GEOPHYSICAL RESEARCH LETTERS, VOL. 23, NO. 23, PAGES 3503-3506,NOVEMBER 15, 1996
The geochemistryof Atlantic hydrothermal particles
E. M. Ludford and M. R. Palmer
Departmentof Geology,BristolUniversity,Bristol,UnitedKingdom
C. R. German
Southampton
Oceanography
Centre,Southampton,
UnitedKingdom
G. P. Klinkhammer
COAS, OregonStateUniversity•Corvalis
Abstract. Particleswere collectedfrom the dilute portion of
neutrallybuoyanthydrothermalplumesfrom four Mid-Atlantic
Ridge sites (MARK, 23øN; TAG, 26øN; Broken Spur, 29øN;
Lucky Strike, 37øN). Comparison of data from proximal
portions of the TAG (Atlantic) [Gertnan et al., 1991; this
study] and North Cleft (Pacific) [Feely et al., 1994] plumes
show that oxyanion (e.g., V) scavengingis more efficient at
TAG, possiblydue to a higher proportionof Fe removed as
sulfidesat North Cleft and/or the more vigorousmixing in the
high energyTAG buoyantplume. Chalcophileelements(e.g.,
Cu) showtwo stageremoval. They are precipitatedas sulfides
during initial mixing of vent fluids with seawater and are
sedimentedfrom the buoyantplume. In the dilute plume they
are scavengedfrom seawaterby Fe oxyhydroxides. The REE
show continued scavengingin the neutrally buoyant plume
mounted on the OSU ZAPS sled [Klinkhammer et al., 1995].
Lucky Strike was sampledduring the 1992 FAZAR program
[Langmuiret al., 1993]. Broken Spur,TAG and MARK were
sampled in 1993 during RRS Charles Darwin cruise 77
[Elderfield, 1993]. After recovery, the filter housingswere
rinsed with clean water, sealedin polythenebags and frozen.
On return to Bristol, the filters were refluxed with cone.
HNO 3 and then diluted to 5% solutions. Semi-quantitative
analysesby ICP-MS were used to set standardconcentrations
for calibrationof analyses(_+5%)by standardadditionsfor V,
Mn, and Cu, with 100 ppb Ga internalstandard,alsoby ICPMS. Rare earth elements(REE) were determinedby ICP-MS
(+10%) at OSU. A1 andP weremeasured
(-+5%)by ICP-AES. Fe
was measured(-+5%)by AAS. The data and samplelocations
arelistedin Table 1. Data areexpressed
asmolesof particulate
andlowerlevelsin 1993samples,
compared
to 1988samples metal per litre of filtered seawater,allowingdirect comparison
with vent-fluid and seawater concentrations.
[German et al., 1990] suggesting that the amount of
scavengingis related to particle recycling.
Discussion
Introduction
The impactof vent fluids on seawaterchemistryis modified
by reactionswithin hydrothermalplumes during mixing with
seawater[e.g., Trocine and Trefry, 1988; Feely et al., 1990;
German et al., 1990, 1991] Hence, an understandingof
processesoperating within plumes is needed to assessthe
impact of hydrothermal activity on the oceans. Vent fluids
have been sampledfrom TAG (26øN), MARK (23øN), Lucky
Strike (37øN) and Broken Spur (29øN) [Edmondet al., 1995;
Colodner et al., 1993; James et a/.,1995], but studies of
particles from the associatedplumes have been confined to
TAG [e.g., Trocine and Trefry, 1988; German et al., 1990,
1991]. In this study we report the first particulatedata from
Broken Spur, MARK and Lucky Strike, and presentnew data
from the more dilute portionsof the TAG plume, which have
allowed for a more detailed understandingof processes
operatingwithin hydrothermalplumes.
During initial mixing of vent fluids with seawater, sulfide
and sulfatemineralsform andmostdropout of the plumeclose
to the vent. Further dilution results in precipitation of Fe
oxyhydroxides,together with scavengingand coprecipitation
of elements
from the vent fluids and enl.rained seawater.
