2-1 the seafloor and ocean marginsquestions - Tagged

The Seafloor and Continental Margins

Introduction

• Overview of oceanic structure focusing on seafloor and continental margins.

Mapping the Ocean Floor

• Bathymetry: Measurement of depth using weighted lines lowered into the ocean.

• Echo Sounder (Sonar):

  • Invented in the 1920s.

  • Primary tool for measuring ocean depth.

  • Functions by reflecting sound waves from the ocean floor and measuring the time for the echo to return.

Advanced Mapping Techniques

• Multibeam Sonar:

  • Utilizes an array of sound sources and listening devices.

  • Produces a detailed profile of a narrow strip of seafloor, allowing for the mapping of larger areas.

Satellite Observations

• Satellites equipped with radar altimeters measure subtle differences in the ocean surface's topography.

• Variations in surface reflect gravitational pull of seafloor features, revealing ridges, valleys, and other geological structures.

• Provides detailed topographical data crucial for understanding seafloor geology.

Major Topographic Divisions of the North Atlantic Ocean

• Diagram illustrating various features:

  • Main continental masses include North America and Africa.

  • Key divisions: Continental margin, Deep-ocean basin, Mid-ocean ridge.

Continental Margins

• Passive Continental Margins:

  • Predominantly found along the Atlantic Ocean.

  • Not associated with tectonic plate boundaries, leading to a stable geological environment.

  • Characterized by little volcanic activity and few earthquakes, resulting in diverse marine ecosystems.

Features of Continental Margins

• Continental Shelf:

  • The submerged extension of the continent which can vary significantly in width across regions (e.g., the broad Texas coast vs. the narrow New England coast).

  • Important for fisheries and underwater ecosystems.

Structure of Continental Margins

• Geological features include:

  • Continental Shelf: shallow areas enriched with diverse marine life.

  • Shelf Break: the point where the continental shelf drops off.

  • Continental Slope: steep slopes leading to the deep ocean, where sediments from the continental shelf accumulate.

  • Continental Rise: a gentle incline formed by sediment deposition.

Continental Shelf Details

• Contains significant mineral deposits, vital for economic resources such as oil and gas.

• Representative states along the U.S. continental shelf include Texas, Mississippi, Alabama, Florida, and Louisiana, noted for their productive fisheries and potential for mineral exploitation.

Boundary Features

• Continental Slope:

  • Marks the seaward edge of the continental shelf, characterized by steep slopes that descend into deeper waters.

  • Represents the transition from continental crust to thinner oceanic crust (gabbro).

Continental Rise

• Typically found where oceanic trenches are absent.

• Acts as a transition from steep continental slope to a gentle incline, accumulating sediment over time.

Understanding Submarine Canyons

• Features that define continental margins, often shaped by erosion from turbidity currents.

• Boundaries marked by thin oceanic crust, contributing to the unique ecological zones.

Sediment Deposition

• Deep-Sea Fans: formed from sediment deposits carried by turbidity currents, these features are essential for understanding sediment transport processes.

Key Concepts in Oceanography

• Questions focus on sediment transport dynamics, the role of turbidity currents, and the composition of continental crust, highlighting fundamental oceanographic principles.

Progressive Settling

• Sediment classification based on grain size grading.

• Includes True/False questions on characteristics of continental margins and turbidites, emphasizing core concepts.

Active Continental Margins

• Characterized by steep continental slopes that descend directly into oceanic trenches, predominantly found along the Pacific Ocean.

Sedimentary Features

• Deformed sediments and remnants of old ocean crust contribute to the formation of accretionary wedges, critical in plate tectonics.

Characteristics of Deep-Ocean Basins

• Deep-Ocean Trenches: Long, narrow, and deep regions predominantly associated with volcanic activity, mostly found in the Pacific Ocean, playing a critical role in subduction.

Overview of Earth’s Deep-Ocean Trenches

• References major trenches like the Mariana and Java trenches, underscoring their significance in geological and ecological studies.

Abyssal Plains

• Considered some of the most level places on Earth, these plains are formed from detritus and marine sediment deposits, characterized by their extreme depths and relatively flat topology.

Seamounts Features

• Seamounts: Volcanic peaks that may form islands or flat-topped formations known as guyots, contributing to biodiversity and localized nutrient upwelling.

Oceanic Ridge Anatomy

• Characteristics of oceanic ridges, recognized as the highest features on Earth’s surface, notable for extensive faulting and volcanic activity.

Seafloor Characteristics

• The seafloor is characterized by a thin sediment cover far from land; seamounts serve as ocean floor volcanoes, influencing ocean circulation patterns.

Oceanic Ridge Characteristics

• The longest topographic features on Earth, with a width of approximately 70,000 km, encompass various oceanic regions through which tectonic activity occurs.

Distribution of Oceanic Ridge Systems

• The distribution of oceanic ridge systems shows varied spreading rates (slow, intermediate, fast) based on plate tectonics research.

Seafloor Spreading Concepts

• Proposed by geologist Harry Hess; seafloor spreading takes place at oceanic ridges, contributing to the creation of new oceanic crust.

Movement of Lithosphere

• New lithosphere moves in a conveyor-belt manner from the ridge crest, continuously reshaping the ocean floor through geological time.

Structure of Oceanic Crust

• Composed of four distinct layers: sediment layer, pillow lavas, sheet dikes, and gabbro, each layer plays a critical role in the structural integrity of oceanic crust.

Hydrothermal Interactions

• Seawater circulates through the oceanic crust; interactions lead to the formation of black smokers at ocean ridges, which are critical to nutrient cycling in deep-sea ecosystems.

Unique Ecosystems

• Black smokers sustain unique ecosystems devoid of sunlight, rich in metal deposits, supporting a wide variety of extremophilic organisms.

Subduction Zone Dynamics

• Related to the demise of ocean basins via subduction processes, critical for understanding plate tectonics and volcanic activity.

Atoll Formation

• An atoll is characterized as a circular reef enclosing a shallow lagoon, formed through complex geological processes over thousands of years, contributing to marine biodiversity.