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Natural and anthropogenic variations in atmospheric
mercury deposition during the Holocene
near Quelccaya Ice Cap, Peru
Samuel A. Beal1, Meredith A. Kelly1, Justin S. Stroup1, Brian P. Jackson1, Thomas V. Lowell2,
and Pedro M. Tapia3
1Department of Earth Sciences, Dartmouth College, Hanover, New Hampshire, USA, 2Department of Geology, University o
Cincinnati, Cincinnati, Ohio, USA, 3Department of Biological Sciences, Universidad Peruana Cayetano Heredia, Lima, Peru
Abstract Mercury (Hg) is a toxic metal that is transported globally through the atmosphere. Emissionsof Hg from mineral reservoirs and recycling between soil/biomass, oceans, and the atmosphere are
fundamental to the global Hg cycle, yet past emissions from anthropogenic and natural sources are not
fully constrained. We use a sediment core from Yanacocha, a headwater lake in southeastern Peru, to study
the anthropogenic and natural controls on atmospheric Hg deposition during the Holocene. From 12.3 to
3.5 ka, Hg uxes in the record are relatively constant (mean ± 1σ : 1.4 ± 0.6 μg m2 a1). Past Hg deposition
does not correlate with changes in regional temperature and precipitation or with most large volcanic
events that occurred regionally (~300–400 km from Yanacocha) and globally. In 1450 B.C. (3.4 ka), Hg uxes
abruptly increased and reached the Holocene-maximum ux (6.7 μg m2 a1) in 1200 B.C., concurrent with
a ~100 year peak in Fe and chalcophile metals (As, Ag, Tl) and the presence of framboidal pyrite.
Continuously elevated Hg uxes from 1200 to 500 B.C. suggest a protracted mining-dust source near
Yanacocha that is identical in timing to documented pre-Incan cinnabar mining in central Peru. During
Incan and Colonial time (A.D. 1450–1650), Hg deposition remains elevated relative to background levels
but lower relative to other Hg records from sediment cores in central Peru, indicating a limited spatial
extent of preindustrial Hg emissions. Hg uxes from A.D. 1980 to 2011 (4.0 ± 1.0μg m2 a1) are 3.0± 1.5 times
greater than preanthropogenic uxes.
1. Introduction
Rapidly rising anthropogenic emissions of mercury (Hg) to the atmosphere during the past decade are
superimposed on a longer-term increasing trend since the industrial revolution [Streets et al ., 2011]. Hg is
transported globally as gaseous Hg0 [e.g., Mason et al ., 1994], deposited to the land/water surface as Hg2+,
andrapidly transferred to biota as extremely toxic methyl-Hg [Harris et al ., 2007], posing a great risk to human
and ecosystem health. An accurate understanding of the global Hg cycle is required to assess the role of
anthropogenic emissions on current and future Hg deposition. Information on the biogeochemical cycling o
Hg primarily comes from reconstructions of Hg deposition over time in sedimentary archives (i.e., lake
sediment, peat, and ice) and from global Hg models. A wealth of lake sediment records from around the
world provide direct evidence for an average 3.5-fold increase in Hg deposition since~ A.D. 1850 [Biester
et al ., 2007], but very few records extend earlier in time. A recent model of global Hg cycling, forced with
estimates of anthropogenic Hg emissions from 2000 B.C. to A.D. 2008 and constant natural emissions, yields asimilar amount of increase (2.6 times) since A.D. 1840 but a much larger increase (7.5 times) since 2000 B.C.
[ Amos et al ., 2013]. The apparent importance of anthropogenic emissions before ~ A.D. 1850 (i.e., during
preindustrial time) and the assumption of constant natural emissions require independent validation with
geophysical evidence, such as Hg contained in sedimentary archives.
Natural variations in Hg emissions to the atmosphere can be caused by changes in volcanism, low-temperature
volatilization, and external factors which affect exchanges between surface Hg reservoirs (soil/biomass, ocean
and atmosphere) [Fitzgerald and Lamborg, 2007]. Terrestrial volcanic Hg sources are somewhat constrained
[Nriagu and Becker , 2003; Pyle and Mather , 2003], but large uncertainties remain in estimates of the inputs from
submarine volcanism [Lamborg et al ., 2006] and low-temperature volatilization [Gustin et al ., 2000] due to
limited observational data. A number of factors are thought to affect the exchange of Hg between surface
BEAL ET AL. ©2014. American Geophysical Union. All Rights Reserved. 1
PUBLICATIONS
Global Biogeochemical Cycles
RESEARCH ARTICLE10.1002/2013GB004780
Key Points:
• Hg deposition did not vary with
past precipitation, temperature,
and volcanism
• Maximum Holocene Hg uxes
occurred ~3 thousand years ago
• Modern Hg uxes are 3 times greater
than natural uxes
Supporting Information:
• Readme
• Table S1
• Table S2
• Table S3
• Table S4
• Table S5
• Figure S1
• Figure S2
• Figure S3
• Figure S4
• Figure S5
Correspondence to:
S. A. Beal,
Citation:
Beal, S. A., M. A. Kelly, J. S. Stroup, B. P.
Jackson, T. V. Lowell, and P. M. Tapia
(2014), Natural and anthropogenic varia-
tions in atmospheric mercury deposition
during the Holocene near Quelccaya IceCap, Peru, Global Biogeochem. Cycles, 28,
doi:10.1002/2013GB004780.
