“Turkey has closed access through the Bosphorus Straits.”
Why?
They have a longstanding International authority - the decision to restrict warships, a power given to Turkey by the Montreux Convention of 1936.
One of the likely reasons that Russia called its invasion a “Special Military Operation” and forbade the use of the word war to describe it, was to prevent NATO member Turkey from activating that closure. Turkey did it anyway - it is their call under the Convention.
The two heavy cruisers that Russia had brought nearby (Syria), will now not be able to participate in the hostilities around the Ukraine.
I suspect if Russia really wanted to, Turkey would allow it.