Bach, W.

Borowski, C.

Breuer, C.

Brunner, B.

Dubilier, N.

Hourdez, S.

Jonda , L.

Jöns, N.

Koloa, K.

Meyerdierks, A.

Müller, I.

Petersen, Sven

Pjevac, P.

Schaen, A.

Shu, L.

Thal, J.

English

OceanRep

International ResearchINTERRIDGE NEWS 31 VOL.21, 2012Interactions between fluids, minerals, and organisms in sulfur-dominated hydrothermalvents in the eastern Manus Basin, Papua New Guinea – A report from RV Sonne Cruise216Wolfgang Bach1, Niels Jöns1, Janis Thal1, Eoghan Reeves1, Christian Breuer1, Liping Shu1, Nicole Dubilier2, ChristianBorowski2, Anke Meyerdierks2, Petra Pjevac2, Benjamin Brunner2, Inigo Müller2, Sven Petersen3, Stephane Hourdez4, AdamSchaen5, Kledy Koloa6, Leo Jonda7 and the MARUM Quest 4000m team81Geoscience Department and MARUM, University of  Bremen, 2Max Planck Institute for Marine Microbiology, 3GEOMAR, Kiel, 4Station BiologiqueRoscoff, 5Bridgewater College, 6Nautilus Minerals, 7University of  Papua New Guinea, 8Volker Ratmeyer, Phillip Franke, Oliver Herschelmann, Steffen Klar,Hoang Anh Mai, Ralf  Rehage, Christian Reuter, Marcel Zarrouk, all at MARUM, University of  Bremen.Figure 1: Map of the eastern Manus Basin.BackgroundMagma-hydrothermal systems in backarc basins are variably affectedby slab-derived flux. The Manus Basin is located in a tectonicallyparticularly active area and exhibits frequent neovolcanic centers ofextreme geochemical variability (Sinton et al., 2003). Intensehydrothermal activity in water depth of  1200-1700 m has beenobserved at many of  these volcanic structures, in particular in theEastern Manus Basin.The PACMANUS (PacificAustraliaCanadaManus) hydrothermalarea – situated on the dacitic to rhyodacitic Pual Ridge andcomprising numerous hydrothermal fields – was discovered roughly20 years ago (Binns and Scott, 1993). Additional French, Germanand Australian expeditions sampled sulfides and drill cores from thePACMANUS area. The sulfide accumulations were found to be richin copper and gold (Moss and Scott, 2001) and it was argued thatPACMANUS might be a modern analogue of  volcanogenic massivesulfide deposits. To test this hypothesis, the PACMANUS field wasdrilled during Leg 193 of  the Ocean Drilling Program, withboreholes reaching as deep as 387 m below the seafloor (Binns et al.,2002). In the mid-1990s, occurrences of  sulfide, sulfur, and bleachedfelsic rock had been observed in the SuSu Knolls area by dredge andTV-sled surveys. Suzette, the northernmost edifice of  SuSu Knolls,International ResearchINTERRIDGE NEWS 32 VOL.21, 2012corresponds to the Solwara1 mining target of  Nautilus Minerals.The cone-shaped North Su volcano south of  Suzette features largeaccumulations of  sulfur and abundant rock bleaching resulting fromacid-sulfate fluid venting. In close proximity to these sulfuric acidvents, black smoker type systems were observed (Tivey et al., 2006).The reasons behind the large range in style and composition ofhydrothermal venting and the consequences of  this variability forlife at these vents remain poorly identified.Cruise reportWe report on the most recent expedition to the Manus Basin, theprimary goal of  which was ROV-based sampling of  hydrothermalsystems in the eastern Manus Basin.  Cruise SO216 of  the GermanRV Sonne took place between June 14th and July 23rd, 2011. Thecruise was a follow-up on an RV Melville cruise with ROV Jason2 in2006, when geophysical mapping, rock sampling and reconnaissancefluid sampling were the primary goals (Tivey et al., 2006; Craddocket al., 2010; Reeves et al., 2011). The specific focus of  the SO216cruise was on vent fluid and biota sampling. The two working areas comprised North Su at 3°48.0'S, 152°06.05'E in about 1200 m waterdepth and PACMANUS at 3°43.5'S, 151°40.4'E in ~1700 m waterdepth. During nightly echosounding surveys with the ship-basedEM-120 system, a comprehensive and detailed map of  the easternManus Basin could be completed (Fig. 1). Twenty-two dives withthe ROV MARUM Quest 4000m were conducted, ten in thePACMANUS and twelve in the North Su area. Samples collectedinclude hydrothermal fluids (using isobaric gas-tight 'Seewald'samplers and teflon KIPS bottles), biological specimen of  ventmacrofauna, microbial filaments and biofilms, as well as volcanicrocks and hydrothermal precipitates. A range of  vent systems wassampled in both working areas (Fig. 1). Geological mapping wascarried out throughout the dives, and sections of  some dives werespecifically committed to mapping certain structures.  