Lecture 13. Oceanography
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4. Freshwater
1. Composition of the Ocean
⑴ Components of the Hydrosphere
① Natural Water = Seawater (97.22%) + Freshwater (2.78%)
② Components of Freshwater
○ Freshwater = Glacial Ice and Permafrost (1.91%) + Groundwater (0.84%) + Others (0.03%)
○ Rainwater dissolves minerals on land, leading to high concentrations of CO32- and Ca2+
③ Components of Seawater
○ Composition of Salts
○ Average salinity of seawater is 35 ‰: 35 grams of salts dissolved in 1 kg of seawater
○ Origin 1: Weathering and erosion of rocks
○ Origin 2: Submarine volcanoes: Explosions of submarine volcanoes contribute to high Cl- concentration
○ Reasons for higher concentrations of CO32- and Ca2+ in freshwater than seawater: Used by organisms
○ Major Elements in Seawater (by mass)
○ Chloride ion (Cl-) : 55.0%
○ Sodium ion (Na+) : 30.6%
○ Sulfate ion (SO42-) : 7.7%
○ Magnesium ion (Mg2+) : 3.7%
○ Calcium ion (Ca2+) : 1.2%
○ Potassium ion (K+) : 1.1%
○ Distribution of Elements in Seawater (molar concentration)
Table 1. Distribution of Elements in Seawater
○ Salinity According to Latitude
○ Equator: Precipitation > Evaporation. Low salinity
○ Mid-Latitudes: Evaporation > Precipitation. High salinity
○ Polar Regions: Intense ice melting. Low salinity
○ (Note) Most deserts form in mid-latitudes
○ Salinity of South Korea
○ Yellow Sea has lower salinity than the East Sea: Yellow Sea is surrounded by land and has characteristics of freshwater
○ Lower salinity in summer compared to winter: High precipitation - evaporation during summer
○ Law of Constant Proportions of Salinity
Table 2. Law of Constant Proportions of Salinity
○ Mechanism: Result of long-term mixing
○ Residence Time of Ions
Table 3. Residence Time of Ions
○ Useful Minerals Extracted from Seawater: Salt, Magnesium, Bromine, etc.
○ Gases Dissolved in Seawater: Oxygen, Carbon Dioxide, Nitrogen, essential for marine life
⑵ Oceanic Structure : Differentiated by changes in temperature with depth
Figure 1. Division of Oceanic Layers
① Mixed Layer (50 m ~ 200 m, 2%): Vertical temperature remains constant
○ Solar energy influence ○, Wind influence ○: Temperature is uniform due to wind-induced mixing
○ Thicker mixed layer during winter: Cooling of surface water due to density-driven circulation increases its thickness
○ Thickest mixed layer at mid-latitudes: Strong winds at mid-latitudes (due to atmospheric circulation)
② Thermocline (200 m ~ 1,000 m, 18%): Rapid decrease in temperature with increasing depth
○ Solar energy influence O, Wind influence X
○ Stability: Lower layer is colder than upper layer. Restricts convective mixing
○ Sea surface slope is opposite to thermocline slope
Figure 2. Sea Surface Slope and Thermocline Slope
③ Abyssal Layer (1,000 m ~, 80%): Formed by polar waters, deep-sea formation
○ Solar energy influence X, Wind influence X
○ Constant temperature regardless of latitude or season: -1 to 3 ℃, average 3.9 ℃
○ Very low temperature, high density, low salinity
○ Maximal density temperature of water decreases with increasing pressure: Explains temperature decrease with depth in abyssal layer
Figure 3. Water’s Maximum Density Temperature vs. Pressure
⑶ Distribution of the Oceans
① Marginal Sea
② Enclosed Sea
⑷ Seafloor and Coastline Features
① Areas within Oceans
○ Basin: Large circular or oval depressions
○ Trench: Long and narrow trench-like depressions near continental margins
○ Deep: Deeper parts within trenches
○ Valley: Gentle slopes leading into deeper areas
○ Farrow: Submarine ridges, perpendicular to coastlines
② Areas Emerging from Oceans
○ Rise: Long, elevated portions rising from deep-sea floor, similar to mountain ranges on land
○ Plateau: High, flat-topped areas with steep sides
○ Bank: Elevated flat areas composed of non-rocky materials, relatively shallow and navigable
○ Reef: Areas with shallow water containing rocky outcrops or coral reefs
⑸ Ocean Depth
⑹ Sea Ice and Icebergs
2. Properties of Seawater
⑴ Temperature of Seawater
⑵ Salinity of Seawater (Reference: 1-⑴-③)
⑶ Density and Specific Gravity of Seawater
⑷ Optical Properties and Transparency of Seawater
⑸ Standard of Seawater Color
⑹ Sound Speed in Seawater
Figure. 4. deep-sea sound velocity profile
① Background Knowledge: Waves are refracted towards the slower side.
