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|
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.|
|The Beast loaded on ROV Jason.|
|Millie and Tamara with the gas extractor.|
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.|
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.