beal etal gbc 2014

8/9/2019 Beal Etal GBC 2014

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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,

[email protected]

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.

Global Biogeochemical Cycles 10.1002/2013GB004780



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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

)


- 1 )

2

4

6

8

1

3

5

7

20

40

60

80

100

120-2000-1000010002000

Year AD/BC


- 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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