Available online at www.sciencedirect.com
Geochimica et Cosmochimica Acta 73 (2009) 148–169
www.elsevier.com/locate/gca
Fluxes of high- versus low-temperature water–rock interactions
in aerial volcanic areas: Example from the Kamchatka
Peninsula, Russia
Céline Dessert a,b,*, Jérôme Gaillardet a, Bernard Dupre b, Jacques Schott b,
Oleg S. Pokrovsky b
a
IPGP, UMR 7579, CNRS-INSU, 4 place Jussieu, 75252 Paris Cedex 05, France
b
LMTG OMP, UMR5563, 14 av. Edouard Belin, 31400 Toulouse, France
Received 21 December 2007; accepted in revised form 5 September 2008; available online 23 September 2008
Abstract
Volcanic areas play a key role in the input of elements into the ocean and in the regulation of the geological carbon cycle.
The aim of this study is to investigate the budget of silicate weathering in an active volcanic area. We compared the fluxes of the
two major weathering regimes occurring at low temperature in soils and at high temperature in the active volcanic arc of Kamchatka, respectively. The volcanic activity, by inducing geothermal circulation and releasing gases to the surface, produces
extreme conditions in which intense water–rock interactions occur and may have a strong impact on the weathering budgets.
Our results show that the chemical composition of the Kamchatka river water is controlled by surface low-temperature weathering, atmospheric input and, in some limited cases, strongly imprinted by high-temperature water–rock reactions. We have
determined the contribution of each source and calculated the rates of CO2 consumption and chemical weathering resulting
from low and high-temperature water/rock interactions. The weathering rates (between 7 and 13.7 t/km2/yr for cations only)
and atmospheric CO2 consumption rates (0.33–0.46 106 mol/km2/yr for Kamchatka River) due to rock weathering in soils
(low-temperature) are entirely consistent with the previously published global weathering laws relating weathering rates of basalts with runoff and temperature. In the Kamchatka River, CO2 consumption derived from hydrothermal activity represents
about 11% of the total HCO3 flux exported by the river. The high-temperature weathering process explains 25% of the total
cationic weathering rate in the Kamchatka River. Although in the rivers non-affected by hydrothermal activity, the main
weathering agent is carbonic acid (reflected in the abundance of HCO
3 in rivers), in the region most impacted by hydrothermalism, the protons responsible for minerals dissolution are provided not only by carbonic acid, but also by sulphuric and
hydrochloric acid. A clear increase of weathering rates in rivers impacted by sulphuric acid can be observed. In the Kamchatka
River, 19% of cations are released by hydrothermal acids or the oxidative weathering of sulphur minerals.
Our results emphasise the important impact of both low and high-temperature weathering of volcanic rocks on global
weathering fluxes to the ocean. Our results also show that besides carbonic acid derived from atmospheric CO2, hydrochloric
acid and especially sulphuric acid are important weathering agents. Clearly, sulphuric acid, with hydrothermal activity, are
key parameters that cause first-order increases of the chemical weathering rates in volcanic areas. In these areas, accurate
determination of weathering budgets in volcanic area will require to better quantify sulphuric acid impact.
Ó 2008 Elsevier Ltd. All rights reserved.
1. INTRODUCTION
*
Corresponding author.
E-mail address: [email protected] (C. Dessert).
0016-7037/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.gca.2008.09.012
Over geologic time scales the content of atmospheric
CO2 is driven by two processes: its release through arc
volcanism, mid-oceanic ridge and metamorphism, and its
High- versus low-temperature weathering in Kamchatka
uptake through chemical weathering of silicate rocks coupled with the storage of organic carbon in sediments. Since
atmospheric CO2 is a greenhouse gas directly impacting
Earth global climate, these two processes probably control
the long term (106 years) climatic evolution of the Earth
(Walker et al., 1981; Berner et al., 1983; Francßois and
Walker, 1992; Goddéris and Francßois, 1995). In the last
decade, many studies have focused on river geochemistry
in order to quantify the global silicate weathering flux
and associated flux of consumed atmospheric CO2 (Stallard
and Edmond, 1983; Négrel et al., 1993; Probst et al., 1994;
Gaillardet et al., 1997; Gaillardet et al., 1999; Galy and
France-Lanord, 1999; Millot et al., 2002; Dessert et al.,
2003). The importance of lithology has been considered
by several authors (e.g. Meybeck, 1986; Bluth and Kump,
1994) who showed that basalts are easily weatherable rocks
when compared to other silicate rocks. In the recent years,
weathering of volcanic rocks has been addressed in several
studies on volcanic islands (Gislason et al., 1996; Louvat
and Allègre, 1997, 1998; Rad et al., 2006; Louvat et al.,
2008), provinces of flood basalts (Benedetti et al., 1994;
Dessert et al., 2001; Das et al., 2005; Pokrovsky et al.,
2005; Vigier et al., 2005) and smaller continental volcanic
regions (Benedetti et al., 2003; Gaillardet et al., 2003; Riotte
et al., 2003). More specifically, the studies of Louvat and
Dessert have emphasised the important contribution of basalts to the global flux derived from continental silicate
weathering and thus to the global carbon cycle. According
to Dessert et al. (2001) the chemical weathering rate of volcanic rocks is 5–10 times higher than the chemical weathering of granite and gneiss. In such case, the atmospheric CO2
consumption flux derived from basalts represents 30% of
the global silicate weathering flux and acts as an important
regulator of the Earth’s environment (Dessert et al., 2003).
This global estimate corresponds to the CO2 consumption
associated to the weathering of volcanic rocks occurring
in soils, shallow groundwaters and rivers at the Earth’s surface temperature. It thus corresponds to the flux of CO2
that is susceptible to be involved in a climatic feedback
where higher surface temperature would lead to higher
CO2 consumption by chemical weathering (Dessert et al.,
2003).
However, a substantial proportion of the alkalinity of
surface waters in volcanic context is derived from higher
temperature water–rock interactions occurring during
hydrothermal circulation. The geochemistry of magmatic
fluids of aerial volcanic regions has been the object of growing interest over the past decade (Armannsson et al., 1982;
Arnorsson et al., 1983; Allard et al., 1991; Aiuppa et al.,
2000; Federico et al., 2002; Gislason et al., 2002; Toutain
et al., 2002; Villemant et al., 2005), aimed at understanding
and monitoring the relationships between groundwaters
chemistry and volcanic activity. Because of their acidic
character (due to the contribution of magmatic acids) and
their high temperature, deep groundwaters in volcanic areas
are strongly aggressive with respect to the host basalt, and
intense rock weathering occurs as indicated by the high
chemical load of these waters. Although high-temperature
water–rock interactions are deeply involved in weathering
budget, their exact contribution to the global continental
149
budget is not known and implicitly assumed to be negligible. That might not be true even if the alkalinity that these
high temperature waters added to the ocean does not depend upon the concentration of CO2 in the atmosphere
and global climate and thus is not involved in any climatic
feedback mechanism. From a chemical weathering point of
view, the high sulphate and chloride load of volcanic thermal waters suggests that proton-donor for chemical weathering is not only carbonic acid (as it is in lower temperature
environments) but also sulphuric and hydrochloric acids.
As we show in this paper, the involvement of other acids
than carbonic acid in chemical weathering reactions might
have unexpected long-term climatic consequences.
The approach we adopted here is to focus on a volcanic
province particularly impacted by hydrothermal alteration
in order to estimate the contribution of the hydrothermal
component to the total weathering budget. We attempt here
to estimate both fluxes of ‘‘low-temperature” and ‘‘high
temperature” chemical interactions. The active arc of Kamchatka Peninsula is an ideal natural laboratory to evaluate
the combined effects of high and low temperature weathering processes, and to discriminate between sulphuric acid,
chloridric acid and carbonic acid mediated alteration. The
Kamchatka province is also a good example of a subduction zone province. Most of the studies on basalt weathering rates that have been published so far concern hotspots
or flood basalts and there is a need for documenting the
weathering rates of island arc provinces or accreted island
arc provinces (for a recent example, see the Stikine province, Gaillardet et al., 2003).
2. GENERAL SETTINGS OF KAMCHATKA
PENINSULA
The Kamchatka Peninsula is located in the far northeast
of Russia. This peninsula is a part of the Pacific rim of fire
and its total area is about 270,000 km2. It is bordered by the
Okhotsk sea on the West, the Bering sea on the East, and
the Pacific Ocean on the southeast (Fig. 1). The northernmost part at 65°N adjoins the Arctic Circle. The Kamchatka Peninsula consists of two mountain ranges
stretched from the north to the south and separated by
the large Kamchatka river valley. One third of the area of
Kamchatka is covered by forests, and the remaining are
lakes and rivers, and low and alpine meadows.
Influenced by western cyclones, the climate varies from
moderate marine at the eastern coast to continental in the
central Kamchatka and north-western mainland. Consequently, the precipitations and temperatures vary considerably from one region to the other. The seasonal climate
fluctuations are characterised by late spring, short and
rainy summer, and long, cold and snowy winter. The Kamchatka river valley, sheltered to east and west by mountain
ranges, displays an extreme climatic contrast with a mean
January temperature of 20 °C and a mean July temperature of +15 °C (Leemans and Cramer, 1991). In spite of
important seasonal contrasts, the mean annual temperature
is uniform over the whole peninsula (2 to 5 °C). Annual
precipitations reach 1100 mm with a maximum of 2600 mm
on the south-eastern coast. Annual river runoff values vary
150
C. Dessert et al. / Geochimica et Cosmochimica Acta 73 (2009) 148–169
Fig. 1. Tectonic structure and distribution of volcanoes in the
Kamchatka arc.
from 300 to 2000 mm and increase from north to south.
The mean annual evapotranspiration factor is around 3.
The Kamchatka peninsula is drained by more than
14,000 rivers and streams, generally less than 10 km long.
The Kamchatka River is the longest river (760 km) and
its total annual discharge is 24.6 km3/yr, corresponding to
an annual runoff of 540 mm/yr (hydrologic station of
Klyuchi). Over 150 groups of hot springs are concentrated
principally in the East-Kamchatka province (e.g. UzonGeyser depression) and in the South-Kamchatka province
(e.g. Paratunka and Mutnovsky geothermal fields).