○ Incident Experiment: When thinking of waves as lines with width, if one end is faster and the opposite end is slower, the wave bends towards the slower side.
○ Elastic waves, regardless of particle waves, are refracted towards the slower side.
② Case 1: Depth ＜ 1,000 m : Sound is refracted downward.
③ Case 2: Depth ＞ 1,000 m : Sound is refracted upward.
④ Sound Channel: Sound channel exists around 1,000 m before and after.
○ Sound travels in a wave pattern around 1,000 m before and after and propagates parallel to the sea surface.
○ Whales and submarines frequently utilize this.
3. **Movement of Seawater
⑴ Speed of Waves
Figure. 5. Deep Sea Waves and Shallow Sea Waves
① Motion direction of water particles on a ship: Direction of wave propagation
② Wave speed general equation
○ Meaning 1: Speed increases with depth (obvious)
○ Meaning 2: Longer wavelength results in higher speed : Easy to understand when imagining a tsunami
③ Case 1: Deep Sea Waves : When depth ＞ 0.5 λ. Also known as surface waves.
○ Water particles form circular orbits.
○ The radius decreases with increasing depth.
○ Speed of deep-sea waves : (Note) It does not mean that the speed of waves infinitely increases with depth.
○ As depth increases, the size of circular motion of water particles decreases.
④ Case 2: Shallow Water Waves : When depth ＜ 0.05 λ. Also known as long waves.
○ As depth increases, only wavelength shortens.
○ Speed of shallow water waves
○ As depth decreases, : propagation speed decreases, wavelength shortens, wave height increases.
⑤ Case 3: 0.05 λ ＜ depth ＜ 0.5 λ : Waves start to be influenced by the seabed.
⑥ Tidal Waves (Tsunamis)
○ Type 1: Storm Tsunamis : Generated by low pressure (typhoon)
○ Reaches coast → Depth decreases → Speed decreases → Wavelength decreases → Wave height increases
○ Type 2: Seismic Tsunamis (Tsunamis) : Generated by vertical movements like earthquakes, volcanoes, and landslides
○ Has very long wavelengths and shares characteristics with shallow water waves
○ Seismic tsunamis occur better with vertical stratification rather than horizontal stratification
⑵ Ocean Currents
① Methods of Investigating Seawater
○ Method based on seawater color
○ Method based on temperature and salinity
○ Method based on ship direction
○ Method based on current meter
○ Method using drifters
○ Electromagnetic method
○ Dynamic method
② Types of Ocean Currents
○ Wind-driven currents: Currents driven by winds
○ Density-driven currents: Currents caused by differences in density
○ Geostrophic currents: Also known as topographic currents
○ Equilibrium between pressure gradient and Coriolis force in currents: Similar to the principle of geostrophic winds in the atmosphere
○ High-pressure areas are positioned to the right of current direction, flowing parallel to isobars
○ Counter currents: Currents that fill empty spaces left by other currents’ movement
③ Warm and Cold Currents
○ Warm currents: Flow from higher to lower latitudes. Examples: California Current, etc.
○ Cold currents: Flow from lower to higher latitudes. Examples: Gulf Stream, Kuroshio Current, etc.
