Short answers, pulled from the story.
The Black Sea is anoxic below roughly 100-200 meters because a permanent density boundary prevents the deep water from mixing with oxygenated surface water. Bacterial decomposition of sinking organic material consumes all available oxygen in the deep water, and the stratification is so extreme that over 90% of the deeper Black Sea volume remains permanently anoxic.
The Black Sea deluge hypothesis, put forward by William Ryan, Walter Pitman, and Petko Dimitrov, proposes that around 5600 BC seawater from the rising Mediterranean breached the Bosporus sill and catastrophically flooded the Black Sea basin. The hypothesis was published in The New York Times in December 1996 and in an academic journal shortly after. Scientists agree the sequence of events occurred but debate its suddenness, exact date, and magnitude.
The earliest known name is the Sea of Zalpa, used by both the Hattians and the Hittites. Ancient Greek sailors knew it as Pontos Axeinos, the Inhospitable Sea, a name first attested in the poet Pindar around 475 BC. The name was later euphemized to Euxeinos Pontos, the Hospitable Sea, which became the standard Greek designation.
The permanently anoxic deep water prevents the bacterial decomposition that normally destroys organic materials such as wood. Because no oxygen reaches the deep layers, ancient ships that sank into the anoxic zone are preserved in excellent condition. The Byzantine wreck Sinop D, found off the coast of Sinop, Turkey, is one example.
The Montreux Convention of 1936 governs passage through the Bosporus and Dardanelles, allowing free transit for civilian ships between the Black Sea and the Mediterranean. Military vessels from countries that do not border the Black Sea face strict restrictions and may only remain in the basin for a limited time. The 1982 amendments to the convention gave Turkey the authority to close the straits at its discretion in both war and peacetime.
The Moskva, flagship of the Russian Black Sea Fleet, was sunk on the 14th of April 2022 by Ukrainian sea-skimming R-360 Neptune missiles in the western Black Sea. It was the largest ship lost in naval combat in Europe since World War II. Russia claimed the sinking was caused by an onboard fire igniting munitions.