Faunal and stable isotopic analyses of benthic foraminifera from the Southeast Seep on Kimki Ridge offshore southern California, USA

Author’s Accepted Manuscript Faunal and stable isotopic analyses of benthic foraminifera from the Southeast Seep on Kimki Ridge offshore southern California, USA Mary McGann, James E. Conrad www.elsevier.com/locate/dsr2

PII: DOI: Reference:

S0967-0645(17)30150-9 https://doi.org/10.1016/j.dsr2.2018.01.011 DSRII4397

To appear in: Deep-Sea Research Part II Cite this article as: Mary McGann and James E. Conrad, Faunal and stable isotopic analyses of benthic foraminifera from the Southeast Seep on Kimki Ridge offshore southern California, USA, Deep-Sea Research Part II, https://doi.org/10.1016/j.dsr2.2018.01.011 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Faunal and stable isotopic analyses of benthic foraminifera from the Southeast Seep on Kimki Ridge offshore southern California, USA Mary McGann1, James E. Conrad2 1 Pacific Coastal and Marine Science Center, U.S. Geological Survey, 345 Middlefield Road, M/S 999, Menlo Park, CA 94025 2 Pacific Coastal and Marine Science Center, U.S. Geological Survey, 2885 Mission St, Santa Cruz, CA 95060 [email protected] [email protected] ABSTRACT We investigated the benthic foraminiferal faunal and stable carbon and oxygen isotopic composition of a 15-cm push core (NA075-092b) obtained on a Telepresence-Enabled cruise to the Southeast Seep on Kimki Ridge offshore southern California. The seep core was taken at a depth of 973 m in the vicinity of a Beggiatoa bacterial mat and vesicomyid clams (Calyptogena) and compared to previously published data of living assemblages from ~714 m, four reference cores obtained at ~1030 m, and another one at 739 m. All of the reference sites are also from the Inner Continental Borderland but with no evidence of methane seepage. No endemic species were found at the seep site and most of the taxa recovered there have been reported previously from other seep or low oxygen environments. Q- and Rmode cluster analyses clearly illustrated differences in the faunal assemblages of the seep and non-seep sites. The living assemblage at Southeast Seep was characterized by abundant Takayanagia delicata, Cassidulina translucens, and Spiroplectammina biformis, whereas the non-seep San Pedro Basin reference assemblage was comprised primarily of Chilostomella oolina and Globobulimina pacifica. Density and species richness were lower at the seep site compared to the non-seep site, reflecting the harsher

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living conditions there. The dead assemblage at the seep site was dominated by Gyroidina turgida compared to Cassidulina translucens at the ~1030 m non-seep site and Cassidulina translucens, Pseudoparrella pacifica, and Takayanagia delicata at the 739 m non-seep site. Density was three times lower at Southeast Seep than at the non-seep sites of comparable water depth but species richness was ~30% higher. Stable carbon isotopic values were considerably depleted in the seep samples compared to the non-seep 13

samples, with a progression from lightest to heaviest average  C values evident at the seep site reflecting microhabitat preference and vital effect: the deep infaunal species of Globobulimina, the shallow infaunal species Uvigerina peregrina, the epifaunal species Cibicidoides wuellerstorfi, and the shallow infaunal but aragonite-shelled species 13

Hoeglundina elegans. The  C values downcore among each benthic species indicates ongoing fluid seepage through at least the last 3800 cal yr B.P. at Southeast Seep. Besides 13

the continual local seepage, evidence from  C values of planktic foraminifera in the seep core suggest two pulses of methane (at 3000 and 3700 cal yr B.P.) were released that were large enough to influence much of the water column. Paired benthic and planktic foraminiferal stable oxygen isotope records provide evidence that there were no paleoenvironmental changes such as increased bottom-water temperature or changes in oxygen isotopic composition of bottom and pore waters during this 3800-year record to induce the methane releases. Instead, Southeast Seep appears to be the result of local faulting providing pathways for fluid to flow to the seafloor at a fault stepover or transpressional bend in the regional strike-slip system.

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Keywords: stable carbon isotopes, benthic foraminifera, southern California, Kimki Ridge, Southwest Seep, Santa Catalina Basin, Calyptogena, Beggiatoa

1. Introduction Benthic foraminifera live either at the sediment-water interface (epifaunal) or within the sediment (infaunal), and have long been used in climate, oceanographic, and environmental reconstructions (e.g., Shackleton and Opdyke, 1973; Boyle and Keigwin, 1982; Sarnthein et al, 2009) as well as for the characterization of marine methane seep sites (e.g., Rathburn et al., 2000, 2003; Bernhard et al., 2001; Hill et al., 2003; Torres et al., 2003; Barbieri and Panieri, 2004; Wiedicke and Weiss, 2006; Martin et al., 2010; Herguera et al., 2010; Panieri et al., 2012, 2014a, b; Mackensen et al., 2017). This study investigates whether the benthic foraminiferal assemblage collected from the Southeast Seep on Kimki Ridge off southern California records evidence of a cold methane seep. In addition, because no water column or pore water samples were collected as part of this 13

study, the  C analyses of the calcite in benthic and planktic foraminiferal tests were used to determine how long Southeast Seep has been an active cold seep area and whether methane releases were localized or influenced much of the water column.

2. Site Characterization The California Continental Borderland has long been the focus of geophysical investigations due to the numerous fault zones located there, and the potential for catastrophic earthquakes and tsunamis that could severely impact the dense population in the area (see discussion in Legg et al., 2015). A major structural feature in the Inner

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Continental Borderland is the San Clemente Fault (SCF) (Ford and Normark, 1980; referred to as the San Clemente Island Fault in Legg et al., 2015). In 2014 and 2016, the U.S. Geological Survey (USGS) and University of Washington (UW) collected multibeam bathymetry, CHIRP sub-bottom profiles, and high-resolution multi-channel seismic reflection profiles to provide detailed imaging of both the SCF and nearby Catalina Fault that border the Catalina Basin (Figure 1; Walton et al., 2016). One feature of interest captured in the USGS-UW imagery was a small ridge located at the northern end of the Catalina Basin and the SCF. This 200 m topographic high lies approximately 25 km west of Catalina Island (Figure 1). A deep-tow geophysical study was first conducted here in April 1976 using the R/V Melville of the Scripps Institution of Oceanography with the purpose of searching for evidence of active faulting (Ford and Normark, 1980). Subsequently, the site was informally named Kimki Ridge by Arne Junger and J.G. Vedder (unpublished data, 1979). The USGS-UW multi-channel seismic reflection profiles imaged several faults in this region that appeared to reach the surface of the sediment sequence, one of which was located along the ridge crest on the western side of Catalina Basin at Kimki Ridge (for details of the seismic surveys see Conrad et al., 2018). These local tectonic conditions suggested the presence of methane seepage and associated authigenic carbonate precipitation in the sediment near and on the seafloor, similar to other cold seeps found along the California borderland such as Santa Monica Basin (Normark and Piper, 1998; Hein et al., 2006; Paull et al., 2008), San Diego Trough (Grupe et al., 2015; Maloney et al., 2015), San Clemente Basin (Lonsdale, 1979; Torres et al., 2002), and Redondo Knoll offshore Palos Verdes and Point Dume (Levin et al., 2016). With this knowledge, one of the authors (JEC) participated in an Ocean

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Exploration Trust teleconference and suggested that Kimki Ridge should be investigated more thoroughly as it was likely the site of active cold seeps.

2. Materials And Methods On August 6, 2016, Ocean Exploration Trust Exploration Vessel (E/V) Nautilus utilized tandem ROVs, Hercules and Argus, to sample sediment, rocks, and macrofauna from Kimki Ridge. The dive (cruise NA075, dive H1554; USGS Core Locator 2017-677DD) was guided via telepresence by author JEC. Of the three seep sites (Northwest Seep, Middle Seep, and Southeast Seep; Figure 2) identified on Kimki Ridge, Southeast Seep had the greatest evidence of seepage. A ~20 cm long push core (NA075-092b) with a diameter of 7 cm was recovered there (33.2867°N latitude, 118.7613°W longitude; Figure 3; Table 1) at 973.1 m water depth in a bed of Calyptogena clams with a Beggiatoa bacterial mat (Figure 4A). The collection site was characterized by water temperature of 4.2°C, salinity of 34.5 psu, and dissolved oxygen concentration of 12.410 µmol/L (0.7 ml/L). Subsequently, approximately 5 cm of sediment at the bottom of the core (Figure 5) was lost during processing. A rock sitting on top of loose sediment on a nearby ledge overhanging the cold seep was also collected (Sample NA075-093; Figure 4B; Table 1). Unfortunately, no additional push cores were taken on the Nautilus cruise from nearby non-seep locations to act as reference material. Therefore, previously published census counts of living benthic foraminifera from a non-seep site in San Pedro Basin in the Inner Continental Borderland (Silva et al., 1996; Figure 1; Table 1) are used as comparative material for the living Southeast Seep assemblage. Two of four PVC tubes

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obtained from box cores at depths of 709-722 m in repeated surveys in April, July, and October 1988 were analyzed; one for the >150 µm-sized foraminifera and another for the 63-150 µm size fraction. Additional comparative material is provided by surface or near-surface sediment from five cores recovered from the Inner Continental Borderland in regions that showed no evidence of methane seepage at a similar depth to the NA075-092b push core (Figure 1). These include gravity cores SC1-G2 and SC2-G1 (USGS core locator S-I2-09-SC) obtained from the eastern end of Catalina Basin and the Gulf of Santa Catalina, respectively, by the R/V Sproul, as well as three vibracores (DR624 VC-379, DR624 VC380, and DR625 VC-382; USGS Core Locator 2014-637-FA) taken by Monterey Bay Aquarium Research Institute’s (MBARI) ROV Doc Ricketts on board the R/V Western Flyer. Sediment cores on these earlier cruises originally were taken to investigate sedimentology, stratigraphy, pore water chemistry, and radiometric age dating to assess neotectonic activity, including the recency of fault motion and potential for fault-related 13

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hazards. Benthic foraminiferal faunal, as well as  C and  O analyses, are presented for all of the cores. To establish a chronology for the Nautilus, USGS, and MBARI cores, seven radiocarbon measurements were obtained from mixed planktic foraminiferal assemblages comprised mostly of Neogloboquadrina dutertrei (d’Orbigny), as well as few Orbulina universa d’Orbigny, Neogloboquadrina pachyderma (Ehrenberg), and Globigerina bulloides d’Orbigny, by accelerator mass spectrometry (AMS) at the National Ocean Sciences AMS (NOSAMS) Facility of Woods Hole Oceanographic Institution. They were used to determine the age of the deposits at the bottom of push core NA075-092b

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(at 10-12 cm; the top of the core was assumed to be modern), at the top (0-1 cm) and bottom (9-10 cm) in core SC2-G1 also from Catalina Basin, and from 6 cm or shallower of the four other reference cores (VC-379, VC-380, VC-382, and SC1-G2) from the Inner Continental Borderland in order to obtain a modern, or near modern, non-seep record. The radiocarbon ages were obtained by a 14C/12C ratio using a 14C half-life of 5,568 years (Stuiver and Polach, 1977) and then were converted to calibrated calendar ages (cal yr B.P.) using the CALIB 7.1 program (Stuiver et al., 2017). The calibrated ages are reported as the peak probability ages and the 2 sigma ranges are also included. A reservoir age of 633 years was used for the planktic foraminiferal samples following Kennett et al. (2000), which is the sum of the global surface-water reservoir age correction of 400 years (Stuiver and Braziunas, 1993) and the regional reservoir-age correction (∆R) of 233±60 years (Ingram and Southon, 1996). Five 1-cm samples (0-5 cm; each 7.5 cm3) from the archive half of Southeast Seep core NA075-092b were analyzed for living benthic foraminiferal constituents. This depth was used because most foraminifera are epifaunal or live within the upper few centimeters (0-5 cm) of the surface (Gooday, 1986; Corliss, 1991 and references therein). In order to identify those individuals that were alive, or recently alive, at the time of collection (Bernhard, 1988, 2000), the samples were immersed in a mixture of 2 g of rose Bengal stain per 1 liter of >70% ethyl alcohol (Lutze and Altenbach, 1991) and left to soak while being gently agitated on a shaker table for two weeks following the FOBIMO protocol (Schönfeld et al., 2012). Twelve additional 7.5 cm3 samples (0-12 cm) taken from the working half of the core, as well as the five samples used for radiocarbon dating from the reference cores, and another sample from reference core SC2-G1 at 1-2 cm

