Paull Fluid Flow Cruise
October 2 - October 8, 2000
October 5, 2000: Day #4
Charlie Paull writes: Dive T215 started 10/05/00 at 14:18 GMT and ended 10/06/00 at 02:06 GMT. The dive started in a ravine (1608 meters), and we began a transect up the ravine to a ledge at approximately 1600 meters, then followed the ledge along the edge of the canyon. At the beginning, the surface was obviously sediment-covered, except for gullies that periodically covered the ledge. After a distance of about one kilometer, we started to encounter scattered clam shells and exposed rubble. Upslope of the shells, there were numerous clusters of tubeworms on rocky substrates. each cluster contained about 50 intertwined tubeworms. During this dive we saw many times more tubeworms than were previously encountered in Monterey Bay.
Living clams were found in sediment-bearing depressions on the rocky surface. We made three closely-spaced transects in this area. The numerous clam shells were largely restricted to the surface of a geologically young slide scar which was approximately 500 meters across. The relatively small population of living clams compared to the large and widespread quantity of dead shells generated some discussion as to whether the shells were generated by the present clam communities or by previously existing, more extensive communities.
Continuing the transect to the North, along the 1600 meter terrace, clam shells were less common, but still occurred in patches. Within the thicker sloping sediment, there were several small communities (less than one meter square) of living clams. Six thermal measurements were taken along the ledge in the course of the day, none showing steep enough temperature gradients to suggest active fluid flow. However the probe was not able to penetrate the sediments associated with the chemosynthetic communities. Along the transects on this dive, indications of seepage related phenomena-clam shells, living clams, tubeworms, discolored sediment-were surprisingly common.