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WHOI scientist Daniel Torres explains the instruments on board the tripod to CTD watch stander Shannon Rauch.

The so-called “tripods” on board the Knorr look like lunar landers, or blobs of giant pollen, depending on how you tilt your head. They’re a kind of mooring: a package of instruments that sits on the ocean floor, measuring the water above and around it.

Deploying moorings, is the primary point of our trip. Tripods are moorings that go in shallow water — about 200 m. A weight in the middle of the tripod sinks the thing to the bottom of the ocean.

In two years, when Bob Pickart and his team return to this spot, a sound signal will release the tripod from the weight; those yellow floats will carry it up to the surface. Hopefully, they’ll be packed with data. 

Brian Hogue prepares attaches a CTD to the rope that will float above the tripod

The Payload

An instrument called an Acoustic Doppler Current Profiler (ADCP) sends up sound signals to measure the velocity of currents flowing above it. Sound signals go out at a particular frequency, bounce off the zooplankton and other particles that travel along with the current, and then return to the ACDP back at a different frequency depending on the speed of the flow. This is called the doppler effect; it is the same concept that makes radar guns that police use to catch speeding drivers. From ADCP data, scientists will know how fast the water in the ocean above the tripod is moving. 

Every 15 minutes, the CTDs — one attached to the tripod, and one attached to the string above it — will collect conductivity (used to determine how salty the water is), temperature, and density data. They’ll take these stats every 15 minutes — in contrast to the 32 measurements per second that the CTDs deployed on the rosette take. But these mooring order viagra australia measurements happen over two years, providing a record of what happens over the course of several seasons. 

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At all hours of the day and night, the team of 6 watchstanders have been taking turns hauling a heavy piece of equipment into and out of the ocean. The Knorr stops, and the watchstanders on duty go through an elaborate ritual of deploying a “CTD rosette.” The instrument collects data on the water as it descends and then ascends — sometimes 3 kilometres deep. It is a process that can take hours. When it’s done, the Knorr moves to the next designated spot in the line of CTD stops, and the whole thing starts over again. Three days of that — 21 stops — provides a snapshot of a section of the ocean that looks like this:

The varying color shows the varying salinity of the water. That purple color depicts fresh, cold, Arctic water, melted from icepacks North of us — with contributions from more local glaciers. The bright red: warm, salty, water, traveling up from the subtropics via the gulf-stream. Lower down, in green and yellow, is a third current. All this water is making its way around the tip of Greenland as “boundary currents” at the moment. It’s headed North West for a bit before they take a turn and go South. 

The CTD data is collected in between stops to place buy phentermine online moorings — long strings of instruments, shown in these pictures as lines and dots. These will take a snapshot of the water every two hours, and only take data where instruments (dots) have been placed.  In contrast, the CTD rosette collects data every few meters as the rosette makes its descent, collecting information along lots of points — which makes for a spatially high-resolution picture of the water.

To get an idea of what a mooring snapshot will look like, Bob Pickart modified the snapshot provided by the CTD rosette, making a map using only measurements that were taken approximately where the mooring instruments will be. That modified map, with reduced resolution, looks like this:

That the picture provided by the “moorings” captures the important contours of the CTD rosette data is encouraging. “You see something like this and you can’t help but get very excited,” says Pickart. 

So, why use moorings at all?

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The Knorr never sleeps. So neither do the scientists on it — or at least not all at the same time. Between sunrise and sunset, two “watch standers” and one marine tech are engaged in a data-collection all-nighter.

Sunday was the fifth night shift of our cruise, the night of the full, close-to-Earth moon, and the night that I chose to sit in. Close to Greenland, we were cruising over the continental shelf: the water is a little shallower here, the currents more interesting, and the work of the watch standers faster-paced.

Preparing to drop the rosette into the ocean at the beginning of the night.

The primary job of the watch standers is to usher a heavy and expensive instrument — called a CTD rosette, for its shape — to the bottom of the ocean. When watch standers Robert Daniels and Mironov Illarion take over at 8 PM, the thing is about 1,000 meters underwater, and rising at 60 meters/minute. Every couple hundred meters it stops, they hit a button that says “fire bottle” on the screen, and it closes one of its grey tubes to add 10 liters of ocean water to its load. Then one of them will press “talk” on a  speaker box and tell an operator to bring the rosette up to a new height. Along its journey, sensors on the rosette measure the salinity, temperature, and density of the water: the “fingerprint” of a current. A lab tech, Elizabeth Bonk, will analyze the salt samples collected by the bottles.

This procedure — a CTD cast — is a staple of oceanography. Illarion and Daniels have both done the casts before — Illarion in the Arctic, and Daniels off the Bering straight. The CTD data they collect here will contribute to a high-resolution snapshot of what the current around Greenland is doing.

Creating this snapshot is, for now, an act of construction work. Illarion and Daniels have showed up to work in steel-toe boots; they add hard hats and orange life-vests to their safety ensemble. (Illarion is also wearing neon yellow overalls, his own sartorial contribution to the “safety” look.) When the rosette returns to the surface, we go outside, and stand on the deck. It is 50 degrees, plus wind chill. Nicholas Matthews, the marine tech on duty tells me to stand inside the garage or put on a hard hat — so he doesn’t get in trouble.

The rosette, on its wire line, emerges from the water. The watch standers hook the metal frame of the rosette with poles longer than they are tall. From a control room above, an operator recoils the wire, and retracts the metal beam that it is hooked on so the rosette swings onto the deck of the boat, and lowers onto a little wooden platform. The watch standers strap it in, and then, with the pull of a lever, the platform moves the rosette from the deck into a little garage, where I am standing. Beneath the light of a heat lamp, Illarion sprays the frame down with a fresh water hose. He and Daniels collect salt samples from each of the six bottles that they fired during the cast.

We go back inside, and then, maybe half an hour buy lasix online later return to the deck-garage to do the reverse: the watch standers move the rosette onto the deck, unstrap it, and the operator lifts it into the ocean. From the control room, we wait for this piece of machinery — which, for all the world, looks like Iron Man’s heart or a slice of a particle collider — to make its way to the bottom of the sea.

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