Fine-
grained oxideshave slow settling velocities and can remain in
the neutrally buoyant plume for long periods. Fe is the
dominantelement in hydrothermalparticles and so is used to
indicate the hydrothermalinput and degree of dilution [e.g.,
German et al., 1991]. As the plume ages,remaining sulfide
and sulfate minerals
dissolve.
The level of Fe decreases with
distancefrom the vent site and so may be usedto infer the age
of particles, although low Fe levels axe also observedat the
upper and lower edgesof the laterally dispersedparticleplume.
Trocine and Trefry [1988] and German et al. [1991]
observeduniform particulateMn levels in the TAG plume, in
the range 100-200 nM/1, although German et al. [1991]
observedincreasingMn (200-300 nM/l) at high (>100 nM/1)
particulateFe levels. Most samplesin this studyshowsimilar
Sampling and Methods
behavior (Fig l a). A few have much higher Mn levels,
typically at low Fe concentrations. Figure lb shows mixing
Particleswere collectedfrom the neutrally buoyantplumes betweenhigh Fe and low Mn/Fe and low Fe and high Mn/Fe,
usingStandAlone Pumps(SAPS) equippedwith lgm pore-size consistentwith mixing between the [:e-rich plume and Mnfilters. SAPS were suspendedfrom the ship, on moorings,or rich backgroundmaterial [cf.Trocine and Trefry, 1988]. The
mixing line passesabove the average Mn/Fe of background
particulatesfrom the deep North Atlantic [Sherrell and Boyle,
Copyright1996by theAmericanGeophysical
Union.
1992] indicatingan additionalsourceof particulateMn. This
may be due to the rift valley topographypreventingdispersal
Papernumber96GL02078.
0094-8534/96/96GL-02078505.00
of the plume. Our data are consistentwith uptakeof dissolved
35O3
3504
LUDFORD
ET AL.: GEOCHEMISTRY
Table1. Elemental
concentrations
in plu
OF PARTICULATES
IN HYDROTHERMAL
•articulates
fromMARK(23øN TAG (26ø1
x andLuck,
øN Longitude
øW InM/1
Fe'IriM/11
A1 Mn pM/1
Im
Depth
ILatitude
V pM/1
Cu pM/1
*C
e'
Snakepit [
317T
317B
323T
323B
3304
3093
3366
3409
329T
329B
3407
3444
TAG
403T
403B
409T
409B
PLUMES
23ø22.13
23ø22.13
23022.09
23022.09
23ø22.12
23ø22.12
'
'
'
'
'
'
44057.06
44ø57.06
44ø57.12
44ø57.12
44ø57.19
44ø57.19
'
'
'
'
'
'
6
3
5
9
3
-
0.89
1.53
2.99
2.01
-
210
112
127
182
8.6
13
4.1
31
530
172
26008.24
26008.24
26008.24
26•08.24
'
'
'
'
44049.58
44049.58
44049.59
44049.59
'
'
'
'
50
38
4
5
0.52
0.62
1.06
0.30
37øN).