The Kamchatka arc is the northern part of the 2000-km
long Kurile-Kamchatka volcanic arc system, related to the
subduction of the Mesozoic Pacific below the Eurasian
plate (Fig. 1). Geodynamic reconstructions (Bazhenov
et al., 1992; Hochstaedter et al., 1994) indicate that convergence and subduction have been active since the Cretaceous
(9 cm/yr). The arc has more than 240 volcanic centres,
among which about 30 are presently active. The global surface of volcanoes is about 90,000 km2, which represents the
third of the Kamchatka peninsula. The Kamchatka volcanoes are also among the most active in the world, having
produced more than 16% of the world on-land volcanic
ejecta (Erlich and Gorshkov, 1979). Volcanism activity in
the Kamchatka arc develops in three volcanic zones nearly
parallel to the Kurile-Kamchatka trench (Figs. 1 and 2): (1)
the western Sredinny Range (SR), (2) the Central Kamchatka Depression (CKD), and (3) the Eastern Volcanic
Front (EVF). SR is the oldest subduction zone; its activity
started during the Cretaceous but, today, it is inactive, except for the Ichinsky volcano. CKD represents a 200 km
wide graben structure consisting of volcanoes generally
younger than 50,000 years. The Klyuchevskoy volcano is
the largest and the highest (4750 m). The mean magma production rate of the Klyuchevskoy group, which includes the
Klyuchevskoy, Bezymianny, Kamen, Tolbachik, and
Ushkovsky volcanoes, is estimated between 0.16 and
0.5 km3/yr according to different authors (Melekestsev
et al., 1991; Grassineau, 1994; Hochstaedter et al., 1996).
This volcanic zone produces around 50% of all the ejecta
erupted from the active volcanoes of the Kurile-Kamchatka
arc (Melekestsev et al., 1991). EVF consists of about 20 active volcanoes (e.g. Gorely, Mutnovsky, Avachinsky and
Karymsky) and many more Holocene to Pleistocene volcanoes. The basement of the Kamchatka arc is mainly composed of metamorphosed plutonic and sedimentary rocks
(Erlich and Gorshkov, 1979).
As in many other volcanic series associated to subduction zones, lavas from Kamchatka are largely tholeiitic to
calco-alkaline and often highly magnesian (Zaimi, 1993;
Kepezhinskas et al., 1997; Turner et al., 1998; Pineau
et al., 1999). Various lithologies are present, from Mg-rich
basalts and basic andesites to dacites and rhyolites. In comparison with N-MORB, lavas are typically enriched in Ba,
Rb, U, Th, K, Sr, Pb and B, and strongly depleted in Nb
(Dupré et al., 1990; Turner et al., 1998; Dorendorf et al.,
2000; Ishikawa et al., 2001). Radiogenic isotopic compositions of Sr, Nd and Pb show that the source of magmas
is more influenced by a sea water-altered oceanic crust than
slab sediments (Dupré et al., 1990; Kersting and Arculus,
1995; Turner et al., 1998; Dosseto et al., 2003). This source
contamination has been confirmed by the small amount of
10
Be present in Kamchatka lavas compared to arc rocks
strongly contaminated by sediments (Brown et al., 1982;
Morris et al., 1990).
3. FIELD AND LABORATORY TECHNIQUES
3.1. Sampling
River samples were collected in April 2000 (annotated
B), August 2000 (annotated A) and September 2000 (annotated C; Fig. 2). Waters were mainly collected in the largest
watershed of the peninsula, the Kamchatka River
(56,000 km2), and in two smaller watersheds, those of the
Paratunka River (1500 km2) and Avacha River
(5090 km2; Fig. 2). We have also sampled two rain waters
and three geothermal springs in August 2000.
Moreover, we have compiled hydrologic and chemical
data of the main rivers of Kamchatka Peninsula during
1970, 1971, 1972 and 1975, delivered by the Russian Hydrological Survey.
3.2. Analyses
During the August and September sampling campaigns,
temperature, pH and alkalinity (by acid–base titration and
Gran method) were measured in the field. For the April
samples, measures were carried out in the laboratory.
Water samples were filtered on site through 0.2 lm cellulose
acetate filters using a Sartorious filtration unit made of
High- versus low-temperature weathering in Kamchatka
151
Fig. 2. Simplified geological map of Kamchatka peninsula. River water samples are marked by a dash, rains by a circle and geothermal
springs by a triangle.
Teflon. Filtered samples for cations, trace elements and Sr
isotopes analyses were acidified to pH 2 with distilled
HNO3 and stored in acid-washed polypropylene bottles.
The samples for anion determination were not acidified.
In water samples, anions and cations were measured by
Ionic Chromatography with a precision better than 5%.
The accuracy of the analysis was assessed by running the
SLRS-4 riverine standard. Dissolved silica concentration
was determined by spectrophotometric measurement. Trace
element concentrations were measured by ICP-MS after
addition of an indium standard solution. The accuracy
of analyses was assessed by running the SLRS-4 riverine
152
C. Dessert et al. / Geochimica et Cosmochimica Acta 73 (2009) 148–169
standard after every ten samples. We have measured strontium isotopic ratios by TIMS using a Finnigan-MAT 261 in
double dynamic mode after specific separation using SrSpecTM resin (Pin et al., 1994). NBS 987 measurements
yielded 87Sr/86Sr = 0.710249 ± 11 (n = 130) during the period of these analyses. Uncertainties on individual 87Sr/86Sr
measurements were always <12 106.
4. RESULTS AND COMMENTS
Concentrations of major and trace elements (Al, Sr, B,
Li, Rb, Ba and Ge) in surface waters, rains and geothermal
springs of Kamchatka are listed in Table 1 and major elements are plotted in Fig. 3 as a function of chlorine
concentration.
4.1. Surface waters
In this study, we distinguished three different classes of
rivers according to the location of their draining area
(Fig. 2): (1) rivers located around the most active volcanoes
(Tolbachik, Klyuchevskoy, and Cheveluch); (2) rivers
draining non-active volcanic area; and (3) the Kamchatka
River which integrates the whole rivers. River waters are
mainly characterised by homogeneous pH ranging from 7
to 8. Some waters are more acidic with pH of 6.4–7 (7 rivers) or more basic with pH of 8–9.4 (8 rivers). TDS (Total
Dissolved Solid) range of values is quite variable, from 11
to 407 mg/l with values higher than 100 mg/l (20% of rivers) generally reflecting rivers draining active volcanic province strongly affected by geothermal springs. TDS values
are similar to those measured in La Réunion island rivers
(Louvat and Allègre, 1997) which range between 20 and
580 mg/l, depending on the contribution of geothermal
contamination. Because of variable geothermal contamination, the chemical composition of river waters displays a
high variability. Aqueous silica concentration ranges between 36 and 799 lmol/l. HCO3 (18–2784 lmol/l) is the
dominant anion species, except for the Mytnyi river (A26)
and the Kamchatka tributary (C24) for which the dominant
species is SO2
4 . Chloride and sulphate concentrations vary
between 7 and 949 lmol/l and 9 and 1273 lmol/l, respectively. Again, the highest concentrations correspond to
the samples located close to the active volcanic area and
thus strongly influenced by volcanic activity (magmatic
degassing and geothermal input; A25, A31-33, C10-12). Nitrate concentrations range from 0.2 to 124 lmol/l with the
highest values (>30 lmol/l) that might be related to anthropogenic pollution (e.g. Roy et al., 1999) or respiring bacteria influence (e.g. Belkova et al., 2007). Some of the rivers
located around volcanoes present also high cations concentrations with Na+ being the dominant species (>500 lmol/l),
followed by Mg2+ (>500 lmol/l), Ca2+ (>340 lmol/l) and
K+ (>75 lmol/l). The other rivers, non- or slightly affected
by geothermal inputs and mainly located in non-active area,
display lower cationic concentrations, similar to those of La
Réunion and Sao Miguel islands (Louvat and Allègre, 1997,
1998), or Deccan Traps (Dessert et al., 2001). With regard to
the Cl and SO4 contents of the Kamchatka River (A27-C28,
A37 and A41), we can clearly discriminate between the
samples located upstream (low contents) and those located
downstream (high contents) from the active volcanic area.
The variation of trace element concentrations reflects also
the degree of hydrothermal impact. Indeed, waters not affected by hydrothermal activity show low concentrations
in Sr (30–690 nmol/l), B (0.2–20 lmol/l), Li (40–600 nmol/l),
Rb (1–15 nmol/l) and Ba (0.3–15 nmol/l) which increase
with hydrothermal inputs. Note that Al concentration varies between 0.07 and 2.28 lmol/l and does not presents
clear relationships with the degree of hydrothermal contamination. If rivers of the Kamchatka peninsula are compared
to other small rivers draining volcanic provinces, it appears
that B concentrations for Kamchatka are higher than those
for La Réunion (0.9–2 lmol/l; Louvat and Allègre, 1997)
and Iceland rivers (0.8–1.4 lmol/l; Arnorsson and
Andresdottir, 1995; Louvat, 1997). This difference can be
explained by the high B content (3–62 ppm) of the volcanic
arc (Popolitov and Volynets, 1982; Noll et al., 1996; Ishikawa et al., 2001) compared to effusive rocks of Iceland and
La Réunion. The 87Sr/86Sr isotopic ratios in the dissolved
load vary between 0.703057 and 0.705258, reflecting both
chemical weathering of volcanic rocks (for Kamchatka
rocks the 87Sr/86Sr isotopic ratios range from 0.70318 to
0.70365; e.g. Turner et al., 1998; Dosseto et al., 2003) and
contribution of atmospheric oceanic-like strontium
(0.70917, Burke et al., 1982). Calcite saturation indexes
(CSI, Table 1) have been calculated from a thermodynamic
model using the measured streamwater pH, calcium and
alkalinity concentrations and river water temperature
(Drever, 1997). The river waters are undersaturated with respect to calcite except: (i) rivers strongly influenced by
hydrothermal fluids which present positive CSI values or
close to 0 (A25, A31-33, C12) and (ii) Plotnikova River
samples characterised by high pH (P9).
For several rivers sampled during the 2000 campaigns,
we obtain chemical and hydrologic data from systematic
surveys by the Russian Hydrologic Survey (RHS). These
data have been published in the annual issues (1971–1972,
1975) of the State Water Cadastre for 7 rivers: Paratunka
(A1-B15), Kozelsky (A21), Kamchatka (A27-C28 and
A37), Anavgai (A35), Andreanovka (A39) and Kavycha
(A40). The data include for each river the water daily discharge and 5–10 measurements per year of major cations,
anions, and silica. For the other rivers, only the mean annual discharge is available. We have plotted in Fig. 4 concentrations of some major chemical species (HCO3, Ca
and Mg) and TDS values as a function of water discharge
for the Kamchatka River (A27-C28). For this river, we
have merged our data set for August and September 2000
with that of years 1971 and 1975. In the absence of discharge data for the year 2000, we have calculated the mean
discharges for August and September months from the daily stream flows of the years 1971 and 1975 (both annual
variations of water discharges are very similar and we assumed that those of the year 2000 were not different). Afterwards, the mean monthly values of water discharge and
concentration were used to calculate the mean annual discharge-weighted concentration for each element (Fig. 4).
