Ground materials, etc. Sometimes, turbidity current deposits formed on continental slopes can extend to the movement of seawater in deep-sea plains, the chemical reaction of dissolved substances in seawater, and the destruction and construction of coastal and seabed rocks and topography by marine life. Marine geological processes include marine erosion, transportation and deposition. The movement modes of seawater are mainly waves, tides, ocean currents and turbidity currents. These four kinds of seawater movements are important driving forces of marine geological processes. Due to the influence of seawater depth and seabed topography, they form different hydrodynamic zones in the ocean. The coastal zone and continental shelf of shallow sea are hydrodynamic areas dominated by waves and tides, while continental slope and deep-sea basin are hydrodynamic areas of ocean currents and turbidity currents. These four mechanical forces can produce marine erosion, transportation and deposition. Mechanical marine erosion is the destruction of coast and seabed caused by hydraulic impact (also called erosion) when seawater moves and abrasion caused by debris carried by seawater. There are three ways of mechanical handling of seawater: ① moving, coarse debris rolling and sliding along the bottom; (2) jumping, that is, coarse debris moves intermittently by jumping; (3) Suspended matter, tiny sundries suspended in water. These three ways vary with the strength of hydrodynamic force and the particle size of debris. Sometimes three modes exist at the same time, sometimes transition and jump coexist, or only pause. When the mechanical power of seawater disappears, precipitation will occur. There are mechanical deposits everywhere in the ocean, but continental shelf and continental slope are the most abundant. The chemical action of water is mainly the dissolution of soluble rocks (also called dissolution) and the chemical reaction of dissolved substances in seawater to form sediments on the seabed.
There are not only many creatures in the ocean, but also many kinds. There are creatures in seawater at different depths, but the seawater on the continental shelf is the most prosperous. The geological process of marine life mainly refers to the deposition of biological remains on the seabed.
Among the three geological functions of the ocean, marine erosion is the most obvious and intense in coastal areas, and sedimentation is the main function of the vast ocean basin. The ocean accounts for about 7 1% of the earth's surface area, and it is the largest deposition site on the earth, with a large number and variety of sediments. There are ancient marine sediments in different geological periods in most areas of modern mainland. Studying marine geological processes, especially seabed sediments, is of great significance for understanding the development history of the earth and developing and utilizing seabed mineral resources. Geological Action of Waves Waves (also called waves) are regular ups and downs of seawater due to wind friction. The size of waves is related to the strength, persistence and openness of the sea. Usually, the wavelength of waves ranges from tens of centimeters to hundreds of meters, and the height of waves ranges from several centimeters to more than ten meters. The fluctuation range of water quality point and the energy related to it decrease with the increase of water depth. They have been greatly reduced when the water depth is half wavelength, so the depth of half wavelength is usually taken as the lower limit of wave influence. In the shallow water area with water depth less than half a wavelength, waves are deformed or even broken due to seabed friction, and become broken waves, forming a complex nearshore current system, which is called broken wave flow. The impact force of ocean waves can reach 9.80665× 104 Pa to 29.4438+0995× 104 Pa. When the wave motion direction is perpendicular to the coast, it produces inflow and outflow perpendicular to the coast; When the wave motion direction is inclined to the coast, the coastal current parallel to the coast is generated due to the refraction of the wave. Waves and their various waves and currents under different conditions are important driving forces in shallow water. Surge current will directly damage the coast. When seawater permeates into rock cracks to compress air, the expansion force of air intensifies rock cracks. Debris carried by waves is also a tool to wear away rocks. The above-mentioned mechanical damage of sea waves to coastal and seabed rocks is called erosion. The movement of gravel with waves is the carrying function of waves. Wave erosion and transportation often occur at the same time. When the hydrodynamic force of waves decreases, the transported objects are deposited.
When the waves scour the rock bank, a sea erosion trough is first formed at the water contact. The groove expands and the upper part collapses, forming a sea cliff. The coast retreated a distance. With the retreat of the steep cliff, the bottom of the trench expands into a platform slightly inclined to the sea, which is called a marine platform. When the sea level drops or the land rises, the platform exposed to the sea presents a stepped zone, which is called the ocean terrace. Under the action of waves, the slope of the platform gradually slows down. Once the energy of waves can't hit the coast and is dispersed and consumed in friction, the destructive power of waves on the seabed rocks in the coastal zone tends to zero. At this time, the cross section of the coastal zone is called the coastal equilibrium section. Due to the differences in rocks and structures that make up the coast, the anti-corrosion ability is also different, and erosion can also form caves, bridges, stone pillars and other landforms.
