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Comparing results from two continental geochemical surveys to world soil
composition and deriving Predicted Empirical Global Soil (PEGS2) reference values
Patrice de Caritat
a,
⁎, Clemens Reimann
b
, NGSA Project Team
1
and GEMAS Project Team
2
a
Geoscience Australia, GPO Box 378, Canberra, ACT 2601, Australia
b
Geological Survey of Norway, PO Box 6315 Sluppen, 7491 Trondheim, Norway
abstractarticle info
Article history:
Received 14 September 2011
Received in revised form 22 November 2011
Accepted 22 December 2011
Available online 21 January 2012
Editor: G. Henderson
Keywords:
regolith
Critical Zone
geochemistry
major elements
trace elements
global soil composition
Analytical data for 10 major oxides (Al
2
O
3
, CaO, Fe
2
O
3
,K
2
O, MgO, MnO, Na
2
O, P
2
O
5
, SiO
2
and TiO
2
), 16 total
trace elements (As, Ba, Ce, Co, Cr, Ga, Nb, Ni, Pb, Rb, Sr, Th, V, Y, Zn and Zr), 14 aqua regia extracted ele-
ments (Ag, As, Bi, Cd, Ce, Co, Cs, Cu, Fe, La, Li, Mn, Mo and Pb), Loss On Ignition (LOI) and pH from 3526
soil samples from two continents (Australia and Europe) are presented and compared to (1) the composi-
tion of the upper continental crust, (2) published world soil average values, and (3) data from other
continental-scale soil surveys. It can be demonstrated that average upper continental crust values do not
provide reliable estimates for natural concentrations of elements in soils. For many elements there exist
substantial differences between published world soil averages and the median concentrations observed
on two continents. Direct comparison with other continental datasets is hampered by the fact that often
mean, instead of the statistically more robust median, is reported. Using a database of the worldwide dis-
tribution of lithological units, it can be demonstrated that lithology is a poor predictor of soil chemistry.
Climate-related processes such as glaciation and weathering are strong modifiers of the geochemical signa-
ture inherited from bedrock during pedogenesis. To overcome existing shortcomings of predicted global or
world soil geochemical reference values, we propose Preliminary Empirical Global Soil reference values
based on analytical results of a representative number of soil samples from two continents (PEGS2).
Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
1. Introduction
The Earth's surface is the interface between the geosphere, pedo-
sphere, biosphere, hydrosphere and atmosphere, and supports
human, animal and plant life. This “Critical Zone”hosts a multitude
of physical, chemical and biological processes active over a range of
spatial and temporal scales; these impact mass and energy exchanges
governing processes as varied and crucial as soil formation, plant
growth, water storage, nutrients cycling, metal and radionuclide
transport, etc. (Brantley et al., 2007). This interface is under growing
stress as the world's population continues to grow and with it the
demand for food, water, energy and raw materials. Therefore, im-
proving our understanding of the chemical composition and vari-
ability of soils at the continental, and ultimately global, scale is
both important and pressing.
Many researchers have attempted to estimate the average chemi-
cal composition and natural variation of element concentrations in
“world soils”(e.g., Bowen, 1979; Kabata-Pendias, 2001; Kabata-
Pendias and Pendias, 1984; Koljonen, 1992; Rauch, 2011; Vinogradov,
1954). The values provided are based on data from existing soil sur-
veys in different parts of the world often combined with estimates
about the geochemical composition of the Earth's crust. In this ap-
proach, the empirical data usually come from surveys covering rela-
tively small areas and with rather few samples (Bowen, 1979;
Earth and Planetary Science Letters 319-320 (2012) 269–276
⁎Corresponding author. Tel.: + 61 2 6249 9378.
E-mail address: Patrice.deCaritat@ga.gov.au (P. de Caritat).
1
E. Bastrakov, D. Bowbridge, P. Boyle, S. Briggs, D. Brown, M. Brown, K. Brownlie, P.
Burrows, G. Burton, J. Byass, P. de Caritat, N. Chanthapanya, M. Cooper, L. Cranfield, S.
Curtis, T. Denaro, C. Dhnaram, T. Dhu, G. Diprose, A. Fabris, M. Fairclough, S. Fanning,
R. Fidler, M. Fitzell, P. Flitcroft, C. Fricke, D. Fulton, J. Furlonger, G. Gordon, A. Green,
G. Green, J. Greenfield, J. Harley, S. Heawood, T. Hegvold, K. Henderson, E. House, Z.
Husain, B. Krsteska, J. Lam, R. Langford, T. Lavigne, B. Linehan, M. Livingstone, A. Lukss,
R. Maier, A. Makuei, L. McCabe, P. McDonald, D. McIlroy, D. McIntyre, P. Morris, G.
O'Connell, B. Pappas, J. Parsons, C. Petrick, B. Poignand, R. Roberts, J. Ryle, A. Seymon,
K. Sherry, J. Skinner, M. Smith, C. Strickland, S. Sutton, R. Swindell, H. Tait, J. Tang, A.
Thomson, C. Thun, B. Uppill, K. Wall, J. Watkins, T. Watson, L. Webber, A. Whiting, J.
Wilford, T. Wilson, A. Wygralak.
2
S. Albanese, M. Andersson, A. Arnoldussen, R. Baritz, M.J. Batista, A. Bel‐lan, M.
Birke, D. Cicchella, A. Demetriades, E. Dinelli, B. De Vivo, W. De Vos, M. Duris, A.
Dusza-Dobek, O.A. Eggen, M. Eklund, V. Ernstsen, P. Filzmoser, T.E. Finne, D. Flight, S.
Forrester,M.Fuchs,U.Fugedi,A.Gilucis,M.Gosar,V.Gregorauskiene,A.Gulan,J.
Halamić,E.Haslinger,P.Hayoz,G.Hobiger,R.Hoffmann,J.Hoogewerff,H.Hrvatovic,
S.Husnjak,L.Janik,C.C.Johnson,G.Jordan,J.Kirby,J.Kivisilla,V.Klos,F.Krone,P.
