Low Saturation State Research Articles

Combined stress of ocean acidification and warming influence survival and drives differential gene expression patterns in the Antarctic pteropod, Limacina helicina antarctica.

The ecologically important thecosome pteropods in the Limacina spp. complex have recently been the focus of studies examining the impacts global change factors – e.g., ocean acidification (OA) and ocean warming (OW) – on their performance and physiology. This focus is driven by conservation concerns where the health of pteropod populations is threatened by the high susceptibility of their shells to dissolution in low aragonite saturation states associated with OA and how coupling of these stressors may push pteropods past the limits of physiological plasticity. In this manipulation experiment, we describe changes in the transcriptome of the Antarctic pteropod, Limacina helicina antarctica, to these combined stressors. The conditions used in the laboratory treatments met or exceeded those projected for the Southern Ocean by the year 2100. We made two general observations regarding the outcome of the data: (1) Temperature was more influential than pH in terms of changing patterns of gene expression, and (2) these Antarctic pteropods appeared to have a significant degree of transcriptomic plasticity to respond to acute abiotic stress in the laboratory. In general, differential gene expression was observed amongst the treatments; here, for example, transcripts associated with maintaining protein structure and cell proliferation were up-regulated. To disentangle the effects of OA and OW, we used a weighted gene co-expression network analysis to explore patterns of change in the transcriptome. This approach identified gene networks associated with OW that were enriched for transcripts proposed to be involved in increasing membrane fluidity at warmer temperatures. Together these data provide evidence that L.h.antarctica has a limited capacity to acclimate to the combined conditions of OA and OW used in this study. This reduced scope of acclimation argues for continued study of how adaptation to polar aquatic environments may limit the plasticity of present-day populations in responding to future environmental change.

Geochemical controls on the elemental composition of siderite: Implications for palaeo-environmental reconstructions

The elemental composition of siderite (FeCO3) has been widely used as a palaeo-environmental proxy, and commonly utilised in the diagnosis of marine influences on Phanerozoic coastal wetland sediments. That siderite might reflect marine or freshwater sources is based on the premise that a marine origin should show an enrichment of Ca and/or Mg, while high concentrations of Mn should reflect precipitation from freshwater. However, the main controls on the elemental composition of siderite, and the degree to which siderite composition reflects parent water chemistry, are poorly understood. To address these issues, we conducted siderite nucleation and seeded growth experiments to examine element partitioning at a variety of saturation states and solution compositions (i.e., cation concentrations, pH, and pCO2). Results indicate a strong preference for Mn uptake over Ca and Mg, even when Mn is present at concentrations far below those of Ca or Mg. This uptake is enhanced at slower growth rates and lower saturation states, which may, in part, reflect surface structural controls on uptake and or a change in the dominant growth mechanism. Ca uptake only occurred during nucleation experiments, while measurable Mg uptake was not observed in experiments conducted at 20 °C, but increased slightly at 55 °C. These results suggest that the chemical composition of siderite does not directly reflect aqueous cation chemistry as previously assumed and is strongly influenced by kinetics rather than equilibrium behaviour. This leads us to conclude that variations in pore water chemistry alone cannot explain the range of Ca and Mg concentrations reported from geological siderites, and that other factors must be considered (such as physical admixtures of multiple carbonate minerals and/or the products of diagenetic recrystallization).

Effect of calcite saturation state on the growth and mortality of Heterocypris incongruens and a proposal for an reference artificial sediment in the sediment toxicity test ISO14371

Since the establishment of the whole-contact sediment toxicity test using Heterocypris incongruens in 2012, this user-friendly method has been widely used for the assessment of many kinds of solid samples, such as sediment, soil, compost, and sewage sludge. There are two endpoints for this method: mortality and growth inhibition. Currently, there is no standard toxicity threshold established for the endpoint of growth inhibition. However, there is evidence showing that the calcite saturation state of the overlying water, which might be different among various samples, influences the growth and survival of H. incongruens. Thus, it is necessary to characterize the influence of the calcite saturation state to ensure that the test results are reliable and comparable among different samples. In the present study, we created artificial sediments comprised of quartz sand and 0–20% calcite particulates to manipulate the calcite saturation state in the overlying water and performed the test using H. incongruens for 6 d. The results show that a low calcite saturation state inhibited the growth of H. incongruens but had no effect on survival rate. The growth of ostracods was linearly related to the calcite saturation index of the overlying water. Additionally, a formula for artificial sediment consisting of 10% calcite and 90% quartz sand for the H. incongruens toxicity test was proposed. This study helps to distinguish H. incongruens growth inhibition caused by calcite saturation from that caused by toxicity.