It first appears that ion concentrations and TDS decrease
with increasing discharge and that the 2000 sampling data
Table 1
Major and trace element concentrations and strontium isotopic ratios in dissolved load of rivers of Kamchatka Peninsula
Sample and location
waters (Aug. 2000)
Paratunka2
12
Karymshina2
10
Bystraya2
10
Avacha2
10
2
Pinachevskaya
7
2
Falchivaya
12
2
Dzendzur
—
Zhupanova2
—
Kozelsky2
5
Bol. Kimitina2
9
Kozyrevka2
8
Klychevskoi1
11
1
Eulechinok
10
Bikchenok1
8
1
Bekesh
14
1
Mytnyi
13
Kamchatka*
12
Belaya2
14
T. Kamchatka1 5
Kirchurich1
13
Tolbachik1
13
1
T. Studenaya
8
1
Studenaya
9
2
Bystraya
—
2
Anavgai
8
Bystraya2
—
Kamchatka
11
Schapina1
10
Andreanovka2 12
2
Kavycha
14
Kamchatka r.
9
2
Kluchevka
6
2
Bystraya M.
9
Bystraya2
13
Plotnikova2
13
Plotnikova2
17
Rains (Aug. 2000)
P1
P2
—
—
7.2
8.2
7.9
7.9
7.7
6.7
6.4
7.3
7.4
7.5
7.5
6.9
6.8
7.7
8.3
7.7
7.7
6.5
8.2
7.7
7.5
8.3
8.4
7.6
7.9
7.0
7.6
7.6
7.3
7.6
7.7
7.7
7.7
7.5
9.0
9.4
206
413
470
525
438
88
1430
538
205
483
711
46
59
389
1575
203
718
446
750
378
2784
2093
1750
445
550
263
736
638
448
693
575
650
504
471
514
383
5.6
5.0
<dl
<dl
Cl
(lmol/
l)
SO4
(lmol/
l)
NO3
(lmol/
l)
SiO2
(lmol/
l)
Na
(lmol/
l)
K
(lmol/
l)
Ca
(lmol/
l)
Mg
(lmol/
l)
Al
(lmol/
l)
B
(lmol/
l)
Li
(nmol/
l)
Rb
(nmol/
l)
Ba
(nmol/
l)
Ge
(nmol/
l)
Sr
(nmol/
l)
R+
(leq/
l)
R
(leq/
l)
TDS
(mg/
l)
CSI
87
27
72
26
90
75
47
203
59
34
20
44
9
7
22
949
45
109
21
41
55
582
945
815
31
26
22
39
89
15
51
13
27
36
41
40
27
81
164
219
130
90
72
48
56
19
203
109
22
9
71
1273
532
145
55
41
158
94
583
491
103
94
70
96
354
62
103
27
39
102
87
57
80
123.7
19.6
25.8
9.3
26.1
2.6
5.0
1.3
83.2
13.5
13.4
2.3
1.9
5.3
21.1
12.1
10.4
5.8
15.2
8.5
1.0
16.3
14.0
14.7
13.1
13.6
11.8
12.7
10.4
9.0
8.0
34.5
12.4
10.8
8.7
0.2
209
165
183
348
446
177
581
491
377
321
460
58
82
126
799
186
353
323
538
128
331
442
364
389
436
340
290
273
148
190
367
178
163
152
193
180
104
308
148
212
205
112
491
244
144
162
246
24
25
335
1665
174
323
180
372
250
1275
1790
1552
210
214
131
177
335
62
189
127
115
130
131
150
126
13
10
8
30
28
20
46
30
5
24
35
3
4
25
82
19
46
25
28
8
76
120
102
31
33
35
27
32
18
25
30
5
22
20
20
20
142
238
333
237
159
54
248
150
88
281
239
30
22
70
940
449
252
126
156
215
421
394
339
170
181
112
279
307
218
290
143
279
243
219
202
175
33
30
65
105
111
19
333
106
25
117
155
12
11
49
1084
135
165
96
124
63
649
593
511
78
108
49
138
271
59
101
136
78
82
73
74
57
0.29
0.23
0.52
0.16
0.44
0.77
0.08
0.44
0.19
0.42
0.26
0.31
0.32
0.70
0.42
0.87
0.73
0.19
0.15
2.28
0.15
0.10
0.94
0.73
0.56
1.12
0.24
0.63
0.20
0.47
0.19
0.09
0.16
0.19
0.14
0.23
0.4
8.0
0.6
5.0
4.8
9.3
19.7
3.4
0.7
1.2
2.7
0.2
0.2
0.7
55.1
2.1
5.5
0.7
1.9
0.5
36.4
59.9
57.4
2.6
3.8
0.8
3.0
11.5
0.7
3.8
1.2
1.5
3.0
2.6
1.0
0.3
166
2399
81
567
533
573
1059
293
120
116
141
48
68
107
5945
290
406
145
553
705
2209
3914
4003
263
412
67
90
872
38
142
257
13
80
100
132
73
7.1
8.3
3.0
16.8
19.2
20.0
28.9
18.1
3.4
10.6
12.6
1.9
2.8
6.1
52.5
11.4
13.6
12.1
15.0
2.9
33.7
52.9
41.3
17.5
19.6
24.1
7.1
16.2
4.7
10.0
22.1
1.7
4.0
4.1
10.0
10.5
14.7
9.0
14.2
20.3
12.6
14.7
14.6
12.1
3.2
19.3
9.2
3.0
2.7
0.3
71.7
28.4
13.2
13.1
4.2
4.3
34.3
17.4
10.3
21.3
27.6
11.9
27.6
30.4
53.9
49.3
9.3
4.8
31.2
30.6
11.8
5.0
0.17
1.40
<dl
<dl
<dl
2.55
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
0.32
0.57
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
<dl
208
557
689
602
280
82
412
234
86
558
389
34
35
43
1650
419
462
206
208
133
667
484
418
319
401
215
628
504
425
885
343
376
552
531
442
251
466
853
950
926
773
276
1698
786
375
983
1067
112
94
599
5794
1362
1203
647
962
812
3492
3883
3352
738
825
489
1040
1522
634
995
714
835
803
736
722
610
518
832
959
885
718
281
1735
711
360
921
987
101
87
560
5091
1324
1127
582
888
758
3555
4220
3561
696
778
437
978
1447
597
958
651
790
757
696
676
569
51
72
82
87
81
31
165
85
51
89
104
11
12
52
407
103
107
65
103
65
284
321
271
77
87
55
93
121
56
85
74
73
68
63
64
55
2.46
0.92
1.07
1.18
1.60
3.70
2.15
1.88
2.59
1.56
1.37
4.15
4.22
2.07
0.40
1.44
1.15
2.83
0.94
1.48
0.52
0.04
0.03
1.68
1.24
2.65
1.24
1.29
1.80
1.13
1.58
1.21
1.40
1.59
0.14
0.13
0.703426. ± 9
0.703383. ± 8
0.703590. ± 9
0.703904. ± 9
0.703522. ± 9
—
0.703456. ± 10
0.703865. ± 10
—
0.703388. ± 10
0.703565. ± 8
0.703740. ± 8
—
0.703484. ± 7
0.703442. ± 9
0.703543. ± 8
0.704057. ± 7
0.703449. ± 8
—
0.703641. ± 7
0.703931. ± 9
0.704017. ± 8
0.703537. ± 9
0.703416. ± 7
—
0.703447. ± 8
0.704441. ± 8
0.703818. ± 8
0.704369. ± 7
0.705258. ± 8
—
—
—
—
—
0.703798. ± 20
2.9
1.7
<dl
<dl
—
—
—
—
—
—
—
—
—
—
—
—
—
—
13.2
3.1
4.3
3.3
12.0
1.5
6.9
1.7
3.5
2.9
1.0
0.6
27.8
10.2
24.6
11.4
1.8
0.8
Sr/86Sr
High- versus low-temperature weathering in Kamchatka
River
A1
A2
A3
A4
A5
A10
A17
A18
A19
A20
A21
A22
A23
A24
A25
A26
A27
A28
A29
A30
A31
A32
A33
A34
A35
A36
A37
A38
A39
A40
A41
A42
A44
A45
A46
A47
T
pH HCO3
(°C)
(lmol/
l)
—
—
(continued on next page)
153
154
Table 1 (continued)
Sample and location
T
pH HCO3
(°C)
(lmol/l)
2040
1495
1539
13,068
11,986
2158
1166
4176
1321
26.8
36.8
5.3
2300
3280
1310
River
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
B11
B12
B13
B14
B15
B16
B17
B18
B19
waters (April 2000)
Paratunka2
—
Mikizha2
—
Bystraya2
—
2
Avacha
—
2
Bystraya
—
2
Plotnikova
—
Bystraya—
Malki2
—
Kluchevka2
Satokhmatch2 —
Kitanzhinetz2 —
Ipukik2
—
Plotnikova2
—
2
Poperechnaya —
2
Topolovaya
—
Paratunka2
—
Karymchina2
—
Gavanka2
—
Ketkinskii2
—
Pinacheva2
—
7.8
7.5
7.6
7.6
7.6
7.6
7.5
490
445
470
590
430
415
500
117
81
37
139
56
52
44
265
258
209
114
68
43
84
43.3
30.5
35.9
31.6
22.9
19.0
19.3
63
36
179
335
143
170
163
519
490
176
291
132
131
139
7.8
7.7
7.5
7.4
7.4
7.7
7.9
7.8
7.7
7.7
7.7
8.0
545
610
425
270
355
510
745
480
390
320
460
795
50
38
36
38
38
25
24
52
91
28
72
227
39
20
21
9
58
148
50
60
124
94
118
98
30.3
44.2
21.3
30.8
0.7
15.3
36.8
49.1
47.8
28.4
30.0
30.1
176
145
256
419
247
172
153
161
171
184
304
535
159
96
134
103
125
165
96
125
124
105
168
453
River
C7
C8
C9
C10
C11
C12
C19
C24
C28
waters (Sept. 2000)
Pinachevski2
—
Pinachevski2
—
2
Esso
—
1
Studenaya
—
Studenaya1
—
Studenaya1
—
T. Tolbachik1 —
T. Tolbachik1 —
Kamchatka*
—
—
257a
—
326a
— 2232a
— 1969a
— 1966a
8.3 2180b
7.2 572b
6.4
18b
7.9 990b
19
18
22
843
855
869
12
17
141
68
54
22
556
572
563
14
57
124
4.3
5.4
8.9
3.9
1.2
4.7
<dl
1.8
1.7
382
415
580
428
426
425
449
114
408
a
20,087 465
17,022 992
5865 157
R+
R
Sr
Ge
Ba
Rb
(nmol/ (nmol/ (nmol/ (nmol/ (leq/l) (leq/l)
l)
l)
l)
l)
1072.3 154,429 732.8
501.2 62,696 977.8
235.0 14,660 311.7
41.8
188.6
56.9
377.84 278
239.11 1926
66.89 2400
20,633 17,467
18,747 21,870
6902
6344
TDS
(mg/l)
CSI
87
Sr/86Sr
1184
1360
451
0.11
1.94
0.86
—
—
—
40
20
67
1
347
373
6.54
0.83
0.08
26
17
7
32
18
16
22
297
278
357
242
203
176
233
62
59
68
133
68
63
82
0.27
0.92
0.31
0.26
0.34
0.42
0.49
10.0
2.8
0.6
5.2
2.0
0.7
2.6
1273
311
62
435
116
123
103
13.4
7.8
2.7
14.7
3.9
7.4
4.0
15.4
12.0
14.3
16.7
28.4
15.8
26.3
1.08
<dl
<dl
<dl
<dl
<dl
<dl
583
603
668
584
528
474
526
1263
1180
1033
1075
691
624
790
1181
1073
961
989
645
573
732
92
83
83
95
58
55
67
1.45
1.66
1.42
1.52
1.71
1.81
1.70
—
—
—
—
—
—
—
8
6
11
50
23
4
5
7
7
9
25
35
229
275
147
72
