Effects of Carbon Dioxide Sequestration on California Margin Deep-Sea Foraminiferal Assemblages

Marine Micropaleontology 72 (2009) 165–175

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Marine Micropaleontology

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Effects of carbon dioxide sequestration on California margin deep-sea foraminiferal assemblages

Erin R. Ricketts a,⁎, James P. Kennett a, Tessa M. Hill a,1, James P. Barry b a Department of Earth Science and the Marine Science Institute, University of California, Santa Barbara, CA 93106, USA b Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, USA article info abstract

Article history: Deep-sea sequestration of CO2 is being considered as a possible mitigation tool to decrease atmospheric CO2 Received 16 November 2005 concentrations and its associated negative effects. This study investigated potential effects of liquid carbon Received in revised form 26 April 2009 dioxide (CO2) injection on deep-sea foraminiferal assemblages. Foraminifera are ideal for this ecological Accepted 29 April 2009 impact investigation because of differing test composition (calcareous and non-calcareous) and thickness, and diverse epifaunal and infaunal depth preferences. The experiment was conducted on August–September Keywords: 2003, at 3600 m off the coast of Monterey Bay, California, aboard the R/V Western Flyer using the ROV carbon dioxide Tiburon. The pH of the site was monitored throughout the experiment. Sediment push-cores were collected foraminifera deep sea (both from the experimental and control sites) and stained to distinguish live (stained) from dead dissolution (unstained) individuals. Effects of CO2 injection on assemblages have been tracked both vertically (to 10 cm California margin depth below sea ﬂoor) and horizontally (up to 10 m from CO2 injection sites), as well as between live and

dead individuals. Within corrals (containing the injected CO2) and their underlying sediments, severe pH changes (near 4.0 units) were recorded. This compares with a record of small average reductions in ocean pH (−0.05 units) combined with large episodic excursions (−1.7 units) over the experimental area due to the

injection of CO2. Exposure to this gradient of low pH caused increased mortality and dissolution of calcareous forms within corrals, as far as 5 m from the injection site, and to at least 10 cm depth in the sediments.

This experiment revealed several major effects of CO2 injection on foraminiferal assemblages in surﬁcial sediments: 1) total number of foraminifera in a sample decreases; 2) foraminiferal species richness decreases in both stained and unstained specimens; and 3) relative percentage of stained (live) forms in the remaining tests increases. Down-core trends (to 10 cm below sea ﬂoor) have revealed: 1) percent agglutinated forms decline and calcareous forms increase with depth; 2) agglutinated species richness decreases with depth; and 3) experimental core assemblages become increasingly similar with depth to those in control cores not

subjected to CO2 injection. These results imply almost complete initial mortality and dissolution in the upper

10 cm throughout the corrals following liquid CO2 injection. Since calcareous foraminifera represent more

than 50% of the total assemblages, this clearly indicates that emplacement of CO2 will result in negative effects to diversity and survivorship of the deep-sea benthic meiofauna. © 2009 Published by Elsevier B.V.

1. Introduction sediments cores (Lea, 2004) indicate a close correlation between

ﬂuctuations in atmospheric CO2 and Earth's global temperature. Current There is increasing concern regarding the effects of rising concentra- concentrations of atmospheric CO2 have lead to increased oceanic pCO2, tions in atmospheric carbon dioxide (CO2) on global climate, with and increasing calcium carbonate dissolution (Sabine et al., 2004), predictions that the Earth's global temperature will rise between 2° and initiating major ecological perturbations in marine ecosystems that will 11 °C during this century (e.g. Senior and Mitchell, 1993; Saunders, 1999; continue as atmospheric CO2 concentrations rise in the future (Caldeira Boer et al., 2000; IPCC, 2001). Furthermore, geologic records such as the andWickett,2003;Feelyetal.,2004). Antarctic Vostok ice core (e.g. Petit et al., 1999) and tropical Paciﬁc Growing consensus on the effects of rising CO2 levels on climate (IPCC, 2001) has lead to consideration of CO2 sequestration in the ⁎ Corresponding author. Now at PARSONS Corporation, Walnut Creek, CA 94596, USA. deep sea as a method of removal of atmospheric CO2 to reduce the Tel.: +1 805 893 3103; fax: +1 805 893 2314. increasing atmospheric concentrations (Marchetti, 1977). At depths E-mail addresses: [email protected], [email protected] (E.R. Ricketts), greater than 2600 m, liquid CO2 is negatively buoyant and forms a [email protected] (J.P. Kennett), [email protected] (T.M. Hill), [email protected] hydrate skin (Haugan and Drange, 1992) due to ambient water (J.P. Barry). 1 Now at Department of Geology and the Bodega Bay Marine Laboratory, University of temperature and pressure; which could effectively remove CO2 from California, Davis, CA 95616, USA. the atmospheric reservoir (Brewer et al., 2005). Studies are needed to

Fig. 3. A frame capture of video taken of a corral (48 cm diameter) being ﬁlled with

liquid CO2. Published with permission from MBARI. Fig. 1. Location of 2003 experimental site (A) offshore Monterey Bay, California. Shading the map indicates increasing water depth.

