Isotopic evidence for the source of lead in the North
Pacific abyssal water
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Citation
Wu, Jingfeng et al. “Isotopic evidence for the source of lead in
the North Pacific abyssal water.” Geochimica et Cosmochimica
Acta 74.16 (2010): 4629-4638.
As Published
http://dx.doi.org/10.1016/j.gca.2010.05.017
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Elsevier
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Author's final manuscript
Accessed
Wed May 25 21:46:12 EDT 2016
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http://hdl.handle.net/1721.1/62573
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Note: This is the revised manuscript. The original version was submitted in November
29, 2009.
Isotopic Evidence for the Source of Lead in the North Pacific Abyssal Water
Jingfeng Wu1, Robert Rember2, Meibin Jin2, Edward A. Boyle3 and A. Russell Flegal4
1
RSMAS, University of Miami, Miami, Florida 33149, USA
2
IARC, University of Alaska Fairbanks, Fairbanks, Alaska 99775, USA
3
EAPS, MIT, Cambridge, Massachusetts 02139, USA
4
University of California Santa Cruz, Santa Cruz, California 95064, USA
Abstract
The absence of accurate measurements of lead (Pb) isotopic composition in the
pristine North Pacific abyssal water has made it difficult to assess the relative importance
of what are believed to be the two major Pb sources: the natural Pb introduced during
preindustrial time and recent anthropogenic Pb resulting from leaded gasoline
combustion and high temperature industrial activities. Here we report a vertical profile of
seawater 206Pb/207Pb ratio and a meridional section of Pb concentration in the North
Pacific Ocean. We observe two to three fold increases in Pb concentration along the
deep-water flow path and a deep-water 206Pb/207Pb ratio (~1.188) substantially lower than
the pre-industrial value (~1.210). These data suggest that anthropogenic Pb has invaded
the North Pacific abyssal water and become the predominant Pb source. A simple model
calculation based on these data indicates that the anthropogenic Pb is transported to the
deep ocean by sinking particles and that this Pb vertical flux has a 206Pb/207Pb ratio that
decreased during the past two centuries.
Introduction
Anthropogenic Pb emissions to the atmosphere by leaded gasoline combustion
and high temperature industrial activities (e.g., fossil fuel combustion and smelting) have
1
increased global atmospheric Pb concentrations by more than 10-fold above natural
levels during the last two centuries (Wolff and Peel, 1985; Boutron et al., 1991; Shotyk et
al., 1998; Pacyna and Pacyna, 2001; Osterberg et al., 2008). These anthropogenic Pb
emission have contaminated much of the world ocean (Schaule and Patterson, 1981;
Flegal and Patterson, 1983; Boyle et al., 1986; Hamelin et al., 1990; Veron et al., 1994;
Wu and Boyle, 1997; Alleman et al., 1999). However, the origin of Pb in the present-day
North Pacific deep water remains unclear. The North Pacific deep water is considered to
be relatively pristine because: (1) it contains the lowest dissolved Pb concentrations in the
world ocean (Schaule and Patterson, 1981; Flegal and Patterson, 1983), (2) the potential
for mixing and advection to inject anthropogenic Pb to abyssal depths is limited because
surface water in the subarctic North Pacific is not sufficiently dense to sink to depths
below ~700 m during winter (Talley, 1993), and (3) the transit of the Antarctic Bottom
Water (AABW) from the Southern Ocean to the North Pacific is slow (with a transit time
of ~500 yr, Stuiver et al., 1983). Although vertical transport by sinking particles has a
potential to supply anthropogenic Pb to North Pacific deep waters, this process has not
been directly observed from previously measured Pb vertical profiles (Schaule and
Patterson, 1981) that show decreasing Pb concentrations with increasing depth in waters
below 700 m and similar deep water Pb concentrations in the North Pacific and South
Pacific (Flegal and Patterson, 1983).
