On the evening of June 7th, 'Xiangyanghong 10' Exploration Geophysics Laboratory. Liang Jin stared at the screen of the shallow profilometer, and fell into contemplation.
The shallow profilometer can reflect the shallow structure of the seabed longitudinally. On the screen image, there is a clear demarcation between the clay-like deposits and the bedrock. The former is light gray, the latter is dark black. Now, it represents the black part of the hard rock. A more stable light gray signal appeared, which means that there are thick sediments on the bottom of the ship where the gravity column can be placed.
Gravity column is a kind of sampling equipment specially used for obtaining seabed sediments. It is cylindrical and its length can be adjusted, ranging from 3 meters to 10 meters; some lead blocks are added at the top, like barbells, each weight For dozens of kilograms, the weight can be adjusted by adding or subtracting lead blocks. As its name suggests, it is directly plunged into the seabed by gravity to obtain a certain depth of columnar sediments. Unlike drilling rigs that drill in hard rocks, gravity columns' eat softly. Do not eat hard ', suitable for working in soft seabed.
Dayang 49 made its first gravity column operation in the fourth segment. As the chief scientist of the section’s chief scientist, Liang Jin was worried that he would not know if the thickness of sediments would hit the stone again because June 5-7 Both operations failed, and the gravity column sampling tube was empty.
'The gravity column is more suitable for operation in the abyssal plains, but this time it works in the midwestern Indian Ocean's mid-ocean ridge. The sediments in this area are thin, and the distribution is limited. The success rate is low. If the embarrassing point just falls on a big rock, it will not To the sample. 'The members of the geological team of the scientific expedition, Ren Fengfeng, an engineer at the Guangzhou Marine Geological Survey, said with a smile that the success or failure of gravity columns depends mainly on luck and morality.
'Although it does not have a high rate of grabbing of television grabs, the gravity column is long enough, deep sampling, and less disturbance.' Liang Jin said that, compared to other samplers, the sediment taken from the gravity column will remain as it is. Sedimentary sequence, reflecting the history of deposition.
Liang Jin decided to try again, but it was not enough. This was also the last attempt. In order to improve the stability and hit rate, he added 250 kilograms of lead blocks to 500 kilograms.
At 5:16 pm, the gravity column entered the water smoothly and was placed on the seabed more than 3000 meters by the cable. Liang Jin squatted back and forth, watching the decentralization data displayed on the lab screen from time to time.
Two hours later, he went to the octagonal building, which controls the operating room of the cable, and paid attention to the progress. Unlike television grabs, the gravity column was blackened by both eyes. The TV grab has a camera and you can choose what you want. If the grab sample is not good, it can be grasped again. For the gravity column, the staff only judges the decentralization condition based on the cable length and tension data. It is affected by many uncertainties, whether the sample can be taken, and only the equipment is recovered to the deck. know.
At a distance of 150 meters from the seabed, the gravity column began to accelerate and was quickly lowered at a speed of 50 meters per minute. At about 7:30, the length of the cable was greater than the water depth, and the maximum tension of the cable suddenly decreased. The staff judged that the gravity column had bottomed out.
The bottom end of the gravity column is a double-layered knife blade, which can stretch and have elasticity. After the squatting, the knife blade is opened and the soft mud is stuffed into the plastic hollow tube of the gravity column. When the cable is pulled up, the knife blade is automatically closed to prevent Sediment leakage.
At 9:21, the gravity column exits water. The team members are waiting in the rear deck to pray. This is a good day's harvest. Open the knife edge and take out the plastic tube. Surprisingly, the plastic cylinder is 110 centimeters in diameter and nearly 3 meters in length. Filled with a tube full of 'mud'. Liang Jin relieved, and everyone happily took the sample back to the laboratory, and take pictures, processing, preservation.
This columnar sample will be sent back to the domestic laboratory as it is, waiting for a subsequent series of analyses. Although the stratification of sediments cannot be seen on the site, we still noticed changes in the sediments when we processed the samples: The deposits at the blade are dark, greenish, and dry; the top sediments are off-white.
'The sediments in this area are conservatively estimated to have a history of 100,000 years. The research data on the deposition history of the midwestern Indian Ocean's mid-ocean ridge is still relatively small. If you are lucky, the sample may also reflect information on nearby hydrothermal activities.' Jin said.
The sediment samples retrieved from the gravity column can help us understand the history of the evolution of the seabed geology. ' Ren Jinfeng introduced that this tube sample can be used for the study of the paleoenvironment of the area, and the element content and sediment age can also be measured. Using sediments The organisms, such as the foraminifera shell, analyze and reconstruct the climate signals of different eras, and compare the change curve with the global climate change curve that has been constructed.
The gravitational column shows the common 'deep mud', which may tell us about the mulberry fields in the southwestern Indian Ocean tens of thousands of years ago.
