Relationships between the stable isotopic signatures of livingand fossil foraminifera in Monterey Bay, California
Jonathan B. Martin and Shelley A. DayDepartment of Geological Sciences, University of Florida, Gainesville, Florida 32611, USA ([email protected])
Anthony E. RathburnGeology Program, Indiana State University, Terre Haute, Indiana 47809, USA
Also at Scripps Institution of Oceanography, IOD-0218, 9500 Gilman Drive, La Jolla, California 92093, USA
M. Elena PerezGeology Program, Indiana State University, Terre Haute, Indiana 47809, USA
Also at Natural History Museum of Los Angeles County, Invertebrate Paleontology, 900 Exposition Boulevard, LosAngeles, California 90007, USA
Chris Mahn and Joris GieskesScripps Institution of Oceanography, IOD-0218, 9500 Gilman Drive, La Jolla, California 92093, USA
[1] Fossil foraminifera are critical to paleoceanographic reconstructions including estimates of past
episodes of methane venting. These reconstructions rely on benthic foraminifera incorporating and
retaining unaltered the ambient isotopic compositions of pore fluids and bottom waters. Comparisons are
made here of isotopic compositions of abundant live and fossil foraminifera (Uvigerina peregrina,
Epistominella pacifica, Bulimina mexicana, and Globobulimina pacifica) collected in Monterey Bay, CA
from two cold seeps (Clam Flats and Extrovert Cliffs) and from sediments �5 m outside of the Clam Flats
seep. Clam Flats has steep d13CDIC gradients (to <�45%), but DIC at Extrovert Cliffs is less enriched in12C (to approximately �22%). Oxygen isotope values of fossil foraminifera at Clam Flats are �1.5%enriched in 18O over the living foraminifera, as well as those of both live and fossil foraminifera at
Extrovert Cliffs, suggesting they may have lived during the last glacial maximum. Statistical comparisons
(Student’s t and Kolmogorov-Smirnov tests) of d13C and d18O values indicate that live and fossil
foraminifera come from different populations at both Clam Flats and Extrovert Cliffs. At Clam Flats, the
difference appears to result from alteration enriching some fossil foraminifera in 12C over live foraminifera.
At Extrovert Cliffs, the fossil foraminifera are enriched in 13C over the live foraminifera, suggesting they
lived prior to the onset of venting and thus that venting began recently. The short time of venting at
Extrovert Cliffs may be responsible for the less alteration there compared with Clam Flats. These results
indicate that preservation of foraminifera is likely to be poor within long-lived cold seeps, but that
foraminifera living in the surrounding sediment may incorporate and preserve broad basin-wide changes in
isotopic compositions of the ambient water.
Components: 14,491 words, 10 figures, 10 tables.
Keywords: methane seeps; carbon isotopes; oxygen isotopes; benthic foraminifera; paleoclimate; pore water geochemistry.
Index Terms: 4806 Oceanography: Biological and Chemical: Carbon cycling; 4870 Oceanography: Biological and
Chemical: Stable isotopes; 4804 Oceanography: Biological and Chemical: Benthic processes/benthos.
G3G3GeochemistryGeophysics
Geosystems
Published by AGU and the Geochemical Society
AN ELECTRONIC JOURNAL OF THE EARTH SCIENCES
GeochemistryGeophysics
Geosystems
Article
Volume 5, Number 4
16 April 2004
Q04004, doi:10.1029/2003GC000629
ISSN: 1525-2027
Copyright 2004 by the American Geophysical Union 1 of 25
Received 8 September 2003; Revised 26 January 2004; Accepted 2 March 2004; Published 16 April 2004.
Martin, J. B., S. A. Day, A. E. Rathburn, M. E. Perez, C. Mahn, and J. Gieskes (2004), Relationships between the stable
isotopic signatures of living and fossil foraminifera in Monterey Bay, California, Geochem. Geophys. Geosyst., 5, Q04004,
doi:10.1029/2003GC000629.
1. Introduction
[2] Fossil foraminifera have long been used to
understand the isotopic evolution of seawater for
paleoceanographic reconstructions [e.g., Emiliani,
1955; Shackleton, 1974, 1977]. For example, re-
cent observations of d13C values of foraminiferal
tests suggest that basin-wide changes in d13CDIC
may result from major release of isotopically light
methane during dissociation of gas hydrate depos-
its [Wefer et al., 1994; Dickens et al., 1995; Kennett
et al., 2000]. These studies depend on the relation-
ship between isotopic compositions of benthic
foraminifera and pore waters and assume that
foraminifera faithfully record and preserve ambient
isotopic compositions. These studies also require
calibrations for biological factors (vital effects) that
alter foraminiferal carbonate isotope signatures
from those controlled by abiotic reactions and the
ambient environmental conditions. A simple rela-
tionship has been found in several slope settings
between the carbon isotopic compositions of
foraminifera tests and the d13CDIC values of pore
water [McCorkle et al., 1990, 1997]. In these
settings, foraminifera living at the greatest depths
in the sediment are increasingly enriched in 12C
compared with foraminifera that live at shallower
depths, in part reflecting a DIC pool that becomes
enriched in 12C during regeneration of organic
carbon. Recent studies have shown, however, that
foraminifera precipitate their tests far from equilib-
rium with the pore waters at cold seeps, where
d13CDIC values can be <�45% [Rathburn et al.,
2003; Torres et al., 2003].
[3] Cold seeps are discharge points for fluids that
originate deep within the sediment column
[Hovland and Judd, 1988]. Fluids include water,
as well as free and dissolved methane, CO2,
H2S from shallow SO4 reduction, and other
oceanographically and atmospherically important
compounds. These compounds provide energy
sources for benthic chemosynthetic-based food
webs [Barry et al., 1996], which can be used to
identify the locations of cold seeps. They also
create large vertical and horizontal gradients of
d13CDIC. The fluxes of these compounds, and their
associated impacts on ocean chemistry and climate,
depend on concentrations, flow rates, spatial dis-
tributions of cold seeps, and perhaps most impor-
tant, the length of time that cold seeps remain
active. That colds seeps are transient has been
shown by fossil vent sites [Carson et al., 1991;
Orange et al., 1999], from modeling of diffusive
decay of chemical and thermal anomalies [Moore
et al., 1988; Fisher and Hounslow, 1990; Shi and
Wang, 1994], and dating of fossil Calyptogena
clams [Lalou et al., 1992; Lallemand et al.,
1992]. The timescale of transience is poorly con-
strained, but will be important for quantifying
long-term fluxes of dissolved components and their
impacts on ocean chemistry and climate.
[4] One scale of transience is observed as varia-
tions in flow rates and reversal in flow from into
and out of the sediment, which occur on timescales
of hours to days [Torres et al., 2002; Tryon et al.,
2002]. The lifetime of cold seeps from initiation to
cessation of flow appears to be longer than these
short term fluctuations in flow velocities. For
example, average flow appeared to be steady state
during repeated visits to and monitoring of cold
seeps over periods ranging from weeks to years
[e.g., Foucher et al., 1992; Martin et al., 1997]. If
transience is caused by variations in pressure
gradients driving flow [e.g., Moore et al., 1990;
Wang et al., 1990; Tobin et al., 1993] or as a result
of porosity reduction by cementation [e.g., Carson
et al., 1991; Orange et al., 1999] then the lifetime
of cold seeps may be on the order of decades to
centuries. Estimating time for long-term transience,
and thus the time-averaged flux of dissolved
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solutes, would require a sedimentary record for the
presence of seeps, possibly found in the carbon
isotopic composition of fossil benthic foraminifera.
[5] Large gradients in d13CDIC also make cold
seeps good locations to study the equilibration
between foraminiferal calcite and ambient
d13CDICvalues [Rathburn et al., 2003]. Foraminif-
era have been shown to live in cold seeps regard-
less of the high concentrations of H2S there
[Rathburn et al., 2000, 2003; Bernhard et al.,
2001]. Complications of equilibration studies may
arise because cold seep waters typically are super-
saturated with respect to carbonate minerals, driv-
ing diagenetic alteration of fossil foraminiferal tests
[Torres et al., 2003]. The relationships between
d13CDIC values of pore waters, foraminiferal isoto-
pic composition, and foraminiferal preservation at
cold seeps and surrounding sediment can be stud-
ied through comparisons of isotopic compositions
of live and fossil foraminifera both inside and
outside of cold seep environments. Only a few
studies have made such comparisons at noncold
seep sites [e.g., McCorkle et al., 1990] and even
fewer have studied the isotopes of live foraminifera
from cold-seep environments [e.g., Rathburn et al.,
2000, 2003; Hill et al., 2003; Torres et al., 2003].
Many studies base their conclusions on relatively
few total samples of foraminifera as well as using
multiple specimens for a single isotope measure-
ment. In this paper we report isotopic composition
of large numbers of live as well as fossil forami-
nifera from within and outside of two distinct cold
seep sites in Monterey Bay, CA. These data allow
us to address questions of the equilibration of
foraminifera with ambient d13CDIC and the poten-
tial record of cold seep venting in the isotopic
composition of fossil foraminiferal tests.
2. Previous Work: Climate, MethaneVenting, and Foraminiferal Records
[6] Evidence for linkages between gas hydrate
dissociation, methane venting, changes in d13CDIC
values of pore water and bottom water, and global
climate change comes from carbon isotopic com-
positions of benthic and high-latitude planktonic
foraminifera coupled with estimates of decreased
stability of gas hydrate with warming bottom
waters [e.g., Paull et al., 1991; Wefer et al.,
1994; Dickens et al., 1995, 1997; Kennett et al.,
2000]. For example, Wefer et al. [1994] found
carbon isotope values that ranged to �5% in the
benthic foraminifera, Bolivina seminuda and
Nonionella auris along the Peruvian margin during
isotope stage 5. Wefer et al. [1994] speculated that
the light isotopic composition was a primary signal
of oxidation of methane released from gas hydrates
along the margin. Similar light isotope excursions
(to �5%) have been found in a variety of benthic
foraminiferal species in Santa Barbara Basin
[Kennett et al., 2000]. The light excursions corre-
late with interstadial periods, suggesting a link to
increased outgassing of gas hydrate methane dur-
ing periodic changes in temperatures of bottom
water in the basin over the past 60,000 years.
According to this idea, at times of increased bottom
water temperatures, gas hydrate dissociation raised
the boundary of methane into depths within the
sediment sufficiently shallow to reach the zone in
which foraminifera live, thereby lowering the
d13CDIC values and isotope ratios of the benthic
foraminifera.
[7] An alternate explanation was provided by Stott
et al. [2002] through observations of modern
d13CDIC gradients and live (stained) benthic fora-
minifera from the Santa Barbara and Santa Monica
basins. Isotope mass balance calculations suggest
that steep DIC gradients and enrichment of 12C in
the upper 2 cm of the basin sediments are not
necessarily influenced by methane oxidation, but
instead can be driven by the oxidation of photo-
synthate carbon. Benthic foraminifera incorporate
the resulting isotope signatures, possibly account-
ing for the light isotopic excursions observed by
Kennett et al. [2000] in the Pleistocene benthic
foraminifera, although this mechanism would not
cause the observed light isotopic excursion in
planktonic foraminifera found in the Santa Barbara
Basin.
[8] Cold seeps have provided good locations to
study the equilibration of foraminifera with pore
water DIC. In Gulf of Mexico cold seeps, forami-
nifera exhibit a wider range in carbon isotopic
compositions (�1.3 to �3.6%) than nonseep fo-
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raminifera [Sen Gupta et al., 1997], but the isotopic
compositions of the foraminifera are far from
equilibrium with the light isotopic compositions
of the DIC [Sen Gupta et al., 1997]. These benthic
foraminifera are considered unaltered because of
careful screening during picking, as well as oxygen
isotopic compositions that retain values that are in
equilibrium with the bottom water temperatures
and isotopic compositions [Sen Gupta and Aharon,
1994; Sen Gupta et al., 1997]. The disequilibrium
of live foraminifera with d13CDIC indicate that
foraminifera in seeps do not directly incorporate
the light d13CDIC values of the seeps, but the wider
range of d13C values than those of foraminifera
living in nonseep locations has been suggested to
be a record of methane venting [Sen Gupta et al.,
1997; Rathburn et al., 2000, 2003].