(Tamburri et al., 2000), this is only a small fraction of deep benthic life assess environmental consequences of this remediation approach on which is dominated by sessile and largely immobile organisms (Rowe the deep-sea ecosystem. Such studies of CO sequestration also 2 et al., 1991). A larger portion of the biomass found at depth is provide an opportunity to assess the inevitable future effects of represented by in situ meiofauna (Bernstein et al., 1978; Rowe et al., associated oceanic pH decrease on calcium carbonate members of the 1991) and the effect of dissassociating liquid CO on these organisms benthic community (Harvey, 2003). 2 requires investigation. Previous investigations (Barry et al., 2005; Experiments CO -1 2 This study (Barry et al., 2005; Experiment CO -5) examined the through CO -4;) have shown that diffusion, dissolution and advective 2 2 effects of CO sequestration on foraminifera. Foraminifera (including mixing of CO from injection sites cause an increase in pCO and 2 2 2 taxa with calcareous and agglutinated tests), as an important element decrease in pH of surrounding waters (Teng et al., 1999; Tsouris et al., of marine sediment communities, are expected to be susceptible to 2004). This has observable negative effects on the benthic fauna, CO -related stress, particularly calcareous taxa. Variable test composi- speciﬁcally on respiration and metabolism (Tamburri et al., 2000; 2 tion (e.g. calcareous and agglutinated; Murray and Alve, 1999), species Barry et al., 2004, 2005; Ishida et al., 2005). While studies have zonation (Gooday and Rathburn, 1999; Gooday et al., 2002), and already been performed on the effects of CO2 on mobile megafauna immobility, facilitate experimental comparisons of CO2-enriched and control sites. Because of these circumstances, the effects of mortality and dissolution on these organisms are measurable as a function of

the distance from CO2 injection both vertically and laterally. Quantitative comparison of foraminiferal assemblages in control relative to exposed samples allows assessment of mortality and

dissolution resulting from the presence of liquid CO2 and its dissolution products (increased pCO2).

Fig. 2. Schematic diagram of experimental area (dashed line) showing location of all corrals as open circles, numbered and designated as C. Individual push-cores indicated by dots. Relative locations of control cores used in this study (CS) are also indicated. Fig. 4. A frame capture of video taken of collection of sediment push-cores at corral 6 Proximal cores (P) are located adjacent to corrals. Distal cores (D) and Seabird CTDs are through remaining hydrate skin shown by arrow. Two cores used in this study are also located close to the center of the corral array. Note corrals C8 and C10 were not sampled shown: within the corral, C6 (at left), and outside the corral, P6 (at right). Published for this study. with permission from MBARI. E.R. Ricketts et al. / Marine Micropaleontology 72 (2009) 165–175 167

Plate I. A) Ammodiscus latus, (slightly oblique view; P2, 1–2 cm), B) Recurvoides turbinatus (CS1B, 1–2 cm), C) Saccamina sphaerica (CS1A, 5–6 cm), D) Paratrochammina challengeri, umbilical view (CS2A, 0–1 cm), E) Paratrochammina challengeri, spiral view (CS2A, 0–1 cm), F) Neogloboquadrina pachyderma, spiral view (CS2A, 0–1 cm), G) Pyrgo murrhina (P9, 8– 9 cm), H) Eggerella bradyi (CSA2, 0–1 cm), I) Haplophragmoides evoluta (oblique view; CS2A, 0–1 cm), J) Neogloboquadrina pachyderma, umbilical view (CS2A, 0–1 cm), K) Globobulimina pacifica (CS2A, 5–6 cm), L) Uvigerina senticosa (C2, 9–10 cm), M) Uvigerina senticosa (CS1A, 9–10 cm), N) Nummulopyrgo globulus, apertural view (P9, 0–1 cm), O) Gyroidina orbicularis, slightly oblique spiral view (CS2A, 1–2 cm), P) Gyroidina orbicularis, oblique umbilical view (CS2A, 0–1 cm), Q) Melonis affinis (C6, 9–10 cm) R) Melonis affinis (CS2A, 9–10 cm) S) Nummulopyrgo globulus, side view (P9, 0–1 cm). Cibicides colombianus is not pictured due to consistently poor specimen preservation in all samples making them too fragile to clean and photograph.