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downcore that was the depth that approximated the age of the lowermost portion of the seep core (see results section), were chosen to investigate the dead foraminiferal assemblage. These latter samples ranged in size from 9.6-46.1 cm3 and were soaked in tap water and similarly agitated on a shaker table. They were not stained because all had been collected 3-8 years earlier and living individuals would no longer be present. After disaggregation, the samples were sieved with tap water through nested 1.0 mm, 150 µm, and 63 µm screens and then air-dried. Benthic foraminifera were picked from the ≥63 µm size fraction. For the living assemblages, the methods of Silva et al. (1996) were followed: the surface sample was picked in its entirety but samples lower in the core were picked after being split into aliquots with the aid of a microsplitter. This method was used because there were few living foraminifera in the 63-150 µm size fraction as well as abundant dead specimens that had to be avoided, making these samples time consuming to pick. For the dead assemblages, benthic foraminifera were picked from splits with the goal of obtaining a statistically valid 300 specimens per sample (Douglas, 1973). The picked specimens were placed on microscope slides and identified, using the nomenclature registered in the World Foraminiferal Database (Hayward et al., 2017). The slides and residues of this study are on file at the U.S. Geological Survey, Menlo Park, California. Several steps were necessary in order to compare the living benthic foraminiferal assemblages of the reference San Pedro Basin box cores (Silva et al., 1996) and Southeast Seep push core samples. First, the census counts of the >150 µm and 63-150 µm size fractions of each of the three Silva et al. (1996) surveys (April, July, and October, 1988), already normalized for 50 cc sediment, were combined separately using the data from

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Box Core 1 and Subcore 1 (i.e., 1-1) and then converted to frequency data using a sum of total living benthic foraminifera in each sample. Second, the living Southeast Seep census counts were also normalized to 50 cc sediment and converted to frequency data. In order to make both data sets comparable, only the samples from 0-5 cm were used, 0.5-cm samples were combined into 1-cm samples where appropriate in the Silva et al. (1996) data set, and the taxonomy from both studies had to be made consistent (Table 2). Finally, these data were analyzed by Q-mode cluster analysis to describe the relationship between the benthic foraminiferal assemblages, grouping together those samples of similar species composition. The analysis used a square root transformation of the data, a Bray-Curtis similarity coefficient, and amalgamated by a group averaged linkage strategy. These methods were chosen because they treat all species equally while providing the most realistic grouping of the samples by depth (Clarke and Gorley, 2006). Primer v. 6.1.6, a statistical software package created by Primer-E, Ltd., was used for this analysis (Clarke and Gorley, 2006). The relative species abundances of the dead benthic foraminifera of the 12 seep and six core reference samples were computed using a sum of the total dead benthic foraminifera in each sample. Once these census counts were converted to frequency data, they were also analyzed by Q-mode cluster using the parameters as above. In addition, the dead foraminiferal census data of the seep and reference core samples were analyzed separately by R-mode cluster analysis to identify those species that commonly occurred together. A similar analysis was not performed on the living census counts because of the small number of samples utilized.

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Stable carbon and oxygen isotopic measurements were performed on benthic specimens belonging to four dominant taxa of the >150 µm size fraction from each of the 12 seep and six core reference samples, if available. These were Cibicidoides wuellerstorfi (Schwager), Globobulimina spp. [Globobulimina auriculata (Bailey) and Globobulimina pacifica Cushman], Hoeglundina elegans (d’Orbigny), and Uvigerina peregrina Cushman. Two planktic species were also analyzed: Neogloboquadrina pachyderma and Globigerina bulloides. These analyses utilized only non-stained (dead) individuals because not enough stained specimens were encountered to run them separately. The benthic and planktic foraminiferal carbonate shells were examined with a light microscope to verify that there were no obvious overgrowths on the shells, as it was not possible to apply more precise methods (e.g., Scanning and Transmission Electron Microscopy, Electron probe micro analysis, and secondary ion mass spectrometry; Torres et al., 2010 and Panieri et al., 2017) in this study. As a result, there is the possibility that some specimens were affected by a small amount of diagenetic alteration. Those specimens that were considered to be pristine were cleaned in an utltrasonic bath in reagent-grade methanol and air-dried. Two to four (usually three) benthic specimens of each taxon were then analyzed for δ13C and δ18O isotopes. Ten to 20 specimens of each of the two planktic foraminiferal species were similarly measured. The analyses were conducted at the University of California, Santa Cruz Stable Isotope Laboratory by acid digestion using an individual vial acid drop ThemoScientific Kiel IV carbonate device interfaced to a ThermoScientific MAT-253 dual-inlet isotope ratio mass spectrometer (IRMS) with a measurement precision of ±0.08 per mil (UCSC Stable Isotope

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Laboratory, 2017). Samples were reacted at 75°C in orthophosphoric acid (specific gravity = 1.92 g/cm3) to generate carbon dioxide and water. Water was cryogenically removed from CO2 and non-condensible gases were pumped away, prior to introduction of the purified CO2 into the IRMS. During each run sequence, calibrated in-house standard Carrera Marble was used to correct the data including a drift correction. Four NBS-18 limestone standards were used in conjunction with Carrera Marble to correct for instrument specific source ionization effects. Two NBS-19 limestone samples were run "as-a-sample" to monitor quality control and long-term performance. Carrera Marble has been extensively calibrated against NIST Standard Reference Materials (NBS-19, NBS-18, and LSVEC) and as part of intercomparison studies with other stable isotope laboratories. Corrected delta values are expressed relative to international standards PDB (PeeDee Belemnite) in ‰ for both δ13C and δ18O.

3. Results Radiocarbon ages from seep areas must be used with caution because they may be affected by old carbon from the seepage fluids (Paull, 1989; Bauer et al., 1990; Pohlman et al., 2010). However, since the 14C age returned for the sample at the bottom (10-12 cm) of push core NA075-092b from Southeast Seep used planktic (i.e., not bottom-dwelling) foraminifera and the 13

 C measured in their shells was -1.56‰ (Table 3), it does not appear the specimens were impacted by these fluids. Therefore, the calibrated age of 3872 cal yr B.P. (2 sigma range of 3765-3972 cal yr B.P.; Table 3) does not need to be corrected for this effect and is valid as

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measured. This calibrated age implies a sedimentation rate of 2.84 cm/1000 years for the seep core. The calibrated radiocarbon ages of the bottom (9-10 cm) and top (0-1 cm) of the non-seep gravity core (SC2-G1) obtained from the same basin (Catalina) as the Southeast Seep core were 6023 cal yr B.P. (2 sigma range of 5925-6124 cal yr B.P.) and 3503 cal yr B.P. (2 sigma range of 3430-3576 cal yr B.P.), respectively (Table 3), yielding a sedimentation rate of 3.77cm/1000 years. These dates imply that core SC2-G1 overlaps the stratigraphic record of the seep core for only ~370 cal yr B.P. (i.e., from ~0-2 cm). The ages of near-surface sediment from the four other reference cores ranged from 486 cal yr B.P. to modern. Foraminiferal density (number of individuals/cm3 of sediment) of benthic foraminifera ranged from 9-26/cm3 (

18/cm3) for the living assemblage and 185-1161/cm3 ( =467/cm3)

for the dead assemblage of the Southeast Seep samples (Table 4). The density was considerably higher (360-2969/cm3, =1419/cm3) for the dead assemblage of the reference non-seep samples. A total of 84 species ( =39 species/sample) of benthic foraminifera were identified in the Southeast Seep core, approximately a third (31) of which were represented by living specimens in the stained samples from the core top down to 5 cm (Appendix 1, 2). The dominant species in the living assemblage (Table 5) were Takayanagia delicata ( =17%), Cassidulina translucens ( =12%), and the agglutinated species ( =18%), of which Spiroplectammina biformis ( =16%) was most abundant. Three other species were common: Loxostomum minuta, Bulimina striata, and Globocassidulina minuta ( =4-7%). The dominant species in the dead assemblage was Gyroidina turgida ( =22), and Cassidulina translucens, Takayanagia delicata, Loxostomum minuta, Pseudoparrella pacifica, and Globocassidulina minuta were common ( =6-11%).

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Fifty-five species were recovered in the non-seep core samples from ~1030 m ( =31 species/sample). In these samples, Cassidulina translucens was dominant ( =30%), and Gyroidina turgida, Globocassidulina subglobosa, Takayanagia delicata, Loxostomum minuta, and Epistominella exigua were of significant abundance ( =5-11%). In the shallower non-seep reference core (SC1-G2, 739 m), 24 species were recovered. Three species were most prevalent (Pseudoparrella pacifica, Cassidulina translucens, and Takayanagia delicata; =15-20%), whereas five others were common (Loxostomum minuta, Gyroidina turgida, Uvigerina peregrina, Epistominella exigua, and Globocassidulina minuta; =5-11%). The Q-mode cluster analysis of the living assemblages segregated the 15 non-seep samples from San Pedro Basin of Silva et al., 1996 (Cluster A, Figure 6) from the five Southeast Seep samples (Cluster B). The dead assemblages of the seep and non-seep cores were also separated into two groups (Figure 7). Cluster C combined the 12 Southeast Seep samples and Cluster D grouped the six non-seep samples. The R-mode cluster analysis of the dead assemblage of both the seep (Figure 8) and non-seep (Figure 9) samples grouped the abundant species into one cluster (E and F, respectively) and numerous other clusters and outliers. 13

Stable carbon isotope ( C) values for the benthic foraminifera in the seep and non-seep samples are presented in Table 6 and plotted on Figure 10. The values show more deviation among the four dominant species in the >150 µm size fraction at the Southeast Seep site than in the reference cores. In the seep samples, the analyses determined the following for each taxon: Hoeglundina elegans (1.62‰ to -0.08‰; ∆ = 1.70‰, (0.81‰ to -5.70‰; ∆ = 6.51‰, 8.02‰,

= 1.21‰), Cibicidoides wuellerstorfi

= -1.02‰), Uvigerina peregrina (-1.61‰ to -9.63‰; ∆ =

= -3.53‰), and Globobulimina spp. (-1.95‰ to –13.49‰; ∆ = 11.54‰,

= -6.44‰).

In the non-seep samples, the results were as follows: Hoeglundina elegans (1.52‰ to 1.81‰; ∆

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= 0.29‰,

= 1.70‰), Cibicidoides wuellerstorfi (0.26‰ to -0.47‰; ∆ = 0.73‰,

Uvigerina peregrina (-0.76‰ to -1.48‰; ∆ = 0.72‰, (1.16‰ to -1.44‰; ∆ = 2.60‰

= -0.04‰),

= -1.02‰), and Globobulimina spp.

= -0.88‰). Stable carbon isotope values for the planktic

foraminifera in the Southeast Seep core (Table 7; Figure 11A) vary downcore between 0.36‰ and -10.35‰ (∆ = 10.71‰,

= -2.07‰) for Neogloboquadrina pachyderma and between -

0.82‰ and -3.74‰ (∆ = 2.92‰,

= -1.80‰) for Globigerina bulloides.

Far less variability was evident for the stable oxygen isotope values for the four benthic species at the seep and non-seep sites (Table 6; Figure 12), as well as the two planktic species at the seep site (Table 7; Figure 11B), than with the stable carbon isotopes. At Southeast Seep, the benthic species Cibicidoides wuellerstorfi ranged from 1.98-3.94‰ (∆ = 1.96‰; Globobulimina spp. 2.85-3.53‰ (∆ = 0.68‰; = 0.48‰;

= 2.64‰),

= 3.14‰), Hoeglundina elegans 3.38-3.86‰ (∆

= 3.53‰), and Uvigerina peregrina 2.92-4.48‰ (∆ = 1.56‰;

= 3.87‰). The

values for the planktic species Neogloboquadrina pachyderma and Globigerina bulloides were 0.21-1.35‰ (∆ = 1.14‰;

= 0.71‰) and -0.30-0.32‰ (∆ = 0.62‰;

= 0.03‰), respectively.

At the non-seep reference sites, the values were 1.99-3.39‰ (∆ = 1.40‰; Cibicidoides wuellerstorfi, 2.71-3.38‰ (∆ = 0.67‰; 3.91‰ (∆ = 0.65‰;

= 2.55‰) for

= 3.07‰) for Globobulimina spp., 3.26-

= 3.50‰) for Hoeglundina elegans, and 2.76-4.33‰ (∆ = 1.57‰;

3.59‰) for Uvigerina peregrina.

