For further explanation, as the images is a bit lacking in detail:
That limestone was laid during the previous interglacial period. That type of coral requires 15 to 20 ft of seawater above it to live.
This has been the norm with other previous interglacials. Scientists can't explain why, but we're actually a lot COLDER than we should be. Atmosphere, tectonic movements - none of them account for why it is actually colder now that it should be.
In something like within a thousand years of the end of the previous ice age, 70% of the ice that covered Greenland melted. To date, despite all that "Greenland loses a football field worth of ice a a summer" talk, 70% of Greenland is still glaciated, so the reverse of what it was 130,000 years ago. And this is after 10,000 years, mind you, when the last time all that ice melted in under 1,000 years (which was actually unusually rapid anyways).