To start our three-year NASA PSTAR research program, we have been invited to bring our Nereid Under Ice (NUI) robotic underwater vehicle aboard a research cruise led by our long-term collaborator and deep ocean explorer Prof. Antje Boetius. Prof. Boetius is the Chief Scientist for this cruise aboard the German icebreaker FS Polarstern, which will be searching for hydrothermal activity on the Gakkel Ridge. She also invited us to sea in 2014 to conduct engineering trials for NUI in preparation for this cruise and her group conducted all of the preliminary work at Karasik Seamount prior to this cruise, so we are doubly indebted to her for this opportunity to make our own particular contributions to the larger effort of understanding the geology, chemistry and microbiology of life on the seafloor of the Arctic Ocean.
The mid-ocean ridge is a roughly 55,000-kilometer (30,000-mile) mountain range that circles the planet almost entirely underwater. The ridge is where new crust is created, as the tectonics plates on either side pull apart or are pushed by volcanic activity along the ridge. The rate of spreading varies widely from fast spreading ridges at 10-20cm/yr to slow and ultra-slow spreading ridges at 1-2cm/yr. Fast-spreading segments resemble a single volcanic cone stretched along the length of the ridge axis, while slow and ultra-slow segments have a a deep central rift valley cut down the center of the ridge that can be hundred of meters deep. And on the Gakkel Ridge, the seafloor spreads at the slowest rate of any mid ocean ridge on Earth.
These differences in shape relate to the rate of magma rising from deep within the Earth: at fast-spreading ridges the rate of supply is high, but at slow ridges the rate is low and perhaps half of all plate spreading happens as a result of stretching, thinning, and faulting of the ocean crust much the way a shelf full of books will rotate and spread if a book-end is taken away.
When scientists first discovered hydrothermal vents, they thought the features could only exist along hot, active, fast-spreading ridges. Later exploration of ridge segments in the Atlantic Ocean, Indian Ocean, and Caribbean has shown not only that this is not the case, but that even ultra-slow ridges can support high-temperature black smokers set in fresh volcanic lavas similar to those first found on fast-spreading segments in the Pacific. Slow and ultra-slow spreading centers have also been found to support a range of high-, medium-, and low-temperature vents such as the Rainbow, Von Damm, and Lost City vents associated with deep, long-lived faults where seawater can penetrate to hot rocks far below the seafloor.
A joint U.S.-German research expedition to the Gakkel Ridge near 87°N in 2001 mapped much of the seafloor using ship-mounted sonar, but missed the Karasik Seamount because a large ice floe was directly over the peak at the time. The two icebreakers doing the mapping passed on either side of the floe and completely missed the entire mountain. More than a decade later, however a different German research team returned, mapped the seamount, and collected water samples with concentrations of methane, a chemical that has previously been associated with all known forms of high- and low-temperature venting at mid-ocean ridges.
On the same cruise, a single grab sample taken from the peak of Karasik recovered basalt rocks typical of ocean crust seafloor and, attached to those, a type of tubeworm previously found at cold seeps along the margins of the continents such as in the Gulf of Mexico (which is quite unlike the setting for Karasik in the middle of the Arctic Ocean), as well as the Von Damm hydrothermal field on the Mid-Cayman Rise. It is interesting to note that the Von Dam site also sits atop an ultra-slow spreading center similar to what we should find near Karasik.
All of this raises some significant questions: Does Karasik hide a new hydrothermal field like those found in the Caribbean at the Von Damm site? Or will the expedition find something completely new? The search for hydrothermal venting in one of the last ocean frontiers on Earth is truly exploration at its finest. Join us to see what it reveals about our planet.