Early Clues: Red Sea "hot brines"

A very early hint of hydrothermal vents came in the 1880s when a Russian ship, Vitaz, sampled waters 600 meters (2,000 feet) deep in the Red Sea off the sacred city of Mecca. The deep waters were curiously warmer than those at the surface. Sixty years later, a Swedish ship, Albatross, also found water in the deep Red Sea to be a few degrees warmer than normal and unusually salty.

At first, scientists thought these “hot brines,” as they called them, were formed by the hot equatorial sun. The sun heated and evaporated surface waters—leaving behind very salty (and therefore denser) waters that sank to the bottom. That may have explained the high salt content of the Red Sea bottom waters, but not the high temperatures.

In 1964, the British research ship Discovery found deep Red Sea waters with temperatures of an astonishing 44°C (111°F). A year later, Woods Hole Oceanographic Institution’s R/V Atlantis II passed through the Red Sea on the way to the Indian Ocean. Although it was four days behind schedule, scientists aboard could not resist stopping to collect a Red Sea sediment sample. The temperature reading was 56°C (133°F). The chief scientist, Rocky Miller, did not believe his own eyes, so he repeated the sampling, this time with a crude device to retrieve a sample of seafloor sediment. They confirmed the 56°C temperature and pulled up black ooze resembling tar that was too hot to touch.

The discovery encouraged the National Science Foundation to send the Woods Hole ship R/V Chain back to the region a year later. The scientists once again found warm deep waters. Even more amazing, however, were the sediment cores they extracted from the seafloor.

The Red Sea sediments were filled with brilliantly colored layers rich in copper, iron, manganese, zinc and other metals. “The color variation is fantastic: all shades of white, black, red, green, blue, or yellow can be observed,” WHOI scientists Egan Degens and David Ross wrote. “Perhaps some of the more colorful Indian sand paintings and Mexican rugs faintly match these sediments in the variation and intensity of their colors.”

The Red Sea is a young ocean with a Mid-Ocean Ridge running through it. Degens and Ross speculated in 1967 that the Red Sea phenomena they found also might be seen in other areas where the seafloor is rifting apart. That proved not only true, but also convenient—because wars and political turmoil in the Middle East made it increasingly difficult to take ships back to the Red Sea.

[ Next: Metal-rich sediments ]

 

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