West Coast Expedition
July 20 - August 30, 2002
West Coast of North America

August 24, 2002: Day #36

Figure 1 shows John Delaney leading a conversation about how to conduct a seep search of the seamount.

Debra Stakes writes: Dive 472 marked the beginning of our work in the Nootka Fracture Zone area. Unlike the Endeavour Ridge dives, we would be doing basic exploration, pursuing tidbits of evidence supporting the presence of undiscovered cold seeps and fluid flow in this area.

One of the results of the EM300 bathymetric survey was an image of a beautifully concentric mud volcano adjacent to the Nootka Fracture Zone. Some provocative data from CTD within the central depression of this mud volcano suggested that it was a result of methane degassing, possibly linked to movement along the transform zone. This topographic feature was thus targeted as the highest priority for possible cold seep sites that could be instrumented as part of the Keck-funded study. We dedicated Dive 472 to determine the extent and location of cold seeps related to this feature. Lively science discussions led by John Delaney (Fig. 1) led to a dive profile that would cross a "moat" around the seamount, climb one side, and then criss-cross the floor of the central depression looking for seep sites.

A lot of work with no seeps to report at the end of the dive.

Figure 2 shows the benthic drawer stuffed with a variety of tools to sample whatever was discovered during the ROV traverse. The drawer carries two of the gas-tight fluid samplers. Because we anticipated low flow rates, an orange bucket was converted into a funnel to concentrate the flow before it was sampled. The drawer also carried eight sediment push cores, two bioboxes and a methane sniffer

Figure 3. The presence of numerous empty clam shells along with galatheid crabs initially made us hopeful of an easy success.

Figure 4. Unfortunately, the only clam shells that we were able to find and collect were empty ones. We found no active seeps and no clams in a living position. There was also no evidence of cold seep carbonates or microbial mat. 

Figure 5. We did see an unusually high number of octopuses, suggesting a mechanism for the apparent random distribution of empty clam shells across the seafloor.


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