Kwecko, L. Kuti, A. Ladenberger, A. Lima, J. Locutura, P. Lucivjansky, D. Mackovych,
B.I.Malyuk,R.Maquil,M.McLaughlin,R.G.Meuli,N.Miosic,G.Mol,P.Négrel,P.
O'Connor,K.Oorts,R.T.Ottesen,A.Pasieczna,V.Petersell,S.Pfleiderer, M. Poňavič,
C.Prazeres,U.Rauch,C.Reimann,I.Salpeteur,A.Schedl,A.Scheib,I.Schoeters,P.
Sefcik, E. Sellersjö, F. Skopljak, I. Slaninka, A. Šorša, R. Srvkota, T. Stafilov, T. Tarvainen,
V. Trendavilov, P. Valera, V. Verougstraete, D. Vidojević, A.M. Zissimos, Z. Zomeni.
0012-821X/$ –see front matter. Crown Copyright © 2012 Published by Elsevier B.V. All rights reserved.
doi:10.1016/j.epsl.2011.12.033
Contents lists available at SciVerse ScienceDirect
Earth and Planetary Science Letters
journal homepage: www.elsevier.com/locate/epsl
Kabata-Pendias, 2001; Vinogradov, 1954). It is debatable how repre-
sentative these values are of real soils from large and varied regions,
whole continents, or indeed all continents. In addition, the samples
behind the estimates often were analysed at different times, in differ-
ent laboratories and using different analytical techniques, and are
thus scarcely comparable.
Though this approach may still be useful to obtain reasonable
estimates of the total concentrations of major elements, it is ques-
tionable whether it provides reliable values for trace elements.
Furthermore, in environmental sciences it is not always realised
that the average world soil or continental crust values provided
in the literature are based on total concentrations, while soil guid-
ance values or action levels are generally defined for element con-
centrations in aqua regia extractions (ISO, 1995; USEPA, 1996). For
instance aqua regia extraction is widely used and is recommended
for the analysis of solid materials in Europe (e.g., BBodSchV, 1999;
Hjelmar and Holm, 1999; Langenkamp et al., 2001; REACH, 2008;
Rodríguez Martín et al., 2006; Twardowska, 2004) and in Asia
(Jung and Osako, 2009; Oh et al., 2010, 2011), and of sampling
media for mineral exploration in Australia (e.g., Hamlyn, 2011). Reli-
able values for trace element concentrations in aqua regia extraction
at the continental-scale have, until now, not been available, but
must be expected, for some elements at least, to be very different
from the total concentrations. This is because aqua regia only has a
limited effect on minerals such as phlogopite (Mg-rich mica), diocta-
hedral mica (muscovite, sericite), quartz, feldspar, plagioclase, am-
phibole, barite, cassiterite, chromite, gahnite, garnet, ilmenite,
monazite, rutile, sphene and zircon (Chen and Ma, 2001; Dolezal
et al., 1968; Foster, 1973; Hamlyn, 2011; Klassen, 2001; Räisänen
et al., 1992; Ryan et al., 2002; Tarvainen, 1995).
Here, new soil data collected and analysed to consistent protocols
from two continents, one in the northern hemisphere (Europe) and
one in the southern hemisphere (Australia), are presented and com-
pared. The data come from continental-scale geochemical mapping
programmes where a large number of samples were collected accord-
ing to detailed and documented protocols, and analysed following a
tight external quality control scheme. Internal project analytical stan-
dards were exchanged between the two projects and they, as well as
international Certified Reference Materials, were analysed with the
same techniques to guarantee comparability of analytical results be-
tween the two continents and estimation of bias, as outlined in
Reimann et al. (2012).
The geology, geomorphology and pedology of Europe and Austra-
lia are complex subjects worthy of detailed discussions far beyond
what can be covered in a brief article. Nevertheless, the most salient
and relevant characteristics of, and differences between, these two
continents (or at least the large parts thereof under study here) are
summarised in the following. Major geological provinces in Europe
are, in decreasing order of prevalence, (1) extended continental
crust, (2) shield, and (3) orogen; in Australia, they are (1) shield,
(2) platform and (3) orogen (USGS, 2011). The most common lithol-
ogies in Europe are (1) plutonic and metamorphic, (2) shales, and (3)
carbonate rocks; in Australia, they are (1) shales, (2) sand, and (3)
plutonic and metamorphic rocks (Amiotte Suchet et al., 2003). Gen-
erally speaking, fresher rock exposures are more common in Eu-
rope, especially northern Europe, than in Australia, mainly because
of the more recent last glaciation in Europe (Holocene, ca 20 ka)
compared to Australia (Early Permian, ca 290 Ma), but also because
Australia has remained tectonically relatively stable for tens or even
possibly hundreds of millions of years allowing weathering under
varying climates to affect surface materials both extensively and
deeply in many places (BMR Palaeogeographic Group, 1990; Gale,
1992; Pillans, 2007; Veevers, 1984). Both continents span a range
of present-day climate zones (Europe: from polar to arid, domi-
nantly temperate; Australia from tropical to temperate, dominantly
arid; Peel et al., 2007) and ecoregions (Europe: from tundra to
Mediterranean forests, woodlands and scrub, dominantly temperate
broadleaf and mixed forests; Australia from tropical and subtropical
grasslands, savannas and shrublands to Mediterranean forests,
woodlands and scrub, dominantly deserts and xeric shrublands;
Olson et al., 2001). Soils vary enormously across such diverse set-
tings (Europe: from spodosols dominating in the north, through
alfisols in the centre, to inceptisols in the south; Australia from ulti-
sols and inceptisols in the north, through vertisols, entisols and ari-
disols in the centre, to alfisols in the southeast and southwest;
USDA, 2005). Given this range of conditions, and the differences be-
tween these two continents, it should be instructive to compare em-
pirical soil geochemistry data from Europe and Australia with world
soil reference values and investigate if any observed differences can
be related back to these conditions.
