Fault system off northern Baja California

May 11, 2015

Eve Lundsten and Susan von Thun write: Today we explored another section of the fault system off northern Baja California that had been previously mapped with MBARI’s AUV. The AUV mapping surveys were conducted in areas where Chief Scientist Charlie Paull suspected that faults are present. With these one-meter-resolution maps, he could then target small areas of interest for core sampling using the ROV.

We’ve mostly seen lots of mud, which is exactly what we were expecting. But on the second dive today, we came across small patches of chemosynthetic animals. First, we saw clam shells, then a few patches of live vesicomyid clams. Later, we saw a small patch of Lamellibrachia worms. These animals live on hydrogen sulfide in the sediment, which would be toxic to most other animals. The chemicals are present in buried sediments and become exposed to seawater by undersea erosion or landslides, giving rise to these small communities of animals. The presence of chemosynthetic communities in the area we explored today is likely due to erosion of sediment in small gullies that cut through slopes and ledges on the seafloor.

Vesicomyid clam siphons (in pink) peek out of the mud. The red dots are lasers spaces 29 centimeters apart as a measurement tool.

Vesicomyid clam siphons (in pink) peek out of the mud. The red dots are lasers spaces 29 centimeters apart as a measurement tool.


Chemosynthetic tubeworms and clams indicate that chemicals in the sediment had been exposed to seawater by erosion or some other sedimentation event.

Chemosynthetic tubeworms and clams indicate that chemicals in the sediment had been exposed to seawater by erosion or some other sedimentation event.

Recently, Mrs. Peoples’ kindergarten class at Valencia Elementary School in Aptos, California, and their fifth-grade buddies decorated Styrofoam cups for us to send down with the ROV. The cups, contained in a mesh bag and attached to the ROV Doc Ricketts, rode along on the ROV while it conducted its survey of the seafloor almost 2,000 meters (1.2 miles) below the sea surface. The immense pressure of the water above compressed the cups to less than half their size. When we return to shore, we’ll send the cups to their creators and hopefully inspire a new crop of young scientists and engineers.

(top) These Styrofoam cups, the size of a standard coffee cup, were decorated by students. (bottom) After riding along on the ROV 2,000 meters beneath the sea surface, the air in the Styrofoam had been squeezed out, shrinking them to less than half their original size.

(top) These Styrofoam cups, the size of a standard coffee cup, were decorated by students. (bottom) After riding along on the ROV 2,000 meters beneath the sea surface, the air in the Styrofoam had been squeezed out, shrinking them to less than half their original size.

—Eve Lundsten and Susan von Thun