Submarine Ring of Fire 2014 - Ironman

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5. December 22

This cruise has been challenging in many ways, mainly due to the weather and the many problems associated with a faulty cable provided for us to use with Jason. The outcome was that we did not get nearly as many remotely operated vehicle (ROV) dives to the seafloor as we had hoped.

On the other hand, the dives we did get were very productive and gave us the opportunity to make observations, collect samples, and conduct many of the experiments that we had set out to accomplish. We were also able to collect other useful data between Jason dives, including CTD casts and tows to search for hydrothermal and eruptive plumes and multibeam sonar data to map new areas and to look for depth changes at seamounts that had already been surveyed.

The highlights of the cruise include:

• Making dives at the newly discovered Urashima vent site in the southern Mariana back-arc, where some iron-sulfide chimneys in the field seem to provide an ideal habitat for iron-oxidizing microbes—one of the main scientific targets of this cruise. We also briefly visited the nearby, previously known Snail vent site in order to collect additional microbe samples and recover long-term experiments left on the seafloor by colleagues during earlier expeditions.
  

  The Jason ROV being deployed. Image courtesy of Submarine Ring of Fire 2014 - Ironman, NOAA/PMEL, NSF. Download larger version (jpg, 3.6 MB).

• Revisiting NW Eifuku seamount, where liquid carbon dioxide (CO₂) is emitted in the Champagne vent field. The hydrothermal vents there provide hydrogen sulfide that supports a huge community of chemosynthetic mussels and other organisms, and yet the high levels of CO₂ make the water very acidic, which makes it harder for organisms to survive. The iron-style vents and associated microbial mats found here seemed to be in the latter phase of their evolution, with lower temperatures measured and more mineralization evident within these mats.
• A similar scenario is evident at NW Rota seamount. During previous expeditions we’ve seen NW Rota actively erupting, and yet it too supports a chemosynthetic ecosystem, but in this case dominated by shrimp. On the one hand, the volcano emits the chemical stew that supports the biological community, but the eruptive activity also makes the habitat very unstable. On this trip, however, the volcano had calmed down and the animals have responded by expanding their populations and territory. We also witnessed the transition of sulfur-dominated vents to the beginnings of iron-dominated vents with associated iron-based microbial mat being newly formed.
  

  The Jason control room during a dive. Image courtesy of Submarine Ring of Fire 2014 - Ironman, NOAA/PMEL, NSF. Download larger version (jpg, 2.7 MB).

• Ahyi seamount was another site of interest because it had erupted in April/May and we found that it was still strongly hydrothermally active. We took the opportunity to remap the seamount to document the depth changes caused by the eruption.
• One of the most exciting surprises during the cruise was to find that Daikoku seamount was apparently erupting, based on high levels of hydrogen in CTD water samples and a new crater at the summit. The more places we explore in the Mariana arc, the more surprises we find, and by revisiting sites we are learning that change is the norm here and occurs much more frequently that we had imagined.
  

  The CTD being deployed over the side. Image courtesy of Submarine Ring of Fire 2014 - Ironman, NOAA/PMEL, NSF. Download larger version (jpg, 2.8 MB).

We greatly appreciate the support we received from the Jason team and the captain and crew of the R/V Revelle. They went above and beyond in their efforts to support our science goals and to help us achieve as much as we could during this expedition. We also thank all the members of the science party who worked at all hours to get the most out of every opportunity we had. In addition, we gratefully acknowledge the agencies that provided the funding for this expedition: the National Science Foundation, the NOAA Office of Ocean Exploration and Research, and NOAA’s Pacific Marine Environmental Laboratory.

The Mariana area is such a fascinating place, we’re already looking forward to our next opportunity to work here – but next time we’re hoping for better luck with the weather!