2-1 the seafloor and ocean marginsquestions - Tagged

The Seafloor and Continental Margins

Chapter 10

Mapping the Ocean Floor

• Bathymetry: The measurement of ocean depth, which is crucial for various marine studies such as navigation, marine biology, and underwater geology. Early methods involved using weighted lines lowered overboard to gauge depth, providing rudimentary data that was limited in both accuracy and efficiency.

• Echo Sounder/Sonar: Developed in the 1920s, this technology revolutionized underwater mapping by measuring ocean depth through the emission of sound waves from a ship. These sound waves reflect off the seabed and return to the ship, allowing for the creation of detailed depth profiles and comprehensive maps of underwater topography. Sonar technology has evolved, improving resolution and depth measurement.

Multibeam Sonar

• This advanced sonar system utilizes an array of sound sources and listening devices, capturing a wide strip of the seafloor profile. It significantly improves the detail of ocean floor mapping compared to single-beam sonar systems, thereby enhancing scientific understanding of underwater geography by identifying seabed features such as ridges, valleys, shipwrecks, and sediment distribution.

Remote Sensing from Space

• Satellites equipped with radar altimeters measure subtle differences in ocean surface height, which result from gravitational pulls of underwater features. This enables scientists to infer the seafloor's geology and topography without direct measurements, allowing extensive mapping of seafloor features even in remote areas.

Major Topographic Divisions of the North Atlantic Ocean

• Key Regions:

  • North America: Encompasses various geological formations and distinct oceanic features, influencing surrounding marine biodiversity.

  • Continental Margin: The submerged area where the continent meets the ocean, consisting of continental shelf, slope, and rise structures, critical for understanding marine ecosystems and resource distribution.

  • Deep-Ocean Basin: The extensive flat areas of the ocean floor, often containing significant geological features such as abyssal plains and trenches shaped by tectonic processes over millions of years.

  • Mid-Ocean Ridge: A continuous underwater mountain range formed by tectonic plate movements, crucial for understanding seafloor spreading and ocean basin formation, as it is actively creating new oceanic crust.

  • Africa: Additionally offers unique geological characteristics that impact oceanic currents, marine species distribution, and biodiversity in the North Atlantic region.

Continental Margins

• Passive Continental Margins: Common in the Atlantic Ocean, these margins are characterized by geological stability and minimal tectonic activity, not coinciding with tectonic plate boundaries, thus exhibiting low volcanic activity and fewer earthquakes. They support diverse marine life and fisheries.

Continental Shelf

• Definition: A submerged extension of the continent, with varying width across regions; it is economically significant due to rich mineral resources, including oil and gas deposits. The continental shelf is vital for food production as it supports a majority of the world’s fisheries and is a site for marine research and ecological studies.

Components of Continental Margins

• Features:

  • Continental Shelf: A gently sloping area rich in biological productivity, important for fishing and recreational activities.

  • Shelf Break: The point where the slope of the shelf increases dramatically, indicative of the transition to the continental slope where depths increase more rapidly.

  • Continental Slope and Rise: Areas connecting the continental shelf to the deep-ocean basin, characterized by deep-sea fans and abyssal plains, which play critical roles in sediment transport and accumulation, influencing benthic community dynamics.

Continental Shelf Features

• Importance: These regions are crucial for fishing industries, energy exploration, and are economically significant due to mineral deposits. Geography varies significantly by region, with notable platforms off the coasts of Texas, Mississippi, Alabama, Florida, and Louisiana, contributing to local and national economies.

Continental Slope

• This region marks the transition where continental crust changes to thinner oceanic crust, primarily composed of gabbro. The slope is steep and directly leads into deep ocean waters, playing a vital role in ocean circulation patterns and supporting unique biological communities.

Continental Rise

• Characterized by a gradual incline in regions absent of oceanic trenches, this zone transitions from the continental slope to the deep ocean floor and facilitates sediment deposition, which supports diverse habitats and marine ecosystems.

Identification Questions

1. The gently sloping submerged area extending from shoreline seaward is known as the continental shelf.

2. Submarine canyons can indeed be eroded by turbidity currents - True.

3. The term for the change from granitic continental crust to basaltic oceanic crust is called the shelf break.

Turbidity Currents

• These sediment-laden currents transport sediment away from the continental slope, leading to accumulation that forms significant geological structures like deep-sea fans, essential for understanding sedimentary processes and the ecological dynamics of marine environments.

Fill-in-the-Blanks Assessment

• Engaged in complex analyses regarding sediment transport dynamics, composition of the seafloor, and associated biodiversity, promoting a comprehensive understanding of marine geology and its implications.

Bedding Types

• Bedding: Refers to the arrangement of sediment layers; graded bedding highlights the progressive settling of sediment particles from larger to smaller grains due to fluctuating current strengths. The processes of deposition and erosion in various marine environments can create unique sedimentary structures.

• The continental rise indeed lies further seaward than the continental slope - True.

• Turbidites form from sediment deposits carried by turbidity currents, not from dead organisms - False.