Thus, the present study aims to address the following questions:
1. How do extensive and consistent empirical datasets from two new
continental-scale surveys compare with world soil values?
2. Can lithology be used as a predictor of soil chemical composition?
3. Can this work covering two continents provide improved world
soil reference values, including –for the first time –aqua regia
extractable concentrations for several elements?
4. What is needed to obtain a robust estimate of global soil
composition?
2. Methods
During the last four years, continental-scale geochemical surveys
have been conducted in Europe and Australia covering 5.6 and
6.2 million km
2
, respectively. These are the Geochemical Mapping of
Agricultural Soils (GEMAS) and the National Geochemical Survey
of Australia (NGSA; www.ga.gov.au/ngsa) projects, briefly described
below. Average sampling densities were 1 site/2500 km
2
for GEMAS
and 1 site/5200 km
2
for NGSA. The GEMAS project sampled agricul-
tural soils (hereafter referred to as ‘Ap’samples for A ploughed hori-
zon), whereas the NGSA project focused on soils developed on
catchment outlet sediments generally similar to floodplain sedi-
ments. The Ap samples from GEMAS (N=2211) were taken as com-
posites of 0 to 20 cm depth, air-dried and sieved to b2 mm using
nylon mesh sieves. The NGSA samples considered here (N = 1315)
are the Top Outlet Sediments (TOS) collected as composites from
0 to 10 cm depth, oven-dried at 40 °C and sieved to b2 mm (or
‘coarse’as the project also used a b75 μm‘fine’fraction) using nylon
mesh sieves (hereafter referred to as ‘Tc’for TOS coarse). Details re-
lating to survey design, sample collection, and preparation are
found in EGS (2008) for GEMAS and in Caritat et al. (2009) and
Lech et al. (2007) for NGSA.
In both projects, samples were analysed for an extensive suite
of total and aqua regia soluble element contents, as well as for other
parameters (Caritat and Cooper, 2011; Caritat et al., 2010; Reimann
et al., 2009, 2011a). In both the GEMAS and NGSA projects, total
major element contents were obtained by X-Ray Fluorescence (XRF)
for Al
2
O
3
, CaO, Fe
2
O
3
,K
2
O, MgO, MnO, Na
2
O, P
2
O
5
, SiO
2
and TiO
2
.
Total trace element contents (As, Ba, Ce, Co, Cr, Ga, Nb, Ni, Pb, Rb,
Sr, Th, V, Y, Zn and Zr) were determined by XRF for the GEMAS sam-
ples and by total digestion (HF + HNO
3
digestion of fused XRF bead)
followed by ICP-MS analysis for the NGSA samples. The aqua regia
extracted elements (Ag, As, Bi, Cd, Ce, Co, Cs, Cu, Fe, La, Li, Mn, Mo
and Pb) were determined in both cases by a similar aqua regia
digestion followed by ICP-MS analysis. Further details are provided
in Reimann et al. (2012).
Early on, Internal Project Standards (IPSs) were exchanged be-
tween GEMAS and NGSA to allow demonstration of inter-
comparability between both geochemical datasets despite the
minor differences in analytical protocols discussed above. These IPSs
were (1) a representative agricultural soil ‘GEMAS-Ap’and (2) a
270 P. de Caritat, C. Reimann / Earth and Planetary Science Letters 319-320 (2012) 269–276
representative grazing land soil ‘GEMAS-Gr’from Europe (EGS, 2008),
and (3) a representative catchment outlet sediment ‘ORIS’(Ovens
River Internal Standard) from Australia (Caritat and Cooper, 2011).
In addition, an IPS from another continental-scale geochemical sur-
vey, ‘SoNE-1’(Soil of Nebraska-1) from the North American land-
scape geochemical survey (Smith et al., 2009) was also analysed
in the analytical streams of GEMAS and NGSA. Reimann et al.
(2012) discuss in further detail the comparability of the continental
soil datasets from GEMAS and NGSA, and conclude that the two
sampling media are indeed comparable at this scale for the elements
under consideration here. Based on the comparison of results for the
exchanged IPSs results for all elements/parameters presented here
were found to be directly comparable between the two continents
(see Reimann et al., 2012, for further detail).
3. Results and discussion
Table 1 shows the composition of the upper continental crust,
several published global or world soil concentration values, average
or median soil composition from other available continents, and the
median total topsoil composition from the new European and Australian
continental-scale surveys (GEMAS Ap and NGSA Tc).
Starting with Clarke and Washington's (1924) famous “Clarke
values,”Taylor and McLennan (1995),Wedepohl (1995) and, more
recently, Rudnick and Gao (2003) have all put considerable effort
into estimating the average geochemical composition of the conti-
nental crust for almost all elements of the periodic table based on
models of the proportions of major rock types making up the crust
and the existing knowledge about their average chemical composi-
tion. The latest values of Rudnick and Gao (2003) are shown in
Table 1 for those elements that are considered in this paper.
Published estimates of the chemical composition of global
(Vinogradov, 1954) or world soils (Bowen, 1979; Kabata-Pendias,
2001; Koljonen, 1992), shown in Table 1, are up to now based on
(1) results of relatively small soil surveys over different lithologies,
(2) estimates of the distribution of different rock types in the Earth
crust, and (3) the existing knowledge about soil-forming processes
in different climatic settings. As such, many of these values can fair-
ly be regarded as representing “expert guesses.”In the next sections,
we will discuss these world estimates in light of continental data-
sets, and compare these datasets to other available results from sim-
ilar soil surveys.
