Award: OCE-1755571

In this project, my research team used a free swimming "autonomous" underwater robot called Sentry to explore close to the seafloor along a volcanic chain in the South Pacific for new forms of hot-spring that could be important in regulating the chemical composition of Earth's oceans and even the levels of carbon dioxide in its atmosphere. In earlier work, I co-led a research expedition across the Pacific from Peru to Tahiti in 2013 during which our team revealed an extraordinary result - that dissolved iron released from deep seafloor hot springs along an underwater volcanic chain in the tropical south Pacific could travel so far (more than 4000km/2500 miles) that it could have an important impact on how much biological activity could occur in the sunlit upper ocean in Antarctica - where iron acts as an essential micronutrient for life - regulating how much surface ocean plants (called phytoplankton) can grow and, hence, how much carbon dioxide gets removed from the atmosphere as they do so. Building on that research, this project sought to investigate where that iron might come from - i.e. how it first escapes from the seafloor. Since the 1970s we have known about submarine "black smoker" vents that, like "Old Faithful" at Yellowstone National Park, loft heated water and chemicals high into the ocean from chains of underwater volcanoes known as mid-ocean ridges. Traditionally, however, we had not expected the chemicals released from those submarine hot springs to travel far afield. Rather, we recognized that the thick cloudy plumes that give "black smokers" their name arise because of the iron-rich minerals that form as soon as hot vent-fluids enter the ocean, settling out to form metal rich (sometimes ore-grade) seafloor deposits close by. Over 40+ years of study, ocean scientists have become increasingly adept at searching for these "Black Smoker" systems which have now been identified in every ocean basin on Earth. For the current project we wanted to answer a new question: were there other kinds of venting at the seafloor, ones that we had not previously looked for, that could be responsible for the leaky iron flux that our 2013 expedition had revealed? To find out, we had to design new ways of looking - instead of searching for chemicals lofted high above the seafloor we needed to use a free-swimming robot (Fig.1) that could follow a pre-programmed path and pick its way carefully along the crest of a submarine volcanic ridge, avoiding collisions with the rough topography, while using in situ sensors to prospect for seafloor fluid flow. In Fall 2021, we searched along 150km (~90 nautical miles) of volcanic ridge in the South Pacific (the long pale-brown linear feature in Fig.2) - one of the most volcanically active regions of seafloor on Earth. Our search was done in three stages, limited by how long the battery packs on our robot could last. As an example, our results from within the middle of our survey are shown on the zoomed-in map in Fig.3. The two red diamonds show the only places where we found hot, chemically anomalous fluids exiting the seafloor laden with mineral "smoke" - the black smokers styles of venting we were already familiar with. But that was only about 10% of everything we discovered. The yellow diamonds show locations where we found warm, chemically anomalous fluids without clouds of minerals gushing from the seafloor as "Black Smokers" do. Lastly, the blue circles show places where waters just above the seabed were chemically "stained" by fluids leaking from the seafloor without no thermal anomaly at all. Our robot-led work revealed where these sources of chemical release were located. Colleagues at sea with us used the information I provided to select where to collect samples from, to analyze what was in each of these different styles of hydrothermal flow. Their shore-based analyses are on-going. Last Modified: 02/01/2023 Submitted by: Chris German