GEOL 1340 Unit 9 Oceans and Coastlines

Global Ocean Coverage

Approximately 70% of Earth's surface is covered with ocean water.

Bathymetry Definition

The form, depth profile, and topography of the ocean floor.

Oceanic vs. Continental Crust Thickness

Oceanic crust is thinner than continental crust.

Oceanic vs. Continental Crust Density

Oceanic crust is denser than continental crust.

Continental Crust Buoyancy

Continental lithosphere floats higher on the mantle because it is less dense and buoyant.

Passive Continental Margins

Characterized by a shelf, slope, and rise without active plate boundaries, formed via rifting and continental crust extension (e.g., Atlantic margins).

Active Continental Margins

Characterized by subduction zone trenches, accretionary prisms, and volcanic arcs (e.g., western South America).

Deepest Ocean Subsurface Zone

The Hadal zone, which includes deep-sea trenches.

Deepest Point on the Ocean Floor

Challenger Deep in the Mariana Trench (~10,898 m / 35,756 ft).

Average Seawater Salinity

3.5% (or 35 parts per thousand) dissolved salt content.

Surface Salinity Drivers

Driven by the balance between freshwater inputs (precipitation/river runoff) and evaporation rates.

Halocline Definition

A subsurface layer where ocean salinity changes rapidly with depth.

Sea-Surface Temperature Distribution

Highest near the tropics and lowest near the poles.

Thermocline Definition

A subsurface ocean layer characterized by a rapid temperature drop with increasing depth.

Surface Ocean Gyres

Large circular surface current loops along ocean basins driven primarily by global wind patterns.

Coriolis Effect Deflection

Deflects moving fluid/air currents to the right in the Northern Hemisphere and to the left in the Southern Hemisphere due to Earth's rotation.

Thermohaline Circulation Driving Forces

Deep ocean circulation driven by density differences controlled by temperature ("thermo") and salinity ("haline").

Global Ocean Mixing Time

Thermohaline circulation completes full global ocean mixing over approximately 1,500 years.

Ocean Upwelling Cause and Effect

Surface winds pushing coastal water offshore pull cold, nutrient-rich deep water upward, driving high biological productivity.

Primary Cause of Tides

The gravitational pull of the Moon and Sun acting on Earth's oceans.

Sublunar Tidal Bulge

The larger ocean bulge that directly faces the Moon, matched by a smaller bulge on the exact opposite side of Earth.

Spring Tides

Extra-high tides occurring during new and full moons when the Sun and Moon align, combining their gravitational pulls.

Neap Tides

Extra-low tides occurring when the Sun is at a right angle to the Moon, partially offsetting lunar gravity.

Sediment Budget Definition

The balance between sediment added to a coast (via rivers, cliff erosion, glaciers) and sediment removed.

Beach Sub-Environments

Includes backshore, berm, foreshore (intertidal zone), and nearshore zone.

Winter Beach Profile

Strong storm waves pull sand offshore to deeper shelves, leaving a narrow, gravelly beach.

Summer Beach Profile

Moderate wave energy moves sand back onshore, rebuilding a wide, sandy beach.

Wave-Cut Notches and Platforms

Wave action undercuts sea cliffs to form notches; repeated cliff collapse leaves behind a flat bedrock wave-cut platform.

Rocky Coast Erosional Features

Headland erosion produces sea caves, sea arches, sea stacks, and tombolos.

Submergent Coast Characteristics

Formed by relative sea-level rise or land subsidence, creating flooded river valleys (estuaries) or drowned glacial valleys (fjords).

Emergent Coast Characteristics

Formed by relative sea-level fall or land uplift, displaying incised rivers, sea cliffs, exposed platforms, and step-like coastal terraces.

Organic Coasts

Coasts shaped primarily by living organisms, such as coastal wetlands (swamps/marshes) and tropical coral reefs.

Groins, Jetties, and Breakwaters

Hard structures that trap longshore sediment transport locally, but accelerate severe erosion down-drift.

Seawalls Impact

Walls designed to reflect wave energy, which concentrate wave scouring at their base, impede sediment exchange, and often destroy the front beach.

Beach Nourishment

Dumping imported sand onto eroded beaches; effective temporarily, but expensive and requires continuous maintenance.