Amiotte Suchet et al. (2003) presented a database of worldwide
lithology based on six major rock types: (1) sand and sandstones,
(2) carbonate rocks, (3) shales, (4) plutonic and metamorphic (i.e.,
shield) rocks, (5) acid volcanic rocks, and (6) basalts with a 1°× 1°
resolution. Table 2 shows the proportions of these rock types for
the whole world (Amiotte Suchet et al., 2003) and those we derived
from their data for the three continental-sized study areas that will
Table 1
Average (AVE) upper continental crust (UCC), several published median (MED) global soil (GS) and world soil (WS) reference values, and average or median values from
continental-scale geochemical survey data from the USA and China (as described in the footnote) compared to the new median soil total concentrations determined by
continental-scale geochemical surveys in Europe (GEMAS Ap) and Australia (NGSA Tc) (this study).
UCC GS WS1 WS2 WS3 USA USA China Ap Tc
AVE MED MED MED MED AVE MED AVE MED MED
Majors —total
(wt%)
Al
2
O
3
15.4 13.5 15.1 13.4 13.6 9.7 12.3 10.5 8.1
CaO 3.6 1.9 2.0 2.1 3.4 1.4 3.1 1.2 0.5
Fe
2
O
3
5.6 5.4 5.0 5.7 3.7 2.8 4.4 3.6 3.2
K
2
O 2.8 1.6 1.7 1.7 1.8 1.8 2.3 1.9 1.2
MgO 2.5 1.0 1.5 0.8 1.5 1.0 1.5 1.0 0.5
MnO 0.10 0.11 0.07 0.13 0.07 0.07 0.05 0.08 0.08 0.04
Na
2
O 3.27 0.85 1.35 0.67 1.62 1.10 1.52 0.79 0.30
P
2
O
5
0.15 0.18 0.17 0.18 0.10 0.15 0.18 0.06
SiO
2
66.6 70.6 59.9 70.6 66.3 66.8 77.5
TiO
2
0.64 0.77 0.67 0.83 0.48 0.42 0.68 0.62 0.58
Traces —total
(mg/kg)
As55 56576 73
Ba 624 500 500 500 362 580 502 391 315
Ce 63 (50) 65 50 49 75 59 42
Co 17 8 10 8 7 9 7 13 9 8
Cr 92 200 80 70 42 54 50 58 64 48
Ga 18 20 12 17 15 12 10
Nb 12 12 10 12 11 13 9
Ni 47 40 20 50 18 19 15 25 21 15
Pb 17 10 17 35 25 19 17 25 21 13
Rb 84 60 65 150 50 67 75 51
Sr 320 300 240 250 147 240 148 186 102 68
Th 11 6 9 9 8 9 9 8
V 97 100 90 90 60 80 67 78 70 55
Y 21 2040122523 2821
Zn 67 50 70 90 62 60 52 69 62 31
Zr 193 300 230 400 300 230 188 263 304
UCC: Upper continental crust, from Rudnick and Gao (2003).
GS: Global soil, from Vinogradov (1954).
WS1: World soil, from Bowen (1979).
WS2: World soil, from Koljonen (1992).
WS3: World soil, from Kabata-Pendias (2001).
USA: Conterminous USA soils, AVE from Shacklette and Boerngen (1984), and MED from Garrett (2009) or Gustavsson et al. (2001).
China: Chinese soil, from Li and Wu (1999).
Ap, Tc: This study.
271P. de Caritat, C. Reimann / Earth and Planetary Science Letters 319-320 (2012) 269–276
be further discussed in this paper. This database of world lithologies
was used in preference to either local continental lithological cover-
ages (where they exist, e.g., Raymond, 2009) or recently developed
world lithological coverages with finer resolution (Dürr et al., 2005).
This is because we are here focussing on how soil composition
over two continents compares to other continents and indeed to
world average soil composition. Thus we need a consistent litho-
logical database at an appropriate resolution. Future work may in-
vestigate the more detailed relationships between lithologies and
soil composition within Europe or Australia, but this is outside the
scope of the present contribution.
Amiotte Suchet et al. (2003) argued that “The main difficulty in
constructing a global data set of rock type exposures on the conti-
nents is that the information given by geological maps is inadequate.
Indeed, geological maps focus on the age of rocks (for sedimentary
rocks), on their deformation and on their structural position (sedi-
mentary basin, mountain range, etc.), but information concerning
the chemical and physical nature of rocks is often insufficient.”We
couldn't agree more. We will examine if differences in soil composi-
tion on different continents (Table 1)reflect different rock propor-
tions (Table 2), and discuss whether these six rock types provide a
representative basis for a good estimate of soil chemical composition
at the continental, and ultimately, global scale.
3.1. Comparison with world soil reference values
A detailed comparison of the Australian and European
continental-scale data was presented in Reimann et al. (2012) and
here we focus on how these new data compare with global soil ref-
erence values from previous workers. Most estimates provided for
global or world soil averages (GS, WS1 to WS3 in Table 1) are
quite similar to one another; our empirical results from two
continental-scale soil surveys do, however, show some deviations
relative to these estimates. For Al
2
O
3
the estimated global soil values
(13.4 to 15.1 wt.%) are much higher than the values presented here
for Europe (10.5 wt.%) and Australia (8.1 wt.%). Rauch (2011)
reported a geospatially weighed mean global soil Al concentration
of 3.9 wt.% (7.4 wt.% Al
2
O
3
), which is lower than the data pre-
sented here but certainly supports our observation that world soil
estimates in Table 1 may be overestimating soil Al content.
CaO in world soil estimates (1.9 to 2.1 wt.%) is also much higher
than empirical data from continental-scale data for either Europe
(1.2 wt.%) or Australia (0.45 wt.%). The higher estimate is not backed
by a higher proportion of carbonates (Table 2) for the world com-
pared to Europe. The same situation is found for Fe
2
O
3
, where global
soil values (5 to 5.7 wt.%) are significantly above what is measured
in Europe (3.6 wt.%) and Australia (3.2 wt.%). Rauch's (2011) soil Fe
concentration of 2.5 wt.% (3.6 wt.% Fe
2
O
3
) is consistent with our data.
