The weather at the bottom of the sea

Eleven kilometres down, at the floor of the Mariana Trench, there is weather. Not our kind — no wind, no rain, no morning — but weather all the same: slow currents that take years to cross the Pacific's basement, occasional blizzards of white sediment, and, along the trench's western edge, warm springs that have been quietly venting since before there were trees. This is a short tour of the calmest climate on Earth. Nothing in it will be urgent.

The temperature

The water at the bottom of the trench holds between one and four degrees above freezing, and has done so for a very long time. Sunlight has never reached it; the nearest warm afternoon is eleven kilometres up. What heat arrives comes from below — from the slow radioactive patience of the planet itself — or from the vents, where seawater that has percolated down through the rock returns carrying minerals and warmth.

At the hottest vents, the fluid emerges at temperatures that would flash into steam at the surface. Here it cannot boil. Under the weight of an entire ocean, boiling is simply not available, and so the superheated water rises instead as a shimmering column, wavering like air over a summer road, until the cold closes over it.

The pressure

The pressure at the bottom is roughly one thousand and eighty-six times the pressure in the room where you're reading this. It is not violent. Nothing about it presses or crushes in any way a resident would notice; the animals that live there — pale shrimp, translucent sea cucumbers, a fish with a face like a disappointed uncle — are at equilibrium with it, as unbothered by the weight of the Pacific as you are by the weight of the sky.

The snow

There is snowfall. It's called marine snow: a perpetual, unhurried drift of organic matter — the microscopic remains of things that lived and finished living far above — settling toward the floor at a few tens of metres a day. A single flake may spend weeks in transit. When it arrives, it joins a sediment layer that accumulates at the rate of a few centimetres per thousand years. The trench floor is, by a wide margin, the least eventful place snow has ever fallen.

The champagne

At one site on the trench's northern arc, researchers found something found almost nowhere else on Earth: droplets of liquid carbon dioxide rising gently through the water, one after another, like a very patient glass of something. They named it the Champagne vent, and the droplets have been rising, as far as anyone can tell, for a very long time, with no occasion in particular to celebrate.

The point, such as it is

There isn't one, and that's rather the idea. Eleven kilometres beneath the busiest ocean on the planet, the weather is one degree above freezing, the snow takes a month to land, and the champagne rises a droplet at a time into the dark. It was doing this last night while you were awake worrying, and it will be doing it tomorrow night, and the night after that.