# How do you measure 407 degrees Celsius?

## Challenge in 3, 000 meters water depth

With a special thermometer developed at the University of Bremen, scientists at 3, 000 meters measured the highest temperature ever recorded in seawater at 407 degrees Celsius. The measurement took place during the 68th Meteor flight on the Mid-Atlantic Ridge at 5 ° South. But with what technology could researchers capture these high temperatures?

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The normal seabed temperature at this depth is between two and three degrees Celsius. All equipment that works here must withstand the enormous pressure and aggressive salt water. But at the hot springs of the deep sea, the black smokers, extremely hot acidic water gushes from meters high chimneys: "Pressure, salt water, corrosive acids and extreme temperatures - this must withstand a device that works in such extreme places as black smokers ", says Hans-Hermann Gennerich, from the University of Bremen. The geophysicist has developed a probe for the University of Kiel that can withstand all these influences. Not so easy, because: "The thermometer must be very thin so that it displays the temperatures very quickly". On the other hand, such a device must still be mechanically stable. This places high demands on the material. A titanium tube would withstand pressure, acid and heat, but it would be too flexible - it would not go anywhere. "And that just is not possible, " explains Gennerich.

### Pressure: 300 kilograms per square centimeter

"The thin rod, which is held in the escaping water, is made of special steel. This is necessary because many additives that make the steel stronger make it more susceptible to corrosion by salts and acids - and the high temperatures increase the caustic effect. "" Because the pressure inside the probe is the same as on the surface, it squeezes Water at 3, 000 meters depth with 300 bar on the housing. That's 300 kilograms per square centimeter, more than when a heavy truck drives over it, "explains Gennerich.

The insulation of the electrical cables was also a concern. "Even Teflon, which normally performs well, evaporates at 270 degrees Celsius. Therefore, we take a thin braid of glass fibers. Even soldered connections will not hold when the solder melts. "Gennerich was not worried that the probe would fail due to the extreme conditions:" We designed the probe for 4, 000 meters of depth and temperatures up to 450 degrees Celsius. Of course, something can always break, but that's an expedition. "Display

### Hot hotter hottest

But even if the probe meets all requirements, the question remains how to position it exactly in the chimney of a black smoker. "Since the view near the black smoker is usually very bad, the pilot of the diving robot orients itself at the temperature display. This is a bit like pot-smoking: warm, cold, warmer, hotter, hotter, hottest. For this game to work up to 4, 000 meters below the helm of the robot aboard the research vessel, the probe must respond to changes very quickly. "But this time the scientists were lucky that the current was weak and the diving robot QUEST of the MARUM marine research institute could park near the chimney and insert the probe directly into the vent.

Therefore, the scientists also know that the record was no accident or measurement error, because the simultaneous sampling of the water takes several minutes and the temperature was constant over this period. Constant hei . In addition, it can be seen on the video footage that the water is boiling. And that's what it does in the pressure conditions exactly at 407 degrees exactly the measured temperature.

(Kirsten Achenbach, RCOM, 29.05.2006 - AHE)