Historic and Industrial Lead within the Northwest Pacific Ocean

Subscriber access provided by University of Newcastle, Australia

Article

Historic and industrial lead within the Northwest Pacific Ocean evidenced by lead isotopes in seawater Cheryl M Zurbrick, Céline Gallon, and A. Russell Flegal Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.6b04666 • Publication Date (Web): 03 Jan 2017 Downloaded from http://pubs.acs.org on January 11, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Environmental Science & Technology is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 32

Environmental Science & Technology

1

1

Historic and Industrial Lead within the Northwest Pacific

2

Ocean Evidenced by Lead Isotopes in Seawater

3

Cheryl M. Zurbrick α,

4

α

5

Santa Cruz, California 95064, United States

6

β

7

California 95064, United States

γ, *

, Céline Gallon β, δ, A. Russell Flegal α, β

WIGS, Environmental Toxicology, University of California Santa Cruz, 1156 High Street,

Institute of Marine Sciences, University of California Santa Cruz, 1156 High Street, Santa Cruz

8 9

KEYWORDS: Lead, Lead isotopes, North Pacific Ocean

10 11

TOC/ABSTRACT GRAPHIC:

12

ACS Paragon Plus Environment


Page 2 of 32

2 13

ABSTRACT

14

We report the continued lead (Pb) contamination of the Northwest Pacific Ocean in 2002 and

15

present the first comprehensive Pb isotope dataset for that region. In the upper ocean, a Pb

16

concentration maxima (64 – 113 pmol kg-1) extended throughout the entire North Pacific

17

Subtropical Gyre (NPSG). We determined most of the Pb in this feature was from industrial

18

emissions by many nations in the 1980s and 1990s, with the largest contributions from leaded

19

gasoline emissions. In contrast, the deep water (> 1000 m) Pb concentrations were lower (6 – 37

20

pmol kg-1), and constituted a mix of background (natural) Pb and anthropogenic Pb inputs from

21

preceding decades. Deep water below the Western Subarctic Gyre (WSAG) contained more

22

industrial Pb than below the NPSG, which was attributed to a calculated 60-fold greater flux of

23

particulate Pb to abyssal waters near the Asian continent. Assuming Pb isotope compositions in

24

the North Pacific Ocean were homogenous prior to large-scale 20th century anthropogenic inputs,

25

this evidence suggests a relatively faster change in Pb isotope ratios of North Pacific deep water

26

below the WSAG versus the NPSG.

27 28


Page 3 of 32


3 29

INTRODUCTION

30

With the nearly global phase-out of leaded gasoline over the past four decades, there has been a

31

dramatic decrease in lead (Pb) concentrations in North Pacific surface waters similar to that

32

observed in the North Atlantic Ocean. 1–3 In the North Atlantic, surface ocean Pb concentrations

33

decreased from an average of 160 pmol kg-1 in 1979 to 30 pmol kg-1 in 1998.4, 5 Concurrently,

34

the central North Pacific surface ocean Pb concentrations decreased from an average of 64 pmol

35

kg-1 in 1977 to 34 pmol kg-1 in 1997 . 2, 6 The residence time of Pb in North Pacific surface

36

waters is 6 - 20 months, 7 and so these declines were primarily attributed to the elimination of

37

leaded gasoline in both Japan in the 1980s and North America in the 1990s. 2, 8, 9

38

Although the central North Pacific Subtropical Gyre (NPSG) surface water Pb

39

concentrations declined by almost 50% over two decades, the decreasing trend has stagnated

40

since then. Previous cruises to the central NPSG documented similar Pb concentrations in 1997 –

41

1999 (34 ± 5 pmol kg-1), 2 2002 (44 ± 8 pmol kg-1), 1 and 2004 – 2005 (35 ± 11 pmol kg-1). 10

42

Studies have shown that atmospheric deposition is the major source of Pb to North Pacific

43

waters. 11, 12 Between 30˚ and 60˚ N the dominant wind direction is from the west and as a result

44

large quantities of aerosols (natural and anthropogenic) are blown from upwind terrigenous

45

sources into the North Pacific Ocean. 13, 14 The persistence of Pb in central NPSG surface waters

46

can be, in part, attributed to the fact that many windward countries (e.g., Indonesia and China)

47

did not complete the phase-out of their leaded gasoline until mid-2000 and Russia did not until

48

2003 (Figure 1a). 15, 16 However, the relatively short residence time of Pb in oceanic surface

49

waters and the systematic phase-out of leaded gasoline in Asia which began in the 1990s

50

suggests elevated Pb concentrations in the North Pacific Ocean must result from more than

51

dwindling leaded gasoline inputs.



Page 4 of 32

4 An alternative hypothesis is that the decrease in leaded gasoline consumption was

52 53

accompanied by a simultaneous increase in industrial atmospheric Pb emissions from booming

54

economies in Asian nations as evidenced by increased coal consumption and metal smelting

55

(Figure 1b, c). Atmospheric Pb measurements support this hypothesis. Chinese aerosols from

56

1994 (before phase-out) had comparable Pb concentrations in 2002 (24 months after phase-out).

57

17 - 19

58

non-ferrous metal smelting, and other industrial activities that produce metallurgic dust. In 2002,

59

aerosol Pb concentrations were collected at sea between Japan and the central NPSG; based on

60

enrichment factors and aerosol back trajectories, the Pb in those marine aerosols was attributed

61

to industrial Pb emissions from Asia. 1

The sustained atmospheric Pb concentrations were found to be a result of coal combustion,

62

In addition, seawater data collected for this region in 2002 – 2004 support the proposal

63

that on-going inputs of industrial Pb emissions are comparable to previous inputs from leaded

64

gasoline emissions in the North Pacific Ocean. Gallon et al. 1 reported isotope ratios (206Pb/207Pb

65

= 1.157 – 1.161) in the surface waters of the Northwest Pacific collected in 2002, which closely

66

matched that of aerosols measured in 2001 over mainland China (206Pb/207Pb ≈ 1.16). 17, 18, 19 In

67

addition, they found Asian Pb isotope signatures in surface waters of the Western Subarctic Gyre

68

(WSAG; 206Pb/207Pb = 1.157 – 1.162) and the central NPSG (206Pb/207Pb = 1.163 – 1.169). In

69

2004, Wu et al. documented a similar Pb isotope ratio (206Pb/207Pb = 1.159) in NPSG surface

70

water. 10 These Pb isotope ratios are very different from the surface water isotope ratios of the

71

NPSG measured in 1979 (206Pb/207Pb = 1.184 – 1.196). 20 At that time, the major sources of Pb in

72

that region were attributed to emissions of leaded gasoline combustion in North America and

73

Asia.

74


Page 5 of 32


5 75

In the ocean interior, Pb is typically representative of when that water mass last

76

ventilated. 21, 22 For deep water in the North Pacific, this is ~1000 years ago. 23 However, the lone

77

stable Pb isotope profile in the central NPSG, collected in 2004, found that deep water Pb isotope

78

ratios were significantly different from pre-industrial Pb isotope ratios. 10 Wu et al. created a

79

mixing model to show that vertical Pb inputs of modern anthropogenic emissions over the past

80

100 years have begun to impact abyssal waters. 10 This isotope change is possible because of low

81

background Pb concentrations and the rapid rate at which particles sink (70 – 300 m d-1) 24, 25 as

82

compared with horizontal advection to the NPSG (~ 60 m d-1). 10, 23 The majority of particle-

83

bound Pb does not solubilize in the deep water column before settling on the ocean floor, so

84

temporal changes in Pb isotope ratios of deep waters are much slower than in upper ocean

85

waters. Therefore we anticipated that the deep water samples would be mostly preindustrial Pb

86

(i.e., background Pb from natural Asian loess deposition and benthic sediments) with a small

87

contribution from vertical inputs of particulate anthropogenic Pb.