Heterotrophy of Oceanic Particulate Organic Matter Elevates Net Ecosystem Calcification

AbstractCoral reef calcification is expected to decline due to climate change stressors such as ocean acidification and warming. Projections of future coral reef health are based on our understanding of the environmental drivers that affect calcification and dissolution. One such driver that may impact coral reef health is heterotrophy of oceanic‐sourced particulate organic matter, but its link to calcification has not been directly investigated in the field. In this study, we estimated net ecosystem calcification and oceanic particulate organic carbon (POCoc) uptake across the Kāne'ohe Bay barrier reef in Hawai'i. We show that higher rates of POCoc uptake correspond to greater net ecosystem calcification rates, even under low aragonite saturation states (Ωar). Hence, reductions in offshore productivity may negatively impact coral reefs by decreasing the food supply required to sustain calcification. Alternatively, coral reefs that receive ample inputs of POCoc may maintain higher calcification rates, despite a global decline in Ωar.

Export of calcium carbonate corrosive waters from the East Siberian Sea

Abstract. The Siberian shelf seas are areas of extensive biogeochemical transformation of organic matter, both of marine and terrestrial origin. This in combination with brine production from sea ice formation results in a cold bottom water of relative high salinity and partial pressure of carbon dioxide (pCO2). Data from the SWERUS-C3 expedition compiled on the icebreaker Oden in July to September 2014 show the distribution of such waters at the outer shelf, as well as their export into the deep central Arctic basins. Very high pCO2 water, up to ∼ 1000 µatm, was observed associated with high nutrients and low oxygen concentrations. Consequently, this water had low saturation state with respect to calcium carbonate down to less than 0.8 for calcite and 0.5 for aragonite. Waters undersaturated in aragonite were also observed in the surface in waters at equilibrium with atmospheric CO2; however, at these conditions the cause of under-saturation was low salinity from river runoff and/or sea ice melt. The calcium carbonate corrosive water was observed all along the continental margin and well out into the deep Makarov and Canada basins at a depth from about 50 m depth in the west to about 150 m in the east. These waters of low aragonite saturation state are traced in historic data to the Canada Basin and in the waters flowing out of the Arctic Ocean north of Greenland and in the western Fram Strait, thus potentially impacting the marine life in the North Atlantic Ocean.

A post-larval stage-based model of hard clam Mercenaria mercenaria development in response to multiple stressors: temperature and acidification severity

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 558:35-49 (2016) - DOI: https://doi.org/10.3354/meps11882 A post-larval stage-based model of hard clam Mercenaria mercenaria development in response to multiple stressors: temperature and acidification severity Cale A. Miller1,*, George G. Waldbusser2 1Huxley College of the Environment, Western Washington University, 516 E. College Way, Bellingham, WA 98225, USA 2College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, 104 COAS Administration Building, Corvallis, OR 97331, USA *Corresponding author: mille454@students.wwu.edu ABSTRACT: Complex biogeochemical processes in the coastal oceans lead to highly variable carbonate chemistry that is further modified by the shifting baseline of pCO2 caused by ocean acidification. Unfavorable carbonate chemistry, which is pervasive in near-shore, shallow-water deposits, due to high rates of organic matter remineralization and the oxidation of reduced metabolites, has been shown to negatively affect benthic calcifying organisms. For settling infaunal bivalve larvae, such as the hard clam Mercenaria mercenaria, pore waters high in CO2 exert a physiological stress on early post-larval development and homeostasis. The effects of acidification have been shown to increase mortality and reduce calcification for ‘just settled’ juvenile M. mercenaria, a life stage that heavily affects adult clam abundance. To better understand the effects of acidification and temperature on this sensitive life stage, we constructed a post-larval stage-based development model that investigated how varying degrees of aragonite saturation state affect post-settlement survival of juvenile M. mercenaria. Initial model simulations predict a similar consistency and trend to field experiments that examined the survival of juvenile Mya arenaria residing in buffered and unbuffered sediments. According to our model, the magnitude of acidification had a large effect on post-larval stage duration, which translated to a 60% decrease in total survivors under high variability compared to low variability saturation state scenarios. By modifying temperature-dependent growth rates, we were able to progress juveniles out of the more sensitive life stages faster and, therefore, determined scenarios in which faster growth can reduce exposure to acidification during more sensitive stages. KEY WORDS: Ocean acidification · Stage-based model · Juvenile clam · Mercenaria mercenaria · Temperature-dependent growth · Post-larval development Full text in pdf format PreviousNextCite this article as: Miller CA, Waldbusser GG (2016) A post-larval stage-based model of hard clam Mercenaria mercenaria development in response to multiple stressors: temperature and acidification severity. Mar Ecol Prog Ser 558:35-49. https://doi.org/10.3354/meps11882 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 558. Online publication date: October 25, 2016 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2016 Inter-Research.