To understand the sources of lead in the North Pacific deep water, we measured
deep-water dissolved Pb concentration gradient along a meridional section from 7 S to
30 N (Fig. 1) and a vertical profile of 206Pb/207Pb at a station at 30 N in the central
North Pacific Ocean (Fig. 2) using ultraclean and high-sensitivity procedures. The
observed Pb concentrations and Pb isotope profiles in the deep water are simulated with a
time dependent one dimensional vertical diffusion/advection model to understand the
mechanism controlling the observed Pb distribution.
Methods
Seawater samples for Pb concentrations and isotopic analysis were collected in
the North Pacific Ocean along a section from -7 S, 158 W to 22 N, 158 W in April
2005 and at a single station locating at 30 N, 140 W in October 2004 (Fig 1), using an
2
automatic ATE/Vane sampler (Wu, 2007). The collected samples were passed through
0.4 µm Nuclepore filters, acidified, and stored at room temperature (Wu et al., 2001, Wu
and Boyle, 2002). Total Pb concentrations in the sample were determined with Mg(OH)2
coprecipitation isotope dilution ICPMS (Wu and Boyle, 1997). The method has a
precision of ~10% at ~2 pM level and a detection limit of ~ 0.5 pM. The Pb
concentrations in the deep waters of the subtropical North Pacific Ocean that we
determined using these sampling, filtration and analytical methods are in excellent
agreement with those reported by Schaule and Patterson (1981) (Fig. 3), suggesting
minimal Pb contamination by these procedures. Our total Pb concentration data are also
in excellent agreement with those independently determined by the MIT group (Fig. 3).
The MIT samples were collected using a 12-unit MITESS sampler (Bell et al., 2002).
The samples were filtered using 0.4 µm Nuclepore membranes. Both filtered and
unfiltered subsamples were acidified to pH 2 with high-purity 6N HCl. Total Pb
concentration in these samples were analyzed by isotope-dilution using a VG PQ2+
quadrupole ICPMS (Wu and Boyle, 1997). The small differences in deep water Pb
concentrations between our data and the MIT data are not understood at present, but
probably result from inter-laboratory differences in the blank estimation. The Pb
concentration in the MIT unfiltered samples fit in with the profile of the filtered samples
indicating that particulate Pb is small.
The lead isotopic ratio in the samples was determined with a method that consists
of Mg(OH)2 coprecipitation, ion exchange column purification and ICPMS measurement
(Reuer et al., 2003). Each measurement requires ~ 250 ml for samples with >20 pM Pb,
and 500-800 ml for samples with 1-15 pM Pb. The 206Pb/207Pb ratio in the purified
samples was determined with a single collector sector field Finnigan Element 2 ICPMS,
with a precision of ~0.1% which is limited by the inherent imprecision of the singlecollector instrument (the actual precision of measurements is shown in Fig. 2 and Table
2b). This precision is ~3 % of the total range of 206Pb/207Pb ratio observed between
surface and deep-ocean. The accuracy of the method was verified by sample replicates
measured with both Element2 ICPMS and MC-ICPMS. Instrumental mass bias was
corrected by adding Tl as an internal standard. The procedural blank for Pb isotope
analysis is 15±5 pg and the 206Pb/207Pb ratio of this Pb blank is 1.17±0.05. The consistent
3
206
Pb/207Pb ratio obtained for replicate samples of different volumes (Table 1) suggests
minimal influence by procedural Pb blank correction.