Received 26 NOV 2013
Accepted 27 MAR 2014
Accepted article online 31 MAR 2014
http://publications.agu.org/journals/http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1944-9224http://dx.doi.org/10.1002/2013GB004780http://dx.doi.org/10.1002/2013GB004780http://dx.doi.org/10.1002/2013GB004780http://onlinelibrary.wiley.com/journal/10.1002/(ISSN)1944-9224http://publications.agu.org/journals/
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reservoirs including biomass burning [Friedli et al ., 2003], permafrost thaw/freeze [Rydberg et al ., 2010], and
oceanic evasion [Strode et al ., 2007].
Use of Hg by humans began as early as 1500 B.C. in Egypt and Peru and continued later in parts of Asia and
the Roman Empire [Nriagu, 1979; Cooke et al ., 2009]. This early use primarily consisted of extracting the
common mineral form cinnabar (HgS) as the bright red pigment vermilion, although there are also early
accounts of metal amalgamation using liquid Hg0 [Nriagu, 1979]. Anthropogenic Hg emissions increased
dramatically in the late sixteenth century when Hg amalgamation for silver extraction was introduced to
South and Central America [Nriagu, 1993]. Hg was emitted during the smelting of cinnabar to form liquid Hg0
which occurred extensively in Huancavelica, central Peru, and during the heating of silver amalgams, which
occurred throughout the Andes but most notably in Potosí, Bolivia (Figure 1) [Robins and Hagan, 2012].
Estimates of preindustrial Hg emissions are based on historical records and anecdotes of past metal use
coupled with assumed emission factors, and they are subject to high uncertainty [Nriagu, 1993; Streets et al .
2011]. In addition, the spatial distribution of Hg emissions from preindustrial mining remains uncertain. Thereis strong evidence for local deposition in highly enriched soils and sediments near mining sites [Cooke et al .
2009; Robins et al ., 2012], limited evidence for regional (~200–500 km) transport [Beal et al ., 2013; Cooke et al .
2013], and no evidence for an impact of preindustrial Hg emissions on a global scale [Lamborg et al ., 2002]
In this study, we reconstruct atmospheric Hg deposition during the Holocene in a sediment core from a
headwater lake in southeastern Peru near Quelccaya Ice Cap (QIC). Past Hg deposition is recorded reliably in
lake sediments and is not affected by diagenetic changes [e.g., Biester et al ., 2007; Rydberg et al ., 2008]. We use
this continuous record of atmospheric Hg deposition and coregistered proxies for paleoenvironmental
change to (1) assess natural variability in Hg deposition by comparing the Hg record to local and regional
paleoclimate conditions and major volcanic eruptions, (2) evaluate the impact of preindustrial anthropogenic
emissions on Hg deposition in the study lake by examining the Hg record during periods of known
0 2 41
km
Yanacocha
YanacochaNegrilla
Huancavelica
HUM
Y To Potosí
65°W70°W75°W80°W
0°
5°S
10°S
15°S
Peru
0 400 800200km
a.) b.)
c.)
QuelccayaIce Cap
Figure 1. (a) Digital elevation model of northwestern South America with the locations of the study lake (Yanacocha), Laguna Negrilla, the mining center of
Huancavelica, and the late Holocene-active volcanoes El Misti (M), Ubinas (U), Huaynaputina (H), and Yucamane (Y) in the Andean CVZ. Black arrows represent
NCEP/NCAR reanalysis V1 annual average vector wind at 500 mb from A.D. 1948 to 2012 [Kalnay , 1996]. (b) False-color Landsat 7 image of Quelccaya Ice Cap (ligh
blue) and the location of Yanacocha. Bedrock ridges are apparent in gray-red colors, whereas glacially carved valleys with vegetation are green. (c) 180° panoram
image of the Yanacocha basin looking toward the east/northeast. The headwall is approximately 100 m above lake surface at its highest point. Red marker denote
approximate coring location for the YC1 and YANA11 cores.
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preindustrial metal use, and (3) quantify the extent of anthropogenic modication to natural Hg cycling by
calculating an atmospheric deposition Hg ux ratio using modern and preanthropogenic Hg uxes.
2. Study Site
The study lake informally known as Yanacocha is located in the South Fork valley on the western side of
Quelccaya Ice Cap (QIC) in the Cordillera Vilcanota of southeastern Peru (13.945°S, 70.875°W, 4910 m above
sea level; Figure 1). Yanacocha is a tarn that occupies 0.036 km2 in a catchment of 0.11 km2. The catchment is
composed of a sparsely vegetated and gently sloping colluvial apron that extends radially ~100 m from the
edge of the lake, beyond which a near-vertical ~100 m high ignimbrite bedrock headwall surrounds the
north, east, and south sides of the lake (Figure 1). Inows are limited to surface runoff from the catchment,
and a single outow on the west side of the lake is active only during the wet season. During the eld season
in June 2011, the lake exhibited constant pH (~8), temperature (~6 °C), and conductivity (~10 μS) with depth
(Figure S1 and Table S1), characteristic of a holomictic lake.