The objective of this experiment was to determine the effects of tests and cements in the effected area and thus calcareous tests in

CO2 injection, and its associated dissociation products, on the survival the experimental area should be reduced in comparison to control and dissolution of benthic foraminifera through the following sample. Furthermore, absence, thinning, or weakness of the observations: calcium carbonate tests in experimental samples (when compared to controls) indicates the inﬂuence of carbonate dissolution

1. If the presence of liquid CO2 increases mortality, the number of live (Berger, 1968; Corliss and Honjo, 1981). (stained) foraminifera in the experimental area should be reduced 3. Due to their composition, non-calcareous agglutinated species relative to control samples. should increase in relative abundance within experimental cores.

2. Decreasing pH in the experimental area due to elevated pCO2 4. Loss in the numbers of stained agglutinated individuals could have (dissolution and dispersal of CO2) will decrease carbonate ion resulted from mortality caused by detrimental effects including concentration leading to the dissolution of calcareous foraminiferal extra- and intracellular acidosis, metabolic depression, and 168 E.R. Ricketts et al. / Marine Micropaleontology 72 (2009) 165–175

Table 1 The number of relict individuals of each dominant foraminiferal species found per centimeter (44 cm3) in control cores.

Agglutinated species data are shaded.

respiration stress as documented by Tamburri et al. (2000) and proximity to Seabird CTDs. Seabird pH sensors attached to the CTDs Seibel and Walsh (2003). measured the pH of near-bottom waters (at discrete depths: 5, 10, 20 and 30 cm above the seaﬂoor) every 15 min at a resolution of ~0.02 pH

2. Regional setting units; monitoring the high pCO2 plume generated by liquid CO2

ACO2 release experiment evaluating the effects of elevated CO2 levels on deep-sea biota was conducted in collaboration with the Monterey Bay Aquarium Research Institute (MBARI) using the R/V Western Flyer and the ROV Tiburon. The experiment was initiated in August 2003 and terminated during September 2003. The experiment was conducted off the coast of Monterey Bay, California (36°42′33.4″ N and 123°31′22.0″ W), at 3600 m depth—the base of the continental rise and within the lysocline (Berger et al., 1982)(Fig. 1). The current at the site had an average speed of 2.9 cm s− 1 and was rotary in nature (Barry et al., 2005). The physical characteristics of the water at the site were described by Barry et al. (2005) with an ambient water temperature of 1.58 °C, O2 concentrations of 120 μM, total alkalinity 2440 μmkg− 1 (WOCE P15 Station 10), in situ pH of 7.78 (SWS) and total carbon (TC) of 2350 μmkg− 1 (WOCE P15 Station 10). Bottom sediments at the experimental site are muds, with the ﬁne fraction (b63 μm) comprising a majority of each sample volume (44 cm3, 1 cm thicknesses) and the sand-sized fraction (N63 μm) forming only b1% of the sediment. The sand-sized fraction itself is predominantly siliceous, consisting of quartz grains (~50%) and radiolarian tests (~40%). The remaining portion of the sand-sized fraction contained glauconite, granular pyrite, and other biogenic shells or fragments. Foraminiferal tests vary in abundance with sediment depth, but even at high abundances form only a minor fraction (153 tests or less).

3. Materials and methods

In August 2003, monitoring equipment and circular PVC corrals (structures that are 48 cm in diameter and 15 cm high) for containment of released liquid CO2 were placed on the ocean ﬂoor in a circular conﬁguration roughly 15 m in diameter (Fig. 2) using the

ROV Tiburon. Each corral was ﬁlled with ~15 L of liquid CO2 (Fig. 3)in the manner developed at MBARI described by Barry et al. (2004). Upon returning to the site in September, a total of 17 push-cores (7.5 cm diameter) were taken to a depth of 10 cm in the sediment at various locations in the corral array to assess the effects of the emplaced CO2. Of these, 4 cores (CS1A, CS1B, CS2A, and CS2B) were taken ~80–100 m from the experimental site to serve as control samples (Fig. 2). One core was taken in each of 5 corrals (C2, C9, C1, C6, and C7). A paired core was taken proximally to the corrals, within 18– 40 cm to each of the cored corrals (P2, P9, P1, P6, and P7) (Fig. 4). Three cores (D1, D2, and D3) were also taken near the center of the Fig. 5. Distribution of stained specimens by dominant species down core; experimental area, ~5–9.5 m from the corrals (Fig. 2) in close A) agglutinated, and B) calcareous. E.R. Ricketts et al. / Marine Micropaleontology 72 (2009) 165–175 169

Table 2 The number of stained individuals of each dominant foraminiferal species found per centimeter (44 cm3) in control cores.