4. Discussion 4.1 Sedimentation Rate The sedimentation rates determined for Southeast Seep push core (2.84 cm/1000 years) and Catalina Basin reference core SC2-G1 (3.77 cm/1000 years) are considerably

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=

lower than those determined at other locations within the inner basins of the California Continental Borderland. Normark and McGann (2004) documented a sediment accumulation rate for the floor of Santa Monica Basin at ODP Site 1015 of about 300 cm/1000 years during the last few thousand years. Later, Normark et al. (2009) determined sediment accumulation rates of 209-244 cm/1000 years for the last ~14,000 years (OIS 1 of Normark et al., 2009; MIS 1 of Lisiecki and Raymo, 2005) of the basin floor of closed basins (Santa Barbara Basin and Santa Monica Basin), 24 cm/1000 years for the open basin situated in the Gulf of Santa Catalina, and <2.6 to 174.3 cm/1000 years for the slope regions of these basins. The authors also reported a rate of 36.7 cm/1000 years in Catalina Basin, whereas Paull et al. (2008) determined rates of 10-64 cm/1000 years at a cold seep site in Santa Monica Basin. In contrast, the sediment accumulation rate at Lasuen Knoll, an interbasin ridge east of Santa Catalina Island (Figure 1), was only 1.2 cm/1000 years (Normark et al., 2009), making it comparable in terms of both the geomorphology of Kimki Ridge (i.e., part of an interbasin ridge, but located west of Santa Catalina Island) and the sediment accumulation rate of the Southeast Seep push core. The low sedimentation rates determined for Southeast Seep and SC2-G1 are expected because Catalina Basin is an isolated and closed basin and both core sites are located far from San Gabriel submarine canyon that is the primary sediment source (Figure 1). The transitions from canyon to channel and channel to fan are located in the eastern, proximal portion of the basin (Roland et al., 2016). In addition, the head of the canyon is well offshore at the edge of San Pedro Shelf, such that it receives little highstand sediment input. Although additional sediment sources include local gullies, smaller submarine

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canyons, and landslides off Santa Catalina and San Clemente Islands (Roland et al., 2016), they are minor and do not greatly impact sedimentation at Kimki Ridge or the SC2-G1 reference site.

4.2 Benthic Foraminiferal Assemblages All 84 benthic foraminiferal species recovered at the Southeast Seep site (Appendix 1, 2) occur at non-seep locations at similar slope depths off southern California and elsewhere along the northeast Pacific margin (Uchio, 1960; Ingle, 1980; Culver and Buzas, 1986; Mackensen and Douglas, 1989; Bernhard, 1992; Bernhard et al., 1997; McGann, 2002, 2015). The absence of endemic benthic foraminiferal species is similar to the findings at other cold seeps (Akimoto et al., 1994; Kitazato, 1996; Bernhard et al., 2001; Sen Gupta et al., 1997, 2007; Rathburn et al., 2000, 2003; Martin et al., 2010). In addition, living representatives of the most abundant taxa occur at the seep site. This suggests downslope displacement and redeposition of benthic foraminifera from considerably shallower biofacies is minimal at Southeast Seep, although transport of propagules (Alve and Goldstein, 2003, 2010) or specimens in their adult phase that grew up away from the seep environment but from similar depth habitats (Bernhard et al., 2010) cannot be ruled out. Faunal differences between the living assemblages of Southeast Seep and the reference site in San Pedro Basin (Silva et al., 1966) are clearly distinguished by the Qmode cluster analysis (Figure 6). Cluster A combined the 15 non-seep reference samples and Cluster B grouped the five seep samples, with only 17% similarity between the assemblages. Both sites are characterized by abundant agglutinated species (17-18%;

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mostly Spiroplectammina biformis) as well as taxa indicative of low-oxygen conditions (i.e., Chilostomella oolina and Globobulimina pacifica in San Pedro Basin and Takayanagia delicata and Cassidulina translucens at Southeast Seep). The latter reflects that fact that both sites are located within the oxygen-minimum zone. At Southeast Seep, the dissolved oxygen concentration was 12.410 µmol/L when the push core was collected, whereas Silva et al. (1996) reported a range of 2.5-17 µmol/L in San Pedro Basin during the 11-year period from January 1977 to May 1988 based on the work of Berelson (1991). The faunal difference in living assemblages between the two sites may reflect slightly different dissolved oxygen concentrations, other environmental factors (i.e., temperature and salinity), depth, sediment grain size, availability and type of food, or microhabitat preferences (e.g., Corliss, 1985; Bernhard, 1989; Corliss and Emerson, 1990; McCorkle et al., 1990; Fontanier et al., 2006). The differences in species distributions may also reflect factors due to fluid emanating at seep sites, including the chemistry of sediment pore waters and flux of methane or hydrogen sulfide across the sediment-water interface (Barry et al., 1996; Bernhard et al., 1997; Rathburn et al., 2000, 2003; Hill et al., 2003; Torres et al., 2003; Wiedicke and Weiss, 2006; Sen Gupta et al., 2007; Martin et al., 2010). Because water chemistry was not analyzed at either Southeast Seep or the references sites of Silva et al. (1996), the factors responsible for the substantial assemblage differences could be a combination of many of these. A clear separation of samples in the Q-mode analysis of the dead foraminiferal assemblages at Southeast Seep and the non-seep MBARI/USGS reference sites (Figure 7, Cluster C, the 12 seep samples; Cluster D, the six non-seep samples) is also evident, with

17

only 65% faunal similarity between the two. The reference samples are further distinguished by water depth, as the five samples from ~1030 m (VC-379, VC-380, VC382, and two from SC2-G1) grouped together first, followed by the addition of SC1-G2 from 739 m with 6% faunal difference from the deeper reference samples. These faunal dissimilarities are due to different species dominating the assemblage at each site (Table 5). At the seep site, Gyroidina turgida was most abundant ( =22%) and Cassidulina translucens was less so ( =11%). In the ~1030 m reference sites, Cassidulina translucens ( =30%) was dominant and Takayanagia delicata and Gyroidina turgida ( =9-11%) were of lesser abundance. The remaining prevalent species (Globocassidulina minuta, Loxostomum minuta, Pseudoparrella pacifica, Epistominella exigua, Gyroidina turgida, and Globocassidulina subglobosa) were present in fairly similar proportions (<8%) at both sites. In contrast, the shallowest reference core (SCIG2) is characterized by dominant Pseudoparrella pacifica ( =20%), Cassidulina translucens ( =15%), and Takayanagia delicata ( =15%), with the other prevalent species similar in abundance to those of the seep and deeper reference cores. The R-mode cluster analysis of the dead assemblage at Southeast Seep (Figure 8) separated the species into those occurring in abundances of ~1- 22% (Cluster E) and rare species of ~ <1% (i.e., the remaining clusters and outliers). Most of the taxa recovered at the seep site that grouped together in Cluster E are considered opportunistic and have been reported previously from other seeps or in areas of high food supply and low oxygen environments, including Bolivina pacifica, Bolivina seminuda, Bolivina spissa, Bulimina striata (= B. mexicana), Buliminella tenuata, Chilostomella oolina, Fursenkoina complanata, Globobulimina pacifica, Gyroidina altiformis, Hoeglundina

18

elegans, Bolivina pseudobeyrichi, Oridorsalis umbonatus, Pseudoparrella pacifica, Rutherfordoides cornuta, Spiroplectammina biformis, Takayanagia delicata, and Uvigerina peregrina (Akimoto et al., 1994; Bernhard et al., 2001; Rathburn et al., 2000, 2003; Fontanier et al., 2002, 2003; Hill et al., 2003; Torres et al., 2003; Wiedicke and Weiss, 2006; Martin et al., 2010; and Panieri et al. 2014a and references therein). Two additional species found at the seep site (Cibicidoides wuellerstorfi and Spirillina vivipara) have also been reported living on vestimentiferan tubeworms at the sedimentwater interface at cold seeps in order to avoid the oxygen depletion and hydrogen sulfide toxicity in the sediment (Mackensen et al., 2006; Sen Gupta et al., 2007). In contrast, the rare species that grouped into the remaining clusters did so with samples of lower species’ abundances combining in each successive cluster. These species typically occur in low abundances in other seep as well as non-seep settings in the northeastern Pacific (Uchio, 1960; Culver and Buzas, 1986; Mackensen and Douglas, 1989; Bernhard, 1992; Bernhard et al., 1997, 2001; McGann, 2002, 2015), appearing not to flourish under either oxygen-stressed or normal environmental conditions. The R-mode cluster analysis of the dead assemblage of the non-seep MBARI/USGS reference samples also grouped the most prevalent species into one cluster (5-38%; Figure 9, Cluster F). As with the assemblages of the seep samples, many of these genera (e.g., Globocassidulina, Epistomienlla, Uvigerina, Bolivina, and Cassidulina) tolerate low-oxygen conditions (Panieri 2006; Panieri et al., 2014a) that are commonly found at these depths in the northwestern Pacific (Ingle, 1980; Berelson, 1991; Robison et al., 2010). The remaining species in the non-seep samples occurred in abundances of <5%.

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4.3 Benthic Foraminiferal Density and Species Richness Benthic foraminiferal density for the living assemblage at Southeast Seep ranged from 9-26 specimens/cm3, averaging 18 specimens/cm3 (Table 4). These values are higher than those reported for living assemblages at most seep sites elsewhere in the North Pacific: 2.8 specimens/cm3 and 5.6-27.6 specimens/cm3 in Monterey Bay off central California (Bernhard et al., 2001 and Rathburn et al., 2003, respectively), 5.5-6.8 specimens/cm3 off the Eel River in northern California (Rathburn et al. 2000), and 1.14.2 specimens/cm3 on Hydrate Ridge off Oregon (Torres et al., 2003). In comparison, the density of the living assemblage for the San Pedro Basin non-seep site was more variable, ranging from 3-68 specimens/cm3, with the mean about 20% higher (22 specimens/cm3; Table 4; Silva et al., 1996). Comparisons of the densities of seep and non-seep living assemblages at other sites show they are variable. Some studies reported densities two to three times higher (Torres et al., 2003; Panieri, 2006) at seep sites compared to control sites, which were attributed to the rich bacterial food sources at the methane seeps. The augmented food supply, in turn, increases foraminiferal reproductive success and, therefore, higher populations (Wiedicke and Weiss, 2006). Other studies found approximately the same values at both (Rathburn et al., 2003; Martin et al., 2010), and still others reported lower values (Sen Gupta et al., 1997; Bernhard et al., 2001; Robinson et al., 2004; Martin et al., 2010; Herguera et al., 2014), particularly beneath bacterial mats such as those found at Southeast Seep (Robinson et al., 2004; Martin et al., 2010). Whereas the density of the living assemblage was about 20% higher at the non-seep site versus the seep site, the density of the dead assemblages at the non-seep

20

MBARI/USGS reference sites was three times higher ( =1419 specimens/cm3) than at Southeast Seep ( =463 specimens/cm3). This trend may reflect the fact that methane and hydrogen sulfide present at seep sites is poisonous to most foraminifera (Torres et al., 2003; Panieri et al., 2014a), resulting in a reduction in their abundance compared to nonseep sites. Unlike benthic foraminiferal species density, species richness at seep sites is less well documented in the literature. Bernhard et al. (2001), Torres et al. (2003), and Martin et al. (2006) found species richness to be generally the same at seep and non-seep sites, whereas Robinson et al. (2004), Panieri et al. (2014a), and Burkett et al. (2016) reported a reduction at seep sites, possibly due to the inability of some species to live in the presence of the harmful gases (Panieri et al., 2014a). Martin et al. (2010) also found the lowest species richness beneath a bacterial mat. Whereas the average species richness of the living assemblage was lowest (12 species/sample) at Southeast Seep compared to the San Pedro Basin non-seep reference site (17 species/sample), the opposite was true of the dead assemblage. An average of 39 species/sample was present at Southeast Seep versus 31 species/sample at the MBARI/USGS non-seep reference sites at ~1030 m and 24 species/sample at the 739 m site (Table 4). It is assumed the reduced species richness in the living assemblage at Southeast Seep reflects the harsher living conditions at vent sites and lower density of specimens. However, it is not clear why the species richness of the dead assemblage is higher at the seep site.

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4.4 Benthic Foraminiferal Stable Carbon and Oxygen Isotopes Three factors influence the stable isotopic signatures of benthic foraminifera: microhabitat preference (McCorkle et al., 1990; Torres et al., 2003; Fontanier et al., 2006; Wiedicke and Weiss, 2006), vital effect (McCorkle et al., 1990; Rathburn et al., 1996; Schmiedl et al., 2004), and inorganic carbonate overgrowths or recrystallization overprinting the original isotopic composition (Torres et al., 2003, 2010; Panieri et al., 2017). In terms of their microhabitat preferences, taxa that live deeper in the sediment 13

exhibit more negative  C values than those higher in the sediment column or at the sediment-water interface, reflecting the dissolved inorganic carbon (DIC) of pore water 13

( CDIC; e.g., McCorkle et al., 1990; Rathburn et al., 1996; Fontanier et al., 2006). This is related to both the increased rate at which organic matter decomposes in the sediment with depth as well as bacterial degradation releasing 12C (Grossman, 1984, 1987; McCorkle and Emerson, 1988, Sackett, 1989; McCorkle et al., 1990). Of the dominant species in the >150 µm size fraction of the seep and non-seep cores, Globobulimina spp. are deep infaunal (>4 cm), Uvigerina peregrina and Hoeglundina elegans are shallow infaunal (0-2 cm), and Cibicidoides wuellerstorfi is epifaunal (0-1 cm) (McCorkle et al., 1990; MacKensen et al., 1993; Fontanier et al., 2002, 2003; 13

Wiedicke and Weiss, 2006). Therefore, Globobulimina spp. has  C values of pore water deeper in the sediment where the dissolved oxygen concentration approaches zero, 13

Uvigerina peregrina and Hoeglundina elegans reflect the  C of pore water just below 13

the sediment-water interface, and Cibicidoides wuellerstorfi has  C values at or close to that of bottom water (McCorkle et al., 1990; Fontanier et al., 2002, 2003).

