CHAPTER VI

THE SEA AROUND US

Patella caerulea

Castello Aragonese is a tiny island that rises straight out of the
Tyrrhenian Sea, like a turret. Eighteen miles west of Naples, it can be
reached from the larger island of Ischia via a long, narrow stone bridge. At
the end of the bridge there’s a booth where ten euros buys a ticket that
allows you to climb—or, better yet, take the elevator—up to the massive
castle that gives the island its name. The castle houses a display of
medieval torture instruments as well as a fancy hotel and an outdoor café.
On a summer evening, the café is supposed to be a pleasant place to sip
Campari and contemplate the terrors of the past.
Like many small places, Castello Aragonese is a product of very large
forces, in this case the northward drift of Africa, which every year brings
Tripoli an inch or so closer to Rome. Along a complicated set of folds, the
African plate is pressing into Eurasia, the way a sheet of metal might be
forced into a furnace. Occasionally, this process results in violent volcanic
eruptions. (One such eruption, in 1302, led the entire population of Ischia
to take refuge on Castello Aragonese.) On a more regular basis, it sends
streams of gas bubbling out of vents in the sea floor. This gas, as it
happens, is almost a hundred percent carbon dioxide.
Carbon dioxide has many interesting properties, one of which is that it
dissolves in water to form an acid. I have come to Ischia in late January,
deep into the off-season, specifically to swim in its bubbly, acidified bay.
Two marine biologists, Jason Hall-Spencer and Maria Cristina Buia, have
promised to show me the vents, provided the predicted rainstorm holds
off. It is a raw, gray day, and we are thumping along in a fishing boat
that’s been converted into a research vessel. We round Castello Aragonese
and anchor about twenty yards from its rocky cliffs. From the boat, I can’t
see the vents, but I can see signs of them. A whitish band of barnacles