[9] Although ecology and isotopic composition of
live infaunal benthic foraminifera are known to
be affected by vital effects and microhabitats
[Corliss, 1985; McCorkle et al., 1990], isotopic
compositions of fossil foraminifera have been
found to differ from live foraminifera at cold
seeps. Rathburn et al. [2000] found fossil foram-
inifera from depths of 10 to 20 cmbsf at seep
sites from the Eel River Basin at the northern
California margin were isotopically lighter by 3 to
7% than living (stained) foraminifera at depth
<4 cmbsf although visual observations indicated
the foraminifera were unaltered and consequently,
the observed differences were attributed to a
primary signal of light isotopic compositions of
the d13CDIC caused by oxidation of methane in the
Eel River Basin.
[10] Care is taken in paleoclimate studies to collect
foraminifera that appear to be unaltered because
the isotopic composition of foraminiferal carbonate
is linked to its preservation state, which depends on
the saturation state in the pore waters [Rathburn et
al., 2000; Stott et al., 2002]. In the Santa Barbara
Basin, Reimers et al. [1996] have shown that
carbonate minerals become supersaturated at
depths below 2 cmbsf and Ca profiles indicate
that authigenic calcite precipitates throughout the
sediment column. Any diagenetic alteration to
foraminiferal tests could modify the record of
methane release.
3. Methods
3.1. Study Locations, Characteristics,and Sampling Methods
[11] Samples were collected from two previously
identified cold seeps in Monterey Bay (Figure 1).
Monterey Bay is located at the boundary between
the North American and Pacific plates, which are
separated by right-lateral strike slip faults including
the San Andreas, Ascension, San Gregorio, and
Monterey Bay fault zones (see Orange et al.
[1999] for review). Along with the strike slip
motion, slight compression forms minor thrust
faults, folds and uplift, which created the bathy-
metric high informally named Smooth Ridge
(Figure 1). The uplift, faulting, and associated
compression may provide driving forces for fluid
flow for cold seeps there, along with density-
induced flow from generation of hydrocarbons
[Martin et al., 1997].
[12] Two cold seep sites were sampled during this
study: Extrovert Cliffs which was sampled on Dive
1780 and is located at 36�46.40N, 122�5.10W in
�955 m water depth, and Clam Flats, which was
sampled on Dive 1781 and is located �15 km
away on Smooth Ridge at 36�44.70N, 122�16.60Win �1000 m water depth (Figure 1). The two sites
are characterized by patchily distributed chemo-
synthetic communities including bacterial mats and
Figure 1. Location map of the two cold seeps sampledas part of this project.
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associated macrofauna such as vesicomyid clams
(Figure 2). The Clam Flat location has been most
intensively studied and has been found to contain
methane at concentrations up to 841 mM [Barry et
al., 1996]. The methane is largely biogenic in
origin, although it may also include some thermo-
genic methane [Martin et al., 1997] and high
molecular weight hydrocarbons [Lorenson et al.,
2002]. Detailed sampling of pore fluids at Clam
Flats revealed strong horizontal gradients in the
pore fluid compositions from within to outside the
communities, which suggest flow is confined to the
regions colonized by chemosynthetic organisms
[Martin et al., 1997; Rathburn et al., 2003].
[13] Samples were collected using the R/V Point
Lobos and ROV Ventana, both operated by the
Monterey Bay Aquarium Research Institute (see
Etchemendy and Davis [1991] for a description of
the capabilities of the ROV Ventana). Suites of
Figure 2. Cold seeps in Monterey Bay. (a) Extrovert Cliffs and (b) Clam Flats. The black dots in Figure 2arepresent the location of cores that are listed by the dots. In Figure 2b the core barrel for core 1781-PC80 is beinginserted into the mud. The set of reference cores at Clam Flats is located �5 m north of the cored sites shown inthe photograph. The turbulent area labeled 1781-PC31 is the location of that core which had just been collected. Thereference core from this site is located �5 m south of the rim of the clam community. In Figure 2a the handle of thecore barrel is �10 cm long. In Figure 2b, �20 cm of the core barrel extends from the sediment.
GeochemistryGeophysicsGeosystems G3G3
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cores were collected from within and outside of
cold seep communities (Table 1). For this study,
four specific areas were targeted including clam
communities and bacterial mats that mark the
location of seeps and sediment several meters from
the seeps. Three cores were collected at three
locations: (1) a clam community at Clam Flats,
(2) bare sediment 5 m north of this clam commu-
nity at Clam Flats, and (3) a clam community at
Extrovert Cliffs (Table 1). The fourth location,
sampled by one core, was a bacterial mat growing
within the clam community that was sampled at
Extrovert Cliffs (Figure 2 and Table 1). Several
other cores were collected throughout the region,
and selected data from these cores are reported in a
companion paper [Rathburn et al., 2003]. Data are
included here only from cores that had sufficient
numbers of live and fossil foraminiferal tests for
statistical analyses.
[14] Each core collected was dedicated to a specific
analysis. One short push core (designated as PC##,
where ## represents the specific core tube number)
was subsampled every two centimeter while at sea
and the sediment was centrifuged immediately to
extract pore water. A second short push core was
sectioned soon after collection over the upper
10 cm at intervals of 0.5 to 1 cm and preserved
in 4% buffered formaldehyde for later staining and
picking of foraminifera (see Rathburn et al. [2003]
for a detailed description of procedures). Hydraulic
piston cores (designated in Table 1 as HPC#, where
# represents the core tube number) are typically 2
to 3 times longer than the push cores. The entire
length of these cores was sectioned every centi-
meter soon after collection. This sediment was
preserved without stain in air-tight plastic bags
for later picking of all benthic foraminifera. Cores
are labeled by dive number: 1780 is the dive to
Extrovert Cliffs and 1781 is the dive to Clam Flats.
3.2. Pore Water Geochemistry
[15] Pore water was separated from the sediment
by centrifugation. Measured chemical analyses of
the pore waters include major and minor elements,
metals, and d13CDIC. Selected elemental data are
reported in Rathburn et al. [2003]; only the alka-
linity and the d13CDIC of the pore water are
included in this paper. Alkalinity was measured
by Gran titration immediately following extraction
of the pore water. The d13CDIC values were mea-
sured using techniques described by Graber and
Aharon [1991]. For this technique, approximately 3
to 5 cm3 of pore water were stored in pre-evacuated
containers (vacutainers) and poisoned with Hg2Cl2.
Gas was extracted from the vacutainers at the
University of Florida (UF) by injection of �100 mlof 100% H3PO4. This gas was cryogenically
cleaned of contaminating gas phases in an off-line
vacuum line, and stored in flame-sealed, 5-mm
diameter glass tubes. Standardization of the method
was achieved with KHCO3, with an isotopic com-
position of �23.91% when measured as a solid.
The KHCO3 was dissolved into two solutions with
concentrations of 400 and 750 mg/g KHCO3, which
was then extracted following the procedures for the
pore waters. A standard was extracted following
every fifth sample and the average value measured
was �23.37 ± 0.20% (1s). Sample data have been
corrected for the difference between the dissolved
and solid isotope ratios of the KHCO3. All gas was
measured automatically with a VG Prism II mass
spectrometer at the University of Florida following
Table 1. Cores and Samples Used in Study
Location and Dive Number Site Description Core Number Use Interval, cm
Extrovert Cliffs Dive 1780 Clam Community 1780-PC30 Stained 0–51780-HPC5 Unstained 0–311780-PC79 Pore water 0–12
Bacterial Mat 1780-PC31 Pore water 0–12Clam Flats Dive 1781 Clam Community 1781-PC31 Stained 0–5
1781-HPC5 Unstained 0–271781-PC80 Pore water 0–17
Reference (5 m north of clam community) 1781-PC71 Stained 0–51781-HPC6 Unstained 0–331781-PC38 Pore water 0–18
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introduction to the instrument by an automated
cracker system.
3.3. Isotopic Analysis of Foraminifera
[16] Push core samples were prepared at Indiana
State University (ISU) and hydraulic piston core
samples were prepared at UF. Push core sediment
was treated with Rose Bengal stain solution fol-
lowing procedures outlined in Rathburn and
Corliss [1994]. Although this technique has draw-
backs [Bernhard, 1988; Corliss and Emerson,
1990], it is the most practical way to separate live
from fossil foraminifera [Rathburn et al., 2000].
Foraminifera that had at least one chamber stained
by Rose Bengal were considered to have been alive
at the time of collection. Foraminifera that were
treated with Rose Bengal, but were not stained
were considered to be dead/fossil. All foraminifera
from the hydraulic piston cores are considered to
be fossil, although some from shallow depths could
have been alive at the time of collection. Many
more unstained than stained foraminifera occur in
the stained push core samples, implying a relatively
small chance of picking live foraminifera from the
unstained samples. The maximum number of live
foraminifera occur at depths of 2 to 3 cmbsf
[Rathburn et al., 2003], and thus the chance of
identifying a live foraminiferan as fossil becomes
negligible at greater depths.
[17] The stained sediment was wet-sieved through
nested 63 and 150 mm mesh sieves and the stained
foraminifera were wet-picked from the >150 mmsize fraction. The nonstained sediment was soni-
cated if necessary to break up the sediment, washed
and wet-sieved through nested 63 and 125 mmmesh
sieves. The samples were washed onto filter paper
and dried at 60�C. Large samples of stained and
unstained sediment were split into manageable size
fractions prior to picking. All foraminifera were
stripped of organic matter by soaking in 15% hydro-
gen peroxide for 20min and then rinsed inmethanol.
All foraminifera were sonicated in methanol to
remove debris. Procedures differed at ISU and UF;
foraminifera processed at ISUwere sonicated before
the hydrogen peroxide treatment and while those at
UF were sonicated after the hydrogen peroxide
treatment. Globobulimina pacifica tests were
broken open and visible debris was removed with a
fine-tipped paint brush. All sampleswere oven-dried
at 60�C prior to loading into the mass spectrometer.
[18] Foraminifera were reacted at 73�C with anhy-
drous phosphoric acid in a Kiel III device connected
to a Finnigan MAT 252 isotope ratio mass spec-
trometer at UF. Approximately 20 mg of test mate-
rial was reacted, which corresponds to roughly one
to six tests per analysis (exact numbers of speci-
mens per analyses are reported in appendix A).
With large specimens, particularly of U. peregrina
and G. pacifica, half of individual tests were
analyzed to reduce the volume of CO2. Data is
reported relative to the PDB standard and precision
was measured with an internal standard of Carrera
marble calibrated with NBS-19. Precision of repli-
cate analyses of the Carrera marble is ±0.04% for
d18O and ±0.08% for d13C.
3.4. Statistical Analysis
[19] Two statistical tests were applied to the data,
including Student’s t test assuming unequal vari-
ance for those populations with normal distribu-
tions and the Kolmogorov-Smirnov two-sample
test (K-S test) for populations that are not normally
distributioned [Siegel and Castellan, 1988]. Both
of these statistical tests assess whether the samples
come from the same population, which can be
expressed as the null hypothesis
H0 : m1 ¼ m2 ð1Þ
where m1 and m2 represent the average values for
two sets of isotopic data from individual forami-
nifera specimens. The populations that are com-
pared with these statistics include the live relative
to fossil foraminifera from clam communities at
Clam Flats and Extrovert Cliffs and the live
relative to fossil foraminifera from the reference
cores at Clam Flats. Additional comparisons were
made between the fossil foraminifera at the clam
community and reference core at Clam Flats.
[20] Normality of all data sets was evaluated using
the Kolmogorov-Smirnov one-sample test by com-
paring the population distribution with a normal
distribution. At Extrovert Cliffs, populations of all
species show normal distributions of both their
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oxygen and carbon isotope ratios for both fossil
and live foraminifera at a significance level of 5%,
allowing the application of the Student’s t-test.