Situated near the eastern edge of the Andes at 4910 m above sea level, Yanacocha likely receives most of its
precipitation from easterly middle-upper troposphere ows in Austral Summer that bring moisture from the
Amazon Basin [e.g., Garreaud et al . [2003]]. Precipitation and atmospheric conditions at the study site have
likely changed with the position of the Intertropical Convergence Zone and El Niño –Southern Oscillation,with drier conditions during modern-day El Niño and wetter conditions during modern-day La Niña [e.g.,
Garreaud et al ., 2003].
An expanded QIC prior to ~12.8 ka (kiloannum; dened here as thousands of years before A.D. 1950) had a
terminus position ~2 km downvalley from Yanacocha, covering the lake with glacial ice [Kelly et al ., 2012].
Retreat of QIC began ~12.3 ka, leaving the Yanacocha catchment by at least 11.6 ka and remaining ~3 km
upvalley of Yanacocha during the Holocene [Kelly et al ., 2012]. The bedrock of the headwall surrounding
Yanacocha prevented inows of QIC meltwater from entering the lake during the Holocene. Therefore, any
material transported to the lake occurred either by surface runoff within the relatively small catchment or
atmospheric deposition.
Yanacocha is removed from major development. The nearest major population center is Cusco, located
~130 km away. Present-day land use in the vicinity of Yanacocha is limited to sparse livestock grazing. We
are not aware of any mining near the margins of QIC, and although there are currently no large-scalemining operations in the region, a large silver-lead-zinc mine is in planning stages ~25 km northwest of
Yanacocha. Small-scale and artisanal gold mining is prevalent in the Amazon basin ~120 km away, but this
mining was shown not to be a major contributor of Hg to high-elevation lakes in southeastern Peru [Bea
et al ., 2013].
3. Methods
3.1. Core Collection and Processing
We collected a long (4 m) sediment core, YANA11, near the center of Yanacocha and at its greatest water depth
(5.5 m) in June 2011. We used a Bolivian coring system from a oating platform to retrieve ~1 m drives of
sediment into polycarbonate tubes, collecting two adjacent cores offset by ~50 cm. Core tubes were capped
kept unfrozen in the eld, and then shipped from Cusco to the National Lacustrine Core Facility (LacCore) at the
University of Minnesota. At LacCore, we split the polycarbonate core tubes and took high-resolution coreimages. Working halves of each core drive were shipped to Dartmouth College for subsequent analyses, and
archive halves are stored at the LacCore repository.
We also collected a short (40 cm) sediment core, YC1, adjacent to the YANA11 core using a gravity corer
that preserves the sediment-water interface. This core was collected prior to YANA11 to avoid disturbance
of the sediment-water interface. YC1 was extruded in the eld at 1 cm intervals and stored in Whirlpak
bags [Beal et al ., 2013].
3.2. Geochemical Analyses
We sampled the YANA11 core at continuous 1 cm intervals using acid-clean polystyrene spoons. The sample
from YANA11 and YC1 were freeze-dried in new polypropylene centrifuge tubes, homogenized in an agate
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mortar and pestle, and subsampled for loss on ignition (LOI), biogenic silica (BSi), major and trace metals, and
heavy mineral separations.
3.2.1. Loss on Ignition and Biogenic Silica
We performed LOI in three stages: 110°C overnight, 550°C for 4 h, and 1000°C for 2 h. BSi was determined at
Northern Arizona University by molybdate-blue reaction and spectrophotometry following Mortlock and
Froelich [1989]. Bulk density was calculated based on water content and assumed densities for the organic
(1.4gcm3), carbonate (2.7 g cm3), and inorganic (2.0 g cm3) components determined by LOI.
3.2.2. Major and Trace Metals
We determined total Hg using a Milestone DMA-80 on ~50 mg subsamples. One of the Standard Reference
Materials (SRMs) IAEA-SL-1 (lake sediment), STSD-1 and STSD-2 (stream sediment), and NIST-1547 (peach
leaves) was run every 10 samples. Measured SRM concentrations (Table S2) were within their published 95%
condence intervals. Sample replicates were run every 10 samples with typical precision (relative percent
difference for n = 2, relative standard deviation for n≥3) of less than 10%. We also extracted ~200 mg
subsamples by strong acid (9:1 HNO3:HCl) in open microwave vessels at 90°C and analyzed the leachates for
metal concentrations (henceforth referred to as Mext) by quadrupole ICP-MS (Agilent 7700x), running
calibration checks and blanks every 10 samples. Typical precision on replicate samples for detectable analytes
was less than 10%. Allconcentrations are expressed as mass of metal per mass of dry sediment. In addition,tota
metals were measured at 0.5 cm resolution on archive core halves by ITRAX core-scanningXRF at the Universityof Minnesota Duluth with a dwell time of 30 s [Croudace et al ., 2006].
3.2.3. Heavy Mineral Separation and Analysis
We separated the heavy mineral fraction of selected samples by mixing ~500 mg of freeze-dried sediment
with 10 ml of sodium polytungstate adjusted to a density of 2.8 g cm3, placing the mixtures in an ultrasonic
bath for 30 min and centrifuging the mixtures for 90 min at 4500 rpm. This separation procedure
accommodates a theoretical minimum cinnabar (8.1 g cm3) particle diameter of 65 nm following the
equation in Plathe et al . [2013]. We rinsed the heavy fraction by following the above ultrasonic and
centrifugation steps with 10 ml of deionizedH2O, repeated 3 times. We digested andanalyzed selected heavy
fraction samples for metal concentrations (henceforth referred to as Mhvy) using the same methods
described above for bulk samples, while accounting for contamination by the heavy liquids with one
procedural blank for every ve samples. For certain nondigested samples, we dried the heavy fractions and
studied them using a scanning electron microscope (SEM; Hitachi TM3000) with energy-dispersive X-ray
spectroscopy (EDS).
