Hydrothermal Exploration of the Mid Cayman Rise using Sentry & Nereus RV Falkor Cruise, May 2013

Chris German,Geology and Geophysics
Jeff Seewald, Chemistry and Geochemistry



The Mid Cayman Rise (MCR), Earth’s deepest and slowest spreading mid-ocean ridge, hosts diverse and abundant submarine venting with at least four distinct sources known to occur along its ~110km axis. This proposal, with support from the Schmidt Ocean Institute, seeks to complete a 25 day cruise aboard the RV Falkor, and complete our exploration of the MCR using WHOI’s deep submergence vehicles Sentry and Nereus. From water-column analyses it is already clear that the MCR hosts at least four vent-sites, each in a distinct geologic setting. Todate, however, only two of these sites (Von Damm, Piccard) have been tracked to source while the other two sites (Europa, Walsh) remain to be located. Our long-term vision is to establish the MCR as a natural laboratory for continuing hydrothermal research.

The Von Damm site is a ~200°C, 2300m deep system, hosted in ultramafic rocks with fluid compositions rich in light organic compounds that may be particularly relevant to understanding pre-biotic chemistry and the origins of life. The same site also hosts unique chemosynthetic fauna including a new species of shrimp similar to those on the Mid-Atlantic Ridge and two different species of tube-worm, one related to East Pacific Rise (vent) and the other to Gulf of Mexico (cold seep) fauna. Just 20km distant, but at more than double the depth, the Piccard site is quite distinct. At >400°C, this volcanic-hosted system represents both the deepest vent-site known and one of the hottest. From a biological perspective, Piccard is quite distinct, too. There are no tube-worms present and the shrimp - although the same species as at Von Damm – appear much smaller, suggesting a distinct and isolated population.

The Walsh site is at 5000m, similar to Piccard, is likely characterized by similarly high temperature venting, yet the chemical composition of its plume indicates that it is hosted in ultramafic rocks like Von Damm.  A key question to be answered, therefore, is what will the Walsh fauna look like? Will it resemble Von Damm because of the similar host-rock and associated fluid-compositions, or Piccard which shares the same physical extremes? Answering these questions will help solve many of the riddles of how animals migrate between sites. At Europa, the discoveries may be even more compelling. We believe this site to be most similar to the Lost City site, found off-axis at the Mid-Atlantic Ridge emitting alkaline fluids and hosting giant carbonate and hydroxide chimneys. Will Europa – sited just ~10km West of Von Damm - be the second such site to be found?

The Schmidt Ocean Institute has generously funded us to a value in excess of $1.5m to track the Walsh and Europa sites to source, providing both shiptime as part of their inaugural year of RV Falkor operations plus the costs required to mobilize Sentry and Nereus aboard ship. This project, in partnership with SOI, will provide the necessary research costs for WHOI PIs Chris German and Jeff Seewald to join and lead that expedition together with WHOI-MIT Joint Program students, Jill McDermott and Guy Evans. We can’t wait to get started!