Results and Discussion
Dissolved Pb concentrations along the meridional section exhibit distinct vertical
and horizontal gradients (Fig. 1, Table 2a). The dissolved Pb concentrations decrease
downward from 30-50 pM in surface waters to 1-4 pM in deep waters, and increase
northward from ~23 pM at 7 S to ~ 51 pM at 30 N in the surface mixed layer and from
~1.5 pM at 7 S to ~ 4 pM at 30 N in waters below 3000 m. These gradients reflect a
southward decrease in the anthropogenic Pb emissions from land, eolian deposition to the
sea surface, and the subsequent downward penetration to the subsurface ocean. The
horizontal gradient corresponds to the dispersion of Asian anthropogenic Pb emissions to
the atmosphere that are highest within the mid-latitudes of the Northern Hemisphere and
the subsequent transport of these Pb emissions across the North Pacific by prevailing
Westerlies (Schaule and Patterson, 1981). The Pb concentration maxima at 200-400 m
depth of subtropical latitudes (15-30 N) reflects the isopycnal transport of anthropogenic
Pb via the advection of subducted North Pacific surface waters. In contrast, the dissolved
Pb concentration (~1.5 pM) in the bottom water (4000-5000 m) at 7 S (Fig. 1) is 2-3 fold
lower than the lowest dissolved Pb concentration previously reported for the world ocean
(Schaule and Patterson, 1981; Flegal and Patterson, 1983). The northward increase of
bottom-water dissolved Pb concentrations implies that anthropogenic Pb is supplied to
this water via vertical Pb input.
Because much of the deep water in the Pacific Ocean is advected from the
Southern Ocean (Warren, 1980) and because water mixing across pycnocline is slow
(Ledwell et al., 1993), if there is no additional Pb input, the dissolved Pb concentrations
should decrease northward along the deep-water flow path as seawater Pb is scavenged
by sinking particulates during the northward transit. The northward increase of bottomwater dissolved Pb from ~1.5 pM at ~7 S to ~3.9 pM at 30 N (Fig. 1) indicates that
additional Pb (~2.4 pM) has been supplied to those deep waters. We suggest that
additional Pb is solubilized from sinking particles during the horizontal deep-water
transit. As previously noted, Pb is scavenged in oceanic surface waters and transported to
4
deep waters, similar to vertical transport of particle reactive radionuclides (Livingston
and Anderson, 1983). Although 210Pb studies indicate the net scavenging of radiogenic Pb
in the deep-water column (Chung and Craig, 1983), studies of thorium (Th) isotopes
indicate that the exchange can be reversible (Bacon and Anderson, 1982 ). The supply of
anthropogenic Pb to the deep water by Pb solubilization from sinking particles that we
propose here is consistent with the isotopic equilibration between dissolved and
suspended particulate Pb reported by Sherrell et al (1992).
Neglecting the effect of vertical and horizontal mixing, the distribution of
dissolved Pb at the bottom water along the meridional section (Fig. 1) can be described
by the equation:
C
 J  kC
t
(1)
where C represents dissolved Pb concentration (pM), J represents the vertical flux of Pb
regenerated from sinking particles (pM/yr) and k represents the rate constant of seawater
Pb scavenging by particles (yr-1). Based on this equation, a value of 0.02 pM/yr for J can
be calculated from the formulation:
J
k (C  C0 e  kt )
1  e kt
(2)
where C is the concentration of dissolved Pb in the bottom water at 30N (4 pM, Fig. 1,
Table 2a), C0 is the concentrations of dissolved Pb in the bottom water at 7S (1.5 pM,
Fig. 1, Table 2a), k is estimated from the GEOSECS 210Pb and 226Ra data determined in
central North Pacific Ocean (0.0025 yr-1, Nozaki et al., 1980), and t (=203 yr) is the time
the bottom water takes to flow from 7S to 30N, provided that there is an average
northward drift of ~ 0.7 mm/s (Munk, 1966).
That proposed scavenging and subsequent diagenetic remobilization of Pb at depth
is supported by the vertical gradient of seawater 206Pb/207Pb ratio that we measured at a
station (140 W, 30 N, SAFe station 5) in the subtropical North Pacific (Fig. 2, Table
2b). In the upper 500 m of the water column, the 206Pb/207Pb ratio is relatively constant
(~1.160). Below 500 m, the ratio rapidly increases with depth to ~1.179 at 1400 m, and
then increases gradually with depth to ~1.188 at 4500 m. The 206Pb/207Pb ratio in those
surface waters (0-500 m) (~1.160) is similar to both the ratio in Ogasawara corals
5
between 1940-2000 (~1.163) (Inoue and Tanimizu, 2008) and the ratio in aerosols
collected in major Japanese and Chinese cities during the 1990s (~1.159) (Mukai et al.,
1993; Bollhofer and Rosman, 2001). This suggests that Pb in the upper 500 m of the
water column is primarily derived from atmospheric deposition of Asian anthropogenic
aerosols that supply Asian anthropogenic Pb to the surface ocean by atmospheric
deposition and to the thermocline waters by vertical mixing and horizontal isopycnal
transport.