3.3. Chronology
The composite record (hencefor th the Yanacocha record) includes YC1 from 0 to 27 cm depth and
YANA11 from 27 to 333 cm depth. We correlated the offset drives from YANA11 based on visual
stratigraphy and then correlated YC1 to YANA11 using LOI550 (R = 0.90, p
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4. Results
4.1. Stratigraphy and Age-Depth Model
The composition of the Yanacocha record is a
diatomaceous gyttja from the top of the core to
a depth of 333cm (Figure 2). Below 333cm, thelithology is uniformly silt and clay. A macrofossi
just above this abrupt transition from silt and
clay to gyttja dates to 12.3 ka and likely marks
the termination of meltwater input caused by
recession of QIC behind the bedrock ridge
surrounding Yanacocha. This basal age is older
than two previously reported 14C ages (both
11.2 ka) in Yanacocha basal sediments from
slightly above the transition in another core
[Kelly et al ., 2012]. The Yanacocha record
exhibits constant sedimentation throughout
the Holocene with no evidence for a hiatus in
either the age-depth model or the stratigraphy
4.2. Holocene Sedimentology
Organic matter (LOI550) and BSi, proxies for
productivity in the lake, each comprise between
~20 and 60% of Yanacocha sediments and are
signicantly inversely correlated throughout
the Holocene (Figure 3). BSi is high (~38–55%)
and LOI550 is low (~10–30%) from 12.3 ka to
6.5 ka (Figure 4), followed by relatively low BSi
(~26–38%) and high LOI550 (~31–50%) from 6.5
to 4.7 ka. Subsequent to 4.7ka, BSi and LOI550
remain within their early Holocene values,except for a brief reversal from 1.1 to 0.6 ka
when BSi is low and LOI550 is high. Total Ti, a
proxy for total lithogenic input, is relatively high
in the early Holocene from ~12.3 to 9 ka,
followed by lower values from ~7 to 5 ka.
Higher than average Ti persists from ~4.8 to
3 ka and then is variable from ~3 ka through
the late Holocene.
4.3. Hg Variability During the Holocene
Hg concentrations in the Yanacocha record
range from a minimum of 13 μg kg1 at
8.9 ka to a maximum of 115μg kg1
at 3.2 ka (Figure 4). Pre-3.5 ka Hg concentrations are relatively stable(mean ± 1σ : 32 ± 9 μg kg1), except from ~10 to 9 ka when Hg concentrations are relatively elevated
(~40–60 μg kg1). An abrupt increase in Hg concentration occurs at 3.4 ka and reaches the Holocene
maximum concentration at 3.2 ka, followed by a steady decline to pre-3.5 ka values by ~2.5ka. Slightly
elevated Hg concentrations (~45 μg kg1) persist from 1.5 to 0.5 ka. An abrupt increase beginning
in ~ A.D. 1480 is followed by consistently elevated concentrations (46–75 μg kg1) until the most recent
sediment in A.D. 2011.
The record of Hg ux is largely a reection of the record of Hg concentration, as it is the product of Hg
concentration and sedimentation rate (Figure S4). Pre-3.5 ka Hg uxes are ~1.0–1.5μg m2 a1, compared to a
maximumof 6.7μg m2 a1 at 3.2ka andaverage post-A.D. 1980 uxes of ~4.1μg m2 a1. The main deviation
of Hg ux from concentration occurs from ~1.5 to 0.5 ka, concurrent with increased LOI550 (Figure 4). Because
Figure 2. Compositeimage for theYANA11 core and theage-depth
model including calibrated 14
C age ranges (blue points) and 210
Pb
ages (red points).
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estimates of Hg ux are subject to high
uncertainty, particularly in older records such as
this one that are dependent upon a limited
number of ages, we use Hg concentrations to
determine secular changes in Hg deposition and
time-averaged Hg uxes to calculate an Hg
ux ratio.
4.4. Heavy Mineral Characterization
The composition and morphology of minerals
contained in the heavy fraction of sediment
(>2.8gcm3) provide insight into the role of
sulde minerals in Hg deposition. We analyzed 14
heavy fraction samples for metal composition and
six heavy fraction samples by SEM, with a particular focus on the period 3.3–3.2 ka that is characterized by a
peak in Feext concentrations and Holocene-maximum Hg concentrations (Figure 5b). We did not identify Hg
suldes in any of the six samples analyzed by SEM, but we found abundant framboidal pyrite in one sample
from 3.3 ka with diameters of 10–15μm (Figure 5a) and Fe, S, and C spectral peaks identied by EDS. Apronounced one-sample peak in concentrations of Fehvy and Shvy at 3.2 ka (Figure 5) has a molar Fe:S ratio o
1:1.79 similar to observed framboidal pyrite and highly elevated concentrations of As hvy, Aghvy, and Tlhvy
[Large et al ., 2001]. Although the Hghvy concentration is relatively elevated in this sample, the percent of Hg in
the heavy fraction (%Hghvy) is not relatively elevated (Figure 5b).