With the exception of the d13C values of the
U. peregrina from the clam community at Clam
Flats, all other pairs of comparisons made at Clam
Flats were not normally distributed and no trans-
formation could be found to convert these data to
normal distributions. Consequently, all data from
Clam Flats were assessed using the K-S test. The
normally distributed data for U. peregrina was also
assessed using Student’s t test and results of both
tests are reported for that species.
4. Results
4.1. Alkalinity and Isotopic Compositionof DIC
[21] Gradients of dissolved constituents of the pore
water vary over short horizontal distances in both
of the sampled cold seeps [Rathburn et al., 2003],
as exemplified in the depth distribution of alkalin-
ity (Figure 3). The steepest gradient occurs at Clam
Flats in core 1781-PC80, which was collected from
the middle of the clam community. In this core,
alkalinity reaches concentrations of 11 mM by the
first subsample at 0–1 cmbsf, reflecting rapid flow
of water across the sediment-water interface [e.g.,
Martin et al., 1996, 1997; Rathburn et al., 2003].
In contrast, alkalinity increases to only �3.5 mM
by 11 cmbsf in core 1781-PC38, which is located
only 5 m from core 1781-PC80. These large
variations in alkalinity gradients over short hori-
zontal distances suggest that flow is largely re-
stricted to the clam communities [Rathburn et al.,
2003]. The gradients of alkalinity at Extrovert
Cliffs are less pronounced than at Clam Flats. For
example, core 1780-PC79 from the clam commu-
nity at Extrovert Cliffs has alkalinity gradients
similar to core 1781-PC38 at Clam Flat which is
located outside of the clam community (Figure 3).
Within the bacterial mat at Extrovert Cliffs
(Figure 2), core 1780-PC31 has alkalinity concen-
trations that reach �20 mM by 8 cmbsf.
[22] Gradients in the values of d13CDIC show
similar trends to the alkalinity concentrations
(Figure 4) and all pore waters are enriched in12C over seawater concentrations. Clam Flat core
1781-PC80 from the clam community shows the
lowest values and the steepest gradients, decreas-
ing to �36.5% in the uppermost centimeter of
sediment and with values <�40% below this
depth (Figure 4). Similar to the alkalinity concen-
trations, the reference core 1781-PC38 at Clam
Flats has a less extreme gradient, although
d13CDIC decreases to �21.6% by 18 cmbsf. At
Extrovert Cliffs, core 1780-PC79 in the clam
community has a slight decrease with depth of
d13CDIC values to �8.6% by 12 cmbsf, reflecting
its slight increase in alkalinity. The bacterial mat
site at Extrovert Cliffs has values of d13CDIC that
decrease more steeply (to values of �22%) than
within the clam communities, also reflecting sharp
Figure 3. Alkalinity versus depth. Core 1780-PC79(open circles) is from a clam community and 1780-PC31 (open squares) is from a bacterial mat atExtrovert Cliff. The two cores are separated by lessthan one meter (e.g., Figure 2). Core 1781-PC80 (soliddiamonds) is from a clam community and 1781-PC38(solid circles) is a ‘‘reference core’’ from outside theclam community at Clam Flats. The two cores areseparated by �5 m.
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horizontal gradients in the values of the d13CDIC
similar to those of alkalinity.
4.2. Isotopic Compositions of Foraminifera
[23] Numerous foraminiferal species were found at
all the cold seeps. Rathburn et al. [2003] discusses
variations in the taxa and isotopic compositions of
live foraminifera, and this paper extends that work
by focusing on the few taxa that are abundant in both
the live and fossil fractions. Four separate species,
including U. peregrina, E. pacifica, B. mexicana,
and G. pacifica, are abundant at Extrovert Cliffs in
cores 1780-PC30 and 1780-HPC5 (Figure 5). There
is little difference in the ranges of either the carbon
or oxygen isotopic compositions of the living and
fossil foraminifera from these cores.
[24] In contrast to the Extrovert Cliffs foraminifera,
only U. peregrina occurs in abundance as both live
and fossil specimens in cores 1781-PC31 and
1781-HPC5 from the clam community at Clam
Flats. Epistominella pacifica and B. mexicana are
abundant as fossils, but few live specimens were
found at this site (Figure 6). The most striking
differences occur in the d18O values of the fossil
foraminifera at Clam Flats, which are �1.5%lower in the fossil foraminifera than the live
foraminifera at Clam Flats and the live and fossil
foraminifera at Extrovert Cliffs (Figures 5 and 6).
The d13C values of the fossil foraminifera exhibit a
wider range and overall lower values than the live
foraminifera at Clam Flats, as well as the live and
fossil foraminifera at Extrovert Cliffs. The lowest
d13C values of �15.6% for all specimens occurs at
the clam community at Clam Flats.
[25] Two species, U. peregrina and E. pacifica,
occur in abundance as both live and fossil speci-
mens in the reference cores 1781-PC71 and 1781-
HPC6 outside of the clam community at Clam
Flats (Figure 7). Fossil specimens of both species
also exhibit oxygen isotopic compositions that are
�1.5% lower than the live foraminifera at Clam
Flats and the fossil and live foraminifera at Extro-
vert Cliffs, but have values similar to the fossil
specimens in the cores from the clam communities
at Clam Flats. In contrast with the oxygen isotopic
compositions, carbon isotopic values are similar
between the live and fossil foraminifera in the
reference site. The carbon isotopic compositions
are fairly constant with depth, particularly com-
pared with the foraminifera from the clam commu-
nities and range between approximately �1 and
�2%.
4.3. Statistical Analyses
[26] At the Extrovert Cliff seep site, the mean
values are similar for isotopic compositions of
individual foraminiferal species (Table 2). None-
theless, the null hypothesis (equation (1)) is
rejected at the 5% confidence level for compar-
isons of carbon isotope ratios of live versus fossil
foraminifera U. peregrina, E. pacifica, and
G. pacifica and for these three species as well
as B. mexicana for the oxygen isotope ratios.
Only B. mexicana has carbon isotope ratios that
can not be shown to be statistically different
Figure 4. The d13CDIC versus depth. Core 1780-79(open circles) is from a clam community and 1780-31(open squares) is from a bacterial mat at Extrovert Cliff.The two cores are separated by less than one meter. Core1781-80 (solid diamonds) is from a clam communityand 1781-38 (filled circles) is a ‘‘reference core’’ fromoutside the clam community at Clam Flats. The twocores are separated by �5 m.
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between live and fossil specimens. Regardless of
the close value to the isotope ratios of live and
fossil foraminifera, the t test suggests that live and
fossil foraminifera at Extrovert Cliffs are derived
from separate populations.
[27] At Clam Flats, the average oxygen isotope
ratios show large differences between the live and
fossil foraminifera at both the clam community
and the reference site with the average d18Ovalues for live foraminifera <3.61% and the
average for the fossil foraminifera >4.52%(Figure 7 and Table 3). Analysis of normality
for the oxygen isotopes shows the populations are
not normally distributed, but for all species,
normal distributions can be achieved for both
the fossil and live populations by disregarding
one to six specimens (total n ranges between 18
and 72; Table 3). To achieve a normal distribu-
tion, outliers are excluded from the fossil forami-
nifera only if d18O values are <4%, and excluded
from the live foraminifera if d18O values are
>4%. Except for the K-S test results for
U. peregrina at the reference site, the null
hypothesis is rejected for all other pairs of foram-
iniferal populations (Table 3). These results
suggest that the fossil and live foraminifera at
Clam Flats come from different populations.
[28] The K-S test was applied to the isotopic
composition of fossil foraminifera in the refer-
ence and clam community sites at Clam Flats
(Table 4). For these comparisons, the null hy-
pothesis was rejected for the carbon isotopic
Figure 5. Isotope ratios of live (filled circles) and fossil (open circles) foraminifera from clam communityat Extrovert Cliffs seep site (Dive 1780 Cores HPC5 and PC30). (a) U. peregrina, (b) E. pacifica, (d) B Mexicana,(d) G. pacifica.
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composition of U. peregrina and E. pacifica but
was not rejected for the oxygen isotopic compo-
sition of either species.
5. Discussion
5.1. Preservation and Alteration of theMonterey Bay Foraminifera
[29] In the Monterey Bay pore fluids, high alkalin-
ity concentrations (Figure 3) associated with
high pH values suggest that carbonate minerals
will also be supersaturated, especially at Clam
Flats [Rathburn et al., 2003]. Regardless of this
supersaturation, scanning electron microscopy of
selected Monterey Bay foraminifera suggests that
their tests have had little diagenetic alteration.
Figure 8 shows examples of E. pacific and
U. peregrina from >20 cmbsf at the Extrovert
Cliffs clam community. These specimens show
no signs of changes in texture or of overgrowths
on the surfaces of the foraminifera to indicate
diagenetic alteration of the foraminiferal calcite
that might cause shifts in the isotopic signature of
the tests when they grew. These depths are well
within horizons that have previously been shown to
Figure 6. Isotope ratios of live (solid circles) and fossil (open circles) foraminifera from clam community at ClamFlats seep site (Dive 1781 Cores HPC5 and PC30). (a) U. peregrina, (b) E. pacifica, (c) B. Mexicana.
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be supersaturated with respect to calcite in similar
organic carbon rich settings of the Santa Barbara
Basin, although not at seep sites [e.g., Reimers et
al., 1996]. The Extrovert Cliff site is characterized
by less steep alkalinity gradients than at Clam
Flats, possibly restricting alteration (Figure 3).
[30] Although alkalinity concentrations are higher
at Clam Flats than Extrovert Cliffs, the Clam Flats’
foraminifera also appear to lack diagenetic alter-
ation (Figure 9) although the live foraminifera
would not be expected to be altered [e.g., Rathburn
et al., 2000]. The similarity of the textures of the
fossil specimens to the live foraminifera reflects
lack of alteration in the fossil foraminifera. Al-
though carbonate alteration has not previously
been reported at Clam Flats, Stakes et al. [1999]
have described perfect pyrite framboid molds of
several species of benthic foraminifera with the
pyrite occasionally encased in high Mg calcite.
This sulfide mineralization reflects rapid sulfate
reduction and high sulfide concentrations in the
area [Barry et al., 1996; Martin et al., 1997]. Not
all foraminifera were observed prior to isotopic
analyses, however, and it is possible that those with
the lightest isotopic values (e.g., Figure 6) could
have been altered. These alterations may be recog-
nizable in shifts of average isotopic compositions
of the fossil and live foraminifera.
5.2. Controls of Isotope Ratios of ColdSeep Foraminifera
[31] At the Extrovert Cliffs clam community, the
mean values for oxygen and carbon isotopic com-
positions of both the fossil and live foraminifera
differ by 0.08 and 0.19% for oxygen and 0.04 and
0.21% for all four of the species that are common
at this site (Table 2). Regardless of these small
differences, results of the t-test analyses suggest
that live and fossil foraminifera originate from
different populations. A couple of possible explan-
ations could be given for this result. One is that the
fossil foraminifera have been diagenetically altered
following death and burial in the seep environment,
regardless of the lack of visual observations for
diagenesis (Figure 8). The values of the mean
Figure 7. Isotope ratios of live (solid circles) andfossil (open circles) foraminifera from the referencesite �5 m outside of the clam community at ClamFlats seep site (Dive 1781 Cores HPC5 and PC 71).(a) U. peregrina, (b) E. pacifica.
Table 2. Student’s t-Test Results, Live Versus FossilForaminifera at Extrovert Cliffsa
Isotope Species n1 n2 mlive mfossil t-test
d13C U. peregrina 27 35 �0.50 �0.60 rejectedE. pacifica 12 70 �0.65 �0.44 rejectedB mexicana 9 18 �0.80 �0.76 not rejectedG. pacifica 26 24 �1.35 �1.04 rejected
d18O U. peregrina 27 35 3.06 3.24 rejectedE. pacifica 12 70 3.18 3.28 rejectedB mexicana 9 18 3.28 3.47 rejectedG. pacifica 26 24 3.32 3.40 rejected
aData are for foraminifera from cores EC-HPC5 and EC-PC30.