144
290
345
264
264
182
217
223
72
71
67
51
58
86
67
31
31
58
90
204
0.41
0.23
0.58
0.18
0.41
0.10
0.07
0.18
0.20
0.51
0.36
0.42
2.8
0.5
0.4
0.2
0.3
0.9
0.5
1.7
6.6
0.2
3.0
6.7
127
33
42
100
72
32
<dl
585
1822
<dl
264
712
4.8
2.3
4.3
49.9
12.2
1.3
1.2
4.8
8.6
3.6
12.8
16.8
7.7
17.0
10.5
13.6
8.5
1.6
18.1
6.8
8.7
8.4
16.4
16.8
<dl
<dl
<dl
<dl
0.58
<dl
<dl
<dl
1.38
<dl
<dl
<dl
321
349
295
208
224
88
496
500
502
246
494
636
770
795
575
398
552
919
925
722
722
595
808
1341
704
732
524
357
509
846
906
701
777
565
798
1247
66
67
57
54
54
75
80
64
67
54
78
126
1.36
1.31
2.02
2.56
2.16
1.40
0.95
1.33
1.57
1.83
1.50
1.06
—
—
—
—
—
—
—
—
—
—
—
—
93 19
104 24
1790 26
1914 120
1927 124
1929 139
136 34
40 11
361
42
101
101
163
359
364
364
108
35
256
51
64
84
589
594
597
96
18
190
0.16
0.15
0.24
0.65
0.64
0.51
0.28
1.16
0.19
0.8
1.0
0.9
78.1
74.8
73.4
1.1
0.4
7.9
244
214
530
4956
4767
4652
225
104
428
20.3
21.2
12.2
51.1
51.0
51.5
37.4
13.3
12.6
11.9
12.6
14.6
14.5
14.3
15.0
63.8
8.2
12.4
<dl
<dl
0.43
<dl
<dl
<dl
<dl
<dl
<dl
241
240
200
487
483
489
215
66
523
416
457
2310
3931
3967
3990
577
156
1294
—
—
—
—
—
4181
635
164
1383
54
60
225
307
309
323
75
17
127
—
—
—
—
—
0.04
2.33
5.00
0.97
—
—
—
—
—
—
—
—
—
Calculated HCO3 concentrations using charge balance; b measured HCO3 concentrations. *Kamchatka River outlet; 1group 1 (rivers located around the most active volcanoes); 2group 2 (rivers draining non-active area).
C. Dessert et al. / Geochimica et Cosmochimica Acta 73 (2009) 148–169
SO4
(lmol/l)
Geothermal springs (Aug. 2000)
A14 S. Academic
83
8.4
A16 S. Karymskoe 70
7.1
A43 S. Malkinskie 65
9.2
NO3
(lmol/l)
Li
B
Al
Mg
Ca
K
Na
SiO2
(lmol/ (lmol/ (lmol/ (lmol/ (lmol/ (lmol/ (lmol/ (nmol/
l)
l)
l)
l)
l)
l)
l)
l)
Cl
(lmol/l)
High- versus low-temperature weathering in Kamchatka
155
Fig. 3. Correlation diagrams between Cl concentrations and anion and cation contents for the dissolved loads of the rivers waters, rain and
geothermal spring samples. : compositional field of the main geothermal water types in Kamchatka (Okrugin and Karpov, 1995; Chudaev
et al., 1999). Group 1: rivers located around the most active volcanoes; group 2: rivers draining non-active area.
are in good in agreement with those of 1971 and 1975. It is
important to note that the samples collected in August and
September show numbers close to the mean annual values.
This observation also stands for the 6 other rivers, implying
that our samples are representative of the mean annual conditions and, therefore, can be used to estimate annual
fluxes.
4.2. Rain waters
Two rain samples were taken at Manskoe village, which
is located in the Kamchatka River valley. Waters were filtered on site through 0.2 lm cellulose acetate filters. The
measured pH ranges from 5.0 to 5.6. The ionic charge balance for major elements is close to 10%. With regard to the
X/Cl molar concentrations ratios (Table 2), it can be noted
that Na/Cl and Mg/Cl are close to the oceanic ratios, which
is in agreement with a previous study in Kuril Islands
(Chudaeva et al., 2006). K/Cl, Ca/Cl, and SO4/Cl ratios
are higher than corresponding ratios in oceans. Such
enrichments in K and Ca have been previously recorded
in Japanese rain waters and explained by the dissolution
of Eolian minerals originating from continental Asia deserts (Nakano and Tanaka, 1997). Finally, the enrichment
in SO4 illustrates the environmental impact of volcanic
emissions on the local environment (Aiuppa et al., 2001;
Chudaeva et al., 2006).
4.3. Geothermal springs
We have reported in Fig. 3 the compositional field of the
main geothermal water types in Kamchatka Peninsula
(Okrugin and Karpov, 1995; Chudaev et al., 1999). Based
on Giggenbach’s classification (Giggenbach, 1988), four main
groups of geothermal waters are distinguishable in terms of
HCO3–SO4–Cl relative contents: the bicarbonate, chloride,
sulphate and chloride–sulphate waters. It appears that our
geothermal spring samples are mainly chloride waters.
The three geothermal springs we sampled have temperatures ranging between 65 and 83 °C, and pH values between
7.1 and 9.2. These hot springs present very high aqueous silica concentrations (1310–3280 lmol/l) which are in the
range of concentrations reported for other Kamchatka
hot springs (Fig. 3). The springs are also characterised by
very high concentrations of Cl (2158–13,068 lmol/l),
HCO3 (1495–2040 lmol/l), SO4 2 (1321–4176 lmol/l)
and NO3 (5.3–36.8 lmol/l). In high temperature volcanic
fields, these elements may have a magmatic origin, may
be released by intense rock leaching, or may illustrate the
influence of respiring bacteria living in such environment.
156
C. Dessert et al. / Geochimica et Cosmochimica Acta 73 (2009) 148–169
Fig. 3 (continued )
Table 2
Mean characteristic X/Cl ratios of the different end members
1000 B/Cl
Na/Cl
Mg/Cl
Ca/Cl
K/Cl
SO4/Cl
HCO3/Cl
SiO2/Cl
*
Ocean
Rain waters
Geothermal springs
(Henderson, 1986)
This study*
Okrugin and Karpov (1995) Chudaev et al., 1999)*
This study
0.76
0.85
0.10
0.02
0.02
0.05
0.09
1.7E4
—
0.70
0.13
0.60
0.53
0.70
—
—
132 ± 40
1.92 ± 0.22
0.05 ± 0.04
0.45 ± 0.15
0.11 ± 0.03
0.51 ± 0.15
1.08 ± 0.32
0.77 ± 0.46
78 ± 19
0.99 ± 0.49
0.07 ± 0.05
0.01 ± 0.01
0.06 ± 0.01
0.35 ± 0.15
0.33 ± 0.19
0.35 ± 0.13
p
End members involved in the estimation of the different weathering fluxes. Error = 2r/ n (n = 10).
Note that the Academic (A14) and Karymskoe (A16)
springs present relatively similar anionic concentrations,
higher than those of in the Malkinskie (A43) spring. This
latter is highly enriched in Na+ (20,087 lmol/l) and K+
(465 lmol/l) and depleted in Ca2+ (40 lmol/l) and Mg2+
(1 lmol/l). The two other springs are characterised by high
concentrations in Na+ (5865–17,022 lmol/l), K+ (157–
992 lmol/l), Mg2+ (347–373 lmol/l) and low concentrations in Ca2+ (20–67 lmol/l). All these geothermal springs
are also enriched in trace elements like Sr, B, Li, Rb, Ba
and Ge. Although these springs discharges are 100–1000
times lower than those of the rivers, their contribution to
the rivers is likely to be significant for the most enriched elements. The chemical compositions of the various hydrothermal groups display a high variability with a wide
range for chlorine-normalised values (Fig. 3). As a result,
any precise estimation of the total hydrothermal spring
contribution is rather difficult because it depends on the relative input of each hydrothermal group. In the following
estimation of the different contributions to the total weathering flux, we have determined a mean composition of the
hydrothermal springs calculated from literature data, taking into account the four main types of geothermal water
in Kamchatka Peninsula (Table 2).
High- versus low-temperature weathering in Kamchatka
Fig. 4. Plots of HCO3, Ca, Mg and TDS values versus discharge of
the Kamchatka River (A27-C28). The two sampling points (August
and September 2000) are reported as well as data of 1971 and 1975
delivered by the Russian Hydrological Survey (RHS), and the
mean annual values obtained from the global database of the RHS.
Our samples are representative of the mean annual conditions.
