Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean

Full text

Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean
Ajay K. Singh
a
, Franco Marcantonio
a,
⁎, Mitchell Lyle
b
a
Department of Geology and Geophysics, Texas A&M University, College Station, TX 77843, USA
b
Department of Oceanography, Texas A&M University, College Station, TX 77843, USA
abstractarticle info
Article history:
Received 31 January 2011
Received in revised form 8 June 2011
Accepted 20 June 2011
Available online xxxx
Keywords:
thorium-230
sediment focusing
boundary scavenging
mass accumulation rate
Panama basin
eastern equatorial Pacific Ocean
Age-model derived sediment mass accumulation rates (MARs) are consistently higher than
230
Th-normalized
MARs in the Equatorial Pacific Ocean during the past 25 ka. The offset, being highest in the Panama Basin,
suggests a significant role for deep-sea sediment redistribution (i.e., sediment focusing) in this region. Here,
we test the hypothesis that downslope transport of sediments from topographically high regions that
surround the Panama Basin is the cause of higher-than-expected xs
230
Th inventories over the past 25 ka in
the deeper parts of the basin. We find little difference in xs
230
Th inventories between the highest and lowest
reaches of the basin. Furthermore, there is no correlation between xs
230
Th-derived sediment focusing factors
and water depth which suggests that the topographic highs do not serve as a source of xs
230
Th. A spatial
analysis suggests that there may be an enhanced scavenging effect on xs
230
Th concentrations in sediment
closest to the equator where productivity is the highest, although further data is necessary to corroborate this.
At the equator xs
230
Th-derived focusing factors are high and range from about 1 to 5 during the Holocene and
about 1 to 11 during the last glacial. In contrast, non-equatorial cores show a smaller range in variability from
about 0.7 to 2.8 during the Holocene and from 0.7 to 3.6 during the last glacial. Based on
232
Th flux
measurements, we hypothesize that the location at which eolian detrital fluxes surpass the riverine detrital
fluxes is approximately 300 km from the margin. While riverine fluxes from coastal margins were higher
during the Holocene, eolian fluxes were higher during the last glacial.
© 2011 Elsevier B.V. All rights reserved.
1. Introduction
Essentially all sediments that reach the pelagic ocean floor are
either derived from the continents through weathering processes or
formed as a result of biological productivity in surface water.
Contemporaneous climatic conditions largely affect the processes
and mechanisms that bring these sediments to the ocean floor. For
example, sediment intervals that record higher biogenic fluxes are
often interpreted as being deposited at a time during which export
production to the seafloor was increased. Similarly, intervals during
which lithogenic particle fluxes are high can represent an intensified
transport of continental material via rivers (if close to a continental
margin) and/or wind. Thus, reconstruction of particle fluxes from
oceanic sedimentary archives can broaden our understanding of past
climate conditions.
Historically and to the present, sedimentary mass accumulation
rates (MARs) have been estimated by multiplying the linear
sedimentation rate (LSR), estimated using dated horizons (oxygen-
isotope- or radiocarbon-derived), with sediment dry bulk density.
This method measures the amount of sediment preserved at the sea
floor but does not discriminate between vertically falling particles and
those redistributed by a variety of horizontal advection processes. The
xs
230
Th constant-flux proxy (CFP) method of determining mass
accumulation rates is thought to “see through”such sediment
redistribution processes and is purported to measure the true vertical
flux (Bacon, 1984; Francois et al., 2004). The idea behind this
constant-flux proxy lies in the different geochemical behavior of
thorium and uranium in the oceanic water column. In seawater,
230
Th
is produced by the α-decay of
234
U. Unlike uranium, which has a
constant seawater concentration, thorium is extremely particle
reactive, and the decay product,
230
Th, is rapidly scavenged onto
sinking particles so that the flux of
230
Th to the ocean floor is identical
to its rate of production in the water column (Bacon, 1984). Hence,
MARs within an interval of sediment can be calculated by dividing the
known production rate of
230
Th by the concentration of
230
Th within
thesameinterval.Hence,theverticalflux of any component
preserved in the sediment, F
i
,can be calculated theoretically using
the following equation:
F1=conc
ðÞ
iβZ
xs230Th0
 ð1Þ
in which (conc)
i
is the concentration of component i; βis the production
rate of
230
Th in the water column (0.0267 dpm m
−3
yr
−1
); Z is the
Earth and Planetary Science Letters xxx (2011) xxx–xxx
⁎Corresponding author at: Department of Geology and Geophysics, 3115 MS, TAMU,
Texas A&M University, College Station, TX 77843, USA. Tel.: +1 979 845 9240; fax: +1
979 845 6162.
E-mail addresses: asingh1@neo.tamu.edu (A.K. Singh),
marcantonio@geos.tamu.edu (F. Marcantonio), mlyle@ocean.tamu.edu (M. Lyle).
EPSL-11000; No of Pages 12
0012-821X/$ –see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.epsl.2011.06.020
Contents lists available at ScienceDirect
Earth and Planetary Science Letters
journal homepage: www.elsevier.com/locate/epsl
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

water depth in m; and [xs
230
Th
o
] is the measured sedimentary
230
Th
activity corrected for decay, in situ production of
230
Th from authigenic
234
U, and detrital
230
Th. The elegance of Eq. 1is that the derived
sedimentary flux is, by definition, solely the vertical component of the
preserved sedimentary flux. Furthermore, one can solve for the
‘normalized’sedimentary flux by measuring the concentration of
xs
230
Th alone. The extent that such normalization works depends on
how realistic the assumption is that the production of
230
Th in the water
column is equal to the flux of the scavenged
230
Th to the underlying
sediments (Bacon, 1984;Francois et al., 2004).If the postulated behavior
of oceanic
230
Th is correct, an added benefit to the constant-flux proxy
methodology is that syndepositional sediment redistribution can be
quantified by integrating the xs
230
Th inventory within an interval of
sediment and comparing it to the integrated production of
230
Th in the
overlying water column over the time of accumulation (Suman and
Bacon, 1989). Indeed, the ratio of these two parameters has been
defined by a physical parameter called the “focusing factor, (Ψ)”
(Suman and Bacon, 1989). A Ψvalue of one implies that sediment has
not been redistributed at the studied site. A Ψvalue greater than one
implies sediment in excess of what has been delivered vertically has
been advected by deep-sea horizontal advection (i.e., focusing) to the
studied site, while a Ψvalue less than one implies winnowing or
removal of sediment from the studied site at the time of sediment
deposition (Francois et al., 2004). Model studies have shownthat 70% of
the ocean floor receives a
230
Th flux within 30% of its production in the
water column (Henderson and Anderson, 2003; Siddall et al., 2008),
implying a sensitivity of the xs
230
Th profiling technique that is typically
within +/−30%. This estimate must be considered somewhat tentative
given the reliance of this result on the assumption that isopycnal and
vertical diffusion is a reasonable approximation of ocean mixing
processes inherent in many ocean models (Siddall et al., 2008).
Although age-model-derived and xs
230
Th-normalized MARs have
been widely used in paleoceanographic research, in some cases the
differently calculated MARs are significantly different, and, therefore,
yield competing interpretations. Perhaps the best known of these
discrepancies exists in the equatorial (west, central and east) Pacific
Ocean (Broecker, 2008; Francois et al., 2007; Higgins et al., 1999;
Kienast et al., 2007; Koutavas et al., 2002; Koutavas and Sachs, 2008;
Kowsmann, 1973; Loubere et al., 2004; Lyle et al., 2005, 2007;
Marcantonio et al., 1996; Marcantonio et al., 2001a; Paytan et al.,
1996; Thomas et al., 2000). Here, xs
230
Th-derived focusing factors,
suggest that horizontal sediment transport almost always is higher
(sometimes several times higher) than the vertical flux. The highest
focusing factors (as high as 5.5; Kienast et al., 2007) are observed
during the last glacial in the eastern equatorial Pacific (EEP) Ocean in
the Panama Basin.
In the Panama Basin, using age-model-derived MARs, many
investigators have concluded that particle fluxes during the last
glacial were as much as 100% higher than those during the Holocene,
and are caused by enhanced primary productivity (Lyle, 1988; Lyle et
al., 2002; Paytan et al., 1996; Pedersen, 1983). However, xs
230
Th
normalized MARs for sediments deposited during the last glacial
suggest calcite fluxes that are 30–50% lower than those during the
Holocene (Loubere et al., 2004). These authors contend that the
higher glacial age-model-derived fluxes are due to sediment focusing
processes in the Panama Basin. In addition, Kienast et al. (2007)
reexamined several sites that were studied by others (Loubere et al.,
2004; Lyle et al., 2005) in the Panama Basin and came to a similar
conclusion; namely, that xs
230
Th-normalized MARs are lower and less
variable than age-model-derived MARs, indicating varying degrees of
sediment focusing.
Lyle et al. (2005) disagree with the interpretation that sediment
focusing is widespread in the Panama Basin, and argue that xs
230
Th
normalization overestimates the degree to which sediment redistri-
bution processes are occurring in the EEP. They reason that the
observed larger-than-expected inventories of sedimentary xs
230
Th in
the EEP, that are in excess of those expected from a constant water
column production rate of
230
Th, can be attributed to increased
boundary scavenging at the surface due to increased productivity
close to the equator, in agreement with an analysis by Broecker
(2008). However, within an efficient (low resolution) ocean circula-
tion model, Siddall et al. (2008) found that particle scavenging effects
are not sufficient to explain the additional xs
230
Th inventories
measured in the Panama Basin. Using the Bern3D ocean model, they
considered particle scavenging over a broad range of particle fluxes
reaching up to 10 times higher than actual measurements in the
equatorial Pacific region. Even at the highest end of this range of
particle fluxes, the model by Siddall et al. (2008) suggests only a two-
fold increase in the flux of
230
Th over the production of
230
Th in water
column due to particle scavenging effects.
Kienast et al. (2007) propose that downslope transport of
sediment from the east-west trending Carnegie Ridge, which forms
the southern boundary of the Panama Basin, might explain the
additional xs
230
Th in sediments of the Panama Basin. In this study, we
test this downslope transport hypothesis by measuring xs
230
Th
inventories of sediments deposited on the Cocos and Carnegie
Ridges—regional topographic highs that surround the Panama Basin.
In general, xs
230
Th inventories in sediment from the tops of ridges
suggest sediment focusing factors that are greater than 1 for both the
Holocene and glacial sediments. More importantly, sediment xs
230
Th
inventories on the ridge tops are similar to those in the previously
studied deeper cores (Kienast et al., 2007). If ridge tops were the
source of extra xs
230
Th inventory in the basin, one would expect their
focusing factors to be less than one and/or lower than those measured
in the basin. We explore the potential causes for the larger-than-
expected xs
230
Th inventories throughout the Panama Basin, including
the effects of particle scavenging on
230
Th fluxes to the seafloor.
2. Methodology
2.1. Site selection and sampling strategies
We chose sites to test whether downslope transport from
surrounding-ridge and within-basin topographic highs can explain
the higher inventories of sedimentary xs
230
Th in the Panama Basin as
suggested by Kienast et al. (2007). Cores were retrieved from the
Carnegie and Cocos Ridges that ranged in depth from 712 m to
2230 m (Fig. 1;Table 1). We also selected two deeper cores (TR 163–
22, just west of the Galapagos platform, and Y69-106P, just south of
the Cocos Ridge) to add to the literature data collected from sites in
the central basin or from the foot of the Carnegie Ridge. Our
philosophy in approaching the sampling of cores here differs from
that of previous studies in that we have sampled intervals at a lower
resolution in order to obtain a broader spatial sampling of the
sedimentary inventory throughout the Panama Basin (a total of 9
cores have been sampled). The consistency between average
sediment focusing factors calculated here and those calculated by
Kienast et al. (2007) at nearby sites (see Fig. 1) shows that we are
justified in our sampling methodology.
Selected cores, in addition to those studied previously (Kienast et
al., 2007; Loubere et al., 2004) at depths greater than 2300 m, provide
for a more complete assessment of the xs
230
Th inventory in the
Panama Basin. Cores in this study were obtained from the core
repositories of Lamont-Doherty Earth Observatory, Oregon State
University and University of Rhode Island. Six or seven sediment
intervals spanning the past 25 ka were sampled from each core.
Sample selection for the Holocene and the last glacial was based on
published age models (Benway et al., 2006; Kienast et al., 2007;
Koutavas and Lynch-Stieglitz, 2003; Lea et al., 2006; Martinez et al.,
2003; Pisias and Mix, 1997)(Table 1). In addition to age models for
each core, we also need information on the dry bulk density (DBD) in
order to calculate average MARs and focusing factors. DBDs for cores
2A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