Numbers of specimens (n), mean values (m) of live and fossilforaminifera, and results of student’s t test.
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isotopic compositions, however, argue against this
explanation. The live foraminifera are considerably
enriched in 13C over the d13CDIC pool, and conse-
quently, precipitation of calcite overgrowths on the
fossil foraminiferal tests should decrease the d13Cvalues of the fossil foraminifera compared to the live
foraminifera. With the exception of U. peregrina,
however, the mean carbon isotopic compositions of
fossil foraminifera are heavier than live foraminif-
era. The average oxygen isotope ratios of fossil
foraminifera are also isotopically heavier than the
live foraminifera. If upward flow increases the
temperature of pore water at the cold seeps [e.g.,
Henry et al., 1996] without changing the d18Owater
values, the foraminifera would be expected to shift
to isotopically lighter values.
[32] A second possible explanation for the differ-
ence between fossil and live foraminiferal isotope
ratios at Extrovert Cliffs is that the fossil forami-
nifera lived prior to the onset of venting and
enrichment of the pore water DIC in 12C through
discharge and oxidation of methane. The shift
toward isotopically light values of the live forami-
nifera suggests that they incorporate some of the
isotopically light DIC, regardless of the large
disequilibrium. The higher d13C values of the fossil
foraminifera suggest that there has been insuffi-
cient time for alteration to occur, or for the car-
bonate saturation state to become sufficiently
supersaturated to drive alteration.
[33] The enrichment in 18O by �1.5% of the fossil
foraminifera at Clam Flats over the live foraminif-
era there and both live and fossil foraminifera at
Extrovert Cliffs does not appear to be caused by
alteration of the fossil foraminifera following
burial. Although the variations with depth are
unknown for d18Owater at these locations, most
water-rock reactions such as clay mineral diagen-
esis tend to deplete the pore water in 18O, which
should decrease the d18O values of overgrowths or
altered tests. The primary process enriching pore
waters in 18O is through gas hydrate dissociation,
but there have been no direct or geophysical
observations (e.g., bottom simulating reflectors)
of gas hydrates in Monterey Bay [e.g., Orange et
al., 1999]. Furthermore, alteration following burial
should occur at temperatures elevated above bot-
tom water values. If there was no change in the
pore water d18O values, an increase in temperature
would result in depletion in 18O in the altered
foraminifera tests with a corresponding decrease
in their d18O values.
[34] The average d18O value for all fossil forami-
nifera at Clam Flats is �4.5%, a value expected for
foraminifera living during the last glacial maxi-
mum [e.g., Shackleton, 1977; Shackleton and
Opdyke, 1973]. Few live foraminifera (1 to 6 per
species) have d18O values >4% and few fossil
foraminifera have d18O values <4%. Excluding
these anomalous isotope ratios from the data sets
creates a normal distribution of the remaining
Table 3. Student’s t-Test and 2 Sample K-S Test Comparisons Live Versus Fossil Foraminifera at Extrovert Cliffsa
Location Isotope Species n1a n2 mlive mfossil K-S Test t-test Excludedb
Seep Site d13C U. peregrina 37 72 �0.91 �2.20 rejected rejected 0d18O U. peregrina 37 72 3.20 4.62 rejected rejected 1
Reference Site d13C U. peregrina 27 55 �1.33 �1.27 not rejected N/A N/AE. pacifica 18 54 �0.76 �0.97 rejected N/A N/A
d18O U. peregrina 27 55 3.31 4.56 rejected rejected 6E. pacifica 18 54 3.61 4.52 rejected rejected 5
aData are for foraminifera from cores CF-HPC5 and CF-PC31 from the clam community and CF-HPC6 and CF-PC71 from the reference site.
Numbers of specimens (n), mean values (m) of live and fossil foraminifera, and results of student’s t and Kolmogorov-Smirnov tests.bNumber of values excluded if d18O > 4% for live foraminifera, and d18O < 4% for fossil foraminifera. Specimens remaining after these
exclusions are normally distributed and are used for the t-test comparisons.
Table 4. K-S Test Comparison of d13C Values at SeepVersus Reference Cores, Clam Flats
Isotope Species K-S Test
d13C U. peregrina rejectedE. pacifica rejected
d18O U. peregrina not rejectedE. pacifica not rejected
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Figure 8. Scanning electron micrographs of two species of foraminifera from core 1780-HPC5 from the ExtrovertCliffs clam community. (a) E. pacifica from 27–28 cmbsf. Scale bar is 100 mm. (b) Area outlined in the box shown inFigure 8a. Scale bar is 10 mm. (c) U. peregrina from 21–22 cmbsf. Scale bar is 100 mm. (d) Area outlined in the boxshown in Figure 8c. Scale bar is 20 mm. The E. pacifica was cleaned but the U. peregrina was not prior tomicroscopic observations.
Figure 9. Scanning electron micrographs of U. peregrina from core 1781-HPC5 and core 1781-PC30 from theClam Flats clam community. (a) Broken live U. peregrina from interval 0–1 cmbsf. Scale bar is 200 mm. (b) Areaoutlined in the box shown in Figure 9a. Scale bar is 10 mm. (c) Broken fossil U. peregrina from 0–1 cmbsf. Scale baris 200 mm. (d) Area outlined in the box shown in Figure 9c. Scale bar is 20 mm. Neither of these specimens wascleaned prior to microscopic observations.
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population on the basis of the K-S one sample test
at the 5% significance level. A normal distribution
would be expected for populations of unaltered
foraminifera, and thus the foraminifera with these
anomalous values may have been misidentified as
being either live or fossil at time of collection.
[35] Clam Flats is located on the apex of Smooth
Ridge (Figure 1), a bathymetric high uplifted
through compression along the restraining bends
of the San Gregorio fault zone [Orange et al.,
1999]. Uplift may have caused slumping and
exposure of sediments deposited during the last
glacial maximum, thereby exposing fossil forami-
nifera that are enriched in 18O. Although slumping
would also expose pore water that had been altered
during burial diagenesis, it is unlikely to have
caused the steep pore water gradients found in
the clam community at Clam Flats. The reference
core, located 5 m from the clam communities, has
only minor increases in alkalinity and d13CDIC
expected from normal burial diagenesis (Figures 3
and 4). A more likely cause for the steep gradients
in alkalinity and d13CDIC is from upward flow in
the cold seep [e.g., Rathburn et al., 2003].
[36] In the Clam Flats clam community cores, the
average carbon isotope values of U. peregrina are
enriched in 12C by 1.29% in the fossil specimens
over the live specimens (Table 3). The most likely
explanation for this shift in isotopic composition is
from diagenetic alteration, regardless of the lack of
evidence for alteration from visual observations
(Figure 9). If these small shifts in d13C values
occurred within a DIC pool that has d13C values
as low as �45%, it would be unlikely to alter
greatly the d18O values of the foraminifera and
cause the 1.5% difference in values observed
between the live and fossil foraminifera. In the
reference cores from Clam Flats, however, there is
no statistical difference in the d13C values of live
and fossil U. peregrina (Table 3), suggesting that
the fossil specimens have not been altered. This
apparent lack of diagenesis is remarkable if they
lived during the last glacial maximum as the
oxygen isotope ratios suggest, which would have
provided a long time for alteration to occur. In
contrast with U. peregrina, the K-S two sample test
comparisons of fossil and live E. pacifica in the
reference core suggest they may come from sepa-
rate populations. The fossil E. pacifica are enriched
in 12C on average by 0.21% compared with live
specimens (Table 3), possibly reflecting alteration.
The extent of alteration is smaller than found
within the clam community (1.29%), however,
reflecting the small gradients of d13CDIC in the
reference core.
[37] The fraction of fossil specimens at Clam Flats
clam community with light carbon isotopic com-
positions also appears to reflect alteration. Al-
though most fossil specimens have values that
fall within the range exhibited by the live forami-
nifera, a few specimens exhibit extremely light
values that decrease to <�15% (Figure 6). The
ratio of fossil foraminifera with d13C values <�2%to the total number of fossil foraminifera is plotted
relative to depth in Figure 10. The deeply buried
foraminifera might be expected to be more altered
than those found near the sediment/water interface
because they would have had a longer time for
alteration to occur as they are buried. There is no
consistent pattern, however, with depth to the
fraction of isotopically light specimens. The depth
interval from 20 to 25 cmbsf has the largest
fraction of isotopically light specimens with 20 to
100% having d13C values <�2%. This depth
distribution shown in Figure 10 suggests that all
fossil foraminifera have had approximately the
same length of exposure to 12C-enriched DIC
pools, as would be expected if they lived during
the last glacial maximum and have been exposed to
cold seep fluids only since venting started.
5.3. Implications
[38] Differences in the d13C values of foraminifera
from within and outside of the Clam Flats cold
seep suggest that large negative shifts in d13Cof tests caused by diagenetic alteration of tests
is restricted to long-lived cold seep locations
(Figures 6 and 7). Cold seep sites are infrequently
distributed on the seafloor and thus sampling fossil
cold seeps is unlikely during deep-sea drilling or
coring from the sea surface. Samples of foraminif-
era collected from drill cores are thus likely to
preserve the ambient conditions of the water in
which the foraminifera lived. For example, isoto-
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pically light values observed during interglacial
stage 5 at the Peruvian margin [Wefer et al.,
1994] and during interstadial periods in Santa
Barbara Basin [Kennett et al., 2000] may be a
primary signal of the ambient conditions at the time
the foraminifera were alive.
[39] Although sites of fossil cold seeps might be
identified through observations of alteration to
foraminiferal tests, this information can not be
used to determine a precise stratigraphic history
of the venting because alteration might have oc-
curred at any time subsequent to the deposition of
the sediments. All foraminifera in sediment
through which methane flowed and was oxidized,
thereby enriching the DIC pool in 12C, would thus
be prone to alteration toward isotopically lighter
d13CDIC values. Consequently, unless the timing of
the alteration could be dated, alteration of forami-
nifera would only provide qualitative information
about the presence or absence of cold seeps.
[40] The number of tests used for an individual
isotopic analysis is critical to the assessment of
isotopic compositions of d13CDIC and any potential
alteration. For the most part, results shown in
Figures 5, 6, and 7 represent measurements of up
to a maximum of six tests per analysis with more
than 75% of the analysis representing a single tests
(appendix A). Prior to development of mass spec-
trometry capable of measuring small amounts of
CO2, isotopic measurements often required large
number of tests per sample, commonly 5 to 40 tests.
A large range in isotopic compositions of live
foraminifera appears to be the primary signal of
extensive methane oxidation, rather than a decrease
in the d13C values of all specimens where the DIC
pool is enriched in 12C [e.g., Sen Gupta et al.,
1997; Rathburn et al., 2000, 2003]. Combining a
large number of specimens into a single isotopic
measurement would dampen this range.
6. Conclusions
[41] Comparisons of live and fossil foraminifera at
and near two cold seeps in Monterey Bay, Cal-
ifornia reveal systematic differences in their isoto-
pic compositions, but the observed differences are
caused by several distinct processes. Live forami-
nifera are far from equilibrium with the ambient
d13CDIC, precipitating tests that are up to 45%higher than the ambient DIC. Similar disequilibrium
has been observed before, but there has been no
adequate explanation of its cause. At Clam Flats,
diagenetic alteration decreases the d13C values of
some of the fossil foraminifera from the cold seep so
that they are shifted toward the light d13CDIC
values found there. The timing of the alteration
is unknown; it could have occurred soon after
the foraminifera died or anytime during modern
venting. Diagenetic alteration is less common
among fossil foraminifera collected 5 meters from
the Clam Flats cold seep. These differences suggest
that fossil foraminifera buried outside of cold seep
environments may be the most likely to preserve a
record of basin-wide pore water compositions.
