Moving the Waters - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 120

Sea level, for example, might have been more than 200 metres
higher than today. Part of this amount would have come from the
melting of virtually all the world's ice—but only part (today, melting
all global ice would only raise sea level by some 70 metres). Part—
maybe a few tens of metres—would have come from thermal expan-
sion of the oceans. And part was likely not related directly to the
world's climate, but reflected global tectonic patterns. If the Creta-
ceous ocean crust was forming faster than it does today, that crust
would have been hotter overall than today and therefore, through
thermal expansion, would have been raised higher, displacing the
overlying ocean water upwards. The increased volcanism would have
belched out more carbon dioxide too, helping to warm the Earth's
climate through an enhanced greenhouse effect.
The ocean waters would have spilled over the continents, submerg-
ing much of their area. This would have blurred the sharp distinction
that exists today between the shallow waters of the continental shelves
and the deep ocean waters. This distinction can be seen physically as
a sharp line (the ocean front) separating clear blue ocean water from
the shelf waters that are often turbid and sediment-laden. It is a key
boundary, typically separating very different communities of marine
organisms.
In the Cretaceous, with its higher sea levels, the ocean front would
have disappeared or become severely blurred. In effect, oceanic con-
ditions moved across on to the continents. The iconic chalk strata that
formed in late Cretaceous times are in effect a deep-sea deposit—the
settling of trillions of coccoliths, complex microscopic skeletons of
calcium carbonate made by single-celled planktonic algae—that
drape what was previously a shallow sea floor or even land.
With little or no ice at the poles, Bill Hay sees the Earth's climate
system as having been held in a less tight grip than it is today. 70 With-
out a supply of cold polar-derived deep waters, circulation in general