Heading towards a new grid

Sleep is a luxury at sea.  You don’t want to miss anything so you better stay awake.  We’re heading towards some new stations to the North of ground zero and will be doing a hexagonal grid around ground zero tonight in search of additional plumes.

In the meantime, I’ll answer some questions posed about the blog.

Several folks have asked what we are measuring out here.  My group is measuring concentrations of dissolved methane, higher alkanes (like ethane and propane), inorganic carbon, and oxygen; inorganic and nutrients; oil and colored dissolved organic matter; dissolved organic carbon; hydrogen sulfide; and major salts.  We measure rates of oxygen consumption and methane oxidation.  We’re also collecting samples to determine the concentration of ATP (an indicator of relative microbial activity) and will do a separate assay to estimate the level of total microbial activity.  Finally, we collect molecular biological samples to look for different types of methane oxidizing bacteria.  Adam Rivers, from the Moran lab at UGA, will be comparing the metatranscriptome from deepwater plume samples versus samples from control depths that lack plumes.  Joanna Green from, from the Miller lab at UGA, will be doing photochemical experiments with plume waters.  The UNC group will conduct more detailed molecular biological studies of the microbial population using both DNA and RNA approaches. The USM group is doing more detailed characterizations of the PAHs and metals in plume samples and the UCSB scientist on board is characterizing the relative degradation state of the oil.  We’ve all been pretty busy.

Someone asked whether the deepwater plumes form because of dispersant use at the wellhead or whether this material is settling down from surface waters into the deepwater, again because of dispersant.   Considering the plume trajectories, they appear to derive from the wellhead.  We do not believe they form from the sinking of oil that was once on the surface.  However, that does not mean the plumes are generated because of dispersant use.  Quite the contrary, plumes like these most likely form through natural processes.  At the temperature and pressure of the reservoir, methane is dissolved in the oil.  When the fluid is expelled at the seafloor, the methane comes out of solution in a fairly violent manner.  This gas expulsion likely fractionates the oil and it is this fractionation that generates the diffuse oil in the plumes.  This process is described in the NRC (2003) report that is given on the resources page of the blog.  Please let me know if you’d like a more detailed description of this.

A couple of people asked whether we are using underwater video to visualize the plumes.  We have not done this yet but Vernon Asper from USM has a deep sea camera on board and we’ll be deploying it Sunday night.  Stay tuned for updates.

Finally someone asked whether there is a “methane cloud” emanating from the wellhead.  The plumes we’ve found are enriched in methane as well as higher alkanes.  The dissolved methane concentrations are higher than we’ve ever seen at comparable depths on previous Gulf of Mexico cruises.  Some of the methane is almost certainly venting to the atmosphere but those fluxes have not been quantified yet to my knowledge.  Scientists on board the R/V Cape Hatteras will be quantifying atmospheric methane fluxes about two weeks from now.  One of our major goals for this cruise is to map the methane concentration fields around the wellhead.  We’ve made good progress towards achieving that goal so far.