Agglutinated species data are shaded.

dissolution during the experiment (one month). These sensor arrays Following staining, the samples were sieved initially at N63 μm and were distributed across the center of the experimental array where it then at N150 μm to separate the larger sub-fraction for picking. There was expected to experience nearly continuous exposure to a were few to no complete foraminiferal tests in the 63 μmto150μm dissolution plume from the CO2 pools within the corrals (Barry fraction due to dissolution associated with the depth of the et al., 2005). experiment within the lysocline (Berger et al., 1982). All foraminifera Each core in this study was sampled at 1 cm increments (for the were picked wet from the N150 μm fraction and separated into stained whole 7.5 cm diameter push-core) down to 10 cm depth, preserved (live) and unstained (dead). Each foraminiferal specimen was then with 4% formalin in filtered seawater to prevent degradation of identified at the species level and mounted on grid slides per sample. organic material, and buffered to a pHN8.3 to prevent dissolution of Individual counts were made for each species separately and sub- the calcareous material. The pH of these samples was monitored until divided by stained and unstained. These counts form the quantitative washing. When pH reached values of 8.3 in a sample, borax buffer basis for this investigation (Appendices B and C). Selected specimens (“Mule Team” borax) was added to maintain the required pH and were photographed with a scanning electron microscope for taxo- prevent dissolution. nomic identification and qualitative evaluation of amounts of We utilized Rose Bengal, a commonly used cytoplasmal stain (e.g. dissolution (Plate I and Appendix A). McCorkle et al., 1997; Bernhard et al., 2001; Rathburn et al.; 2003), to label live foraminifera in each sample. Samples sat for a minimum of 4. Results one week before further analysis. While Rose Bengal is commonly used, it has previously been shown that cells dead at time of collection Approximately fifty taxa (Appendices B and C), from both stained that had yet to undergo significant tissue decay can also acquire stain and unstained portions of the samples, were identified in the suite of and thus be considered a portion of the live fraction (e.g. Bernhard, cores examined; of these the dominant species (those comprising N1% 2000; Bernhard et al., 2001). It is therefore possible that foraminifera, of total foraminiferal tests found in controls; Appendix A) are shown which died at or near the time of CO2 emplacement, may acquire stain on Plate I. No previous investigations have quantitatively described if they had not fully degraded. Thus, only tests that were fully stained the benthic foraminiferal assemblage at these depths in this region. By (all chambers were stained within the test) were considered living (or far the most abundant species is Globobulimina pacifica; 32% (six recently living) at the time of collection. Even fully-stained tests may hundred individuals) of the total number of tests found in control represent individuals that died due to CO2 injection and their soft cores are individuals of this species (Table 1). This genus is infaunal tissues remained preserved.

Fig. 7. Total number of stained tests for each core (grouped as core types). Control cores Fig. 6. Total number of foraminiferal tests (stained and unstained) subdivided according exhibit approximately twice the number of stained individuals (avg.=129) compared to major foraminiferal groups for each core type. with experimental cores (avg.=62). 170 E.R. Ricketts et al. / Marine Micropaleontology 72 (2009) 165–175 and pervasive on the California margin in low oxygen conditions remaining foraminiferal tests are partially or completely in-ﬁlled with (Cannariato et al., 1999). The remaining dominant calcareous species pyrite. are Uvigerina senticosa, Gyroidina orbicularis, Nummulopyrgo globulus, According to data from the stained fraction of tests, most of these Cibicides colombianus, and Pyrgo murrhina—together comprise 17% of dominant taxa are epifaunal and appear to have been living between 0 the total number of tests in the control cores. The agglutinated species and 1 cm in the sediments including most of the agglutinated forms are dominated by Ammodiscus latus and Recurvoides turbinatus (Fig. 5 and Table 2). These taxa include forms consistently identiﬁed in (~22%) in almost equal measure. The remaining agglutinated species earlier studies as epifaunal: Cibicides, Gyroidina, Pyrgo, and Recur- (Saccamina sphaerica, Paratrochammina challengeri, Eggerella bradyi voides (Corliss and Chen, 1988; Hunt and Corliss, 1992). The and Haplophragmoides evoluta) make up roughly 14% of control core distribution of U. senticosa and S. sphaerica are clearly epifaunal in assemblages. Of these agglutinated forms, two of the dominant our study; however, earlier investigations variously identify Uvigerina species (E. bradyi and H. evoluta) had calcareous cements and were as infaunal, epifaunal, or both (Corliss and Chen, 1988; Rathburn and highly susceptible to carbonate dissolution. Approximately 10% of the Corliss, 1994; and Corliss and van Weering, 1992) and Saccamina as

