- By Richard Gray
- BBC future
5 hours before
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Around the wreck of the Titanic, sunlight is quickly absorbed by the water and cannot penetrate more than 1,000 meters to the surface.
In the fall of 1911, a huge chunk of ice broke off a glacier southwest of the vast Greenland Ice Sheet. Over the next few months, it slowly drifted southward, gradually being melted by ocean currents and winds.
Then, on the cold, moonless night of April 14, 1912, a 125-meter-long iceberg—all that remained of the roughly 500-meter-long chunk of ice that had left a Greenland fjord the previous year—collided with the ocean liner RMS Titanic, which was sailing on its maiden voyage from Southampton, UK to New York, USA. The ship sank in less than three hours, taking more than 1,500 passengers and crew with it. The wreck now lies nearly 3.8 km below the waves, nearly 400 miles (640 km) southeast of the Newfoundland coast.
Icebergs still pose a hazard to shipping: In 2019, between March and August, 1,515 icebergs drifted south enough to enter transatlantic shipping lanes. But Titanic’s final resting place comes with its own perils, making tours of the world’s most famous wreck a daunting challenge.
After a five-person submersible carrying fare-paying passengers on a trip to the wreck of the Titanic went missing, the BBC has taken an interest in this region of the seabed.
Navigate the depths
The depths of the ocean are dark. Sunlight is absorbed very quickly by water and cannot penetrate more than 1,000 meters from the surface. Beyond, the ocean has plunged into perpetual darkness. Because of this, the Titanic is located in an area known as the “Midnight Zone”.
Previous expeditions to the wreck site have described a descent of more than two hours in total darkness before the seabed suddenly appeared in the light of the submersible.
Because line of sight is limited beyond the few meters illuminated by the truck-sized submersible’s edge lights, navigating at this depth is a real challenge, and it’s easy to get disoriented on the seabed. .
However, detailed maps of the Titanic wreck, compiled through decades of high-resolution scanning, can provide landmarks when objects are visible. The sonar also allows the crew to see features and objects beyond the small area of light illuminated by the submersible.
Dive pilots also rely on a technique called inertial navigation, which uses a system of accelerometers and gyroscopes to track their position and orientation relative to a known starting point and speed. OceanGate’s Titan submersible is equipped with a state-of-the-art autonomous inertial navigation system, which it combines with an acoustic sensor called Doppler Velocity Log to estimate the craft’s depth and speed relative to the seabed.
Nonetheless, passengers on previous Titanic voyages using OceanGate have described how difficult it is to navigate once you’ve landed at the bottom of the ocean. Mike Reiss, a TV comedy writer who worked on The Simpsons and took part in a voyage on OceanGate on the Titanic last year, told the BBC: “When you hit rock bottom you don’t know where you are. We must have that.” tossed blindly at the bottom of the ocean, knowing full well that the Titanic was somewhere, but it was so dark that the biggest thing under the ocean was only 500 meters away from us and we spent ninety minutes with it spent looking for her.”
crushing depths
The deeper an object sinks in the sea, the more the water pressure around it increases. On the sea floor, at a depth of 3,800 m, the Titanic and everything around it is subjected to a pressure of about 40 MPa, which is 390 times higher than on the surface.
“To put that in perspective, it’s about 200 times the pressure of a car tire,” Robert Blasiak, an oceanography researcher at Stockholm University’s Stockholm Resilience Center, told Stockholm’s Today show. BBC Radio 4. “That’s why you need a very thick-walled submersible.” The titanium sub’s carbon fiber and titanium walls are designed to allow it to operate at a maximum depth of 4,000 metres.
We are probably more familiar with the strong surface currents that can throw boats and swimmers off course, but the depths of the ocean are also riddled with underwater currents. Although generally not as powerful as those found at the surface, they can still displace large amounts of water. They can be fed by surface winds affecting the water column below, by tides in the deep sea, or by differences in water density due to temperature and salinity, called thermohaline currents. Rare events called benthic storms, which are usually associated with surface eddies, can also produce strong, sporadic currents that can wash materials onto the seafloor.
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The thick, reinforced walls of their submersible protect the crews from the crushing pressures of the deep.
The available information on the underwater currents surrounding the Titanic, which is divided into two main parts after the separation of the bow and stern during the sinking, comes from studies of the shapes of the seabed and the movement of the squid around the wreck.
