Methane fluxes and gas hydrates as well as seismic activity in the Okhotsk Sea

Global Geology 2): 161-16 2006)Article l:1673-9736(2006)2-016103Methane fluxes and gas hydrates as well as seismic activityin the okhotsk seaanatoly Obzhirovv.I. Il'ichev Pacific Oceanological Institute FEB rAs, vladivostok 690041 RussiaAbstract: The research works of methane concentration in water column of the Okhotsk Sea from 1984 to2005 were reviewed. And some regularities of methane distribution in water column in the north-East Sakhalinslope of the Okhotsk Sea were concludedKey words: methane fluxes gas hydrate Okhotsk SeaLaboratory of gas geochemistry Pacific Oceanological Institute FEB RAs studied methaneIn the first time in the Okhotsk Sea gas hydrateconcentration in water column of the Okhotsk seawas discovered in the North-West Paramushir slopefrom 1984 to 2005. Before it mostly goal was to usein expedition 1986 Akademik Keldysh( Zonenshainhane and heavy hydrocarbon gases like indicatoret al., 1987). Gas hydrate was found in near surto search oil-gas deposit( obzhirov 1993). In first face sediment(1-5 m below bottom in area whereperiod( before 1988)was determined background methane bubbles are going up from sediment to wamethane concentration in water column in the almostter column bSR bottom simulating reflectionallareaof the Okhotsk sea. ItwasGaedice et al., 1997) shows that thickness of gasbottom water. Above oil-gas depohydrate layer in this area is about 200 m. Bubbles ofcentration in bottom water increased usually aboutgas( most methane created hydro-acoustic anomalyin echogram like flare 200-300 m long. MethaneIn 1988 a few methane flares was found inconcentration inside flare was more than 1 000 ml/L. ItNorth Sakhalin shelf and slope for the first timeharply decreased in water column outside flare(Obzhirov, 1992 ). The second period investigation Over stable gas hydrate field methane concentrationof the hydrocarbon gas and gas hydrate was starting in bottom water was like background about 40-50from 1988 to 1998. Meanwhile, methane distribmI/L. It is supported that anomaly of methane contion in water column was studied, and methane flux cennosition of gas hydratehydrate were found in sediment in the中国煤化工hane that consist underNorth-East shelf and slope of the Okhotsk Sea. EvCNMHGery year there was many new methane bubbles fluxesvia zone fault especially in period seismic activityThis regularity was used to search gas hydratearea with bubbles methane concentration increased in in Sakhalin North-East shelf and slope. In 1988A100-10detme5in column water( from bottom to Obzhirov and colleagues in expedition Morskoy162Anatoly ObzhirgGeophisic found flare of methane like of it in Para- of area with methane flux and gas hydrate in themushir area( Obzhirov et al., 1992). In 1991 GOkhotsk Sea. There were many different projectsGinsburg and v. soloviev organized expedition inand memorandums of international cooperation toOkhotsk Sea in the ship" Geolog Petr Antropovstudy process forming and destroying gas hydrateMostly goal this expedition was to search andsource and volume methane flux and other regularistudy gas hydrate in sediment of the Okhotsk Seaty. There were organized Russian-GermanyResult of this expedition was very success. In expeKOMEX-project(1998-2004 )and Russian-Japandition was found gas hydrate as well as the secondKorea CHAOS-projects( 2003, 2005). In this peritime in the North-West Paramushir slope in the od the research found more than 150 new flares,disknown gas hydrate area ) and the first time in Northcovered new areas with gas hydrate, watched moreEast Sakhalin slopedetail methane distribution in east sakhalin shelfBefore it sediment core 5 m long was taken inand slope Okhotsk Sea and calculated methane fluxmethane bubble flux area in 1988( Obzhirov et alo atmosphere.1992). In the interval 2-5 m below surface sedi-There were following regularity of methane diment was destroyed. Much methane istribution in water column in the north-East sakhalinthis interval and smell of sulphide hydrogen is slope of the Okhotsk Seafeeled. It was indicator that sediment consist gas hy-(1) Background methane concentration usuallydrate but it was not visible because core of sediment is 50-70 ml/L in surface water, 100-120 mI/Llayered long time inside gravity coring equipmentin subsurface layer( depth 75-100 m ) It decreasesA. Obzhirov told about it G. Ginsburg and V.to direction to bottom layer to 15-20 ml/L in deSoloviev before expedition 1991 and showed this area part of Sea of Okhotsk( 1 000 m depthwith methane flux in the map. In expedition 19912)Anomalies of methane concentration arethey investigated this area and vicinity around itfound in water column in the shelf and slope of eastThey found about 10 new methane fluxes and gas Sakhalin area. Sources of methane are usually oil-gashydrate in sediment in this area( ginsburg et al., deposit and (or )gas hydrate. In this cause methane1993 ). There were found gas