Study Notes on Marine Ecology and Oceanography

Introduction to Marine Ecology and Oceanography

Plate Tectonics and the Ocean Floor

  • Definition of Plate Tectonics:

    • Describes the theory of Earth's lithosphere being divided into tectonic plates that move horizontally on the asthenosphere.

    • These movements lead to major geological features on Earth including volcanoes, earthquakes, fault lines, and mountain ranges.

  • California Terrane and Tectonic Plates:

    • Various plates involved:

    • North American Plate

    • South American Plate

    • African Plate

    • Eurasian Plate

    • E. African Subplate

    • Madagascar Plate

    • Australian Plate

    • Antarctic Plate

    • Locations of mid-ocean ridges and subduction zones highlighted.

    • Former Positions of Continents: Indicates past plate movements and locations of former landmasses.

Sea-Floor Spreading

  • Concept of Sea-Floor Spreading:

    • Occurs at oceanic ridges where new oceanic crust is created as tectonic plates pull apart.

    • Key Features:

    • Rift valleys along oceanic ridge crests indicate tension and are floored by basaltic lava flows.

    • New oceanic crust is generated as sea floors move apart.

Evidence for Continental Drift

  • Alfred Wegener's Hypothesis:

    • Suggested by Wegener based on:

    • The fit of continental outlines.

    • Fossil evidence across continents.

    • Geological similarities.

    • Key concept: The continents were once part of a supercontinent called Pangea.

    • Pangea broke apart, leading to the drifting of continents to current positions.

Fitting the Continents Together

  • Visual References: Illustrations depicting Pangea and its fragments.

  • Ancient Climates:

    • Evidence of glaciation in tropical areas, direction of glacial flow supports the theory of continental drift.

  • Rock Sequences: Matching sequences indicating similar ages and rock types across continents.

Sea-Floor Spreading Mechanism

  • Mechanics of Spreading:

    • Sea floor moves apart at oceanic ridges.

    • New crust is continuously added at the edges where tectonic plates move apart.

  • Rate of Sea-Floor Spreading: Varies from 1 to 10 cm per year for each side of a ridge.

Magnetic Evidence and Ocean Floor Features

  • Paleomagnetism:

    • Involves the study of Earth's past magnetic fields learned through rock formations.

    • As basaltic rocks solidify, magnetic minerals align with the Earth's magnetic field creating a record of geomagnetic reversals.

    • Measurements reveal alternating patterns of magnetic anomalies on the sea floor.

Tectonic structures and Moving Plates

  • Global Distribution of Earthquakes:

    • Concentrated along mid-ocean ridges, transform faults, trenches, and island arcs.

    • Earthquakes are generally shallow near mid-ocean ridges but can be deep in subduction zones.

Subduction and Its Impacts

  • Subduction Process:

    • Occurs when one tectonic plate moves under another into the mantle.

    • Leads to the creation of mountain ranges and can trigger destructive earthquakes.

  • Wadati-Benioff Zone: Indicates a zone of seismic activity parallel to a subduction trench, suggesting deeper seismic occurrences along with the descending plate.

Plate Tectonic Theory Concepts

  • Types of Plate Boundaries:

    • Divergent boundaries: Plates move apart, leading to rift valleys and new ocean floor formation.

    • Convergent boundaries: Plates collide resulting in ocean trenches and mountain ranges.

    • Transform boundaries: Plates slide past one another, causing faults and earthquakes.

Wilson Cycle

  • Definition: A sequence of stages in the life cycle of an ocean basin from formation to closure.

  • Stages:

    • Embryonic: Formation of rift valleys as continents split.

    • Juvenile: Initial sea floor formation and diverging continental fragments.

    • Mature: Widening ocean basin with developing trenches and subduction.

    • Declining: Subduction erases sea floor; oceanic ridge diminishes.

    • Terminal: Continents collide forming a mountain chain, effectively leading to the ocean basin's end.

Summary of Key Features in Oceanic Crust

  • Age Patterns: Analysis of ocean crust ages depicted in millions of years before present, detailing the formation and inactivity of certain regions.

  • Global Changes: Continuous interaction of plate tectonics shaping Earth's surface, influencing natural disasters and geological structures on the planet.