Median K
2
O from Australia (1.2 wt.%) is lower than the global soil
estimates (1.6 to 1.7 wt.%), while the European value (1.9 wt.%) is
only slightly above. For MgO, MnO, and Na
2
O, the European soil me-
dians (1, 0.08, and 0.79 wt.%) fall within the reported global soil
range (0.8 to 1.5 wt.%, 0.07 to 0.13, and 0.67 to 1.35 wt.%, respective-
ly), but the Australian data are all below that range (0.5, 0.04, and
0.3 wt.%). Median for SiO
2
in Europe (66.8 wt.%) is within the global
soil range (59.9 to 70.6 wt.%), but the Australian median soil value
is significantly higher than this range (77.5 wt.%). In terms of TiO
2
,
the new continental data from Europe (0.62 wt.%) and Australia
(0.58 wt.%) closely agree and suggest that the previously published
global soil estimates (0.67 to 0.83 wt.%) may be too high.
For total trace elements, the European median for As (7 mg/kg) is
above, and the Australian median (3 mg/kg) below, the available
world soil values (5 to 6 mg/kg). The Australian median value for Ba
(315 mg/kg) is well below the world soils range (362 to 500 mg/
kg). For Ce and Ga, the median soil values from Australia (42 mg/kg
and 10 mg/kg) are below the global soil ranges (49 to 65 mg/kg and
12 to 20 mg/kg). With a median of only 15 mg/kg of Ni, the Australian
soils are again below the published soil range (18 to 50 mg/kg). The
world values for Sr (147 to 300 mg/kg) appear to be significantly
above empirical data from both Europe (102 mg/kg) and Australia
(68 mg/kg). The Australian data suggest lower V (55 mg/kg) and
much lower Zn (31 mg/kg) content than global soil estimates (60 to
100 mg/kg and 50 to 90 mg/kg). For Co, Cr, Nb, Pb, Rb, Th, Y and Zr,
the new European and Australian median values fall within the previ-
ously published world soil range of values.
3.2. Comparison with data from other continental scale surveys
Table 1 also compares the new European and Australian median
values to the median or average values from two other continental-
scale surveys, the conterminous USA (Garrett, 2009; Gustavsson
et al., 2001; Shacklette and Boerngen, 1984) and China (Li and Wu,
1999). A first observation is that several authors of large geochemical
datasets provide average values, i.e., arithmetic means, while other
authors have chosen to use median values as the more representative
value for the central tendency of geochemical datasets. The different
methods of estimating a central tendency for a given dataset are dis-
cussed in detail in Reimann et al. (2008), who concluded that for
geochemical data the median is the preferred statistical measure.
Geochemical data are closed data (Aitchison, 1986) and do not plot
in the Euclidian space, however, the calculation of the mean is
based on Euclidian distances (Filzmoser et al., 2009). Furthermore,
the mean will invariably yield biased (typically high) values for
skewed data. The comparability of these datasets is thus limited
from the outset due to fundamental differences between the statisti-
cal estimators.
Still, some striking differences can be observed between these
datasets. The largest difference observed between continental median
values is for Na
2
O. The 1.4 and 3.6 times higher Na
2
O content of
American soils (median 1.10 wt.%) relative to European (0.79 wt.%)
and Australian (0.30 wt.%) soils can not be explained by a coastal/sea-
spray influence, since the conterminous USA has a lower coastal
length (~ 10,000 km for all States except Alaska) than Australia
(26,000 km) or the GEMAS area (91,000 km for EU plus Norway)
(CIA, 2008). The USA does not have a greater abundance of exposed
Na-silicate or salt-bearing rock types either (see sandstones, shales
and plutonic/metamorphic rocks in Table 2), with the exception of
acid volcanics, which are considerably higher in the USA (14%) com-
pared to Europe (0.5%) and Australia (3.7%). These rocks contain Na-
feldspars as shown by Eberl and Smith (2009; their Fig. 9). Still, this
does not satisfactorily explain why the order of median Na
2
O soil
content is USA> Europe ≫Australia. Thus, the explanation likely
lies at least in part in differences in weathering regimes being re-
sponsible for the Na distributions observed, in particular the leach-
ing of this soluble cation from Australia's mature soils.
The CaO content of soil is marginally higher in the USA (1.4 wt.%)
than in Europe (1.2 wt.%) but 3.1 times higher than in Australia
(0.5 wt.%). This is in overall agreement with the lithological distribu-
tion (Table 2), which suggests that the USA study area has more car-
bonate rocks (19%) than the European (14%) and especially the
Australian (4%) study areas. The median MgO contents for the three
continents follow a similar pattern of USA (0.99 wt.%) ~ Europe
(0.95 wt.%)> Australia (0.5 wt.%) and is probably related to the car-
bonate distribution as well. Of course, Ca and Mg are not exclusively
sourced from carbonate lithologies, and calc- and mafic-silicates
also release these cations during hydrolysis. In many ways, it was
expected that Australia, with its predominantly semi-arid to arid
climate and relatively common pedogenic carbonates, which are
reflected in the distribution of soil pH (Caritat et al., 2011), would
have a higher median CaO soil content than the more temperate con-
tinents, but this is not the case. Instead the soil CaO and MgO contents
272 P. de Caritat, C. Reimann / Earth and Planetary Science Letters 319-320 (2012) 269–276
are approximately proportional to the carbonate rock proportions for
these three study areas, namely USA~ Europe = 2 −3 × Australia.