On the gentle sandy coast, waves mainly carry and deposit gravel through inflow and outflow or coastal current. The inflow advances to the land along the beach, and after the inflow power is exhausted, the backwater retreats to the sea along the slope under the action of gravity. The incoming flow brings the gravel to the shore, some coarse ones stay at the end where the waves reach, and some fine ones flow to the sea with the return flow. Debris is is constantly rounded and classified in the round-trip transportation of inflow and outflow. When the power of seawater disappears, they pile up along the coast into gravel beaches, beaches and underwater sandbars. The debris carried along the coast is mainly sand, which moves longitudinally roughly parallel to the coast. This longitudinal movement is most active at a depth of about 4 meters. Its speed depends on many factors, usually increases with the enhancement of waves and the decrease of the particle size of the transported object, and it is the fastest when the wave motion direction intersects the coast at an angle of 45. If the coastal current meets the bay, the velocity decreases, and the sediment is deposited at the mouth of the bay, forming a sand mouth with one end connected to the land. The height and elongation of the sand mouth can form a barrier in the coastal zone and form a semi-isolated lake inside.
The geological function of tides The periodic fluctuation of seawater under the tidal force of the moon and the sun is called tide, and the horizontal movement of seawater at the same time as the periodic fluctuation is called tidal current. Tides have changed the range of the breaking wave zone, and enhanced or weakened the marine erosion in coastal areas. On the flat silt and muddy coast, tidal current can affect a wide range. The tidal current stirred the sediment, washed the beach and etched a slender tidal ditch. In narrow straits and estuaries, the tidal height surges and the velocity increases. When the tide ebbs, the tide rushes down, digging up the sediment at the bottom of the canyon or estuary and bringing it into the sea.
Geological function of ocean current The large-scale flow of seawater along a fixed path is called ocean current or ocean current. The surface ocean current is mainly caused by the density difference between wind and seawater, and the thickness of the water layer is generally less than 100 m; Deep-sea currents are mainly related to seawater density. Generally, the speed of ocean current does not exceed 0.5 ~ 1.5 m/s, and decreases with the increase of water depth, which constitutes the so-called isodepth current with different water depths and different velocity. The geological function of ocean current is mainly to slowly transport suspended matters such as sediment and clay from shallow sea to deep sea. The velocity difference and entrainment capacity difference of equal depth flow affect the particle size and entrainment mode of its entrainment. In addition, the different deposition rates of transported substances and the appearance of turbulence all determine the distance of ocean current transportation.
The geological process of turbidity current is a kind of high-density water flow containing a lot of suspended solids, which mainly flows down the bottom slope by its own weight. Turbid flow has a great carrying capacity. Turbid flow with a velocity of 3 m/s can carry rocks weighing up to 30 tons. There are a lot of soft mud and loose debris saturated with water on the continental slope. Under the induction of external factors such as wind and waves, tidal current and submarine earthquake, these soft mud can easily liquefy and flow down the slope. Therefore, turbidity current mostly comes from the outer edge of continental shelf or estuary. When the turbidity current moves along the continental slope to the deep-sea plain, it etches a narrow deep-sea canyon with deep bottom and steep walls. Turbidite flows out of the canyon and reaches the deep-sea plain, its speed drops sharply, and a large amount of debris accumulates, forming long or tongue-shaped sediments or fan-shaped land, which is called turbidite fan. Turbid sediments are composed of typical terrigenous debris, and there are biological remains in shallow water, which are classified and layered.
Seabed sediments marine sediments can be divided into three types: mechanical, chemical and biological. There are sediments all over the sea floor, but there are many kinds of sediments on the continental shelf. The continental shelf is the most important sedimentary area in the ocean. Marine sediments are mainly debris brought into the ocean by rivers and winds, followed by organic components such as biological debris and microbial decomposition substances. In addition, there is a small amount of volcanic ash in the sediments, as well as meteorites and cosmic dust particles from space. Marine sediments are closely related to the marine sedimentary environment. Generally, according to the marine sedimentary environment with different seawater depths, marine sediments can be divided into: coastal zone (the water between high tide line and low tide line), shallow sea zone (shallow low tide ~ 200m deep water), semi-deep sea (200 ~ 2500m deep water) and deep sea (more than 2500m deep water).
① Coastal sediments. It is mainly mechanical debris distributed in beaches and tidal flats, that is, sand, biological bones and shell debris with different particle sizes. Chemical deposits such as rock salt, gypsum and potassium salt can be formed by evaporation in lakes with dry climate. Under humid climate conditions, the lake can become a coastal swamp, and a large number of coal-forming materials accumulate.