5. LOW-TEMPERATURE VERSUS HIGHTEMPERATURE WATER–ROCK INTERACTIONS IN
THE KAMCHATKA PENINSULA
The chemical denudation of rocks in active volcanic
regions is produced by the combination of several mecha-
157
nisms. An attempt to represent the different water–rock
interaction processes is shown in Fig. 5. This figure arbitrarily separates the low-temperature processes from hightemperature processes occurring when water is circulating
deep-enough to be heated, but of course a gradual variation
of temperature range is occurring. In volcanic areas, carbonic acid derived from the dissolution of atmospheric or
soil CO2 in water is not the only proton-donor, especially
at high temperature. Volcanism is also a source of acidity
either through the emission of gaseous CO2, H2S or SO2
(that is oxidised into H2SO4) and, to a lesser extent, HCl
and HF or through the leaching by rainwater of volcanic
gases in ashes (Flaathen and Gislason, 2007). This excess
of acidity characterising volcanic regions might be concentrated in the local atmosphere (the study of Aiuppa et al.,
2001 shows that rainwater on Mount Etna is enriched in
volcanic F, Cl and SO4 species) and it can diffuse in the soil,
in flank aquifers and along fractures of the volcanoes
(where the diffused degassing is maximised). The oxidation
of sulphide minerals in rocks and fumaroles deposits is an
additional source of protons in volcanic regions through
the formation of sulphuric acid. Only few informations
are available on the chemical composition of volcanic emissions in the Kamchatka peninsula. Gases sampled during
the Tolbachik eruption in 1975 were mainly composed of
H2O, HCl and H2 and of HF, SO2, H2S and CO2, to a lesser
extent (Menyailov and Nikitina, 1980). A great variability
among volcanoes and eruptive events however exists
(Delmelle and Stix, 2000; Oppenheimer, 2003).
In the following section, we attempt to evaluate the proportions of riverine solutes deriving from low-temperature
chemical weathering and high-temperature water–rock
interactions. The allocation of solutes to high- versus lowtemperature is essentially based on chlorine concentrations
in river waters. For such an evaluation, a critical parameter
is the concentration of cyclic chlorine in the river (i.e. issued
from rainwater). Based on rivers not affected by hydrothermal inputs, we conservatively fixed it at 40 lmol/l
(=[Cl]P1 fevap; Table 1). This implies that if river chlorine
concentration is lower than 40 lmol/l, solutes are considered not to be influenced by high-temperature processes
and that if it is higher, solutes are influenced by rains and
both low and high-temperature mechanisms. We have reported in Fig. 6 the distribution of Cl versus B concentrations for the river waters of Kamchatka Peninsula and for
bibliographic data of hot springs of Kamchatka (Okrugin
and Karpov, 1995; Chudaev et al., 1999). The straight line
characterises the signature of ocean with a high Cl/B ratio
equal to 1318 (Henderson, 1986). The signature of volcanic
rocks of Kamchatka varies between 5 and 15 (Popolitov
and Volynets, 1982; Bindeman and Bailey, 1994; Noll
et al., 1996; Taran et al., 1997; Ishikawa et al., 2001). As
previously observed in Iceland by Arnorsson and Andresdottir (1995), geothermal springs of Kamchatka have low
Cl/B ratios similar to those of rocks. The Cl/B ratios in rivers range from 5 (Falchivaya, A10) to 213 (Ipukik, B11).
The global content of Cl and B in river waters can thus
be interpreted as a mixture between two endmembers:
atmosphere and rock-hydrothermalism. Taking into account
the variation of the rock-hydrothermalism endmember, we
158
C. Dessert et al. / Geochimica et Cosmochimica Acta 73 (2009) 148–169
Fig. 5. Sketch diagram of the diversity of water–rock interactions in volcanic context.
calculated some mixing curves for different initial concentrations of chlorine in rain water (Fig. 6, grey fields). Because we do not have Boron data of rain waters in
Kamchatka, we have considered oceanic rain. We note that
the distribution of all rivers data can be explained by a mixture with rain water containing between 5 and 40 lmol of
chlorine.
½Clriv ¼ ½Clrain þ ½Clgeoth
ð1Þ
½X riv ¼ ½X rain þ ½X LT W þ ½X geoth
ðX ¼ SO4 ; Na; K; Ca; Mg; and SiO2 Þ
½SiO2 rain ¼ 0
ð2Þ
The content of solutes coming from precipitations is determined from the cyclic chlorine concentration, [Cl]rain
(640 lmol/l), and chlorine normalised ratios of rain in
Kamchatka (Table 2):
X
½X rain ¼ ½Clrain ð3Þ
Cl rain
If river chlorine concentration is higher than 40 lmol/l, the
remaining chlorine is assumed arising from geothermal
springs:
½Clgeoth ¼ ½Clriv 40 lmol=l
ð4Þ
The content of solutes coming from high-temperature
weathering is determined from the geothermal chlorine content and the chlorine normalised ratios of hot springs in
Kamchatka (Table 2):
X
½X geoth ¼ ½Clgeoth ð5Þ
Cl hot-springs
The remaining solutes are coming from low-temperature
weathering.
Carbon of HCO3 has atmospheric and hydrothermal
origins, depending on the variable hot-spring input:
½HCO3 riv ¼ ½HCO3 atm þ ½HCO3 geoth
HCO3
½HCO3 geoth ¼ ½Clgeoth Cl hotsprings
ð6Þ
ð7Þ
The uncertainty related to the using of cyclic chlorine
concentration and mean hydrothermal composition in
the estimation of weathering budgets might be considered. On the light of the distribution of Cl versus B
concentrations in river waters (Fig. 6), we propose three
different error propagation calculations for cyclic chlorine concentration.
[B]riv 6 1 lmol/l and [Cl]riv 6 40 lmol/l: the geothermal influence is negligible and we arbitrarily consider
a maximum 25% input for geothermal chlorine (minimum 75% of cyclic chlorine).
[B]riv > 1 lmol/l and [Cl]riv > 40 lmol/l: the geothermal
input is important and represents the major chlorine
contribution for many rivers. We consider an error of
25% on the cyclic chlorine concentrations (±10 lmol/
l; in agreement with an evapotranspiration factor varying between 2 and 4).
[B]riv > 1 lmol/l and [Cl]riv 6 40 lmol/l: the geothermal input might be non-negligible for these rivers
because of the relatively high boron concentrations.
We arbitrarily consider an error of 50% on the cyclic
chlorine concentrations.
High- versus low-temperature weathering in Kamchatka
159
1E+5
Cl (µmol/l)
1E+4
1E+3
(C
an
e
Oc
1E+2
8)
Hot springs
31
=1
l/B
Cl rain=40µmol/l
1E+1
5)
rivers of group 1
rivers of group 2
Kamchatka R.
hot spring samples
<1
Cl rain=5µmol/l
ck
Ro
1E+0
1E-2
1E-1
/B
Cl
<
(5
1E+0
1E+1
1E+2
1E+3
1E+4
B (µmol/l)
Fig. 6. Distribution of Cl and B in river waters and geothermal springs of Kamchatka Peninsula (starts: this study; white field: literature
data). The straight line characterises the signature of ocean with a high Cl/B ratio equal to 1318. The signature of volcanic rocks of
Kamchatka varies between 5 and 15. As volcanic rocks and hot springs have the same Cl/B ratio, the global content of Cl and B in river waters
can be interpreted as a mixture between two endmembers: the atmosphere and the rock-hydrothermalism. All the river data can be explained
by a mixture with an oceanic rain containing between 5 and 40 lmol/l of Cl (symbolised by grey fields which take into account the variation of
the rock-hydrothermalism endmember).
For each river and each chemical species, we take into
account the error on cyclic chlorine concentration and the
uncertainties on the mean hydrothermal composition
(Table 2) to propagate global uncertainties.
We have reported in Fig. 7 the proportion of each dissolved species arising from each endmember in the chemical
composition of six rivers. In the Bikchenk, Paratunka and
Kamchatka (A41) rivers, rain inputs and solutes derived
from the weathering at low-temperature of rocks are the
two main sources of elements. The rainwater influence on
dissolved species is in decreasing order: Cl, K, SO4, Na,
Ca and Mg. In contrast, solutes in the Studenaya, Avacha
and Kamchatka (A27) rivers are strongly impacted by
water–rock interactions at high temperature. The proportion of geothermal Cl can reach 95% of the global Cl content in rivers located around the most active areas (Fig. 7).
Concerning the origin of Carbon, the hydrothermal contribution is relatively negligible (<5%) for most of the rivers
but can reach at least 50% of HCO3 concentrations in rivers
strongly influenced by hot springs around active volcanoes
(e.g. A33). In the case of the Kamchatka River, the hydrothermal contribution is only significant downstream from
the active volcanic area and reaches 11% of the global
HCO3 content. This high-temperature weathering contribution is dominant for rivers located in the active area and is
significant for most of the elements, except for Mg. Indeed,
because of the low value of the mean hydrothermal Mg/Cl
ratio, the Mg hot spring contribution is negligible and the
remaining low-temperature weathering contribution is then
over-estimated for several rivers around active volcanoes.
The sum of cations (Na, K, Ca, Mg) derived from hightemperature processes, TDSCat-geoth, varies between 0 and
60 mg/l and the sum of solutes (cations plus anions and dis-
solved silica) TDSgeoth between 0 and 235 mg/l. This contribution can reach 80% of the total cationic load (TDSCat)
and 70% of the TDS in rivers located in the active area.
The TDS values arising from low-temperature weathering
are relatively homogeneous (25–45 mg/l). Some rivers located in the active volcanic zone still have high
TDSCat,LT-W (>20 mg/l) and TDSLT-W (>60 mg/l). This
emphasises the potential strong impact of ashes and fumarole minerals leaching around volcanic edifices on river
chemistry. Indeed, substantial amounts of Cl, SO4, F, Ca,
Na and K and metals can be released from this leaching
process (Varekamp et al., 1984; Quisefit et al., 1989;
Flaathen and Gislason, 2007). These high TDSLT-W values
are also linked to the young age of the rocks and the highly
alterability of the tephra which exhibit high surface area
(Dahlgren et al., 1999). Several authors (Gislason et al.,
1996; Kennedy et al., 1998) have shown that the age of volcanic rock is an important parameter of the chemical
weathering.
The volume-weighted mean concentrations of each contribution of the two rivers groups and of the Kamchatka
River outlet are listed in Table 3. The rain input is homogeneous for the three groups with a TDSCat,rain value close to
2.1–2.6 mg/l and a TDSrain value varying from 5.2 to
6.7 mg/l. The geothermal input is significant for most of
the elements (except Mg), even if the discharges of hot
springs are 100 to 1000 times lower than those of the rivers.
