oceanography

Unit One: Physical and Chemical Oceanography

The Oceans

• The world ocean is divided into five major divisions:

  • Pacific

  • Atlantic

  • Indian

  • Arctic

  • Newly designated (2021) Southern

• Ocean Coverage by Hemisphere:

  • _% of the southern hemisphere is covered in ocean

  • _% of the northern hemisphere is covered in ocean

Latitude and Longitude

• Latitude and longitude are essential for describing geographical position.

• Latitude:

  • Definition: The angular distance north or south of the equator.

  • Measurement: Runs from 0º at the equator to 90º at the poles.

• Longitude:

  • Definition: Semicircles running pole to pole displaying angular distance.

  • Measurement: Runs from 0º (prime meridian) to 180º.

The Poles

• Geographic poles differ from geomagnetic poles due to Earth's tilt.

• The angle between the geographic poles and the geomagnetic poles is referred to as the Magnetic Declination.

Nautical Charts

• Comparison between maps and nautical charts:

  • Maps: Primarily represent land.

  • Nautical Charts: Depict water-related information.

• A nautical chart is primarily concerned with navigable water areas and includes:

  • Coastlines

  • Harbors

  • Obstructions

  • Currents

  • Depth

Properties of Water

• Water possesses several noteworthy properties that are crucial for life:

  • High surface tension

  • High thermal conductivity

  • Low density (in its solid form)

  • Universal solvent

Seawater

• Composition of seawater:

  • 96.5% pure water

  • 3.5% dissolved solids from rivers.

• Salinity:

  • Definition: The total amount of dissolved material in water.

  • Global average salinity: 34.7 ppt (parts per thousand).

• Major dissolved solids in seawater:

  • 55.04% - Chloride (Cl-)

  • 30.61% - Sodium (Na+)

  • 7.68% - Sulfate (SO4²-)

  • 3.69% - Magnesium (Mg²+)

CTD (Conductivity, Temperature, Depth)

• CTD: An important tool for oceanographers, measures:

  • Conductivity

  • Temperature

  • Depth

• Additional instruments can be attached:

  • Niskin bottle: collects water samples at various depths.

  • Oxygen sensor to measure dissolved oxygen content.

Bathymetry

• Bathymetry: Measurement of ocean depths and charting the ocean floor's shape or topography.

• SONAR (Sound Navigation and Ranging):

  • Components: A transmitter and a receiver.

• Sound waves travel at approximately m/sec in seawater.

Ocean Geomorphology

• Continental Shelf: The underwater extension of a continent.

• The Continental Slope: An abrupt steepening of the bottom at the outer edge of the shelf.

• Abyssal Plain: The deep, flat, sediment-covered bottom of the ocean.

  • The abyssal plain may be broken by:

  • Trenches: Deep troughs.

  • Seamounts: Isolated underwater mountains.

Plate Tectonics

• The Earth’s crust is divided into tectonic plates that float and ride on the surface.

• The movement of these plates over time is known as Plate Tectonics.

• Causes of plate movement:

  • Oceanic ridges are volcanic activity centers creating new crustal material, leading to seafloor spreading.

Ocean Zones

• Two major zones of the ocean basin:

  • Neritic Zone:

  • Definition: The warm, nutrient-rich water extending to the edge of the continental shelf, containing 90% of all marine species.

  • Oceanic Zone:

  • Definition: Includes all waters beyond the continental shelf.

• Water column zones based on depth:

  • Euphotic Zone:

  • Depth: 0 - 200 m, also known as the photic zone (lighted).

  • Mesopelagic Zone:

  • Depth: 200 - 1,000 m, lower boundary is defined by the 10ºC isotherm.

  • Bathypelagic Zone:

  • Depth: 1,000 - 2,000 to 4,000 m, temperature ranges from 10ºC to 4ºC.

  • Also referred to as the bathyal zone (benthic zone).

  • Abyssopelagic Zone:

  • Depth: to 6,000 m, overlying the plains of ocean basins, also referred to as the abyssal zone.

  • Hadopelagic Zone:

  • Depth: 6,000 - 10,000 m, includes the open water of the deep trenches, known as the hadal zone (benthic zone).

Ocean Currents

• Ocean currents are vast streams of water moving through the oceans:

  • Surface Currents: Driven primarily by wind.

  • Deep Currents: Driven by density differences in water (temperature and salinity).

• Coriolis Effect: The deflection of Earth's winds and currents due to Earth’s rotation, creating large circular currents known as gyres.

• Turbidity Current: Caused by underwater landslides, characterized by a sudden increase in sediment and density in water.

Great Ocean Conveyor Belt

• Reference to the global pattern of ocean circulation characterized by the movement of warm and cold water currents, which play a critical role in regulating the Earth’s climate and heat distribution.

Ocean Waves

• Waves: Periodic up-and-down movements of water that transfer energy.

• Wave Characteristics:

  • Wavelength: The length measured from crest to crest or trough to trough.

  • Period: The time taken for one complete wave to pass a given point.

  • Wave Speed Equation: $ext{wave speed} = \frac{\text{wavelength}}{\text{period}}$

• Factors determining wave size:

  • Wind speed

  • Duration of wind activity

  • Fetch (distance wind travels over water)

• Breakers: Waves that topple over themselves as they approach the shore.

Tides

• Tides: The periodic predictable rise and fall of the sea level over a specific time interval, influenced by gravitational interactions and forces.

• Gravitational interactions include:

  • The gravitational attraction of the Moon.

  • The gravitational attraction of the Sun.

• Tidal Frequency Types:

  • Diurnal Tides: One low tide and one high tide per day.

  • Semidiurnal Tides: Two highs and two lows per day.

  • Mixed Tides: A combination of diurnal and semidiurnal tides.

Tidal Range

• Tidal Range: The difference in elevation between high tide and low tide.

• Spring Tides: Occur during new and full moons, resulting in larger tidal variations due to sun-moon alignment.

• Neap Tides: Occur during the first and third quarter moon phases, resulting in smaller than normal tidal variations.