V19-27 and Y69-106P were estimated based on the CaCO
3
content in
Lyle et al. (2002). For cores RC8-102 and MV0005A-27JC, DBDs were
estimated from CaCO
3
concentrations in Ruddiman (1992) and
Kienast et al. (2007) using the equation in Snoeckx and Rea (1994)
(DBD (g cm
−3
)=1/(3.6–0.0279×% CaCO3)). DBD for core TR163-22
was estimated in Lea et al. (2006). For cores TR163-11, TR163-33 and
ME0005A-43JC, average DBDs are estimated using carbonate content
of nearby cores ODP 1241, ME0005A-27JC and ODP 1242, respectively
(Mix et al., 2003 [ODP Leg 202 Scientific Results]). For core TR163-38
we averaged the DBD of three nearby cores (TR163-33, V19-27 and
ME0005A-27JC) with similar sedimentary lithologies and histories.
The average DBD is the least constrained for core V21-29, for which
we assumed an average value of 0.6 g cm
−3
. In order to compare our
dataset with that of Kienast et al. (2007) and Loubere et al. (2004),we
averaged our xs
230
Th-derived MARs and age-model-derived MARs
similarly for two time slices, one for a specified interval covering the
entire Holocene (0–13 ka), and one for a specified interval in the last
glacial (13–25 ka). We used broad time intervals in order to reduce
errors in sedimentation rates caused by errors from assigned ages.
2.2. Radionuclide isotope measurement
Radionuclide measurements followed the procedures described
in Pourmand et al. (2004). Approximately 0.3–0.5 g of dried and
homogenized sediment was spiked with known amounts of
236
U
and
229
Th (spikes used for isotope dilution analysis of uranium and
thorium isotopes). Sample and spike mixtures were digested using
HCl, HNO
3
,HClO
4
and HF acids. After complete sediment digestion
Fig. 1. Map showing location of studied cores in the Panama Basin. Red circles represent cores analyzed here and yellow circles represent cores studied previously (Kienast et al.,
2007; Loubere et al., 2004). Focusing factors are bracketed next to each core identification (first number in bracket represents Holocene (0–13 ka) focusing factor and second number
represents glacial (13–25 ka) focusing factor. This map has been generated using GeoMapApp software available at http://www.geomapapp.org.
Table 1
230
Th-derived Mass Accumulation Rates (MARs), age-model-derived MARs, and focusing factors in Panama Basin sediments during the Holocene and glacial. Equatorial cores
(within ±2°N and S) are shown in bold letters (other cores are non-equatorial). Margin cores are shown in light shade of gray (all other cores are non-margin cores), and deep
cores are located at water depths greater than 2300 m (see text for discussion). Subdivision of these cores into equatorial and non-equatorial, margin and non-margin, and, shallow and
deep cores are mutually inclusive. All MAR values have a common unit (g cm
−2
ka
−1
). Data from Kienast et al. (2007) are italicized.
3A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

Th and U were separated and purified from the digested solution
using ion exchange chromatography. Uranium and thorium isotope
ratios were measured on an Element XR magnetic sector ICP-MS at
Texas A&M University (Table 2). Th and U were analyzed separately
to avoid isotopic interferences during mass spectrometer measure-
ments.
238
U abundance sensitivity at lower masses (
234
U,
235
Uand
236
U) was corrected assuming an exponential decrease in
238
U
counts toward lower masses. In most cases the
238
Uabundance
sensitivity was about 1.5 ppm at 3 amu and 0.6 ppm at 4 amu.
Similarly, the
232
Th abundance was approximately 3.2 ppm at 2 amu
and 1.3 ppm at 3 amu. Mass bias was determined by measuring
the
238
U/
235
U in each sample in the case of uranium analyses, and by
bracketing thorium analyses with measurements of the
238
U/
235
U
in the U500 standard and assuming similar fractionation between
uranium and thorium. Mass bias corrections ranged from about 0.1
to 0.3‰/amu.
Table 2
Uranium, thorium results for Panama Basin cores (see Fig. 1 for location).
Cores Depth
(cm)
Years
(a)
238
U
(dpm/g)
xs
230
Th
o
(dpm/g)
232
Th
(dpm/g)
V19-27 Water depth =1373 m Latitude=−0.46 Longitude = −82
35.5 4500 3.66 1.65 1.08
45.5 5500 1.58 1.17 1.73
64.5 10091 1.48 1.98 0.59
84.5 15218 2.23 1.94 0.23
94.5 17389 2.65 1.94 0.20
114.5 22000 3.82 2.19 0.22
RC8-102 Water depth =2180 m Latitude=−1.4 Longitude = −86.8
2 5600 0.73 4.22 0.10
15 9050 5.14 3.85 0.10
45 15500 4.65 2.04 0.05
60 17850 2.53 3.19 0.09
75 19800 2.73 3.30 0.09
105 23800 5.93 2.43 0.09
TR163-11 Water depth= 1950 m Latitude= 6.4 Longitude = −85.8
11 4900 1.83 5.11 0.28
16 9000 2.59 5.21 0.31
22 13200 3.25 4.67 0.31
28 16200 4.92 5.25 0.28
33 18830 5.00 4.62 0.27
39 25340 3.93 4.85 0.26
V21-29 Water depth =720 m Latitude=−1.0 Longitude = −89.3
19 3933 2.17 1.77 0.04
57 9394 3.20 1.80 0.05
76 12269 3.44 1.71 0.05
95 14856 7.06 1.51 0.05
114 16146 4.96 1.52 0.04
133 16808 4.98 2.02 0.05
ME0005A-43JC Water depth= 1368 m Latitude= 7.8 Longitude = −83.6
3 857 4.52 1.92 0.40
43 6808 5.01 1.82 0.38
83 10710 4.53 1.48 0.32
123 14726 5.57 1.62 0.37
163 18600 4.35 1.80 0.37
206 21920 3.91 1.37 0.32
TR163-22 Water depth= 2830 m Latitude= 0.5 Longitude = −92.4
37 4000 2.23 6.65 0.09
75 10600 3.69 5.29 0.09
112 14500 3.72 5.10 0.11
150 18200 5.01 5.55 0.15
187 21800 4.58 5.29 0.20
225 25300 3.77 5.27 0.17
Y69-106P Water depth= 2870 m Latitude= 2.9 Longitude =−86.5
2 4456 1.01 6.52 0.17
11 7861 2.89 5.73 0.19
20 11876 3.62 6.24 0.26
35 20783 2.51 4.57 0.20
44 26127.2 3.15 6.14 0.23
TR163-38 Water depth =2200 m Latitude=−1.3 Longitude = −81.5
19 4560 2.76 2.07 0.68
38 8510 3.39 1.82 0.90
57 10910 6.43 2.48 0.50
76 13730 6.60 2.11 0.48
95 16500 7.32 1.91 0.59
114 19000 7.56 1.85 0.47
133 22750 8.74 2.25 0.56
TR163-33 Water depth =2230 m Latitude=−1.9 Longitude = −82.5
30 5580 3.78 3.48 0.38
45 8410 3.47 3.13 0.29
60 10900 3.22 2.69 0.25
75 19700 3.87 2.72 0.30
90 21200 4.13 2.67 0.33
4A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

