Chapter 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
> ○ 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
> 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
> 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
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**
> 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**
> 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. >> ○ [Subcritical, supercritical flow is possible](https://jb243.github.io/pages/2489). > 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**
>> ○ 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**
>> ○ **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
>>> ○ 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 ⑶ [Tidal Phenomenon](https://jb243.github.io/pages/344)
## **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
## **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 >> ○ [Tidal Flat Phenomena](https://jb243.github.io/pages/344) >> ○ 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
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