Hydrothermal activity and long-term monitoring at

Southern East Pacific Rise

-Preliminary results of the Ridge Flux SEPR'97

Leg 2 cruise-

Kanlaro FUJI OKA*1 ICyohiko M1TSUZAWA*1 Masataka KJNOSHITA*2

shipboard scientific party*3

During tthc Ridsc Fl"x SEPR'9? Lep 2 cruise 9 dives were successfully accomplished by the

"Siitnkai 6500." The surface ship "Yokosuko" was also used Jo launch and recover instruments

and to make geophysical measurements at (ho super-fast spreading ridge on the East Pacific Rise

during a 34 dayemise (rum Valparaiso. Chile (depart 25 October, 1994) to Papeete. Talnti (arrive

19 September. 1997). Preliminary results of this cruise are briefly summarized in this paper.

* 1 Deej>Soa Research Department, JAMSTliC

* 2 School of Mui In*? Sciunce and Technology. Tokni llnivojsky

*3 Tsugio SHIBATA. Kacuky of Si-icnc?. Okayama UpivonuJy. Jim ichno ISHlliASHl.

University of Tokyo. Masalo JOSHIMA. Geological Survey t>f Japan. Kiminori

SKITASHIMA. Cenlral Reso≪uch Institme of Klccinc I'owcr Ind 11*11* (CRIKIM). Akiluko

MARUYAMA. Department of Applied Microbiology National Infinite ot Bioscience and

Human-Tech no l"gy. James COWIvN. University of Hawaii. Kevin ROK..NOAA/1'MKL.

I/o mi SAKAMOTO. JAMS HCC. Kci OKAMUHA. OKI. Uuiv of ToUjo. *≪≪>mi WOW.

In dilute of KioltJffiwil Soieitocs Univashy of r^ituiba, an<l torn KOHfCKA. Nippon Marine

Kntci |≫ i≫,u ) t<l

JAMSTEC J Deep Sea Res . M mm)21

1. Introduction

The present cruise or submersible "Shinkai 650CP and

R/V "Yokosuka" is the second leg of South East Pacific

Rise Ridge Flux '97 Expedition which is a part of the 6

year program "Ridge Klux Project" funded by the Science

and Technology Agency of Japan, in collaboration with the

NOAA/VENTS program to evaluate the heat and material

fluxes emanating from the fastest spreading ridge at the

Southern East Pacific Rise. As a pre-cursor to this cruise,

an extensive CTDT tow≫yo survey was conducted during

the R/V "Melville" cruise in December, 1993 where

massive plumes were mapped along much of the fast

spreading ridge axis. During the MODE '94 Leg 3 and Leg

4 cruises "Yokasuka" and "Shiukai $500" had 30 dives at

the sites RM04(14 °S). 11 (14'SO'S), 24 (17e30'S), 23

(17 °35*5). 28 (18°2$'S) . 29 08 ° 10- ll'S), and OSC1822

(18 °22'S), obtaining chemical, penological, and biological

samples as well as bathymetric, gravimetric find magnetic

data. R/V "Gyre" cruise in 1995 TAMU square obtained

side scan sonar image along the ridge Extensive studies

on the geology, geophysics, geochemistry and biology of

the southern East Pacific Rise have been published on our

study areas (See references). In 1997,"Yokosuka" and

"Shinkai 6500* revisited SEPR sites during the first leg.

