The Mark 4 nuclear bomb was an American nuclear bomb design produced starting in 1949 and in use until 1953. The Mark 4 was based on the earlier Mark 3 Fat Man design, used in the Trinity test and the bombing of Nagasaki. The bomber, which was on a mission to simulate a nuclear strike, was on its way to Carswell Air Force in Texas when its engines caught fire. The 17-person crew had to parachute out and five of them died. The plane crashed on land but the bomb was not found amidst the wreckage. Crew members have said they ditched the bomb in the ocean first. It is a mystery that has baffled historians for more than half a century. Now, a commercial diver may have stumbled across the Mark IV bomb in the waters off Canada's west coast. The Canadian government, however, said that it was more likely to be the unexploded bomb (altho, however, haven’t confirmed that yet).
Gigantic Bloop sound in the Pacific Ocean
In 1997, the Bloop was heard on hydrophones across the Pacific. Bloop was an ultra-low-frequency and extremely powerful underwater sound detected by the U.S. National Oceanic and Atmospheric Administration (NOAA) in 1997. Several articles in the years that followed popularised one suggestion that the Bloop might have been the sound of an unknown animal due to the "organic" nature of the noise, a theory that elevated the Bloop to the level of a great unsolved mystery.
By 2012 NOAA concluded that the noise was ice-related.
The theory of a giant animal making noises loud enough to be heard across the Pacific was more fantasy than science. Dziak explained to us the NOAA's findings, and confirmed that "the frequency and time-duration characteristics of the Bloop signal are consistent, and essentially identical, to icequake signals we have recorded off Antarctica". He explained: "We began an acoustic survey of the Bransfield Strait and the Drake Passage in 2005 which lasted until 2010. It was in the analysis of this recent acoustic data that it became clear that the sounds of ice breaking up and cracking are a dominant source of natural sound in the southern ocean. Each year there are tens of thousands of what we call 'icequakes' created by the cracking and melting of sea ice and ice calving off glaciers into the ocean, and these signals are very similar in character to the Bloop."
Disappearance of Amelia Earhart
One of the biggest mysteries of the Pacific involves pioneering American aviator Amelia Earhart. Amelia Mary Earhart was an American aviation pioneer and author. Earhart was the first female aviator to fly solo across the Atlantic Ocean. In an attempt to make a circumnavigational flight of the globe in 1937 in a Purdue-funded Lockheed Model 10-E Electra, Earhart disappeared over the central Pacific Ocean near Howland Island. Around 3 pm Lae time, Earhart reported her altitude as 10000 feet but that they would reduce altitude due to thick clouds. Around 5 pm, Earhart reported her altitude as 7000 feet and speed as 150 knots. Earhart's 7:58 am transmission said she couldn't hear the Itasca and asked them to send voice signals so she could try to take a radio bearing. This transmission was reported by the Itasca as the loudest possible signal, indicating Earhart and Noonan were in the immediate area. They couldn't send voice at the frequency she asked for, so Morse code signals were sent instead. Earhart acknowledged receiving these but said she was unable to determine their direction. The mystery is though that garbled messages were heard after the assumed crash, which led investigators to conclude that the plane did not ditch in the sea since the electrics would have shorted. Some have suggested that Earhart and Noonan survived and landed elsewhere, but were either never found or killed, making en-route locations like Tarawa unlikely. Most historians hold to the simple "crash and sink" theory, but a number of other possibilities have been proposed, ranging from plausible-but-unlikely to outlandish conspiracy theories.