hydrate in water depth comes to water column and create methane anomalyfrom 400 to 800 m and in near surface sediment (inin bottom water and different layer as well as in surterval about 0.5-6 m below bottom ) Gas of itface water. It increases in surface water to 500consist mostly methane. Core of sediment after000 ml/L and in bottom water to 20 000-25 000about half hour destroved because methane vent out ml/Lfrom decomposition gas hydrate. Sediment with gas3)There was found many methane bubbleshydrate consisted methane usually more than flare in North-East Sakhalin shelf and slope. Moni10 ml/L. It is more than background in 1 000 timetoring of it show that number of it growth from 2 inBy these investigations it is discovered that the1988 to about 150 in 2005. It is connection with innterest to study methane bubbles fluxes and gas hytectonic activity this area. As adrate in Okhotsk Sea very increased in Russian and中国煤化工and methane comes tointernational sciences. It is third period from 1998 toCNMHGell2005 for studying methane fluxes and gas hydratefrom under gas hydrate. It is supported earthquakesand it is continued now. Most tasks are to study of 6 and more magnitude Kuril( 1994), Neftegorskmore detail complex of geology geophysics, gas (1995), Uglegorsk( 2001), Hokkaido( 2004 )andgeochemistry rphology and other characteristic other with less magnitude than 6. It is reason thatMethane fluxes and gas hydrates as well as seismic activity in the Okhotsk Sea16we can use it like criterion to look historical phouse effect and to drive global Climate Change. Itearthquake and prognosis of it nowwill increase in period seismo-tectonic activity this(4)Many new flares appeared may be in period2000-2002 because they are never seen before 1999(10)Background methane concentration in sedGeomar Report, 1999: 2002). It means thatiment is usually 1-5 mI/L in horizon from surfacethis period 2000-2002)there was seismo-tectonicsediment to 200 cm. It connects with sulphate-reactivity. As a result zone faultduction process. The deeper methane in core increasmethane )comes to surface. It is conformedes to 10-50 ml/L to depth10 mepisodes of the earthquakes that were in Sakhalin in(11) Methane concentration sharply increases2000,2001and2002 yearsto 100-1 000 mI/L as well as almost in surface sed(5) Methane anomaly and bubbles flux of itthat create hydro-acoustic image may use like criteria(12)In upper layer sediment in the Northto search gas hydrate and oil-gas depositSakhalin slope there was found 9 new gas hydrate ar-(6) Anomaly of methane in water column may eas( CHAOS-project, 2003: 2005 ) They usuallymigrate with water layer with water current. In located in bubble flare area. It is possible a seconOkhotsk Sea it is usually moves from shelf to slope young has hydrate that form from methane fluxand deep part of Okhotsk Sea as well as in bottomwhich is going from under gas hydrate capand in intermediate and in surface water. Water lay(13)G. Ginsburg and V Soloviev were one ofers with methane anomaly from shelf intrude to wathe first scientists who discovery gas hydrates in theter columns in the slope isNorth-East sakhalin shelf of the Okhotsk sea(7) Down part of water column in area"ObzhiReferencesroy" flare consist different methane concentrationGaedice C, Baranov B V, Obzhirov A I, Lelikov e P, Belykhwater layers. Bottom layer in this area has highIN, Basov E I. 1997. Seismic stratigraphy BSR distrimethane concentration (4 000-6 000 ml/L)ution and venting of methane-rich fluids west off Para-About 500 m in depth( about 100-150 m uppermushir and Onecotan Islands, northern Kurils. Marinebottom )methane decreases to 10-20 time. higherreology,1l6259276layer( 200- 250 m from bottom again methaGeomar Report. 1999. Edit. Nicole Biebow. No 82. Kielconcentration increases. It is connection with changeGeomar Report. 2002. Edit. Nicole Biebow. No 88, Kielactivity flux methane bubbles and mobility waterlaversGinsburgg D, Soloviev V A, Cranton R E. 1993. Gas(8) Anomaly of methane concentration (500drate from continental slope offshore from Sakhalin I2 500 ml/L) is found in water column in area ofland, Okhotsk Sea. GeoMarine Letters 41-48shelf and slope Terpenia Bay Barite Mound of DeruObzhirov A. 1993. Gas geochemical fields of bottom water ingin Basin and in South-East Sakhalin of it. Sourcesmarines and oceans. Moscow: Nauka, 139of methane in this are oil-gas bearing sediment inObzhirov A. 2002. Methane monitoring in the Sea of Okhotelf and may be gas hydrate in slope中国煤化工50(9) Average methane flux from sediment toCNMH Ghenko Y. 1992. Effect ofsound-scattering in bottom water in the Okhotsk Seawater column and to atmosphere in shelf area ofPacific Geology 2: 119-121Okhotsk Sea is 0. 1 Tg per year. So, methane fluxZonenshain l p, murdmaa io baranoyb v. 1987. Underfrom sea of okhotsk wille increase methane conwater gas source in the Okhotsk Sea of West Paramushircentration方携 here that will be added to greenIsland. Oceanologia, 27. 725-800