15 dives were dedicated on the deployment of long'term

monitoring systems prepared for one*year measurements

(current, depth, distance from ridge axis, and so on). 25

long-term monitoring instruments were deployed either

from the surface ship or by the Shinkai manipulator at

three sites (RM24, RM2S, and RM28) in the Southern

East Pacific Rise. The first cruise demonstrated ;t new

style in the use of mannecl-submersiblcs. The "Shinkai

6500" has proven to he capaible and powerful enough to

do such complex ta≪ks

Although the various devices are still recording data

and will b<* recovc*i*ed in fall 1998, we intend to present a

shori summary of the 1997 SJvPR U*g 2 cruise in this

report In addition, all the devices were successfully

recovcivd by "AllanMs" and "Alvin", in ic)9H September

2. Objectives

The second leg focused more on sampling and

observations of the hydrothermal systems and their

environs. The main objectives of this cruise were five fold;

The fn*st objective is the evaluation of heat ;ind material

fluxes. It includes 1) Chemical and biological budget at

two different hydrothermal areas through the chemical

analyses of hydrothermal fluids from diffuse and high

temperature black and white smokers, collected with

water samplers, pump/filter sampler and in-situ Mn, pH,

CTDT sensors , 2) Dispersion process of hydrothermal

fluids, plume, particle and microbiota with time and

distance from the chimney, using the CTD RMS and

Niskin samplers.

The second target is the long-term monitoring of

hydrothermal systems. We plan to carry out 1) Heat flow

measurement using Moored heat flow arrays, 2) In-situ

observation of the hydrothermal field by CTD, current,

temperature, pressure, ncphelicity. and 3) Monitoring

particle flux using sediment traps sunouiiding site RM24.

The third target is geological and biological mapping of

hydrothermal fields and the regional distribution of lavas

and tectonic features along and across ridge.

The fourth objective is geophysical characterization of

the ridge crest. It is based on the analyses of magnetic

propeties and intensity using a proton, and a three

component magnetometers, and an ht*silu three component

magnetometer carried by the submersible to estimate the

magnetic structure under the ridge crest, and gravimetry

data.

The fifth objeclive in modeling of the evolution of the

fast spreading ridge by elucidating the relationships and

order of various kinds of events.

To attain the above objectives we used an ORI Pump

water sampler, SMAP, Niskin water sampler. In-situ pump

particle sampler, titanium piston gas-light sampler and

eight cylinder pump sampling system to collect

endmcmber samples of focused and diffusively flowing

vent fluids and fixed volume water bottles closed by

silastic springs to capture plume samples. We used CTD.

CTDKM.S. I*<er Raman, Nephelomeler. Plankton trap

and net. pH sensor, and OAMOS II. Ill (m-situ Mn

analyser) (,o≪i>My>≪ieaI measurements were mad'- using

the Zabnton. a moored long-term heat flow monitoring

jAMSTEC J Deep SeR Res.. >4 (l≪m

system and Manatee. a long-teim in*#iUi environmental

inonilorins? system to investigate ihe physical and

chemical strucUu-e of the plume at KM28 and RM24. Wo

also deployed <1 Sediinoni Trap mooiings surrounding the

hj^cofIkeririsires a( KM24 to m<?a$≪jv (he flax of paitki?

related (he hydro (hernial input. We oblalncd a set of

complete video jword from silong the scafloor track linos

JAMSTSC J. Deep Sea Res., 14

and collided numerous rock, sulfide and biolugicyl

samples by submersible.

3. Preliminary results

3-1. Topography and geology

A topographic awvey conducted KM 24. 23 and

2S. b<*lwwn (17"20' and I8*30'i≫). using the MS W X1til(i

23

narrow Btam sysiem, obtained a balhy metric map from

2300 survey ruiles of this ridge crcs'. Precise topographic

maps weit drawn for (he survey ;>reas, from north '<>

south. RM24, 23. 29, OSC -1822, RM28. and OSC 1837

Three traverses across and along ridge w<?ix? made using

the submersible "Shinkai 650<T at KM 24 and KM28 ;md

10 basement hard rock samples and one |>us!) cor<* were

(>l>lHilKtl.

Reexamination of (he topographic maps made from the

Melville and Yokusuka cruises identified seven different

segments, A10 C, from the Gareu Fracture Zone south to

the OSC 1903 at 19°03'S, based on the discontinuities of

both depth and tectonic elements. However, based on the

axial depth profile this portion of the ridge is basic Ally

three segments. I. II. III.