The 206Pb/207Pb (~1.160) ratio that we observed at ~400 m at 140 W 30 N (Fig. 2)
is lower than that (~1.211) reported by Flegal et al. (1986) at a comparable depth in the
northeast Pacific (141°00’W, 48°00’N). This difference may result from the spatial
variation between the two sites or differences in the predominant source of anthropogenic
lead to the North Pacific during the two sampling periods. We believe that the first
alternative is more likely, because the anomalously high ratio observed in the earlier
profile was tentatively attributed to the lateral transport of US gasoline lead in the
California Counter Current, which is a coastal phenomenon that has negligible impact on
oceanic waters in the North Pacific. The older (1980) values (Flegal et al., 1986)
corresponds to that of lead additives in US gasoline during the 1970s-1980s, that were
phased out nearly two decades ago (Wu and Boyle, 1997). During the 1970s-2000s,
Asian anthropogenic Pb emissions increased dramatically, primarily due to the
combustion of fossil fuels and the protracted use of leaded gasoline in that region. For
example, during 1970s-2000s, the annual consumption of coal in China increased by ~3
fold (Chan and Yao, 2008). The current predominant influence of Asian anthropogenic
emissions on Pb fluxes to the North Pacific is also indicated by temporal variations in
lead isotopic compositions in cities along the west coast of North America, e.g.,
206
Pb/207Pb ratios in central California declined from ~1.21 to ~1.16 between the early
1980s and 2000, which is considered due to the replacement of anthropogenic lead
emissions within the US with those from Asia (Bollhofer and Rosman, 2001).
In contrast, the 206Pb/207Pb ratio (~1.188) that we observed at 4500 m is lower
than those of natural lead in the North Pacific (Fig. 2). These include the 206Pb/207Pb
ratios of Holocene sediments (~1.214) (Jones et al., 2000), Pleistocene sediments
(~1.195) (Chow and Patterson, 1962), and pelagic sediments and ferromanganese nodules
6
(~1.210) (Ling et al., 1997; Onions et al., 1998). These differences indicate that
anthropogenic Pb inputs have lowered 206Pb/207Pb ratios of deep water in the North
Pacific below pre-anthropogenic values.
Plotting 206Pb/207Pb vs. 1/[Pb] for depths below ~700 m (Fig. 4a) shows the
interception of two linear segments between 800-1500 m and 1500-4500 m that coincides
with depths where linear salinity vs. temperature relationships were observed (Fig. 4b),
suggesting that the distribution of anthropogenic Pb at these depths reflects mixing within
two different water masses. To further understand these results, we use a vertical
advection/diffusion model that included a time dependent vertical Pb flux from sinking
particles to simulate the Pb concentration and isotopic data at depths below 1500 m. The
simulation uses the formulations:

K
 2C
C
C

 kC  J 
 2z
z
t
(3)
K
 2 (RC)
(RC)
 (RC)

 kRC  JRJ 
 2z
z
t
(4)
where C represents Pb concentration (pM), R represents 206Pb/207Pb ratio, z represents

depth (positive upward and equal to zero meter at sea surface), t represents time (year), J
represents vertical Pb flux (pM/yr), RJ represents 206Pb/207Pb ratio of vertical Pb flux, K
represents vertical turbulent diffusivity (assumed to be constant with depth),  represents
vertical velocity (positive upward), and k represents Pb scavenging rate constant (yr-1).