Seasonality in planktic foraminifera of the central California coastal upwelling region

Abstract. The close association between planktic foraminiferal assemblages and local hydrography make foraminifera invaluable proxies for environmental conditions. Modern foraminiferal seasonality is important for interpreting fossil distributions and shell geochemistry as paleoclimate proxies. Understanding this seasonality in an active upwelling area is also critical for anticipating which species may be vulnerable to future changes in upwelling intensity and ocean acidification. Two years (2012–2014) of plankton tows, along with conductivity–temperature–depth profiles and carbonate chemistry measurements taken along the north-central California shelf, offer new insights into the seasonal dynamics of planktic foraminifera in a seasonal coastal upwelling regime. This study finds an upwelling affinity for Neogloboquadrina pachyderma as well as a seasonal and upwelling associated alternation between dominance of N. pachyderma and Neogloboquadrina incompta, consistent with previous observations. Globigerina bulloides, however, shows a strong affinity for non-upwelled waters, in contrast to findings in Southern California where the species is often associated with upwelling. We also find an apparent lunar periodicity in the abundances of all species and document the presence of foraminifera even at very low saturation states of calcite.

Coccolithophore responses to environmental variability in the South China Sea: species composition and calcite content

Abstract. Coccolithophore contributions to the global marine carbon cycle are regulated by the calcite content of their scales (coccoliths) and the relative cellular levels of photosynthesis and calcification rates. All three of these factors vary between coccolithophore species and with response to the growth environment. Here, water samples were collected in the northern basin of the South China Sea (SCS) during summer 2014 in order to examine how environmental variability influenced species composition and cellular levels of calcite content. Average coccolithophore abundance and their calcite concentration in the water column were 11.82 cells mL−1 and 1508.3 pg C mL−1, respectively, during the cruise. Water samples can be divided into three floral groups according to their distinct coccolithophore communities. The vertical structure of the coccolithophore community in the water column was controlled by the trophic conditions, which were regulated by mesoscale eddies across the SCS basin. The evaluation of coccolithophore-based calcite in the surface ocean also showed that three key species in the SCS (Emiliania huxleyi, Gephyrocapsa oceanica, Florisphaera profunda) and other larger, numerically rare species made almost equal contributions to total coccolith-based calcite in the water column. For Emiliania huxleyi biometry measurements, coccolith size positively correlated with nutrients (nitrate, phosphate), and it is suggested that coccolith length is influenced by light and nutrients through the regulation of growth rates. Larger-sized coccoliths were also linked statistically to low pH and calcite saturation states; however, it is not a simple cause and effect relationship, as carbonate chemistry was strongly co-correlated with the other key environmental factors (nutrients, light).

Assessment of continuous acoustic respiratory rate monitoring as an addition to a pulse oximetry-based patient surveillance system.

Technology advances make it possible to consider continuous acoustic respiratory rate monitoring as an integral component of physiologic surveillance systems. This study explores technical and logistical aspects of augmenting pulse oximetry-based patient surveillance systems with continuous respiratory rate monitoring and offers some insight into the impact on patient deterioration detection that may result. Acoustic respiratory rate sensors were introduced to a general care pulse oximetry-based surveillance system with respiratory rate alarms deactivated. Simulation was used after 4324 patient days to determine appropriate alarm thresholds for respiratory rate, which were then activated. Data were collected for an additional 4382 patient days. Physiologic parameters, alarm data, sensor utilization and patient/staff feedback were collected throughout the study and analyzed. No notable technical or workflow issues were observed. Sensor utilization was 57%, with patient refusal leading reasons for nonuse (22.7%). With respiratory rate alarm thresholds set to 6 and 40breaths/min., the majority of nurse pager clinical notifications were triggered by low oxygen saturation values (43%), followed by low respiratory rate values (21%) and low pulse rate values (13%). Mean respiratory rate collected was 16.6±3.8breaths/min. The vast majority (82%) of low oxygen saturation states coincided with normal respiration rates of 12-20breaths/min. Continuous respiratory rate monitoring can be successfully added to a pulse oximetry-based surveillance system without significant technical, logistical or workflow issues and is moderately well-tolerated by patients. Respiratory rate sensor alarms did not significantly impact overall system alarm burden. Respiratory rate and oxygen saturation distributions suggest adding continuous respiratory rate monitoring to a pulse oximetry-based surveillance system may not significantly improve patient deterioration detection.

