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populations, all isolated, have evolved similar anatomy.
Creatures of the ocean deeps include some of the oldest and
best-preserved fauna on the planet. One of Jamieson’s landers had
caught on camera a chimera—from a family of fish that evolved around
280 million years ago—tussling with a shark.
One of the biggest mysteries about these places relates to the
depth range of fish. No one has ever seen any below 8,200 meters.
So, what’s up with the last 3,000? The explanation, Jamieson thinks,
is that fish are biochemically constrained from passing below that
point. Paul Yancey, a Whitman College biologist who would join
a future Five Deeps dive, has proposed that the answer lies in os-
molytes, compounds that protect the proteins inside animal cells
from damage caused by extreme pressure. Yancey discovered that
the concentration of an osmolyte known as
TMAO in fish cells increases with depth.
Since 2011, Jamieson and Yancey have biop-
sied dozens of fish species and plotted their
osmolytes. At 8,200 meters, the cells were
saturated. No way to add more TMAO.
Vescovo lit up at this story. “It’s the in-
verse of the death zone,” he said, referring to
the altitude at which the human body can no
longer acclimatize to a drop in oxygen lev-
els. Generally, it’s around 8,000 meters up.
Jamieson has a theory about this under-
water line: He speculates that it was once
the full-ocean depth. Most of the world’s
trenches are within a few hundred meters of
8,000, and they’re all flat. But the deepest
points—those few 9,750-plus-meter drops—
are not flat at all. They’re pits, created, he
thinks, when seafloor plates split.
Perhaps numerous animals evolved to
exist down to 8,200 meters, but only some
went deeper after those rifts occurred.
Given time, or environmental necessity—
say, rapidly warming seas—maybe fish will
evolve the ability to get there too.
hen Vescovo passed 8,200
meters in the Puerto Rico
Trench on December 20,
2018, Limiting Factor officially
became the deepest-diving
operational submersible on the planet. Two
months later, Vescovo became the first per-
son ever to dive the Southern Ocean’s South
Sandwich Trench, which sits in the nether
region between Argentina and Antarctica.
“We know more about Mars than we know
about the South Sandwich Trench,” he said.
That leg required a full month aboard Pres-
sure Drop. And the weather, cold and blustery,
was a concern the whole way. The crew had
to pick up an ice pilot to navigate the ship
around icebergs. But luck broke the right way.
On the day of the dive, the conditions were
perfect: clear weather, calm ocean.
The attempt itself was not. Around 4,500
meters, a little more than halfway down,
Vescovo lost communications with the sur-
face; this time, it was an effect of the frigid
water. The crew could hear Vescovo, but he
couldn’t hear them. “I decided to keep going
Under Construction
Limiting Factor midbuild;
its core is a titanium
sphere flanked by foam.
POPSCI.COM•FALL 2019 57