Geochemistry 3 Volume 5 Geophysics Geosystemsusers.clas.ufl.edu/jbmartin/website/Publications/Martin et al 2004 G3... · associated impacts on ocean chemistry and climate, depend

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

GeochemistryGeophysicsGeosystems G3G3

martin et al.: stable isotopic signatures 10.1029/2003GC000629

2 of 25

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-


martin et al.: stable isotopic signatures 10.1029/2003GC000629martin et al.: stable isotopic signatures 10.1029/2003GC000629

3 of 25

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.



4 of 25

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.



5 of 25

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



6 of 25

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



7 of 25

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.



8 of 25

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.



9 of 25

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.



10 of 25

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.



11 of 25

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.



12 of 25

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



13 of 25

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.



14 of 25

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-



15 of 25

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.



16 of 25

[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)


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.



17 of 25

Table A2. Extrovert Cliffs, Core 1780-HPC5


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



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



18 of 25

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.


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


Table A2. (continued) Table A3. Clam Flats, Core 1781-PC31


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



19 of 25



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


Table A4. Clam Flats, Core 1781-HPC5


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



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



20 of 25


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



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



Table A5. Clam Flats, Core 1781-PC31


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



21 of 25



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


Table A6. Clam Flats, Core 1781-HPC6


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



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



22 of 25

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


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


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


Table A6. (continued) Table A6. (continued)



23 of 25

the University of Alaska, Fairbanks (NOAA-NURC grants

UAF98-0043 and FP004999).

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