22

13

The downcore  C values for the four species are presented in Figure 10. In the seep 13

samples, each taxon was depleted in  C compared to the non-seep samples (Figures 10A and 10B-F, respectively) and the microhabitats of the three calcite-shelled species 13

were reflected in their  C values. The deep infaunal species of Globobulimina recorded 13

the lightest average  C values (-6.08‰), the shallow infaunal species Uvigerina peregrina was heavier (-3.53‰), and the epifaunal species Cibicidoides wuellerstorfi heavier still (-0.71‰). The trend was somewhat different in the non-seep cores. The variance between the species was far less than in the seep core and although the epifaunal taxon Cibicidoides wuellerstorfi was still the heaviest of all (0.10‰), the deep infaunal 13

species of Globobulimina recorded heavier  C values (-0.89‰) than the shallow infaunal species Uvigerina peregrina (-1.18‰). The aragonite-shelled shallow infaunal species Hoeglundina elegans (Fontanier et al., 13

2002, 2003; Wiedicke and Weiss, 2006) was consistently enriched in  C in both the seep ( =1.21‰) and non-seep ( =1.68‰) cores compared to the calcite-shelled species (Figures 10A and 10B-F). These heavy values are thought to be reflective of a taxonspecific vital effect related to the mineralogy of the biogenic carbonate during biomineralization, possibly due to external factors such as food supply (most likely 13

bacteria) (McCorkle et al., 1990). Other studies have recorded similarly heavy  C values (e.g., McCorkle et al., 1990; Fontanier et al., 2006; Sarnthein et al., 2009), although this was not found to be the case in Martin et al. (2010) who attributed their reported minimum values of -35.7‰ to the influence of carbon that was derived from sulfate dependent anaerobic oxidation of methane.

23

13

Unfortunately, no  CDIC samples were obtained from the pore water or at the sediment-water interface at the Southeast Seep to compare with the benthic foraminiferal 13

13

 C results. Such  CDIC values can be extremely low at some sites with active methane 13

seepage (e.g., -6 to -48‰ at Hydrate Ridge; Torres et al., 2003). Instead, the average  C value for rocks collected at the site was greatly depleted (-45.75‰; Conrad et al., 2018), indicating the presence of biogenically derived methane in the fluids (Bohrmann et al., 1998) most likely linked to authigenic carbonate precipitation driven by anaerobic oxidation of CH4 via sulfate reduction (Conrad et al., 2018). 13

Since nearly all of the benthic foraminiferal  C values (except for some specimens of Globobulimina spp.) at Southeastern Seep were in the range expected for organic matter decomposition (0 to -4‰; Torres et al., 2003), it appears the foraminifera were 13

calcifying during periods of little fluid discharge when pore water  CDIC values were higher (Torres et al., 2003; Herguera et al., 2014) or calcified their tests in locations that were geochemically less active and then were transported and colonized the seep sites 13

(Bernhard et al., 2010). Highly negative  C values for Globobulimina spp. have been reported in many studies (e.g., Grossman, 1984, 1987; McCorkel et al., 1990, 1997; Schmiedl et al. 2004; Fontanier, 2006; Martin, 2010) as have those for Uvigerina peregrina (-9.63‰ at Southeast Seep; -15.2‰ in Martin, 2010), Cibicidoides wuellerstorfi (-5.70‰ at the Southeast Seep), and Hoeglundina elegans (-35.7‰ in Martin, 2010). These values are considerably more negative than reported for living species in box cores from a non-seep area off central California (Uvigerina peregrina 0.50 to -1.26‰, Globobulimina pacifica 1.40 to -1.85‰ and Cibicidoides wuellerstorfi 0.01 to -0.20‰; McCorkle et al., 1997). Particularly high negative values may reflect

24

13

primary calcification in contact with C depleted DIC, or overprinting of the original isotopic composition by inorganic carbonate overgrowths or recrystallization (Torres et al., 2003; Panieri et al., 2017). The latter seems most likely for the Globobulimina spp. at Southeast Seep, as values more negative than -12‰ were measured in three samples 13

(Figure 10A). Furthermore, the large variability seen in the  C values of the dead Southeast Seep specimens compared to the dead non-seep reference samples (Hoeglundina elegans ∆ = 1.70‰ vs. ∆ = 0.29‰, Cibicidoides wuellerstorfi ∆ = 6.51‰ vs. ∆ = 0.73‰, Uvigerina peregrina ∆ = 8.02‰ vs. ∆ = 0.72‰, and Globobulimina spp. ∆ = 11.54‰ vs. ∆ = 2.60‰) as well as living box core specimens (Uvigerina peregrina ∆ = 0.76‰, Globobulimina pacifica ∆ = 3.25‰, and Cibicidoides wuellerstorfi ∆ = 0.21‰; McCorkle et al., 1997) may correlate with the amount and persistence of the fluid flow, where variability is more pronounced and values more negative when methane is actively vented versus times when flow is diminished or intermittent (Martin, 2010). The stable oxygen isotopes measured on the benthic foraminifera of the seep core (Figure 12A) show little variation for some species downcore (i.e., Hoeglundina elegans ∆ = 0.48‰ and Globobulimina spp. ∆ = 0.68‰), similar to the trend seen in the non-seep cores (∆ = 0.65‰, and ∆ = 0.67‰, respectively; Figures 12B-F), and as reported by Panieri et al. (2014a) and Burkett et al. (2016). However, this was not the case for Cibicidoides wuellerstorfi and Uvigerina peregrina, as they were characterized by more variation downcore at both the seep and non-seep sites (Cibicidoides wuellerstorfi ∆ = 1.96‰ vs. ∆ = 1.40‰ and Uvigerina peregrina ∆ = 1.56‰ vs. ∆ = 1.57‰). Furthermore, 18

 O values of dead Cibicidoides wuellerstorfi (1.98-3.94‰) and Uvigerina peregrina (2.92-4.48‰) from the Southeast Seep site were more positive and far less stable than in

25

the living assemblages off central California (Cibicidoides wuellerstorfi = 2.41-2.66‰, ∆ = 0.25‰; Uvigerina peregrina = 2.57-2.75‰, ∆ = 0.18‰; McCorkle et al., 1997).

4.5 Methane Releases at Southeast Seep Despite the fact that no bubbles or visible fluid were flowing out at Southeast Seep during the ROV investigation (Conrad et al., 2018), evidence suggests that methane seepage is presently occurring at the site by the existence of surficial clustered Calyptogena vesicomyid clams and Beggiatoa bacterial mats that are indicative of organic-rich reduced sediments (Jørgensen, 1977; Barry et al. 1996; Preisler et al., 2007). 13

The presence of isotopically depleted  C values of the carbonate rocks and, especially, 13

consistently more negative benthic foraminiferal  C values downcore among each species when compared to the non-seep site (also found in other seep and laboratory studies; e.g., Hill et al., 2004 and Wollenberg et al., 2015), indicates intermittent methane seepage through at least the last 3800 cal yr B.P. at Southeast Seep. 13

Peaks in highly negative  C values were recorded by the calcareous benthic species at 4.5, 7.5, 8.5, and 10.5 cm downcore as well as the aragonite-shelled species Hoeglundina elegans at 10.5 cm (i.e., despite its apparent taxon-specific vital effect), suggesting local seepage of methane significantly impacted the benthos at ~1600, 2650, 3000, and 3700 cal yr. B.P. (Figure 13A). The two lower peaks in the benthic record at 8.5 and 10.5 cm are also seen in the planktic record (Figure 13B). Therefore, it appears there was enough methane released at 3000 and 3700 cal yr B.P. to influence much, if not all, of the water column. This is despite the fact that gas ebullition of methane released into the water column is most often trapped below the pycnocline (Gentz et al., 2014) and

26

the two planktic foraminifera measured for stable isotopes (Globigerina bulloides and Neogloboquadrina pachyderma) typically live above the pycnocline (Field, 2004; Iwasaki et al., 2017, and references therein) which is generally situated at ~50 m or less off southern California (Field, 2004; Fiedler et al., 2013). However, vertical mixing across the pycnocline is a common occurrence, resulting from internal waves, background mean shear, and turbulence (Strange and Fernando, 2001). When upwelling conditions prevail, most prominently in the spring and summer off southern California (Bogard et al., 2015), the pycnocline breaks down (Halpern, 1976; Kundu and Beardsley, 13

1991). Therefore, the peaks in  C values measured in the planktic foraminiferal shells should reflect times when the two species did indeed come in contact with methane gas bubbles. This could have occurred during upwelling or other periods of oceanic turbulence, or while they were living below the thermocline in response to increased food availability (Sautter and Thunnell, 1991; Field, 2004). Methane releases in the marine environment are thought to be triggered by a perturbation in the stability of gas hydrate reservoirs within the seafloor due to paleoenvironmental changes such as bottom water warming, glacial unloading with associated changes in pressure regimes, thinning of hydrate stability zones, and evolution of fluid pathways in response to hydrostatic pressure decreases (Crémière et al., 2016), or due to mechanical disruption of sediments by large slope failures (Katz et al., 2001; Paull et al., 2003), localized slumping (Paull et al., 2008), erosion (Eichhubl et al., 2000; Naehr et al., 2000; Bangs et al., 2010), or seismic activity (Paull et al., 2008; Maloney et al., 2015; Conrad et al., 2018). These processes may occur on timescales from instantaneous to decades to thousands of years (Crémière et al., 2016).

27

There is no compelling evidence at Southeast Seep of paleoenvironmental changes over the last 3800 cal yr B.P. that might have been responsible for the methane releases into the water column (Kennett et al., 2000; Panieri et al., 2014b). Although the increased 18

values of  O in the epifaunal species Cibicidoides wuellerstorfi and shallow infaunal species Uvigerina peregrina from the seep core compared to the living assemblages 18

might suggest a change in bottom-water temperature, the stability in the  O records of the two other species (deep infaunal Globobulimina spp. and shallow infaunal 18

Hoeglundina elegans) do not support this hypothesis. Similarly, the  O values of the planktic species Neogloboquadrina pachyderma (0.21-1.35‰, ∆ = 1.14‰) and Globigerina bulloides (-0.30-0.32‰, ∆ = 0.62‰) did not change significantly downcore (Figure 11B). Since paleoenvironmental changes do not appear to be responsible for the release of methane recorded in the Southeast Seep push core, mechanical disruption of the sediments in the vicinity of Kimki Ridge may be the trigger. Neither catastrophic slope failure, localized slumping, nor erosion is evident at the core site, but seismic reflection profiles show chimney-like fluid pathways along the limbs and in the axis of the anticline forming Kimki Ridge, with a system of closely spaced faults located at the axis that may serve as pathways to allow fluid flow to the seafloor (Conrad et al., 2018). These local tectonic conditions suggest that transpression is an important component in the formation and localization of fluid seeps at Southeast Seep and elsewhere along Kimki Ridge, with seep formation most likely occurring at a fault stepover or transpressional bend in this strike-slip system (Conrad et al., 2018). A similar causation was hypothesized for active

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methane seepage in Santa Monica Basin (Paull et al., 2008) and San Diego Trough (Maloney et al., 2015). Massive methane releases have been hypothesized in many locations in the world’s oceans and through geologic time. Examples include the Jurassic in Europe (Hesselbo et al., 2000), the Miocene in Italy (Conti and Fontana, 2011), and globally at the end of the Paleocene (Latest Paleocene Thermal Maximum; Dickens et al., 1995). Off California, methane releases have been reported for the upper Neogene (Kennett and Fackler-Adams, 2000), as well as four millennial-scale releases in Santa Barbara Basin that were thought to affect the entire water column from ~44.1-37.05 ka yrs. (Kennett et al., 2000). Unfortunately, the timing of Holocene methane releases at cold seeps off southern California has not been well documented. Most of the studies investigated only recent, surface seepage or push cores of limited length that were not dated. These include San Diego Trough (Grupe et al., 2015; Maloney et al., 2015), San Clemente Basin (Lonsdale, 1979; Torres et al., 2002), and Redondo Knoll offshore Palos Verdes and Point Dume (Levin et al., 2016). In Santa Monica Basin, however, Paull et al. (2008) obtained a chronology for eight vibracores collected in 2005 at a seafloor mound seep site (i.e., the mud volcano of Hein et al., 2006) that demonstrated the presence of Vesicomya elongata and Lucinoma shells and shell hash in the upper (near-surface) sediment. Vesicomya shells are indicative of cold seeps, whereas both Vesicomya and Lucinoma live in sulfiderich environments (Barry et al., 1996; Hein et al., 2006). Many of these cores also had sediment with mousse-like texture that occurs when cores have undergone gas exsolution during coring (Paull and Ussler, 2001). The presence of these molluscs and the characteristic sediment texture indicates that methane has impacted the site over the last

29

~700-5200 cal yr B.P. (Paull et al., 2008), but no individual large methane releases were identified in their study. The chronology of Paull et al. (2008) can also be applied to undated cores obtained at this same site in 2003 (Hein et al., 2006). Vesicomya and Lucinoma shells were recovered in three cores down to core depths of 105, 140, and 200 cm, and violent degassing of hydrate was also evident in one of these cores from 162-212 cm (Hein et al., 2006). Using the average sedimentation rate of 37 cm/1000 years determined by Paull et al. (2008), the estimated age of these shell deposits are ~2840, 3780, and 6600 cal yr B.P., and the hydrate that degassed was from ~4380-5730 cal yr B.P. Although the timing of ongoing methane seepage over the last 3800 cal yr B.P. evident at Southeast Seep on Kimki Ridge compares favorably with that at the seafloor mound site in Santa Monica Basin (Hein et al., 206; Paull et al., 2008), no evidence of the two large methane releases at 3700 and 3000 cal yr B.P. at Southeast Seep were reported in Santa Monica Basin or elsewhere off southern California.