The mean HCO3 concentration derived from atmospheric
CO2 varies between 443 and 761 lmol/l, the higher values
corresponding to the Kamchatka River. Dissolution of
atmospheric CO2 is the major source of protons involved
in weathering interactions (Fig. 8). It represents almost
30% of the anionic sum involved in weathering processes
160
C. Dessert et al. / Geochimica et Cosmochimica Acta 73 (2009) 148–169
Fig. 7. Stack column diagrams showing the proportions of Cl, HCO3, Na, Ca, Mg, K, SO4, SiO2, TDSCat and TDS arising from each
endmember in the chemical composition of six rivers.
for the active area and reaches 70% for the non-active area.
The hydrothermal HCO3 and Cl inputs are significant for
active area (18% and 17%, respectively) and decreases at regional scale for the Kamchatka River (8% and 7%, respectively). However, a substantial amount of this anionic
budget is provided by SO4 which is derived from sulphide
oxidation and volcanic degassing, and represents almost
19% of the anionic content of Kamchatka River. In such
a scheme, a non-negligible part of the cations delivered by
rock weathering are not balanced by bicarbonate ions but
by sulphate ions.
6. DISCUSSION
6.1. Low-temperature weathering and associated atmospheric
CO2 consumption rates
The consumption rate of atmospheric CO2 associated
with the low-temperature weathering of volcanic rocks
has been calculated from the mean annual runoff and rivers
HCO3 concentrations derived from atmospheric CO2 dissolution (Table 4). The rivers located around active volcanoes present the most contrasted rates, ranging from
0.005 to 0.59 106 mol/km2/yr with a mean value of
0.33 106 mol/km2/yr. The Kamchatka River watershed
is characterised by homogenous rates varying between
0.33 and 0.46 106 mol/km2/yr. Values are slightly higher
for rivers draining Neogene and older lithologies, varying
between 0.14 and 1.21 106 mol/km2/yr with a mean value
of 0.47 106 mol/km2/yr. These high rates are explained by
higher runoff values (mean runoff around 1200 mm/yr).
These results confirm the importance of basaltic weathering on the global flux derived from silicate weathering. If
we consider the rate of Kamchatka River outlet as being the
most representative of the Peninsula (the largest watershed), the total atmospheric CO2 consumption flux
resulting from the weathering of the volcanic rocks of the
peninsula (90 103 km2) is close to 35.6 109 mol/yr.
Dessert et al. (2003) predicted from their weathering law
a global atmospheric CO2 flux of about 31 109 mol/yr
for the whole Kamchatka Peninsula in agreement with measured flux of this study. The cationic weathering rates have
been determined from TDSCat, LTW and the mean annual
runoff (Table 4). The cationic weathering rates vary
between 0.6 and 39.2 t/km2/yr with a mean value of
7 t/km2/yr for the rivers in active area, between 4.7 and
43.1 t/km2/yr with a mean value of 13.7 t/km2/yr for rivers
draining Neogene–Paleogene rocks, and close to 8 t/km2/yr
117.0
6.7 ± 1.6
46.5 ± 2.3
40.7 ± 7.2
22.4 ± 8.6
24.1
2.6 ± 0.6
—
15.8 ± 2.3
5.7 ± 1.9
380
—
—
315 ± 46
65 ± 42
125
40 ± 10
—
—
85 ± 10
135
28 ± 7
—
64 ± 20
43 ± 15
854
—
761 ± 38
—
93 ± 33
44
21 ± 5
—
13 ± 6
10 ± 6
254
24 ± 6
—
192 ± 23
38 ± 16
outlet
342
28 ± 7
—
151 ± 36
163 ± 37
Kamchatka River
Total
Rain
Atmospheric
LT-W
Geothermal
178
5 ± 1.2
—
169 ± 22
4 ± 3.1
71.0
5.5 ± 1.0
27.0 ± 0.9
31.7 ± 2.1
5.0 ± 2.5
15.4
2.1 ± 0.4
—
12.0 ± 0.9
1.3 ± 0.6
239
—
—
224 ± 9
15 ± 8
54
35 ± 7
—
—
19 ± 10
96
23 ± 4
—
65 ± 7
8±3
464
—
443 ± 10
—
21 ± 11
18
14 ± 2
—
3 ± 0.7
1 ± 0.8
208
20 ± 4
—
179 ± 9
9±4
201
25 ± 4.5
—
139 ± 22
37 ± 15
Group 2
Total
Rain
Atmospheric
LT-W
Geothermal
69
4 ± 0.9
—
64 ± 3
1 ± 0.5
173.0
5.2 ± 1.1
38.4 ± 7.2
41.8 ± 12.0
87.0 ± 19.1
42.1
2.1 ± 0.4
—
17.2 ± 3.6
22.8 ± 3.5
326
—
—
122 ± 52
204 ± 58
381
32 ± 7
—
—
349 ± 9
373
22 ± 4
—
180 ± 51
171 ± 48
1007
—
629 ± 115
—
378 ± 120
55
15 ± 3
—
6±5
34 ± 7
304
19 ± 4
—
137 ± 35
148 ± 33
842
22 ± 4
—
160 ± 60
660 ± 64
344
4 ± 0.9
—
324 ± 15
16 ± 14
HCO3 (lmol/l)
K (lmol/l)
Mg (lmol/l)
Ca (lmol/l)
Na (lmol/l)
River groups
Group 1
Total
Rain
Atmospheric
LT-W
Geothermal
Table 3
Mean weighted concentrations of dissolved species for each contributions and each group of rivers
SO4 (lmol/l)
Cl (lmol/l)
SiO2 (lmol/l)
TDScat (mg/l)
TDS (mg/l)
High- versus low-temperature weathering in Kamchatka
161
for the Kamchatka River outlet. The specific rates of lowtemperature weathering have been determined from
TDSLTW and runoff; they range from 3.6 to 109 t/km2/
yr with a mean value of 16 t/km2/yr for the rivers in active
area, from 15.2 to 87.4 t/km2/yr with a mean value of
33.7 t/km2/yr for rivers draining Neogene–Paleogene rocks,
and close to 21 t/km2/yr for the Kamchatka River at the
mouth.
All cationic fluxes are reported in Fig. 9a as a function of
HCO3 fluxes coming from atmospheric CO2 for all rivers.
The dashed straight line represents the charge balance
(slope of 1) and we note that for the majority of rivers
the cationic fluxes are higher than HCO3 fluxes, confirming
the presence of other anionic species. The charge balance is
almost verified if we consider the additional SO4 fluxes
resulting from low-temperature weathering (Fig. 9b). Even
far from volcanic active area and from any direct influence
of volcanic degassing, SO4 coming from sulphide oxidation
provides a substantial amount of the anionic flux. It is interesting to note that the higher the contribution of sulphuric
acid, the higher the denudation rates. This proves that silicate weathering is increased by the contribution of sulphuric acid. Many studies have reported a significant
contribution of sulphide oxidation to the silicate weathering
budget (Galy and France-Lanord, 1999; Gaillardet et al.,
2003; Millot et al., 2003; Spence and Telmer, 2005; Calmels
et al., 2007; Lerman et al., 2007). If we consider the lowtemperature budget of the Kamchatka River, almost
85 eq% of the cationic weathering flux can be attributed
to minerals dissolution by carbonic acid and 15 eq% by sulphuric acid.
Finally, we have plotted in Fig. 10 the mean cationic
denudation rates determined for rivers of Kamchatka and
rivers draining other active volcanic provinces as a function
of mean annual runoff. The dashed straight lines represent
constant values of TDSCat,LT-W. Compared to the other active provinces, the cationic denudation rates of Kamchatka
are among the lowest found. The TDSCat,LT-W from the
Kamchatka are also the lowest, similar to what is found
in Iceland. These low values are associated with the low
temperatures observed in these provinces. We have reported in a previous study (Dessert et al., 2003) a global
relationship between TDSCat,LT-W and surface temperature
in river draining basaltic rocks. Using this relationship, the
calculated cationic weathering rates for the Kamchatka
area is in agreement with the data presented in this contribution, assuming annual river runoff ranging from 520 to
1200 mm/yr and mean annual temperature close to
2.5 °C. This result aims at confirming the validity of the
Dessert et al. (2003) weathering law for a large variety of
climatic and geologic settings, from subtropical to polar
environments.
6.2. High-temperature weathering budget
The geothermal carbon flux has been computed for few
rivers from discharge (runoff surface) and riverine HCO3
contents coming from hot springs (Table 5). The rivers located close to active volcanoes display high fluxes ranging
from 0.10 to 0.24 109 mol/yr. Kamchatka River at the
162
C. Dessert et al. / Geochimica et Cosmochimica Acta 73 (2009) 148–169
Fig. 8. Proportion of anionic species involved in river chemistry and chemical weathering (eq%).
mouth presents homogeneous flux, with a mean value of
2.28 109 mol/yr (±35%). This is equivalent to ca. 11%
of the global HCO3 budget of the Kamchatka River. The
cationic weathering rates resulting from high-temperature
water/rock interactions vary between 0.23 and
0.65 109 eq/yr for the rivers of the active area and is negligible for other rivers. Note that the Tolbachik River displays high-temperature cationic flux larger than the one
resulting from low-temperature weathering. For Kamchatka River outlet, the high-temperature weathering process still represents almost 25% of the global cationic
weathering rate (6.16 109 eq/yr or 1.36 105 t/yr). Using
the Kamchatka River flux as representative of the whole
Peninsula, we obtain a total high-temperature cationic flux
of 12.15 109 eq/yr (2.7 105 t/yr; 30% confidence interval) for the Peninsula.
It appears that the contribution of volcanic activity is
more important in term of cationic fluxes than in term of
HCO3 fluxes. Again, this is due to the fact that a part of
the cations delivered by rock weathering are not balanced
by bicarbonate ions but by sulphate and chlorine ions, released from SO2, H2S, or HCl gases emissions and from
pyrite weathering. The global high-temperature weathering
budget for the Kamchatka watershed is probably underestimated because all the small rivers draining active volcanoes in the South of the peninsula and along the Pacific
coast do not belong to the Kamchatka River watershed.
For instance, the cationic weathering flux of the small Etna’s aquifer is enhanced by the initial acidity of magmatic
CO2-rich groundwater, and estimated at 1.4 105 t/yr
(Aiuppa et al., 2000). But these data cannot be directly
compared to data presented here, since they refer to river
runoff (this work) instead of groundwater. The high-temperature weathering fluxes have been determined from
TDSHTW and discharge; they range from 0.13 to
0.25 105 t/yr for the rivers in active area. The mean
high-T chemical weathering flux of the Kamchatka River
is about 3.28 105 t/yr, equivalent to 25% of the global
weathering budget of the river. Considering the high-temperature weathering budget of the Kamchatka River, we
obtain a global high-temperature weathering flux of
6.48 105 t/yr for the Peninsula and 35% is induced by carbonic acid, 33% by sulphuric acid and 32% by chloridric
acid. Despite significant uncertainties in estimating the contribution of each endmember, our results illustrate the
importance of the high-temperature weathering process in
the aqueous cycling of elements in shallow volcanic
environment.