[Er
' ' pM/1
pM/1
2.49
2.18
1.74
1.97
1.08
-
0.91
0.80
0.59
0.69
0.30
0.09
0.034
0.026
0.017
0.023
0.011
-
0.13
0.11
0.08
0.09
25
5.7
30
257
631
42
10
0.03
-
0.040
0.021
0.015
0.016
0.003
-
189
193
190
339
239
174
32
27
1405
647
40
20
0.98
1.36
1.43
2.54
0.89
1.04
0.60
0.91
0.046
0.050
0.020
0.024
0.18
0.20
0.10
0.11
0.070
0.078
0.025
0.027
I
3340
3440
3081
3231
Broken
SpurI
106B
502T
502B
509T
509B
520T
520B
526T
526B
528T
528B
2728
2890
2953
2727
2827
2688
2888
2840
2940
2763
2863
29ø10.11
29010.04
29010.04
29009.73
29009.73
29009.85
29009.85
29009.24
29009.24
29ø09.17
29ø09.17
'
'
'
'
'
'
'
'
'
'
'
43010.34
43010.50
43010.50
43010.46
43010.46
43010.54
43010.54
43010.57
43•10.57
43ø10.51
43ø10.51
'
'
'
'
'
'
'
'
'
'
'
3
4
4
2
9
2
14
9
9
10
7
0.19
1.14
1.34
1.00
0.94
0.88
1.88
0.93
0.63
1.11
0.97
150
173
882
165
215
182
3780
150
209
130
152
5.9
38
21
11
13
19
27
259
225
10
4.9
101
368
466
267
899
38
769
480
435
102
61
1.54
1.73
1.72
1.60
1.66
1.73
1.30
1.89
1.12
1.80
1.25
0.48
0.70
0.58
0.51
0.59
0.55
0.58
0.73
0.41
0.75
0.44
0.019
0.027
0.021
0.020
0.025
0.025
0.021
0.030
0.015
0.032
0.018
0.09
0.09
0.08
0.08
0.10
0.08
0.10
0.13
0.06
0.13
0.07
0.022
0.023
0.020
0.013
0.033
0.026
0.035
0.045
0.016
0.048
0.016
SL-25
SL-31
SL-39
1780
1000
2270
37016.92
37ø16.81
36027.82
'
'
'
32•14.64
32014.65
33ø37.16
'
'
'
10
1.4
34
0.79
1.37
1.56
260
150
1810
50
10
520
50
30
930
0.81
1.23
2.32
0.57
0.37
1.51
0.024
0.004
0.066
0.16
0.11
0.46
0.054
0.023
0.18
7000
4.3e7
1.5e8
1.8e7
5.44
4720
9540
4940
21.4
2350
6120
2320
1.06
1720
3540
2480
6.2
510
1100
400
5.5
99
290
68
Seawater
29øNFluid
26øNFluid
23øNFluid
1
2.0e6
5.6e6
2.6e6
1000
2.5e8
6.8e8
4.5e8
BrokenSpurfluid datafrom [ameset al. (1995), TAG andMARK from Edmondet al. (1995) andMitra et al. (1994).
*A completeset of REE data are availablefrom the authors.
10000
I []MARK
I X Lucky
Strike
ß
[]
100
2•)
,
0.1
•
40
!
De
60
,
ß
0.01
background
•O•
0.001
)articulates
0.1
I
10
100
1000
Fe (nM/I)
Figure 1. Particulatedata from Atlantic plumesa) Mn vs Fe
concentrationsb) Mn/Fe ratio vs Fe concentrations(symbols
as in Fig. la, open circles= TAG 1988 [German et al., 1991].
Mn by Fe-rich particles,but at a rate which is slow, suchthat
mixing with background material obscurescorrelation with
hydrothermalFe.
Trace elementversusFe plots show three typesof behavior
in neutrally buoyanthydrothermalplumes [Trocine and Trefry,
1988; Feely et al., 1990; German et al., 1990, 1991], 1) linear
correlation, characteristicof conservativemixing (e.g., V); 2)
negative deviation from mixing, indicating removal with
respect to Fe (e.g., Cu); 3) positive deviation from mixing,
indicative of continued scavenging beyond initial
coprecipitation(e.g., REE).
Linear relationships are seen for elements occuring as
oxyanionsin seawater,e.g., V [Middleburg et al., 1988; Feely
et al., 1990] (Fig. 2). This probably reflects changesin the
surface charge of Fe oxyhydroxides. At pH <6.7, in the
buoyant plume where acidic vent fluids are concentrated,
FeOOH has a positive surfacecharge [Stumm and Morgan,
1981] and is an effective anion scavenger. As the vent fluids
are dilutedby seawater,the pH increasesand the surfacecharge
becomes negative so the Fe oxyhydroxides become more
efficient cation scavengers.The V/Fe ratio is lower (2.76) in
plume particlesfrom the North Cleft site, Juande Fuca Ridge,
North Pacific [Feely et al., 1994] than at TAG (4.54) (Fig. 2).