88

The goal of this project was to determine the spatial distribution of Pb within the

89

Northwest Pacific Ocean at a point in time when atmospheric emissions of Pb were changing in

90

Asia, both to investigate anthropogenic perturbations to the North Pacific Ocean and to establish

91

a baseline for future studies of environmental change. We analyzed the Pb concentrations and

92

isotope ratios at 9 vertical profiles collected in 2002, near the beginning of a massive

93

industrialization period in Asia. These measurements were compared with the isotope signatures

94

of potential Pb sources and atmospheric Pb emissions estimates for the prior 30 years.



Page 6 of 32

6 95

EXPERIMENTAL SECTION

96

Seawater samples were collected from 1 May to 3 June, 2002, aboard the R/V Melville during

97

the Intergovernmental Oceanographic Commission’s 4th Global Investigation of Pollution in the

98

Marine Environment expedition (Figure 2). The voyage began in the Kuroshio Current near

99

Japan and had stations in both the WSAG and the NPSG. During the transect, waters were also

100

sampled in the Oyashio Current and Kuroshio Extension. 26 The warm Kuroshio Current flows

101

northward along the coast of Japan and the cold Oyashio Current flows southward from the

102

WSAG. Where the two currents meet the Oyashio subducts under the Kuroshio and they jet

103

eastward as the Kuroshio Extension. 26 The subsurface waters follow the same flow path, moving

104

at a reduced rate, 27 whereas deep waters move at a much slower rate. 23, 28

105

Seawater was collected at 9 vertical profile stations using 30 L GO-FLO ™ bottles,

106

which were modified for trace metal clean sampling and hung on a Kevlar ® line. 29 Unfiltered

107

subsamples were taken in an onboard trace metal clean laboratory under HEPA filtered air (Class

108

100) and collected in acid-cleaned 2 L low-density polyethylene bottles. Samples were acidified

109

with 8 mL ultrapure (sub-boiling quartz distilled) HCl and stored until processing and analysis

110

(2009 – 2012). Lead is highly contamination prone, but the agreement between this dataset and

111

those values reported for the North Pacific previously (see Figure 3c) demonstrates the high

112

quality of these samples.

113

The total dissolvable (dissolved + particles) Pb concentrations in seawater were measured

114

at the UC Santa Cruz Marine Analytical Lab using an on-line chelating resin extraction system 30

115

connected to a Thermo ELEMENT XR™ magnetic sector high resolution inductively coupled

116

plasma mass spectrometer (HR ICP-MS) as detailed in Zurbrick et al. 31 The Pb procedural

117

blanks, which were analyzed concurrently, were less than 6 pmol kg-1, the precision was within


Page 7 of 32


7 118

5%, and the detection limit was 5 pmol kg-1. All sample concentrations reported here are

119

corrected for the analytical blank by subtraction of the average blank on the corresponding

120

analytical day. For 6 samples, this blank accounted for 25% - 50% of the total Pb analyzed,

121

which is relatively high, but not enough to preclude the utility of these data. Lead isotopes in these samples were also processed and subsequently analyzed at UC

122 123

Santa Cruz using the method of Zurbrick et al. 32 Briefly, Pb was extracted from seawater (50 –

124

800 mL) using Toyopearl AF-Chelate 650 M ™ ion-exchange resin and eluted in a 1 mL extract

125

of ultrapure quartz-distilled 1.5 N HNO3; the Pb concentration in the extracts was ~ 5 nmol kg-1.

126

Extraction blanks comprised of ultra-high purity (18 MΩ cm) water (Millipore Milli-Q ®

127

Academic with Ultrapure Ionex Cartridge) acidified to pH ≈ 1.8 were less than 30 pg (0.1 – 1.3

128

pmol kg-1). The extracts were analyzed with HR ICP-MS in counting mode. Measurements of

129

204

130

natural abundances of mercury isotopes (204Hg/202Hg = 0.22988). Isotope ratios were calibrated

131

with concurrent measurements of National Institute of Standards and Technology (NIST)

132

standard reference material 981 (common lead) as listed in the Supplemental Information (SI,

133

available online). Replicate extractions and analyses of seawater samples (n = 2 – 9) had average

134

standard errors (2 σ) of 2‰ for 206Pb/207Pb and 4‰ for 208Pb/207Pb`. This precision agreed well

135

with our previously reported reproducibility for GEOTRACES intercalibration seawater. 32 The

136

206

137

in this work, but the values are included for reference in the SI.

138

Pb were corrected for isobaric interferences from 204Hg by monitoring 202Hg and assuming

Pb/204Pb ratios measured had standard errors (2 σ) of ~ 74 ‰. This large error precluded usage

Atmospheric Pb emissions from coal combustion, vehicular gasoline and metal smelting

139

were estimated for relevant countries. Details of methodology and the estimated values are

140

presented in the SI, part 2. In brief, the data for coal and road sector gasoline consumption were



Page 8 of 32

8 141

taken from the World Bank (data.worldbank.org). Lead from coal was calculated as in Lee et al.

142

33

143

quantity of coal burned, the average Pb content of coal was calculated for the available Asian

144

countries (China, Indonesia and India), 15, 34 - 35 and atmospheric Pb emissions from power plants

145

was assumed to be 80%. 15 Lead from gasoline was calculated in a similar manner, with

146

consideration for each nation’s annual gasoline consumption and the corresponding Pb-gas

147

concentration at that point in time and an atmospheric emission from tailpipes of 76%. 33 Smelter

148

emissions were estimated based on each nation’s annual plant production of Pb, Zn, Ni and Cu as

149

summarized by the USGS Commodity Statistics and Information (http://minerals.usgs.gov/

150

minerals/pubs/commodity/) and emission factors from 1995 for Asia calculated by Pacyna and

151

Pacyna. 36 Emissions factors were unavailable for Ni production, so we assumed the most

152

conservative value of emissions, equal to Zn smelter emissions.

153

RESULTS & DISCUSSION

154

All total dissolvable Pb concentration and isotope ratios discussed are provided in Table S1-1. In

155

this data set there were two outliers. The 20 m depth sample at Station 5 had the highest Pb

156

concentration of the entire dataset, and anomalous 206Pb/207Pb and 208Pb/206Pb ratios. Similarly,

157

the deepest sample (5,400 m) at Station 7 had an elevated Pb concentration and isotope ratios

158

which were most similar to those in the surface mixed layer. We found the isotope ratios of these

159

two samples were not an analytical artifact through replicate measurements, and decided the

160

distinct values were a result of bottle or sampling contamination. Therefore, these samples were

161

not included in the interpretation of these data.

where each country’s annual eletricity production from coal combustion was converted to

162


Page 9 of 32


9 163

Upper Ocean Water Across the transect, the mixed layer depth varied from 12 – 110 m. In the

164

Kuroshio Current mixed layer (0 to 48 m), 26 Pb concentrations were ~105 pmol kg-1 and in the

165

WSAG mixed layer (0 to 110 m) Pb concentrations were 64 – 72 pmol kg-1 (Figure 3a, b). In

166

contrast, the NPSG mixed layer (0 to 49 m) had lower concentrations (44 – 51 pmol kg-1; Figure

167

3c), which agrees well with measurements from the 1990s and mid-2000s. 2, 10 Overall, the

168

mixed layer Pb distributions are in agreement with dust flux models which show that more

169

atmospheric-borne dust lands in the Kuroshio and relatively less undergoes long-range transport

170

to the NPSG. 13, 37 – 40 In addition, the isotope ratios of WSAG and Kuroshio waters (206Pb/207Pb