The stratigraphic relationships of the basalt lavas, both

JAMST6C J. Deep Sea Res , J4 iwwi)

ilg. 3 baihymdiy and ship's hack imoj> of the rm 23 and 2j.

|>illow an-] shod flows, consist of ihicc different units

･ oflecnitg i heir different age and sediment cover:

SfrdimeiU-freo (1.0). slightly stdiment-covci'cd (1.1). and

scdimemed (1.2). The distribution of (he young lava flows

wcif mapped lor ihc notation position of ≫iie KM 24. The

hydroUu-rmal fit-Id at KM 24 oecupies the older hiva field

at I he Oasis sin- SedinieiUc'd :uu ＼ slightly sedimeim-d

lavas arc d isl ri bo * c<i on * 1** n≪m k areas o f i lt<-, id gc.

JAMSTEC J. Dwi) Sea Res.. 1* dww

The side scan sonnar data of the TAMU2 smvey using

1VV "Gyre" were- compared wilh both dive observation*

and a topographic map. Hie RM2$ sire axial graben was

well correlated with the black, narrow band and the

western cro&l well correlated wilh the while, nanow

straight limamonts. At siie RM24 axial black. and nam>w

lineament* are well correlated with the young lava flow

which was (raced to the noith during dov south

2a

113* 12'W

Pig. 4 Dive tracks au<J the locfiion of ihe long-icrm monjiorinjz systems af irte RM 2i.

during dive #390. Careful work of this kind will reveal

f-xkiing con-elsilions.

High resolution mapping of fhe distribution of hydiotber-

mal foe used vents, diffuse flow, large organkms, types of

basalt and Instrument deployments were carried out at *iu*

KM24. near Hie Oasis. Kaminari. Malsu, and Kohfi

hydrotlwrmal site* based 015 ibe precise observation* of

si"Vci'dI dives (dives MHO, V'M. #:?≪>. #394. iiixr

2H

#398).

3-2. Geophysics

A peophysical survey was carried out along combined

irack lines of 2,300 miles as Jo gravity, ami magnetics Of

ihese. the magnctotrioier results show ihe sharp bundai'y

bo I worn Hrlnni'K'* /MaUiyama. eoirosporifling to aboil I

0.78 Ma 'Hk* av≪*iafif spj vadium iale wa< estimated and lhe

JAMSTEC J. Deee Se? Res., 14 (h*j*i

113' 12'W

Klg. f> baihynv?! ly and <liw nwk map of the RM 23

results show that the spreading rat? of (lie easten side r>l

Uie ridge was much faster than (hat of (lie wesleni *i<k* (ai

RM23. I7°30'S. 7.23cra/y m western lialf and 7.U0 cm/y in

the eastern lialf; af RM29, l^lO'S. 8.2≪cm/y W. 5.85 cm/y

IC: at KM2K. ltTSO'S. 8.17 cm/y W and ft. 15 cin/y 10.

3-3. Geochemistry

Hydrolhermal fluid and pari ides were collodcd from

JAM$Tgc J. Deep Sea Res . 14

two rklge segments of (he Southern Kast Pacific Rise 10

reveal various geochemieal processes associaied with

hydiot hernial activity. Diffuse hydrolhertnal effluents

{temperatures of 6.5'C and 10.5*0 were sampled from

two locations in the Oasis hydrol hernial field ol RM2-1

(l^SO'S) Particles in the hychothennal effluent wpre also

colU'dctl by in-si in filtraiion for microbiological and

biogcochemical siudics. V＼>ni fluul (measured lemp. was

27

＼:＼n fi BaJhymMry dive track mai> ami itic location of ili≪* loiitf-iirm sysieam ni Uic RM 28

26and SOtiX). respectively) and particles were

sampled from two black smokers ai RM28 (18°2G*S>.

