Introduction to Oceanography – UGC NET – Detailed Notes

Introduction

• The Earth is divided into several plates, and each plate consists of continental and oceanic parts.

• The continental section forms the landmass and is subdivided into continental shelf, slope, and rise.

• The continental shelf contains remnant landforms that were submerged due to sea-level rise.

• The deep ocean regions constitute the oceanic plate, which is formed by the generation of new oceanic crust at convergent and divergent boundaries.

• During earlier cold climatic phases, large quantities of water were locked in ice sheets and glaciers, leading to a reduction in sea level and ocean extent.

• Plate tectonics controls the distribution of continents and oceans and plays a crucial role in the expansion and destruction of ocean basins.

• The oceanic crust is youngest at the mid-oceanic ridge and becomes progressively older as it moves away due to plate movement.

• Oceanic sedimentation is regulated by the supply of detritus from rivers, winds, and biological productivity.

• Slumping is an important process supplying sediments to the continental rise.

• The oceanic plate receives a negligible amount of sediment from land sources.

• Chemical and physical processes regulate the biogeochemical cycles of the ocean.

• The ocean exhibits a layered structure, with density increasing with depth.

• Salinity decreases in the halohaline layer, while temperature decreases in the thermocline.

• The physical, chemical, and biological properties of the ocean significantly influence Earth processes and help regulate the global climate.

Physiography of Oceans

• The Earth formed as a molten mass of gases billions of years ago.

• As the Earth cooled, released gases and water vapour led to the formation of the atmosphere and water on the globe.

• During the formation of the core, mantle, and crust, water migrated from the deeper interior of the Earth to the crust.

• Nearly 96% of Earth’s water is stored in the oceans.

• The oceans have a vast horizontal extent stretching over several hundred kilometres.

• The ocean covers about 71% of the Earth’s surface area.

• The vertical extent of the ocean is variable, with an average depth of about 3.7 km.

• The physiography of the ocean is crucial as it determines the amount of water stored in the oceans.

• The exchange of water between the ocean and other water reservoirs controls the degree of submergence of the continental margins under the ocean.

Physiographic Subdivision of Ocean

• The physiography of the ocean is controlled by ongoing geologic processes of the Earth.

• Most of the oceans are relatively young compared to the age of the Earth.

• This is because oceanic crust is continuously created at divergent boundaries and destroyed at convergent boundaries.

• The persistent destruction of oceans and reorganization of continents have repeatedly reshaped the ocean basins.

• The current phase of continental reorganization began with the breakup of Pangaea, the supercontinent.

• As a result, the oceanic crust does not exceed an age of about 200 million years.

• Consequently, the physiographic features of the ocean change and evolve through time.

Subdivision of Ocean

• The submerged parts of continents are termed the continental margin, while crust formed at divergent boundaries through tectonic activity is called the oceanic region.

• The physiographic features of the ocean floor are shaped by tectonic and hydrological processes, which regulate the volume of ocean water.

• Based on their origin and degree of submergence, ocean margins are classified into continental margins and oceanic margins.

• The continental margin represents the portion of the continent that is presently submerged beneath the sea.

• The continental crust is characterized by a relatively low density of about 2.7 g/cm³.

• The oceanic crust, formed through volcanogenic processes, has a higher density of about 2.9 g/cm³.

• The continental crust has a thickness of several kilometres, whereas the oceanic plate is comparatively thin.

The Continental Margin of the Ocean