5. Conclusions The presence of Calyptogena vesicomyid clams, Beggiatoa bacterial mats, carbonate 13

rocks with depleted  C values that indicate formation from biogenic methane, and benthic foraminiferal stable carbon isotopic values that were considerably depleted, provides abundant evidence that the Kimki Ridge Southeast Seep site is impacted by methane fluid seepage. Differences in living and dead benthic foraminiferal faunal composition, density, and species richness further distinguish the seep and non-seep sites. 13

The seep site benthic foraminiferal  C values reflect microhabitat preference and vital

30

effect, as the calcitic taxa were more depleted with depth from epifaunal to deep infaunal, and the shallow infaunal aragonitic taxon (Hoeglundina elegans) had the heaviest values. 13

Fairly consistent  C values among each species downcore in the push core taken in a Kimki Ridge vent crater suggests the fluid seepage has occurred at Southeast Seep for at 13

least the last ~3800 cal yr B.P. The benthic and planktic foraminiferal  C records suggest two pulses of methane were released about 700 years apart that impacted much of 18

the water column, whereas the paired  O records provide evidence that these releases were not the result of paleoenvironmental changes. Instead, seismic reflection profiles suggest they are most likely due to local faulting that provided pathways for fluid to flow to the seafloor in this strike-slip system.

Acknowledgements We would like to thank the captain, crew, and science party of the Exploration Vessel (E/V) Nautilus and the Ocean Exploration Trust (OET) for taking ROV push core NA075-092b that was the subject of this investigation. The push core is archived at the University of Rhode Island, Graduate School of Oceanography. Nautilus ship time was provided by National Oceanic and Atmospheric Administration OER grant NA15OAR0110220 and support for the curation and distribution of the geological samples used in this study was provided by National Science Foundation grant OCE1258771 to the University of Rhode Island. We also wish to acknowledge the work of Colin Carney and Dyke Andreasen of the University of California, Santa Cruz Stable Isotope Laboratory for providing the stable carbon isotopic analyses. Ruth Martin of the Burke Museum, University of Washington, kindly offered suggestions regarding the

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sampling protocol and Charles Paull of the Monterey Bay Aquarium Research Institute made recommendations regarding possible reference cores and the effect of old carbon on radiocarbon measurements. Technical assistance was generously provided by Brian Reed. This work was supported by funding from the U.S. Geological Survey Coastal and Marine Geology Program. Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Particular thanks are due two anonymous reviewers for their helpful comments that greatly improved this manuscript. Appendix 1. Relative species abundances, species richness, and density of living benthic foraminifera in the >63 µm size fraction identified in Southeast Seep push core NA075092b and non-seep cores collected in San Pedro Basin in 1988 by Silva et al. (1996). For comparative purposes, the benthic foraminiferal specimen counts are normalized to 50 cc and the taxonomy used in this study was applied to the Silva et al. (1996) census data (see Table 2).

N A 0 7 50 9 2 b 01 Species/Samp c les m

McGann and Conrad (this study) N N N A A A 0 0 0 7 7 7 5- 5- 50 0 0 9 9 9 2 2 2 b b b 1- 2- 32 3 4 c c c m m m

Silva et al., 1996; 1-1 (Box Core 1-Subcore 1) N A 0 7 50 9 2 b 45 c m

A p r il 1 9 8 8 0 1 c m

A p r il 1 9 8 8 1 2 c m

Amorphina pacifica

A p r il 1 9 8 8 2 3 c m

A p r il 1 9 8 8 3 4 c m

A p r il 1 9 8 8 4 5 c m

J u l y 1 9 8 8 0 1 c m 0

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J u l y 1 9 8 8 1 2 c m

J u l y 1 9 8 8 2 3 c m

J u l y 1 9 8 8 3 4 c m

J u l y 1 9 8 8 4 5 c m

O c t . 1 9 8 8 0 1 c m

O c t . 1 9 8 8 1 2 c m

O c t . 1 9 8 8 2 3 c m

O c t . 1 9 8 8 3 4 c m

O c t . 1 9 8 8 4 5 c m

[unknown species; sponge?] Bolivina pacifica Cushman & McCulloch

. 2 1 1 7 1. . 1 7

5. 1

0 . 6 1 0 0 0 4 0 1 0 0 . . . . . . . . . 6 9 1 4 5 5 1 7 1

Bolivina peirsonae Uchio Bolivina pseudobeyrichi (Cushman)

Bolivina seminuda Cushman Bolivina spissa Cushman

Bulimina pagoda Cushman Bulimina striata Cushman Bulimina truncana Gümbel Buliminella tenuata Cushman

5. 1

1 2. 5

5 1 0 0 . . . . 6 7 2 7 1 . 1

0 0 0 0 . . . . 5 4 2 3

2 2 1 0 0 2 1 0 1 1 . . . . . . . . . . 7 2 9 5 4 1 4 1 1 1 0 0 . . 6 2

0. 5 0. 5 3. 8. 5 3

1 6. 7

1. 0

5. 6 1 0 7 2 . . . 1 4 6 0 0 . . 3 4

2. 0

Cancris inaequalis (d'Orbigny)

Cassidulina translucens Cushman &

0 . 4

1 1. 1

Bolivina subargentea Uchio Bulimina marginospinata Cushman and Parker

2 7 1 3 . . . 5 3 4

2 1. 7

2 8. 5. 5. 3 6 0

33

0 0 0 3 . . . . 7 1 2 0 0 . 2

3 1 5 3 5 3 9 . . . . . 4 9 3 0 0 0 . 7

Hughes 0 . 4

Cassidulina sp.

Chilostomella oolina Schwager

1 1 3 1 3 . . . . 9 4 3 1 1 3 2 2 0 3 0 0 . . . . 2 8 1 6

0. 5

Chilostomella ovoidea Reuss

Cibicides kullenbergi Parker Cibicides mckannai Galloway & Wissler Cibicidoides wuellerstorfi (Schwager)

Dyocibicides biserialis Cushman and Valentine Ehrenbergina compressa Cushman Epistominella exigua (Brady)

1 2 . 1 1 2 . 1

5 3 4 4 4 0 0 2 8 3 . . . . . . . . . . 0 6 1 4 4 6 8 5 1 9 3 3 4 3 3 1 1 1 9 7 9 3 6 2 5 1 2 0 . . . . . . . . . . 5 8 3 0 2 4 2 1 9 9

2. 0 1. 0 0 . 1

0. 5

0 . 1

0. 5 1. 0 0. 5

4. 6. 5. 2 3 6

0 . 1 1 7 0 0 1 . . . . 1 4 4 9 3 2 . . 2 3 0 3 3 7 . . . . 1 6 1 5

Epistominella smithi (Stewart & Stewart) Fursenkoina apertura (Uchio) Fursenkoina bramlettei (Galloway & Morrey)

Fursenkoina

0 . 0

2.

34

1 1 0 0 0 5 . . . . . 3 2 2 3 8

1 3 1 . . 0 7 4 9 . . 8 2 7 0 2 2 3 7 0 1 . . . . . . . . 0 7 2 7 5 9 6 1

1 9 . 5 6 . 5 2 . 4

1 2 3 0 . . 4 1

3 4 . . 9 6

cornuta (Cushman)

0 0 2 1 1 0 . . . . . 4 5 7 4 5 0 0 0 0 2 0 0 0 . . . . . . . . 2 1 1 4 5 4 0 2 0 . 1 0 3 . . 9 4

Fursenkoina delicatula (Uchio) Fursenkoina rotundata (Parr) Fursenkoina sandiegoensis (Uchio) Fursenkoina seminuda (Natland)

Globobulimin a auriculata (Bailey)

0 . 5 1 . 7

0 . 9 3 . 2 2 5 2 . . 0 1

Globobulimina hoeglundi Uchio

Globobulimina pacifica Cushman

Gyroidina turgida (Hagenow)

2 5 0 . . . 2 8 3

2 . 8

0. 5

Globobulimina barbata (Cushman)

Globocassidul ina minuta (Cushman) Globocassidul ina subglobosa (Brady)

0 0 0 . . . 0 1 1

3. 5

0 . 2 0 . 3 1 9 . 4

0 . 4 0 . 4 4 1 . 9

0 . 7 5 1 . . 7 4 4 8 3 . . 6 3

0 . 7 2 . 9

0 . 2 2 . 5 1 8 4 . . 6 4

0 . 2 2 . 3 2 1 . 6

0 . 4 2 . 2 2 5 . 1

0 . 7 0 . 7

0 . 3 0 . 5

0 . 1 0 . 6 1 2 8 7 . . . 6 3 2

0 . 8 2 7 . 6

0 . 4 1 6 . 3

1 5. 2. 6 5

5. 6 1 2 1 6. 6. 0. 2. 6 7 8 5

3 . 4

1 5 1 . . . 4 6 6 0 . 0

Lenticulina sp.

2 4. 8. Loxostomum 0. minuta (Natland) 0 3 8

1 2 8 . . 2 7

1 5 6. . 7 2

35

0 9 8 4 8 . . . . . 4 4 5 5 1

Melonis barleeanus (Williamson) Nonionella stella Cushman & Moyer Praeglobobulimi na spinescens (Brady)

Pseudoparrell a pacifica (Cushman) Pyrgo murrhina (Schwager) Takayanagia delicata (Cushman) Trochammina vesicularis Goës

Uvigerina spp. Valvulineria araucana (d'Orbigny)

Agglutinated Total specimens (normalized to 50 cc sediment) Species Richness (no. species/samp le) Foraminiferal density (no. individuals/1 cc sediment)

1. 0 1 2 1 1 2 1 1 1 1 1 7 4 5 4 2 . . . . . . . . . . . . . . . 7 1 5 5 5 6 4 4 2 3 1 2 7 2 5 1. 0 4. 5

6. 3

0. 5 1 2 1 2 8. 4. 9. 2. 2. 3 6 2 5 2 1. 0 0 . 9 2 . 4 1 5 . 4

3. 0 2. 0

4. 2

5 1 1 4. 8. 2. 2. 5 3 5 5 1 3 2 0

5 1 2

3 0 *

5

2 6

1 0

1 1 7 0

1 . 1 2 . 1 2 4 . 1

0 . 1 9 . 5

1 . 3 1 . 3

0 . 5 0 . 9 3 9 5 4 . . . 7 7 3

1 . 7 0 . 7 3 9 . 5

0 . 6 0 . 5 2 2 . 9

0 . 1 0 . 1 1 3 . 7

0 0 0 . . . 4 2 2 0 0 . . 7 2 2 4 4 2 . . . 1 2 5

0 . 2 0 . 1 1 5 . 0

1 . 1 0 . 3 2 2 0 6 . . 1 1

1 1 1 2 2 3 1 6 2 1 4 8 2 3 2 6 1 0 1 4 3 6 9 6 5 4 0 2 5 8 0 1 2 2 5 9 1 8 7 7 0 9 7 9 3 7 5 0 9 7 8 8

