If you have ever walked barefoot along a river or seaside, you will find that there are endless wave-like traces on the river bed and beach washed by the current. These are wave-like traces. For geologists, ripple marks are an important rock structure because the existence of ripple marks means the flow of water. If ripples are found on the rock, it means that the rock was once soft sand, and scientists can also use it to determine the current situation at the time. In shallow waters, wave traces on the seabed are very common because waves on the sea surface can stir up the sediment on the seabed. But in the 1960s, photos taken from the deep seabed at a depth of 4000 meters showed that there were also ripple marks on the seabed! Waves on the sea surface cannot affect the deep seabed, and ripple traces cannot be formed by internal waves and turbid currents, because the formation of ripple traces requires relatively "stable" water flow. So scientists speculate that there is a special current on the seabed.
Since 1978, scientists have conducted 10 years of on-site observations on the seabed of the North Atlantic Ocean, placing sophisticated scientific instruments on the seabed at a depth of 4800 meters to measure changes in deep-sea currents. This is the HEBBLE project. Observations confirmed the existence of deep-sea currents. Scientists call it a contour current because it always flows along the isobath line of the seabed topography. The current velocity is usually low, generally only 15 to 20 cm/s. But don't underestimate this kind of contour current. It is the most important "porter" on the seabed, carrying sediment and various sediments on the seabed all the time. This seemingly "casual" slow-motion continues to "carve" the rugged seabed, leaving a series of "footprints"-seabed ripple marks-on the rocks on the seabed. Another major discovery of the HEBBLE project was the observation of "undersea storms" in the deep sea. When a "storm" occurs, the velocity of flow on the seabed suddenly increases several times, and the sediment on the seabed is stirred up and becomes turbid,"you can't see your fingers", just like a sandstorm on land. This phenomenon occurs about 10 times a year and lasts for 2 to 20 days each time. The formation mechanism of "submarine storms" has not yet been fully understood, but the discovery of deep-sea currents has changed people's understanding of the deep-sea environment.