Sunday, July 16, 2017

The Thin Line - First Jason Dive

By Teresa Atwill, Teacher at Sea

What happens in the rocks beneath the ocean floor at volcanoes and mid-ocean ridges? 

How do the gases, fluids and heat from the magma and hot rocks below interact with seawater and the microbes that live in the rock-water interface? 

Cartoon showing the water and chemistry circulation at mid-ocean ridges
Amazingly this is one of the largest habitats for microbial life on our planet! Some scientist estimate that there may be more microbial life beneath the seafloor than anywhere else on the planet – the so-called “sub-seafloor biosphere”. How do these interactions at mid-ocean ridges that occur throughout our oceans play a role in the greater chemistry and heat balance in our oceans and the planet?

To answer these questions the chemists and microbiologists on board collect hydrothermal vent fluids from the thin interface between the rocky crust and the open ocean and try to deduce from them what is happening beneath the seafloor. To understand how hard this is to do, think of the analogy of doctors trying to determine what is going on in your body with only an ability to look at your skin, analyze your breath and if they are lucky take a blood sample.

Dave Butterfield explaining the different types of venting at Axial.
Dave Butterfield is the lead scientist for our first Jason dive of our research cruise. For the last few days, Dave with the help of Kevin Roe, Tamara Baumberger, Srishti Kashyap, and Camilla Wilkinson has been prepping the sampling instruments that will ride down on Jason and will be used to collect vent fluid samples at different sites during the dive. There are two main types of sites to be sampled - focused jets of high-temperature water on mineral chimneys and warm diffuse venting issuing through animal communities. The instrument that goes on Jason for vent fluid sampling is the nicknamed “The Beast”, due to it’s large size and its enormous appetite for vent samples (16 water samples, 6 DNA filters, 2 gas-tights, and sensors). After this most recent retrofit of Jason “The Beast” barely fits into Jason’s underbelly.

Gas Chemistry
The Beast loaded on ROV Jason.
In addition, Camilla and Tamara have 5 gas-tight sample bottles going on Jason’s first dive. These will be used to sample the gases coming out at high temperature vents. The amazing thing about these sample bottles is that they can keep the samples they collect at the same high pressure as at the seafloor, even after they are brought back aboard the ship. This allows us to capture and analyze all the gases in the vent fluids before they come out of solution and escape when the pressure is reduced.

Millie and Tamara with the gas extractor.
Once back on the ship these sample bottles will have the gas extracted and this gas will be placed into glass ampoules. There are two types of gas ampoules used. The first is made of aluminum silicate and will be used for storing samples to be tested back on shore for helium and neon. The second type of ampoule (made of Pyrex glass) will be used for holding samples to be tested for total gas levels, methane, hydrogen, carbon dioxide, oxygen, nitrogen, ethane and butane.

Srishti hopes to collect 1-3 hydrothermal chimney rock samples (preferably more sulfide than anhydrite rich) for spectral analysis and microbial enrichments. Srishti is a graduate student and will be trying to grow novel heat-loving microbes that live at temperatures between 55-80°C and consume different types of iron oxide minerals. Who knew microbes eat rocks! Apart from enrichments, the chimney samples will also be used for spectral analysis to get a better understanding of the mineralogy associated with the cultured microbes. Most of these analyses will be done when back in the lab, but we will begin the enrichments on ship. Srishti also plans to filter the diffuse vent fluid samples for DNA analyses led by Julie Huber. These samples will be used to continue a long-term time series to evaluate the changes in the microbial communities at these vent sites related to volcanic activity. Microbes collected on filters will be analyzed once back in Woods Hole, MA.

Vent Fluid Chemistry
CTD being recovered from the ship.
The majority of the water sample bottles on Jason (and in our CTD casts) are set to hold samples for Dave Butterfield’s chemical analyses. Dave and Kevin will run some measurements on the ship and store some samples for additional measurements later. With other ongoing projects it can take up to six months for Dave and Kevin to finish all of the analyses on these samples. Hydrogen and methane analyses are run with a gas chromatograph at sea, as well as pH, hydrogen sulfide, and dissolved silica.

To learn about what is happening below the seafloor, back at his lab in Seattle, the samples collected at sea will be tested for methane, hydrogen, major elements (sodium, chloride and others), mineral-forming metals (iron, copper, zinc), trace elements (cesium, uranium, molybdenum and others), nutrients and dissolved organic carbon.

You could say that Dave Butterfield has been obsessed with Axial Seamount, which was the site of his first submersible dive to the seafloor as a grad student in 1986. 2017 marks the 19th year of a near-annual time series started in 1998 (the NeMO project).
Dave Butterfield (left) and Kevin Roe (right) working on fluid samples collected from Axial.

This is an unprecedented record and can be used to look at how the hydrothermal chemistry changes over time and is affected by the volcano’s periodic eruptions. By analyzing this thin layer at the interface between the ocean and this submarine volcano our understanding of what is happing in the rocks below the surface is greatly increased.