171

= 1.159 – 1.170; 208Pb/206Pb = 2.095 – 2.113) were different from the NPSG surface mixed layer

172

(206Pb/207Pb = 1.171 – 1.180; 208Pb/206Pb = 2.080 – 2.095). While the Pb concentrations imply

173

there was less Pb input to the NPSG than the more coastal regions, the isotope ratios highlight

174

the relatively greater input of anthropogenic Pb to the coast. The surface mixed layer findings are

175

in good agreement with the surface ocean samples, collected on this same expedition, previously

176

discussed by Gallon et al. 1 The most striking feature of the Pb distribution was the subsurface Pb maxima that

177 178

persisted throughout most of the section at σƟ = 25.4 – 26.5 (250 – 500 m depth range; Figure

179

S1-2). The highest concentrations were observed in the Kuroshio Current near the coast of Japan

180

(Station 1: 78 – 113 pmol kg-1), and elevated Pb concentrations were observed offshore, south of

181

the Kuroshio Extension (Stations 4 – 6: 70 – 85 pmol kg-1) and in the NPSG (Stations 7, 8, 9: 75

182

– 86 pmol kg-1). Despite the differences in concentrations across the section, Pb isotope ratios

183

were similar throughout the subsurface Pb maxima feature (206Pb/207Pb = 1.160 – 1.170,

184

208

Pb/206Pb = 2.099 – 2.112), indicating a similar source of Pb to the water mass.



Page 10 of 32

10 185

The WSAG was the only region surveyed where a subsurface Pb maxima was not

186

observed, and instead Pb concentrations were highest near the surface (σƟ = 26.3 – 26.5). The

187

lack of subsurface maxima is less likely a result of the very sparse sampling resolution within the

188

250 – 500 m depth range and more likely a result of several physical processes. Located close to

189

land, the WSAG receives relatively large atmospheric inputs of Pb, 1 but we also hypothesize

190

lateral continental margin inputs increase surface Pb concentrations. Previous studies have

191

documented plumes of both particulate and dissolved trace metals (e.g., Fe, Mn, Al) advecting

192

laterally near ~ 150 m into the WSAG which originated in the Sea of Okhotsk or at the Kuril-

193

Kamchatka margin. 41 - 43 Deep winter convection then brings entrained particles and dissolved

194

metals to the surface ocean, obscuring a distinct lateral input signal. Nishioka et al. 43 found that

195

dissolved Fe from this advective process was comparable in magnitude to atmospheric Fe

196

deposition. Nagaoka et al. 11 conducted a time series study of particulate Pb at the same location

197

as our Station 2 from 2005 – 2007 (Figure 3b); they found the majority of particulate Pb at 770

198

m and 5100m was of anthropogenic origin (78 – 90%), with the remaining fraction likely from

199

the continental shelf. These parallel lines of evidence support our dual input hypothesis, although

200

we are unable to assign definite contributions from the atmospheric and continental margin

201

sources for these samples.

202

The lateral input of Pb from the continental margin potentially extends far beyond the

203

WSAG, as the shelf-derived plume is comprised of “very small particles, whose inherent sinking

204

rates are slow” (Lamborg et al. 42, pp 1564). Surface water of the WSAG flows southeast and

205

subducts south of the SubArctic Front, forming North Pacific Intermediate Water. 44, 45 The

206

subducted WSAG water lies at a depth just below the subsurface Pb maxima observed in the

207

NPSG. Although the exported WSAG water is lower in concentration than the NPSG subsurface


Page 11 of 32


11 208

maxima, it is still relatively elevated in Pb concentration (63 – 83 pmol kg-1) and its isotope

209

signatures (206Pb/207Pb = 1.158 – 1.170, 208Pb/206Pb = 2.095 – 2.117) are indistinguishable from

210

the subsurface maxima feature. This isotope similarity highlights that WSAG Pb inputs were

211

either 1) dominated by atmospheric inputs with minor margin input, or 2) continental shelf

212

sediments are highly contaminated with anthropogenic Pb and so the contributions of

213

atmospheric versus advected Pb cannot be determined – but regardless the majority of the Pb is

214

from human activities.

215

We used our Pb concentration data in conjunction with those of Wu et al. 10 and the

216

approximate water mass ages to assess the extent of Pb contamination in the upper ocean from

217

the 1970s until the mid-2000s. Details are presented in the SI, part 3. In brief, the North Pacific

218

was divided into four sub-regions: the Kuroshio Current and Extension, WSAG, central NPSG,

219

and eastern NPSG (Figure S1-1). For each region the water column was partitioned into layers

220

based on water density (σƟ) which corresponded with CFC-derived ages (Figure S1-2). 27, 44

221

“Excess Pb” for each layer was calculated by subtracting the background Pb concentration at

222

1500 m (σƟ = 27.6) from the average Pb concentration within each layer. This background is 100

223

– 200 years old, 46 and was considered a conservative over-estimate of pre-industrial Pb

224

concentrations because deep water Pb concentrations slowly increase over time as small

225

quantities of modern Pb attached to sinking particles rain down through the deep ocean. 10

226

Therefore, the resulting excess Pb estimate is likely an underestimate of pre-industrial Pb

227

concentrations. Although this is not the ideal way to calculate background, it serves as a

228

conservative estimate with the available information. Excess Pb for each layer was integrated

229

over the volume of water for that sub-region (Tables S1-6, -7) and the excess Pb quantities were

230

then compared against possible emissions sources from the preceding decades.



Page 12 of 32

12 231

The upper ocean Pb concentration maxima (4 – 12 years old) had a much larger Pb

232

excess (132 Gg) compared to the mixed layer depth waters (0 – 5 years old; 69 Gg). However,

233

normalized to years of input, both the mixed layer and shallower portion of the maxima (4 -7

234

years old) had similar Pb excesses (11 – 14 Gg year-1) in contrast with the deeper portion of the

235

maxima (7 – 12 years old; 20 Gg year-1). The older waters (12 – 35 years old; 3 – 10 Gg year-1)

236

had less excess Pb which corresponds to scavenging of Pb and export over time, lower

237

atmospheric Pb emissions during the 1970s – 1980s, or a combination of the two.

238 239

Sources of Lead Natural and anthropogenic Pb sources and their isotope ratios were compared

240

against the calculated excess Pb and the seawater Pb isotope ratios (Figure 4). In the mixed layer

241

Pb had integrated over a 5 year time period so we focused on the aerosol data available for the

242

years 1997 - 2002. Regional aerosol signatures are the integration of multiple Pb sources

243

including naturally occurring Asian loess and industrial emissions from coal combustion and

244

metal smelting. Prior to the phase-out of leaded gasoline, tetraethyl Pb additives also contributed

245

to the aerosol Pb isotope composition. Individual source identities were analyzed where data was

246

available.