 between the very
Our assumption is that there is a depth range in the deep Pacific
deep core of incoming “Common Water” (a mixture of North Atlantic Deep Water,
Circumpolar Waters and Antarctic Bottom Water, which enters the Pacific at around
3500 - 4000 m depth) and the low salinity core associated with Antarctic Intermediate
water at around 1000 m depth. Water properties are maintained at the ends of this range
by horizontally flowing water, which fix the concentrations of the various properties. In
between, the property concentrations are determined by a combination of vertical
advection, vertical (turbulent) diffusion, in situ processes of biogeochemical
production/consumption and particle regeneration/scavenging. While few parts of the
ocean can be regarded as satisfying these assumptions, such model has been applied to
7
describe vertical distribution of salinity, temperature, 14C, dissolved O2, and 226Ra in the
deep waters of the Pacific Ocean (Munk, 1966; Craig, 1969). Munk and Wunsch (1998)
have pointed out that despite the oversimplication of this model and dramatic advances in
physical oceanographic modeling since it was first presented, this simple model captures
the essence of the vertical structure of the deep Pacific circulation. The limited Pb isotope
ratio and concentration data that we determined in this study do not allow for modeling
using more sophisticated three dimensional GCM models.
The model is run for 200 years (t = 0-200 yr) from a depth-independent initial (t =
0) Pb concentration of 1.50 pM according to the deep water dissolved Pb concentration
measured at 7 ºS (Fig. 1, Table 2a) and an initial 206Pb/207Pb ratio of 1.210 based on
sediment and Mn nodule data (Chow and Patterson, 1962; Ling et al., 1997; O’Nions et
al., 1998). The model uses a time step of 0.01 yr, a depth step of 500 m, and a boundary
condition that allows the Pb concentration and the 206Pb/207Pb ratio at 1500 m and 4500 m
to vary from the initial (t = 0 yr) values (C =1.50 pM and R = 1.210, same for all depths)
to the values at t = 200 yr (C-4500 = 3.95 pM, R-4500 = 1.188, C-1500 = 12.73 pM and R-1500
= 1.179) according to time series Pb concentration recorded in Ogasawara corals (Inoue
and Tanimizu, 2008) and dissolved Pb concentrations measured in the subtropical North
Pacific since 1980 (Fig. 1, Table 2a, Schaule and Patterson, 1981, Flegal and Patterson,
1983). The model uses vertical turbulent diffusivity (K = 1.265 cm2/s) and vertical
velocity (  = 2.30.8  10-7 m/s) that are derived from the vertical distribution of
salinity, dissolved oxygen, C and (CO2) determined at a nearby GEOSECS station (#
202, 33.1 ºN, 139.6 ºW), and the Pb scavenging rate constant (k = 0.0025 yr-1) that is

estimated from the GEOSECS 210Pb and 226Ra data determined in central North Pacific
Ocean (Nozaki et al., 1980). The model uses a 206Pb/207Pb ratio of the vertical Pb flux (RJ
) that is constant with depth, but decreases linearly with increasing time from 1.210 at t =
0 to 1.181 at t = 170 yr and from 1.181 at t = 170 yr to 1.160 at t = 180 yr, and then
remains constant at 1.161 between t = 180 yr and t = 200 yr, according to 206Pb/207Pb
ratio recorded in the Ogasawara corals (Inoue and Tanimizu, 2008). A trial and error
method is used to determine the optimal values of parameter a (0.019 pM/yr), b (0.035 yr1
) and c (310-4 m-1) for the empirical relationship J  a(1 bt)e cz that allows a best fit

8
between the model derived Pb concentration and isotopic composition and the observed
values.
As shown in Fig. 5, while the modeled Pb concentration and 206Pb/207Pb ratio
agree well with the measured values at t = 200 years (Figs 5a-b), the model-derived
206
Pb/207Pb ratio vs. 1/[Pb] plot (Fig. 5c) do not show straight lines at t = 50 and100
years. Such non-linear 206Pb/207Pb ratio vs. 1/[Pb] plot results from the Pb input and
removal that act as extra two end members superimposing on the linear two end-member
mixing line. The apparent straight line in the 206Pb/207Pb vs. 1/[Pb] plot (Fig. 4a and t =
200 years in Fig. 5c) is the coincidental result of time dependent vertical mixing
modulated by the input of Pb regenerated from sinking particles and Pb removal by
sinking particles. These processes also lead to the observed increase of 206Pb/207Pb ratio
with depth (Fig. 2) because the water at the greater depths receives a lower vertical flux
of anthropogenic Pb with a low 206Pb/207Pb ratio.