Fig. 8. A) Average numbers of tests (abundance) counted throughout the length of cores (per 1 cm thickness) for each of the 4 different core types and, B–E) foraminiferal test types (calcareous benthic, planktonic, and agglutinated benthic) as represented in: B) control cores (CS1A, CS1B, CS2A, and CS2B); C) corral cores (C2, C9, C1, C6, and C7); D) proximal cores (P2, P9, P1, P6, and P7); E) distal cores (D1, D2, and D3). E.R. Ricketts et al. / Marine Micropaleontology 72 (2009) 165–175 171 infaunal (Hunt and Corliss, 1992). Species residing predominantly increases at this depth (Fig. 8B). At all depths, control cores have below the sediment water interface (infaunal) in our study depths substantially higher numbers of tests compared with all other core include G. pacifica (4 cm maximum abundance with a total range from types (Tables 1–5). 0 to 6 cm; Fig. 5B) and R. turbinatus (maximum abundance at 2 cm) (Fig. 5A). 4.2. Corral cores Results are presented here (see Figs. 6 and 7) in the order of control, corral, distal, and proximal core treatments. Controls are presented After emplacement in the corrals, liquid CO2 dissolved slowly first to establish a frame of reference; corral cores are presented next as (with varying amounts remaining within each corral at time of they most directly reflect the effects of CO2 injection, while distal cores retrieval), forming a low pH plume that was advected and dispersed reflect the effects over distance. Results from proximal cores are by near-bottom currents. The presence of an episodic and weak pCO2- presented last because they exhibited the most complex response to rich plume derived from the corrals was reflected in measurements

CO2 injection for reasons addressed in the discussion. from the in situ pH electrodes. This was measured as mild pH perturbations approximately every few hours of −0.05 pH units with

4.1. Control cores pCO2 increasing to 578.7 μatm (TC=2322 μM) from pCO2 =511.2- μatm, (TC=2306.1 μM) (Barry et al., 2005). The effects of the pCO2- The downcore distribution of foraminifera is similar among the rich plume were evident when comparing experimental cores to four control cores (CS1A, CS1B, CS2A, and CS2B), including: number control cores. Mean values were utilized to illustrate the overall trends tests (mean=474, SD =81.5) (Fig. 8A and B), species richness in test preservation per core type and at each depth interval for the (mean=36.5, SD=4.43), and dominance of individual species total assemblage. The details of individual foraminiferal assemblages (Appendices B and C). This similarity is observed between individual in each sample are shown in Appendices A and B, and are well pairs of cores taken within 30 cm of each other and between the sets reﬂected by mean values used in this analysis. of cores separated by ~125 m (Appendix B and C). This resemblance is Compared with cores taken from control sites corral cores (C2, C9, also apparent in the number of agglutinated, planktonic (Fig. 6), and C1, C6, and C7), those collected from within CO2 corrals, lack calcareous tests. Stained tests make up roughly 27% of the specimens planktonic foraminifera, and have greatly reduced numbers in each core, with an average of 129 stained individuals per control (mean=145 SD=53) of benthic foraminiferal specimens (Fig. 6) core (Fig. 7). Even thick-shelled individuals containing protoplasm and species diversity (Appendices A, B and C). Of the tests that remain show visible staining through the test wall. Calcareous specimens in in these cores 70–100% are agglutinated taxa (Table 3). In addition, the the control cores are generally well preserved although some hyaline stained fraction of corral cores also contain considerably fewer specimens may still exhibit minor dissolution effects such as pitting specimens (~62 tests on average; Fig. 7) and fewer species largely (Fig. 9). The number of foraminiferal tests in control cores decrease represented by dominant species (Appendices A, B and C). Stained exponentially from ~100 specimens present at 0–1cmto~40 specimens also represent a higher percentage (43%) of remaining specimens at 9–10 cm (Fig. 8A and B). Agglutinated taxa decline tests. Overall, corral cores exhibit a much lower foraminiferal substantially below 4 cm while the number of calcareous tests abundance at all intervals in comparison to control (~80–100 m away) and proximal cores (18–40 cm outside corrals). The uppermost interval (0–1 cm) of the corral cores exhibit a clear decrease in the average number of tests (24 tests) compared with immediately deeper levels in the core—in distinct contrast with control cores containing the highest abundances in the upper centimeter (Fig. 8A). The tests that remain in the uppermost centimeter of the corral cores are almost completely dominated by agglutinated taxa (Fig. 8C). One calcareous species, N. globulus (Plate I), is present as stained individuals at abundances equal to those observed in control cores. The 1–2 cm interval contains the highest abundance of tests in corral cores (40 tests). Following peak abundances at 1–2 cm, the number of tests in corral cores declines distinctly (Fig. 8C) parallel to the decline with depth seen in control cores. At depths of 7–10 cm a slight increase occurs in the number of calcareous specimens found in corral cores.

