I doubt that this was “carved out” by glacial runoff, seeing as that would mean the sea level was at least 1,400 feet lower than what we have now.
Just looked it up, during the last “ice age” [officially we are still in the “ice age”] sea levels were estimated to be 400 feet lower than now. We only have 6.75 more years until that number becomes 400.5 feet and everyone dies.
“I doubt that this was “carved out” by glacial runoff, seeing as that would mean the sea level was at least 1,400 feet lower than what we have now.”
It was carved out by several cycles of glacial runoff as sea levels fluctuated producing seawater/freshwater interfaces which are corrosive.