247

Asian loess is the main natural Pb contributor to the North Pacific surface water. As

248

expected, loess isotope ratios are an end-member in the mixing line of possible Pb sources to the

249

seawater in this work (Figure 4a). –47 - 49 World inventories estimate 4 – 9% of total atmospheric

250

Pb is from natural sources. 36, 50 However, these inventories were based on total atmospheric Pb

251

emissions during the peak of leaded gasoline consumption, biasing the former natural

252

percentages toward the low-end in present times. Settle and Patterson 51 previously calculated the

253

natural aeolian Pb flux to the North Pacific as, at most, 3 ng cm-2 yr-1, or about 2 Gg each year


Page 13 of 32


13 254

(North Pacific ≈ 43 million km2). In near-surface waters (< 200 m) this Pb equates to less than

255

20% of the excess Pb, ruling out a much dustier climate over the past 20 years as the main source

256

of sustained excess Pb. A low flux of natural Pb to the North Pacific is further supported by large

257

aerosol Pb enrichment factors measured concurrent to our sample collection, 1 as well as large

258

enrichment factors for other industrial pollutants like Ag and Se. 14

259

In evaluating the anthropogenic sources of Pb to the North Pacific, we assumed

260

deposition to the ocean was 30% of industrial atmospheric emissions as in Nriagu 52 and Rauch

261

and Pacyna. 53 The isotope composition of Pb aerosols of several countries (Malaysia,

262

Philippines, South Korea, Vietnam and Singapore) were similar to Pb signatures of near-surface

263

seawater in the North Pacific, 33, 54 - 56 but those nations were determined to be minor sources

264

because their industrial Pb emissions were far less (< 4%) than the calculated excess Pb in the

265

upper water column (Figure 4a; SI). Other countries (e.g., Mongolia, Thailand) had neither the

266

mass of industrial Pb emissions nor similar aerosol isotope ratios to be considered of importance.

267

54, 56

268

North Pacific was also not considered to be of importance because its landmass is mostly south

269

of 30˚ N and prevailing winds carry the majority of those emissions to the Indian Ocean. 33, 57

270

Consequently, only three countries were determined to have both similar aerosol Pb isotope

271

compositions and substantial (> 10%) industrial Pb inputs to the North Pacific: Japan, Russia and

272

China.

273

Despite large atmospheric Pb emissions in India, its contributions of industrial Pb to the

The calculated Japanese emissions in 1997 – 2002 were 10 ± 3% of the excess Pb in

274

near-surface waters. Their emissions were largely influenced by industrial activities as opposed

275

to gasoline (unleaded) or other combustion sources (Figure 1). Japan was the first nation to

276

completely phase-out its use of leaded gasoline, in 1986. 8 As a result, atmospheric Pb emissions



Page 14 of 32

14 277

from 1997 – 2002 were dominated by metal smelting (∑ =15 Gg Pb; 206Pb/207Pb = 1.182), 58 coal

278

combustion (∑ = 7.6 Gg Pb; 206Pb/207Pb = 1.157 – 1.209), 59 and influenced to a much lesser

279

extent by municipal solid waste incineration (MSW; 0.6 Gg Pb; 206Pb/207Pb = 1.160). 11, 59 The

280

integrated atmospheric Pb isotope composition (206Pb/207Pb = 1.156 – 1.162) 55 and each

281

individual source are indistinguishable from the near-surface waters of this study, indicating

282

Japanese Pb aerosols contribute to the Pb found in the North Pacific (Figure 4b). In addition, the

283

close proximity of Japan to the North Pacific Ocean means a 30% deposition rate of aerosols to

284

the ocean is likely an underestimate of what was transported to the North Pacific. This

285

determination is supported by the elevated Pb concentrations in surface waters by its coast. 1 If

286

the Japanese industrial Pb deposition rate was 50%, its contribution would have been 17 ± 4 % of

287

the excess Pb, which is still far less than the contributions from Russia and China.

288

Russian emissions of atmospheric Pb from 1997 – 2002 were 20 ± 4% of the excess Pb in

289

near-surface waters, and the main contributor to aerosol Pb was the continued use of leaded

290

gasoline (∑ = 33 Gg Pb; 206Pb/207Pb = 1.135 – 1.149). 60 Much smaller contributions were made

291

by coal combustion (∑ = 5.6 Gg Pb; 206Pb/207Pb = 1.103 – 1.179) 61 and metal smelting (∑ = 6.6

292

Gg Pb; 206Pb/207Pb = 1.202 – 1.212). 61 These three sources bracketed the isotope composition of

293

both the aerosols measured in Russia during the late 1990s (206Pb/207Pb = 1.146 – 1.163) 55, 61 and

294

the near-surface seawater samples of this work (Figure 4b). By coupling the atmospheric

295

emissions estimate with the similarity of Pb isotopes in aerosols and seawater it is apparent that

296

the Pb in the mixed layer water was, in part, a reflection of Russian leaded gasoline emissions

297

and industrial aerosol inputs.

298 299

Atmospheric Pb emissions from China in 1997 – 2002 were 44 ± 10% of the excess Pb in near-surface waters, and were derived from a mix of leaded gasoline and industrial activities.


Page 15 of 32


15 300

Atmospheric Pb emissions estimates were similar for leaded gasoline (∑ = 41 Gg Pb) and coal

301

combustion (∑ = 35 Gg Pb) due to the ongoing phase-out of leaded gasoline through 2000 and

302

increased use of coal at the end of the 20th century (SI Tables S1 – 3). In addition, metal smelting

303

increased during this time period (∑ = 24 Gg Pb). The isotope composition of Chinese coal

304

(206Pb/207Pb = 1.14 – 1.22) 34 was a range around that of atmospheric Pb measured over eastern

305

China (Shanghai) in 1999 – 2002 (206Pb/207Pb = 1.16) 18, 19 and mixed layer water (Figure 4b).

306

Leaded gasoline (206Pb/207Pb = 1.10 – 1.12) 18 and Pb ores (206Pb/207Pb = 1.02 – 1.18) 58 fall along

307

the mixing line of potential Pb sources to these waters. The integrated Pb isotope composition of

308

these sources (i.e., eastern Chinese aerosols) was indistinguishable from the near-surface

309

seawater Pb isotope ratios. This similarity supports our determination that a large portion of the

310

Pb originated from Chinese emissions.

311

Due to overlapping isotope signatures among possible sources, isotope ratios alone

312

cannot uniquely pinpoint the dominant sources of Pb to the water in this work. By coupling

313

isotopic data with atmospheric emissions estimates it becomes clear that the major sources of Pb

314

in near-surface waters were leaded gasoline from Russia and China, on-going coal combustion in

315

China, and on-going metal smelting in Japan and China. Collectively, all 12 countries evaluated

316

in this work accounted for 96 ± 20 % of the excess Pb in near-surface waters. Possible sources of

317

error in this figure include: no estimate for natural Pb advected from the continental margin,

318

assumed solubility of dust near 100%, no estimate for Pb losses in the water column due to

319

scavenging and export, the errors associated with the terrestrial emission versus atmospheric

320

deposition rate, and over-estimates of leaded gasoline emissions.

321

The atmospheric Pb emissions inventories were repeated for 1990 – 1998 and compared

322

to the subsurface Pb concentration maxima at σƟ = 25.4 – 26.5. During this earlier time period,



Page 16 of 32

16 323

annual atmospheric Pb emissions were 10 – 20% higher than in 1997 – 2002 (SI, part 1) due to a

324

much larger consumption of leaded gasoline in China and Russia. 15 Limited aerosol Pb isotope

325

signatures from China and Russia in the mid-1990s (206Pb/207Pb ≈ 1.150) 17, 18, 61 were lower than

326

at the turn of the 21st century (206Pb/207Pb ≈ 1.160), presumably due to a greater use of leaded

327

gasoline. 17, 18, 55 The Pb isotope composition of the subsurface Pb maxima (206Pb/207Pb = 1.163 ±

328

0.002) reflected this enriched 206Pb aerosol input, and was isotopically distinguishable from the

329

near-surface waters (206Pb/207Pb = 1.169 ± 0.006), particularly in the NPSG (Figure 3). Therefore

330

we believe the majority of the Pb in this subsurface feature originated from leaded gasoline

331

emissions in Russia and China during the 1990s.