○ (Note) Don’t memorize the types of warm and cold currents separately; refer to the following Tropical Circulation
○ Cold currents have relatively higher temperature and salinity compared to warm currents
○ Convergence zones: Points where warm and cold currents meet. Various marine species can be found here
④ Coriolis Effect and Ocean Currents
Figure. 6. Ekman Transport
○ Ekman depth: Depth at which seawater flows in the opposite direction of the wind. Also known as the Ekman layer or friction layer
○ Northern hemisphere currents flow clockwise, while southern hemisphere currents flow counterclockwise due to the Coriolis effect
○ In the northern hemisphere, the average flow of water in the Ekman layer is perpendicular to the wind direction towards the right
○ The direction of surface water movement is 45° to the right of the wind direction
○ Tip: Topographic currents are formed in the direction of the wind and often accompany Ekman transport
⑤ Major Global Ocean Currents
○ High-density water generated in the Arctic Ocean mostly flows into the North Atlantic
○ Ocean Conveyor Belt
⑥ Ocean Currents near Korea
Figure. 6. Ocean Currents near Korea
○ Tip: North Korea-made bronze: North Korean Current, Kuroshio Current, Yellow Sea Cold Current, East Sea Warm Current
○ Others: Liman Current, Tsushima Warm Current
⑦ Thermohaline Circulation 1: Horizontal Circulation of Seawater
○ Tropical circulation: Circulation flowing from 0° to 60°. Wind → Ekman transport → Sea surface slope → Topographic currents
○ Tropical circulation transports the most heat energy
○ Trade winds and westerlies cause sea surface elevation at latitude 30°
○ Types of topographic currents: North Equatorial Current, South Equatorial Current, North Pacific Current (North Atlantic Current), East/West Boundary Currents
○ Northern hemisphere and southern hemisphere currents appear symmetrically (e.g., North Equatorial Current and South Equatorial Current)
○ South Pacific Current combines with the Antarctic Circumpolar Current
○ Comparison of East/West Boundary Currents
Table. 4. Comparison of East/West Boundary Currents
○ Strengthening of Westward Currents: As the prevailing force increases towards higher latitudes, the sea surface slope in the Western Pacific becomes larger than in the Eastern Pacific
○ Equatorial Countercurrent
○ A current flowing from west to east along the equator due to
the difference in sea surface elevation caused by North Equatorial Current and South Equatorial Current
○ A type of topographic current
⑧ Thermohaline Circulation 2: Vertical Circulation of Seawater
○ Type 1: Intermediate Current
○ Type 2: Deep Sea Current
○ Surrounding seawater becomes saltier due to freezing, increasing its density
○ Saltier water sinks, forming deep-sea water
○ Such deep-sea water is generated in high-latitude areas
○ The circulation of deep-sea water is slower than that of surface water due to negligible influence of wind, etc.
