Interdisciplinary Investigation of the Pescadero Basin

The Gulf of California
The Gulf of California (GOC) is a relatively young feature of our planet. Its formation is estimated to have started ~12.5 million years ago when Baja California began to break away from the North American continent. The GOC is the northernmost portion of the East Pacific Rise, a mid-ocean ridge that extends down to Antarctica. Several tectonic plates move away from the Pacific Plate along the East Pacific Rise, creating a spreading center. Spreading centers are tectonic boundaries where new crust (the outermost layer of our planet) forms. The Gulf of California spreading varies from the rest of the East Pacific Rise because it is where the North American Plate begins to move alongside the Pacific Plate, transitioning into a transform fault. The transform motion dominates farther north and is known as the San Andreas fault system.

The movement results in both spreading and sliding between the two plates and, over time, have opened up four deep ocean basins known as the Guaymas, Carmen, Farallon, and Pescadero Basins. Guaymas and Pescadero basins contain documented hydrothermal vents, but there has been little exploration and mapping of the Carmen and Farallon Basins. Leg One of the expedition will focus on multibeam mapping the Carmen and Farallon Basins to better characterize these geologic features and inform future scientific endeavors in the region. Mapping the Carmen and Farallon basins will also aid in understanding the opening of the Southern Gulf of California, as the science team searches for features affiliated with the opening of the Gulf.

Hydrothermal Vents in the GOC
The hydrothermal vents in the Pescadero Basin vary significantly from other known vent communities physically, chemically, and ecologically. The temperature, chemical make-up, and animals that live on these vents are unlike vents found in other parts of the world. Due to the shape and surrounding land, the GOC facilitates heavy sedimentation of the Pescadero Basin. Debris runs into the basin from surrounding watersheds, and organic matter sinks to the bottom from photosynthetic organisms living in the surface waters. Most hydrothermal vent communities exist in deeper, offshore regions that do not experience sediment build-up. This sedimentation affects the chemistry and make-up of the hydrothermal vents. The vents observed in Pescadero Basin are uniquely composed of hydrothermal carbonates and clear, shimmering water around 290 degrees Celsius. These fluids have a higher pH and produce calcite-rich mineral deposits rather than the sulfides of more commonly observed vents. Hot water reacting with sediment forms organic gases and hydrothermal petroleum, a process that usually requires deep burial of organic-rich sediment and millions of years.

Leg Two of the expedition will concentrate on heat flow of the hydrothermal vents and their surrounding areas. ROV SuBastian will be fitted with a temperature probe, and the scientists will take measurements at intervals starting near the vents and then moving away to create heat flow profiles. Mapping heat flow is essential for understanding hydrothermal circulation (the movement of hydrothermal fluids around the basins and GOC) and thermally-driven processes.

Communities of the Pescadero Basin Vents
No light penetrates to the bottom of the Pescadero Basin. Instead of relying on photosynthesis as the basis of the food web, microbes living on hydrothermal vents generate energy through chemical energy or ‘chemosynthesis’. The microbes in the Pescadero Basin use diverse sources of chemical energy including methane and hydrocarbons, as well as hydrogen and hydrogen sulfide gases dissolved in the hydrothermal fluid. Extremophilic microbes persist throughout the vent environment and are adapted to a large range of temperatures from above boiling point of water to the frigid cold temperatures of the deep sea. Some microbes are adapted to living in symbiosis with animals like tubeworms and anemones, while others live within chemical-rich sediments or exist endolithically, living within the interior of hydrothermal minerals. During Leg Three of the expedition, the scientists will document the diversity of different extremophilic microbes living across steep temperature gradients on and around the Pescadero Basin vents and characterize the menu of chemical compounds they use to create energy and grow

Alongside characterizing the microbial communities, the scientists will also investigate the larger animals living near the vents during Leg Three of the expedition. The 2018 expedition revealed that three primary animals are foundational within the Auka and JaichMaa ’ja’ag vents: a species of tubeworm, a blue scale worm, and a chemosynthetic anemone. The anemone is the first-ever cnidarian documented to have a symbiotic relationship with microbes and rely on chemosynthesis. In addition to examining the known animals, the scientists hope to find new species living around Pescadero Basin hydrothermal vents.