The model results are not sensitive to both the vertical resolution and the initial
condition as its influence on the initial condition tends to decrease with time and
disappears totally after 200 years and because the vertical influx through the boundary is
adjusted according to the initial and final conditions. Since sinking particles supply Pb to
the entire water column within relatively short time period, the boundary conditions at
z=-1500 m and -4500 m are assumed to evolve to the present according to the shape of
the Pb coral curve representing Pb input function to the surface water (Inoue and
Tanimizu, 2008). However, Pb concentration in water at deeper depths tends to vary by
smaller magnitude constrained by the initial and final boundary because organic matter
remineralization flux decreases with increasing depth. With this reduced magnitude at the
boundary, the deeper water does take longer time to reach steady state than the shallower
water. The above model can be better constrained in the future by an improved knowledge
of atmospheric Pb input function and past distribution of seawater Pb concentration and
isotopic ratio via measurements of Pb in surface and deep sea corals.
The above model simulation demonstrates that the observed Pb concentration and
isotopic composition can be reproduced from an initial Pb concentration of 1.50 pM and
4
an initial 206Pb/207Pb of 1.210 if the downward Pb flux ( J  0.019(1  0.035t )e3 x10 z )
9
decreases with depth, increases with time, and has a depth independent 206Pb/207Pb ratio
that decreases with time. According to this model, the vertical profile of 206Pb/207Pb ratio
in the central North Pacific Ocean chronicles the Pb isotopic composition of historic
inputs of anthropogenic Pb to this region. The increase in 206Pb/207Pb with depth suggests
a decrease in the isotopic ratio of anthropogenic Pb flux to the North Pacific Ocean over
the past few centuries. On a triple-isotope plot (208Pb/206Pb vs 206Pb/207Pb, Fig. 6), our
water column data falls on the trend line between Pacific pre-anthropogenic Fe-Mn crusts
(Blanckenburg et al.1996) and East Asian aerosols (China, Vietnam, Japan) (Bollhofer
and Rosman, 2001) and above the trend of US and Central American aerosols (Bollhofer
and Rosman, 2001) and the California Current seawater data reported by Flegal et al.
(1984). These data imply that the 2004 SAFe water column Pb is dominated by mixing
between modern Asian aerosol sources and natural Pb in the deepest water.
Conclusion
The preceding data and model corroborate the hypothesis that atmospheric inputs
of anthropogenic Pb to the North Pacific have been effectively scavenged in surface
waters, rapidly injected to deep waters by particle transport, and then partially
remobilized to elevate dissolved Pb in the abyssal North Pacific Ocean by ~ 2.4 pM.
This mechanism differs from the long established record in the North Atlantic where the
source waters are more recently introduced by means of themohaline circulation
(Alleman et al., 1999). In the Pacific where the influence of the advection is greatly
attenuated, the Pb sources appear to be the accumulative atmospheric deposition over the
meridian and the particle scavenging over longer industrial time scales. Our results imply
that vertical transport of Pb supplied to the surface ocean by eolian and fluvial Pb sources
may be important in the budget of preindustrial Pb in the North Pacific deep water.
Acknowledgements. We are grateful to Ruixin Huang for helping model calculation, the
SAFe cruise chief scientist Ken Johnson and the captain and crews of R/V Wecoma and
R/V Melville. We thank Dominik Weiss and an anonymous reviewer for constructive
comments that improve the manuscript. This work is supported by funding from
NSF(OCE-0325031, (OCE-0325031, OCE-0220978, OCE-0321402, OCE-0728930 and
ARC-0612538) and CNSF grants (No.40776042).
10
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Figure Captions
Fig. 1. Seawater dissolved Pb section in the North Pacific along 140-158 °W.