In order to determine the true unsupported sedimentary
230
Th
xs
,
measured concentrations of
230
Th (Table 2) were corrected for
detrital
230
Th and in situ growth of
230
Th from authigenic
234
U
using Eq. 2.
230Thxs
= 230Thmeas−
233U
232Th
!
det
×232Thmeas
"#
−"238Umeas −
233U
232Th
!
det
×232Thmeas
()
×(1−e−λ230t

+λ230
λ230−λ234
×e−λ234t
−e−λ230t

×
234U
233U
!
sw
−1
!)#
ð2Þ
The subscripts xs, meas, det and sw refer to excess (unsupported),
measured, detrital and seawater, respectively. λ
230
and λ
234
are the
decay constants for
230
Th and
234
U, respectively. For the detrital
238
U/
232
Th activity ratio, we assumed a ratio of 0.7, which is the best
estimate for the U/Th activity ratio of detrital material delivered to the
Pacific Ocean (Henderson and Anderson, 2003). All calculations used
a seawater
234
U/
238
U activity of 1.146 (Robinson et al., 2004). In all
cases, except for Holocene intervals in cores closest to the margin (see
our definition of “margin cores”below), the detrital
230
Th amounted
to less than 5% of the total measured
230
Th. Only for one of the
Holocene samples of one margin core was the correction significant
(~50% in sample from 45 to 46 cm in core V19-27). Authigenically-
produced
230
Th made up between 20 and 30% of the measured
230
Th
in all samples, similar to the amount found in sediments studied by
Kienast et al. (2007). Finally, xs
230
Th activities were corrected for
decay since time of sedimentary deposition.
2.3. Replicates and blanks
One quadruplicate and three replicates were run (Table 3). The
average external reproducibility was 12.4% for total uranium
concentration, 2.6% for
230
Th concentration and 2.1% for
232
Th
concentration. The poor average reproducibility for uranium was
due to the uranium reproducibility of one sediment sample from core
V21-29. This one sample had an average external reproducibility of
42.8%. We are uncertain as to why the uranium reproducibility of this
one sample is so poor. Not including the uranium reproducibility
results for core V21-29 leads to an average uranium reproducibility of
about 2.2%, similar to the thorium reproducibility. For samples that
have been replicated, the replicate averages are displayed in Table 3.
Our thorium and uranium blanks consistently make up less than 1% of
analyte, and therefore no blank corrections were necessary.
2.4. Core chronologies
Focusing factors are the ratio of the inventory of sedimentary
230
Th
xs
averaged over some depth interval to its production in the
overlying water column. The greatest uncertainty in the focusing
factor is caused by inaccuracies in the age model (Francois et al., 2004;
Kienast et al., 2007). We tried to avoid age model problems in our
calculations by choosing well-constrained, best available age models
for our cores, and to average the data over longer time spans.
Age models for cores V19-27, RC8-120 and V21-29 are based on
oxygen isotope records of planktonic foraminfera (G. sacculifer and G.
ruber) and 10 planktonic radiocarbon dates (N. dutertrei:Koutavas
and Lynch-Stieglitz, 2003). Age models for cores TR163-38 and
TR163-33 are based on high-resolution (~0.5 to 1 ka) planktonic δ
18
O
records and 3 radiocarbon dates on N. dutertrei, while the age model
for TR163-11 is based on high-resolution (~0.5 to 1 ka) planktonic
δ
18
O(Martinez et al., 2003). The age model for core ME0005A-43JC is
based on combination of planktonic δ
18
O stratigraphy as well as six
radiocarbon dates on N. dutertrei (Benway et al., 2006). Core
chronology of TR163-22 is based on δ
18
OinG. ruber and nine
radiocarbon dates (Lea et al., 2006)onN. dutertrei. The chronology of
Y69-106 is based on planktonic δ
18
O stratigraphy (Pisias and Mix,
1997). Hence, of the nine cores analyzed here, all have oxygen isotope
stratigraphy, and seven have ages calibrated by radiocarbon dating.
Errors introduced into our focusing factor calculations because of
chronological uncertainty are less than 30%. A 30% misestimate of the
Holocene MAR, for example, would require that we misplace the MIS
2/1 boundary by ~ 4 kyr.
Table 3
Uranium, thorium isotopes reproducibility results (STDev represents one standard
deviation from the mean, %rsd represents the relative standard deviation in %).
Core ID Depth (cm) [
235
U]
(dpm/g)
[
238
U]
(dpm/g)
[
230
Th]
(dpm/g)
[
232
Th]
(dpm/g)
V21-29 76 0.21 4.52 2.16 0.04
76 0.29 6.28 2.22 0.05
76 0.43 9.40 2.27 0.05
76 0.17 3.62 2.00 0.05
Average= 0.27 5.95 2.16 0.05
STDev= 0.12 2.55 0.12 0.001
%rsd= 42.84 42.84 5.51 2.80
TR163-33 30 0.17 3.78 3.77 0.38
30 0.19 4.04 3.93 0.39
30 0.18 3.86 3.83 0.40
Average= 0.18 3.89 3.84 0.39
STDev= 0.01 0.13 0.08 0.01
%rsd= 3.41 3.43 2.20 2.63
ME0005A-43JC 3 0.19 4.16 No data No data
3 0.18 4.00 2.17 0.39
3 0.19 4.09 2.12 0.38
Average= 0.19 4.08 2.14 0.38
STDev= 0.004 0.08 0.03 0.01
%rsd= 1.91 1.91 1.41 1.72
ME0005A-43JC 123 0.25 5.53 2.37 0.37
123 0.25 5.41 2.37 0.38
123 0.26 5.55 2.42 0.37
Average= 0.25 5.50 2.38 0.38
STDev= 0.004 0.08 0.03 0.005
%rsd= 1.42 1.42 1.31 1.27
Table 4
Spatio-temporal variability of
232
Th flux in the Panama Basin.
232
Th flux data for the first
five cores are from a previous study (Kienast et al., 2007), while the remaining data are
from this study. Bold letters represent cores that are close to continent (see Results and
discussion).
Core ID Approximate distance
from continent
(km)
232
Th flux
(dpm/m
2
/a)
Holocene Glacial Glacial/holocene
ME0005-24JC 600 1.9 2.6 1.3
Y69-71 600 1.8 2.5 1.4
ME0005-27JC 155 6.3 5.4 0.9
TR163-19 1250 0.8 1.2 1.4
TR163-31 250 7.2 8.9 1.2
V19-27 100 29.2 3.9 0.1
RC8-102 650 1.4 1.6 1.2
TR163-11 400 2.9 3.0 1.0
V21-29 900 0.5 0.5 1.1
ME0005A-43JC 100 7.7 8.0 1.0
TR163-22 1300 1.1 2.2 1.9
Y69-106P 850 2.6 3.0 1.2
TR163-38 40 19.8 14.9 0.8
TR163-33 140 5.8 6.8 1.2
5A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

