After completing work in the ASHES hydrothermal field, the R/V Thompson transited across Axial caldera to the International District hydrothermal field. It is here that a diverse, cabled underwater laboratory is installed to monitor and interact with (in real-time) hydrothermal vents, fluid chemistry, seismicity and biological communities as part of NSF’s Ocean Observatories Initiative.
ROPOS’s first dive into the field was focused on three active hydrothermal chimneys – El Gordo, Diva, and Escargot. El Gordo is a small, animal covered chimney that hosts a vent fluid and microbial DNA sampler (called the RAS-PPS), a digital still camera, and mass spectrometer (for measuring gas concentrations in the vent fluids). Diva is a small white chimney that hosts an instrument that measures hydrogen sulfide concentrations, temperature, and pH (or acidity) of the high temperature, gas-rich fluids exiting this chimney. Finally, Escargot hosts a temperature – chlorinity sensor that monitors changes in fluid chemistry resulting from subseafloor processes that includes boiling. During this, and follow-on dives in the field, we will be replacing these instruments.
At El Gordo, scientists on the ship e-mailed and spoke with UW APL engineers who were controlling the fluid and DNA samplers (water depth here is 4987 ft beneath the ocean’s surface) from over 300 miles away in Seattle. They “talked” to the samplers and commanded them to take a vent fluid and DNA sample prior to recovery of the instrument mooring that was installed in 2014. New DNA research at seafloor vents suggests that the vents may be microbial “islands,” with each chimney – vent site hosting its own unique community of microorganisms. How these micro-ecosystems evolve is not yet known, hence this is one of the reasons we have a coupled fluid – DNA sampler at this site that will allow investigation of microbial community composition over time.
We also took samples of the gas-rich fluids (carbon dioxide, hydrogen sulfide, hydrogen, methane) exiting Diva and Escargo and measured temperatures of the active vents – Diva was the hottest vent, emitting fluids at 280°C (536°F). While at El Gordo, the high definition Zeus Plus camera on ROPOS imaged the chimney walls – spotting “spiders of the deep” called pycnogonids. These 8 legged “spiders" (arthropods) perhaps forage on bacteria growing on the outer walls of the sulfide structures. In some places, the rocks are “alive” with these spiders, which are commonly about 1 inch across.