Why is this 2,500 year old shipwreck so well-preserved?

In 2017, researchers off the Bulgarian coast discovered the oldest intact shipwreck ever found. This ancient Greek vessel was not only nearly 2,500 years old, but was just one of 65 shipwrecks found at the bottom of the Black Sea in remarkable condition. So, why does the Black Sea contain so many well-preserved shipwrecks? Helen Farr and Jon Adams dive into the depths of the unique body of water. [Directed by Yuriy Polyashko, Darvideo Animation Studio, narrated by Pen-Pen Chen].