V is an oxyanion in seawater and largely conservative,
althoughAtlantic levels are slightly lower (23 nM/kg) than in
the Pacific (30-35 nM/kg) [Middleburg et al., 1988]. The
LUDFORD
ET AL.: GEOCHEMISTRY
OF PARTICULATES
IN HYDROTHERMAL
PLUMES
3505
3000
1500
-e-PaCificI'
'
-o-AtlanticI
•
1ooo
2000
.©
•
ø•
> 500 •' •
Q'Q'•23.97
+2.76x
r=
1
•
. ---y •-2.s•+,.5,• ,= •
0
•
0
'
100
'
200
'
300
•inear
(1ooo
400
0
oø
50
Fe (n M/I)
Figure 2. V vs Fe particulateconcentrations
in plumes from
the Pacific (North Cleft [Feely et al., 1994] and the At]antic
(TAG [Ger•n et al., 1991' •d this study]).
higher V/Fe ratio in Atlantic particles, suggeststhe TAG
particles are more efficient oxyanion scavengersthan those
from North Cleft.
Hence, scavenging may not be an
equilibrium process with a constant distribution coefficient
between dissolvedand adsorbedoxyanions. This may reflect
limitation by the number of scavengingsites on particles or
kinetic controls. Site limitation i•nplies differences in
particle compositionat the two sites;if a higher proportionof
particulate Fe present as sulfides rather than oxyhydroxides
would reducethe scavengingefficiencyof particlesat a given
Fe level. The H2S/Fe ratio of North Cleft vent fluids are
higherthan at TAG [Butterfieldand Massoth,1994; Edmondet
al., 1995] favoring formation of Fe sulfides, although most
sulfides drop out close to the vent site [Feely et al., 1994].
The TAG hydrothermalsite is one of the largest, with the
plume rising up to 400 m [Rudnickiand Elderfield, 1993], but
the North Cleft field is smaller (plume only rises 150 m above
its source) [Baker et al., 1993]. Hence, particles in the TAG
buoyant plume may undergo more vigorous mixing (and more
efficient scavenging) with entrained seawater during the
interval the Fe oxyhydroxidesmaintain a positive charge.
Speerand Hellrich, [1995] suggestthat plumesgrow for up
to a month before becomingunstableand sheddingfrom their
source. Rotation of parcelsof fluid due to rotationof the Earth
is thought to result in a barocyclinic vortex pair, an
anticyclonicvortex of plume fluid at the spreadinglevel and a
cyclonicvortex of ambientfluid aroundthe risingplume. This
is thoughtto limit entrainmentof ambimt fluid into the rising
plume, resulting in recycling of plume fluid from above,
consistentwith recycling of particles [German and Sparks,
1993]. Laboratory experiments[Hellrich and Battisti, 1991]
show that as a plume grows it becomesunstable, parcels of
fluid are shed off axis and the processbegins again. The
timescaleof this processis ~2 weeks. During recycling, the
particles pass through the buoyant plume and may become
positively charged and continue to scavenge oxyanions.
Hence, extensiverecyclingat TAG, may also explain the more
efficientscavengingof V comparedto North Cleft.
Chalcophile elements, e.g. Cu, show negative deviations
from a mixing line with Fe, indicatir•gpreferential removal
from the buoyantplume due to settlingof densesulfidesduring
initial mixing of seawater with vent fluids [German et al.,
1991] or dissolutionof suspendedsulfizleswith reprecipitation
of Fe oxides and release of dissolvedCu [Metz and Trefry,
1993]. Maximum particulateCu/Fe ralios in the TAG (0.028)
and MARK (0.07) plumesoccurat higtt Fe levels. Decreasing
particulateCu/Fe ratios at higher dilulion are consistentwith
removalof Cu in the dilute plume. At Broken Spur maximum
particulateCu/Fe ratios are at low Fe levels (2-4 riM/l). This
100
150
200
250
Fe (n M/I)
Figure 3. ParticulateCu vs Fe concentrationsin the Atlantic
plumes (symbolsas in Fig. l a).
may indicate that Cu is reprecipitatedwith oxyhydroxidesin
the more dilute plume. At low Fe levels (_<50nM/1) at Broken
Spur, Cu showsa positive deviationfrom linear mixing (Fig.