332 333

Deep Water In deep water (operationally defined as > 1000 m), Pb concentrations decreased

334

from 40 pmol kg-1 to less than 10 pmol kg-1 (Figure 3, Table S1-1). The 206Pb/207Pb ratios

335

increased with depth from 1.172 to greater than 1.185 at the three deepest stations, while the

336

208

337

concentrations agree within 7 pmol kg-1 of other profiles taken in 1977 and 2004 (Figure 3c), 6, 10

338

due to the long (~ 100 years) residence time of Pb in the ocean interior. 46

339

Pb/206Pb ratios decreased from 2.089 to less than 2.065. In the central NPSG, these Pb

The isotope ratios of the deep water were a mix of background and anthropogenic Pb.

340

Ferromanganese (FeMn) nodules and benthic sediments, dated to more than 200 years old, along

341

with Asian loess were used as representative end-members of background Pb. The isotope ratios

342

of seawater in depths > 1500 m (206Pb/207Pb = 1.172 – 1.194) were similar, but slightly lower,

343

than those of North Pacific FeMn nodules (1.194 ± 0.004), 11, 62 benthic sediments (1.191 ±

344

0.006) 63 and Asian loess (1.197 ± 0.007; Figure 4). 47 - 49As proposed by Wu et al., 10 mixing

345

small quantities of surface-derived anthropogenic Pb over a long period of time could have


Page 17 of 32


17 346

produced the Pb isotope ratios observed in the North Pacific deep water. In the WSAG where

347

particle export is high, 64 the effect in deep water could be amplified more so than in the open

348

ocean. Atmospheric Pb emissions from 1971 – 2002 were dominated by leaded gasoline (540

349 350

Gg Pb; SI) followed by coal combustion (155 Gg Pb) and smelter emissions (98 Gg Pb) (Tables

351

S1-3, 4, 5). Each of these sources has an isotope ratio capable of altering the deep water Pb

352

signature away from the background composition. Many nations contributed to these emissions,

353

and it is clear that leaded gasoline has impacted both near-surface and abyssal North Pacific

354

waters.

355 356

Spatial Trend In the deepest waters, there is a spatial trend in the isotope ratios from west to

357

east, despite the fact that they were in the same oceanic water mass. In the WSAG (Station 2), Pb

358

concentrations were 2 – 6 times higher than in the NPSG (Stations 7 and 9) at depths greater than

359

1500 m (Figure 3). Additionally, the 206Pb/207Pb ratios increased (1.172 to 1.193) from west to

360

east in these profiles. This observation hinges on just a handful of data points, which we justify

361

in the following discussion.

362

As demonstrated in this work and by Wu et al., 10 Pb in the deep water of the North

363

Pacific is dependent on both vertical inputs and horizontal ones. Lead concentration and isotope

364

composition differences between deep water below the WSAG and NPSG are due to differential

365

Pb fluxes to the deep water. First, the WSAG receives 2 – 10 times more atmospheric dust input

366

than the central NPSG due to its proximity to land. 13, 38 – 40, 51 The plume from the continental

367

margin, concentrated with particles, also impacts the WSAG more than the NPSG. 42 The greater

368

particulate Pb input to upper ocean water in the WSAG means there is a greater pool of Pb



Page 18 of 32

18 369

available to be exported to those deep waters. Second, scavenging and subsequent particle export

370

is also greater in the WSAG than the NPSG. During the VERTIGO program, Lamborg et al. 64

371

documented that the total mass flux of particles in the WSAG (230 – 960 mg m-2 d-1) was greater

372

than in the NPSG (50 – 80 mg m-2 d-1). The enhanced scavenging and export flux in the WSAG

373

can be attributed to relatively higher primary productivity in surface waters resulting from the

374

upwelling conditions in this region. Third, the flux attenuation in the upper 500 m of the WSAG

375

(20 – 54%) was lower than in the NPSG (60 – 80%), possibly due to differing particulate

376

composition. 11, 64 - 66 Together, the flux and attenuation measurements indicated two to three

377

times as many particles sank below 500 m in the WSAG than in the NPSG. These indirect

378

measurements are supported by the greater particle Pb concentrations (1.4 ± 0.5 pmol kg-1) in the

379

WSAG relative to the NPSG (0.6 ± 0.1 pmol kg-1) measured on particles (>0.4 um) at depths

380

greater than 1000 m from this cruise (P.L. Morton, personal communication). Using particle flux as a proxy for Pb inputs to the deep ocean, we estimate the differential

381 382

particulate Pb fluxes to the deep water as: ∆F = ∆atmos • ∆p • ∆sink

383 384

where ∆F is the difference in Pb flux to waters below 500 m between the WSAG and NPSG,

385

∆atmos is the ratio of aerosol inputs to the surface waters of the WSAG versus the NPSG (= 2 – 3),

386

37, 40

387

9 ± 6), 64 and ∆sink is the ratio of particles that sink below 500 m without remineralizing in the

388

WSAG versus the NPSG (= 2.7 ± 1.3). 64, 65

∆p is the ratio of particle flux in the lower euphotic zone of the WSAG versus the NPSG (=

389

The calculated difference in particulate Pb flux to deep waters (∆F) is 60 times greater in

390

the WSAG than the NPSG. The relatively greater flux does not equate with a 60 fold increase in

391

the concentration of Pb in those waters, as the majority of the Pb remains in the particulate phase


Page 19 of 32


19 392

and settles onto the ocean floor. 11 Rather, the elevated flux in the WSAG results in a larger pool

393

of particulate Pb relative to the NPSG. These particles, with anthropogenic isotope signatures,

394

increase total dissolvable Pb concentrations and have a greater Pb isotope effect in WSAG deep

395

water relative to the NPSG.

396

We hypothesize that Pb isotope compositions of abyssal water in the WSAG can change

397

measurably on the timescale of 1 – 2 decades based on these seawater observations in

398

conjunction with the estimated 60-fold difference in Pb flux to deep water and Wu et al.’s model

399

for the NPSG. 10 In that model, Wu et al. showed vertical Pb inputs in the central NPSG have

400

doubled the concentration of Pb in the deep waters and changed the 206Pb/207Pb isotope ratios by

401

14‰ over the past century which agrees closely with these NPSG measurements. Assuming Pb

402

in the North Pacific Ocean was homogenous in isotope composition prior to large-scale

403

anthropogenic inputs, 10 the change in 206Pb/207Pb isotope ratios for the WSAG would be 25‰,

404

implying an accelerated change in Pb isotope ratios of WSAG deep water relative to the NPSG.

405

We expect the Pb isotope ratios of the deep waters will increasingly reflect the aerosol inputs

406

from ongoing industrial Pb emissions, particularly in the WSAG. With Pb isotope ratio detection

407

limits as low as 1‰, 67 we anticipate changes in Pb isotope ratios of the WSAG abyssal water to

408

be detectable on decadal intervals.

409

In the 14 years since these samples were collected, several changes to atmospheric Pb

410

emissions have happened. Russia has eliminated use of leaded gasoline, and rapid

411

industrialization among many Asian countries has continued to grow dramatically. Countries

412

such as South Korea and Indonesia have each doubled their coal consumption between 2002 and

413

2016, and in 2014 China was responsible for 50% of the total coal consumed globally (BP:

414

www.bp.com/statisticalreview). In addition, metal smelting in Malaysia doubled, and it tripled in



Page 20 of 32

20 415

China in the same time period (USGS: http://minerals.usgs.gov/minerals/pubs/commodity/).

416

These activities have the potential to elevate Asian atmospheric Pb emissions above their pre-

417

2000 levels. 68 Therefore, future studies of the Northwest Pacific Ocean are warranted both to see

418

how continued emissions are impacting the deep ocean and to monitor on-going sources of Pb

419

contamination in near-surface waters. This work provides documentation of the vast

420

contamination of the North Pacific Ocean during the previous three decades, and serves as a

421

crucial baseline against which future studies can interpret their findings.

