Ocean basin

Geographical terminology

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synonym Sea basin (Sea basin) generally refers to ocean basin

This entry is made by Compilation and application of scientific encyclopedia entries of "Science Popularization China" to examine.

Ocean basin is a structure with many low and flat areas at the bottom of the ocean, surrounded by relatively high seamounts, which is similar to a basin on land Sea basin perhaps Marine basin 。 It is the main part of the ocean floor. for example Persian Gulf Basin 、 East China Sea Basin 、 Pearl River Mouth Basin wait.

Chinese name: Ocean basin
Foreign name: Ocean basin
Definition: Structures similar to terrestrial basins
Status: The main part of the ocean floor

Technology: Deep sea drilling technology
Age: Generally no more than 160 million years
Evolution time: It has never stopped since the birth of the earth
Discipline: Structural geology

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brief introduction

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Ocean basin

The ocean basin is at the bottom of the ocean with many low and flat areas, such as Persian Gulf Basin 、 East China Sea Basin 、 Pearl River Mouth Basin 。 It is also called "deep sea basin" and "sea basin". A large circular or oval depression distributed in the deep ocean. The bottom of the basin is very gentle, and it is usually surrounded by ridges, so the bottom of the basin is also called the abyssal plain, such as Aleutian abyssal plain, Bering abyssal plain, etc.^[1]

Main features

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Ocean basin refers to a huge round or oval seabed depression. Typical oceanic crust 。 It is often surrounded by sea ridges or seamounts, with a depth of 3000~6000m, and most of them are 4000~5000m deep. The general area is higher than 10km, and the total area accounts for more than 70% of the ocean area, which is the main body of the ocean. The bottom of the basin is relatively flat, with an average slope of about 20~40 '.^[1]

origin

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The sea level change caused by glaciers refers to the sea level fluctuation caused by the repeated advance and retreat of the glacier boundary due to climate warming. During the geological period of cold climate, ice sheets formed around the polar regions, and the amount of seawater in the ocean was relatively reduced, and the sea level was reduced accordingly; When the climate warms, the ice sheet melts, the ice water flows back to the sea, and the sea level rises again. As for the range of sea level rise and fall, scientists in different countries have different estimates. This mainly depends on how to estimate the thickness of the Antarctic continent's ice sheet and calculate the world's ice reserves. It is estimated that 95% of the world's ice reserves are in the Antarctic region, about 30 million cubic kilometers. If one day, the ice in Antarctica and Greenland (accounting for 99% of the total global ice reserves) suddenly melts, the sea level of the world's oceans will rise by 100 meters. Of course, the possibility of this happening is very small. The most likely scenario is that all glaciers will gradually melt over thousands of years. At the same time, the melting of glaciers will also be accompanied by the rise of a continent and the settlement Because the load of a large area is transferred from land to sea due to the melting of glaciers.^[1]

Theoretical theory

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The sea level change caused by crustal structure refers to the local or global sea level change caused by certain crustal movement. Local crustal movements can cause regional Sea level change 。 This is due to the change of the distance between the sea surface and the land surface caused by the crustal rise and fall. The rise and fall of global sea level is caused by some change in ocean basin volume, subsidence of ocean floor crust or formation of new ocean basin. The increase of the total volume of the world ocean basin will lead to the decrease of sea level; On the contrary, the ocean floor crust rises and some ocean basins disappear, which can raise the sea level. Plate tectonics It is believed that the sea level change and Seafloor spreading Rate related. Mid ocean ridge The accretionary material is hot, and gradually cools and becomes dense with time, so the ocean floor lithosphere sinks with time in the process of lateral expansion and movement. If the expansion rate of the ocean floor is very fast, and the ocean floor at a certain distance from the top of the mid ridge does not have enough time to cool to the "normal" level, the ocean floor will be higher than normal. Therefore, even if the total amount of seawater remains unchanged (most scholars believe that the amount of seawater has basically not changed since the Paleozoic), the sea level will also rise due to the reduction of the volume of the ocean basin. contrary, Seafloor spreading When the speed is very slow, the sea level will decrease. In fact, the sea level changes caused by the change of the seafloor spreading rate have a period of millions of years, and the change range can reach 300~500 meters.^[1]

Related disputes

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Although global Geological tectonic movement It plays a decisive role in the sea level changes during the whole geological history, but scientists believe that the quaternary period (More than 1 million years in geological history), glaciation has the greatest impact on sea level changes. For nearly one million years, with the alternation of ice age and ice age, the global sea level has fluctuated. About 35000 years ago, the sea level was approximately close to the position. A glaciation caused a general decline in sea level. At the peak of the last glacial period (about 15-2000 years ago), the sea level was about 130 meters lower than today. When the sea level was low in the ice age, a large area of shallow sea on the continental shelf emerged as land. At that time, Japan and China, Asia and North America (along the Bering Strait), Britain and the European continent, Australia and New Guinea were all connected (Chinese marine geologists found that the ancient coastline of the East China Sea was in Okinawa Trough Outer edge of the continental shelf on the west slope). Later, due to climate warming, the glaciers melted, and the sea level gradually increased. The world sea level is still in the process of rising. Because the factors that cause sea level changes are very complex, and there are many shortcomings in survey and measurement technology, people's understanding of the history and development prospects of sea level changes has certain limitations. Sea level rise may be temporary or part of the long-term water cycle on the earth. Will the development trend of this process cause new glaciation? In a word, people cannot make a final explanation for the problem of sea level rise.^[1]

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