Buoyani plume water from a smoker was also collected ≪(

KM28 wain# Nit≫ktn botllen

Resampling of vent fluids from HM2R and combining

ih<* rcsulis from the W.i Naiuilr ami 1994 Shinkiii shiclie*

allowed us Jo invfsuL';il<' time series changes in (he

olK-mishy of hydcolhernial dix^hargc-s. Onboard analysis

y.H

of 1-fcS, Cl. Si. COj revealed large changes in the fluid

chemishy from vapor-like w> brine-like Analysis oi various

addition;!) chemical secies is proposed in order lo study

gcochemical characteristics dining ihe evolution of

h yd rot hernial systems.

An [>H s<*nsor and a manganese analyzer (named

(iAMOS) were developed Un the in-siui measurement of

ihi' chermeal properties of sod water in lhe vicinity of the

JAMST6C J Deep Sea Res., 14 (1W

hydrotheriiially active regions. Both instruments were

attached to the submersible during many dives and

successfully collected data fi om the water column and the

deepwatcr above the seafloor.The GAM OS study revealed

variations in the ratio of manganese concentration to

temperatwe anomaly, 0/ up to ovev an order of magnitude

depending on the styie of venting in the hydvothermal

fields at RM24.

Tlie in-si tu pH sensor and Eh sensors were deployed

near the seaflooi for a year-long time-series monitoring

experiment, Together with die results of pailiele flux trap

experiments and other geophysical and visual monitoring

instruments, their results wiil provide key information for

the estimation 0/ the geochemical flux from hydrothci mal

activities.

3-4.Biology and Microbiology

Observation of the benthopelagic animal communities.

The relative predominance of filter*feeders and detritus-

feeders in the hydrolhermal ecosystem of the Oasis at

RM24 site indicated that the chemosyiiiheiic primaiy

production should bo larger than other sites, Fmihermore,

lc suggests that free-living microbes and microbial mats

may be more productive In tins environment than that at

oilier sites. Distribution of these benihopelagic animals

were actually plotted on a map of the Oasis sue tiom dive

observations ancl dive produced with observations video

tapes for Ihe fii*st time.

In-situ measurement by Raman and

Nepheiometer

i77eft$ui?nten> by and NepJicJwneier ikm

successfully done ai (he Oasis site, showing lb at some

signals ai*c attributable to microbial activilies.

Sampling of microorganisms and zooplankton

Many microbial sample* for dh-ecl coumitig, culitvaiioii

and biomass csil million weif* successfully collected from

boih diffused and focussed vent walei*. Jan*? amounts of

microbial panic I c samples were also obtained from

hydrolhermal fluids and plumes by Pump-filter sampler

We also successfully collected /ooplwikion samples usintf

a plankton net and irsp samplers.

JAMST8C J Oeep Sea ftes, 14

3-5. Deployment of the instruments

During this cruise, several instruments were deployed

at RM24 and RM28. The Medusa #4 was deployed at the

shimmering water site on a small terrace, 2-3m south of

SF6' s black smoker at RM2S, dining dive #392. During

this dive, Manatee #01 was re-directed toward the black

smokers. It was re-located about 5m southeast of the

northern black smokers.

Two heat flow instruments were deployed on one of the

diffuse flow sites ("Oasis site" at RM24; 17 °25.6'S. 113 °

12.3"W, 2,600m). 2ABUTON, a thermal-blanket type long-

lenn heat flow meter is designed to determine heat flow in

sediment-free environments. Mer shofl-term measurements

at three sites, it was finally deployed near the Oasis site

during dive #398 on a thinly-scdimcnted basalt. The other

histnuricnt, a moored heat How array, was deployed near the

center of Oasis site. It consists of 5 temperature sensors and

a anient meter, and they are moored up to 50 in above sea

floor.

In addition, four particle flux trap arrays were moored at

RM24. Trap mooring #1 is deployed near the Oasis site,

however its precise position is unknown due to a

transponder problem. Trap mooring #2 is positioned at the

western slope on the axial dome: and Trap mooring #3 is

on the eastern slope on the axial dome: and Trap mooring

#4 is deployed adjacent to Matsu site.