6.3. The sulphur budget
In volcanic area, natural acids that react with silicate
minerals are not limited to carbonic acid. Important contributions are also coming from other acids, such as the sulphuric and the hydrochloric acids resulting from volcanic
degassing, oxidation of reduced sulphur minerals (pyrite)
and H2S gas, and leaching of volcanic ashes. These addi-
High- versus low-temperature weathering in Kamchatka
163
Table 4
Specific rates of CO2 consumption, cationic weathering and silicate weathering involved in low-temperature water/rock interactions
Sample and location
Group 1 (active zone)
A22
Klychevskoi
A23
Eulechinok
A24
Bikchenok
A25
Bekesh
A26
Mytnyi
A29
T. Kamchatka
A30
Kirchurich
A31
Tolbachik
A32
T. Studenaya
A33
Studenaya
A38
Schapina
C10
Studenaya
C11
Studenaya
C12
Studenaya
C19
T. Tolbachik
C24
T. Tolbachik
p
Mean value ± 2r/ n
Group 2 (non-active zone)
A1
Paratunka
A2
Karymshina
A3
Bystraya
A4
Avacha
A5
Pinachevskaya
A10
Falchivaya
A17
Dzendzur
A18
Zhupanova
A19
Kozelsky
A20
Bol. Kimitina
A21
Kozyrevka
A28
Belaya
A34
Bystraya
A35
Anavgai
A36
Bystraya
A39
Andreanovka
A40
Kavycha
A42
Kluchevka
A44
Bystraya M.
A45
Bystraya
A46
Plotnikova
A47
Plotnikova
B1
Paratunka
B2
Mikizha
B3
Bystraya
B4
Avacha
B5
Bystraya
B6
Plotnikova
B7
Bystraya-M.
B8
Kluchevka
B9
Satokhmatch
B10
Kitanzhinetz
B11
Ipukik
B12
Plotnikova
B13
Poperechnaya
B14
Topolovaya
B15
Paratunka
B16
Karymchina
B17
Gavanka
B18
Ketkinskii
B19
Pinacheva
Runoff
(mm/yr)
678
678
678
861
565
565
678
268
473
473
473
473
473
473
268
268
Surface
(km2)
1480
3350
522 ± 87
2303
1970
1637
1023
927
2003
810
810
2829
437
372
538
527
511
542
819
928
739
880
1241
1272
1630
2303
1343
1637
1023
1241
1272
880
739
1339
1339
1339
1630
1339
1339
2303
1970
542
625
927
241
2330
4480
1170
1580
1190
948
642
642
241
Atm. CO2 cons. rate
106 (mol/km2/yr)
Cat. weathering rate
106 eq/km2/yr (t/km2/yr)
LT weathering rate
(t/km2/yr)
0.03 ± 0.001
0.04 ± 0.001
0.26 ± 0.005
0.51 ± 0.25
0.11 ± 0.01
0.42 ± 0.01
0.25 ± 0.02
0.59 ± 0.05
0.53 ± 0.15
0.43 ± 0.12
0.28 ± 0.02
0.52 ± 0.12
0.51 ± 0.13
0.61 ± 0.12
0.15 ± 0.001
5.0E03 ± 0.001
0.06 ± 0.004 (1.14)
0.05 ± 0.003 (0.96)
0.37 ± 0.01 (7.65)
2.66 ± 0.40 (39.25)
0.70 ± 0.02 (13.13)
0.48 ± 0.02 (9.23)
0.46 ± 0.04 (8.96)
0.47 ± 0.10 (6.97)
0.53 ± 0.15 (6.58)
0.46 ± 0.13 (5.82)
0.60 ± 0.03 (10.38)
0.68 ± 0.18 (10.20)
0.68 ± 0.18 (10.17)
0.68 ± 0.19 (10.16)
0.15 ± 0.003 (2.76)
0.03 ± 0.003 (0.57)
4.57 ± 0.19
4.60 ± 0.15
16.40 ± 0.51
109.02 ± 32.25
46.49 ± 1.15
28.11 ± 0.82
21.72 ± 2.02
6.97 ± 3.21
10.83 ± 9.76
8.90 ± 7.45
30.70 ± 2.33
15.59 ± 11.20
15.98 ± 11.45
15.27 ± 11.24
10.10 ± 0.24
3.57 ± 0.19
0.33 ± 0.11
0.43 ± 0.13 (6.98 ± 2.05)
0.48 ± 0.02
0.74 ± 0.04
0.77 ± 0.02
0.48 ± 0.03
0.37 ± 0.02
0.18 ± 0.02
1.01 ± 0.05
0.42 ± 0.02
0.58 ± 0.03
0.21 ± 0.01
0.26 ± 0.005
0.24 ± 0.004
0.23 ± 0.01
0.28 ± 0.01
0.14 ± 0.01
0.37 ± 0.01
0.63 ± 0.01
0.48 ± 0.01
0.44 ± 0.02
0.58 ± 0.01
0.65 ± 0.03
0.62 ± 0.01
0.94 ± 0.08
0.54 ± 0.04
0.77 ± 0.02
0.49 ± 0.04
0.51 ± 0.02
0.51 ± 0.02
0.44 ± 0.02
0.39 ± 0.01
0.82 ± 0.02
0.57 ± 0.01
0.36 ± 0.01
0.58 ± 0.01
0.68 ± 0.01
1.00 ± 0.01
1.08 ± 0.03
0.66 ± 0.05
0.17 ± 0.005
0.27 ± 0.02
0.55 ± 0.07
0.91 ± 0.05 (17.75)
1.30 ± 0.14 (26.69)
1.45 ± 0.03 (28.16)
0.68 ± 0.09 (12.43)
0.52 ± 0.07 (9.25)
0.34 ± 0.11 (6.88)
0.89 ± 0.12 (14.18)
0.50 ± 0.05 (9.31)
0.83 ± 0.08 (16.83)
0.41 ± 0.01 (7.66)
0.35 ± 0.01 (6.52)
0.32 ± 0.01 (5.99)
0.34 ± 0.02 (6.72)
0.39 ± 0.02 (7.36)
0.23 ± 0.01 (4.70)
0.49 ± 0.01 (9.30)
0.79 ± 0.05 (14.94)
0.57 ± 0.03 (10.78)
0.62 ± 0.05 (11.69)
0.78 ± 0.05 (14.63)
0.78 ± 0.07 (14.75)
0.88 ± 0.04 (16.92)
2.13 ± 0.016 (43.14)
1.28 ± 0.08 (26.17)
1.55 ± 0.05 (30.13)
0.68 ± 0.07 (11.91)
0.67 ± 0.07 (12.47)
0.62 ± 0.06 (11.57)
0.59 ± 0.04 (11.03)
0.48 ± 0.04 (9.03)
0.95 ± 0.04 (17.88)
0.65 ± 0.04 (12.17)
0.40 ± 0.04 (8.01)
0.73 ± 0.05 (13.91)
1.15 ± 0.02 (21.96)
1.16 ± 0.02 (22.25)
1.37 ± 0.11 (27.01)
0.95 ± 0.08 (18.26)
0.28 ± 0.01 (5.38)
0.38 ± 0.04 (6.88)
0.62 ± 0.09 (9.94)
15.99 ± 6.07
60.29 ± 2.55
65.76 ± 8.74
77.59 ± 1.37
38.88 ± 5.23
36.47 ± 3.95
39.36 ± 5.51
36.29 ± 7.21
33.88 ± 2.67
80.81 ± 2.38
24.01 ± 0.57
19.55 ± 0.70
18.49 ± 0.37
23.09 ± 1.07
24.45 ± 0.88
18.59 ± 0.39
20.63 ± 0.40
31.29 ± 2.61
20.12 ± 1.26
26.80 ± 2.09
32.81 ± 1.75
32.97 ± 3.29
44.11 ± 1.58
87.43 ± 10.49
53.45 ± 3.75
76.55 ± 2.07
31.26 ± 3.39
25.95 ± 3.48
25.00 ± 3.32
24.07 ± 1.80
16.90 ± 1.80
29.50 ± 1.03
32.74 ± 1.09
41.64 ± 1.17
43.00 ± 2.29
52.51 ± 1.15
38.81 ± 1.10
53.85 ± 6.41
47.07 ± 4.88
15.23 ± 0.52
21.80 ± 1.89
31.67 ± 3.06
(continued on next page)
164
C. Dessert et al. / Geochimica et Cosmochimica Acta 73 (2009) 148–169
Table 4 (continued)
Atm. CO2 cons. rate
106 (mol/km2/yr)
Cat. weathering rate
106 eq/km2/yr (t/km2/yr)
LT weathering rate
(t/km2/yr)
927
927
542
0.24 ± 0.01
0.30 ± 0.01
1.21 ± 0.01
0.34 ± 0.01 (6.45)
0.38 ± 0.01 (7.20)
1.22 ± 0.01 (26.75)
32.50 ± 0.77
33.91 ± 0.73
45.94 ± 0.52
1195 ± 180
0.47 ± 0.06
0.72 ± 0.11 (13.72 ± 2.16)
33.72 ± 3.91
0.33 ± 0.01
0.45 ± 0.01
0.44 ± 0.006
0.46 ± 0.03
0.46 ± 0.04
0.57 ± 0.03
0.52 ± 0.01
0.46 ± 0.05
21.78 ± 3.15
24.98 ± 1.56
27.85 ± 0.66
20.55 ± 4.22
Sample and location
Runoff
(mm/yr)
C7
C8
C9
Pinachevski
Pinachevski
Esso
p
Mean value ± 2r/ n
Kamchatka River
A27
Kamchatka*
A37
Kamchatka
A41
Kamchatka r.
C28
Kamchatka*
520
607
772
520
Surface
(km2)
45,600
12,000
218
45,600
(8.37)
(10.44)
(9.49)
(8.03)
The underlined values are excluded from the interval: mean ± 2r and are not considered in the determination of the mean rates; *Kamchatka
River outlet.
Fig. 9. Relationship between low-temperature cationic weathering rates, atmospheric HCO3 fluxes, and sum of SO4 (LT-W) + atmospheric
HCO3 fluxes. group 1: rivers located around the most active volcanoes; group 2: rivers draining non-active area. The charge balance is almost
verified if SO4 flux is taken into account. It emphasises the important contribution of sulphuric acid, especially for high weathering fluxes.
tional acids have a non-negligible impact on chemical
weathering intensity as showed in Fig. 9.