North American soils contain less Fe
2
O
3
(2.8 wt.%) than Australian
soils (3.2 wt.%), which are themselves below the European value
(3.6 wt.%). If Fe
2
O
3
abundance is related mainly to the abundance of ba-
saltic rocks, then one would expect a ranking for the conterminous USA
(1.5% basalt) somewhere between Europe (0.5%) and Australia (4%),
but this is not the case. It must be noted here that the original American
survey of Shacklette and Boerngen (1984) deliberately sampled sub-
soils at a depth >20 cm to avoid possible effects of surface contami-
nation; this could explain some of the observed differences,
particularly for Mn and Fe oxides. This observation exemplifies how
difficult it is to arrive at really comparable soil values for any large
area. Small differences in sample medium, sample preparation or an-
alytical protocols can have substantial effects on the observed ele-
ment concentrations and render such datasets unfit for comparison,
unless measures to ensure comparability, like exchanging IPSs and
checking the results for mutual consistency, are implemented.
China has a much higher Al
2
O
3
content (12.3 wt.%) than Europe
(10.5 wt.%), USA (9.7 wt.%) or especially Australia (8.1 wt.%), but
this could be partly due to the fact that it is an average value rather
than a median (see discussion above).
It is perhaps for K
2
O that soil composition is most obviously not
reflecting rock composition: whereas the order of decreasing K-
silicate-bearing shale abundance is Australia (44%)>Europe (37%)
>USA (23%), the order of K
2
O abundance is Europe (1.9 wt.%)~USA
(1.8 wt.%)>Australia (1.2 wt.%). Of course K
2
O can also originate from
feldspars and micas in sandstones and granites, and here Australia
has similar sandstone and plutonic/metamorphic abundances (24 and
20%) to the USA (23 and 19%). Europe has a low proportion of sand-
stone (10%) but a much higher proportion of plutonic/metamorphic
(39%) rocks. For K
2
O, this simple lithology schema does not satisfac-
torily explain the observed distributions either. As for Na
2
O above,
it is likely that weathering plays a dominant role in the abundance
of K
2
O, also a relatively mobile element in soils, on those three
continents.
As far as total trace elements concentrations are concerned, the
largest difference between the continents is observed for Sr, where
the median for the USA (148 mg/kg) is over 2.1 and 1.4 times greater
than for Australia (68 mg/kg) and Europe (102 mg/kg), respectively.
This is consistent with the similar findings regarding Ca above, and
to some extent also Mg, and is related to the preponderance of car-
bonate lithologies there.
For As, the USA soils (5.6 mg/kg) contain 1.8 times the median
content in Australia (3.1 mg/kg) but are somewhat lower than in
Europe (7 mg/kg). Zn follows the same pattern with the USA soils
(52 mg/kg) falling between the Australia (31 mg/kg) and European
(62 mg/kg) medians. Both As and Zn are more abundant in shale
and schist than in any other common rock type (Reimann and
Caritat, 1998), so lithology fails to explain the As distribution in
soil as Australia has considerably more abundant shale than either
Europe or the USA (Table 2). For Zn, another rich source can be
found in basaltic rocks, which are more common in Australia
than in the USA, and very rare in the GEMAS area, thus not provid-
ing a satisfactory explanation for the high soil Zn values being found
in Europe.
Median Ba in the USA (502 mg/kg) is 1.6 and 1.3 times greater
than in Australia (315 mg/kg) and Europe (391 mg/kg), respectively.
Median Pb in the USA (17 mg/kg) is intermediate between Europe
(21 mg/kg) and Australia (13 mg/kg). Both Ba and Pb are abundant
in feldspar, plagioclase and mica, which are main constituents of
granite and shale, lithologies that are more represented in both
Australia and Europe than in the USA. Thus, like for K
2
O, the simple
rock type schema does not explain the levels of these trace elements
observed in soil from these three continents.
For the geochemically ‘inert’Zr, which is most abundant in grey-
wacke and sandstone, the median soil composition (Australia
304 mg/kg>Europe 263 mg/kg>USA 188 mg/kg) is also inconsistent
with the relative proportions of Amiotte Suchet et al.'s (2003) sand-
stone category (Australia 24%~ USA 23% ≫Europe 9.5%).
In terms of total Cr concentration, the soils of Australia (48 mg/kg)
and Europe (64 mg/kg) are respectively similar to, and more ele-
vated than, those from the USA (50 mg/kg). For Ni, the soils of Aus-
tralia and the USA have the same median value of 15 mg/kg, much
lower than for Europe (21 mg/kg). Since both Cr and Ni are consid-
erably more common in ultramafic and mafic rocks than in other
rock types (e.g., Reimann and Caritat, 1998), one would expect a
strong control being exerted on their soil concentration by the abun-
dance of these lithologies. However, here too, the distribution of
basalt lithology, which is Australia≫USA>Europe (Table 2), falls
short of explaining soil composition as revealed by continental-scale
sampling. One problem with the database of Amiotte Suchet et al.
(2003) may be the “plutonic and metamorphic rocks”category con-
taining rocks of very different chemical composition. For example,
greenstone belts in Scandinavia, with their high Ni and Cr values,
fall into this category although, based on geochemical considerations,
they would probably be better classified as “basalts.”
The data presented herein for soil composition from two conti-
nents and compared to a third continent, thus appear to indicate
that parent material, i.e., the type of rock substrate, is a poor predictor
of soil composition at this scale, and/or that the existing geological
databases on the spatial distribution of rock types (as opposed to
rock age) are deficient.