4.3. Distal cores

Cores taken in the central portion of the experimental area (D1, D2, and D3; 7.5 m distant from the corrals and near CTDs; see Fig. 2), have very similar numbers of specimens (Table 4; Fig. 8E) to corral cores, contain few to no planktonic foraminifera (Fig. 5), and few stained specimens (Fig. 7). Despite these similarities to corral cores (Fig. 8C), half of the tests in distal cores are calcareous, and thus more similar in composition to cores taken just outside (~18–40 cm) of the corrals (proximal) with lower abundances of agglutinated tests (Fig. 8E).

4.4. Proximal cores

Fig. 9. SEM photographs of Globobulimina paciﬁca surface ultrastructure showing the Cores located within 18–40 cm of the CO2 corrals (P2, P9, P1, P6, presence of enlarged and dissolution pitting in a control core specimen (upper image) and P7), exhibit the greatest variability in foraminiferal preservation from this study compared with a pristine specimen (lower image) unaffected by compared to other core types (Fig. 6). Three proximal cores follow dissolution from a shallower site (CO2-6; 3100 m water depth, unpublished) near Monterey Bay. Scale bars are 10 μm. trends similar to control cores while the two remaining proximal 172 E.R. Ricketts et al. / Marine Micropaleontology 72 (2009) 165–175

Table 3 Total number of tests (stained and unstained) for each dominant foraminiferal species per centimeter (44 cm3) in corral cores.

Agglutinated species data are shaded.

Table 4 Total number of tests (stained and unstained) for each dominant foraminiferal species per centimeter (44 cm3) in distal cores.

Agglutinated species data are shaded. cores are similar to distal cores (Fig. 6). The abundance of agglutinated The remaining specimens in all of the experimental cores usually taxa is identical in both control and proximal cores at all intervals exhibit thinner tests, are fragile, and easily fragmented (Plate I and (Tables 1 and 5); however, calcareous taxa are less abundant on Fig. 9). This is visible in light microscopy as disarticulation of outer average in proximal cores until approximately 8 cm depth where the chambers, complete disassociation of agglutinated species with number of tests found in proximal cores increases towards numbers of calcareous cements, perforate taxa appearing sugary due to severe tests seen in controls (Fig. 8D). Proximal cores still contain a majority dissolution pitting, and smoothing of raised surface textures. Taxa of the calcareous taxa and abundances of calcareous tests increase resistant to dissolution were either non-calcareous agglutinated or with depth (Fig. 8D). milliolid taxa.

Table 5 Total number of tests (stained and unstained) for each dominant foraminiferal species per centimeter (44 cm3) in proximal cores.

Agglutinated species data are shaded. E.R. Ricketts et al. / Marine Micropaleontology 72 (2009) 165–175 173

