Guest Blog: The SeepDOM Project

Guest blog post by Anna Hildebrand (University of Maryland Center for Environmental Science)

In some ways, not much had changed after a year. The familiar walk to the Wet Lab at all hours of the day, the cheese set out at 3pm daily, the cupcakes with “Happy Birthday Sawyer” written in bright pink icing. The R/V Atlantis was familiar and comforting despite the whirlwind of scientific activity and various cruises that had taken place since August of 2023, each with their own unique objectives and stories.

Our work this year was a continuation of last year on cruise AT50-14. Formally, our project is known as “Collaborative Research: Investigating the source and flux of dissolved organic carbon released from methane seeps to the deep-ocean” and was funded by the National Science Foundation in 2021. Among our project team, this is shortened (for obvious reasons) and affectionately referred to as “SeepDOM” (the DOM standing for Dissolved Organic Matter).

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Figure 1. OsmoSampler #3 and push cores at the Lapham osmo deployment location near Einstein’s Grotto. Credit: UW/NSF-OOI/WHOI; J2-1634; V24.

The collaborative aspect of this research comes from partnerships between us (the University of Maryland Center for Environmental Science), the United States Geological Survey, Florida State University, Woods Hole Oceanographic Institute, GEOMAR, and MARUM. Between all of these institutions, we are seeking to answer four key questions: (1) How much methane-derived fossil (very old) dissolved organic carbon (DOC) do seeps contribute to the oceans? (2) To what extent is methane-derived carbon incorporated into DOC during anaerobic oxidation of methane?, (3) Is seep DOC bioavailable or recalcitrant when released into the deep ocean? and (4) How does the flux of DOC to the water column vary over time?

So why exactly does this matter? Marine DOC is one of the largest reactive carbon reservoirs on Earth yet its sources are poorly understood. We’re interested in the transfer of carbon between methane seeps and this DOC reservoir. To understand how climate change will affect carbon cycling, we need to understand the system that we’re working with, and methane seeps could be a significant piece of that puzzle.

Figure 2. Jason coming back on deck with the osmosamplers and push cores from J2-1634. Credit: M. Elend, University of Washington; V24

Last year we had a team of 22 people working around the clock to answer those questions. Given that methane is seeping from the sediments, this work translates (mostly) to sediment cores- and a lot of them. Sediment cores can be taken in many ways, but this year involved the remotely operated vehicle (ROV) Jason. We had an ambitious plan to collect 36 push cores (push, because Jason pushes them into the sediment to collect them) and retrieve 4 OsmoSampler crates. OsmoSamplers work through osmosis and use a salt gradient to slowly pull in water from the sediments or overlying water into a spool of copper coil with a very small inner diameter. These sections can then be cut back in the lab, with the water inside representing a snapshot in time from the period of deployment. These were deployed in order to address question #4 and had to be picked up this year. The amount of shipboard work planned for this year was intense but with 22 people it should have been feasible- right? Wrong! We went from 22 people down to 2. So, how did we do it? That’s where the VISIONS program comes in.

Like any good plan, we had backup plans. And backup plans for the backup plans. But you don’t necessarily want to end up at your last resort. With the help of the VISIONS program participants, we sectioned and processed 40 cores (there were opportunities for more cores, which we of course couldn’t resist). Many of these students had diverse interests- from physical oceanography to biology to applied mathematics. But that didn’t matter. Each of them was inquisitive, hard-working, and enthusiastic- and this was despite the sulfidic smell that accompanied the uncapping of most of the cores.

There were many times when students would show up at the Wet Lab after long hours of logging events in the Jason van, completely unprompted and eager to help. It was a pleasure to hear about their passions, interests, and experiences. We could not have accomplished our goals without them. Thank you to Léo, Erik, Roy, Elena, Jood, Zariel, Catherine, José, and Naomi. We wish you all the best.

VISIONS student Léo Couchon and graduate student Anna Hildebrand holding a push core from J2-1634. Credit: L. Lapham, University of Maryland Center for Environmental Science; V24

On a similar note, the support from the ship, Jason team, and OOI-RCA was instrumental in making our science successful. A research cruise is often designed to be as efficient as possible, with science objectives as the main priority. While we found that this operation was an efficiently-run, well-oiled machine, it was also very different. There was something special about a cruise that places such a high emphasis on student learning and appreciation for a world that few get the opportunity to experience. Thanks to Mike Vardaro, Katie Bigham, and the RCA team for making that objective a reality on Leg 2.