Fig. 10. Plots of the mean low-temperature cationic weathering
rates versus runoff for different active volcanic provinces (Gislason
et al., 1996; Louvat, 1997; Louvat and Allègre, 1997; Benedetti
et al., 2003). Kamchatka rates fall perfectly into the range expected
for rivers having runoff values from 520 to 1200 mm/yr with a
mean temperature close to 2.5 °C (Dessert et al., 2003).
We already mentioned that the sulphate anion is the
most abundant anionic specie after bicarbonates (Fig. 8)
and that volcanic chlorine anion is negligible at the global
scale for the Kamchatka River watershed. The total SO4
flux (LTW + geothermal) is significant for most of the
rivers (Table 5). This flux varies from 0.03 to
0.40 109 eq/yr for the rivers of the non-active area and
reaches 1.04 109 eq/yr for the Schapina River strongly
influenced by hot springs. The sulphate flux is close to
5 109 eq/yr for Kamchatka River at the mouth and the
total amount exported at the regional Peninsula scale is
about 10 109 eq/yr (about 0.5 106 t/yr). This flux could
appear non-significant compared to the total continental
riverine sulphate input of 0.96 1012 eq/yr (Berner and
Berner, 1996). But the global flux of sulphate ions arising
from all active volcanic arcs is probably important and
the non-negligible contribution of the cations delivered by
sulphuric acid attack may have consequences on the carbon
cycle perspective (Calmels et al., 2007). Indeed, concerning
the Kamchatka River, the SO4 2 flux represents about
20 eq% of the anionic sum (Fig. 8) and chemical weathering
is incontestably more intense in such geological settings.
It is so far difficult to generalise the results of these study
at a global scale. The balance between carbonic and sulphu-
Table 5
Carbon, sulphur, cationic weathering and silicate weathering fluxes involved in low-and high-temperature processes
Sample and location
HCO3 flux 109 (mol/yr)
Atm
Geoth
Cation rate 109 (eq/yr)
Total
LT
Geoth
Weathering rate 105 (t/yr)
Total
LT
Geoth
S flux 109 (eq/yr)
Total
LT + geoth
0.86 ± 0.07
0.94 ± 0.07
0.24 ± 0.07
0.10 ± 0.07
1.10
1.04
0.70 ± 0.15
2.01 ± 0.10
0.65 ± 0.15
0.23 ± 0.10
1.35
2.24
0.10 ± 0.05
1.03 ± 0.08
0.25 ± 0.05
0.13 ± 0.08
0.35
1.16
0.06
1.04
Group 2
A1 Paratunka
A20 Bol. Kimitina
A21 Kozyrevka
A35 Anavgai
A36 Bystraya
A39 Andreanovka
A40 Kavycha
A46 Plotnikova
B6 Plotnikova
B15 Paratunka
0.12 ± 0.005
0.49 ± 0.02
1.16 ± 0.02
0.33 ± 0.01
0.22 ± 0.02
0.44 ± 0.01
0.60 ± 0.01
0.42 ± 0.02
0.33 ± 0.01
0.26 ± 0.007
—
—
0.00
—
—
—
0.01 ± 0.01
—
0.01 ± 0.01
0.01 ± 0.007
0.12
0.49
1.16
0.33
0.22
0.44
0.61
0.42
0.34
0.27
0.22 ± 0.01
0.96 ± 0.02
1.57 ± 0.04
0.46 ± 0.02
0.36 ± 0.02
0.58 ± 0.01
0.75 ± 0.04
0.50 ± 0.04
0.40 ± 0.03
0.33 ± 0.03
—
—
0.00
—
—
—
0.03 ± 0.03
—
0.03 ± 0.03
0.02 ± 0.03
0.22
0.96
1.57
0.46
0.36
0.58
0.78
0.50
0.42
0.35
0.15 ± 0.01
0.56 ± 0.01
0.88 ± 0.03
0.29 ± 0.01
0.29 ± 0.01
0.25 ± 0.01
0.30 ± 0.02
0.21 ± 0.02
0.16 ± 0.02
0.13 ± 0.02
—
—
0.01 ± 0.03
—
—
—
0.02 ± 0.02
—
0.02 ± 0.02
0.01 ± 0.02
0.15
0.56
0.89
0.29
0.29
0.25
0.31
0.21
0.18
0.14
0.07
0.40
0.27
0.09
0.09
0.10
0.13
0.04
0.03
0.04
Kamchatka river
A27 Kamchatka*
A37 Kamchatka
A41 Kamchatka r.
C28 Kamchatka*
15.05 ± 0.46
5.40 ± 0.12
0.10 ± 0.002
20.98 ± 1.36
1.82 ± 0.46
—
—
2.74 ± 1.36
16.87
5.40
0.10
23.71
20.98 ± 1.65
6.84 ± 0.36
0.11 ± 0.002
20.98 ± 2.26
5.02 ± 1.65
—
—
7.30 ± 2.26
25.99
6.84
0.11
28.27
9.93 ± 1.44
3.00 ± 0.19
0.05 ± 0.001
9.37 ± 1.92
2.68 ± 1.44
—
—
3.89 ± 1.92
12.61
3.00
0.05
13.26
5.47
0.96
0.01
4.56
Kamchatka Peninsula
35.55 ± 1.67
4.50 ± 1.67
40.05
41.40 ± 3.85
12.15 ± 3.85
53.55
6.48 ± 3.33
25.53
9.90
*
19.05 ± 3.33
High- versus low-temperature weathering in Kamchatka
Group 1
A31 Tolbachik
A38 Schapina
Kamchatka River outlet.
165
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C. Dessert et al. / Geochimica et Cosmochimica Acta 73 (2009) 148–169
ric acids involved in chemical weathering reactions depend
on numerous parameters such as type and nature of volcanic emissions or geodynamic context. Clearly, more work
remains to be done to establish the budget of chemical
weathering arising from both carbonic and sulphuric acids
in active volcanic environments and how it is impacting global CO2 consumption rates.
7. CONCLUSION
The chemical composition of the rivers from the Kamchatka Peninsula illustrates the importance of low- and
high-temperature weathering processes in the acquisition of
river chemistry in active volcanic areas. Water rock interactions are intensified not only because higher temperature favours intense chemical weathering but also because carbonic
acid derived from atmospheric CO2 is not the only acid that
attacks the rocks. Sulphuric acid and chloridric acid also help
destabilizing silicate minerals. This feature, pointed out here
for the Kamchatka Peninsula, is probably a general feature in
all volcanic settings when water is available.
In Kamchatka Peninsula, the chemical composition of
river waters is controlled by low-temperature weathering
of volcanic rocks occurring in soils, rain input, and in some
cases, by volcanic activity through high-temperature
leaching and volcanic degassing. The calculation of the
proportions of each chemical species provided by each
end-member is realised using the elemental chlorine ratios
of hot springs, rains and rivers. The rain input is homogeneous in all rivers and never exceed 25% of cations. The
high-temperature weathering induced by volcanic activity
is significant for cationic contents and reaches 80% for rivers draining the most active volcanic area. At the Peninsula
scale, rock weathering neutralises acidity from carbonic
acid (about 75%), sulphuric acid (about 20%) and hydrochloric acid (7%). We do see a clear increase of weathering
intensity with the contribution of sulphuric acid to chemical
weathering. The low-temperature weathering contribution
is roughly constant for rivers of the most active area and
rivers non-impacted by hydrothermal activity. In the region
non-impacted by the hydrothermal activity, acidity is
mostly derived from the dissolution of soil/atmospheric
CO2 in waters (70%), the remainder being mostly due to
the contribution of sulphuric acid, mainly formed by the
oxidative weathering of sulphur minerals.
We calculated the CO2 consumption rates and chemical
weathering rates resulting from low and high-temperature
water/rock interactions. The annual average atmospheric
CO2 consumption flux at the Peninsula scale is close to
35.6 109 mol/yr (±5%) when the hydrothermal CO2 consumption flux is close to 4.5 109 mol/yr (±35%), which
represents 11% of the total riverine CO2 flux of the Peninsula. The low-temperature cationic weathering rates are between 7 and 13.7 t/km2/yr and fall perfectly into the range
expected for rivers having runoff values from 520 to
1200 mm/yr and mean temperature close to 2.5 °C. Thus,
our study on Kamchatka rivers is consistent with the global
picture established for rivers draining volcanic areas
(Dessert et al., 2003). The high-temperature weathering
process represents 25% of the total cationic weathering rate.
Although the Kamchatka Province is not the most hydrothermalized province among the volcanic areas of the
world, our study demonstrates the importance of both considering low and high-temperature weathering of volcanic
rocks on weathering and atmospheric CO2 consumption
budgets to the ocean. An important feature of high temperature water–rock interaction is the involvement of sulphuric
acid that clearly enhances the release of cations from rocks.
We think that an important effort should be made to characterise the different types of water–rock interactions occurring in other aerial volcanic areas and their respective
contributions to the release of cations. Because the weathering of basalts and volcanic rocks is a major source of cations to the ocean today and because it may have been even
more important in the geological past, it is of prime importance to better understand the links between volcanism,
geodynamics, sulphuric acid degassing and atmospheric
CO2 to improve the global carbon models.
ACKNOWLEDGMENTS
This work was supported by the French program funded by the
INSU-CNRS (PNSE). We thank S.V. Sourenkov and S.M. Fazlulin for assistance in obtaining river samples. We also thank the
Russian Hydrological Survey for providing hydrologic data of
the main rivers of Kamchatka Peninsula. We are grateful to P.
Brunet, F. Candaudap, J. Escalier, R. Freydier, S. Gardoll, C.
Gorge and M. Valladon for their support in the different analyses.
We are particularly grateful to E. Lemarchand for his support in
boron analyses and to Y. Godderis for discussions, calculation of
calcite saturation indices, and comments on the manuscript. The
geologic map of Kamchakta was realised by P. Eicheine. Moreover, D. Calmes, M. Polvé and J.-P. Toutain are acknowledged
for their fruitful comments. We are also grateful to S. Krishnaswami, S.R. Gislason and two anonymous reviewers for their constructive reviews of this manuscript. The geologic map of
Kamchakta was realised by P. Eicheine. Moreover, D. Calmes,
M. Polvé and J.-P. Toutain are acknowledged for their fruitful
comments. We are also grateful to S. Krishnaswami, S.R. Gislason
and two anonymous reviewers for their constructive reviews of this
manuscript. TPGP contribution # 2407.
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Associate editor: S. Krishnaswami