4. Summary and future study

We deployed vauous kind of long-term monitoring

systems at the RM24 and RM28 in the Southern East

Pacific Rise 10 have a year monitoring of the current

direction and current velocity, flow rate of the

hydrothennal activity, observation of the variation of the

chimneys, heat flow values, deep sea measurement,

hydrophone, chemical changes, and so on. We will liy to

recover all (he sysieni during R/V Atlantis and Alvin

cruise in 1998 fall and will analyze the dala which will be

successfully obtained during a year-long nincaswemeni

and evaluate the heat and material fluxes from the fastesi

ridge and the decinvater above (he seafloor. The (1AMOS

study revealed vanations in (lie ratio of manganese

concent rati on lo (etnperslure anomaly, of up to ovei an

ordor of magnitude depending 011 the style of venting iu

I he hydrotheimal Held* s≪

29

Fjg. 7 Photographs of the survey area

1. Submarine pillow Java

4. Pump Sampling

2 Pillar

7. Ｍａｎalｅｅ

The in-situ PH sensor alld Eh sensors were deployed

ｎｅａｌｌ the seafloor for ａ year-long time-series monitoring

experiment. Together with the results of particle flux tliip

experiments ａｎｄ other geophysical and visual n10nit ｏring

instruments, their results ｗⅢprovide key information ｆｏr

lhe est ｉｍａtior10ft ｈｅ ｇｅｏｃｈｅｍｉｃａｌｎｕχfｒｏｍ ｈydr ｏthel･nial

activities.

Ackn 【】wledgrnents

￥ｌｅ express its thanks t ｏ ａ１１ １１１ｅ ｏｉ ｃｅrｓ ａｎｄ crews of

lhe “￥ｏｋｏｓｕka‘' and "Shinkai 6500" team lhal assured

smooth and safe operations over g dives alld deployment

of ｖariQ ｕｓ instrumentation lo the scaflooi･, ａｎｄ the niglit

ol) ｅraliolls At the SEPR. We (hank Takuya Hirano.

pr ｅsidellt of JAMSTEC. Sleeve Hammond, NOAA ａｌｌｄ

ＶＩＰ'ｓ of bQlh institutions 101･ their basic support and

cooperation of this cruise from (he ｂｅｉ ｎｎｉ昭 ｏｎ ｌ､ｅ plan.

We lhank l･!,I(illo ｓllila ，Ｒ. Ｋｕralle ， Ｍ. Ｋａｄｏyｕ and

ＳＴａshiro lbl･ thei ｒ ｖｉｇｏrol 】ｓ &uppo 】-t and help during (he

pieparalio 】1101･the cruise｡

Weilldel]led to T.Urabe and lhe 01hcl･ ａ ｇ ｌ scientists

fol･lheil-cl･ilicaldi ｓｃｕｓｓiollollhel 】ｒｅｖioｕｓ cruise l でsuits.

cheeiy enlhusiasii all(lkilld hclp d ｕ)ing llle lime in p011

at Ｖａｌ卩al･ai ｓｏ. Ｗ ｅ ａｌｓｏ thall 】i J.I.ｕptoll ，Ｂ.Enlbl･ ｅy.

Ｄ. Ｂult ｅｒfield ，Ｔ. Ｈｉｇａshihal･a. H.Seki. T.Gamo ; Ⅲd

H.Kawaliata fol･ 11e]ping plirn this ｅｘpedilion alld their help

111 1･eal 11111e by email. Ｗ ｅ ａｌ･e also illdebled lo P-Johiisoii

for making “Ｚａｂｕ10111' instrument alld for critical ad ｖｉｃｅ

concerning il ｓ de ｖel り|)lllenl alld iillci ‘prel;111011 1111d

T.Yamazaki and K.Ki ｓi】ｎｏｌ,)forllleil･ hell);|11d cl･ilical

JAMSTEC J. Deep Sea Ｒｅｓ.，1411 悗心

8.Zab ｕtｏｎ

advice.

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