3. Results
Our MAR and xs
230
Th results in addition to those studied
previously (Kienast et al., 2007) are presented (Table 1) with respect
to their temporal and spatial (latitudinal, bathymetric and distance
from continental margin) variability. In order to investigate temporal
variability of MARs and sediment focusing factors, and to be
consistent with the study of Kienast et al. (2007), we average such
parameters for intervals of sediment deposited during the Holocene
(0–13 ka; the Holocene) and the last glacial (13–25 ka; glacial). To
describe the latitudinal spatial variability of xs
230
Th-derived MARs
and focusing factors, we have divided all cores (Table 1)into
equatorial cores (nine out of fifteen cores that are located within
±2° of equator) and non-equatorial cores (six out of fifteen cores that
are located outside ±2° of equator). Our subdivision of latitudinal
spatial variability into equatorial and non-equatorial cores is based on
the fact that most of the upwelling driven productivity, which may
have an effect on the scavenging efficiency of
230
Th, is taking place
close to the equator (Broecker, 2008; Thomas et al., 2000). To describe
the bathymetric spatial variability, which in effect is a way to test the
downslope transport mechanism to explain higher inventory of
xs
230
Th in the deeper parts of the basin, we have chosen a bathymetric
division of 2300 m. We use the terms “shallow”for cores collected at
depths b2300 m (Table 1) and “deep”for those collected at depths
N2300 m (Table 1). The shallowest sill depth in the Panama Basin is
close to 2300 m (Lonsdale, 1977; Lonsdale and Malfait, 1974), and is
located at a saddle in the Carnegie Ridge. This location may serve as
one entryway through which deep water enters the Panama Basin
from the Peru Basin (Tsuchiya and Talley, 1998)—the other being the
Peru trench, at a similar depth, in the eastern part of the basin. An
additional spatial variability constraint is distance from the continen-
tal margin. We have used our
232
Th flux data (discussed in Section 4.3)
to divide the studied cores into “margin”(within 300 km of con-
tinental margin; Table 4) and “non-margin”cores (more than 300 km
away from continental margin; Table 4).
232
Th flux is a proxy for
continentally-derived detrital material (Anderson et al., 2006;
Marcantonio et al., 2001b; McGee et al., 2007; Pourmand et al.,
2004; Winckler et al., 2008). The division of cores into margin and
non-margin cores is based on a dramatic decrease in the detrital flux
with respect to distance from the continental margin (occurs at
approximately 300 km; see Section 4.3).
3.1. Spatio-temporal variability of mass accumulation rates (MARs)
For all nine cores analyzed here and the six cores from Kienast et al.
(2007),xs
230
Th-normalized and oxygen isotope age-model-derived
MARs were calculated and averaged for sediments deposited during the
Holocene and glacial (Table 1). For the equatorial cores, average
xs
230
Th-normalized MARs for sediment deposited during the Holocene
and glacial are 1.7 and 1.8 g cm
−2
ka
−1
, respectively, suggesting no
significant temporal change in xs
230
Th-normalized MARs. In contrast,
the average oxygen isotope age-model-derived MAR for the same cores
was higher by ~50% during glacial compared to that measured during
Holocene (5.4 g cm
−2
ka
−1
versus 3.6 g cm
−2
ka
−1
). Similarly,
xs
230
Th-normalized average MARs for sediment in the non-equatorial
cores are 1.5 and 1.6 (g cm
−2
ka
−1
) during the Holocene and glacial,
respectively. Again,there is an insignificanttemporal change in xs
230
Th-
normalized MARs measured in non-equatorial cores for sediment
deposited during the Holocene and glacial. Average oxygen isotope age-
model-derived MARs for sediment deposited in the non-equatorial
cores are 2.4 and 3.5 (g cm
−2
ka
−1
) during the Holocene and glacial,
respectively. There is no difference between the Holocene and glacial
average xs
230
Th-normalized MARs for sediments analyzed in the
margin cores (each 2.1 g cm
−2
ka
−1
). In contrast, in the same
margin cores, the average age-model-derived MARs are higher (35%)
during the last glacial (4.2 g cm
–2
ka
–1
) than during the Holocene
(3.1 g cm
–2
ka
–1
)(Table 1). Similarly, the average xs
230
Th-normalized
MAR of the non-margin cores is 1.3 g cm
–2
ka
–1
during the Holocene
compared to 1.4 g cm
–2
ka
–1
during glacial. For the non margin
cores, average age-model-derived MARs are always higher (3.1 and
4.9 g cm
–2
ka
–1
) for the Holocene and glacial, respectively; (Table 1)
than MARs determined using xs
230
Th normalization.
The average xs
230
Th-normalized MARs for shallow cores are 1.8 and
1.9 (g cm
–2
ka
–1
) for sediments deposited during the Holocene and
glacial,respectively. Forthe same shallow cores, the averageage-model-
derived MARs are 3.0 and 4.5 g cm
–2
ka
–1
for the Holocene and glacial,
respectively (Table 1). For the deep cores, the average xs
230
Th-derived
MARs are 1.3 and 1.5 (g cm
–2
ka
–1
) during the Holocene and glacial,
respectively, versusage-model-derived MARs of 3.3 and4.7 (g/cm
2
/ka)
during the same time periods. The xs
230
Th-normalized method of
calculating MARs reveals higher MARs for the shallower cores in
comparison to those for the deeper cores, in contrast to the age-model
method, which suggests similar MARs regardless of depth.
3.2. Spatio-temporal variability of xs
230
Th-derived sediment focusing
factors
Sediment focusing factors were calculated and averaged for
sediments deposited during the Holocene and glacial. During the
last glacial, average focusing factors of all cores are 50% more than
those during the Holocene (3 versus 2; our data and data from Kienast
et al., 2007;Table 1). Focusing factors in equatorial cores display
greater variability than those in non-equatorial cores, and range from
~1 to 5 in the Holocene, and from ~1 to 11 in glacial. The percentage
increase in Holocene to glacial change of focusing factors in the
equatorial cores ranges from no change (TR163-38) to about 170%
(V21-29). Average focusing factors for equatorial cores are 2.3 and 3.6
during the Holocene and last glacial, respectively. In the non-equator
cores, the percentage increase in focusing factor from the Holocene
to glacial ranges from 12% (TR163-11) to 118% (TR163-31). Only one
non-equatorial core, Y69-106P, has a lower focusing factor (~36%)
during the last glacial (Table 1). This core resides within the Panama
Basin at the base of the Cocos Ridge at a water depth of 2870 m. Also,
average focusing factors for non-equatorial cores are 1.6 and 2.1 for
the Holocene and glacial, respectively (Table 1). Cores closest to the
equator not only have the highest focusing factors in the Panama
Basin over the past 25 ka, but also the greatest relative temporal
change in focusing factors, i.e., higher focusing factors during glacial
than in the Holocene.
For margin cores, the average focusing factors during the Holocene
and glacial are 1.6 and 2.1, respectively, so glacial focusing factors are
on average 31% greater than the Holocene. For non-margin cores
these factors are 2.3 for the Holocene and 3.5 for the glacial (Table 1).
For non-margin cores, the increase in average focusing factor during
glacial compared to the Holocene is greater (52%).
Cores studied here and by Kienast et al. (2007) have water depths
that range from 712 to 3209 m (Table 1). Nine of these fifteen cores
were at or close to the tops of ridges that bound the Panama Basin
(Carnegie and Cocos Ridges), and have depths of less than 2300 m.
These shallower cores have average focusing factors during the
Holocene and glacial of 1.8 and 2.9, respectively. Focusing factors for
these shallower cores vary from 0.7 (TR163-11, depth 1950 m) to 3.9
(V21-29, depth 712 m) in the Holocene (Fig. 4), and from 0.8 (TR163-
11, depth 1950 m) to 10.5 (V21-29, depth 712 m) in the glacial. The
shallowest core, V21-29 has the highest focusing factors during both
the Holocene (4.5) and glacial (12). Similarly, the average focusing
factor of our deeper cores during the Holocene and glacial is 2.3
and 3.0, respectively. For cores Y69-106P and TR163-22, the deepest
cores studied by us here within the basin proper, focusing factors
were 1.1 and 2.3 during the Holocene, and 0.7 and 3.7 during the
glacial, respectively 2. No significant correlation exists between
focusing factors and depth of cores (Fig. 2).
6A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