3) and increasingCu/Fe ratios with decreasingFe (Fig. 4a).
Similar patterns are seen at North Cleft [Feely et al., 1994]
(Fig. 4b). Hence, Cu showstwo-stagebehavior;precipitation
and removal by settling-dissolution during early plume
evolution, removing most of the dissolvedCu from the vent
fluids [German et al., 1991; Metz and Trefry 1993], followed
by scavengingof Cu from seawaterin the dilute plume.
REE exhibit positive deviationsfrom a linear mixing trend
with particulateFe, indicative of continuedscavengingin the
neutrally buoyant plume [German et al., 1990]. The REE/Fe
ratios in fluids from MARK, TAG and Broken Spur are similar
(1.06-1.09x10
-6) [Mitraet al., 1994;Klinkhammer
et al.,
1994; James et al., 1995].
The minmnum REE/Fe ratios in
particles
[e.g.,
Nd/Fe(min
) TAG1.8x10
-5]arehigher
than
in
fluids, indicating that the REE are derived from seawaterin
addition to vent fluids [German et al., 1990].
ParticulateREE concentrations
in the TAG particlesare half
those in the 1988 data set [German et al., 1990], e.g., 32B,
[Fe] 49 nM/1, [Nd] 2.0 pM/1 [Germanet al., 1990]; 403T, [Fe]
50 nM/1, [Nd] 0.89 pM/1. Extensiveparticlerecyclingat TAG
[German and Sparks, 1993] may also explain the differencein
REE between 1988 and 1993, and may reflect different
residencetimes of Fe oxyhydroxidesin the recycling plumes
at the different sampling times.
150
o
!
'•x
100
LL
50
0
•1t
ø ,.,•,
•ø o
o
0
50
o
Ooo
100
o
150
o
200
250
O15
x
v10
0
100
200
300
400
Fe (nM/I)
Figure 4. a) Particulate Cu/Fe vs Fe concentrations in
Atlantic plumes (symbols as in Fig. l a). b) ParticulateCu/Fe
ratios vs Fe concentrations in North Cleft site, Juan de Fuca
Ridge [Feely et al., 1994] plume.
3506
LUDFORD ET AL.: GEOCHEMISTRY
OF PARTICULATES
Conclusions
IN HYDROTHERMAL
PLUMES
phosphorous
distributionsin the northeastPacific,Earth Planet. Sci.
Lett., 96, 305-318, 1990.
Particleswere collectedfrom the dilute plumesat the MARK
(23øN), TAG (26øN), Broken Spur (29øN) and Lucky Strike
(37øN) vent sites on the Mid-Atlantic Ridge. Comparisonof
the TAG data with those from the North Cleft field, Pacific
[Feely et al., 1994] show that the oxyanion scavenging
efficiency at TAG is greater. This may be due to a limited
number of scavengingsites on the Pacific particles (due to a
higher proportion of Fe sulfides), more turbulent mixing in
the higher energy TAG site, leading to more effective
scavenging, or more extensive recycling of particles in the
buoyant plume. Comparison of data from this study with
samplescollected from proximal portions of the TAG plume
[German et al., 1990, 1991] show chalcophile elements
undergotwo-stagereaction. Cu is preferentiallyremovedfrom
the buoyantplume as sulfides,leading to negativedeviations
from a linear mixing line with particulateFe levels [German et
al., 1991]. At greaterdilution there is scavengingof Cu from
seawater by Fe oxyhydroxides, leading to elevated Cu/Fe
ratios in the dilute plume. The REE show continuedreaction
with particles, with higher REE/Fe ratios in the dilute plume.
Continual scavengingof REE from seawaterin the neutrally
buoyant plume confirms that hydrothermal systemsare a net
sink for REE. The different REE levels in the TAG particles,
between 1988 [German et al., 1990] and this data set, may be
due to different residence times of Fe oxyhydroxides in
recycling plumes [Speerand Helfrich, 1995].