Fig. 2. Comparison of seawater 206Pb/207Pb ratio at 30°N, 140°W (SAFe Station) with the
ratios reported for pelagic sediment (Chow and Patterson, 1962), Holocene sediments
(Jones et al., 2001) and ferromanganese nodules (Ling et al., 1997; O’Nions et al., 1998).
13
Fig. 3. Comparison of Pb profile at 30°N, 140°W with the MIT profile determined at the
same station and the profile determined by Schaule and Patterson (1981) at 32.7 °N, 145
°W in the central North Pacific Ocean.
Fig. 4 (a) 206Pb/207Pb ratio vs. 1/[Pb] plot for waters below 800 m showing two linear
segments converging at 1500 m. In this projection, linear mixing between end-members
of fixed concentration and isotopic composition results in linear trends. (b) T-S diagram
for waters below 800 m showing two linear segments converging at ~1500 m.
Fig. 5. Vertical distribution of modeled and measured Pb concentration (a) and
206
Pb/207Pb ratio (b) and the plot of 206Pb/207Pb ratio vs. 1/(Pb concentration (c) for water
below 1500 m. The Pb concentration and 206Pb/207Pb ratio are simulated using
4
J  0.019(1 0.035t)e 310
z
pM/yr, RJ = 1.121-1.181 at t = 0-170 yr, RJ = 1.181-1.160 at t
= 170-180 yr and RJ = 1.160 at t = 180-200 yr. The data point at z = -3500 m is estimated

by interpolation from the data at z = -3000 m and -4000 m.
Fig.6. 206Pb/207Pb vs. 286Pb/267Pb plot comparing our seawater results (Table 2b) with the
data reported for Pacific surface water (Flegal et al., 1984), aerosols (Bollhofer and
Rosman, 2001) and Fe-Mn nodule (Blanckenburg et al.1996).
Table 1. Seawater 206Pb/207Pb ratio determined by Mg(OH)2 coprecipitation Element2
ICPMS. A) North Atlantic (1994-1998)27; B) North Atlantic (1997); C) North Pacific at
2500 m (2005, SAFe station).
206
Sample ID
Pb/207Pb
Pb (pg)
Sample volume (ml)
A
1.17600.002 >2000
250
B
1.17540.001 >2000
250
C
1.18450.002 165
125
C
1.18370.003 330
250
C
1.18240.001 660
500
14
Table 2a. Seawater dissolved Pb concentration plotted in Fig. 1b. The samples for
profile at 30 °N, 140 °W were collected in October 2004 during SAFe cruise and the rest
of samples were collected in April 2005 during WOC305 cruise. UF represents unfiltered
sample.
Longitude
Latitude
Depth (m)
<0.4 µm Pb (pM)
140 °W
30 °N
25
30
50
100
150
200
300
400
500
600
700
800
1000
1500
2000
2500
3000
3500
4000
4500
0
60
50.6
54.5
61.7
64.5
74.5
72.7
61.5
53.8
45.7
38.0
23.0
12.4
8.3
8.4
6.3
6.6
5.2
5.2
4.8
4.7
52.1 (MIT, UF)
53.3(MIT)
80
109
175
308
428
575
61.4(MIT)
61.7(MIT)
69.2(MIT)
77.2(MIT)
71.2(MIT)
57.1(MIT)
15
158 °W
22 °N
158 °W
16 °N
158 °W
12 °N
158 °W
8 °N
874
1237
1459
1736
2000
2476
2958
4000
4500
30.7(MIT)
17.7(MIT)
16.0(MIT)
12.3(MIT)
10.2(MIT)
10.0(MIT)
9.0(MIT, UF)
7.0(MIT)
5.6(MIT, UF)
15
30
50
75
150
200
400
600
800
1000
1500
2500
3500
4500
30
100
200
400
600
800
2000
3000
4000
5000
15
50
75
100
200
400
600
800
15
30
50
34.31
33.56
32.85
35.65
40.46
51.54
66.95
52.67
30.58
19.32
11.57
6.83