A summary of  the preliminary observations is provided here. Thisreport supersedes a communication in the previous issue ofInterRidge News by Adam Schaen, whose account of  participationin SO216 with an InterRidge travel bursary was inadvertentlypublished as the cruise report. A detailed cruise report can bedownloaded from:http://elib.suub.uni-bremen.de/edocs/00102250-1.pdf.North SuThe North Su volcano host countless hydrothermal vent sites, whichfall into three categories: (i) black smoker vents, (ii) white smokervents, and (iii) diffuse vents. While the black smokers cluster in thesummit area, white smoker vents are common in a 120 m long and50 m wide, east-west-trending area south of  the main summit. Thedense coverage with thick white smoke (most likely made up ofsulfur particles) renders mapping and sampling in this areaparticularly challenging.The black smokers are up to 9 m high spires and occur in waterdepths ranging from 1150 to 1200 m (Fig. 2). They show an innerlining of  dense chalcopyrite, surrounded by a pyrite-sphalerite-richouter layer and a Fe-Mn-oxide coating. In the westernmost extensionof  the black smoker clusters, a vent at 1190 m water depth wasfound, which shows flashing typical of  fluid boiling. Thetemperatures measured (332°C max.) correspond to the boilingtemperature of  seawater at 124 bar. The chimneys at the summit arehosted mainly in volcanic ash, which is often cemented by barite toform hard slabs. Where these slabs are broken up, clear fluids ventat the seafloor. More fluid seepage has been observed in numerouslocations downslope, in particular in large patches of  diffuse venting90 m northeast of  the summit in 1200 m water depth. This sitefeatures a diverse fauna (snails, mussels, tubeworms, fish, barnacles),which is associated with the venting of  14-30°C warm fluids throughfans of  poorly sorted talus.A prominent ash cone is located 100 m south of  the summit andfeatures numerous small craters on the top and smooth flanks withmore blocky pyroclastic deposits. The cratered summit featuresextensive white staining and currents have created ripples in the fineFigure 2: Black smokers at North Su.Figure 3: White smokers in the Sulfur Candles area.International ResearchINTERRIDGE NEWS 33 VOL.21, 2012ash. This cone was not observed when North Su was mapped duringthe Magellan cruise in 2006. The new ash cone buried steep wallsand talus slopes with countless white smoker vents, some of  whichwere sampled in 2006.The newly discovered Sulfur Candles area is the easternmost andmost spectacular of  the white smoker clusters. It features hundredsof  white smoker vents, many of  which also emanate what appearsto be gas bubbles, but is likely liquid CO2 (Fig. 3). We hypothesizethat the slowly rising bubbles contain liquid CO2, forming when thetemperature drops below 31°C. At 3°C (ambient temperature at1200 m depth), liquid CO2 converts to CO2-clathrate at theinterface with seawater. This behavior was documented by collectionof  liquid CO2 bubbles at Sulfur Candles. Prominent bubble flareswere also visualized using the ship-based Parasound system. TheSulfur Candles site is situated in volcaniclastic sediments, which areimpregnated with liquid sulfur around the vents. The sulfur isexuded when water and bubbles vent at the seafloor where it formssub-meter-high, chimney-like structures (Fig. 3). The sulfurchimneys grow fast (in minutes), but do not grow tall. Most of  the sulfur is hence not located in chimneys. Additional sulfur tricklesdownslope and pools in certain areas, where it forms denseaggregates composed of  thousands of  anastomosing sulfur fingersthat coalesced to meter-thick irregular pods and flows.PACMANUSThe PACMANUS hydrothermal area comprises severalhydrothermal vent sites on the Pual Ridge in a 2.5 km2 area in 1640to 1780 m water depth (Fig. 1). The Fenway, Snowcap, Tsukushi,Satanic Mills, Roman Ruins, and Roger's Ruins hydrothermal ventsites were visited. Nautilus Minerals discovered additionalhydrothermal vent sites in the area (Solwara 6, 7, and 8), from whichwe collected first high-temperature fluid samples.The Fenway hydrothermal field comprises an anhydrite-hosted blacksmoker complex (Big Papi), two small chimney clusters 50 mnortheast and northwest of  Big Papi, and a large patch