Parameters other than rock composition of course play a signifi-
cant role in soil formation by modifying the chemical composition
inherited from the parent material during pedogenesis (i.e., climate,
organisms, relief, time; see Jenny, 1941; Shaw, 1930). Only now that
continental geochemical surveys and world lithological databases
are becoming available, can it be shown how strong continental-
scale climate is as a modifier of the chemical signal inherited from
parent material. In the case of Europe, the southerly extent of the
ice sheet during the last (Quaternary) glaciation has a profound im-
pact on geochemical patterns expressed in soils (Reimann et al.,
2012). This is a result of scraping clean the Baltic shield and exposing
fresh plutonic and metamorphic rocks at the surface, as well as leav-
ing behind coarse glacial sediment consisting of crudely ground bed-
rock material, with a low capacity for adsorbing trace elements. Areas
receiving unusual amounts of rainfall also often show specific geo-
chemical signals. In Australia, the influence of past climates is ex-
pressed by the extensive and, in places, intensive, weathering that
has occurred at least episodically probably since the Paleozoic, and
through the Mesozoic and Cenozoic (BMR Palaeogeographic Group,
1990; Gale, 1992; Li and Vasconcelos, 2002; Nott, 1995; O'Sullivan
et al., 2000; Pillans, 1997, 2007). This has resulted in an intense leach-
ing of mobile cations released by the breakdown of rock-forming
minerals, with a subsequent impoverishment of these elements in
the soil, and concomitantly an increase in levels of elements held in
weathering resistant mineral phases. Weathering end-member
Table 2
Relative areal proportions of six major lithological types as presented by Amiotte
Suchet et al. (2003) for the world, and those recalculated from their data for the project
areas of NGSA and GEMAS (this study) as well as the conterminous USA (Shacklette
and Boerngen, 1984) denoted as ‘USA48’.‘SAND’stands for sand and sandstones,
‘CARB’carbonate rocks, ‘SHAL’shales, ‘PLME’plutonic and metamorphic (i.e., shield)
rocks, ‘ACVO’acid volcanic rocks, and ‘BASA’basalts.
SAND CARB SHAL PLME ACVO BASA TOT
WORLD 20% 13% 28% 31% 2.4% 6.0% 100%
NGSA 24% 4.3% 44% 20% 3.7% 4.0% 100%
GEMAS 9.5% 14% 37% 39% 0.5% 0.5% 100%
USA48 23% 19% 23% 19% 14% 1.5% 100%
273P. de Caritat, C. Reimann / Earth and Planetary Science Letters 319-320 (2012) 269–276
minerals and regolith types are commonly reported to be enriched in
Si (quartz, clay minerals; silcrete), Al (illite, smectite, kaolinite and its
polymorphs, gibbsite; bauxite), Fe (goethite, hematite; laterite), Zr
(zircons and other resistates; heavy mineral sands) and Ti (ilmenite,
rutile, anatase; silcrete) (Dixon and Weed, 1977; Dixon and Young,
1981; Gilkes and Suddhiprakarn, 1979; Kronberg and Nesbitt, 1981;
Nesbitt and Markovics, 1997; Taylor et al., 1992; Wilson, 1999;
Zeissink, 1969). Judging from the new national-scale soil dataset
and especially comparing it to Europe and the USA, it appears that
the only elements in which the Australian samples are enriched are
Si and Zr, and not Al or Fe or Ti as could have been expected. This
raises questions about the real effects of weathering at this scale
and the perhaps greater than hitherto speculated mobility of Al, Fe
and Ti. A confounding factor, however, is that bauxites, laterites and
heavy mineral sands were not targeted sampling media in Australia
(but nor were they in Europe and the USA).
3.3. The Predicted Empirical Global Soil reference values based on two
continents (PEGS2)
It follows from the above discussion that published world or
global soil reference values have some similarities but also some im-
portant differences when compared to empirical soil geochemical
data obtained from surveys of whole continents. This is attributed
to the fact that these reference values are calculated often starting
from an upper crust composition, which is a calculated estimate
based on geophysical and some geochemical models. It is clear from
Table 1 that the upper continental crust chemistry is at best a very
crude estimator or predictor of soil composition. For instance, all
major elements except SiO
2
and TiO
2
are overestimated by between
25% (P
2
O
5
) and 600% (Na
2
O) compared to the median of soil concen-
trations measured over large areas such as Europe and Australia. The
situation is similar for the total trace elements reported: only As, Ce,
Nb, Pb and Y are close to (within 25% of) crustal values; Th, Rb, Zn,
V, Ga, Cr, Ba, Co, Ni, Sr are overestimated up to nearly four-fold, and
Zr is underestimated by 68%.
In Table 3 an improved, but interim, reference value for world
soils based on the median values for the data from the two new
continental-scale soil geochemical datasets from both hemispheres
is presented. This value is called the Preliminary Empirical Global
Soil value based on two continents, or PEGS2; it is calculated as the
median value between the GEMAS and NGSA medians. In the future
as more (inter-comparable) continental datasets become available, a
PEGS3, PEGS4, etc., can be put forward in the literature, by similarly
taking medians of the three, four, etc., values available. Apart from
presenting data for total major and trace element contents, the
PEGS2 values include for the very first time a global soil estimate for
aqua regia extractable elements. Note that a strict quality control pro-
gram was implemented in the GEMAS and NGSA projects to allow
the resulting data to be demonstrably comparable (Reimann et al.,
2012).
The data for trace elements in world soil provided by Kabata-
Pendias (2001) come closest (Table 1) to the PEGS2 (Table 3) esti-
mates provided here and based on empirical results from two
continental-scale soil surveys. Most interesting deviations between
PEGS2 and the values provided by Kabata-Pendias (2001) are clearly
higher PEGS2 values for Y (by a factor of ~2), Cr and Rb, and lower
PEGS2 values for Sr, Pb and Zn.
4. Conclusions
New geochemical surveys of soils in Europe (N=2211) and Austra-
lia (N=1315), covering 5.6 and 6.2 million km
2
respectively, have
been carried out in such a way as to be demonstrably comparable.
Using Internal Project Standards and analysing Certified Reference
Materials it was possible to demonstrate comparability between both
datasets as well as acceptable precision and bias for all 10 major oxides
(Al
2
O
3
,CaO,Fe
2
O
3
,K
2
O, MgO, MnO, Na
2
O, P
2
O
5
,SiO
2
and TiO
2
)as
well as for Loss On Ignition (LOI) and pH, for 16 total trace elements
(As, Ba, Ce, Co, Cr, Ga, Nb, Ni, Pb, Rb, Sr, Th, V, Y, Zn and Zr), and also
for 14 aqua regia soluble elements (Ag, As, Bi, Cd, Ce, Co, Cs, Cu, Fe,
La, Li, Mn, Mo and Pb).
