OceTHE OFFICIALa MAGAZINEn ogOF THE OCEANOGRAPHYra SOCIETYphy EARLY ONLINE RELEASE Posted October 7, 2016 CITATION 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), https://doi.org/10.5670/oceanog.2016.85. DOI https://doi.org/10.5670/oceanog.2016.85 COPYRIGHT This article has been published in Oceanography, Volume 29, Number 4, a quarterly journal of The Oceanography Society. Copyright 2016 by The Oceanography Society. All rights reserved. USAGE Permission is granted to copy this article for use in teaching and research. Republication, systematic reproduction, or collective redistribution of any portion of this article by photocopy machine, reposting, or other means is permitted only with the approval of The Oceanography Society. Send all correspondence to: [email protected] or The Oceanography Society, PO Box 1931, Rockville, MD 20849-1931, USA. DOWNLOADED FROM HTTP://WWW.TOS.ORG/OCEANOGRAPHY REGULAR ISSUE FEATURE EXPLORING THE “SHARKCANO” Biogeochemical Observations of the Kavachi Submarine Volcano (Solomon Islands) By Brennan T. Phillips, Matthew Dunbabin, Brad Henning, Corey Howell, Alex DeCiccio, Ashton Flinders, Katherine A. Kelley, Jarrod J. Scott, Simon Albert, Steven Carey, Rami Tsadok, and Alistair Grinham Oceanography58 Oceanography | Vol.29, | VolNo..429, | NoEarly.4 Online Release ABSTRACT. An expedition to the Kavachi submarine volcano (Solomon Islands) Tuni, 1987). The most detailed investiga- in January 2015 was serendipitously timed with a rare lull in volcanic activity that tion prior to this study, which took place EXPLORING THE “SHARKCANO” permitted access to the inside of Kavachi’s active crater and its flanks. The isolated during a single day in May 2000, was con- Biogeochemical Observations of the Kavachi Submarine Volcano (Solomon Islands) location of Kavachi and its explosive behavior normally restrict scientific access to ducted from an approximate 1 km perim- the volcano’s summit, limiting previous observational efforts to surface imagery and eter surrounding the actively erupting peripheral water-column data. This article presents medium-resolution bathymetry of main peak. That study provided insights the main peak along with benthic imagery, biological observations of multiple trophic into the eruptive processes of Kavachi levels living inside the active crater, petrological and geochemical analysis of samples based on conductivity- temperature- from the crater rim, measurements of water temperature and gas flux over the summit, depth (CTD) casts and surface imagery and descriptions of the hydrothermal plume structure. A second peak was identified (see Baker et al., 2002). A magnitude 8.1 to the southwest of the main summit and displayed evidence of diffuse-flow venting. earthquake that shook the entire region Microbial samples collected from the summit indicate chemosynthetic populations in April 2007 prompted the reconnais- dominated by sulfur-reducing ε-proteobacteria. Populations of gelatinous animals, sance of a conspicuous surface plume fol- small fish, and sharks were observed inside the active crater, raising new questions lowing a subaerial eruption visible from about the ecology of active submarine volcanoes and the extreme environments in a nearby island (Wunderman, 2007). which large marine animals can exist. The latest published evidence of activ- ity was obtained by NASA’s EO-1 sat- INTRODUCTION eruptions has prevented scientists from ellite on January 29, 2014 (NASA Earth The New Georgia Island Group is the observing the proximal area of Kavachi’s Observatory, 2014), and it appears simi- result of a complex tectonic configu- summit crater. lar in behavior to the 2007 eruption. ration, characterized by subduction of Of the roughly 30 active submarine vol- This study was conducted during a the active Woodlark Spreading Center canoes known worldwide, only a few have quiescent phase, which allowed for the (WSC) beneath the Solomon Islands been observed during or closely following first closeup look inside and around the intra-oceanic arc. This triple junction is an active eruption, for example, Northwest shallow summit of Kavachi. Our research the site of active volcanism, crustal uplift Rota-1 (W.W. Chadwick et al., 2010), team took advantage of this rare lull in that closely matches subducted bathy- West Mata (Resing et al., 2011), El Hierro volcanic activity to gather geological, metric features from the WSC, and a pro- (Santana-Casiano et al., 2013), Kick’em biological, and oceanographic observa- posed “slab window” that leaves astheno- Jenny (Devine and Sigurdssson, 1995), tions using relatively simple equipment spheric mantle in direct contact with a and