Recorded in August of 1991, Upsweep consists of a "long train of narrow-band upsweeping sounds of several seconds in duration each." The source of Upsweep has been tracked to a location of inferred volcanic seismicity and seems to be seasonal, reaching its peaks in Spring and Autumn. The source level was strongest in 1991 and has been declining ever since but can still be captured on the hydrophones throughout the Pacific Ocean. Upsweep is more precisely located near Antarctica, about 2,500 miles west of the southern tip of South America. It was originally believed that the Upsweep sound might be fin whales but this theory was debunked in 1996 when researchers argued there wasn't enough variation in the tone for it to be created biologically.
Bloop is perhaps the most well-known unidentified sound. At least it's the first one I heard of many years ago. Bloop was captured in 1997. The sound is apparently consistent with the noises generated by "icequakes" or large icebergs scraping along the ocean floor. What's creepy about Bloop is that it is several times louder than the loudest recorded animal, the blue whale. However, some believe that maybe Bloop is evidence of an even larger life form lurking in the depths of the oceans. Interestingly enough, no other Bloops have been recorded since 1997.
Recorded in 1997, Train rises to a quasi-steady frequency. Once again, the origin is likely to be a very large iceberg grounded in the Ross Sea near Cap Adare. Interstingly, Train was the unidentified sound I was able to gather the least amount of information on during my research.
So, lovely readers, how do you feel about these unidentified sounds? Are they not creepy at all? Are they slightly unnerving? Do you believe them all to be iceberg shifts or volcanic activity or is it possible there is something else down there producing these noises? I guess we are left only to rely on science as best we can in this situation, but if even the greatest scientists classify these sounds as "unidentified", is it possible that they could be made by something we couldn't even imagine? *shudders again for good measure*