5. Discussion
5.1. Depositional Pathway
We rst test the hypothesis that atmospheric deposition is the primary source of Hg to Yanacocha by comparing
Hg concentrations and sedimentology in the Yanacocha record during the entire record (12.3 to 0 ka) and jus
R2 = 0.5317
p < 0.001
0
10
20
30
40
50
60
0 10 20 30 40 50 60
B
S i ( % )
LOI550
(%)
12 ka
Figure 3. Correlation between organic matter (LOI550) and BSi
content in the Yanacocha record from 12 to 0 ka.
Figure 4. Hg deposition (concentration and ux) and coregistered proxies of environmental conditions (LOI550 and BSi) and
lithogenic input (Ti) in the Yanacocha record from 12.3 ka to A.D. 2011. Dashed line represents Holocene average total Ti.
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the preanthropogenic period (dened and
used herein as 12.3 to 3.5 ka, based on
previous records and historical information
[Nriagu, 1979; Martínez-Cortizas et al ., 1999;
Cooke et al ., 2009]). Previous millennial-scaleHg records in lake sediments relate changes
in Hg uxes to groundwater level [ Jacobson
et al ., 2012], lithogenic input from weathering
within the catchment [Thevenon et al ., 2011],
and mobilization of Hg from soils [Cannon
et al ., 2003]. However, the lack of correlations
of Hg concentration with LOI550 and with Ti
(Figure 6) shows that organic matter and
lithogenic input, respectively, do not have
signicant effects on Hg deposition in
Yanacocha. The only statistically signicant
correlation is between Hg and LOI550 during
the preanthropogenic period, but thiscorrelation has a very weak effect
(R2 = 0.049). The absence of increased Hg
deposition when lithogenic input was
relatively high during the lake’s early stage
(~12.3 to 11 ka; Figure 4) indicates that
weathering of surrounding bedrock is not a
signicant source of Hg. Based on these
correlations, the small catchment area, and the
lack of stream inputs, we conclude that
atmospheric Hg deposition is the primary
source of Hg to Yanacocha sediments.
One exception to this interpretation is thebrief association of increased Feextconcentrations and framboidal pyrite with
near-maximum Hg concentrations from 3.3 to
3.2 ka. Framboidal pyrite often contains many
heavy metals including Hg [e.g., Schoonen
[2004]], presumably due to the af nity that Hg
has for S and the large pyrite surface area
afforded by the crystallite subunits within
each framboid (e.g., Figure 5a). Chemical
preservation of framboidal pyrite is not
inuenced by diagenesis in lake sediments
[Suits and Wilkin, 1998]. Framboidal pyrite is
formed either in euxinic water columns or
within upper sediments, near the sediment-
water interface, where anoxic conditions
occur [Suits and Wilkin, 1998]. The relatively
large diameters of the observed framboids
(10–15μm; Figure 5a) and low modern water
sulfate concentration (238 μg L1; Table S1)
are consistent with formation within the
sediment as opposedto within the water column [Wilkin et al ., 1996]. Therefore, we hypothesize that framboida
pyrite was formed within Yanacocha’s uppermost sediments due to external input of oxidized Fe and S, which
may have sequestered Hg from the lake during the period of elevated Feext concentrations from 3.3 to 3.2 ka
5
10
0.2
0.4
0.6
F e
/ F e
( % )
F e
( g k g )
Fehvy
S
( g k g )
Shvy
5
10
0.2
0.4
0.6
C u
/ C u
( % )
C u
( m g k g )
Cuhvy
40
80
1200 1 2 3 4 5 6 7
H g ( µ g k g )
Hghvy
0
20
40
5
10
15
H g
/ H g
( % )
H g
( µ g k g ) A g
( µ g k g
)
Aghvy
0
5
10
1.0
4.0
2.0
2.0
A s
/ A s
( % )
A s
( m g k g )
Ashvy
2345
0.5
0.4
0.3
0.2
0.1
67
F e
( g k g )
0.0
0.2
0.4
0 1 2 3 4 5 6 7
T l
( m g k g )
Age (ka)
Tlhvy
b.)
10 µm 10 µm
a.)
Figure 5. (a) SEM images of framboidal pyrite from the heavy mineral
fraction of a Yanacocha sediment sample at 3.3 ka. (b) Comparison of
the timing of the Hg peak at ~3 ka with framboidal pyrite presence
(lled square) and absence (open squares), extractable Fe concentra-
tions, and heavy mineral fraction metal concentrations (gray lines with
diamonds) and percentages (black circles). Gray shading highlights the
~100 year period of elevated Feext concentrations.
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in the Yanacocha record, Hg
concentrations and uxes remain
relatively constant during
preanthropogenic time (Figure 4).
