High Temperature Vent Fluid and Seawater Don't Mix

At least, they don’t mix without something remarkable happening – the near instantaneous formation of microscopic mineral particles. This is the “black smoke” you may have heard about and seen in pictures. A lot of people on this cruise are interested in what happens at the seafloor: what types of microbes are there and how they make their living, as well as how the mineral chimneys form. But some of us are interested in the “smoke,” which forms a “plume” as it rises 100’s of feet above the ocean floor. People have been looking at deep sea “smoke plumes” for years; but, because of some unresolved questions a few us* recently decided to take a second closer look at these “smoke” particles. So we sharpened our pencils and we lined up the best new laboratory methods for looking at such things and we even invented our own tool for getting samples from the parts of the “plume” that were hard to get to before. And we began the process of collecting and analyzing new samples. 

Now up until this cruise we had collected about sixty samples and completed a full analysis of just a hand full; but the really interesting thing has been that when we* looked at those samples with our newest tools (X-Ray Synchrotron Spectroscopy at the Univ. of California Berkeley’s Advanced Light Source) we found that they didn’t look anything like what we expected (Breier et al. 2009; Toner et al. 2009). The mineral particles were covered in “goo” – which is short hand for the more scientific sounding phrase transparent exopolymer – which is scientific jargon for organic carbon of an unknown origin. Basically these particles, which so far have all come from the high dispersing part of the “plume”, are what we call micro-aggregates of the mineral particles we knew about and the organic carbon that we didn’t know about. We don’t know where this organic carbon is coming from – it could be from microbial activity, or some mixing of mineral particles and the organic residues (body parts and excretions) common in seawater, or it could in some way be coming out of the vents.

If you want to know why we care, we’ll give you two reasons. First, if the formation of this micro-aggregate structure turns out to be common then it means the currently excepted conceptual model of “plume” formation (the two processes just described) is incomplete. It doesn’t explain the complete formation process and it doesn’t account for the different characteristics of a micro-aggregate versus a bare mineral particle. That’s important because a mineral particle covered in ‘goo’ doesn’t react with seawater the same way a bare mineral particle would; and, a micro-aggregate sinks much more slowly than an individual mineral particle – and can be transported much further away from a vent than they otherwise would. Second, particle formation in vent plumes is an extreme example of a more general process that happens in many other parts of the environment: rivers, estuaries, the surface ocean, and the middle ocean depths – a more general process that is a very important factor determining how chemicals move through the hydrosphere (scientific jargon for all the water on the planet). Plume particles are quite distinct from the particles that form in these other cases. But scientifically that makes them very useful because they may highlight parts of the particle formation process (microbial action for instance) that are less prominent in the other cases. Thus by studying these ‘plume’ particles we have the chance to learn something new and true for particle formation in all these other places.

*We are Chip Breier, Brandy Toner, Greg Dick, Karthik Anantharaman, Jason Sylvan, Sarine Fakra, Matthew Marcus, Katrina Edwards, Sheri White, and Chris German.

 Breier, J. A., et al., A suspended-particle rosette multi-sampler for discrete biogeochemical sampling in low-particle-density waters. Deep-Sea Research I (2009), doi:10.1016/j.dsr.2009.04.005

 Toner, B. M., et al., Preservation of iron(II) by carbon-rich matrices in a hydrothermal plume. Nature Geoscience 2 (2009), 197–201.