Figure 10. Ratio of fossil foraminifera from the ClamFlats clam community with d13C values <�2% to totalnumber of foraminifera at particular depth interval.
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[42] At Extrovert Cliffs, the d13C values of fossil
and live foraminifera are similar, although the
averages of the two populations are statistically
distinct at the 5% significance level. In contrast
with Clam Flats, fossil foraminifera at Extrovert
Cliffs have d13C and d18O values that are isotopi-
cally heavier than the live foraminifera. This shift
can not be caused by diagenetic alteration of the
foraminiferal carbonate within the isotopically light
DIC pool and suggests that fluid flow from the cold
seep may have only recently been initiated. Al-
though foraminifera are far from equilibrium with
the DIC pool at cold seeps, they do incorporate a
small amount of the isotopically light DIC found
there. The relatively short time for flow compared
with the Clam Flats seep site may in part be the
cause of the differences in pore water gradients of
alkalinity, d13CDIC found at the two sites, and the
greater amount of alteration of the Clam Flats
foraminifera.
[43] The oxygen isotopic compositions of the fossil
foraminifera at Clam Flats are �1.5% higher than
the live foraminifera there and are similarly
enriched over both the live and fossil foraminifera
at Extrovert Cliffs. These values suggest that the
fossil foraminifera at Clam Flats lived during
glacial times, possibly the last glacial maximum,
Table A1. Extrovert Cliffs, Core 1780-PC30
SpeciesDepth,cmbsf na
Live/Fossil
d13C,%
d18O,%
Bulimina mexicana 0.5 3 Live �0.82 3.26Bulimina mexicana 1.25 2 Live �0.70 3.26Bulimina mexicana 1.25 2 Live �0.72 3.29Bulimina mexicana 2.25 3 Live �0.80 3.30Bulimina mexicana 2.25 3 Live �0.70 3.29Bulimina mexicana 3.5 4 Live �0.85 3.28Bulimina mexicana 4.5 3 Fossil �0.83 3.33Bulimina mexicana 4.5 3 Live �0.92 3.36Bulimina mexicana 4.5 4 Live �0.81 3.20Bulimina mexicana 4.5 3 Live �0.89 3.28
Epistominella pacifica 0.5 4 Live �0.79 3.09Epistominella pacifica 0.5 3 Live �0.73 3.10Epistominella pacifica 1.25 3 Live �0.78 3.30Epistominella pacifica 1.25 4 Live �0.53 3.11Epistominella pacifica 1.25 3 Live �0.50 3.22Epistominella pacifica 1.25 4 Live �0.72 3.23Epistominella pacifica 2.25 3 Live �0.73 3.14Epistominella pacifica 2.25 2 Live �0.63 3.17Epistominella pacifica 2.25 2 Live �0.59 3.15Epistominella pacifica 2.25 2 Live �0.53 3.15Epistominella pacifica 2.25 2 Live �0.63 3.29Epistominella pacifica 2.25 2 Live �0.60 3.21
Globobulimina pacifica 0.5 1 Live �0.92 3.28Globobulimina pacifica 0.5 1 Live �1.36 3.28Globobulimina pacifica 0.5 1 Live �0.74 3.30Globobulimina pacifica 0.5 1 Live �1.46 3.28Globobulimina pacifica 1.25 1 Live �1.29 3.45Globobulimina pacifica 1.25 2 Live �1.84 3.33Globobulimina pacifica 1.25 1 Live �1.43 3.25Globobulimina pacifica 1.25 1 Live �0.91 3.49Globobulimina pacifica 1.75 2 Live �2.14 3.39Globobulimina pacifica 1.75 2 Live �2.17 3.35Globobulimina pacifica 2.25 2 Live �1.98 3.33Globobulimina pacifica 2.25 1 Live �1.15 3.38Globobulimina pacifica 2.25 1 Live �0.92 3.34Globobulimina pacifica 2.25 1 Live �0.41 3.38Globobulimina pacifica 2.75 1 Live �1.20 3.33Globobulimina pacifica 2.75 1 Live �1.68 3.41Globobulimina pacifica 2.75 2 Live �2.23 3.27Globobulimina pacifica 3.5 1 Live �1.06 3.28Globobulimina pacifica 3.5 2 Live �0.91 3.29Globobulimina pacifica 3.5 3 Live �1.72 3.25Globobulimina pacifica 3.5 2 Live �1.22 3.27Globobulimina pacifica 4.5 2 Live �0.93 3.30Globobulimina pacifica 4.5 1 Live �1.81 3.23Globobulimina pacifica 4.5 2 Live �1.34 3.26Globobulimina pacifica 4.5 3 Live �1.47 3.33
Uvigerina peregrina 0.5 1 Live �0.85 2.83Uvigerina peregrina 0.5 1 Live �0.54 3.01Uvigerina peregrina 0.5 1 Live �0.32 3.19Uvigerina peregrina 0.5 1 Live �0.71 3.06Uvigerina peregrina 1.25 1 Live �0.43 3.01Uvigerina peregrina 1.25 1 Live �0.76 3.16Uvigerina peregrina 1.25 1 Live �0.57 3.25Uvigerina peregrina 1.75 1 Live �0.56 3.09Uvigerina peregrina 1.75 1 Live �0.51 3.03Uvigerina peregrina 1.75 1 Live �0.49 3.07
Table A1. (continued)
SpeciesDepth,cmbsf na
Live/Fossil
d13C,%
d18O,%
Uvigerina peregrina 2.25 1 Live �0.47 3.20Uvigerina peregrina 2.25 1 Live �0.50 3.01Uvigerina peregrina 2.75 1 Live �0.57 3.23Uvigerina peregrina 2.75 1 Live �0.77 3.23Uvigerina peregrina 2.75 1 Live �0.27 3.11Uvigerina peregrina 3.5 1 Live �0.33 2.97Uvigerina peregrina 3.5 1 Live �0.78 2.87Uvigerina peregrina 3.5 1 Live �0.36 3.26Uvigerina peregrina 3.5 1 Live �0.59 2.98Uvigerina peregrina 4.5 2 Fossil �0.65 3.06Uvigerina peregrina 4.5 2 Fossil �0.95 3.20Uvigerina peregrina 4.5 1 Live �0.59 2.59Uvigerina peregrina 4.5 1 Live �0.04 3.11Uvigerina peregrina 4.5 1 Live �0.45 2.91Uvigerina peregrina 4.5 1 Live �0.43 3.14Uvigerina peregrina 4.5 1 Live �0.36 3.40Uvigerina peregrina 4.5 1 Live �0.37 3.15Uvigerina peregrina 4.5 1 Live �0.36 3.10Uvigerina peregrina 4.5 1 Live �0.49 2.66
aNumber of specimens run for the analysis.
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Table A2. Extrovert Cliffs, Core 1780-HPC5
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Bulimina mexicana 0.5 3 �0.72 3.26Bulimina mexicana 4 2 �1.04 3.28Bulimina mexicana 4 2 �1.00 3.05Bulimina mexicana 5.5 2 �0.91 3.72Bulimina mexicana 13.5 3 �0.84 3.68Bulimina mexicana 14.5 2 �0.73 3.51Bulimina mexicana 14.5 2 �0.71 3.49Bulimina mexicana 19.5 1 �0.56 3.52Bulimina mexicana 21.5 3 �0.97 3.28Bulimina mexicana 21.5 3 �0.69 3.14Bulimina mexicana 22.5 2 �0.87 3.49Bulimina mexicana 22.5 2 �0.56 3.42Bulimina mexicana 23.5 1 �0.57 3.64Bulimina mexicana 23.5 3 �0.69 3.39Bulimina mexicana 24.5 2 �0.71 3.37Bulimina mexicana 25.5 2 �0.52 3.89Bulimina mexicana 29.5 2 �0.66 3.94
Epistominella pacifica 0.5 1 �0.50 3.22Epistominella pacifica 0.5 1 �0.41 3.47Epistominella pacifica 0.5 1 �0.47 3.48Epistominella pacifica 1.5 2 �0.64 3.34Epistominella pacifica 1.5 2 �0.52 3.24Epistominella pacifica 2.5 1 �0.42 3.35Epistominella pacifica 4 1 �0.33 3.23Epistominella pacifica 4 1 �0.52 3.20Epistominella pacifica 5.5 2 �0.52 3.26Epistominella pacifica 7.5 3 �1.06 3.03Epistominella pacifica 8.5 1 �0.78 3.51Epistominella pacifica 9.5 1 �0.43 3.24Epistominella pacifica 10.5 1 �0.50 3.20Epistominella pacifica 10.5 1 �0.27 3.19Epistominella pacifica 11.5 1 �0.41 3.28Epistominella pacifica 11.5 1 �0.27 3.27Epistominella pacifica 12.5 1 �0.47 3.19Epistominella pacifica 12.5 1 �0.39 3.22Epistominella pacifica 13.5 1 �0.40 3.19Epistominella pacifica 13.5 1 �0.43 3.34Epistominella pacifica 14.5 1 �0.36 3.21Epistominella pacifica 14.5 1 �0.13 3.54Epistominella pacifica 14.5 2 �0.47 3.16Epistominella pacifica 15.5 1 �0.33 3.35Epistominella pacifica 15.5 1 �0.51 3.46Epistominella pacifica 16.5 1 �0.39 3.29Epistominella pacifica 16.5 1 �0.31 3.40Epistominella pacifica 16.5 1 �0.46 3.43Epistominella pacifica 16.5 1 �0.47 3.29Epistominella pacifica 16.5 1 �0.45 3.32Epistominella pacifica 16.5 1 �0.54 3.07Epistominella pacifica 16.5 1 �0.44 3.46Epistominella pacifica 16.5 1 �0.39 3.36Epistominella pacifica 16.5 2 �0.57 3.13Epistominella pacifica 16.5 1 �0.34 3.37Epistominella pacifica 17.5 1 �0.50 2.31Epistominella pacifica 17.5 1 �0.31 3.60Epistominella pacifica 18.5 1 �0.50 3.23Epistominella pacifica 18.5 1 �0.39 3.40Epistominella pacifica 18.5 1 �0.39 3.34Epistominella pacifica 19.5 1 �0.39 3.25Epistominella pacifica 19.5 1 �0.42 3.34
Table A2. (continued)
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Epistominella pacifica 20.5 1 �0.26 3.27Epistominella pacifica 20.5 1 �0.40 3.53Epistominella pacifica 21.5 1 �0.41 3.29Epistominella pacifica 21.5 1 �0.23 3.36Epistominella pacifica 22.5 1 �0.34 3.31Epistominella pacifica 23.5 1 �0.21 3.16Epistominella pacifica 23.5 1 �0.44 3.22Epistominella pacifica 24.5 1 �0.49 3.24Epistominella pacifica 24.5 2 �0.51 3.25Epistominella pacifica 25.5 2 �0.50 3.28Epistominella pacifica 25.5 2 �0.50 3.34Epistominella pacifica 26.5 1 �0.32 3.15Epistominella pacifica 26.5 1 �0.29 3.15Epistominella pacifica 27.5 1 �0.32 3.30Epistominella pacifica 27.5 4 �0.60 3.22Epistominella pacifica 28.5 1 �0.38 3.47Epistominella pacifica 29.5 1 �0.34 3.30Epistominella pacifica 29.5 1 �0.29 3.18Epistominella pacifica 29.5 1 �0.31 3.27Epistominella pacifica 29.5 1 �0.56 3.23Epistominella pacifica 29.5 1 �0.38 3.26Epistominella pacifica 29.5 1 �0.22 3.28Epistominella pacifica 29.5 1 �0.40 3.02Epistominella pacifica 29.5 2 �0.62 3.20Epistominella pacifica 29.5 2 �0.54 3.23Epistominella pacifica 31.5 1 �0.39 3.45Epistominella pacifica 31.5 2 �0.68 3.26Epistominella pacifica 31.5 3 �0.80 3.28
Globobulimina pacifica 4 3 �0.73 3.33Globobulimina pacifica 4 3 �0.78 3.38Globobulimina pacifica 10.5 2 �1.37 3.36Globobulimina pacifica 11.5 1 �1.04 3.31Globobulimina pacifica 11.5 1 �1.03 3.40Globobulimina pacifica 13.5 2 �1.17 3.61Globobulimina pacifica 14.5 2 �1.08 3.37Globobulimina pacifica 14.5 2 �1.11 3.40Globobulimina pacifica 15.5 1 �1.03 3.26Globobulimina pacifica 21.5 1 �1.35 3.37Globobulimina pacifica 21.5 2 �1.07 3.30Globobulimina pacifica 21.5 1 �0.90 3.40Globobulimina pacifica 21.5 3 �0.81 3.49Globobulimina pacifica 21.5 1 �1.08 3.37Globobulimina pacifica 21.5 1 �0.97 3.40Globobulimina pacifica 22.5 1 �0.61 3.38Globobulimina pacifica 22.5 1 �1.07 3.33Globobulimina pacifica 23.5 1 �1.69 3.42Globobulimina pacifica 23.5 2 �1.04 3.29Globobulimina pacifica 26.5 1 �1.09 3.35Globobulimina pacifica 26.5 1 �1.19 3.42Globobulimina pacifica 29.5 1 �0.87 3.30Globobulimina pacifica 29.5 2 �0.83 3.68Globobulimina pacifica 29.5 3 �1.02 3.71
Uvigerina peregrina 0.5 1 �0.70 3.26Uvigerina peregrina 0.5 4 �0.95 3.17Uvigerina peregrina 1.5 0.5 �0.30 3.06Uvigerina peregrina 1.5 0.5 0.01 3.22Uvigerina peregrina 1.5 0.5 �0.12 3.27Uvigerina peregrina 4 1 �0.35 3.33
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and that the sediment may have been buried and
subsequently exhumed. This exhumation is unlikely
the cause of steeper pore water gradients found in
cold seeps at Clam Flats relative to Extrovert Cliffs
because pore fluids located �5 m from the Clam
Flats cold seep do have lower gradients.