○ Stronger circulation of deep-sea water results in stronger surface currents and smaller temperature differences between high and low latitudes (∵ energy transport)
○ Type 3: Bottom Current
○ (Note) Equatorial Undercurrent
⑨ Deep-sea circulation and surface circulation are interconnected, forming significant circulation in the ocean
4. Freshwater
⑴ Formation of Lakes
⑵ Properties of Lakes
① Water Temperature
○ Tropical lakes: Lakes with a surface temperature of over 4°C throughout the year
○ Temperate lakes: Lakes with a maximum temperature of over 4°C and a minimum temperature of under 4°C
○ Polar lakes: Lakes with a surface temperature of under 4°C throughout the year
② Water Color
③ Chemical Composition
⑶ Movement and Changes in Lakes
① Changes in Lakes
② Lake Markers
⑷ River Systems
① Equilibrium Rivers and Antecedent Rivers
② Antecedent Rivers
③ River Capture
⑸ Discharge and Flow Curves
⑹ Formation of Groundwater
⑺ Composition of Groundwater
① Water Hardness
② Chloride Ions
⑻ Classification of Hot Springs
① Intermittent Springs
⑼ Hot Spring Therapy
① Simple Springs
② Saline Springs
③ Sulfur Springs
④ Radioactive Springs
⑤ Mineral Springs
⑽ Hot Springs in South Korea
Table. 5. Hot Springs in South Korea
5. Intertidal Zones
⑴ Understanding Intertidal Zones
① Broad flat areas of sand or pebbles along the seashore that are submerged during high tide and exposed during low tide
② Components: Estuarine ecosystem, intertidal ecosystem, subtidal ecosystem
○ Estuarine ecosystem = Part of the marsh vegetation + α
○ Intertidal ecosystem = Other part of marsh vegetation + intertidal zone
○ Subtidal ecosystem = High tide zone + low tide zone
③ Causes of Formation
○ Wave action
○ Waves : Weakening as storms reach the seashore
○ Wave Action : Erosion caused by waves, leading to the creation, transport, and deposition of soil, sand, and gravel, forming tidal flats
○ Depositional Phenomena : Accumulation of sediment from rivers, with a significant amount of organic matter, forming deposits
④ Functions
○ Economic Value : Provides about 50% of fish, and nearly 100% of crustaceans and mollusks
○ Natural Purification Function : Filters pollutants through marsh vegetation and tidal flats, preventing eutrophication
○ Natural Disaster Mitigation and Climate Regulation : Acts as a buffer zone where land meets the sea, mitigating rapid changes
○ Ecological Habitat : Mostly a comfortable breeding ground for marine life and birds
Example : Ramsar Convention
○ Cultural and Educational Value
⑵ Environmental Conditions and Distribution of Intertidal Zone Organisms
① Definition and Classification of Benthic Organisms
○ Marine organisms are broadly divided into three categories
○ Category 1: Plankton : Drifts along water currents due to weak or no swimming ability
○ Category 2: Nekton : Capable of self-propelled swimming
○ Category 3: Benthos : Inhabits the seafloor, including tidal flats and rocky areas
○ Benthic Plants : Divided into green algae, brown algae, red algae, and seagrasses
○ Benthic Animals : Classified based on habitat, biological lineage, food type, and size
○ Diet includes not only herbivory and carnivory but also detritivory, filter feeding, and scavenging
② Environmental Factors of Benthic Organisms
○ Physical Factors : Waves, tides, seawater, substrate, light, water temperature, etc.
○ Waves
○ Forming foam → Blocks light penetration
○ Increases dissolved oxygen and intertidal zones
○ Tides
○ Different patterns of species distribution, significant diurnal temperature variation due to exposure time
○ Induces reproductive and feeding activities, creating a rhythm of daily activities
○ Seawater
○ Disperses certain organisms and nutrients through seawater movement
○ Substrate
○ Divided into hard and soft substrates, providing shelter and nutrients
○ Light
○ Light affects plant growth and reproduction through photosynthesis
○ Acts as a cue for animals, indicating time and guiding behavior
○ Water Temperature
○ Since many marine animals are poikilothermic, their lives vary with changes in water temperature
○ Chemical Factors
○ Salinity
○ The amount of dissolved salts in 1,000 liters of seawater, measured in parts per thousand (‰)
○ Average is around 35 ‰
○ Dissolved Oxygen Content : The amount of oxygen dissolved in seawater
○ Biological Factors
○ Predation : The process of detecting food presence, locating it, attacking, processing, and consuming it
○ Food
○ Space
○ Dispersion
○ Movement
6. Utilization of the Ocean
⑴ Ocean Thermal Energy Conversion : Generating power using temperature difference between deep and surface water
⑵ Tidal Power Generation : Utilizing the difference in water levels to generate power
⑶ Wave Power Generation : Using the force of waves to rotate turbines through compressed air
① When waves hit, seawater compresses air within the generator
② The displaced air turns the turbine, generating electricity
⑷ Deep-sea water at depths of 1,000 to 4,000 m : Premium bottled water market
Input : 2016.06.22 20:54