Active Continental Margin

• Features: The presence of a trench indicates an active continental margin characterized by volcanic arcs and accretionary wedges arising from tectonic activity and the dynamic interaction between oceanic and continental plates.

Characteristics of Active Margins

• Defined by a continental slope that descends steeply into a deep-ocean trench, primarily located around the Pacific Ocean, showcasing intense geological activity, seismicity, and rich biodiversity due to unique geological features.

Accretionary Wedges

• Formed from deposits of deformed sediments and fragments of oceanic crust, these structures accumulate at active margins and provide insight into tectonic processes that shape the oceanic environment.

Features of Deep-Ocean Basins

• Deep-Ocean Trenches: These long and narrow features represent some of the deepest oceanic areas on Earth, predominantly located in the Pacific and fruitfully impacting global tectonics and associated volcanism.

Earth's Deep-Ocean Trenches

• Encompassing various trenches like the Philippine Trench and Mariana Trench, these regions are hotspots for tectonic activity, hosting unique ecosystems and influencing global oceanic circulation patterns.

Abyssal Plains

• Characterized as the flattest regions on Earth, situated far from land, where thick deposits of sediment accumulate over geological time, which are essential for supporting marine biodiversity and hosting benthic organisms.

Seamounts

• Seamounts: Isolated volcanic peaks rising from the ocean floor, some of which emerge as islands or become guyots due to erosion processes. They serve as critical habitats for various marine species and are areas of high biological productivity.

Distance from Sediment Sources

• In oceanic environments, sediment coverage tends to be thinner in areas far from land-derived sources, and the composition of sediments varies with proximity to land. The statement that seamounts are underwater volcanoes is True.

Anatomy of the Oceanic Ridge

• Features broad swells along divergent plate boundaries, areas associated with high heat flow and substantial volcanic activity, which contribute to the development of the ocean floor and various geological formations.

Characteristics of Oceanic Ridges

• Recognized as the longest continuous topographic feature on Earth's surface, extending over 70,000 km and covering about 20% of the Earth’s surface, illustrating the dynamic nature of oceanic geology and plate tectonics.

Oceanic Ridge System Distribution

• Differentiates spreading rates across various oceanic ridge systems globally, contributing significantly to our understanding of geological processes, plate movements, and associated geophysical phenomena.

Seafloor Spreading

• A concept formulated by Harry Hess, demonstrating the process occurring at ocean ridges where tectonic plates diverge, leading to the creation of new oceanic crust and reshaping oceanic geology over geological timescales.

New Lithosphere Creation

• Occurs through a conveyor-belt mechanism, moving new lithosphere away from ridge crests, with active rifting zones typically spanning 20 to 30 km in width, indicative of ongoing tectonic activity.

Structure of the Oceanic Crust

• Composed of four distinct layers:

  1. Unconsolidated sediments: Surface layer of loose materials.

  2. Pillow lavas: Formed by underwater volcanic activity, exhibiting rounded shapes.

  3. Sheeted dike complex: Composed of vertically oriented sheets of basaltic rock.

  4. Gabbro (ophiolite complex): The lower layer, composed of coarse-grained rock formed from cooled magma beneath the ocean floor. This layered structure is crucial in understanding the composition and geological history of the oceanic crust.

Rock Types in Oceanic Crust

• Includes:

  • Deep-sea sediment: Accumulated materials found at the ocean bottom, reflecting the condition and processes of marine environments.

  • Basaltic pillow lavas: Formed by underwater volcanic activity, contributing to the geological complexity of oceanic regions.

  • Sheet dike complex: Composed of vertical sheets of basaltic rock that form during tectonic activity.

  • Gabbro: The lower layer of oceanic crust, formed from cooled magma, critical in understanding the formation of oceanic lithosphere.

Identifying Ocean Features

• An oceanic ridge is a long mountain range on the ocean floor related to seafloor spreading, integral for various oceanic processes and ecosystems.

Hydrothermal Vents

• These formations arise from interactions between seawater and oceanic crust, producing unique ecosystems such as black smokers, which support life independent of sunlight through chemosynthesis, showcasing extreme life adaptations.

Ecosystems around Black Smokers

• Unique ecosystems that depend on thermal energy and mineral-rich fluids, characterized by diverse life forms that thrive without sunlight, highlighting the adaptability of life in extreme environments.

Destruction of Oceanic Lithosphere

• Driven by tectonic processes in subduction zones, this phenomenon leads to the gradual demise of ocean basins, ultimately leading to their closure as tectonic plates interact dynamically.

Atolls

• Defined as curved or circular coral reefs enclosing shallow lagoons, often containing low inner islands that provide rich biodiversity and have significant ecological importance. They represent important marine ecosystems, providing habitat and protection for numerous species.

Summary of Atolls

• Atoll characteristics include expansive shallow lagoons enclosed by robust reef structures, vital for marine life and offering coastal protection, crucial for sustaining marine biodiversity and fisheries.