[44] These results indicate that isotopic composi-
tion of fossil foraminifera may be useful for
recording the presence of methane oxidation in
pore waters, but that diagenetic overprinting of
the primary signal could occur, particularly where
methane fluxes in cold seeps create steep gradients
with depth of increasing carbonate saturation and
decreasing d13CDIC values. Visual observations of
foraminifera may not be a reliable technique to sort
altered from nonaltered foraminifera. The altered
foraminifera should be most common at cold seep
locations and thus basin-wide changes in the d13Cvalues of the DIC pool from these point sources of
methane may be faithfully recorded by the forami-
nifera outside of the seep locations.
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Uvigerina peregrina 5.5 1 �0.60 3.36Uvigerina peregrina 10.5 0.5 �0.22 3.12Uvigerina peregrina 10.5 1 �0.25 3.25Uvigerina peregrina 11.5 1 �0.75 3.24Uvigerina peregrina 11.5 2 �0.83 3.34Uvigerina peregrina 11.5 0.5 �0.44 3.09Uvigerina peregrina 11.5 0.5 �0.66 3.22Uvigerina peregrina 12.5 3 �1.00 3.15Uvigerina peregrina 13.5 1 �0.28 3.48Uvigerina peregrina 13.5 1 �0.51 3.24Uvigerina peregrina 14.5 2 �0.94 3.23Uvigerina peregrina 14.5 1 �0.50 3.36Uvigerina peregrina 14.5 0.5 �0.62 3.22Uvigerina peregrina 14.5 0.5 �0.51 3.12Uvigerina peregrina 15.5 1 �0.25 3.20Uvigerina peregrina 15.5 0.5 �0.08 3.10Uvigerina peregrina 16.5 1 �0.91 3.22Uvigerina peregrina 20.5 1 �0.72 3.40Uvigerina peregrina 20.5 3 �0.87 3.32Uvigerina peregrina 21.5 1 �0.82 3.36Uvigerina peregrina 21.5 1 �0.77 3.08Uvigerina peregrina 22.5 1 �0.55 3.15Uvigerina peregrina 22.5 1 �0.71 3.25Uvigerina peregrina 23.5 5 �0.97 3.25Uvigerina peregrina 25.5 1 �1.05 3.12Uvigerina peregrina 25.5 1 �0.60 3.73Uvigerina peregrina 26.5 2 �0.72 3.28
aNumber of specimens run for the analysis.
Table A2. (continued) Table A3. Clam Flats, Core 1781-PC31
SpeciesDepth,cmbsf na
Live/Fossil
d13C,%
d18O,%
Bulimina mexicana 0.5 5 Live �1.03 3.80Bulimina mexicana 1.25 2 Fossil �1.04 4.89Bulimina mexicana 1.25 3 Fossil �2.24 4.65Bulimina mexicana 2.25 3 Fossil �1.19 4.72Bulimina mexicana 3.5 4 Live �1.06 3.30Bulimina mexicana 4.5 3 Fossil �1.18 4.71Bulimina mexicana 4.5 2 Fossil �1.51 4.71Bulimina mexicana 4.5 6 Live �1.17 3.22
Epistominella pacifica 1.75 2 Fossil �1.09 4.61Epistominella pacifica 1.75 2 Fossil �1.11 4.65Epistominella pacifica 2.25 2 Live �0.92 3.15Epistominella pacifica 2.75 3 Fossil �1.20 4.59Epistominella pacifica 2.75 2 Fossil �1.19 4.61Epistominella pacifica 2.75 1 Live �0.99 4.56Epistominella pacifica 2.75 1 Live �1.02 4.63Epistominella pacifica 2.75 1 Live �1.01 4.66
Globobulimina pacifica 1.25 1 Live �3.87 3.42Globobulimina pacifica 2.25 1 Live �3.49 3.30Globobulimina pacifica 4.5 2 Live �4.56 3.20
Uvigerina peregrina 0.5 2 Live �1.36 3.09Uvigerina peregrina 0.5 2 Live �1.18 4.04Uvigerina peregrina 1.25 0.5 Fossil �1.34 4.63Uvigerina peregrina 1.25 0.5 Fossil �1.03 4.83Uvigerina peregrina 1.25 1 Fossil �1.35 4.62Uvigerina peregrina 1.25 1 Fossil �1.85 4.49Uvigerina peregrina 1.25 1 Live �0.89 3.11Uvigerina peregrina 1.25 1 Live �0.62 3.21Uvigerina peregrina 1.25 1 Live �0.43 3.12Uvigerina peregrina 1.25 1 Live �0.69 3.12Uvigerina peregrina 1.75 0.5 Live �0.55 3.16Uvigerina peregrina 1.75 1 Live �0.49 3.28Uvigerina peregrina 1.75 1 Live �0.74 3.21Uvigerina peregrina 1.75 1 Live �0.22 3.25Uvigerina peregrina 1.75 0.5 Live �0.21 3.21Uvigerina peregrina 1.75 1 Live �0.57 3.15Uvigerina peregrina 1.75 0.5 Live �0.97 3.10Uvigerina peregrina 2.25 1 Fossil �1.57 4.58Uvigerina peregrina 2.25 1 Fossil �1.04 4.65Uvigerina peregrina 2.25 1 Fossil �1.31 4.58Uvigerina peregrina 2.25 1 Live �2.05 3.04Uvigerina peregrina 2.25 1 Live �1.13 3.17Uvigerina peregrina 2.25 0.33 Live �0.81 3.21Uvigerina peregrina 2.25 0.33 Live �1.14 3.07Uvigerina peregrina 2.25 0.33 Live �0.94 3.12Uvigerina peregrina 2.25 0.5 Live �0.10 3.43Uvigerina peregrina 2.75 1 Live �1.82 3.18Uvigerina peregrina 2.75 1 Live �1.12 3.15Uvigerina peregrina 2.75 1 Live �0.25 3.21Uvigerina peregrina 2.75 0.5 Live �0.75 3.25Uvigerina peregrina 2.75 0.5 Live �1.39 3.27Uvigerina peregrina 3.5 2 Fossil �2.03 4.62Uvigerina peregrina 3.5 1 Fossil �1.40 4.73Uvigerina peregrina 3.5 1 Fossil �1.30 4.58Uvigerina peregrina 3.5 1 Live �1.17 3.15Uvigerina peregrina 3.5 1 Live �0.83 3.22Uvigerina peregrina 3.5 1 Live �1.82 3.09Uvigerina peregrina 3.5 0.5 Live �1.30 3.14
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Table A3. (continued)
SpeciesDepth,cmbsf na
Live/Fossil
d13C,%
d18O,%
Uvigerina peregrina 3.5 0.5 Live �0.72 3.16Uvigerina peregrina 3.5 0.5 Live �1.04 3.12Uvigerina peregrina 4.5 1 Fossil �1.40 4.64Uvigerina peregrina 4.5 1 Fossil �1.21 4.78Uvigerina peregrina 4.5 1 Fossil �1.04 4.82Uvigerina peregrina 4.5 1 Fossil �1.36 4.58Uvigerina peregrina 4.5 3 Fossil �1.92 4.59Uvigerina peregrina 4.5 2 Live �0.95 3.14Uvigerina peregrina 4.5 2 Live �1.53 3.14Uvigerina peregrina 4.5 2 Live �0.78 3.07Uvigerina peregrina 4.5 1 Live �0.78 3.28Uvigerina peregrina 4.5 1 Live �1.05 3.23Uvigerina peregrina 4.5 1 Live �0.86 3.23Uvigerina peregrina 4.5 1 Live �0.51 3.13
aNumber of specimens run for the analysis.
