Leg 6 

Leg Summary:  

Leg 6 will be a geological investigation of submarine canyon processes in the regions of seafloor faulting off La Paz and Bahia Concepcion. The ROV will be used to study tectonics and sedimentation as they relate to canyon formation. Video imaging and manipulator sampling will be conducted in rock wall areas, combined with core samples in areas of sedimentation. The down-canyon transport of sediments will be documented using shallow water rhodoliths as tracers. Onshore faults in these regions contain hot water springs that suggest the possibility that submarine vents may be discovered by the ROV offshore. If vent communities are present, they will be compared with those examined during leg 4. The instrument package deployed in Guaymas Basin during leg 2 will be recovered. The leg 6 coordinator is Dr. Gary Greene of MBARI, and the Mexican collaborator is Dr. Jorge Ledesma Vazquez from the Universidad Autonoma de Baja California. 

History & Purpose: 

Leg 6 of the MBARI Oceanographic Expedition to the Gulf of California is associated with studies of submarine canyon sedimentary processes and tectonics. We plan to investigate submarine canyon formation along the transcurrent fault boundaries of the southwestern parts of the Gulf in the La Paz and Bahia Concepcion areas. These canyons are constrained by wrench-fault tectonics, formed since the Gulf started to open in this region 3-5 million years ago. Since the faults onshore in the vicinity of our offshore investigation sites contain hot water springs, we anticipate discovering submarine vents and possibly vent communities during our dives.  

In addition, we will document the transport of sediment down the canyons using naturally occurring shallow water red algae (rhodoliths) as tracers. Rhodoliths were recovered in the past from deep-sea cores taken from the submarine canyon offshore of La Paz and we suspect that these hard coralline algae commonly occur within the submarine canyons that we intend to investigate.  

To properly investigate the submarine canyons’ formation and processes we will use the ROV Tiburon to observe and sample rock walls and sediment within our study areas. Areas where seafloor seeps are found will be sampled to determine fluid chemistry and any biological communities at the seeps will be sampled to determine their genetic development. Submarine canyons are major conduits for the transport of sediment to the deep-sea floor. This process is not well understood. This investigation will add considerable knowledge to submarine canyon processes in general, using Baja canyons as a proxy or case study to document down canyon transport using rhodolith tracers.