3.3. Spatio-temporal variability of
232
Th fluxes
Average
232
Th fluxes, estimated using the xs
230
Th-normalized
MARs are calculated for the Holocene and last glacial (Table 4). During
the Holocene and last glacial an apparently exponential decay of
detrital fluxes away from the continent is observed.
232
Th fluxes were
higher during glacial than those during the Holocene in all cores with
the exceptions of Carnegie Ridge cores V19-27, ME0005-27JC and
TR163-38, which are closest to the South American margin (Fig. 3).
232
Th fluxes derived using oxygen isotope age models show similar
glacial-interglacial trends in margin and non-margin cores. This is
because changes in
232
Th fluxes are controlled almost entirely by
changes in
232
Th concentration. In general, sites that are within about
300 km of a continental margin (see Section 4.3) have
232
Th fluxes
that are up to an order of magnitude higher throughout the past 25 ka
compared to the same fluxes at sites that are further than 300 km
from a continental margin.
4. Discussion
4.1. xs
230
Th from ridge tops surrounding Panama Basin
Previous
230
Th studies suggest significant amounts of lateral
redistribution of sediments (i.e., focusing factor values N1) in the
deeper sections (2700–3200 m) of the Panama Basin (Kienast et al.,
2007; Kusch et al., 2010; Loubere et al., 2004). Similar xs
230
Th
inventories with focusing factor values N1 have been found
throughout the equatorial Pacific Ocean suggesting that sediment
focusing is a widespread phenomenon throughout the equatorial
sector of the western (Higgins et al., 2002), central (Marcantonio et
al., 1996, 2001a), and eastern (Broecker, 2008; Kienast et al., 2007;
Loubere et al., 2004; McGee et al., 2007) Pacific Ocean. Focusing factor
values are highest for the equatorial Pacific Ocean in the Panama Basin
where much contention over their meaning has arisen (Broecker,
2008; Francois et al., 2007; Kienast et al., 2007; Loubere et al., 2004;
Lyle et al., 2005, 2007).
Kienast et al. (2007) hypothesized that this extra sedimentary
xs
230
Th in the Panama Basin may have been derived from the top
(shallower regions) of the Carnegie Ridge through downslope
transport of sediments. Here, we further test this hypothesis by
measuring xs
230
Th in seven cores located in the topographically
highest regions (i.e., ridge tops; 712–2230 m) of the Panama Basin to
test downslope transport. While there clearly is erosion over parts of
the Carnegie Ridge (Malfait and van Andel, 1980), other parts of the
Carnegie Ridge, e.g., around V19-27 are clearly depositional, as we will
discuss later.
For all but one of seven shallow cores (TR163-11), focusing factors
are greater than 1 for both the Holocene and glacial (Fig. 2). If the
underlying assumption of the xs
230
Th normalization technique is
correct (i.e., that the flux of
230
Th to the ocean floor is constant), the
ubiquitous presence (hills and basins) of inventories of xs
230
Th that
are greater than what is expected from water column production
alone means that sediment focusing is taking place everywhere in the
Panama Basin, even near the tops of ridges (Fig. 2). Moreover, the
average focusing factors in the topographically highest regions of the
basin (1.8 and 2.9 for Holocene and last glacial, respectively) are
similar to those recorded in the deepest parts of the basin (2.3 and 3.0
for Holocene and last glacial, respectively).
Our finding that focusing factors are greater than 1 on or near the
tops of ridges does not agree with the typical observation from high
resolution seismic reflection studies that show basins catch more
sediment than hills, with occasional erosion from highs (Mollenhauer
et al., 2002; Tominaga et al., 2011). Two hypotheses could explain
the observation, either that (1) the sediments sampled on top of
the ridges exhibit ponding (local focusing from surrounding ridge
Fig. 3. Variation of
232
Th flux as measured by distance between core location and
continental margin for sediment deposited during A) the Holocene (0–13 ka) and
B) the last glacial (13–25 ka). Panel C) displays the ratio of the glacial
232
Th flux to the
Holocene
232
Th flux.
232
Th flux has been plotted at the same vertical scale for the
Holocene and glacial for comparison. Long-dashed line in panel C separates cores which
are proximal to the continent from cores which are more distant.
Fig. 2. Bathymetric distribution of average focusing factors for Panama Basin sediment
deposited during the Holoc ene (0–13 ka) and glacial (13–25 ka). Gray squares
represent data from Kienast et al. (2007) and black circles represent data obtained in
this study.
7A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

terrain), or (2) the cores receive their extra inventories of
230
Th in
another way that is not reflective of horizontal sediment movement.
Several seismic reflection profiles of the seafloor in the Panama
Basin (available at www.geomapapp.org) clearly show some erosion-
al and nondepositional surfaces in the topographically highest regions
of the basin. For example, the seismic profile from the Vema cruise
V2104 that passed across the V21-29 site (core with the highest
focusing factor) shows that about 2/3 of the seafloor in the vicinity of
the core is bare, and fits with the idea that some horizontal advection
has taken place at the site of V21-29. Areas around the Carnegie Ridge
gap (~85–86°W) are clearly erosional (Lonsdale and Malfait, 1974;
Malfait and van Andel, 1980). These regions have not yet been studied
for their
230
Th systematics but parts have been surveyed in 2010 and
will be studied in the future.
It is clear that in deeper parts of the Panama basin that the xs
230
Th
technique suggests extensive sediment focusing, and that the flux of
laterally advected sediments are 2–4 times greater than the flux of
that which is rained vertically through the ocean (Kienast et al., 2007).
Sedimentological evidence for significant horizontal transport around
the Panama basin is also extensive (Lonsdale and Malfait, 1974;
Malfait and Van Andel, 1980). The earliest sedimentological mapping
of the Panama Basin is based on grain size distribution (Dowding,
1977), visual observations of erosional surfaces (Heezen and Rawson,
1977), mineralogy (Heath et al., 1974), coarse component of surface
sedimentary cover (Kowsmann, 1973), distribution of suspended
particles (Plank et al., 1973), and textural and dispersal patterns (Van
Andel, 1973). Much of this and seismic work on the ridges (Lonsdale
and Malfait, 1974; Malfait and van Andel, 1980; Van Andel, 1973)
suggest that the sedimentary cover in significant parts of the basin is
heavily reworked by deep water currents, most notably at saddles in
ridges and to the north of saddle. The studies by Lonsdale and Malfait
(1974) and by Malfait and Van Andel (1980), in the Carnegie Gap area
of Carnegie Ridge, found areas of erosion that have a complete
absence of sediment cover, and where downslope transport probably
occurred. One can surmise that such regions of erosion or non-
deposition should contain deficits of
230
Th or, at the very least, show
much smaller inventories of
230
Th than those in the deeper parts of
the basin. With more detailed studies (in progress) near where the
sediments should have been transported, these movements can be
better quantified.
Other parts of the Carnegie Ridge, around V19-27 for example, are
clearly depositional and probably have not supplied much additional
sediment to the Panama Basin (Fig. 4). On ridges especially, one must
worry about sampling bias, i.e., that piston cores tend to be taken from
basins where the sediments are thickest (Francois et al., 2007). The
area around V19-27 was surveyed for drilling on ODP Leg 202 (Site
1239; Mix et al., 2003), so good information exists about the sediment
cover (Fig. 4). About 20% of the ridge top was surveyed while trying to
locate Site 1239. Of the area surveyed about 75% was thickly covered
with sediment. All the smooth topography in Fig. 4 represents
sediment-covered terrain, for example. Even the highest portion of
the ridge just north of V19-27 has discontinuous sediment cover.
Along line 6 it is possible to estimate how variable the average
sedimentation rates have been based on the depth to the first major
seismic horizon compared to its depth at Site 1239. Site 1239,
incidentally, has a sedimentation rate of 4.8 cm/kyr in the upper 50 m,
only slightly lower than that of V19-27 (5.2 cm/kyr). Along line 6, 60%
of the profile has a sedimentation rate between 0.5 and 1.5× that of
Site 1239, 15% of the profile has rates N1.5× that of Site 1239, and a
little less than 20% of the profile has sedimentation rates ~0.5× that of
Site 1239. Based on this and inspection of the other seismic lines, the
site at V19-27 actually has a sedimentation rate only slightly higher
than average, and is, therefore not an anomalously “ponded”site in
comparison to the rest of the ridge where sedimentation appears
uniform. Lastly, the observation that focusing factors are not less than
one at V19-27 suggests that this site and the entire ridge area
surrounding it likely did not serve as a source of focused sediment in
the deeper parts of the Panama Basin.
Other site surveys were made along Cocos and Carnegie Ridge in
order to locate other shallow drillsites for ODP Leg 202 (b2300 m)
sites 1238, 1239, 1241 and 1242 (Mix et al., 2003; see UTIG marine
seismic data portal, http://www.ig.utexas.edu/sdc/cruise.php?
cruiseIn=nemo03mv). The seismic reflection profiles show erosional
areas but also many areas of sediment accumulation. The flanks of the
ridges, e.g. around Site 1238 on the S flank of Carnegie Ridge, are
mostly depositional regions. Areas of nondeposition on the ridges are
significantly smaller than the areas estimated in the simple box model
used to articulate the problem of ridge sources of
230
Th and sediment
(Lyle et al., 2007).
If sampling bias is not an issue, and the source of additional
sedimentary xs
230
Th inventory is not derived within the basin from
the ridge tops, then it is possible that there is an extra-basinal source
of xs
230
Th which derives from the Peru Basin located south of the
Panama Basin. Sedimentary xs
230
Th from the Peru Basin might be
laterally advected into the Panama Basin along with bottom water
through the Ecuador Trench and/or across the central saddle of the
Carnegie Ridge (Lonsdale, 1977). However, we do not have any
evidence that Peru Basin sediment is a source of sedimentary xs
230
Th.
Based on the strong temporal correspondence of alkenone, total
organic carbon and foraminifera fractions (from fine-grained to
coarse-grained) in late-glacial to Holocene sediments of the Panama
Basin, Kusch et al. (2010) argue that the source of any additional
xs
230
Th has to be transported in a syn-depositional fashion from a
local source of xs
230
Th. If the source is extra-basinal, one would expect
to see a temporal decoupling among sediment fractions with different
grain sizes since the finest grain particles that might be transported
long distances (Kusch et al., 2010) would be, presumably, older. There
is the possibility that upwelled intermediate and surface currents
might transport very fine particles from surrounding, less distal, shelf
regions toward the Panama Basin bringing additional xs
230
Th which
could explain higher focusing factors found throughout the region.
Indeed, research has shown that finer particles have higher
inventories of xs
230
Th (Kretschmer et al., 2010; McGee et al., 2010)
and, in some cases, cause an overestimation of focusing factors
Although fine-grained sediment transport from-mid-depth waters is a
possibility, there is no data to suggest that this occurs. We therefore
consider alternative explanations.
4.2. Potential for boundary scavenging effects in the Panama Basin
The main assumption of the
230
Th CFP technique is that the flux of
230
Th to the ocean floor is equal to the production of
230
Th by the decay
of
234
U in the water column. For
230
Th to be a perfect CFP, the residence
time of
230
Th should be zero, and it should be scavenged instanta-
neously as modeled in Eq. (1). Most researchers agree that there is a
limit to this assumption. The extent of lateral movement of
230
Th in the
water column is defined by its residence time in the ocean (τ
230Th
). In
turn, its residence time is defined by the extent to which thorium is
particle reactive (i.e., the degree to which Th is insoluble in seawater).
It is obvious from measurements of dissolved
230
Th in the water
column that the τ
230Th
in the ocean is not zero. General circulation
models which impart oceanic particle-flux fields (e.g., Henderson
et al., 1999; Marchal et al., 2000; Siddall et al., 2005, 2008) estimate a
τ
230Th
of about 20 yrs, suggesting that within 70% of the world's oceans
the flux of
230
Th is within about 30% of its production rate.
The margins of the Pacific Ocean, for example (Anderson et al.,
1983; 1990; Lao et al., 1992, 1993), are regions with increased particle
fluxes where the flux of
230
Th is higher than its known production
rate. The increased scavenging efficiency of
230
Th in such regions leads
to what is known as the boundary scavenging effect. In such cases, the
230
Th normalization technique would underestimate MARs, and
overestimate the degree to which sediment focusing takes places.
8A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