5.20
4.20
31.01
30.11
31.00
56.98
55.02
33.09
25.02
8.74
6.00
4.17
25.65
25.99
25.00
30.66
37.45
27.32
21.21
15.82
28.14
23.80
24.36
16
158 °W
4 °N
158 °W
0 °N
158 °W
4 °S
158 °W
7 °S
30.63
45.17
29.87
26.15
18.75
14.24
11.83
5.50
23.12
22.57
24.70
23.65
23.16
35.58
19.34
14.74
23.12
24.83
27.26
26.24
26.43
24.28
21.37
21.09
22.99
25.14
22.13
17.24
12.53
10.10
4.79
3.24
2.34
24.49
23.84
22.92
22.60
22.69
21.97
18.42
14.01
23.29
22.68
22.80
19.22
19.89
75
100
200
400
1000
1500
3500
4500
15
30
50
75
100
200
400
600
800
15
30
50
100
125
175
200
225
300
400
600
800
1000
2000
3000
4000
15
30
50
75
100
200
400
800
15
30
75
100
200
17
17.06
15.26
13.25
10.26
3.10
1.52
1.50
400
600
800
1000
2000
3000
4000
5000
1.54
Table 2b. Seawater 206Pb/207Pb ratio plotted in Fig. 3. The samples were collected in
October 2004 during SAFE cruise.
Longitude
Latitude
Depth (m)
140 °W
30 °N
50
200
400
600
800
1000
1500
2000
2500
3000
4000
5000
206
Pb/207Pb ratio
1.1587
1.1589
1.1587
1.1610
1.1661
1.1695
1.1797
1.1813
1.1824
1.1835
1.1863
1.1875
18
208
Pb/206Pb ratio
2.1141
2.1097
2.1105
2.1080
2.0989
2.0980
2.0820
2.0844
2.0847
2.0851
2.0845
2.0822
a
b
Fig. 1. Seawater dissolved Pb section in the North Pacific along 140-158 °W.
19
20
Fig. 2. Comparison of seawater 206Pb/207Pb ratio at 30°N, 140°W (SAFe Station) with
the ratios reported for pelagic sediment (Chow and Patterson, 1962), Holocene sediments
(Jones et al., 2001) and ferromanganese nodules (Ling et al., 1997; O’Nions et al., 1998).
21
Pb (pM)
0
20
40
60
80
0
Depth (m)
1000
2000
3000
Wu SAFe, filtered
S & P (1981), unfiltered
4000
MIT SAFe, filtered
MIT SAFe, unfiltered
5000
Fig. 3. Comparison of Pb profile at 30°N, 140°W with the MIT profile determined at the
same station and by Schaule and Patterson (1981) at 32.7 °N, 145 °W in the central North
Pacific Ocean.
22
Fig. 4a. 206Pb/207Pb ratio vs. 1/[Pb] plot for waters below 800 m showing two linear
segments converging at 1500 m. In this projection, linear mixing between endmembers of fixed concentration and isotopic composition results in linear trends.
23
Fig. 4b. T-S diagram for waters below 800 m showing two linear segments converging
at ~1500 m.
24
a
25
b
26
c
Fig. 5. Vertical distribution of modeled and measured Pb concentration (a) and
206
Pb/207Pb ratio (b), and the plot of 206Pb/207Pb ratio vs. 1/(Pb concentration) (c) for water
below 1500 m. The Pb concentration and 206Pb/207Pb ratio are simulated using
4
J  0.019(1 0.035t)e 310
z
pM/yr, RJ = 1.121-1.181 at t = 0-170 yr, RJ = 1.181-1.160 at t
= 170-180 yr and RJ = 1.160 at t = 180-200 yr. The data point at z = -3500 m is estimated

by interpolation from the data at z = -3000 m and -4000 m.
27
Fig.6. 206Pb/207Pb vs. 286Pb/267Pb plot to compare our seawater results (Table 2b) with the
data reported for Pacific surface water (Flegal et al., 1984), aerosols (Bollhofer and
Rosman, 2001) and Fe-Mn nodule (Blanckenburg et al.1996).
28