Ocean Forms - Ocean Worlds: The Story of Seas on Earth and Other Planets - page 39

There was more than weather control to contemplate in the film,
though. The half-crazed human survivors, living on their makeshift
raft homes, did not much go in for fishing, as short of food as they
were (although our hero did single-handedly overpower the obliga-
tory sea-monster, prior to dispensing monster steaks all round). Here
the perspiring scriptwriter might have been on to something. On the
real Earth of today, part of the water evaporated from the oceans later
falls on to land as rain. The water, passing through rock and soil, dis-
solves a variety of mineral and organic nutrients, then returns that to
the sea via river flow. In the sea, those washed-in nutrients feed the
growth of the plankton that is the base of the rich and diverse marine
biology that we know (see Plate 1).
Far from the land, in the middle of the oceans, there are what
amount to ecological deserts, where primary productivity (through
photosynthesis) in the sunlit surface water is very low because the
nutrient flood does not reach so far. These nutrient scraps are soon
used up by what few plankton there are, which die and sink into deep
water. What little replenishment does arrive comes as far-travelled
windblown dust (blown from distant lands that would be absent in a
water world), or is stirred up from deeper water by storms.
Something like that would be the ecology of a true water world. It
would not be a completely biologically sterile world. There would
still be those nutrients at depth, dissolved from undersea volcanoes
and such, but it would be hard to get those into the sunlit surface
waters. A real water world would be impoverished compared with
our current riches. On the kind of tenuous food base that would
result, sea monsters would find it hard to scrape a living. It would not
be easy, either, to evolve energetic, intelligent, complex mer-people
on such a world.
Conversely, take a world with not very much water: one where
that water would be restricted to a few scattered shallow seas and a