of  diffuseventing in the northern part. Big Papi vents 304°C black smokerfluids through sparse chimneys around the base of  the anhydritemound (Fig. 4). The activity of  venting is much weaker than in 2006,when boiling (358°C) black smoker fluids emanated from countlessorifices at the mound's summit. The Fenway hydrothermal moundis partly collapsed and covered with anhydrite blocks and sand.Through these deposits, venting of  70-110°C hot, clear fluids occursand several fluid samples were collected. The sulfide chimney atFenway exhibits a thick chalcopyrite lining and outer parts that arerich in sphalerite and marcasite with a Mn/Fe-oxide coating. Fenwayis hosted predominantly in fine pyroclastic sediment, in particularthe diffuse patch north of  Big Papi. That area was a focus point ofbiological sampling and Symcatcher incubation experiments. Itfeatures snails (mainly Ifremeria nautilei), mussels (Bathymodiolusmanusensi) and several species of  tubeworms, commonly in a patchystyle of  distribution.Solwara 8 is located 300 m southeast of  Big Papi and featuresclusters of  up to 12 m high and Cu-rich chimneys and porous, morebulbous Zn-rich ones. We recorded a temperature of  304°C whensampling fluid venting from a chalcopyrite-lined orifice sticking outof  a beehive structure.The top of  the Snowcap knoll is decorated with countless patchesof  diffuse fluid seepage. Two reentry funnels mark the ODP Site1188 drilled to depths up to 387 m in 2000. On the northwesternside of  Snowcap lies a small field of  sulfide chimneys (variably Cu-and Zn-rich) populated with snails and Paralvinella. These chimneysvent clear to light gray fluids with temperatures of  ≤224°C, but thepresence of  abundant dense chalcopyrite suggests higher ventingtemperatures in the past. Immediately southwest of  the chimneycluster is a mound of  native sulfur, which is densely populated bysnails and is surrounded by sediments.Satanic Mills features numerous clusters of  sulfide chimneys; thelargest one extends for 60 m from north to south and is about 10 to15 m wide. The chimneys grow directly on top of  fresh block lava,in particular near flow fronts of  lava with little chimney debris lyingFigure 4: Venting at Big Papi, in the Fenway hydrothermal field. Figure 5: Vigorous venting of black smoker fluids at Solwara 7.International ResearchINTERRIDGE NEWS 34 VOL.21, 2012around. Fluid temperatures up to 345°C and local CO2 bubblingwere observed. Tsukushi was relatively inactive, though venting ofmoderate-temperature clear fluids and oxide mounds were observed,similar to 2006.Roman Ruins, Roger's Ruins, and Solwara 6 and 7 form a northwest-southeast trending line, roughly perpendicular to the strike of  PualRidge. Solwara 7 is hosted in a field of  block lava and consists of  a50-m diameter main cluster of  vents and a smaller accumulation ofactive chimneys just south of  it. The highest temperature of  venting(348°C) was measured here in vigorously venting black smokerfluids issuing from a small chimney that grows on top of  sulfiderubble (Fig. 5). Roger's Ruins, located 200 m southeast of  Solwara7, comprises a small cluster of  mostly inactive vents. Its activity wasmuch greater in 2006, in particular in the area of  Marker 8, whichwas very active in 2006, but appeared inactive in 2011. Extensiveareas around Roman Ruins are covered with Fe-oxyhydroxidedeposits that occasionally form chimneys. Although there isabundant venting of  shimmering water through these mounds, nomacrofauna could be observed here. The northeastern part ofRoman Ruins is mostly inactive, in contrast to the situation in 2006,when lots of  black smoker activity was observed there. The centralpart of  Roman Ruins features copious amounts of  sulfide chimneyrubble, which is exposed on the southeastern flank of  the ridge withthe active black smokers.  