earth

Moving on the bottom of the sea, catching the “winding” to settle down

At the end of April, the famous science magazine Science published an article I wrote for the co-authors, which focused on the effects of vortexes on the surface of the ocean on the migration of biomes deep in the ocean. To put it simply, it is the story of how the submarine biomes move on the “windmill” of the ocean surface vortex.

Mid-ocean ridge – the birthplace of the black chimney on the seabed

This story begins with the mid-ocean ridge. The mid-ocean ridge is a huge mountain range deep in the ocean, where it is also the place to create new oceanic oceanic crust. In the volcanic crater of the mid-ocean ridge, the hot magma rises from the mantle and gradually cools, forming a new oceanic crust in combination with the softened rock around it. The newly formed oceanic crust squeezes the existing crust on both sides of the mid-ocean ridge and expands outward. Finally, swooping back to the ground at the junction edge of the plate. Therefore, the oceanic crust was born in the mid-ocean ridge and died in the collision between the plate and the plate, so that the metabolism is not limited.

[Distribution of the global mid-ocean ridge (source: USGS). 】

There are many submarine volcanoes associated with the mid-ocean ridge. Sometimes these volcanoes are exposed to the sea to form islands, the most famous of which is Iceland. Although the mid-ocean ridge was such a huge topographical structure, it was not until the 1950s that scientists had a comprehensive understanding of its distribution through a large number of ocean surveys.

It is precisely because the magma in the deep ocean ridge is rising, so there is a special geological wonder near the middle ridge – hydrothermal outlet – this structure is similar to the hot spring on the land. It is formed in such a way that cold seawater enters the deep part of the oceanic crust along the cracks of the seabed rocks and reacts to the rocks that are heated by the magma. The seawater after the reaction becomes a high-temperature, high-pressure mineral-rich water called “hydrothermal fluid”. The hot liquid from the upper part ejected from the top of the oceanic crust and met the cold sea water. During the hydrothermal cooling process, minerals are precipitated from them, and the near-precipitate is deposited around the discharge port. Over time, a high-low, chimney-like spout is formed. If the hot liquid sprayed from the “chimney” is rich in metal ions and sulfur ions, when the hot liquid is mixed with the cold sea water, the black metal sulfide will precipitate quickly, and a “black chimney” with “smoke smoke” will form. There are also some small chimneys that emit hot liquid at a slightly lower temperature, have a lower flow rate, and contain more silicon and calcium ions, which become a “white chimney” from silica and gypsum.

[Left picture: Schematic diagram of the formation process of black chimney. 1) The icy seawater seeps into the seabed through the gap; 2) The high temperature seawater reacts with the rocks in the seabed formation, and the seawater becomes a complex hydrothermal fluid; 3) the density of the hydrothermal fluid is small, thus It rises through the seabed rock formation; 4) The hot liquid leaves the chimney and mixes with the cold sea water, and the black metal sulfide quickly precipitates to form a black “smoke” (source: WHOI). Right: The black chimney of the sea that is smoky (source: wikipedia). 】

“Rose Garden” – the magical hydrothermal ecosystem

The mid-ocean ridge not only breeds geological wonders such as the black chimney on the sea floor, but, even more surprisingly, there is a special kind of biome in this corner that is forgotten by the sun. In 1977, the world-renowned manned submersible Alvin (ALVIN) accidentally discovered near the hydrothermal outlet when he was inspecting hydrothermal activity in the mid-ocean ridge of the Galapogos Islands in the Eastern Pacific. A biome that is even more vibrant than the rainforest. – It is a beautiful scenery, with snow-like dense microbes, white shellfish, crabs, purple fish, shrimp, and the most amazing thing is that there are large pieces of red and white roses like blooming roses. “Flowers”, so the scientists gave this place a beautiful name – “Rose garden”.