Statistical analyses were conducted to test the hypothesis that C). Even at 10 cm depth the number of calcareous specimens is still trends in numbers of tests seen in experimental cores were in fact due substantially lower than at equivalent depth in control cores (Fig. 8B to exposure to liquid CO2 injection. In order to compare all core and C). However, a sporadic reappearance of calcareous forms below treatments in one test and account for pairing in some core types, a 7 cm suggests the effects of CO2 exposure were diminishing with depth modified one-way ANOVA was used. Proximal cores were excluded in the sediment. Nevertheless, the 10 cm deep cores available from this from this test due to liquid CO2 spillage during filling of some corrals, experiment were of insufficient length to determine the absolute exposing these proximal sediments directly to liquid CO2 resulting in depth of influence of the liquid CO2 (and associated pCO2 and pH variable CO2 exposure within this core type and a confounding depression) on foraminiferal assemblages. variable. This analysis resulted in a p-value of 0.013, indicating that The foraminiferal assemblages in the proximal cores are more there is a statistically significant difference between control cores and similar to control cores because of the occurrence of calcareous both distal and corral cores. benthic and planktonic tests. Nevertheless, a clear decrease in the number of specimens occurs throughout most of the core length when 5. Discussion compared to the controls (Fig. 8D) in addition to a decrease in preservation of the remaining calcareous tests (Plate I). This indicates The experimental site was deep within the lysocline (3600 m) as that proximal cores have undergone dissolution as a result of the represented on the California margin (Berger et al., 1982). As a result, presence of a low-pH plume generated by liquid CO2 in nearby corrals. the relict foraminiferal assemblages had undergone partial dissolution The greatest disparity between the cores occurred in the uppermost prior to injection and clearly showed signs of dissolution independent centimeter, reflecting greatest effect of CO2 at the sediment–water of the experiment. Evidence for natural dissolution can be seen in the interface. The number of tests found in proximal cores more closely relative paucity of planktonic foraminifera in control cores with values approaches those in control cores with increasing depth, indicating ranging from zero (14 of 40 samples) to 18 tests per interval (high decreasing dissolution and thus decreasing pCO2 with depth (also values were found only in the uppermost centimeter). A high seen in corral cores). The two proximal cores (P1 and P2) with abundance of radiolaria, indicative of the well-known, high-produc- extremely low abundances of tests are adjacent to corrals that had tivity, surface waters of this region (Venrick, 2000), suggests that spillage or overflow when they were filled with liquid CO2 and thus planktonic foraminifera would have been present in larger numbers in the sediments were directly exposed. The control-like pattern of surface water than in the control core sediments. Numbers of foraminiferal distribution in the three remaining proximal cores is preserved foraminifera are reduced due to dissolution caused by the thus possibly explained by an inferred up-current location of the cores sediments depth within the lysocline. Other evidence supporting such relative to the CO2-rich experimental plume generated by the dissolution includes surface pitting and thinning of tests visible in experiment. This variability in proximal core exposure is the hyaline calcareous species found in control cores (Fig. 9)and confounding variable responsible for inconclusive statistical results differential dissolution between different benthic taxa which has and the reason proximal cores were excluded from the ANOVA test. been well documented for the deep sea (Corliss and Honjo, 1981). Surprisingly, data from the distal cores was different in total test The distinct exponential decrease (Fig. 8) in the average number of abundance relative to the proximal cores, resulting in part from the tests with depth in control cores is primarily the result of a decrease in distinctly low numbers of agglutinated taxa in the upper three the natural preservation of agglutinated taxa from 2 to 4 cm. This centimeters. Furthermore, numbers of calcareous taxa are also represents the well-known tendency for fragmentation and poor reduced relative to the proximal cores. The distal cores therefore, preservation of agglutinated taxa with increasing sediment depth exhibit stronger dissolution effects 5 m away from the closest corral (Murray and Alve, 1999). Without this loss of agglutinated tests, the compared to three of the proximal cores (18–40 cm from corrals), an relative down-core abundance of foraminiferal tests would be reason- unexpected result. The reason for this is unclear; however water ably uniform. The abundance of calcareous tests increases below 4 cm, current and pH data (Barry et al., 2005) suggested that greater corresponding with the maximum abundance of the dominant infaunal dissolution in distal cores can be attributed to repeated episodic species, G. pacifica. Since the effects of CO2 dissolution were relatively exposure to the pCO2-rich plumes emanating from the corrals. This uniform in the upper 10 cm of sediments, depth of residence did not episodic exposure was possible because irrespective of the current affect the survivability of benthic foraminiferal specimens in this study. direction, which varied throughout the experiment, there was always Comparison of foraminiferal assemblages between the experi- an up-current corral to act as a source. mental and control cores clearly indicates that calcium carbonate The distinctly lower numbers of stained foraminifera in corral and dissolution affected all assemblages. The observed decrease can be distal cores (Fig. 6; 7) indicate that the addition of liquid CO2 caused explained by examining the down-core trends (Fig. 8), which show significant mortality in the benthic foraminifera. Mortality results that calcareous foraminifera in the 0–1 cm interval (where most taxa from increased pCO2 which causes metabolic changes such as extra- or stained) underwent dissolution in all experimental core types due to intracellular acidosis, depression and respiration stress. Nevertheless, the presence of high pCO2 waters from the dissociation of liquid CO2. stained foraminifera were still present in all cores. This is consistent Because the greatest amounts of dissolution were found within the with a companion study of foraminiferal assemblages exposed to surface sediments in all experimental cores, this effect cannot be due injected CO2 that were interpreted to exhibit survivorship, particularly to the lateral transport of pCO2-rich waters within the sediment, but in thecate and agglutinated forms (Bernhard et al. 2008). The rather resulted from the downward diffusion of the plume from the presence of Rose Bengal stained individuals in the experimental water column into the sediments. cores of our study may not necessarily indicate survival of benthic

The distinct absence of calcareous tests in the corral cores (Fig. 6) foraminifera exposed to injected CO2; instead this may indicate the shows that liquid CO2 release causes an increase in dissolution of lack of decay of organic material in deceased specimens at time of calcareous taxa in sediments directly below the CO2 pool. This reflects collection. The preferential preservation of stained individuals in the response to an increase in pore waters from the same experimental experimental cores may have resulted from the enhanced protection site (Thistle et al., 2005). These observations imply a greater areal from the presence of cellular material (Thistle et al., 2005). extent of effected sediments from such plumes. The remaining assemblage in the corral cores is dominated largely by non-calcareous 6. Conclusions agglutinated taxa which are resistant to dissolution (Fig. 8C). A slight increase in the number of calcareous foraminifera below 7 cm in corral Lack of planktonic tests and the presence of dissolution pits in cores suggests a dilution of the effect of CO2 penetration (Fig. 8A and calcareous taxa suggest that, due to the depth of the study area, the 174 E.R. Ricketts et al. / Marine Micropaleontology 72 (2009) 165–175 foraminiferal assemblage was already subjected to carbonate dissolu- Globobulimina pacifica Cushman, 1927. Calcareous, thin, finely tion prior to CO2 exposure. These pre-existing conditions (Corliss and perforate. Honjo, 1981) weakened carbonate tests and made assemblages more Gyroidina orbicularis d'Orbigny, 1826. Calcareous, perforate, vulnerable to small perturbations in pH as experienced in the granular. experimental area. Down-core foraminiferal trends included a decline Haplophragmoides evoluta Natland, 1938. Originally referred to as: in agglutinated individuals and relative increase in calcareous forms. Haplophragmoides columbiensis Cushman var. evolutum, Cushman and

