The coccolithophore Emiliania huxleyi.
Ulf Riebesell is a biological oceanographer at the GEOMAR-Helmholtz
Centre for Ocean Research in Kiel, Germany, who has directed several
major ocean acidification studies, off the coasts of Norway, Finland, and
Svalbard. Riebesell has found that the groups that tend to fare best in
acidified water are plankton that are so tiny—less than two microns
across—that they form their own microscopic food web. As their numbers
increase, these picoplankton, as they are called, use up more nutrients,
and larger organisms suffer.
“If you ask me what’s going to happen in the future, I think the
strongest evidence we have is there is going to be a reduction in
biodiversity,” Riebesell told me. “Some highly tolerant organisms will
become more abundant, but overall diversity will be lost. This is what has
happened in all these times of major mass extinction.”
Ocean acidification is sometimes referred to as global warming’s
“equally evil twin.” The irony is intentional and fair enough as far as it
goes, which may not be far enough. No single mechanism explains all the
mass extinctions in the record, and yet changes in ocean chemistry seem
to be a pretty good predictor. Ocean acidification played a role in at least
two of the Big Five extinctions (the end-Permian and the end-Triassic) and
quite possibly it was a major factor in a third (the end-Cretaceous).
There’s strong evidence for ocean acidification during an extinction event
known as the Toarcian Turnover, which occurred 183 million years ago, in
the early Jurassic, and similar evidence at the end of the Paleocene, 55
million years ago, when several forms of marine life suffered a major
crisis.
“Oh, ocean acidification,” Zalasiewicz had told me at Dob’s Linn.
“That’s the big nasty one that’s coming down.”
WHY is ocean acidification so dangerous? The question is tough to
answer only because the list of reasons is so long. Depending on how
tightly organisms are able to regulate their internal chemistry,