Site U1496

Unexpected discovery of a serpentinite‐hosted chemosynthetic ecosystem on Asùt Tesoru Seamount, Mariana Forearc

“…These are fauna typical of vent and seep habitats (Chen et al, 2016; Xu et al, 2022; Zhou et al, 2019) and indicate active seepage in this area supporting a chemosynthetic ecosystem—which we name the ‘Big Blue Seep’ (BBS). This discovery is unexpected because previous expeditions did not notice any sign of chemosynthesis‐based fauna (Fryer et al, 2018; Hulme et al, 2010). As crusts were not available for the present study, future studies of these materials are needed to confirm its carbonate nature and reveal more information on the nature of the seep fluid.…”

“…These were located at a diameter of approximately 80 m between the IODP Holes U1496A and U1496B (Figure 1), and majority of the active patches were adjacent to either Holes U1496A or U1496B. These two holes were untreated, whereas U1496C was capped with a casing pipe and re‐entry cone (Fryer et al, 2018). One patch of carbonate‐like crust (18°06.6251′ N 147°06.1076′ E, 1240 m deep) was found directly above Hole U1496B, which has been filled in or crusted over (Figure 2a,b; 18°06.5957′ N 147°06.1028′ E, 1243 m deep), the central part appeared to be slowly seeping out white, smoky geofluid.…”

“…Fluids up to pH 12.5 under slab conditions have been confirmed from the southwestern conical summit with three circular mounds by gravity and piston coring (Mottl et al, 2004), concentrated on the largest mound about 350 m in diameter. In January 2017, scientific drilling by the International Ocean Discovery Program (IODP) drilled three holes here (Figure 1a; Holes U1496A, 40.8 mbsf; U1496B, 36.0 mbsf; and U1496C, 105.0 mbsf) (Eickenbusch et al, 2019; Fryer et al, 2018). Though visual explorations with subsea camera and also remotely operated vehicle (ROV) have been conducted, there has been no report of either fluid springs as evidenced by carbonate or brucite structures, nor the presence of geofluid‐associated ecosystems (Fryer et al, 2018; Hulme et al, 2010).…”

“…In January 2017, scientific drilling by the International Ocean Discovery Program (IODP) drilled three holes here (Figure 1a; Holes U1496A, 40.8 mbsf; U1496B, 36.0 mbsf; and U1496C, 105.0 mbsf) (Eickenbusch et al, 2019; Fryer et al, 2018). Though visual explorations with subsea camera and also remotely operated vehicle (ROV) have been conducted, there has been no report of either fluid springs as evidenced by carbonate or brucite structures, nor the presence of geofluid‐associated ecosystems (Fryer et al, 2018; Hulme et al, 2010). Here, we present results from a recent ROV survey, the first to confirm the presence of a chemosynthesis‐based community on this seamount concentrated around white carbonate‐like crusts.…”

“…Furthermore, the discovery of the 5700 m deep Shinkai Seep Field (SSF) facing the Challenger Deep with dense vesicomyid clam colonies confirmed that serpentinite‐hosted seeps can support lush chemosynthesis‐based communities (Ohara et al, 2012; Okumura et al, 2016), much like those famously known from hydrothermal vents (Corliss et al, 1979; Levin, 2005). Despite this, South Chamorro Seamount (13°7′ N, 146°00′ E, located about 125 km east of Guam) has been the sole serpentinite mud volcano with a seep ecosystem (Fryer & Mottl, 1997), even when many others have been explored by submersibles and coring (Fryer et al, 2018; Hulme et al, 2010). The seep community on South Chamorro Seamount is dominated by bathymodioline mussels, though ‘tubeworms', squat lobsters, and snails in genera Desbruyeresia and Phymorhynchus have also been reported (Chen et al, 2016; Fryer & Mottl, 1997).…”