Broecker (2008) suggests that enhanced particle flux due to
enhanced upwelling and associated higher productivity along the
equator delivers larger-than-expected inventories of xs
230
Th to the
underlying sediments. This extra xs
230
Th is speculated to be supplied
by “lateral mixing of equatorial waters with water adjacent to the
equator”(Broecker, 2008), in essence, a boundary scavenging effect
along the equator. In contrast, a recent model paper detailing the
behavior of
230
Th in the open-ocean equatorial Pacific suggests that a
particle flux effect cannot explain the higher than expected inventories
of
230
Th in equatorial Pacific sediments (Siddall et al., 2008). However,
this result relies on the approximation of ocean mixing processes at the
equator by isopycnal and vertical diffusion terms (Siddall et al., 2008).
The exchange of deep waters through the Panama Basin is
relatively rapid, and potentially the large particulate fluxes and
rapid exchange of water could interact to be an effective stripping
mechanism of
230
Th. The residence time of water within the basin is
short because of high geothermal heating (50–80 yrs; Detrick et al.,
1974). Other estimates of the Panama Basin water residence time
range from 42 yrs (Mix et al., 1995 [ODP138 Scientific Results]) to less
than 50 yrs (Lonsdale, 1977). These estimates are on the order of the
residence time of thorium in sea water, suggesting the potential for a
greater flux of
230
Th to underlying sediments.
To investigate the possibility that there are enhanced removal
rates of
230
Th in regions of high particle flux within the Panama Basin,
Fig. 4. Bathymetric and seismic profiles from ODP Leg 202 Site survey (ODP Leg 202 Initial Reports volume, seismic data from NEMO-3, available at the University of Texas Marine
Seismic Data Portal; http://www.ig.utexas.edu) from the top of Carnegie Ridge. It shows the position of core V19-27 studied here relative to the location of ODP Site 1239.
Bathymetric map shows locations of bare zone near rugged topography towards the north as well as sediment accumulation zones just south of ridge tops.
9A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

and given the potential for overestimating the degree of sediment
redistribution, we compared
230
Th-derived focusing factors (Fig. 1;
Table 1) between equatorial and non-equatorial regions (see Section 3
for definition of regions) using our data and data from Kienast et al.
(2007). We excluded continental margin cores that are influenced by
high riverine inputs (Section 4.3) because we wanted to restrict our
analysis to the open ocean. There does seem to be a general
relationship between proximity to the equator (a region of high
particle flux) and higher apparent focusing factors (Fig. 1). This holds
true during both the Holocene and the last glacial, with the latter
period having proportionally higher apparent focusing factors.
Indeed, cores closest to the equator where primary production is
the greatest today have focusing factors that are about twice as high
during the last glacial than during the Holocene (average focusing
factor of 3.6 versus 2.3, respectively; Table 1;Fig. 1). This finding is
corroborated by a recent latitudinal transect study in the eastern
equatorial Pacific, west of Panama Basin at 110°W, that show
latitudinal distribution in focusing factor where the highest focusing
factor was recorded near the equator (McGee et al., 2007). For the
non-equatorial cores, the average xs
230
Th-derived focusing factors are
smaller and more similar (~1.6 versus 2.1) during both the Holocene
and last glacial, respectively (Table 1;Fig. 1). If we are to take the
model of Siddall et al. (2008) at face value, then
230
Th-derived fluxes
can, at most, only overestimate focusing (or underestimate MARs) by
a factor of 1.3. For the equatorial cores, therefore, average focusing
factors can, at most be reduced to about 2.8 and 1.8 for the last glacial
and Holocene, respectively. Although our data point toward the
possibility that enhanced focusing factors nearest the equator may be
a consequence of increased productivity and enhanced scavenging
efficiency of
230
Th (greater than that predicted by the model of Siddall
et al., 2008), additional sediment data is required to further evaluate
this possibility. There is the additional caveat that surface reactions
with different particle types, such as carbonates (Chase et al., 2002)
and hydrothermal manganese (Frank et al., 1994), may also have an
effect on the scavenging efficiency of xs
230
Th. Hence, it may be
possible that current models underestimate the
230
Th-particle flux (or
scavenging efficiency) effect, which may be greater than 30%. The
pertinent question is: is it possible to obtain better estimates of the
scavenging effect so that we can quantitatively unravel it from
calculated focusing factors based on
230
Th systematics? Additional
water column
230
Th data is required to rigorously measure the
particle-flux effect on
230
Th. Specifically the extent to which a
latitudinal diffusion gradient in dissolved
230
Th concentration exists,
with lowest dissolved concentrations at the equator where produc-
tivity is the greatest, needs to be investigated.
4.3.
232
Th fluxes in the Panama Basin
232
Th fluxes are used as a proxy for the flux of detrital continental
material, and have been useful in deciphering past dust dynamics and
changes in wind patterns/strength associated with climate change
(Anderson et al., 2006; Marcantonio et al., 2001b; McGee et al., 2007;
Pourmand et al., 2004; Winckler et al., 2008). Here, we use
230
Th-
derived
232
Th fluxes in order to easily compare our detrital fluxes with
other studies. More importantly (as we note in Section 3.3), although
absolute detrital fluxes calculated using age-model-derived MARs are
not identical with those calculated using
230
Th-derived MARs, relative
differences from core to core remain the same. Dust flux analyses
based on
232
Th data suggest that there were two-fold increases in
eolian fluxes during glacial in the central equatorial (Anderson et al.,
2006) and eastern equatorial Pacific Ocean (McGee et al., 2007). In our
study, the core furthest to the west at 92.4°W (core TR 163–22), the
glacial/the Holocene
232
Th flux ratio is about 2, identical to the
Glacial/Holocene ratios at both 110°W (McGee et al., 2007) and
140°W (Anderson et al., 2006). It is clear that the major part of the
detrital fractions at these last two locations is eolian. Hence, based on
the similar Glacial/Holocene
232
Th flux ratios, we interpret our detrital
signal at 92.4°W to be predominantly eolian derived. Comparing
average
232
Th flux over the past 25 ka, we find similar values at 140°W
and 110°W (~ 0.6 dpm m
−2
a
−1
). At 92°W, however, the average
232
Th flux is 1.8 dpm m
−2
a
−1
(Table 3), or 3 times higher than that at
140°W and 110°W. East of 92°W, great increases in the detrital flux
(average flux over 25 ka as high as 17 dpm m
−2
a
−1
) are due to the
non-eolian detrital component, which is most likely made up of clays
transported to the margin by riverine runoff and diffused out to sea.
Although most of the measured
232
Th fluxes in our non-margin
cores are higher in glacial than in the Holocene (Fig. 3;Table 3), three
out of the six margin cores closest to the margin (Table 3), including
those studied by Kienast et al. (2007), have higher
232
Th fluxes during
the Holocene (Fig. 3). As one moves away from the continent the
glacial/the Holocene detrital flux ratio (Fig. 3C) increases. Margin
cores which record higher terrigenous runoff during the Holocene
have glacial/Holocene
232
Th flux ratios less than 1 (Fig. 3C), while
non-margin cores have glacial/the Holocene
232
Th flux ratios greater
than 1. We suggest that the increase in this ratio, as distance to the
margin increases, represents an increase in the detrital component
being more influenced by eolian-relative to riverine-borne material.
Furthermore, we believe the higher detrital fluxes for the cores closest
to the margin are due to increased continental runoff during the
Holocene in Central America and northern South America in
agreement with a recent study by Rincón-Martínez et al. (2010).
The significant spatial distribution of our cores (Fig. 1), in addition to
those studied previously (Kienast et al., 2007),enablesusto
approximate the threshold distance where the detrital component
transitions from being mainly composed of river-borne material
versus being mainly composed of wind-blown material (Fig. 3).
Indeed, this threshold distance may be coincident with the location at
which the glacial/Holocene detrital flux ratio is approximately equal
to 1, i.e., at about 300 km (Fig. 3).
5. Summary and conclusions
In the Panama Basin, xs
230
Th-derived MARs are lower than age-
model derived MARs, and lead to the prediction that significant
sediment focusing (i.e., lateral redistribution of sediments by deep-
sea currents) occurs. Downslope transport from surrounding ridge
tops has been proposed as a source for excess inventory of xs
230
Th
found in the deepest parts of the basin. We have tested this hypothesis
and find a ubiquitous presence of larger-than-expected inventories of
xs
230
Th on the tops and flanks of ridges that surround the Panama
Basin. Focusing factors in these regions are as high as those in the
deeper parts of the basins suggesting the ridges and flanks are not
supplying the high inventories of xs
230
Th to the deep basin.
The spatio-temporal distribution of focusing factors and MARs is
such that the highest average values are those determined for
sediment deposited during the last glacial in the equatorial cores.
Lowest sediment focusing factors (still greater than 1, for the most
part) are determined for the non-equatorial cores during the
Holocene. Higher equatorial focusing factors during the glacial could
be related to scavenging effects on
230
Th driven by higher productivity
in the Panama Basin. To determine whether this is the case, more data
is needed: specifically, a complementary latitudinal transect study of
water column
230
Th between high- and low-particle flux regions, and
better control on the erosional areas. Based on
232
Th flux measure-
ments, we hypothesize that the location at which eolian (as opposed
to riverine) fluxes dominate the detrital flux occurs at approximately
300 km from the margin.
Acknowledgements
Sediment samples were provided by the core repositories at
Lamont–Doherty Earth Observatory (supported by NSF grant OCE-07-
10 A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