[Rose Garden near the hydrothermal outlet (Source: National Geographic, Photograph by Emory Kristof). 】

[Beautiful “rose” is a tubular worm that is now almost a typical representative of the submarine hydrothermal ecosystem. The tubular worm is a large-scale animal that lives near the hydrothermal port at a temperature of 15 ° C to 20 ° C (source: WHOI). 】

The lonely sea floor has been so busy since the “rose garden”.

Unlike our common photosynthesis-based ecosystems, the ecosystem at the hydrothermal outlet is based on the synthesis of chemical energy. In this small system, bacteria that can take advantage of the sulphide in the hydrothermal fluid are the most basic organisms. Based on the energy provided by these bacteria, a variety of other organisms live in the hydrothermal outlet. In 2007, I also had the privilege of taking the Alvin to the mid-Pacific mid-ridge of more than 2,400 meters. There, I witnessed the 2m long tubular worms, shellfish, white crabs and pink-purple ugly fish, all living very pleasantly.

Ocean whirlpool – moving windmill

Beautiful things are always short-lived. Similarly, the rose garden that lives by the “smoke” that exports the hot liquid is not long. The hydrothermal outlet is unstable and sometimes erupts suddenly on a large scale. As the research progressed, oceanographers discovered a strange phenomenon: almost all organisms near the hydrothermal outlet would die when a relatively large eruption occurred, but after the eruption, the biome would reappear soon. At the new hydrothermal outlet.

Perhaps you will feel that the emergence of new communities is a natural phenomenon, but in fact, it is not so easy to “move a home” in a tubular worm that is symbiotic with the chemically synthesized bacteria in the seabed biome. First, the temperature at the bottom of the sea is very low. In the waters of the East Pacific Ocean we observed, the water temperature is about 2 °C. The larvae of tubular worms can’t survive for a long time at such low temperatures, about a month or so. In addition, these biological larvae have little ability to swim, so they cannot swim to the new hydrothermal outlet. One of the more likely reasons was that the currents near the mid-ocean ridge brought the larvae past, but later the scientists observed that the currents on the seabed were very weak, the closest to the hydrothermal outlets we observed after the eruption. There are also more than 300 kilometers of biomes. It is impossible for very weak currents to transport larvae to such a distant place before they die.

What more powerful “winding” will there be? From 2004 to 2005, we placed more than 10 current meters in the middle ridge of the Eastern Pacific, hang them on the floats anchored on the sea floor so that they could measure current changes at different depths of the sea floor. In addition, we have placed instruments that measure the number and sediment of biological larvae. Through observation, we found that most of the time, the flow field near the mid-ocean ridge is relatively weak and stable, but at some time the flow rate will suddenly reverse and the intensity will increase significantly. When we analyzed the satellite data of the same period, we found that when the velocity of the seabed changes, a mesoscale vortex with a diameter of more than 300 kilometers passes through our observation point. Then, combined with numerical models and observations of biological larvae and sediments, we speculate that it is the large vortex on the surface of the sea that affects the seabed several kilometers deep, and the current caused by it causes the worm larvae of the hydrothermal vent to catch up. Moving the ride.

[The geographical location of the study area, the white five-pointed star in the picture shows the study observation point. The mesoscale vortex created by the Gulf of Twant-Pek and the Papagayo Gulf affects the East Pacific Seamount. East Pacific Rise: East Pacific Seamount; Mexico: Mexico; Gulf of Tehuantepec: Gulf of Twentepec; Gulf of Papagayo: Papagayo Bay (Source: Adams et al ., 2011, Science)

In addition to explaining the migration of hydrothermal export biomes, our work has found another problem. The intensity and quantity of these mesoscale vortices in the eastern Pacific have a relationship with the El Niño phenomenon that has brought many disasters to mankind. That is to say, when the El Niño phenomenon occurs, not only will we humans be affected, but even creatures hiding several kilometers below the sea will be indirectly affected by these large eddies. This also tells us that the earth is a highly coupled system, and it really counts as “leaving the whole body.”

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