In contrast, the southwestern extension ofRoman Ruins has volcanic rock talus exposed on the slopes. Thispart is also more hydrothermally active than the northeastern end ofthe field. The area between Roman Ruins and Solwara 6 is coveredby variably sedimented block lava. Solwara 6 is also situated in blocklava flows. There are a few inactive chimneys in the western part ofthe system; other areas show diffuse venting. Nautilus Mineralsreported more activity in this area during their 2007 survey, includingactive black smokers.Summary and outlookThe hydrothermal systems in the eastern Manus Basin reveal anextraordinary variability in fluid chemistry, both on a spatial and ona temporal scale. This variability is obviously tied to the changes inmagmatic activity including magma degassing of  SO2 and CO2. AtNorth Su, we were able to document a volcanic eruption that musthave happened between 2006 and 2011 and led to a drastic changein the location and style of  acid-sulfate fluid venting. AtPACMANUS, activity, temperatures and gas contents of  fluids haveundergone marked changes since 2006.With the samples collected, we will address a number of  questions:What are the gas-water-rock interactions and fluid mixing processesin the subsurface and how do they mediate mass flux to the seafloor?What energy sources in volcanic magma-hydrothermal systemsreach the seafloor and how are they used by microorganisms? Andhow do they determine the physico-chemical environment of  thevent fauna? Moreover, we would like to know how the differentchemical compositions of  vent fluids influence the composition ofbiocoenoses. What are the dominant metabolic reactions in thedifferent habitats and how much biomass can potentially beproduced? Finally, we will investigate what kinds of  symbioticrelationships have evolved within the different hydrothermal systemsof  the Eastern Manus Basin and how they are influenced by thevariable fluid chemistry. Characterization of  sulfur species in fluids,with emphasis on sulfur redox intermediates and their roles aselectron donors and/or as electron acceptors for microbial growthis another goal of  post-cruise studies. We are also interested inlearning what sulfur-oxidizing asymbiotic microorganisms dominatethe geochemically distinct diffuse vents and how they fix carbon.AcknowledgementsWe thank the Captain, Lutz Mallon, and the officers and crew ofthe RV Sonne for their professional handling of  the ship and thealways very generous and kind assistance in all science operations.Many thanks to Drs. Jeff  Seewald, Peter Girguis and Dieter Garbe-Schönberg for letting us use their instruments and equipment. Wethank the Department of  Foreign Affairs of  Papua New Guinea forthe research permission. Adam Schaen thanks InterRidge for travelsupport. The DFG-Excellence Cluster MARUM is thanked forvaried budgetary and logistical support. We are primarily funded bya grant (03G0216) from the Bundesministerium für Bildung undForschung (BMBF) awarded to Wolfgang Bach and co-PIs. Dr.Barbara Tanner (Projektträger Jülich) is thanked for helpful advicein obtaining and managing the grant.ReferencesBinns R.A. and Scott S.D. (1993) Actively forming polymetallicsulfide deposits associated with felsic volcanic rocks in the easternManus Basin, Papua New Guinea. Econ. Geol. 88, 2226-2236.Binns R.A., Barriga F.J.A.S., Miller D.J. et al. (2002) Proc. ODP Init.Results 193 [CD-ROM]. Ocean Drilling Program, Texas A&MUniversity.Craddock P.R., Bach W., Seewald J.S., Rouxel O.J., Reeves E. andTivey M.K. (2010) Rare Earth Element Abundances inHydrothermal Fluids from the Manus Basin, Papua New Guinea:Indicators of  Sub-seafloor Hydrothermal Processes in Back-ArcBasins. Geochimica et Cosmochimica Acta 74(19): 5494-5513.Moss R. and Scott S.D. (2001). Geochemistry and mineralogy ofgold-rich hydrothermal precipitates from eastern Manus Basin,Papua New Guinea. Can. Mineral. 39, 957-978.Reeves E.P., Seewald J.S., Saccocia P., Walsh E., Bach W., CraddockP., Shanks W.C., Sylva S., Pichler T. and Rosner M.(2011).Geochemistry of  hydrothermal fluids from the PACMANUS,Northeast Pual and Vienna Woods vent fields, Manus Basin, PapuaNew Guinea. Geochimica et Cosmochimica Acta 75(4): 1088-1123.Sinton J.M., Ford L.L., Chappell B. and McCulloch M.T. (2003).Magma genesis and mantle heterogeneity in the Manus back-arcbasin, Papua New Guinea. J. Petrol. 44, 159-195.Tivey M.A., Bach W., Seewald J., Tivey M.K. and Vanko D. (2006).Cruise Report R/V Melville MAGELLAN-06 Woods HoleOceanographic Institution.

Interactions between fluids, minerals, and organisms in sulfur-dominated hydrothermal vents in the eastern Manus Basin, Papua New Guinea – A report from RV Sonne Cruise 216

Interactions between fluids, minerals, and organisms in sulfur-dominated hydrothermal vents in the eastern Manus Basin, Papua New Guinea – A report from RV Sonne Cruise 216

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