4 2 7

9 6 0

8 *

8

9

2 1 1 1 1 1 1 1 1 1 2 2 2 1 1 6 6 9 5 3 7 7 8 7 0 3 3 0 4 4

2 3

9

1 9

3 1 2 2 4 1 4 6 3 5 3 9 5 7 6 2 4 2 0 3 6 9 8 2

36

* includes three agglutinated species Appendix 2. Relative species abundances, species richness, and density of dead benthic foraminifera in the >63 µm size fraction identified in Southeast Seep push core NA075092b, and non-seep MBARI/USGS reference cores SC1-G2, SC2-G1, DR624 VC-379, DR624 VC-380, and DR625 VC-382. D N N D R N N N N N N N N N N A A R 6 A A A A A A A A A A 0 0 6 2 0 0 0 0 0 0 0 0 0 0 7 7 2 4, 7 7 7 7 7 7 7 7 7 7 5 5 4, V 5 5 5 5 5 5 5 5 5 5 - - V C - - - - - - - - 0 0 C 0 0 0 0 0 0 0 0 0 0 9 9 - 3 9 9 9 9 9 9 9 9 9 9 2 2 3 8 2 2 2 2 2 2 2 2 2 2 b b 7 0 b b b b b b b b b b 1 1 9 2. 9 0 1 2 3 4 5 6 7 8 0 1 1 5 - - - - - - - - - - - 1 1 2 3 4 5 6 7 8 9 1 1 5 5. 0 c c c c c c c c c 1 2 c 5 c m m m m m m m m m c c m c m Species/Sampl m m m es Ammoglobiger ina 0. 0. 0. 0. 0. 0. 0. globigerinifor 3 6 9 3 3 3 6 mis (Parker & Jones) 0. Astacolus sp. A 3 Bolivina pacifica 1. 0. 0. 1. 1. 0. 1. 1. 1. 0. 0. 0. 0. Cushman & 5 6 6 3 4 9 3 6 8 8 6 9 9 McCulloch

37

D R 6 2 4, V C 3 8 2 2. 5 5. 5 c m

S C 1 G 2 4 6 c m

S C 2 G 1 0 1 c m

1. 6

1 . 8

0. 2

0 1 . . 3 2

S C 2 G 1 1 2 c m

Bolivina pseudobeyrichi Cushman Bolivina seminuda Cushman Bolivina spissa Cushman

Bolivina sp. A Bulimina marginospinat a Cushman & Parker Bulimina pagoda Cushman Bulimina spinifera Cushman Bulimina striata Cushman Bulimina truncana Gümbel Buliminella elegantissima (d'Orbigny) Buliminella tenuata Cushman Cassidulina translucens Cushman & Hughes Cassidulina sp. A Cassidulina sp. B Chilostomella

0. 6

0. 0. 9 6

0. 0. 3 3

0 . 3

0. 3

0 . 5 4 3 5 2. 3. 1. 2. 2. 2. 2. 4. 2. 3. 3. 2. 4. 2. 4. . . . 1 6 3 6 0 0 9 0 2 2 4 1 0 0 8 4 3 8 0 0. 0. . 3 3 3 2. 1. 1. 1. 1. 1. 1 3 3 4 3 1

0. 3

0. 3. 1. 7 1 6

0. 0. 0. 3 3 3

2. 1

0. 9

0. 3

0 . 5

0. 0. 3 2 0 . 3

0. 3 1. 2. 8 3 0. 9

0. 3

2. 0. 4. 1. 4. 1. 4. 2. 3. 0 3 3 5 6 6 2 1 3 1. 1. 3 4

0. 6

0. 8 0 0 . . 3 8

0. 9

1. 0. 0. 0. 0. 0 6 5 5 3

0 . 3 0 1. 1. 0. 0. 1. 0. 1. 0. 0. . 2 3 6 6 6 6 8 3 9 3 1 1 1 1 1 1 1 1 2 3 2 9. 8. 8. 8. 5. 5 3. 3. 3. 2. 2. 2. 1. 1. 1. 6. 5 8 9 0 7 . 3 8 1 1 9 1 6 6 5 8 1 0. 3

0. 0. 3 7 0. 3 0. 0.

0. 3 0. 3 0.

38

1. 0. 3 3 0. 0. 1. 0.

0 . 6 3 3 3 4 . . 8 1 0 . 3

0 0

oolina Schwager Cibicides kullenbergi Parker Cibicides mckannai Galloway & Wissler Cibicidoides wuellerstorfi (Schwager) Cushmanina striatopunctat a (Parker & Jones)

3

3

3

1. 2. 1. 8 6 6

3

2

6

1. 1. 0. 1. 1. 2. 0. 2. 3 1 3 0 2 4 8 4

. . 9 3 0 . 3 0 . 5

2. 0. 1. 0. 0. 0. 2. 0. 2. 1. 0. 3. 0. 1. 1. 1 7 0 9 7 3 6 3 5 1 8 0 9 2 2 0. 0. 3 7

0. 9

0. 6

0. 3

1. 2

0. 0. 0. 3 3 3 0. 0. 3 3

0. 3

0. 3

0. 0. 0. 0. 0. Dentalina sp. A 3 3 3 3 3 0. 0. 0. Dentalina sp. B 3 3 6 0. Dentalina sp. C 3 Eggerella bradyi (Cushman) Ehrenbergina 2. 0. 0. 1. 0. compressa 4 3 3 2 7 Cushman Epistominella exigua (Brady) Evolvocassiduli na bradyi (Norman) Fissurina cucurbitasema Loeblich & Tappan Fissurina lucida (Williamson) Fissurina marginata (Montagu)

3

0. 3

1 . 5 5 4 2. 3. 5. 5. 7. 4. 3. 6. 2. 3. 4. 3. 7. 5. 3. . . 7 6 4 8 2 9 5 3 2 7 5 0 1 0 2 3 8 0. 3

0. 3

2. 0. 1. 0. 3. 0 9 1 8 3

0. 3

0. 7

0. 0. 9 5

0. 3

0. 5 0. 3

0. 0. 3 3

0. 3

0 . 3

0. 3 0. 0. 0. 6 6 3

39

0. 3

0. 3

0 . 3

1 . 9 6 . 9

Frondicularia gigas Church Fursenkoina bramlettei (Galloway & Morrey) Fursenkoina complanata (Egger) Fursenkoina cornuta (Cushman) Fursenkoina seminuda (Natland) Globobulimina affinis (d'Orbigny) Globobulimina auriculata (Bailey) Globobulimina pacifica Cushman Globocassiduli na minuta (Cushman) Globocassiduli na subglobosa (Brady) Gyroidina altiformis Stewart & Stewart Gyroidina gemma Bandy Gyroidina quinqueloba Uchio Gyroidina turgida (Hagenow) Hanzawaia

0. 3 0. 9

0. 6

0. 3

0. 6

0. 5

0. 0. 1. 0. 0. 0. 0. 0. 6 3 0 9 3 3 3 8

0. 1. 3 3

0. 6

0. 9

0. 0. 3 7

0. 3

0. 3

0. 9

0 0 . . 3 3 0 0 . . 6 5

0. 0. 1. 1. 3 6 7 0 0. 6

0. 7

0. 1. 0. 3 7 4

0. 3 1. 0. 0. 0 6 9

2. 0. 0 2

0 . 9

0 . 3 0 . 3 0 . 5

0. 0. 6 6 0. 1. 0. 0. 0. 0. 0. 0. 0. 6 0 9 8 5 6 6 3 4

0 . 9

0. 3 5 . 3 1 0 3. 3. 5. 4. 5. 2. 5. 6. 3. 2. 4. 2. 9. 7. 1. . 2 0 1 9 6 9 9 3 7 6 5 7 6 3 4 9 8. 7. 2. 5. 5. 5. 6. 5. 5. 5. 3. 4. 3. 3. 2. 3 6 9 5 9 4 2 3 6 5 4 8 7 5 2

0. 3

0. 3

1. 2

0. 5

0. 3

0. 0. 2. 0. 1. 5 3 2 3 4

2 . 4 5 . 3

0 . 6 0 . 6 5 . 7

2 . 1

0. 3

1 . 2 2 2 2 1 2 1 2 1 2 1 2 2 1 1 7 9. 4. 0. 6. 8. 2. 9. 0. 7. 3. 8. 6. 4. 2. 3. . 3 2 1 8 8 0 4 0 9 9 9 3 1 0 0 7 0. 0. 0. 0. 0. 0. 1. 2. 0. 1. 1. 2. 1. 0. 1. 1. 1. 1. 0. 0. 0 6 6 6 4 1 0 6 3 6 2 2 6 6

40

4 . 5 5 . 1

5 . 0

nitidula 3 (Bandy) Hoeglundina 0. 0. 0. elegans 3 3 9 (d'Orbigny) Islandiella californica 0. (Cushman & 3 Hughes) Lagena 0. elongata 3 Dunikowski Lagena sulcata (Walker & Jacob) Laticarinina pauperata (Parker & Jones) Lenticulina 0. orbicularis 3 (d'Orbigny) Leptohalysis 0. scotti (Chaster) 3 Loxostomum minuta (Natland) Melonis barleeanus (Williamson) Nonionella digitata Nørvang Nonionella japonica var. mexicana Cushman & McCulloch Nonionella stella Cushman & Moyer Planulina

3

6 0. 1. 9 2 0. 3

9

3

3

0. 0. 0. 0. 3 3 5 6 0. 3

0. 3

0 0 . . 6 8

0. 0. 6 4 1. 5 0. 0. 0. 3 3 2

0. 3 0. 3 0. 3

1 8 5 5. 3. 6. 7. 5. 7. 5. 7. 5. 5. 6. 4. 6. 5. 3. 0 . . 0 9 1 8 3 1 9 9 9 0 9 2 5 0 6 . 4 0 7 0. 1. 0. 0. 1. 0. 1. 1. 1. 0. 1. 1. 6 3 6 6 6 6 2 0 6 5 1 2 0 . 3 0 . 3

0. 3

0. 0. 3 6

0. 0. 0. 3 3 6 0.

41

2. 3

ornata (d'Orbigny) Pseudoparrella pacifica (Cushman) Pullenia bulloides (d'Orbigny) Pullenia salisburyi Stewart & Stewart Pyrgo murrhina (Schwager)

3 1 5 5 5. 4. 3. 6. 4. 6. 8. 5. 3. 5. 5. 6. 3. 1. 1. 9 . . 6 3 2 1 6 6 8 0 7 8 6 9 1 2 8 . 4 0 8 0. 0. 3 7

0. 3

0. 6

0. 7

0. 3

0. 3 0 . 3

0. 3 0. 2

0. 3

Pyrgo sp. A Quadrimorphi na laevigata (Phleger & Parker)

0. 3

0. 3

0. 0. 0. 0. 3 6 3 3

0. 3

0. 9

0 . 3 0 . 6 0 0 . . 6 3

0. 3

Quinqueloculin a sp. A Reussoolina 0. 1. 0. 0. 0. 0. 0. 1. 1. 0. 0. 0. laevis 3 0 6 6 3 3 3 0 2 3 5 3 (Montagu) Rotorbinella 1. 2. 1. 0. 1. 1. sp. A 9 0 3 9 2 3 Rutherfordoide 2. 2. 1. 1. 2. 0. 2. 2. 0. 1. 2. 1. s rotundata 4 3 6 4 6 9 1 6 9 8 4 2 (Parr) Sigmoilina sp. A Siphouvigerina proboscidea (Schwager) Spirillina vivipara Ehrenberg Spiroloculina fragilis Uchio

0. 3

0. 0. 6 2

0. 3 0. 0. 9 2

1. 4. 3. 2. 3. 4. 4. 2. 3. 1. 4. 4. 1. 2. 3. 5 6 8 9 6 6 7 0 1 6 0 8 9 0 8 0. 3

0. 3 0. 3

42

1 . 5 0 . 8 2 2 . . 1 4

Spiroplectamm ina biformis 0. 1. 1. (Parker & 3 0 3 Jones) Takayanagia delicata (Cushman) Textularia earlandi Parker Trifarina angulosa (Williamson) Trochammina vesicularis Goës Uvigerina dirupta Todd Uvigerina juncea Cushman & Todd Uvigerina peregrina Cushman Valvulineria araucana (d'Orbigny) Verneuilinulla advena (Cushman) Total specimens Species Richness (no. species/sampl e) Foraminiferal density (no. individuals/1 cc sediment)

2. 1. 1. 2. 0. 2. 1. 2. 1. 2. 4. 0 4 2 0 6 9 9 4 2 6 0

0 . 9

0 . 5

1 1 1 1 1 4. 7. 7. 7. 6. 6. 5. 8. 9. 8. 8. 4. 6. 4 0 0 4. 2. 7 2 7 8 3 0 6 3 6 4 0 8 1 . . . 8 2 8 8 6 0 . 3 1 1. 1. 1. 0. 1. 0. 1. 0. 1. 1. . 6 2 1 3 3 3 1 8 5 0 1 0. 3 0. 3 0. 3 5 . 3 2 1. 1. 2. 2. 5. 3. 2. 1. 1. 3. 3. 4. 0. 1. 1. . 5 6 2 6 9 1 1 3 9 7 4 2 9 2 0 4 3. 1. 2. 3. 1. 2. 1. 1. 1. 1. 1. 1. 4. 1. 2. 2 3 2 2 6 3 8 7 9 8 6 8 6 5 0

