Marine Micropaleontology 72 (2009) 165–175 Contents lists available at ScienceDirect Marine Micropaleontology journal homepage: www.elsevier.com/locate/marmicro 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 0377-8398/$ – see front matter © 2009 Published by Elsevier B.V. doi:10.1016/j.marmicro.2009.04.005 166 E.R. Ricketts et al. / Marine Micropaleontology 72 (2009) 165–175 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