Results suggest that due to CO2 emplacement, the total number of McCulloch, 1939. Finely agglutinated with calcareous cement. foraminifera in experimental cores decreases, foraminiferal diversity Neogloboquadrina pachyderma (Ehrenberg); Kennett & Srinivasan decreases in both stained and unstained specimens, the number of 1980. Original designation: Aristospira pachyderma Ehrenberg, 1861. foraminiferal tests declines, and the relative percentage of stained Calcareous, perforate. foraminifera is higher while actual numbers of stained individuals Nummulopyrgo globulus (Hofker); Hofker, 1983. Original designa- decrease. This is consistent with the results of Ishida et al. (2005) who tion: Pseudopyrgo globulus, 1976, Calcareous, imperforate, porcelaneous. demonstrated lower population density of foraminifera in CO2 Paratrochammina challengeri Brönnimann and Whittaker, 1988. exposed sediments on the Japanese margin. Major mortality and Finely agglutinated with abundant, non-calcareous cement. increased dissolution of calcareous forms resulted from exposure to Pyrgo murrhina (Schwager); Cushman, 1929. Original designa- liquid CO2 and its associated dissolution products (high pCO2 and tion: Biloculina murrhina Schwager, 1866. Calcareous, imperforate, lowered pH). Since calcareous foraminifera represent more than 50% porcelaneous. of the total assemblages, this clearly indicates that emplacement of Recurvoides turbinatus (Brady). Original designation: Haplophrag-

CO2 will result in negative effects to diversity and survivorship of the mium turbinatum Brady, 1881. Coarsely agglutinated with non- deep-sea benthic meiofauna. Furthermore, the presence of remaining calcareous cement. stained foraminiferal tests (predominantly non-calcareous forms) Saccamina sphaerica M. Sars, 1868. Coarsely agglutinated with non- within the experimental cores do not necessarily indicate survival calcareous cement. after exposure, but rather may indicate foraminiferal tissue that Uvigerina senticosa Cushman, 1939. Calcareous, perforate. resisted decay following death. This slow rate of decomposition was also noted in other meiofaunal assemblages at depth (Carman et al., Appendix B. Supplementary data 2004; Thistle et al., 2005). The strongest effects of liquid CO injection were found both in the 2 Supplementary data associated with this article can be found, in sediments directly overlain by CO pools and areas repeatedly bathed 2 the online version, at doi:10.1016/j.marmicro.2009.04.005. by a pCO2-rich plume. Carbonate dissolution in sediments not directly overlain by liquid CO2 resulted from transport of the pCO2-rich plume in bottom waters. Sporadic effects were seen in areas where the References plume was obstructed or ephemeral. Although the abundance and Barry, J.P., Buck, K.R., Lovera, C., Kuhnz, L., Whaling, P.J., Peltzer, E.T., Walz, P., Brewer, P.G., diversity of foraminiferal assemblages in experimental cores became 2004. Effects of direct ocean CO2 injection of deep-sea meiofauna. Journal of increasingly similar to those in control cores with greater depth, Oceanography 60, 759–766. dissolution of carbonate taxa was evident to a minimum of 10 cm Barry, J.P., Buck, K.R., Lovera, C., Kuhnz, L., Whaling, P.J., 2005. Utility of deep-sea CO2 release experiments in understanding the biology of a high CO2 ocean: effects of depth and as distant as 5 m. Future studies of liquid CO2 emplacement hypercapnia on deep-sea meiofauna. Journal of Geophysical Research, Oceans 110 should attempt to remove the complicating variable of pre-existing (C9), C09S12. doi:10.1029/2004JC002629. dissolution due to significant depth within the lysocline and obtain Berger, W.H., 1968. Planktonic foraminifera — selective solution and paleoclimatic interpretation. Deep-sea Research 15 (1), 31. longer cores to determine the full penetration of CO2-induced Berger, W.H., Bonneau, M.C., Parker, F.L., 1982. Foraminifera on the deep-sea floor: dissolution. lysocline and dissolution rate. 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