Originally Posted by Chris Scott
... has anything been said about the possible depths of the mud in these lower-lying plains and, in particular, the valleys? Sure I'm not the only one wondering.
If you are thinking about debris sinking into the sediment and disappearing, that's not likely. Deep sea sediments (as opposed to river out-wash in shallow areas) are composed mainly of the skeletons of microscopic organisms. These accumulate slowly, in a geologic time sense. While I expect that accumulation rates vary greatly, due to variation in density of organisms living in shallow water, the order of magnitude is about 1m of sediment in 2 million years. The sea floor near the mid ocean ridges (as for the AF447 site) have relatively thin sediment deposits because the sea floor is young. The sediments thicken across the abyssal plains approaching the older continental shelves. That is just background.
While I can't say the depth of sediment in this area, I am not aware of any places where objects tend to sink into the sediment, whether thin or thick (I suppose there are exceptions). Deep sea instruments and moorings having solid steel anchors weighing from 100's to 1000's of kg are routinely dropped from ships, and the anchors don't sink out of sight. I'm sure most of the parts of an a/c will be sitting proud on the sea floor, just like the boilers and tea cups from ship wrecks.
Edit: As usual, things are more complex than imagined. More information about marine sedimentation can be found in many sources, for example
http://tinyurl.com/2bue2qj contains some data on the composition of sediments near the AF447 site, in the last few slides. Also, this abstract
AAPG/Datapages, Inc. Document Citation lists much faster sedimentation rates for the equatorial Atlantic, of cm/1000years, or 1m/50-100Kyears. My figure for 1/2Myears was based on a report of a core of only 10's of meters giving a 65Myr record; not sure where that core was collected. Search first.