422

423

AUTHOR INFORMATION

424 425 426 427 428 429 430 431 432 433 434

* Corresponding Author: Tel.: +1 617 324 4984; fax: +1 617 253 8630. E-mail address: [email protected] (C.M. Zurbrick). γ

Present Address: Dept. of Earth Atmosphere and Planetary Sciences, E25-612; MIT; 45 Carleton Street; Cambridge, MA 02142, United States Present Address: California Regional Water Quality Control Board; 320 W. 4th Street #200; Los Angeles, CA 90013, United States. δ

Notes: The authors declare no competing financial interest.

435

ACKNOWLEDGEMENTS

436

We thank R. Franks for his analytical assistance, K. Bruland and C. Edwards for their insights,

437

P.L. Morton for sharing his particulate Pb data, the Captain and crew of the R/V Melville for

438

making this research possible, the science party leaders C. Measures, W. Landing, and G. Cutter

439

for organizing the expedition and M. Ranville, K.C. Filipino, W. Landing, J. Donat, and R.

440

Powell for collecting these samples. We also thank Stephen Galer and several anonymous

441

reviewers for their suggestions which vastly improved this paper. We thank the


Page 21 of 32


21 442

Intergovernmental Oceanographic Commission for funding this baseline cruise, as well as the

443

National Science Foundation for its financial support through the Graduate Research Fellowship

444

Program and grant OCE- 0751681.

445 446

SUPPLEMENTAL INFORMATION

447

SI. Includes table of all seawater data presented in this work. Contains methods for calculating,

448

and the estimated values of, leaded gasoline, coal, and metal smelting emissions from Asian

449

nations. Details “excess Pb” box model calculations and values.

450



Page 22 of 32

22 451

REFERENCES

452 453 454 455

(1)

Gallon, C.; Ranville, M. A.; Conaway, C. H.; Landing, W. M.; Buck, C. S.; Morton, P. L.; Flegal, A. R. Asian industrial lead inputs to the North Pacific evidenced by lead concentrations and isotopic compositions in surface waters and aerosols. Environ. Sci. Technol. 2011, 45, 9874–9882.

456 457 458

(2)

Boyle, E. A.; Bergquist, B. A.; Kayser, R. A.; N, M. Iron, manganese, and lead at Hawaii Ocean Time-series station ALOHA : Temporal variability and an intermediate water hydrothermal plume. Geochim. Cosmochim. Acta 2005, 69, 933–952.

459 460

(3)

Wu, J.; Boyle, E. A. Lead in the western North Atlantic Ocean: Completed response to leaded gasoline phaseout. Geochim. Cosmochim. Acta 1997, 61, 3279–3283.

461 462 463

(4)

Schaule, B. K.; Patterson, C. C. Perturbations of the natural lead depth profile in the Sargasso Sea by industrial lead. In Trace Metals in Seawater; Wong, C. S., Ed.; Plenum Press, 1983; pp. 487 – 504.

464 465 466

(5)

Boyle, E.A.; Lee, J.-M.; Echegoyen, Y.; Noble, A.; Moos, S.; Carrasco, G.; Zhao, N.; Kayser, R.; Zhang, J.; Gamo, T.; Obata, H.; Norisuye, K. Anthropogenic lead emissions in the ocean: The evolving global experiment. The Oceanogr. Soc. 2014, 27, 69–75.

467 468

(6)

Schaule, B. K.; Patterson, C. C. Lead concentrations in the northeast Pacific: evidence for global anthropogenic perturbations. Earth Planet. Sci. Lett. 1981, 54, 97–116.

469 470

(7)

Nozaki, Y.; Thomson, J.; Turekian, K. K. The distribution of 210Pb and 210Po in the surface waters of the Pacific Ocean. Earth Planet. Sci. Lett. 1976, 32, 304–312.

471 472 473

(8)

O’Brien, E.; Gethin-Damon, Z.; Roberts, A. Chronology of leaded gasoline / leaded petrol history. The Lead Education and Abatement Design Group; 2011. Online: www.lead.org.au

474 475

(9)

Thomas, V. M. The Elimination of Lead in Gasoline. Annu. Rev. Energy Environ. 1995, 20, 301–324.

476 477

(10)

Wu, J.; Rember, R.; Jin, M.; Boyle, E. A.; Flegal, A. R. Isotopic evidence for the source of lead in the North Pacific abyssal water. Geochim. Cosmochim. Acta 2010, 74, 4629–4638.

478 479 480

(11)

Nagaoka, D.; Shigemitsu, M.; Minagawa, M.; Noriki, S. Anthropogenic Pb in settling particulate matter in the Northwestern Pacific examined using stable isotopes of Pb. J. Oceanogr. 2010, 66, 117–132.

481 482

(12)

Flegal, A. R.; Patterson, C. C. Vertical concentration profiles of lead in the Central Pacific at 15 ° N and 20 ° S. Earth Planet. Sci. Lett. 1983, 64, 19–32.


Page 23 of 32


23 483 484 485 486 487

(13)

Duce, R. A.; Liss, P. S.; Merrill, J. T.; Atlas, E. L.; Buat-Menard, P.; Hicks, B. . B.; Miller, J. M.; Prospero, J. M.; Arimoto, R. .; Church, T. M.; Ellis, W.; Galloway, J. N.; Hansen, L.; Jickells, T. D.; Knap, A. H.; Reinhardt, K. H.; Schneider, B.; Soudine, A.; Tokos, J. J.; Tsunogai, S.; Wollast, R.; Zhou, M. The atmospheric input of trace species to the world ocean. Global Biogeochem. Cycles 1991, 5, 193–259.

488 489 490

(14)

Ranville, M.A.; Cutter, G.A.; Buck, C.S.; Landing, W.M.; Cutter, L.S.; Resing, J.A.; Flegal, A.R. Aeolian contamination of Se and Ag in the North Pacific from Asian fossil fuel combustion. Environ. Sci. Technol. 2010, 44, 1587–1593.

491 492

(15)

Li, Q.; Cheng, H.; Zhou, T.; Lin, C.; Guo, S. The estimated atmospheric lead emissions in China, 1990–2009. Atmos. Environ. 2012, 60, 1–8.

493 494 495 496

(16)

Artemyev, I.Y.; Oak, V.M.; Zhukov, A.D.; Ivanenko, S.; Mitrokhin, S.S.; Reznik, V.M.; Reshulsky, S.N. Federal Law N 209067-3 On limitation of turnover of leaded gasoline in the Russian Federation. State Law of the Russian Federation. 2002, http://www.lawrussia.ru/texts/legal_149/doc149a777x242.htm

497 498 499

(17)

Wang, W.; Liu, X;.; Zhao, L.; Guo, D.; Tian, X.; Adams, F. Effectiveness of leaded petrol phase-out in Tianjin, China based on the aerosol lead concentration and isotope abundance ratio. Sci. Total Environ. 2006, 364, 175–187.

500 501 502

(18)

Chen, J.; Tan, M.; Li, Y.; Zhang, Y.; Lu, W.; Tong, Y.; Zhang, G.; Li, Y. A lead isotope record of Shanghai atmospheric lead emissions in total suspended particles during the period of phasing out of leaded gasoline. Atmos. Environ. 2005, 39, 1245–1253.

503 504 505 506

(19)

Zheng, J.; Tan, M.; Shibata, Y.; Tanaka, A.; Li, Y.; Zhang, G.; Zhang, Y.; Shan, Z. Characteristics of lead isotope ratios and elemental concentrations in PM10 fraction of airborne particulate matter in Shanghai after the phase-out of leaded gasoline. Atmos. Environ. 2004, 38, 1191–1200.