51761), Oregon State University (supported by NSF grant OCE-
0648164), and University of Rhode Island (supported by NSF grant
OCE-06-44625). This research is funded by NSF grant OCE-0851056 to
FM and ML. We thank Ken and Jane Williams for their generous
support of the radiogenic geochemistry isotope facility at Texas A&M
University. We thank Mark Siddall and two anonymous reviewers for
constructive comments.
References
Anderson, R.F., Bacon, M.P., Brewer, P.G., 1983. Removal of Th-230 and Pa-231 from the
Open Ocean. Earth and Planetary Science Letters 62 (1), 7–23.
Anderson, R.F., Lao, Y., Broecker, W.S., Trumbore, S.E., Hofmann, H.J., Wolfi, W., 1990.
Boundary scavenging in the Pacific-Ocean —a comparison of Be-10 and Pa-231.
Earth and Planetary Science Letters 96 (3–4), 287–304.
Anderson, R.F., Fleisher, M.Q., Lao, Y., 2006. Glacial-interglacial variability in the
delivery of dust to the central equatorial Pacific Ocean. Earth and Planetary Science
Letters 242 (3–4), 406–414.
Bacon, M.P., 1984. Glacial to interglacial changes in carbonate and clay sedimentation in
the Atlantic-Ocean estimated from Th-230 measurements. Isotope Geoscience 2
(2), 97–111.
Benway, H.M., Mix, A.C., Haley, B.A., Klinkhammer, G.P., 2006. Eastern Pacific warm pool
paleosalinity and climate variability: 0–30 kyr. Paleoceanography 21, PA3008.
doi:10.1029/2005PA001208.
Broecker, W., 2008. Excess sediment
230
Th: transport along the sea floor or enhanced
water column scavenging? Global Biogeochem. Cycles 22, GB1006. doi:10.1029/
2007 GB003057.
Chase, Z., Anderson, R.F., Fleisher, M.Q., Kubik, P.W., 2002. The influence of particle
composition and particle flux on scavenging of Th, Pa and Be in the ocean. Earth and
Planetary Science Letters 204, 215–229.
Detrick, R.S., Williams, D.L., Mudie, J.D., Sclater, J.G., 1974. Galapagos spreading center —
bottom-water temperatures and significance of geothermal heating. Geophysical
Journal of the Royal Astronomical Society 38 (3), 627–637.
Dowding, L.G., 1977. Sediment dispersal within Cocos Gap, Panama Basin. Journal of
Sedimentary Petrology 47 (3), 1132–1156.
Francois, R., Frank, M., Rutgers van der Loeff, M.M., Bacon, M.P., 2004. 230Th
normalization: an essential tool for interpreting sedimentary fluxes during the
late Quaternary. Paleoceanography 19, PA1018. doi:10.1029/2003PA000939.
Francois, R., et al., 2007. Comment on “Do geochemical estimates of sediment focusing
pass the sediment test in the equatorial Pacific?”by M. Lyle et al. (2005).
Paleoceanography 22, PA1216. doi:10.1029/2005PA001235.
Frank, M., Eckhardt, J.-D., Eisenhauer, A., Kubik, P.W., Dittrich-Hannen, B., Segl, M.,
Mangini, A., 1994. Beryllium 10, thorium 230, and protactinium 231 in Galapagos
Microplate sediments: implications of hydrothermal activity and paleoproductivity
changes during the last 100,000 years. Paleoceanography 9, 559–578.
Heath, G.R., Moore, T.C., Roberts, G.L., 1974. Mineralogy of surface sediments from
Panama-Basin, Eastern-Equatorial Pacific. Journal of Geology 82 (2), 145–160.
Heezen, B.C., Rawson, M., 1977. Visual observations of contemporary current erosion
and tectonic deformation on Cocos Ridge Crest. Marine Geology 23 (1–2), 173–196.
Henderson, G.M., Anderson, R.F., 2003. The U-series toolbox for paleoceanography.
Reviews of Mineralology and Geochemistry 52, 493–531.
Henderson, G.M., Heinze, C., Anderson, R.F., Winguth, A.M.E., 1999. Global distribution
of the Th-230 flux to ocean sediments constrained by GCM modelling. Deep-Sea
Research Part I-Oceanographic Research Papers 46 (11), 1861–1893.
Higgins, S.M., Broecker, W., Anderson, R., McCorkle, D.C., Timothy, D., 1999. Enhanced
sedimentation along the equator in the western Pacific. Geophysical Research
Letters 26 (23), 3489–3492.
Higgins, S.M., Anderson, R.F., Marcantonio, F., Schlosser, P., Stute, M., 2002. Sediment
focusing creates 100-ka cycles in interplanetary dust accumulation on the Ontong
Java Plateau. Earth and Planetary Science Letters 203 (1), 383–397.
Kienast, S.S., Kienast, M., Mix, A.C., Calvert, S.E., Francois, R., 2007. Thorium-230
normalized particle flux and sediment focusing in the Panama Basin region during
last 30,000. Paleoceanography. doi:10.1029/2006PA001357.
Koutavas, A., Lynch-Stieglitz, J., 2003. Glacial-interglacial dynamics of the eastern
equatorial Pacificcoldtongue–Intertropical Convergence Zone system reconstructed
from oxygen isotope records. Paleoceanography 18. doi:10.1029/2003PA000894.
Koutavas, A., Sachs, J.P., 2008. Northern timing of deglaciation in the eastern equatorial
Pacific from alkenone paleothermometry. Paleoceanography 23, PA4205.
doi:10.1029/2008PA001593.
Koutavas, A., Lynch-Stieglitz, J., Marchitto, T.M., Sachs, J.P., 2002. El Nino-like pattern in
ice age tropical Pacific sea surface temperature. Science 297 (5579), 226–230.
Kowsmann, R.O., 1973. Coarse components in surface sediments of Panama-Basin,
Eastern Equatorial Pacific. Journal of Geology 81 (4), 473–494.
Kretschmer, S., Geibert, W., Rutgers van der Loeff, M.M., Mollenhauer, G., 2010. Grain
size effects on
230
Thxs inventories in opal-rich and carbonate-rich marine
sediments. Earth and Planetary Science Letters 294, 131–142.
Kusch, S., Eglinton, T.I., Mix, A.C., Mollenhauer, G., 2010. Timescales of lateral sediment
transport in the Panama Basin as revealed by radiocarbon ages of alkenones, total
organic carbon and foraminifera. Earth and Planetary Science Letters 290 (3–4),
340–350. doi:10.1016/j.epsl.2009.12.030.
Lao, Y., Anderson, Broecker, W.S., Trumbore, S.E., Hofmann, H.J., Wolfli, W., 1992.
Transport and burial rates of Be-10 and Pa-231 in the Pacific-Ocean during the
Holocene Period. Earth and Planetary Science Letters 113 (1–2), 173–189.
Lao, Y., Anderson, R.F., Broecker, W.S., Hofmann, H.J., Wolfli, W., 1993. Particulate fluxes
of Th-230, Pa-231, and Be-10 in the northeastern Pacific-Ocean. Geochimica Et
Cosmochimica Acta 57 (1), 205–217.
Lea, D.W., Pak, D.K., Belanger, C.L., Spero, H.J., Hall, M.A., Shackleton, N.J., 2006.
Paleoclimate history of Galapagos surf ace waters over the last 135,000 yr.
Quaternary Science Reviews 25 (11–12), 1152–1167.
Lonsdale, P., 1977. Inflow of bottom water to Panama Basin. Deep-Sea Research 24 (12),
1065–1101.
Lonsdale, P., Malfait, B., 1974. Abyssal dunes of foraminiferal sand on Carnegie Ridge.
Geological Society of America Bulletin 85, 1697–1712.
Loubere, P., Mekik, F., Francois, R., Pichat, S., 2004. Export fluxes of calcite in the eastern
equatorial Pacific from the Last Glacial Maximum to the present. Paleoceanography
19, PA2018. doi:10.1029/2003PA000986.
Lyle, M., 1988. Climatically forced organic-carbon burial in equatorial Atlantic and
Pacific Oceans. Nature 335 (6190), 529–532.
Lyle, M., Mix, A., Pisias, N., 2002. Patterns of CaCO3 deposition in the eastern tropical
Pacific Ocean for the last 150 kyr: evidence for a southeast Pacific depositional spike
during marine isotope stage (MIS) 2. Paleoceanography 17 (2), 1013. doi:10.1029/
2000PA000538.
Lyle, M., Mitchell, N., Pisias, N., Mix, A., Martinez, J.I., Paytan, A., 2005. Do geochemical
estimates of sediment focusing pass the sediment test in the equatorial Pacific?
Paleoceanography 20, PA1005. doi:10.1029/2004PA001019.
Lyle, M., Pisias, N., Paytan, A., Martinez, J.I., Mix, A., 2007. Reply to comment by R.
Francois et al. on “Do geochemical estimates of sediment focusing pass the
sediment test in the equatorial Pacific?”: further explorations of 230Th normal-
ization. Paleoceanography 22, PA1217. doi:10.1029/2006PA001373.
Malfait, B.T., Van Andel, T.H., 1980. A modern oceanic hardground on the Carnegie
Ridge in the eastern Equatorial Pacific. Sedimentology 27, 467–496.
Marcantonio, F., Anderson, R.R., Stute, M., Kumar, N., Schlosser, P., Mix, A.C., 1996.
Extraterrestrial 3He as a tracer of marine sediment transport and accumulation.
Nature 383, 705–707.
Marcantonio, F., Anderson, R.F., Higgins, S., Stute, M., Schlosser, P., Kubik, P.W., 2001a.
Sediment focusing in the central equatorial Pacific ocean. Paleoceanography 16, 260–267.
Marcantonio, F., Anderson, R.F., Higgins, S., Fleisher, M.Q., Stute, M., Schlosser, P., 2001b.
Abrupt intensification of the SW Indian Ocean monsoon during the last
deglaciation: constraints from Th, Pa, and He isotopes. Earth and Planetary Science
Letters 184, 505–514.
Marchal, O., Francois, R., Stocker, T.F., Joos, F., 2000. Ocean thermohaline circulation and
sedimentary Pa-231/Th-230 ratio. Paleoceanography 15 (6), 625–641.
Martinez, I., Keigwin, L., Barrows, T.T., Yokoyama, Y., Southon, J., 2003. La Nina-like
conditions in the eastern equatorial Pacific and a stronger Choco jet in the northern
Andes during the last glaciation. Paleoceanography 18 (2), 1033.
McGee, D., Marcantonio, F., Lynch-Stieglitz, J., 2007. Deglacial changes in dust flux in the
eastern equatorial Pacific. Earth and Planetary Science Letters 257 (1–2), 215–230.
McGee, D., Marcantonio, F., McManus, J.F., Winckler, G., 2010. The response of excess
230
Th and extraterrestrial
3
He to sediment redistribution at the Blake Ridge,
western North Atlantic (2010). Earth and Planetary Science Letters 299 (1–2),
138–149. doi:10.1016/j.epsl.2010.08.029.
Mix, A.C., Pisias, N.G., Rugh, W., Wilson, J., Morey, A., Hagelberg, T., 1995. Benthic
foraminiferal stable isotope record from Site 849, 0–5 Ma: Local and global climate
changes. In: Pisias, N.G., Mayer, L., Janecek, T., Palmer-Julson, A., van Andel, T.H.
(Eds.), Proc. ODP,/Scientific Res ults/138, College Station, TX (Ocean Drilling
Program), pp. 371–412.
Mix, A.C., Tiedemann, R., Blum, P., et al., 2003. Proc. ODP, Init. Repts., 202: College Station,
TX (Ocean Drilling Program). doi:10.2973/odp.proc.ir.202.2003.
Mollenhauer, G., Schneider, R.R., Muller, P.J., Spiess, V., Wefer, G., 2002. Glacial/
interglacial variability in the Benguela upwelling system: spatial distribution and
budgets of organic carbon accumulation, Global Biogeochem. Cycles 16 (4), 1134.
doi:10.1029/2001GB001488.
Paytan, A., Kastner, M., Chavez, F.P., 1996. Glacial to interglacial fluctuations in
productivity in the equatorial Pacific as indicated by marine barite. Science 274
(5291), 1355–1357.
Pedersen, T.F., 1983. Increased productivity in the eastern Equatorial Pacific during the
last glacial maximum (19,000 to 14,000 Yr Bp). Geology 11 (1), 16–19.
Pisias, N.G., Mix, A.C., 1997. Spatial and temporal oceanographic variability of the
eastern equatorial Pacific during the late Pleistocene: evidence from Radiolaria
microfossils. Paleoceanography 12 (3), 381–393.
Plank, W.S., Ronald, J., Pak, H., Zaneveld, V., 1973. Distribution of suspended matter in
Panama Basin. Journal of Geophysical Research 78 (30), 7113–7121.
Pourmand, A., Marcantonio, F., Schulz, H., 2004. Variation in productivity and eolian
fluxes in the northeastern Arabian Sea during the past 110 ka. Earth and Planetary
Science Letters 221, 39–54.
Rincón-Martínez, D., Lamy, F., Contreras, S., Leduc, G., Bard, E., Saukel, C., Blanz, T.,
Mackensen, A., Tiedemann, R., 2010. More humid interglacials in Ecuador during
the past 500 kyr linked to latitudinal shifts of the equatorial front and the
Intertropical Convergence Zone in the eastern tropical Pacific. Paleoceanography
25, PA2210. doi:10.1029/2009PA001868.
Robinson, L.F., Belshaw, N.S., Henderson, G.M., 2004. U and Th concentrations and
isotope ratios in modern carbonates and waters from the Bahamas. Geochimica et
Cosmochimica Acta 98, 1777–1789.
Ruddiman, W., 1992. Calcium carbonate database. IGBP PAGES/World Data Center for
Paleoclimatology Data Contribution Series #92-001. NOAA/NGDC Paleoclimatology
Program, Boulder, Colorado, USA.
Siddall, M., Henderson, G.M., Edwards, N.R., Muller, S.A., Stocker, T.F., Joos, F., Frank, M., 2005.
231 Pa/
230
Th fractionation by ocean transport, biogenic particle flux and particle type.
Earth and Planetary Science Letters 237, 135–155. doi:10.1016/j.epsl.2005.05.031.
11A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020