For many elements there exist substantial differences between
published world soil averages and the median concentrations ob-
served on two continents. Further, average crustal values are not
related to average soil values. They should not be used for providing
background or reference values for soils. Only real soil analyses
from very large areas provide a reasonable estimate of average world
soil composition.
Table 3
Median (MED) soil values determined by continental-scale geochemical surveys in Eu-
rope (GEMAS Ap) and Australia (NGSA Tc), and the derived Preliminary Empirical
Global Soil estimate based on two continents (PEGS2).
Ap Tc PEGS2
MED MED
Majors —total
(wt%)
Al
2
O
3
10.5 8.1 9.3
CaO 1.2 0.5 0.8
Fe
2
O
3
3.6 3.2 3.4
K
2
O 1.9 1.2 1.6
MgO 1.0 0.5 0.7
MnO 0.08 0.04 0.06
Na
2
O 0.79 0.30 0.55
P
2
O
5
0.18 0.06 0.12
SiO
2
66.8 77.5 72.2
TiO
2
0.62 0.58 0.60
Traces —total
(mg/kg)
As 735
Ba 391 315 353
Ce 59 42 51
Co 989
Cr 64 48 56
Ga 12 10 11
Nb 13 9 11
Ni 21 15 18
Pb 21 13 17
Rb 75 51 63
Sr 102 68 85
Th 988
V705563
Y282125
Zn 62 31 47
Zr 263 304 284
Traces —aqua regia
(mg/kg)
Ag_AR 0.038 0.012 0.025
As_AR 5.7 1.6 3.6
Bi_AR 0.17 0.12 0.15
Cd_AR 0.18 0.04 0.11
Ce_AR 29 29 29
Co_AR 7.8 6.3 7.0
Cs_AR 1.1 0.8 1.0
Cu_AR 15 11 13
Fe_AR 17,632 16,500 17,066
La_AR 15 14 14
Li_AR 12 5.7 8.7
Mn_AR 462 279 370
Mo_AR 0.42 0.20 0.31
Pb_AR 15 7 11
Other parameters
LOI (%) 8.7 5.5 7.1
pH 5.8 5.7 5.7
274 P. de Caritat, C. Reimann / Earth and Planetary Science Letters 319-320 (2012) 269–276
Using a database on the worldwide distribution of lithological
units it can be demonstrated that there is little relation between the
spatial distribution of these units and the observed chemistry of the
soils. Perhaps only CaO and MgO in Australian soils are to a degree
commensurate with the abundance of carbonate and mafic litholo-
gies, and SiO
2
with the abundance of sandstone. Even median Al
2
O
3
,
Fe
2
O
3
, TiO
2
and MnO are lower in Australia than in Europe and/or
USA, suggesting a greater solubility than perhaps hitherto suspected.
The poor coincidence between lithology and soil geochemistry at the
continental scale may be partly due to the fact that geological maps
are based on age relations while good lithological maps of the world
are direly missing. Furthermore past and present climates (and
climate-related processes) play an often underestimated role in de-
termining the chemistry of soils.
To overcome the above shortcomings of predicted global or world
soil geochemical reference values, Preliminary Empirical Global Soil
reference values based on mutually consistent data from two conti-
nents (PEGS2) are proposed to be used for comparison and normali-
sation purposes. It is hoped that more continental datasets will be
added to this estimate in the near future.
Acknowledgements
The GEMAS project is a cooperation project of the EuroGeoSurveys
Geochemistry Expert Group with a number of outside organisations
(e.g., Alterra in The Netherlands, the Norwegian Forest and Landscape
Institute, several Ministries of the Environment and University De-
partments of Geosciences in a number of European countries, CSIRO
Land and Water in Adelaide, Australia) and Eurometaux. Very special
thanks are due to Ilse Schoeters, who arranged the Expert Group's
contact with Eurometaux and made this all possible, and to Robert
G. Garrett of the Geological Survey of Canada, who established the
first contact between Ilse and the Geochemistry Expert Group's chair-
man. The analytical work was co-financed by the following organisa-
tions: Eurometaux, Cobalt Development Institute (CDI), European
Copper Institute (ECI), Nickel Institute, Europe, European Precious
Metals Federation (EPMF), International Antimony Association (i2a),
International Manganese Institute (IMnI), International Molybdenum
Association (IMoA), ITRI Ltd. (on behalf of the REACH Tin Metal Con-
sortium), International Zinc Association (IZA), International Lead
Association-Europe (ILA-Europe), European Borates Association
(EBA), the (REACH) Vanadium Consortium (VC) and the (REACH)
Selenium and Tellurium Consortium. Finally, the Directors of the Eu-
ropean Geological Surveys and the additional participating organisa-
tions are thanked for making sampling of almost all of Europe on a
tight time schedule possible.
The NGSA project was part of the Australian Government's On-
shore Energy Security Program 2006–2011, from which funding sup-
port is gratefully acknowledged. NGSA was led and managed by
Geoscience Australia and carried out in collaboration with the geolog-
ical surveys of every State and the Northern Territory under National
Geoscience Agreements. The Directors from the Geological Survey
of Queensland (GSQ), Geological Survey of New South Wales
(GSNSW), GeoScience Victoria (GSV), Mineral Resources Tasmania
(MRT), Primary Industries and Resources South Australia (PIRSA),
Geological Survey of Western Australia (GSWA) and Northern Terri-
tory Geological Survey (NTGS) are warmly thanked for supporting
the NGSA. This project would not have been feasible without land-
owners granting permission to access the sampling sites. This manu-
script was prepared while PdC was a visiting scientist at the
Geological Survey of Norway in July–August 2011; he gratefully ac-
knowledges the receipt of a Development Award from Geoscience
Australia and the hospitality of the Geological Survey of Norway,
which made this possible. PdC published with permission from the
Chief Executive Officer, Geoscience Australia.
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