Axial Seamount (W.W. Chadwick and methodologies. We report here on thin overlying crust (Mann et al., 1998; et al., 2012, and references therein). our initial results, which include evi- J. Chadwick et al., 2009). The Kavachi Despite these limited studies, active sub- dence of diffuse-flow venting on a con- submarine volcano (8°59'S, 157°58'E) is marine volcanoes are considered import- firmed second peak, a megafaunal com- situated ~30 km northeast of the sub- ant natural laboratories for observing the munity living inside the active crater, duction zone and rises abruptly to the effects of ocean acidification on marine and insights into the eruptive processes surface from more than 1,000 m water animals (e.g., Hall-Spencer et al., 2008), and magma source characteristics of depth (Figure 1). By far the most active with Kavachi being an extreme example Kavachi’s active volcanism. volcano in the region, Kavachi is known of such an environment. for frequent phreatomagmatic (denoting Kavachi erupts nearly continuously. METHODS explosive water-magma interaction) and Reports of airborne steam and ash visible This work was conducted in January 2015 subaerial eruptions leading to occasional from shore are common, and the forma- with operations based out of Gatokae ephemeral island emergence (Johnson tion and erosion of multiple islands over Island, Western Province, Solomon and Tuni, 1987). The remote geographic the past century indicate the summit is Islands. Approaches to the summit crater location and inherent danger of frequent in a constant state of flux (Johnson and were made after several days of observing inactivity from a safe perimeter—normal eruptive activity for Kavachi is audible FACING PAGE. Article co-authors Alistair Grinham and Matthew Dunbabin prepare an autonomous on the surface, and no such sounds were surface drifter for deployment over Kavachi’s summit crater. Photo is taken looking north toward Vangunu Island, with the volcano’s surface plume visible in the middleground where the water heard during the course of this expedi- changes color from dark blue to light blue-green.” tion. All equipment used was lightweight, Oceanography | December 2016 | http://dx.doi.org/10.5670/oceanog.2016.85 relatively low cost, and deployed using transmission, and atmospheric pCO2 general trend depicting the volcano, sim- small boats. Down-looking images of the were deployed as described by Dunbabin ilar to swath editing in multibeam sonar seafloor paired with water-column mea- (2016). Total CO2 flux was calculated processing. This “cleaned” point-cloud surements were made using a GoPro using the drifter’s measurements of flux (~85,000 soundings; see online supple- camera in a deep-rated housing, battery- per unit area, which was extrapolated mental Figure S1) was then used to create powered lights, and a National Oceanic to represent the total size of the bubble three individual continuous curvature and Atmospheric Administration/Pacific zone. A downward-looking camera was spline surfaces, each with unique spatial Marine Environmental Laboratory mounted on the drifter, which logged its extent and resolution. This multisurface (NOAA/PMEL) Miniature Autonomous position, and after multiple runs through approach was necessary in order to accu- Plume Recorder (Walker et al., 2007) the bubble zone it was possible to esti- rately represent varying degrees of data mounted on an instrument frame that mate the total surface area by noting the density over the study area, with the most was raised and lowered with an electric appearance and disappearance of bubbles soundings concentrated at the summit fishing reel. Baited drop-camera record- on camera footage. caldera, and the least at the foot of the vol- ings were achieved using an autonomous We measured bathymetry with cano (Flinders et al., 2014). The three sur- National Geographic Remote Imaging a Lowrance HDS-5 echosounder faces (100 m study-wide, 35 m volcano- DropCam following methods described (50/200 kHz). IVS Fledermaus software focused, and 7 m summit-focused) were by Friedlander et al. (2014). Surface drift- was used to manually remove sound- then blended to create a single individual ers measuring water temperature, light ings that qualitatively deviated from a surface for visualization. Blending con- straints ensured that within each specific area, only the highest resolution surface 157°E 158°E 159°E 160°E would be used. Santa Scuba divers collected rock and bac- Isabel Vangunu terial samples by hand. Major and trace 8°S New element analyses were conducted using Georgia a Perkin Elmer Optima 3100 XL induc- 8.98°S Kavachi 9°S tively coupled plasma atomic