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.