Table A4. Clam Flats, Core 1781-HPC5
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Bulimina mexicana 0.5 1 �0.97 4.65Bulimina mexicana 0.5 1 �1.16 4.59Bulimina mexicana 0.5 1 �0.69 3.71Bulimina mexicana 1.5 1 �1.12 4.66Bulimina mexicana 1.5 1 �1.63 4.65Bulimina mexicana 1.5 2 �3.25 4.73Bulimina mexicana 2.5 1 �1.75 4.70Bulimina mexicana 2.5 1 �0.89 4.71Bulimina mexicana 2.5 1 �0.85 5.33Bulimina mexicana 3.5 1 �0.90 4.52Bulimina mexicana 3.5 1 �10.36 4.52Bulimina mexicana 3.5 1 �1.16 4.64Bulimina mexicana 4.5 1 �1.09 4.71Bulimina mexicana 4.5 1 �0.87 4.71Bulimina mexicana 4.5 1 �1.06 4.63Bulimina mexicana 5.5 1 �0.90 4.59Bulimina mexicana 5.5 1 �2.23 4.67Bulimina mexicana 6.5 1 �0.97 4.74Bulimina mexicana 6.5 1 �1.98 4.54Bulimina mexicana 7.5 1 �0.83 4.62Bulimina mexicana 7.5 1 �1.23 4.69Bulimina mexicana 8.5 2 �1.44 4.44Bulimina mexicana 8.5 2 �1.71 4.53Bulimina mexicana 9.5 1 �5.55 4.49Bulimina mexicana 9.5 1 �0.86 4.62Bulimina mexicana 10.5 1 �1.21 4.68Bulimina mexicana 10.5 2 �1.40 4.45Bulimina mexicana 11.5 1 �1.07 4.56Bulimina mexicana 11.5 1 �6.32 4.58Bulimina mexicana 12.5 1 �1.09 4.56Bulimina mexicana 12.5 1 �1.73 4.78Bulimina mexicana 13.5 1 �1.15 4.62Bulimina mexicana 13.5 1 �1.09 4.55Bulimina mexicana 14.5 1 �1.90 4.36Bulimina mexicana 14.5 1 �2.12 4.58Bulimina mexicana 15.5 1 �5.41 4.50Bulimina mexicana 15.5 2 �1.31 4.54
Table A4. (continued)
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Bulimina mexicana 16.5 1 �2.28 4.75Bulimina mexicana 16.5 1 �1.14 4.51Bulimina mexicana 17.5 2 �11.26 4.61Bulimina mexicana 17.5 3 �3.65 4.51Bulimina mexicana 17.5 1 �1.41 4.56Bulimina mexicana 17.5 1 �1.85 4.55Bulimina mexicana 18.5 2 �1.22 4.54Bulimina mexicana 18.5 3 �1.58 4.59Bulimina mexicana 19.5 1 �5.15 4.74Bulimina mexicana 19.5 2 �4.01 4.44Bulimina mexicana 20.5 1 �6.61 4.56Bulimina mexicana 20.5 1 �13.01 4.55Bulimina mexicana 21.5 2 �1.04 4.41Bulimina mexicana 21.5 2 �0.94 4.52Bulimina mexicana 22.5 2 �2.99 4.63Bulimina mexicana 22.5 3 �5.23 4.44Bulimina mexicana 23.5 3 �2.55 4.55Bulimina mexicana 24.5 1 �9.62 4.58Bulimina mexicana 24.5 2 �8.66 4.54Bulimina mexicana 25.5 1 �9.23 4.52Bulimina mexicana 25.5 1 �3.44 4.55Bulimina mexicana 26.5 1 �1.50 4.60Bulimina mexicana 26.5 1 �1.25 4.83
Epistominella pacifica 0.5 1 �1.04 4.51Epistominella pacifica 0.5 1 �0.79 4.55Epistominella pacifica 0.5 1 �0.89 4.52Epistominella pacifica 1.5 1 �0.67 4.54Epistominella pacifica 1.5 1 �0.83 4.49Epistominella pacifica 1.5 1 �0.82 4.53Epistominella pacifica 2.5 1 �0.82 4.64Epistominella pacifica 2.5 1 �0.81 4.52Epistominella pacifica 2.5 1 �1.50 4.56Epistominella pacifica 3.5 1 �0.65 4.73Epistominella pacifica 3.5 1 �7.33 4.48Epistominella pacifica 3.5 1 �0.66 4.56Epistominella pacifica 4.5 1 �0.68 4.58Epistominella pacifica 4.5 1 �0.83 4.60Epistominella pacifica 4.5 1 �0.85 4.71Epistominella pacifica 5.5 1 �8.55 4.49Epistominella pacifica 5.5 1 �0.94 4.73Epistominella pacifica 6.5 1 �1.07 4.19Epistominella pacifica 7.5 1 �0.80 4.56Epistominella pacifica 7.5 1 �6.27 4.51Epistominella pacifica 8.5 1 �1.15 4.60Epistominella pacifica 8.5 1 �1.13 4.50Epistominella pacifica 9.5 1 �0.99 4.48Epistominella pacifica 9.5 1 �0.87 4.64Epistominella pacifica 10.5 1 �0.93 4.52Epistominella pacifica 10.5 2 �1.44 4.46Epistominella pacifica 11.5 1 �1.10 4.54Epistominella pacifica 11.5 1 �0.79 4.47Epistominella pacifica 12.5 1 �0.87 4.55Epistominella pacifica 12.5 2 �1.81 4.47Epistominella pacifica 13.5 1 �0.90 4.50Epistominella pacifica 13.5 1 �1.11 4.53Epistominella pacifica 14.5 1 �0.86 3.10Epistominella pacifica 14.5 1 �1.67 4.50Epistominella pacifica 15.5 2 �1.59 4.40Epistominella pacifica 15.5 2 �1.31 4.51
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SpeciesDepth,cmbsf na
d13C,%
d18O,%
Epistominella pacifica 16.5 2 �1.76 4.47Epistominella pacifica 16.5 2 �1.02 4.62Epistominella pacifica 17.5 1 �1.01 4.41Epistominella pacifica 17.5 1 �0.80 4.57Epistominella pacifica 17.5 1 �1.43 4.58Epistominella pacifica 17.5 2 �1.37 4.49Epistominella pacifica 18.5 1 �0.68 4.66Epistominella pacifica 18.5 1 �0.90 4.55Epistominella pacifica 19.5 1 �1.01 4.70Epistominella pacifica 19.5 1 �1.02 4.47Epistominella pacifica 20.5 1 �9.03 4.55Epistominella pacifica 20.5 1 �1.05 4.51Epistominella pacifica 21.5 2 �1.61 4.65Epistominella pacifica 21.5 2 �1.41 4.50Epistominella pacifica 22.5 2 �2.86 4.49Epistominella pacifica 22.5 2 �2.22 3.58Epistominella pacifica 23.5 1 �1.39 4.52Epistominella pacifica 23.5 2 �1.63 4.54Epistominella pacifica 24.5 2 �1.03 4.48Epistominella pacifica 24.5 2 �3.85 4.48Epistominella pacifica 25.5 1 �0.73 4.51Epistominella pacifica 25.5 1 �1.29 4.47Epistominella pacifica 26.5 1 �0.88 4.56Epistominella pacifica 26.5 1 �0.85 4.79
Uvigerina peregrina 0.5 1 �1.14 4.63Uvigerina peregrina 0.5 1 �7.63 4.59Uvigerina peregrina 0.5 1 �1.18 4.65Uvigerina peregrina 1.5 1 �1.20 4.67Uvigerina peregrina 1.5 1 �0.99 4.75Uvigerina peregrina 1.5 1 �1.15 4.59Uvigerina peregrina 2.5 1 �0.92 4.83Uvigerina peregrina 2.5 1 �1.04 4.66Uvigerina peregrina 3.5 1 �1.21 4.69Uvigerina peregrina 3.5 1 �1.73 4.54Uvigerina peregrina 3.5 1 �1.26 4.74Uvigerina peregrina 3.5 1 �1.30 4.61Uvigerina peregrina 4.5 1 �1.21 4.59Uvigerina peregrina 4.5 1 �1.16 4.71Uvigerina peregrina 4.5 1 �1.21 4.63Uvigerina peregrina 5.5 1 �1.26 4.56Uvigerina peregrina 5.5 1 �1.56 4.66Uvigerina peregrina 6.5 1 �4.18 4.76Uvigerina peregrina 6.5 1 �1.30 4.60Uvigerina peregrina 7.5 1 �1.64 4.78Uvigerina peregrina 7.5 1 �1.08 4.62Uvigerina peregrina 8.5 1 �1.65 4.54Uvigerina peregrina 8.5 1 �1.29 4.51Uvigerina peregrina 9.5 1 �4.17 4.47Uvigerina peregrina 10.5 1 �1.42 4.73Uvigerina peregrina 10.5 1 �1.67 4.60Uvigerina peregrina 11.5 1 �2.06 4.50Uvigerina peregrina 11.5 1 �1.34 4.67Uvigerina peregrina 12.5 1 �1.45 4.52Uvigerina peregrina 12.5 1 �1.32 4.48Uvigerina peregrina 13.5 1 �0.78 4.66Uvigerina peregrina 13.5 1 �2.10 4.63Uvigerina peregrina 14.5 1 �1.73 4.55Uvigerina peregrina 15.5 1 �1.39 4.79Uvigerina peregrina 15.5 1 �2.23 4.72
Table A4. (continued)
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Uvigerina peregrina 16.5 1 �5.33 4.50Uvigerina peregrina 16.5 1 �1.37 4.57Uvigerina peregrina 17.5 1 �1.25 4.62Uvigerina peregrina 17.5 1 �1.70 4.55Uvigerina peregrina 18.5 1 �1.53 4.55Uvigerina peregrina 18.5 1 �1.20 4.62Uvigerina peregrina 19.5 1 �1.30 4.47Uvigerina peregrina 19.5 1 �1.36 4.59Uvigerina peregrina 20.5 1 �2.00 4.57Uvigerina peregrina 20.5 1 �15.58 4.56Uvigerina peregrina 21.5 1 �5.03 4.53Uvigerina peregrina 21.5 1 �1.23 4.91Uvigerina peregrina 22.5 1 �4.52 4.53Uvigerina peregrina 22.5 1 �5.72 4.60Uvigerina peregrina 23.5 1 �1.52 4.58Uvigerina peregrina 23.5 1 �14.12 4.57Uvigerina peregrina 24.5 1 �3.46 4.62Uvigerina peregrina 24.5 1 �2.26 4.67Uvigerina peregrina 25.5 1 �1.20 4.56Uvigerina peregrina 25.5 1 �1.34 4.56Uvigerina peregrina 26.5 1 �1.36 4.54Uvigerina peregrina 26.5 1 �4.19 4.62
aNumber of specimens run for the analysis.
Table A4. (continued)
Table A5. Clam Flats, Core 1781-PC31
SpeciesDepth,cmbsf na
Live/Fossil
d13C,%
d18O,%
Epistominella pacifica 0.5 3.0 Live �0.79 3.81Epistominella pacifica 0.5 3.0 Live �0.74 3.11Epistominella pacifica 0.5 2 Live �0.32 3.09Epistominella pacifica 1.25 2.0 Live �0.76 3.96Epistominella pacifica 1.25 3.0 Live �1.29 4.64Epistominella pacifica 1.25 1.0 Live �0.88 4.61Epistominella pacifica 1.75 2.0 Live �0.93 4.68Epistominella pacifica 1.75 2.0 Live �0.77 3.74Epistominella pacifica 2.25 1.0 Live �0.34 3.25Epistominella pacifica 2.25 3.0 Live �0.78 3.57Epistominella pacifica 2.25 2.0 Live �0.78 3.26Epistominella pacifica 2.75 2.0 Live �0.76 3.11Epistominella pacifica 2.75 3.0 Live �0.94 3.54Epistominella pacifica 2.75 2.0 Live �0.86 3.18Epistominella pacifica 3.5 1.0 Live �0.88 4.62Epistominella pacifica 3.5 2.0 Live �0.64 3.08Epistominella pacifica 3.5 2.0 Live �0.68 3.05Epistominella pacifica 4.5 1 Live �0.48 3.25
Globobulimina pacifica 0.5 1.0 Live �2.54 3.23Globobulimina pacifica 1.25 0.5 Live �1.89 3.15Globobulimina pacifica 1.25 0.5 Live �1.60 3.20Globobulimina pacifica 1.75 1.0 Live �1.85 3.20Globobulimina pacifica 1.75 1.0 Live �2.31 3.19Globobulimina pacifica 1.75 1.0 Live �1.10 3.17Globobulimina pacifica 2.25 2.0 Live �1.10 3.20Globobulimina pacifica 2.25 1.0 Live �2.07 3.16Globobulimina pacifica 2.75 1.0 Live �1.68 3.24Globobulimina pacifica 3.5 2.0 Live �2.30 3.12
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Table A5. (continued)
SpeciesDepth,cmbsf na
Live/Fossil
d13C,%
d18O,%
Globobulimina pacifica 3.5 <1 Live �1.88 3.18Globobulimina pacifica 3.5 <1 Live �2.23 3.17
Uvigerina peregrina 0.5 1.0 Live �1.35 4.62Uvigerina peregrina 0.5 1.0 Live �0.93 3.09Uvigerina peregrina 0.5 1.0 Live �1.28 3.19Uvigerina peregrina 0.5 1.0 Live �1.36 4.47Uvigerina peregrina 0.5 1.0 Live �1.41 2.93Uvigerina peregrina 0.5 1.0 Live �1.35 2.80Uvigerina peregrina 1.25 1.0 Live �1.11 3.09Uvigerina peregrina 1.25 2.0 Live �1.17 3.08Uvigerina peregrina 1.25 2.0 Live �1.39 3.06Uvigerina peregrina 1.75 1.0 Live �1.64 4.12Uvigerina peregrina 1.75 2.0 Live �1.49 4.51Uvigerina peregrina 2.25 1.0 Live �1.66 3.12Uvigerina peregrina 2.25 1.0 Live �2.07 3.14Uvigerina peregrina 2.25 1.0 Live �1.62 3.09Uvigerina peregrina 2.25 1.0 Live �0.77 3.14Uvigerina peregrina 2.25 1.0 Live �0.59 3.08Uvigerina peregrina 2.25 1.0 Live �1.14 3.19Uvigerina peregrina 2.75 1.0 Live �1.27 3.06Uvigerina peregrina 2.75 4.0 Live �1.32 2.99Uvigerina peregrina 3.5 1.0 Live �0.71 2.98Uvigerina peregrina 3.5 1.0 Live �1.18 3.06Uvigerina peregrina 3.5 1.0 Live �1.80 2.99Uvigerina peregrina 3.5 1.0 Live �1.34 3.08Uvigerina peregrina 3.5 2.0 Live �1.62 3.44Uvigerina peregrina 4.5 1 Live �1.76 3.43Uvigerina peregrina 4.5 1 Live �0.78 3.55Uvigerina peregrina 4.5 1 Live �1.80 3.13
aNumber of specimens run for the analysis.
