about 100,000 years. Signup and view all the answers

What is primarily noted about ocean trenches?

They are the most mysterious and least understood parts of the ocean. Signup and view all the answers

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

Shelf break Signup and view all the answers

How wide can the continental shelf vary around the world?

Less than 1 km to 1500 km Signup and view all the answers

Which region is noted for having a broad continental shelf?

The British Isles Signup and view all the answers

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

Fisheries Signup and view all the answers

What contributes to the formation of the continental shelf?

Wave erosion and river-borne silt Signup and view all the answers

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

Hudson Bay Signup and view all the answers

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

Coral reef builders Signup and view all the answers

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

High economic importance for fisheries Signup and view all the answers

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

Calypso Deep Signup and view all the answers

What does the GEBCO World Map provide information about?

Major topographical features of the ocean floor Signup and view all the answers

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

2500 meters Signup and view all the answers

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

Red Sea Signup and view all the answers

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

Private maritime exploration companies Signup and view all the answers

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

Using soundings and sonar Signup and view all the answers

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

New features are continuously being discovered. Signup and view all the answers

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

South China Sea Signup and view all the answers

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

It is the most important saline lagoon ecosystem. Signup and view all the answers

What primarily contributes to the sorting action of beach material?

The difference in energy of swash and backwash. Signup and view all the answers

Which of the following best describes the characteristic of swash?

It has the full force of the wave behind it. Signup and view all the answers

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

The difference in power between swash and backwash. Signup and view all the answers

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

Subduction Signup and view all the answers

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

To inhibit longshore drift. Signup and view all the answers

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

Oceanic Ridges Signup and view all the answers

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

Erosion occurring at other locations along the coast. Signup and view all the answers

What depth is considered the maximum for the continental shelf?

200 m. Signup and view all the answers

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

2 cm per year Signup and view all the answers

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

8%. Signup and view all the answers

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

Atlantic Ocean Signup and view all the answers

What can result when two oceanic plates collide?

Volcanic island arc development Signup and view all the answers

The Mariana Trench is formed by which tectonic interaction?

Subduction of oceanic plate beneath another oceanic plate Signup and view all the answers

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

Creation of deep oceanic trenches and volcanic islands Signup and view all the answers

What may ultimately cause the Atlantic Ocean to shrink?

Formation of a new subduction zone Signup and view all the answers

What does sonar stand for?

Sound Navigation and Ranging Signup and view all the answers

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

Sounding weights and lines Signup and view all the answers

What frequency range do modern echo sounders typically operate in?

15 - 50 kHz Signup and view all the answers

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

They can be focused into narrow beams for precise echoes. Signup and view all the answers

What is primarily developed from echo-sounding measurements?

Nautical charts Signup and view all the answers

What limitation did early sounding weight methods have?

They were ineffective in determining sediment composition. Signup and view all the answers

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

An acoustic transducer Signup and view all the answers

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

Narrow directional beams Signup and view all the answers

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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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.