5.2.2. Temperature
While Holocene paleotemperature
proxies in the Central Andes are scarce
some paleotemperature information
has been inferred from past glacier
extents of QIC [Kelly et al ., 2012;
Thompson et al ., 2013; Stroup et al .,
2014]. Radiocarbon ages of in situ
plants show that QIC was smaller than
at present prior to ~7 ka, suggesting
relatively warm conditions during this
time. A subsequent advance of QIC that
overran and entombed plants dating to
between ~7 and 5 ka [Thompson et al .,2006, 2013; Buffen et al ., 2009], during
relatively dry middle Holocene
conditions (see section 5.2.1), was likely
inuenced by cooling. Relatively
constant Hg concentrations and uxes
from ~8 to 5 ka (Figure 4) suggest that
regional temperatures did not strongly
inuence atmospheric Hg deposition in
Yanacocha. This nding is consistent
with an Hg record from lake sediments
in arctic Canada in which there is no
relationship between Hg deposition
and Holocene temperature changes[Cooke et al ., 2012].
5.3. Volcanism and Hg Deposition
Volcanic eruptions with a Volcanic
Explosivity Index (VEI)≥6 (i.e., Plinian
eruptions that inject volcanic gases into
the stratosphere) are known to have
occurred throughout the Holocene
[Siebert and Simkin, 2002]. Hg records
from peat cores in Switzerland [Roos-
Barraclough et al ., 2002] and ice cores in
Wyoming, United States [Schuster et al ., 2002], report short-lived (~100 year for peat, ~1–10 year for ice) peaksin Hg deposition, usuallymanifested as a greater than tripling of Hg ux, that are similar in timing to explosive
volcanic eruptions in both the Northern and Southern Hemispheres. Based on the temporal resolution of the
Yanacocha record (median = 26 years per sample), we would expect to nd Hg peaks during times of known
volcanic eruptions. However, Hg deposition in the Yanacocha record during the preanthropogenic period is
relatively stable, and eruption-related increases in Hg deposition are not distinguishable from the noise
(Figure 4). Continuous volcanic degassing and more frequent smaller eruptions may contribute signicant
amounts of natural Hg to the atmosphere [Pyle and Mather , 2003] but similarly cannot be distinguished in the
Yanacocha record.
The Andean Central Volcanic Zone (CVZ) is located ~300–400 km from Yanacocha (Figure 1) and has
hosted a number of Plinian eruptions since ~3.5 ka (Figure 7). The VEI 5 eruption of the volcano Yucamane
LY2
LY1
10
102
103
104
Huaynaputina
UbinasEl Misti
Yucamane
4
5
6
0 1 2 3 C V Z E r u p
t i o n s ( V E I )
Age (ka)
Negrilla
0
25
50
75
100
H g F l u x ( µ g m - 2 a
- 1
)
H g F l u x ( µ g m - 2 a
- 1 )
2
4
6
8
1
3
5
7
20
40
60
80
100
120-2000-1000010002000
Year AD/BC
H g F l u x ( µ g m - 2 a
- 1 )
P b
e x t
( m g k g - 1 )
H g C o n c .
( µ g k g - 1 )
Figure 7. The Yanacocha Hg (green and blue) and Pb (red) records com-
pared with Hg ux records from Laguna Negrilla [Cooke et al ., 2013] and
two lakes near Huancavelica (LY1 and LY2) [Cooke et al ., 2009]. Also shown
are volcanic eruptions with a VEI of ≥4 in the Andean CVZ during the past
4000 years [Siebert and Simkin, 2002]. Gray shading highlights the early
and later phases of anthropogenic metal use in the Andes as dened by
Cooke et al . [2009].
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(~3270 14C yr B.P.) [Siebert and Simkin, 2002] roughly overlaps in timing with the abrupt increase in Hg and
Feext concentrations and framboidal pyrite appearance from ~3.3 to 3.2 ka. Deposition of volcanic sulfate
and Fe to Yanacocha from this eruption may have provided adequate reactants for framboid formation within
the lake’s surface sediments and sequestration of Hg from the water column or volcanic ash. Further evidence
for volcanism at ~3.2 ka comes from highly enriched Ashvy, Aghvy, and Tlhvy concentrations in Yanacochasediments (Figure 5b), which, in addition to having an af nity for framboidal pyrite [Schoonen, 2004; Neumann
et al ., 2013], are also emitted predominantly from volcanic sources [Kellerhals et al ., 2010]. If volcanism were
responsible for the sharp increase in Hg concentration at ~3.3ka, then the Hg is retained in the less dense
fraction of sediment (< 2.8gcm3) or in nanometer-scale particles because of near-constant %Hghvy during
this time (Figure 5b).
The largest eruption in the CVZ during the Holocene was the VEI 6 eruption of the volcano Huaynaputina,
historically dated to 19 February, A.D. 1600. Ashfall from this eruption with particle diameters of ~20 μm is
registered in ice cores from QIC [Thompson et al ., 1986], and lava ows on Huaynaputina have a similar Fe
content (~3–6 wt %) to those on Yucamane [Mamani et al ., 2008]. Hg concentrations in the Yanacocha record
do not register this volcanic eruption, but instead generally decline between A.D. 1590 and 1730 (Figure 7)
This nding is consistent with a lake sediment record from Southern Chile that shows relatively constant Hg
uxes within and subsequent to visible tephra layers from three separate Holocene eruptions [Hermanns and
Biester , 2013]. In contrast to the peat and ice core records that show volcanic Hg peaks, the overall lack of
volcanic events registered in the Yanacocha Hg record from both regional and global eruptions suggests tha
large volcanic events during the Holocene had negligible decadal- to century-scale effects on atmospheric
Hg levels.
5.4. Anthropogenic Activity and Hg Deposition
5.4.1. 1450–500 B.C.
