Phillips, B.T., M. Dunbabin, B. Henning, C. Howell, A. DeCiccio, A. Flinders, K.A. Kelley, J.J. Scott, S. Albert, S. Carey, R. Tsadok, and A. Grinham. 2016. Exploring the “Sharkcano”: Biogeochemical observations of the Kavachi submarine volcano (Solomon Islands). Oceanography 29(4):160–169, https://doi.org/10.5670/ oceanog.2016.85.
Submarine volcanoes are volcanoes that sit below the ocean surface. Active submarine volcanic eruptions can have a large influence on the environment and the ecosystems in their vicinity. For example, the plumes and gases emitted during volcanic eruptions can increase the water temperature, and change the chemistry and pH of the surrounding seawater. Observations and data collection of the unique environments hosted by submarine volcanoes are difficult to make because of the peril associated with getting too close.
One such active submarine volcano is Kavachi. Kavachi is set in a tectonically active subduction zone northeast of Australia near the Solomon Islands (figure 1). The volcano summit is 1000m higher than the surrounding seafloor and sits around 25m below the sea surface. Plumes from Kavachi’s eruptions are often observed from the Solomon Island (figure 2). The explosive nature of the area has hindered efforts to investigate the geomorphology and water quality, although the environment in Kavachi’s caldera is considered an extreme environment.
Prior knowledge of Kavachi submarine volcano was obtained in 2000 during a day of observations made around the volcano parameter. Then, in 2007, an eruption and earthquake prompted the investigation of a surface plume. For the most part though, there is still much more to learn about Kavachi.
Lucky for us, in 2015, a group of scientists visited Kavachi during a period of calm. The lull in volcanic activity enabled them to deploy data collection instruments, collect video and photographic footage, and collect geological, biological, and hydrological samples. It was an exciting opportunity to investigate the relatively mysterious Kavachi submarine volcano.
In 2015, a research crew visited the Kavachi submarine volcano while it was dormant, enabling them to collect samples, data, and make observations that are typically restricted. After watching and listening for activity from a distance for multiple days, the researchers moved closer for detailed observations. They collected information about hydrothermal characteristics, geology (bathymetry, petrology, geochemistry, plume structure), and biology (various trophic levels), fluid chemistry, and gas flux.
Investigators made due with a dearth of fancy equipment and technology. They used lightweight, low cost, and small instruments to accomplish their tasks. For photograph collection a specially housed GoPro ® camera was attached to a stick and was deployed and recovered with a fishing reel. Observations of larger animals were made using baited National Geographic cameras lowered to 50 meters water depth. Water quality above Kavachi was monitored with surface drifters that measure temperature, light transmission, and atmospheric carbon dioxide. Outgassing, identified by bubbles in the water column, was assessed from a camera attached to the drifter. Bathymetry was mapped using echosounder technology; because some areas had more data than others, the final bathymetric map was constructed using a multi-surface approach, which brings three layers, each with a different resolution and size of area covered, together to create a single image that represents the underwater volcano. SCUBA divers collected rock and micro-organic samples during the trip. The geochemical analysis and biological analysis of the collected specimen was completed onshore. Geochemical analysis included major and trace elements while biological analysis included DNA extraction.
The observations that scientists made in January of 2015 reveled a lot of neat characterizes about Kavachi. First off was the confirmation of a secondary peak, who’s existence had only every been speculated. Secondly, they learned that from that secondary peak there is diffusive flow. They also learned that carbon dioxide gas and warm water are venting from inside the crater. Additionally, scientists were pleasantly surprised to discover a multi-trophic level mega faunal community living in the extreme conditions of the Kavachi’s caldera. Lastly, they were able to derive information about the microbial community based on DNA results and geochemical analysis.
Geomorphology: Researchers learned that Kavachi has an elongated crater (120 x75 m) surround by a 24-meter high rim and a summit that sits 24 meters below sea level (Figure 1 in the original text). The secondary peak is 260 meters below sea level.
Petrology/Geologic Samples: Rocks containing fragments of other volcanic rocks (termed volcaniclastic) were collected from the summit of Kavachi (figure 5 original article). Scientists learned that volatile degassing in part drove the basaltic and mafic eruptions. The elemental components suggest that the subducted slab fluid is not influencing the magma at Kavachi, and that the magma source is likely a forearc mantle that is depleted because of previous melting events.
Hydrothermal Plumes: The orange and cloudy plume emitted as a result of normal volcanic processes lowered visibly in the water column. Surface drifters revealed that the average temperature of the plume was elevated 13 degrees C above surrounding seawater (figure 3a original article). A single fluid sample collected had a pH 1.9 lower than the ambient seawater. The plume fluids are mixed with the overlying surface waters by wind driven surface currents.
Outgassing: On the rim of the volcano gas bubbles can be observed floating towards the ocean surface (figure 2a in the original article). Thick plumes limited the visibility of the bubbles, however a SCUBA diver who got close enough to touch the gas bubbles commented that their skin felt uncomfortable when contact was made. Surface drifters exposed that the water above the diffusing bubbles was 300% higher in carbon dioxide than surrounding seawater (figure 3b original article).
Biology: Researchers observed both macro and micro, and benthic and pelagic organisms (figure 2b-2f in the original article). The micro-community of bacterial mats is not uncommon in an environment that has high sulfur content, a low pH, and an elevated temperature, like Kavachi. Scientists photographed and collected samples of orange and white microbial mats living up to a depth of 100 meters. The entirety of microbial DNA analyzed was related to Sulfurimonas (figure 4 original article), a genus of chemolithoautorophic bacteria that are known to utilize sulfur and carbon dioxide in acidic hydrothermal environments; they are often associated with white mats. Scientists noted the absence of Zetaproteobacteria. They were surprised by the absence because Zetaproteobacteria are typically associated with orange mats and iron oxidation in hydrothermal systems. Scientists speculate that the outgassing described above could be a source of food for chemolithoautorophic organisms, however more work still needs to be done.
The observation of large marine animals (check out this cool video!!), like scalloped hammerhead sharks, silky sharks, Bluefin trevally, and snapper, in the extreme environment or Kavachi was exciting because a multi trophic level system was unexpected. Observations of multiple fish and zooplankton species were also made. The researchers focused on the macro community may be able to use the Kavachi ecosystem to investigate the toughness of organisms when they are faced with sudden environmental changes. It also enables researchers to study the survival of organisms when sea surface temperature and acidity are elevated.
Studying submarine volcanoes to understand the geological significance, chemical influence, and biological importance, are all solid reasons to continue learning about Kavachi and other submarine volcanoes. The existence of natural marine environments that are warmer and more acidic than the average ocean have a huge potential to provide insight into ecosystem response to climate change; by 2100 it is projected that the ocean will have a pH .4 lower and a temperature 4 degrees C higher than present day. The extreme nature of the Kavachi environment with respect to temperature and pH could even enable scientists to understand how ecosystems have responded to periods of increased volcanic activity in Earth’s history.