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MISSION DISPATCH - DAY 3 Today's Weather - images courtesy of NOAA & RSMAS Dispatch by Dr. Karla Parsons-Hubbard July 30, 2001 On July 26th and 27th we had bad weather. We have some very interesting sites on the monotonous open shelf and slope off of Galveston, but there was a large ground swell that prevented the sub from being 
launched. We waited all day the 26th and 27th and it did not improve. We got
up at sunrise on the 28th and realized that it was still too rough to
launch, so we made the decision to leave the site and move on to our next
site. This was a difficult decision because the transit time from the
Galveston shelf east is too great to have any hope of getting back there
this cruise. Those are the pitfalls of fieldwork, however, and we will just
have to move on and collect from that site the next time we come out.
By Sunday July 29 we were working at the East Flower Garden Banks in a large brine pool. Here a large salt dome intersects the sea floor and seeps dense salty water. The brine is so highly concentrated that it forms a pool about 20 cm deep below the regular seawater. The pool lies in a depression surrounded by coral 
reef. The brine flows out of the pool downslope through a well-defined
canyon shown in the figure (image above - captured from video by George Staff). The water
in the brine cannot support many organisms, but there is a white bacterium
that thrives on the sulfide that is found in the brine. In the picture of
the stream, the central channel is defined by the white bacteria living on
the floor of the stream.
In 1993 we deployed shells and wood in the brine pool, the brine stream, and on the surrounding reef. The shells deployed in the brine pool itself are pristine except for some possible precipitation of black mineral material and some stained areas from the sulfide. The crabs and urchins placed in the pool are essentially "pickled". The crab came up after 8 years with soft 
tissue still intact. The crab carapace has lost some of its calcium
carbonate and instead of being hard is somewhat rubbery. This has possible
implications for fossil preservation.
The most rare and beautiful fossils are those that have soft tissues preserved in the rock. The brine pool setting may be an analog to ancient environments condusive to spectacular preservation of whole animals. (Figure at left - experiments in the brine pool - captured still from video taken by George Staff). Interestingly, although the delicate crabs show exquisite preservation, the shells (clams and snails) in the brine stream (where salinity is still quite high, but not as high as the pool itself) are becoming dissolved. The calcium carbonate on 
the shell has thinned and some shells have holes in them. The sulfides have
probably become sulfuric acid and are dissolving the shells away. (figure at right -
a dissolved turritellid - Meagan Cummings). Thus hard
skeletons of calcium carbonate would not be expected to remain long enough
to become fossils.
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