An early phase of increased atmospheric Hg deposition in the Yanacocha record began at 1450 B.C. (3.4 ka)
reached a maximum at 1200 B.C. (3.15 ka), and remained elevated until at least 500 B.C. (2.45 ka; Figure 7).
This peak is not associated with a change in any of the other bulk analytes in the Yanacocha record except fo
a brief peak in Feext concentrations from 1340 to 1240 B.C. associated with the presence of framboidal pyrite
and discussed above. A mining dust source of Fe and S for framboidal pyrite formation is unlikely due to the
low solubility of most sulde ore minerals. However, increased concentrations of Cuhvy, Cohvy, Nihvy, Mohvy,and Pbhvy from 1650 to 1500 B.C. (Figures 5b and S5) suggest an early mining dust source to Yanacocha.
These metals are commonly found together within the same sulde deposits and can be accessible at the
surface in areas affected by glaciation in Peru [Petersen, 1965]. This period of enhanced chalcophile
deposition preceded the abrupt increase in Hg deposition at 1400 B.C. and is concurrent with a slight
monotonic increase in Hg concentration and ux. Following the peak in Hg deposition at 1200 B.C. , the
endurance of elevated Hg deposition (5.0 to 6.8 μg m2 a1) for nearly a millennium implies a persistent
local anthropogenic source of Hg to Yanacocha. Furthermore, the shapes of Hg concentration and ux
peaks, characterized by onsets with abrupt increases and subsequent slow declines to background levels, are
similar to preindustrial anthropogenic peaks found in cores from the headwater lake Laguna Negrilla in Peru
(Figure 7) [Cooke et al ., 2013] and a saltwater lagoon in France [Elbaz-Poulichet et al ., 2011]. Near-constant %Hghvy(Figure 5b) suggests that Hg from mining during this time was likely emittedeither as ultrane (< 65 nm diameter
cinnabar particles or as Hg0 /Hg2+ that was subsequently bound to less dense materials.
The timing of the early phase of Hg deposition in Yanacocha is identical to precolonial cinnabar mining
registered in the lakes LY1 and LY2 located ~10 km from Huancavelica (Figure 7) [Cooke et al ., 2009]. Cooke
et al . [2009] found that the Hg deposited during pre-Incan time was primarily bound as cinnabar, and neither
an increase in Hg uxes nor a distinct change in Hg isotopes was observed during pre-Incan time in a
sediment core from Laguna Negrilla, located ~200 km southeast of Huancavelica (Figure 1) [Cooke et al .,
2013]. This spatial limitation of Hg emissions from Huancavelica would have likely precluded the longer
distance transport to Yanacocha, located ~460 km southeast of Huancavelica (Figure 1), which suggests tha
the early phase of Hg deposition in Yanacocha is from pre-Incan metal use near the catchment.
We hypothesize that the early phase of anthropogenic Hg deposition in Yanacocha was due to a three-part
sequence of events. First, mining of a nearby polymetallic sulde deposit provided minimal Hg contributions
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to Yanacocha from 1650 to 1450 B.C. Second, a combination of nearby mining emissions, potential volcanic
emissions, and/or an af nity of Hg for framboidal pyrite caused the abrupt increase in Hg deposition from
1450 to 1200 B.C. Third, ongoing nearby mining supplied decreasing amounts of Hg to Yanacocha from
1200 B.C. to at least 500 B.C.
5.4.2. A.D. 1480–2011
A later phase of enhanced atmospheric Hg deposition in Yanacocha is registered from ~ A.D. 1480 to 2011.
Increased Hg concentrations (55–
73 μg kg1
) from ~ A.D. 1480 to 1640 (Figure 7) may reect both cinnabarmining in Huancavelica, rst by the Inca from ~ A.D. 1450 and then by the Spanish from A.D. 1564 onward
[Cooke et al ., 2009], and the concurrent growth of Ag rening using Hg amalgamation throughout the Andes
beginning~ A.D. 1570 [Robins and Hagan, 2012]. A simultaneous peak in Pbext concentrations from ~ A.D.
1500 to 1670 (Figure 7) is similar in timing to the initial use of Pb for smelting Ag ores [Guerrero, 2012]. If Hg
was cotransported with aerosol-based smelting emissions, it must either reside as cinnabar with particle
diameters less than 65 nm (because %Hghvy does not change substantially (Figure 5b)) or as Hg adsorbed to
less dense aerosols. Atmospheric transport of Hg from Huancavelica to Laguna Negrilla between ~ A.D. 1450
and 1650 is supported by a pronounced increase in Hg uxes (~10 fold increase, up to 82 μg m2 a1;
Figure 7) and a shift in the mass-dependent fractionation of Hg isotopes [ Cooke et al ., 2013]. The relatively
small increase in Hg deposition in Yanacocha compared to Laguna Negrilla suggests that Hg emissions from
Huancavelica were, at least during the time of Inca control (~A.D. 1450–1564), predominantly in the solid
phase and decreased in spatial extent with distance from Huancavelica.