Siddall, M., Anderson, R.F., Winckler, G., Henderson, G.M., Bradtmiller, L.I., McGee, D.,
Franzese, A., Stocker, T.F., Muller, S.A., 2008. Modeling the particle flux effect on
distribution of 230Th in the equatorial Pacific. Paleoceanography 23, PA2208.
doi:10.1029/2007PA001556.
Snoeckx,H., Rea, D.K., 1994.Dry bulk densityand CaCO3 relationships in upperQuaternary
sediments of the eastern equatorial Pacific. Marine Geology 120, 327–333.
Suman, D.O., Bacon, M.P., 1989. Variations in Holocene sedimentation in the North-
American basin determined from Th-230 measurements. Deep-Sea Research Part
a-Oceanographic Research Papers 36 (6), 869–878.
Thomas, E., Turekian, K.K., Wei, K.Y., 2000. Productivity control of fine particle transport
to equatorial Pacific sediment. Global Biogeochemical Cycles 14 (3), 945–955.
Tominaga, M. , Lyle, M., Mitchell, N.C., 2011. Se ismic interpretation of pelagic
sedimentation regimes in the 18–53 Ma eastern equatorial Pacific: basin-scale
sedimentation and infilling of abyssal valleys. Geochemistry, Geophysics, Geosys-
tems 12 (3). doi:10.1029/2010GC003347 22 pp.
Tsuchiya, M., Talley, L.D., 1998. A Pacific hydrographic section at 88 degrees W: Water-
property distribution. Journal of Geophysical Research-Oceans 103 (C6), 12899–12918.
Van Andel, T.H., 1973. Texture and dispersal of sediments in Panama-Basin. Journal of
Geology 81 (4), 434–457.
Winckler, G., Anderson, R.F., Fleisher, M.Q., Mcgee, D., Mahowald, N., 2008. Covariant
glacial–interglacial dust fluxes in the equatorial Pacific and Antarctica. Science 320
(5872), 93–96.
12 A.K. Singh et al. / Earth and Planetary Science Letters xxx (2011) xxx–xxx
Please cite this article as: Singh, A.K., et al., Sediment focusing in the Panama Basin, Eastern Equatorial Pacific Ocean, Earth Planet. Sci. Lett.
(2011), doi:10.1016/j.epsl.2011.06.020