507 508

(20)

Flegal, A. R.; Schaule, B. K.; Patterson, C. C. Stable isotopic ratios of lead in surface waters of the central Pacific. Mar. Chem. 1984, 14, 281–287.

509 510 511

(21)

Veron, A.J.; Church, T.M.; Rivera-Duarte, I.; Flegal, A.R. Stable lead isotopic ratios trace thermohaline circulation in the subarctic North Atlantic. Deep-Sea Res. II 1999, 46, 919– 935.

512 513 514 515

(22)

Noble, A.E.; Echegoyan-Sanz, Y.; Boyle, E.A.; Ohnemus, D.C.; Lam, P.J.; Kayser, R.; Reuer, M.; Wu, J.; Smethie, W. Dynamic variability of dissolved Pb and Pb isotopic composition from the U.S. North Atlantic GEOTRACES transect. Deep-Sea Res. II 2015, 116, 208–225.

516 517

(23)

Matsumoto, K. Radiocarbon-based circulation age of the world oceans. J. Geophys. Res. 2007, 112, C09004.



Page 24 of 32

24 518 519

(24)

Honjo, S.; Manganini, S. J. Annual biogenic particle fluxes to the interior of the North Atlantic Ocean; studied at 34°N 21°W and 48°N 21°W. Deep. Res. I 1993, 40, 587–607.

520 521

(25)

Berelson, W. M. Particle settling rates increase with depth in the ocean. Deep. Res. II 2002, 49, 237–251.

522 523 524

(26)

Measures, C. I.; Cutter, G. A.; Landing, W. M.; Powell, R. T. Hydrographic observations during the 2002 IOC Contaminant Baseline Survey in the western Pacific Ocean. Geochemistry Geophys. Geosystems 2006, 7, 1–14.

525 526

(27)

Fine, R.A.; Maillet, K.A.; Sullivan, K.F.; Willey, D. Circulation and ventillation flux of the Pacific Ocean. J. Geophys. Res. 2001, 106, 22159–22178.

527 528

(28)

Mantyla, A.W.; Reid, J.L. Abyssal characterization of the World Ocean waters. Deep-Sea Res. 1983, 30, 805–833.

529 530 531

(29)

Brown, M. T.; Landing, W. M.; Measures, C. I. Dissolved and particulate Fe in the western and central North Pacific: Results from the 2002 IOC cruise. Geochemistry Geophys. Geosystems 2005, 6, Q10001.

532 533 534 535 536

(30)

Ndung’u, K.; Franks, R. P.; Bruland, K. W.; Flegal, A. R. Organic complexation and total dissolved trace metal analysis in estuarine waters : comparison of solvent-extraction graphite furnace atomic absorption spectrometric and chelating resin flow injection inductively coupled plasma-mass spectrometric analysis. Anal. Chim. Acta 2003, 481, 127–138.

537 538 539

(31)

Zurbrick, C. M.; Morton, P. L.; Gallon, C.; Shiller, A. M.; Landing, W. M.; Flegal, A. R. Intercalibration of Cd and Pb concentration measurements in the northwest Pacific Ocean. Limnol. Oceanogr. Methods 2012, 10, 270–277.

540 541

(32)

Zurbrick, C. M.; Gallon, C.; Flegal, A. R. A new method for stable lead isotope extraction from seawater. Anal. Chim. Acta 2013, 800, 1–7.

542 543 544

(33)

Lee, J.-M.; Boyle, E.A.; Suci Nurhati, I.; Pfeiffer, M.; Meltzner, A.J.; Suwargadi, B. Coral-based history of lead and lead isotopes of the surface Indian Ocean since the mid20th century. Earth Planet. Sci. Lett. 2014, 298, 37–47.

545 546 547 548

(34)

Diaz-Somoano, M.; Kylander, M.E.; Lopez-Anton, M.A.; Suarez-Ruiz, I.; MartinezTarazona, M.R.; Ferrat, M.; Kober, B.; Weiss, D.J. Stable lead isotope compositions in selected coals from around the world and implications for present day aerosol source tracing. Environ. Sci. Technol. 2009, 43, 1078–1085.

549 550 551 552

(35)

Masto, R.E.; Ram, L.C.; Selvi, V.A.; Jha, S.K.; Srivastava, N.K. Soil contamination and human health risks in coal mining environs. In: Proceedings of the 1st International Conference on Managing the Social and Environmental Consequences of Coal Mining in India. New Delhi, India. 2007.


Page 25 of 32


25 553 554 555

(36)

Pacyna, J.M.; Pacyna, E.G. An assessment of global and regional emissions of trace metals to the atmosphere from anthropogenic sources worldwide. Environ. Rev. 2001, 9: 269–298.

556 557 558

(37) Mahowald, N.M.; Baker, A.R.; Bergametti, G.; Brooks, N.; Duce, R.A.; Jickells, T.D.; Kubilay, N.; Prospero, J.M.; Tegen, I. Atmospheric global dust cycle and iron inputs to the ocean. Global Biogeochem Cycles 2005, 19, GB4025.

559 560

(38)

Zender, C. S.; Bian, H.; Newman, D. Mineral Dust Entrainment and Deposition (DEAD) model: Description and 1990s dust climatology. J. Geophys. Res. 2003, 108, 4416:D14.

561 562 563

(39)

Ginoux, P.; Chin, M.; Tegen, I.; Prospero, J. M.; Holben, B.; Dubovik, O.; Lin, S.-J. Sources and distributions of dust aerosols simulated with the GOCART model. J. Geophys. Res. 2001, 106, 20255–20273.

564 565 566

(40)

Serno, S.; Winckler, G.; Anderson, R.F.; Hayes, C.T.; McGee, D.; Machalett, B.; Ren, H.; Straub, S.M.; Gersonde, R.; Haug, G.H. Eolian dust input to the Subarctic North Pacific. Earth Planet. Sci. Lett. 2014, 387, 252–263.

567 568 569 570

(41) Nishioka, J.; Ono, T.; Saito, H.; Nakatsuka, T.; Takeda, S.; Yoshimura, T.; Suzuki, K.; Kuma, K.; Nakabayashi, S.; Tsumune, D.; Mitsudera, H.; Keith Johnson, W.; Tsuda, A. Iron supply to the western subarctic Pacific: Importance of iron export from the Sea of Okhotsk. J. Geophys. Res. 2007, 112, C10012.

571 572 573

(42)

Lamborg, C.H.; Buesseler, K.O.; Lam, P.J. Sinking fluxes of minor and trace elements in the North Pacific Ocean measured during the VERTIGO program. Deep-Sea Res. II 2008, 55, 1564–1577.(43)

574 575

(43)

Lam, P.J.; Bishop, K.B. The continental margin is a key source of iron to the HNLC North Pacific Ocean. Geophys. Res. Lett. 2008, 35, L07608.

576 577 578

(44)

Watanabe, Y.W.; Karada, K.; Ishikawa, K. Chlorofluorocarbons in the central North Pacific and southward spreading time of North Pacific intermediate water. J. Geophys. Res. 1994, 99, 25195–25213.

579 580

(45)

Talley, L.D. Distribution and formation of North Pacific Intermediate Water. J. Phys. Oceanogr. 1993, 23, 517–537.

581 582 583

(46)

Nozaki, Y.; Zhang, J.; Takeda, A. 210Pb and 210Po in the equatorial Pacific and the Bering Sea: the effects of biological productivity and boundary scavenging. Deep-Sea Res. II 1997, 44, 2203–2220.

584 585

(47) Wu, F.; Sai, S.; Ho, H.; Sun, Q.; Ho, S.; Ip, S. Provenance of Chinese Loess : Evidence from Stable Lead Isotope. Terr. Atmos. Ocean. Sci. 2011, 22, 305–314.