0. 3

3 . 0 1 . 5

5 . 3 0 . 3

0. 0. 3 3

3 3 9

3 0 4

3 1 3

3 4 6

3 0 4

3 5 0

3 4 0

3 0 2

3 2 2

3 8 0

3 7 7

3 3 2

3 2 4

3 4 3

5 0 0

3 3 3 3 3 7 8 4 8

4 5

4 0

3 7

3 6

3 3

3 9

4 1

3 8

3 9

4 4

3 9

4 1

2 8

3 8

3 0

2 3 2 4 2 9

3 2 6

2 5 9

3 0 5

1 8 5

3 2 4

3 7 3

1 1 6 1

5 1 5

4 5 8

5 4 1

5 3 6

5 6 7

3 6 0

5 0 8

7 4 1

2 2 5 3

43

2 9 6 9

1 6 8 0

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Nature 348, 230-232, 1990.Berelson, W.M., 1991. The flushing of two deep-sea basins, southern California borderland. Limnol. Oceanogra. 36, 1150-1166. Bernhard, J.M., 1988. Postmortem vital staining in benthic foraminifera: duration and importance in population and distributional studies. J. Foraminifer. Res. 18, 143-146. Bernhard, J.M., 1989. The distribution of benthic foraminifera with respect to oxygen concentration and organic carbon levels in shallow-water Antarctic sediments, Limnol. Oceanogr., 34(6), 1131-1141, 1989. Bernhard, J.M., 1992. Benthic foraminiferal distribution and biomass related to porewater oxygen content: Central California Continental Slope and Rise. Deep-Sea Res. 39, 585–605. Bernhard, J.M., 2000. Distinguishing live from dead foraminifera; methods review and proper applications. Micropaleo. 46(1), 38-46. Bernhard, J.M., Buck, K.R., Barry, J.P., 2001, Monterey Bay cold-seep biota: Assemblages, abundance, and ultrastructure of living foraminifera. Deep-Sea Res. I 48, 2233–2249. Bernhard, J.M., Martin, J.B., Rathburn, A.E., 2010, Combined carbonate carbon isotopic and cellular ultrastructural studies of individual benthic foraminifera: 2. Toward an understanding of apparent disequilibrium in hydrocarbon seeps. Paleoceanogr. 25, PA4206, doi:10.1029/2010PA001930. Bernhard, J.M., Sen Gupta, B.K., Borne, P.F., 1997. Benthic foraminiferal proxy to estimate dysoxic bottom-water oxygen concentrations: Santa Barbara Basin, U.S. Pacific Continental Margin. J. Foraminifer. Res. 27, 301–310.

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Bogard, S.J., Pozo Buil, M., Di Lorenzo, E., Castro, C.G., Schroeder, I.D., Goericke, R., Anderson, C.R., Benitez-Nelson, C., Whitney, F.A., 2015. Changes in source waters to the southern California Bight. Deep-Sea Res. II 12, 45-52. Bohrmann, G., Greinert, J., Suess, E., Torres, M., 1998. Authigenic carbonates from the Cascadia subduction zone and their relation to gas hydrate stability. Geology 26, 647– 650. Boyle, E.A., Keigwin, L.D., 1982. Deep circulation of the North Atlantic over the last 200,000 years: Geochemical evidence. Science 218, 784-787. Burkett, A.M., Rathburn, A.E., Pérez, M.E., Levin, L.A., Martin, J.B., 2016, Colonization of over a thousand Cibicidoides wuellerstorfi (foraminifera: Schwager, 1866) on artificial substrates in seep and adjacent off-seep locations in dysoxic, deep-sea environments. Deep-Sea Res. I 117, 39-50, http://dx.doi.org/10.1016/j.dsr.2016.08.011. Clarke, K.R., Gorley, R.N., 2006. PRIMER v. 6, user manual/tutorial: Prime-E Ltd., Plymouth, UK, 190 p. Conrad, J.E., Walton, M.A.L., Prouty, N.G., Kluesner, J.W., Maier, K.L., McGann, M., Brothers, D.S., Dartnell, P., 2018. Seafloor Fluid Seeps on Kimki Ridge, offshore southern California: Links to Active Strike-Slip Faulting. Deep-Sea Res., 10.1016/j.dsr2.2017.11.001 Conti, S., Fontana, D., 2011. Possible relationships between seep carbonates and gas hydrates in the Miocene of the northern Apennines. J. Geol. Res. 2011, Art. 920727, 19, doi:10.1155/2011/920727.

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Walton, M.A.L., Roland, E.C., Brothers, D.S., Kluesner, J., Maier, K.L., Conrad, J.E., Hart, P.E., 2016. High-resolution geophysical constraints on fault structure and morphology in the Catalina Basin, Southern California Inner Continental Borderland (abs). Abstract OS21A-1941, 2016 Fall Meeting, American Geophysical Union, San Francisco, CA, 12-16 Dec. Wiedicke, M., Weiss, W., 2006. Stable carbon isotope records of carbonates tracing fossil seep activity off Indonesia. Geochem. Geophys. Geosyst. 7, Q11009, doi:10.1029/2006GC001292. Wollenburg, J.E, Raitzsch, M., Tiedemann, R., 2015, Novel high-pressure culture experiments on deep-sea benthic foraminifera — Evidence for methane seepagerelated δ13C of Cibicides wuellerstorfi. Mar. Micropaleo. 117, 47–64, http://dx.doi.org/10.1016/j.marmicro.2015.04.003. Figure and Table Captions Figure 1. Map of the California Continental Borderland with the location of the Southeast Seep core site NA075-092b on Kimki Ridge at 973 m depth, the non-seep San Pedro Basin reference site of Silva et al. (1996), and the five non-seep MBARI/USGS reference cores (SC2-G1, DR-624 VC-379, DR624 VC-380, and DR625 VC-382 at ~1030 m depth, and SC1-G2 at 739 m depth). Figured modified from the base map of Dartnell et al. (2015) and fault map of Maier et al. (2016). Contour intervals 100 m for 1-200 m water depths; 200 m for >200 m water depth. Figure 2. Shaded relief bathymetry of the western part of Catalina Basin, showing the location of potential fluid seeps (Northwest Seep, Middle Seep, and Southeast Seep; white circles) along Kimki Ridge.

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Figure 3. Shaded relief bathymetry of Middle and Southeast Seeps on Kimki Ridge. White circles show location of images A and B in Figure 4. Figure 4: ROV photographs from dive NA075 on Kimki Ridge. A. ROV arm sampling push core NA075-092b on the Southeast Seep crater floor in the vicinity of a Calyptogena clam bed and Beggiatoa bacterial mat (whitish film at lower center). B. ROV arm sampling authigenic carbonate rock (NA075-93) on a ledge of Southeast Seep. Photographs courtesy of Ocean Exploration Trust. Figure 5: Photograph of Southeast Seep push core NA075-092b. Styrofoam present in the core barrel void at the top of the core. Photograph courtesy of Ocean Exploration Trust. Figure 6. Q-mode cluster diagram of the living assemblages of five samples from Southeast Seep push core NA075-092b and 15 samples from the non-seep reference cores of Silva et al. (1996) from San Pedro Basin (Boxcore 1, Subcore 1; i.e., 1-1). The samples are listed by cm interval and were grouped into two clusters. Cluster A combined all of the non-seep San Pedro Basin reference core samples and Cluster B combined all of the Southwest Seep samples. Figure 7. Q-mode cluster diagram of the dead assemblages of 12 samples from Southeast Seep push core NA075-092b and the six samples from the non-seep MBARI/USGS reference cores SC1-G2, SC2-G1, DR624 VC-379, DR624 VC-380, and DR625 VC-382. The samples are listed by cm interval and were grouped into two clusters. Cluster C combined all of the Southeast Seep samples and Cluster D combined all of the non-seep reference core samples. Figure 8. R-mode cluster diagram of the benthic foraminiferal species in the dead assemblages of the 12 samples from Southeast Seep push core NA075-092b. One

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association (E) grouped the species with abundances averaging ~1-22%. Most of these taxa are opportunistic that have been reported from other seeps or low oxygen environments. The remaining clusters and outliers added on the rare (~ <1%) species. Figure 9. R-mode cluster diagram of the benthic foraminiferal species in the dead assemblages of the six samples from the non-seep MBARI/USGS reference cores SC1G2, SC2-G1, DR624 VC-379, DR624 VC-380, and DR625 VC-382. Most of the species that were grouped into one association (Cluster F) are those that prevail in low oxygen environments. They occurred in abundances from 5-38%. The remaining clusters and outliers added on the more rare (<5%) species. Figure 10. Stable carbon isotopic signatures of the four dominant benthic foraminiferal taxa of the >150 µm size fraction (deep infaunal species of Globobulimina, shallow infaunal species Uvigerina peregrina, epifaunal species Cibicidoides wuellerstorfi, and shallow infaunal and aragonite-shelled species Hoeglundina elegans) plotted with depth and age in (A) Southeast Seep push core NA075-092b, (B) Catalina Basin reference core SC2-G1, and Inner Continental Borderland reference cores (C) DR624 VC-380, (D) DR625 VC-382, (E) DR624 VC-379, and (F) SC1-G2. Values are plotted at the mid13

point of the sampling interval. The mean  C values for each taxon are presented. Figure 11. (A) Stable carbon and (B) oxygen isotopic signatures of the planktic foraminifera Neogloboquadrina pachyderma and Globigerina bulloides of the >150 µm size fraction plotted with depth and age in Southeast Seep push core NA075-092b. 13

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Values are plotted at the mid-point of the sampling interval. The mean  C and  O values for each taxon are presented.

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Figure 12. Stable oxygen isotopic signatures of the four dominant benthic foraminiferal taxa (Globobulimina spp., Uvigerina peregrina, Cibicidoides wuellerstorfi, and Hoeglundina elegans) of the >150 µm size fraction plotted with depth and age in (A) Southeast Seep push core NA075-092b, (B) Catalina Basin reference core SC2-G1, and Inner Continental Borderland reference cores (C) DR624 VC-380, (D) DR625 VC-382, (E) DR624 VC-379, and (F) SC1-G2. Values are plotted at the mid-point of the sampling 18

interval. The mean  O values for each taxon are presented. Figure 13. Stable carbon isotopic signatures of (A) the four dominant benthic foraminiferal taxa (Globobulimina spp., Uvigerina peregrina, Cibicidoides wuellerstorfi, and Hoeglundina elegans) and (B) the planktic foraminifera Neogloboquadrina pachyderma and Globigerina bulloides of the >150 µm size fraction plotted with depth 13

and age in Southeast Seep push core NA075-092b. Three highly negative  C values (>12‰) for Globobulimina spp. and one (>-10‰) for Neogloboquadrina pachyderma, thought to be due to contamination by inorganic carbonate overgrowths or recrystallization, were deleted. Horizons with hypothesized methane releases shown.

Table 1. USGS cruise locator, collection date, location (latitude and longitude), and water depth of the Southeast Seep push core NA075-092b, non-seep MBARI/USGS reference cores SC1-G2, SC2-G1, DR624 VC-379, DR624 VC-380, and DR625 VC-382, and the non-seep San Pedro Basin reference cores (1-1) of Silva et al. (1996).

Collection Date

Latitude (°N)

Longitude (°W)

Water Depth (m)

NA075-092b

August 6, 2016

33.286728

118.761345

973.1

NA075-093

August 6, 2016

33.286773

118.761348

973.8

USGS Cruise Locator

Core

2017-677-DD 2017-677-DD

63

S-I2-09-SC

SC1-G2

March 26, 2009

33.338882

118.127893

739

S-I2-09-SC

SC2-G1

March 26, 2009

33.174432

118.100142

1028

2014-637-FA

DR624 VC-379

June 21, 2014

32.913963

117.758561

1035.8

2014-637-FA

DR624 VC-380

June 21, 2014

32.914136

117.759979

1029.3

2014-637-FA

DR625 VC-382 Silva et al. (1996), 1-1 Silva et al. (1996), 1-1 Silva et al. (1996), 1-1

June 21, 2014

32.921253

117.763289

1035.7

April 8, 1988

33.599333

118.347833

722

July 11, 1988

33.600500

118.348167

709

October 11, 1988

33.600333

118.348667

710

n.a. n.a. n.a.