Feely, R.A., and 5 others, Composition and sedimentation of
hydrothermalplume particles from North Cleft segment,Juan de
FucaRidge,J. Geophys.Res.99, 4985-5006, 1994.
German, C.R., G.P. Klinkhammer, J.M. Edmond, A. Mitra, and H.
Elderfield, Hydrothermalscavengingof rare-earthelementsin the
ocean,Nature 345, 516-518, 1990.
German,C.R., A.C. Campbell,J.C. Edmond,Hydrothermalscavenging
at the Mid-Atlantic Ridge: Modification of trace element dissolved
fluxes, Earth and Planet. Sci. Lett. 107, 101-114, 1991.
German, C.R., R.S.J. Sparks, Particle recycling in the TAG
hydrothermal
plume,Earth and Planet.Sci Lett 116, 129-134, 1993.
Helfrich, K.R., and T. Battisti, Experiments on baroclinic vortex
sheddingfrom hydrothermalplumes,J. Geophys.Res., 96, 1251112518, 1991.
James, R.H., H. Elderfield, and M.R. Palmer, The chemistry of
hydrothermalfluids from the Broken Spur site, 29øN Mid-Atlantic
Ridge, Geochim.Cosmochim.Acta 59 651-659, 1995a.
Klinkhammer, G.P., H. Elderfield, J.M. Edmond, and A. Mitra,
Geochemical implications of rare earth element patterns in
hydrothermal fluids from the mid ocean ridges, Geochim.
Cosrnochim.Acta, 58, 5105-5113, 1994.
Klinkhammer,G.P., C.S. Chin, C. Wilson, and C.R. German,Venting
from the Mid-Atlantic Ridge at 37ø17'N: the Lucky Strike
hydrothermalsite,Geol. Soc.SpecialPublication87, 87-97, 1995.
Langmuir,C.H., and 18 others,Geologicalsettingand characteristics
of
theLucky Strikeventfield at 37ø17'Non the Mid-AtlanticRidge,Eos
74 (43), 99, 1993.
Middleburg,J.J.,D. Hoede,H.H. Van der Sloot,C.H. Van der Weijden,
andJ. Wijktra, Arsenic,antimonyand vanadiumin the North Atlantic
Ocean, Geochirn. Cosmochirn.Acta, 52, 2871-2878, 1988.
Metz, S, andJ.H. Trefry, Field and laboratorystudiesof metaluptake
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Mitra, A., H. Elderfield and M.J. Greaves, Rare Earth Elements in
Acknowledgements. We thankthe mastersandcrewsof the ships
usedin this studyandthe Chief Scientists,C.H. Langmuir(FAZAR) and
H. Elderfield (CD77). We thank A. Kemp (Bristol) and A. Ungerer
(OSU) for assistanceon the ICP-MS. This manuscriptbenefitedfrom
commentsfrom two anonymousreviewers. The work was supportedby
a NERC CASE studentship,
the NERC BRIDGE programandNATO.
submarinehydrothermalfluids and plurnesfrom the Mid-Atlantic
Ridge,Marine Chem.,46, 3,217-235, 1994.
Rudnicki, M.D., and H. Elderfield, A chemical model of the neutrally
buoyantplume above the TAG vent field, 26 degreesN, MidAtlanticRidge,Geochirn.Cosrnochim.
Acta 57, 2939-2957, 1993.
Sherrell, R.M., and E.A. Boyle, The trace metal compositionof
suspendedparticles in the oceanic water column near Bermuda,
Earth Planet. Sci. Lett., 111,155-174, 1992.
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Feely, R.A., G.J. Massoth,E.T. Baker, J.P. Cowen,M.F. Lamb, and K.A.
Krogslund, The effect of hydrothermalprocesseson midwater
M.R. Palmer,Departmentof Geology,Universityof Bristol,Queens
Road, Bristol BS8 1RJ, UK. (e-mail: M.R.Palmer•bfis.ac.uk)
C.R. German, SouthamptonOceanographyCentre, Southampton
(Received:September
25, 1995;revised:March28, 1996;
accepted:May 6, 1996.)