② Shallow sea sediments. Shallow sea area accounts for 25% of the ocean area, but the sediments in this sea area account for 90% of all marine sediments. There are three types of shallow sea sediments: clastic sediments are mainly sandy, and the particle size of clastic sediments generally decreases from shallow water to deep water, because waves weaken with the increase of sea depth. However, due to the influence of tidal current, ocean current, seabed fluctuation and continental erosion intensity, the grain size of modern shallow sea sediments is not all coarse near the shore and fine far from the shore. Biological deposition is mainly sediment formed by biological relics, and its composition is mainly calcium carbonate. In the tropical and subtropical warm seas, there are coral reefs with coral skeletons as the main part, supplemented by the bones and shells of other creatures, which are called coral reefs. Chemical deposits are mainly colloids of oxides and hydroxides of iron, manganese, aluminum and silicon from the mainland, which flocculate into oolitic or pea-like deposits when they meet seawater electrolytes.
③ Semi-abyssal zone sediments. Usually mainly terrigenous mud, with a small amount of chemical deposits and biological deposits. In the development areas of turbidity current and submarine ground slip, there may be coarse debris from shallow sea, and glacial debris and volcanic debris can be seen in some areas. The most widely distributed sediment on continental slope is blue ooze formed in reducing environment; Red ooze is distributed outside the estuaries of tropical and subtropical coasts, and green ooze is developed at the junction of continental shelf and continental slope.
④ Deep-sea sediments. Usually, plankton remains are dominant, and there are few terrestrial materials. The deposition rate is very slow. The biological sediments in the deep sea area are usually all kinds of biological ooze; Include diatom ooze and radiolarian ooze siliceous ooze; Calcareous ooze includes foraminiferal ooze, pteropod ooze and pebble ooze. In addition, there are deep-sea brown clay and a small amount.
======================================
Interaction between ocean and atmosphere
The relationship between ocean and atmosphere is quite close, because they are not only fluids, but also in direct contact with each other.
The influence of the atmosphere on the ocean
Atmospheric density and specific heat are smaller than seawater, so the influence on seawater mainly comes from wind or convection. For example, the wind flowing along the coast for a long time will not only affect the direction of surface current, but also cause the vertical movement of seawater.
Influence of airflow on ocean current
Image source: South Edition High School Basic Ball Science
For example, in the upper right picture, the continental margin wind blows from south to north, and the ocean current will flow to the open sea under the action of wind and Coriolis force, forming an upwelling along the coast; On the contrary, when the wind flows from north to south, it will make the current flow to the land direction and form a downward flow near the coast.
Atmospheric circulation will also affect the salinity of seawater surface. For example, in subtropical high pressure areas, atmospheric convection is dominant, the air is dry and warm, and the evaporation on the sea surface is greater than precipitation, resulting in high salinity.
water cycle
In nature, water vapor can not only provide fresh water for the land, but also balance the heat of the earth's atmosphere through three-state change, evaporation, condensation and precipitation.
Seawater accounts for the vast majority of the earth's hydrosphere. The water on the sea surface evaporates into the atmosphere, flows into the air, cools and condenses into clouds, which can produce precipitation on land, so the water cycle can be regarded as a natural seawater desalination process. In addition, water will absorb heat when it evaporates and dissipate heat when it condenses. Water vapor itself is an important greenhouse gas, and cloud is the main reflector of sunlight, which means that the water cycle process will also affect the heat budget of the atmosphere.
water cycle
Image source: South Edition High School Basic Ball Science
El Ni?o phenomenon
El Nino phenomenon refers to the abnormal warming of the sea surface in the equatorial southeast Pacific every two to seven years, which leads to the global climate anomaly. El Nino phenomenon is the result of the interaction between the atmosphere and the ocean.
Usually, the east wind blows mainly in the South Pacific near the equator, and the seawater keeps flowing westward, resulting in an upwelling in the Southeast Pacific. The seawater from below not only brings rich nutrients, but also makes the sea surface temperature lower.
When the El Nino phenomenon occurs, the equatorial easterly wind weakens or even blows the westerly wind, the original upwelling disappears and the sea surface temperature rises.
The change of sea surface temperature leads to the change of atmospheric convection and the climate is also affected. For example, the east coast of the Pacific Ocean is usually dry and rainy, and the west coast is wet and rainy, but the year of El Ni? o is just the opposite, which leads to flooding on the east coast and forest fires on the west coast are out of control.
The influence of the ocean on the atmosphere
The influence of the ocean on the atmosphere lies not only in the fact that the current will affect the climate, but also in the fact that the sea surface temperature will affect the humidity and convection of the atmosphere. As far as the current winter situation in Taiwan Province Province is concerned, due to the influence of Kuroshio, the temperature in the southern and eastern regions will be higher than that in China's coastal areas.
Sea surface temperature will also affect weather phenomena. For example, the sea surface with water temperature above 27 degrees Celsius can form a typhoon.