The shift to elemental Hg production for silver mining between A.D. 1564 and 1810 likely inuenced more
globally distributed Hg emissions [Nriagu, 1993; Robins and Hagan, 2012]. Decreased Hg concentrations and
uxes in the Yanacocha record from ~ A.D. 1650 to 1750 are followed by a general increase coincident in
timing with estimated maximum Hg0 emissions in South and Central America from ~ A.D. 1750 to 1810
[Nriagu, 1993]. However, increasing Hg uxes are not evident during this period in Laguna Negrilla (Figure 7)
or in two lakes ~65 km west of Yanacocha [Beal et al ., 2013]. The spatially inconsistent signal of Hg uxes in
this region suggests that mining dust continued to contribute signicant amounts of Hg to certain lakes and
that any increase in Hg deposition due to anthropogenic Hg0 emissions was relatively negligible during the
preindustrial period. A more localized distribution of preindustrial Hg emissions is consistent with new
chemical modeling by Guerrero [2012] that shows solid calomel (Hg2Cl2) comprised up to 90% of Hg losses
from Ag rening in the Hispanic New World. Post-industrial increases in Hg deposition in the Yanacocha
record were likely caused by global Hg0 emissions.
5.4.3. Modern Flux Ratio
The extent of anthropogenic modication to natural Hg cycling is typically represented by an Hg ux ratio,
which is the ratio of recent Hg uxes to background uxes that occurred at some earlier time (i.e., from A.D
1800 to 1850 in most sediment records). Table 1 lists mean Hg concentrations and uxes in the Yanacocha
record for key time periods during the Holocene, weighted on the length of time each sample represents.
Because of the evidence for signicant pre-A.D. 1850 anthropogenic deposition in the Yanacocha record,
natural Hg uxes are likely only represented prior to 3.5 ka in this record. Whereas Hg concentrations remain
remarkably constant from 12.3 to 3.5 ka, Hg uxes gradually decrease with increasing age (Table 1). This is
likely an artifact of the age-depth model. We therefore calculate a best approximation of the Hg ux ratio in
the Yanacocha record as time-weighted mean post-A.D. 1980 uxes (4.0μg m2 a1) over pre-3.5 ka uxes
(1.4μg m2 a1), yielding a ux ratio of 3.0 ± 1.5. This ux ratio, which accounts for total anthropogenic
Table 1. Time-Weighted Means for Hg Flux and Concentration During Periods Representative of Natural an
Anthropogenic Conditions
Flux (μg m2
a1
) Concentration (μg kg1
)
Period Mean σ Mean σ n
Pre-8 ka 1.0 0.4 31 11 58Pre-6 ka 1.2 0.5 31 10 91
Pre-3.5 ka 1.4 0.6 32 9 189
Post-A.D. 1980 4.0 1.0 68 4 5
Post-A.D. 2000 3.4 0.3 70 1 2
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modication to the global Hg cycle during the Holocene, is in good agreement with sediment records that
use the period A.D. 1800 to 1850 as background uxes from two other lakes in southeastern Peru (i.e.,
4.0 ± 1.0) [Beal et al ., 2013] and from lakes around the world (i.e., on average 3.5) [Biester et al ., 2007]. The
discrepancy between our Holocene Hg ux ratio (3.0 ± 1.5) and the modeled 7.5-fold enrichment since
2000 B.C. by Amos et al . [2013] indicates that preindustrial Hg emissions were either not as globally
distributed as assumed in the model or were not as persistent in labile surface reservoirs. Revised
accounting for losses of Hg0 to the atmosphere from preindustrial mining may improve the accuracy of
global Hg models and help reconcile them with sedimentary records.
6. Conclusions
During the preanthropogenic period, atmospheric Hg deposition recorded in Yanacocha was relatively
constant and did not vary with changes in local and regional climate. Holocene volcanic eruptions are
generally not registered in the Hg record despite a number of Plinian eruptions that occurred both globally
and within the Andean CVZ. An early phase of enhanced Hg deposition in Yanacocha began in 1450 B.C.
(3.4 ka) likely due to a combination of nearby mining emissions and volcanic input of Fe and S that led to
framboidal pyrite formation and possible Hg sequestration between ~ 1340 and 1240 B.C. The endurance o
this early phase of enhanced Hg deposition until 500 B.C. is coincident with known pre-Incan cinnabar mining
in Huancavelica. The limited spatial distribution of Hg emissions from Huancavelica and the magnitude of Hg
uxes during this early phase, which are greater than modern uxes, indicate a separate and nearby mining
source of Hg to Yanacocha, likely from within the Cordillera Vilcanota. Increased concentrations of Hg and
Pbext from ~ A.D. 1480 to 1640 suggest sources of Hg to the lake rst from Incan cinnabar mining and then
from colonial Hg production and Ag rening. The agreement of the Holocene ux ratio determined from the
Yanacocha record with ux ratios determined from post-industrial lake sediment records suggests that
preindustrial Hg emissions either were not well distributed globally or did not have a long-lasting impact on
the global atmospheric Hg burden.
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Acknowledgments
This research was supported by NSF
Awards EAR-1003460 to Kelly and EAR-
1003072to Lowell, and a LacCore visiting
graduate student award to Beal. Wethank Colby Smith, Hannah Baranes,
Yves and Elena Chemin, and the
Crispin Family for eld work and
logistics; Amy Myrbo, Devon Renock,
and Jenny Howley for lab assistance;
and Colin Cooke and David Pyle for
providing constructive reviews of this
manuscript. The primary data for this
paper can be accessed for free in the
supporting information.
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