Table A6. Clam Flats, Core 1781-HPC6
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Bulimina mexicana 0.5 3 �1.14 4.59Bulimina mexicana 1.5 2 �1.06 4.51Bulimina mexicana 1.5 2 �1.27 4.54Bulimina mexicana 1.5 3 �1.21 4.56Bulimina mexicana 2.5 2 �1.1 4.58Bulimina mexicana 2.5 1 �0.75 4.03Bulimina mexicana 2.5 3 �1.15 4.6Bulimina mexicana 2.5 3 �1.2 4.47Bulimina mexicana 3.5 3 �1.21 4.55Bulimina mexicana 3.5 2 �1.05 4.51Bulimina mexicana 3.5 3 �1.3 4.61Bulimina mexicana 3.5 2 �1.12 4.69Bulimina mexicana 5.5 3 �1.26 4.67Bulimina mexicana 5.5 1 �1.15 4.47Bulimina mexicana 6.5 2 �0.91 4.53Bulimina mexicana 6.5 2 �1.13 4.64Bulimina mexicana 7.5 2 �1.09 4.68Bulimina mexicana 7.5 3 �1.16 4.44Bulimina mexicana 8.5 1 �2.16 4.58Bulimina mexicana 8.5 3 �2.9 4.71
Table A6. (continued)
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Bulimina mexicana 9.5 2 �0.91 4.67Bulimina mexicana 9.5 4 �1.25 4.56Bulimina mexicana 10.5 1 �1.12 4.73Bulimina mexicana 10.5 2 �1.24 4.54Bulimina mexicana 11.5 3 �1.23 4.56Bulimina mexicana 11.5 3 �1.39 4.56Bulimina mexicana 12.5 2 �1.18 4.67Bulimina mexicana 13.5 2 �1.13 4.74Bulimina mexicana 13.5 3 �1.33 4.68Bulimina mexicana 14.5 3 �1.16 4.53Bulimina mexicana 15.5 3 �1.29 4.57Bulimina mexicana 16.5 4 �1.2 4.58Bulimina mexicana 17.5 1 �0.93 4.75Bulimina mexicana 18.5 1 �0.7 4.56Bulimina mexicana 18.5 2 �1.05 4.67Bulimina mexicana 19.5 2 �1.13 4.58Bulimina mexicana 20.5 2 �1.34 4.6Bulimina mexicana 21.5 1 �0.92 4.57Bulimina mexicana 22.5 1 �0.85 4.54Bulimina mexicana 23.5 1 �0.89 4.63Bulimina mexicana 23.5 1 �0.94 4.7Bulimina mexicana 24.5 2 �1.16 4.54Bulimina mexicana 25.5 1 �1.19 4.53Bulimina mexicana 26.5 3 �1.25 4.54Bulimina mexicana 27.5 3 �1.54 4.46Bulimina mexicana 28.5 1 �1.27 4.65Bulimina mexicana 29.5 3 �1.2 4.59Bulimina mexicana 30.5 2 �1.26 4.59Bulimina mexicana 31.5 1 �1.05 4.68Bulimina mexicana 31.5 1 �1.18 4.64Bulimina mexicana 32.5 1 �0.94 4.68
Epistominella pacifica 0.5 1 �1.37 4.42Epistominella pacifica 1.5 1 �0.77 4.51Epistominella pacifica 1.5 1 �0.84 4.43Epistominella pacifica 1.5 1 �2.77 4.63Epistominella pacifica 1.5 1 �0.9 4.8Epistominella pacifica 2.5 2 �0.91 4.58Epistominella pacifica 2.5 2 �0.73 3.68Epistominella pacifica 2.5 1 �0.94 4.44Epistominella pacifica 2.5 1 �0.85 4.61Epistominella pacifica 3.5 1 �0.86 4.47Epistominella pacifica 3.5 1 �0.94 4.47Epistominella pacifica 3.5 1 �0.91 4.44Epistominella pacifica 3.5 1 �0.72 4.55Epistominella pacifica 4.5 2 �0.95 4.48Epistominella pacifica 4.5 1 �0.89 4.5Epistominella pacifica 5.5 2 �0.93 4.53Epistominella pacifica 5.5 1 �0.67 4.45Epistominella pacifica 6.5 2 �0.98 4.55Epistominella pacifica 6.5 2 �0.93 4.55Epistominella pacifica 7.5 1 �0.74 4.59Epistominella pacifica 7.5 1 �0.97 4.53Epistominella pacifica 8.5 1 �1.73 4.54Epistominella pacifica 8.5 1 �0.84 4.57Epistominella pacifica 9.5 3 �0.88 4.17Epistominella pacifica 9.5 2 �0.78 3.71Epistominella pacifica 10.5 2 �1.09 4.63Epistominella pacifica 10.5 3 �0.87 4.66Epistominella pacifica 11.5 2 �1 4.61
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Appendix A
[45] The appendix provides tables with the follow-
ing data: (1) the number of individual tests mea-
sured for each isotopic analysis of the foraminifera,
(2) whether the foraminifera were live or fossil at
the time they were collected, and (3) all d13C and
d18O values. The appendix is divided into six
separate tables, one each for the six cores that
provided foraminifera (From Extrovert Cliffs: Core
1780-PC30, Table A1 and Core 1780-HPC5,
Table A2; and from Clam Flats: Core 1781-PC31,
Table A3; Core 1781-HPC5, Table A4; Core 1781-
PC31, Table A5; and Core 1781-HPC6, Table A6).
The data are separated by species within the tables.
Acknowledgments
[46] We gratefully acknowledge the crews of the R/V Pt.
Lobos and ROV Ventana, who were professional and helpful
throughout the sea-going operations. Geoff Wheat provided
great help with logistics. We thank Jason Curtis for his help in
the stable isotope lab. Reviews by James Kennett and Marta
Torres are appreciated for helping to clarify ideas as well as
improving presentation of these ideas. The project was funded
by NOAA’s National Undersea Research Program through the
West Coast and Polar Regions Undersea Research Center at
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Epistominella pacifica 11.5 2 �1.03 4.63Epistominella pacifica 12.5 1 �1.07 4.67Epistominella pacifica 13.5 2 �1.02 4.5Epistominella pacifica 13.5 2 �0.97 4.49Epistominella pacifica 14.5 1 �0.74 4.71Epistominella pacifica 15.5 2 �0.91 4.49Epistominella pacifica 15.5 1 �0.7 4.61Epistominella pacifica 16.5 1 �0.87 4.56Epistominella pacifica 17.5 1 �0.74 4.51Epistominella pacifica 18.5 1 �0.76 4.59Epistominella pacifica 19.5 1 �0.81 4.56Epistominella pacifica 20.5 1 �1.35 4.65Epistominella pacifica 21.5 1 �0.89 4.8Epistominella pacifica 22.5 2 �1 4.46Epistominella pacifica 23.5 1 �0.83 4.62Epistominella pacifica 23.5 1 �0.91 4.59Epistominella pacifica 24.5 1 �0.94 4.53Epistominella pacifica 25.5 1 �1.09 4.48Epistominella pacifica 26.5 2 �0.99 4.54Epistominella pacifica 27.5 1 �0.95 4.59Epistominella pacifica 28.5 2 �1.17 4.57Epistominella pacifica 29.5 2 �1.17 4.41Epistominella pacifica 30.5 1 �0.63 4.59Epistominella pacifica 31.5 2 �1.12 4.53Epistominella pacifica 31.5 2 �1.06 4.58Epistominella pacifica 32.5 3 �1.09 4.52
Uvigerina peregrina 0.5 1 �1.48 4.49Uvigerina peregrina 1.5 1 �1.47 4.48Uvigerina peregrina 1.5 1 �1.1 4.58Uvigerina peregrina 1.5 1 �1.38 4.44Uvigerina peregrina 1.5 1 �1.05 4.58Uvigerina peregrina 2.5 1 �1.16 4.51Uvigerina peregrina 2.5 1 �1.32 4.57Uvigerina peregrina 2.5 1 �1.27 4.49Uvigerina peregrina 3.5 1 �1.26 4.49Uvigerina peregrina 3.5 1 �1.21 4.5Uvigerina peregrina 3.5 1 �1.52 4.46Uvigerina peregrina 3.5 1 �1.3 4.51Uvigerina peregrina 4.5 1 �1.3 4.55Uvigerina peregrina 4.5 1 �1.12 4.66Uvigerina peregrina 4.5 1 �1.18 4.59Uvigerina peregrina 4.5 1 �1.1 4.62Uvigerina peregrina 5.5 1 �1.29 4.52Uvigerina peregrina 5.5 1 �1.12 4.59Uvigerina peregrina 6.5 1 �0.99 4.51Uvigerina peregrina 6.5 1 �1.18 4.55Uvigerina peregrina 7.5 1 �1.29 4.62Uvigerina peregrina 7.5 1 �1.07 4.56Uvigerina peregrina 8.5 1 �1.11 4.8Uvigerina peregrina 8.5 1 �1.21 4.64Uvigerina peregrina 9.5 1 �1.13 4.56Uvigerina peregrina 9.5 1 �1.39 4.72Uvigerina peregrina 10.5 1 �1.3 4.61Uvigerina peregrina 10.5 1 �1.3 4.62Uvigerina peregrina 11.5 1 �1.75 4.72Uvigerina peregrina 11.5 1 �1.26 4.67Uvigerina peregrina 12.5 1 �1.16 4.53Uvigerina peregrina 13.5 1 �1.04 4.66Uvigerina peregrina 13.5 1 �0.85 3.49
SpeciesDepth,cmbsf na
d13C,%
d18O,%
Uvigerina peregrina 14.5 1 �1.38 4.6Uvigerina peregrina 15.5 1 �1.47 4.67Uvigerina peregrina 15.5 1 �1.51 4.62Uvigerina peregrina 16.5 3 �1.49 4Uvigerina peregrina 17.5 1 �1.24 4.66Uvigerina peregrina 18.5 1 �1.3 4.67Uvigerina peregrina 19.5 1 �1.46 4.48Uvigerina peregrina 20.5 1 �1.53 4.48Uvigerina peregrina 21.5 1 �1.19 4.62Uvigerina peregrina 22.5 1 �1.36 4.53Uvigerina peregrina 23.5 1 �1.4 4.54Uvigerina peregrina 23.5 1 �1.41 4.55Uvigerina peregrina 24.5 1 �1.18 4.64Uvigerina peregrina 25.5 1 �1.03 4.53Uvigerina peregrina 26.5 1 �1.38 4.54Uvigerina peregrina 27.5 1 �1.59 4.56Uvigerina peregrina 28.5 1 �1.32 4.55Uvigerina peregrina 29.5 1 �1.38 4.66Uvigerina peregrina 30.5 1 �1.42 4.66Uvigerina peregrina 31.5 1 �1.12 4.93Uvigerina peregrina 31.5 1 �1.15 4.59Uvigerina peregrina 32.5 1 �1.36 4.6
aNumber of specimens run for the analysis.
Table A6. (continued) Table A6. (continued)
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the University of Alaska, Fairbanks (NOAA-NURC grants
UAF98-0043 and FP004999).
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