Page 26 of 32

26 586 587 588

(48)

Sun, J.; Zhu, X. Temporal variations in Pb isotopes and trace element concentrations within Chinese eolian deposits during the past 8Ma: Implications for provenance change. Earth Planet. Sci. Lett. 2010, 290, 438–447.

589 590

(49)

Jones, C. E.; Halliday, A. N.; Rea, D. K.; Owen, R. M. Eolian inputs of lead to the North Pacific. Geochim. Cosmochim. Acta 2000, 64, 1405–1416.

591 592

(50)

Nriagu, J.O. A global assessment of natural sources of atmospheric trace metals. Nature 1989, 338: 47–49.

593 594 595

(51) Settle, D. M.; Patterson, C. C. Magnitudes and sources of precipitation and dry deposition fluxes of industrial and natural leads to the North Pacific at Enewetak. J. Geophys. Res. 1982, 87, 8857–8869.

596 597

(52)

Nriagu, J.O.; Pacyna, J.M. Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature 1988, 333: 134–139.

598 599

(53)

Rauch, J.N.; Pacyna, J.M. Earth’s global Ag, Al, Cr, Cu, Fe, Ni, Pb and Zn cycles. Global Biogeochem. Cycles 2009, 23: GB2001.

600 601

(54)

Bollhofer, A.; Rosman, K. Isotopic source signatures for atmospheric lead : The Northern Hemisphere. Geochim. Cosmochim. Acta 2001, 65, 1727–1740.

602 603 604

(55)

Bollhofer, A.; Rosman, K. J. R. The temporal stability in lead isotopic signatures at selected sites in the Southern and Northern Hemispheres. Geochim. Cosmochim. Acta 2002, 66, 1375–1386.

605 606

(56)

Bollhofer, A.; Rosman, K. J. R. Isotopic source signatures for atmospheric lead: The Southern Hemisphere. Geochim. Cosmochim. Acta 2000, 64, 3251–3262.

607 608

(57)

Tindale, N.W.; Pease, P.P. Aerosols over the Arabian Sea: Atmospheric transport pathways and concentrations of dust and sea salt. Deep-Sea Res. II. 1999, 46, 1577–1595.

609 610

(58)

Sangster, D. F.; Outridge, P. M.; Davis, W. J. Stable lead isotope characteristics of lead ore deposits of environmental significance. Environ. Rev. 2000, 8, 115–147.

611 612 613

(59)

Sakata, M.; Kurata, M.; Tanaka, N. Estimating contribution from municipal solid waste incineration to trace metal concentrations in Japanese urban atmosphere using lead as a marker element. Geochem. J. 2000, 34, 23–32.

614 615 616

(60)

Mukai, H.; Tanaka, A.; Fujii, T.; Nakao, M. Lead isotope ratios of airborne particulate matter as tracers of long-range transport of air pollutants around Japan. J. Geophys. Res. 1994, 99, 3717–3726.

617 618

(61)

Mukai, H.; Machida, T.; Tanaka, A.; Vera, Y. P.; Uematsu, M. Lead isotope ratios in the urban air of eastern and central Russia. Atmos. Environ. 2001, 35, 2783–2793.


Page 27 of 32


27 619 620 621

(62)

Ling, H. F.; Burton, K. W.; Nions, R. K. O.; Kamber, B. S.; Geochimie, D.; Jussieu, P.; Cedex, P. Evolution of Nd and Pb isotopes in Central Pacific seawater from ferromanganese crusts. Earth Planet. Sci. Lett. 1997, 146, 1–12.

622 623

(63)

Chow, T. J.; Patterson, C. C. The occurrence and significance of lead isotopes in pelagic sediments. Geochim. Cosmochim. Acta 1962, 26, 263 – 308.

624 625 626 627 628

(64)

Lamborg, C. H.; Buesseler, K. O.; Valdes, J.; Bertrand, C. H.; Bidigare, R.; Manganini, S.; Pike, S.; Steinberg, D.; Trull, T.; Wilson, S. The flux of bio- and lithogenic material associated with sinking particles in the mesopelagic “twilight zone” of the northwest and North Central Pacific Ocean. Deep Sea Res. Part II Top. Stud. Oceanogr. 2008, 55, 1540– 1563.

629 630 631

(65)

Karl, D. M.; Christian, J. R.; Dore, J. E.; Hebel, D. V.; Letelier, R. M.; Tupas, L. M.; Winn, C. D. Seasonal and interannual variability in primary production and particle flux at Station ALOHA. Deep Sea Res. Part II 1996, 43, 539–568.

632 633 634

(66)

Buesseler, K.O.; Boyd, P.W. Shedding light on processes that control particle export and flux attenuation in the twilight zone of the open ocean. Limnol. Oceanogr. 2009. 54, 1210–1232.

635 636 637 638 639

(67)

Boyle, E.A.; John, S.; Abouchami, W.; Adkins, J.F.; Echegoyen-Sanz, Y.; Ellwood, M.; Flegal, A.R., Fornace, K.; Gallon, C.; Galer, S.; Gault-Ringold, M.; Lacan, F.; Radic, A.; Rehkamper, M.; Rouxel, O.; Sohrin, Y.; Stirling, C.; Thompson, C.; Vance, D.; Xue, Z.; Zhao, Y. GEOTRACES IC1 (BATS) contamination-pronce trace element isotopes Cd, Fe, Pb, Zn, Cu and Mo intercalibration. Limnol. Oceanogr. Methods 2012, 10: 653–665.

640 641 642

(68)

Tian, H.; Cheng, K.; Wang, Y.; Zhao, D.; Lu, L.; Jia, W.; Hao, J. Temporal and spatial variation characteristics of atmospheric emissions of Cd, Cr, and Pb from coal in China. Atmos. Environ. 2012, 50, 157–163.

643

(69)

Schlitzer, R.; Ocean Data View, 2015, odv.awi.de



Table of Contents/Abstract Graphic Table of Contents/Abstract Gra 84x46mm (300 x 300 DPI)


Page 28 of 32

Page 29 of 32


Figure 1. Atmospheric Pb emission estimates for a) gasoline, b) industrial coal combustion and c) smelting of Pb, Ni, Cu and Zn (data and references in SI: Tables S1-3, -4, -5). Figure 1 158x197mm (300 x 300 DPI)



Figure 2. Map of IOC-4 expedition with station numbers. The warm Kuroshio Current flows northward along the coast of Japan and the cold Oyashio Current flows southward from the Western Subarctic Gyre. Where the two currents meet the Oyashio subducts under the Kuroshio and they jet eastward as the Kuroshio extension. 26 Figure made in Ocean Data View. 69 Figure 2 236x144mm (300 x 300 DPI)


Page 30 of 32

Page 31 of 32


Figure 3. Lead concentrations and isotope ratios in a) the Kuroshio Current and Extention, b) the WSAG, and c) NPSG. Particulate Pb throughout the column of the WSAG (collected in 2005 – 2007) is isotopically similar to surface waters. 11 Previous Pb profiles in the central NPSG are similar to data presented here, 2, 6, 10 although the Pb isotope ratios have changed in the surface waters. 20 Hatched bars represent Pb isotope composition of North Pacific sediments and FeMn nodules. 11, 62, 63 Figure 3 222x279mm (300 x 300 DPI)



Figure 4. Triple isotope plots of Stations 1 – 9 (shallow < 200 m; deep > 200 m) along with a) global aerosol signatures and b) probable sources which contributed to the Pb in these seawater samples. Figure 4 254x250mm (300 x 300 DPI)


Page 32 of 32

Historic and Industrial Lead within the Northwest Pacific Ocean

Recommend Documents