Part of Titanic’s wreckage is known to lie near a section of seabed affected by a southward-flowing cold-water current known as the Western Boundary Undercurrent. The flow of this “undercurrent” creates shifting dunes, ripples and ribbon-like patterns in seafloor sediment and mud that have allowed scientists to understand their strength. Most of the formations observed on the seabed are associated with relatively weak or moderate currents.
The sand waves at the eastern edge of Titanic’s debris field — the scattered personal belongings, accessories, fittings, coal and parts of the ship itself that were buried during the sinking — indicate the existence of an east-west bottom current within the main wreck site, they claim the scientists, the currents are trending from northwest to southwest, possibly due to larger debris changing direction.
South of the front, the currents appear to be particularly erratic, running northeast-northwest-southwest.
Many experts believe that the wreckage of these currents will eventually bury the wreckage of the Titanic in the sediment.
Gerhard Seiffert, a deep-sea marine archaeologist who recently led an expedition to scan the Titanic wreckage in high resolution, told the BBC he didn’t think the currents in the area were strong enough to pose a threat to a submersible – assuming that was the case with electricity.
“I am not aware of any currents that could pose a hazard to a functioning seagoing craft on the Titanic site,” he said. “In our mapping project, the currents posed a challenge to mapping accuracy and did not pose a safety risk.”
sediment flows
After more than a hundred years at the bottom of the sea, the Titanic gradually fell into disrepair. The initial impact of the two main parts of the ship upon impact with the seabed caused large parts of the wreck to be twisted and deformed. Over time, microbes that feed on the ship’s iron have formed icicle-like “resilience” abilities, accelerating the wreck’s decay. In fact, scientists estimate that the higher bacterial activity at the stern of the ship — which is due in large part to the greater damage it sustained — is causing the ship to deteriorate 40 years faster than the front.
“The wreck keeps collapsing, mainly due to corrosion,” says Mr. Seiffert. A little every year. But as long as you keep a safe distance – no direct contact, no penetration through the openings – no damage should be feared.
Although extremely unlikely, sudden sediment flows to the seabed have damaged and even washed away man-made objects on the seabed.
The most important events – like the severing of the transatlantic cable off Newfoundland in 1929 – are triggered by seismic phenomena such as earthquakes. Awareness of the danger posed by these events is growing, although there is no evidence that such an event was associated with the disappearance of the Titan submarine.
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The Titanic is slowly collapsing as ocean pressure, moving sediments, and iron-eating bacteria erode its structure.
Over the years, researchers have identified evidence that the seabed surrounding the Titanic wreck was affected by massive underwater landslides in the distant past. Huge amounts of sediment appear to have tumbled down the continental slope from Newfoundland, creating what scientists call the “corridor of instability.” They estimate that the last of these “destructive” events occurred tens of thousands of years ago, forming layers of sediment up to 100 meters thick. But these events are extremely rare, says David Piper, a marine geology researcher with the Geological Survey of Canada, who spent many years surveying the seabed around Titanic. He compares these events in frequency to the eruption of Mount Vesuvius or Mount Fuji – on the order of once every tens or hundreds of thousands of years.
Other phenomena known as turbidity currents — where water picks up sediment and flows along the continental slope — are more common and can be triggered by storms. “We show a repeat interval of about five hundred years,” says Piper. However, the topography of the seabed in the area is expected to direct sediment flows toward a structure known as “Titanic Valley,” which would mean they would not reach the wreck at all.
According to Seiffert and Piper, it is unlikely that such an event could have played a role in the disappearance of the Titan submersible.
Other geological features surrounding the wreck site have yet to be explored. On a previous Titanic expedition with OceanGate, Paul-Henry Nargeolet, a former French Navy diver and dive pilot, visited a mysterious anomaly he discovered with sonar in 1996. It turned out to be a rocky reef covered in marine life. He hoped to visit another site he had discovered on previous expeditions near the wreck of the Titanic.
As the search for the missing ship continues, few clues exist as to what may have happened to the Titan and her crew. But in such a harsh and inhospitable environment, the risks of visiting Titanic’s wreckage are just as relevant today as they were in 1986, when the first people to set eyes on the ship from its wreckage embarked on the journey below.