Table 2. Comparative taxonomy of the living benthic foraminifera recovered in the reference box cores reported for San Pedro Basin (Silva et al., 1996) and Southeast Seep. The species identified by Silva et al. (1996) were assigned the names used in this study and compiled in Appendix 1. McGann and Conrad (this study) n.a. Loxostomum minuta (Natland) Bolivina pacifica Cushman & McCulloch n.a. Bolivina seminuda Cushman Bolivina spissa Cushman n.a. Buliminella tenuata Cushman Bulimina striata Cushman Bulimina truncana Gümbel Bulimina marginospinata Cushman and Parker Bulimina pagoda Cushman Buliminella tenuata Cushman n.a. Cassidulina translucens Cushman & Hughes n.a. Chilostomella oolina Schwager n.a. Cibicides kullenbergi Parker Cibicides mckannai Galloway & Wissler Dyocibicides biserialis Cushman and Valentine Ehrenbergina compressa Cushman Epistominella exigua (Brady) n.a. Gyroidina turgida (Hagenow) n.a. n.a. Fursenkoina cornuta (Cushman) n.a.

64

n.a. n.a. n.a. Globobulimina auriculata (Bailey) n.a. n.a. n.a. Globocassidulina minuta (Cushman) Globocassidulina subglobosa (Brady) n.a. Bolivina pseudobeyrichi (Cushman) Melonis barleeanus (Williamson) n.a. Cibicidoides wuellerstorfi (Schwager) Praeglobobulimina spinescens (Brady) Pseudoparrella pacifica (Cushman) Pyrgo murrhina (Schwager) Takayanagia delicata (Cushman) Trochammina vesicularis Goës Uvigerina peregrina Cushman Valvulineria araucana (d'Orbigny) Ammoglobigerina globigeriniformis (Parker & Jones) & Goesella flintii Cushman & Spiroplectammina biformis (Parker & Jones)

Table 3. Radiocarbon ages, calibrated peak probability ages (calendar ages), and 2-sigma ranges for Southeast Seep push core NA075-092b and non-seep MBARI/USGS reference cores SC1-G2, SC2-G1, DR624 VC-379, DR624 VC-380, and DR625 VC-382. Calibrated Peak Radiocarbon Probability Age (Calendar Age) 14 ( C yr B.P.) (cal yr B.P.)

NOSAMS Accession Number

Core

Depth in Core (cm)

OS-131474

NA075-092b

10-12

-1.56

4,130±30

3,872

3,765-3,972

OS-86760

SC1-G2

4-6

1.34

875±25

286

241-378

OS-134255

SC2-G1

0-1

1.23

3,840±20

3,503

3,430-3,576

OS-131473

SC2-G1 DR624 VC379 DR624 VC380 DR625 VC382

9-10

1.79

5,860±25

6,023

5,925-6,124

1-5

1.66

1,090±15

486

451-516

2.5-5.5

1.66

190±15

modern

modern

2.5-5.5

1.58

795±15

204

134-264

OS-113522 OS-120755 OS-113526

13

∂ C (‰)

65

2-sigma Range (cal yr B.P.)

Table 4. Benthic foraminiferal species richness and density for the living and dead assemblages from Southeast Seep (NA075-092b), the non-seep San Pedro Basin reference samples (1-1) of Silva et al. (1996), and the six non-seep MBARI/ USGS reference cores. The number of benthic foraminiferal specimens for the living assemblages are normalized to 50 cc following Silva et al. (1996).

Samples

Number of benthic foraminiferal specimens

Species richness (no. species/ sample)

Benthic foraminiferal density (no. individuals/ 1 cc sediment)

1320 512 1170 427 960

30 5 8 8 9

26 10 23 9 19

1607 698 1115 267 157 440 1020 2129 809 227 2457 3398 1618 359 283

26 16 19 15 13 17 17 18 17 10 23 23 20 14 14

32 14 22 5 3 9 20 43 16 5 49 68 32 7 6

339 304 313 346 304 350 340 302 322

45 40 37 36 33 39 41 38 39

326 259 305 185 324 373 1161 515 458

Living Assemblages Southeast Seep NA075-092b, 0-1 cm NA075-092b, 1-2 cm NA075-092b, 2-3 cm NA075-092b, 3-4 cm NA075-092b, 4-5 cm Reference (Silva et al., 1996) 1-1, April 1988, 0-1 cm 1-1, April 1988, 1-2 cm 1-1, April 1988, 2-3 cm 1-1, April 1988, 3-4 cm 1-1, April 1988, 4-5 cm 1-1, July 1988, 0-1 cm 1-1, July 1988, 1-2 cm 1-1, July 1988, 2-3 cm 1-1, July 1988, 3-4 cm 1-1, July 1988, 4-5 cm 1-1, October 1988, 0-1 cm 1-1, October 1988, 1-2 cm 1-1, October 1988, 2-3 cm 1-1, October 1988, 3-4 cm 1-1, October 1988, 4-5 cm Dead Assemblages Southeast Seep NA075-092b, 0-1 cm NA075-092b, 1-2 cm NA075-092b, 2-3 cm NA075-092b, 3-4 cm NA075-092b, 4-5 cm NA075-092b, 5-6 cm NA075-092b, 6-7 cm NA075-092b, 7-8 cm NA075-092b, 8-9 cm

66

NA075-092b, 9-10 cm NA075-092b, 10-11 cm NA075-092b, 11-12 cm Reference (MBARI and USGS) DR624 VC-379, 1-5 cm DR624 VC-380, 2.5-5.5 cm DR625 VC-382, 2.5-5.5 cm SC1-G2, 4-6 cm SC2-G1, 0-1 cm SC2-G1, 1-2 cm

380 377 332

44 39 41

541 536 567

324 343 500 338 334 378

28 38 30 24 32 29

360 508 741 2253 2969 1680

Table 5. Summary of the average relative abundance of the significant taxa for the living and dead assemblages of Southeast Seep push core NA075-092b at 973 m depth, the living assemblages of the non-seep San Pedro Basin reference cores (Silva et al., 1996), and the dead assemblages of the non-seep MBARI/USGS reference cores SC1-G2, SC2G1, DR-624 VC-379, DR624 VC-380, and DR625 VC-382.

Sam ples Livin g Asse mbla ges Sout heas t See p NA0

W a t e r D e p t h ( m )

A g g l u ti n a t e d

B ol iv in a p a ci fi c a

B ol iv in a s pi s s a

B ul i m in a st ri a t a

B uli m in ell a te n u at a

C as si du lin a tra ns lu ce ns

C hil os to m ell a o oli n a

9 7

1 7

3. 3

3 .

5 .

0. 4

12 .1

0. 1

Average abundance % G lo b o E c C pi E a hil st pi Gl s os o st ob si to mi o ob d m n mi uli ul ell ell e mi in a a nll na a ov ex a pa m oi ig s cif in de u mi ic ut a a thi a a

3. 3

67

4. 3

Glo bo cas sid ulin a su bgl ob os a

G yr oi di n a tu rg id a

L ox os to m u m mi n ut a

1.1

7. 7

6. 5

Ps eu do pa rre lla pa cifi ca

T ak ay an ag ia de lic at a

U vi g e ri n a s p p .

2. 2

17 .4

0 .

75092b , 0-5 cm Refe renc e (Silv a et al., 1996 ) 11, April , July, & Octo ber 1988 , 0-5 cm

3

. 6

6

7

7

3. 3 7 1 4

1 6 . 7

1 . 6

6. 1

4. 7

18 .8

0. 0 1

5. 9

18 .8

0 . 5

0. 8

3. 8

2 1. 6

5. 8

5. 5

7. 3

9. 0

5. 7

3. 3

10 .9

Dea d Asse mbla ges Sout heas t See p NA0 75092b , 012 cm Refe renc e (MB ARI and USG S) DR6 24 VC379,

9 7 3

1 0 2 8 1 0 3 6

3 . 7

2 . 6

1. 1

0. 6

2 . 7

2 . 5

4 . 0

0 . 4

0. 7

10 .9

0. 1

4. 3

0. 1

29 .6

0. 4

5. 4

68

0. 02

5. 5

3. 3

4.0

7.7

2 . 0

3 . 3

1-5 cm DR6 24 VC380, 2.55.5 cm DR6 24 VC382, 2.55.5 cm SC2 -G1, 0-1 cm SC2 -G1, 1-2 cm SC1 -G2, 4-6 cm

7 3 9

0 . 9

0. 3

4 . 4

0. 3

15 .1

0. 9

5. 3

5. 3

7. 7

0.9

1 0. 7

19 .8

5 . 3

14 .8

Table 6: Stable carbon and oxygen isotopic measurements of the four dominant benthic foraminiferal taxa of the >150 µm size fraction (Cibicidoides wuellerstorfi, Globobulimina spp., Hoeglundina elegans, and Uvigerina peregrina) for Southeast Seep push core NA075-092b and non-seep MBARI/USGS reference cores SC1-G2, SC2-G1, DR624 VC-379, DR624 VC-380, and DR625 VC-382. NA075-092b Dept h in core (cm)

Cibic idoid es wuell ersto rfi

Specie s

0-1

δ C (‰)

13

δ O (‰)

18

-0.20

2.32

DR624 VC-379

SC2-G1 13

δ C (‰) 0.20

18

δ O (‰)

13

δ C (‰)

3.39

69

18

δ O (‰)

DR624 VC-380 13

δ C (‰)

18

δ O (‰)

DR625 VC-382 13

δ C (‰)

18

δ O (‰)

SC1-G2 13

δ C (‰)

18

δ O (‰)

1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12

-0.15 0.81 -0.26

2.53 3.94 2.36

-0.11 -0.67

2.34 2.53

0.13 -5.70 -1.05

3.04 3.20 2.48

-0.50 -4.44 -0.09

2.44 2.56 1.98

Globobulimina spp.

0-1 1-2

-5.70

3.35

2-3

-5.29

3.03

3-4

-2.14

2.85

4-5

-3.93

2.90

5-6

-2.23

3.22

10-11 11-12

12.38 -6.26 12.98 13.49 -4.48 -1.95

0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12

1.32 1.62 1.51 1.44 1.46 1.34 0.98 1.43 1.37 0.81 -0.08 1.33

3.48 3.56 3.46 3.43 3.60 3.46 3.44 3.53 3.86 3.71 3.43 3.38

0-1

-2.35

3.89

1-2

-1.97

4.34

2-3

-1.79

2.92

6-7 7-8 8-9

Uvigerina peregrina

Hoeglundina elegans

9-10

3-4

-1.61

3.53

0.02

2.51

0.07 0.12

2.49

0.03 0.26 0.14 0.47

1.16 1.44 1.07 0.90 0.83 1.25 1.17

0.17

2.27

0.13

2.42

1.99

0.24

2.25

0.92

2.93

1.67

3.26

3.21 2.39 2.50 2.68

3.38 3.09 3.05 3.20

1.13

3.15 0.84

3.16

0.64

3.14

3.09 3.01 3.06

3.27 3.44 3.16

1.20 1.20

3.09 2.71

2.92 2.87

3.74

1.77 1.73 1.57 1.52 1.61 1.77 1.68 1.76 1.75 1.81

1.03 1.25 0.81 1.07

3.47 3.49 3.91 3.45 3.46 3.46 3.41 3.44 3.45 3.43

1.61

3.72 1.69

3.55

1.75

3.50

3.59 3.17 3.96

1.48

3.73

70

2.99

1.28

2.97

1.11

2.95

4-5

-9.63

4.48

5-6

-4.57

4.05

6-7

-1.86

3.87

7-8

-4.48

3.70

8-9

-3.99

4.23

9-10

-3.00

3.37

10-11 11-12

-5.28 -1.82

4.21 3.68

1.02 1.15 0.86 0.76 0.99 1.29

3.95

0.94

2.76

4.15 4.30 4.33 4.08 3.26

Table 7. Stable carbon and oxygen isotopic measurements of the planktic foraminifera Neogloboquadrina pachyderma and Globigerina bulloides of the >150 µm size fraction for Southeast Seep push core NA075-092b. NA075-092b core (cm)

13

δ C

(‰)

18

δ O

(‰)

Neogloboquadrina pachyderma

Depth in

0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12

-0.49 -0.08 0.04 -0.79 -1.69 -2.36 -3.31 -1.14 -2.70 -10.35 -2.34 0.36

0.61 0.52 0.21 0.74 0.67 0.66 0.84 0.73 0.60 1.35 0.75 0.81

Globigerina bulloides

Species

0-1 1-2 2-3 3-4 4-5 5-6 6-7 7-8 8-9 9-10 10-11 11-12

-0.96 -1.70 -1.40 -1.94 -1.53 -1.94 -2.00 -2.13 -1.48 -3.74 -2.00 -0.82

-0.03 -0.30 -0.04 -0.16 0.07 0.27 0.32 0.24 -0.05 0.10 -0.01 -0.01

71

72

73

74

75

76

77

78

79

80

81

82

83

84