Geochemistry of two shallow CO2 seeps in Shikine Island (Japan) and their potential for ocean acidification research

Shallow CO2 seeps, where CO2 gas is venting underwater, offer great potential for studies into the effects of ocean acidification at the ecosystem level. To our knowledge, only two tropical system and two temperate systems of such seeps have been described worldwide. Here we describe two new temperate systems: the Mikama Bay and Ashitsuke sites, located on Shikine Island, Japan. The Mikama Bay site is located in a shallow bay. Investigation of the gas and water chemistry showed that the gas contained 98% CO2 and up to 90 ppm H2S. Total alkalinity was constant in time and space with an average of 2265±10 μ mol kg−1. Mapping of Eh and pH showed that the low pH zones were the largest when currents were moderate. Under moderate currents, Eh values were globally higher and total sulfides concentration lower, supporting that a longer residence time of the bay water allow the oxidation of the sulfides to sulfates. Zones suitable for acidification studies: with a pH lower than 8.0, low saturation state of calcite and aragonite, and non-detectable sulfide concentration, can be defined a few meters from the main venting zone. The second site, Ashitsuke, is located in the inter-tidal zone on a shore composed of boulders. Several areas showed reduced pH sometimes restricted to a few meters and up to 20 m long along the shoreline. Temperature was higher in some of the reduced pH zones suggesting the presence of hot springs in addition to vents. This paper also highlights the need for discovering additional CO2 seeps, which by their nature often lack comparable replicates and can be confounded by factors other than CO2. In this regard, Japan offers great potential as it is home to numerous active volcanoes, representing potential venting sites in climates ranging from tropical to sub-polar.

On the Frontline: Tracking Ocean Acidification in an Alaskan Shellfish Hatchery

The invasion of anthropogenic carbon dioxide (CO2) into the ocean is shifting the marine carbonate system such that saturation states of calcium carbonate (CaCO3) minerals are decreasing, and this is having a detrimental impact on early life stages of select shellfish species. The global, secular decrease in CaCO3 saturation states is occurring on top of a backdrop of large natural variability in coastal settings; progressively shifting the envelope of variability and leading to longer and more frequent exposure to adverse conditions. This is a great concern in the State of Alaska, a high-latitude setting vulnerable to rapid changes in the marine carbonate system, where an emerging shellfish industry plans major growth over the coming decades. Currently, the Alutiiq Pride Shellfish Hatchery (APSH) in Seward, Alaska is the only hatchery in the state, and produces many shellfish species with early life stages known to be sensitive to low CaCO3 saturation states. Here we present the first land-based OA measurements made in an Alaskan shellfish hatchery, and detail the trends in the saturation state of aragonite (Ωarag), the more soluble form of CaCO3, over a 10-month period in the APSH seawater supply. These data indicate the largest changes are on the seasonal time scale, with extended periods of sub-optimal Ωarag levels (Ωarag < 1.5) in winter and autumn associated with elevated water column respiration and short-lived runoff events, respectively. The data pinpoint a 5-month window of reprieve with favorable Ωarag conditions above the sub-optimal Ωarag threshold, which under predicted upper-bound CO2 emissions trajectories is estimated to close by 2040. To date, many species in production at APSH remain untested in their response to OA, and the data presented here establish the current conditions at APSH as well as provide a framework for hatchery-based measurements in Alaska. The current and expected conditions seen at APSH are essential to consider for this developing Alaskan industry.

Occurrence of aragonite corrosive water in the North Yellow Sea, near the Yalu River estuary, during a summer flood

To understand seawater CaCO3 saturation state (Ωarag for aragonite and Ωcal for calcite) dynamics in river-dominated ocean margins, we investigated the carbonate system and ancillary parameters in the North Yellow Sea, near the Yalu River estuary, during and after a summer flood (August and September 2013, respectively). During the flood period, nearshore Ωarag ranged from 0.76 to 1.61 and Ωcal ranged from 1.22 to 2.53. Aragonite undersaturation values were associated with quite low salinity of 14.58–25.18 and a broad dissolved oxygen saturation range from 58% to 102%. A week after the flood period, aragonite undersaturated waters together with the estuarine plumes disappeared. Based on field data analyses and simplified model simulation, we suggest that net community respiration/remineralization and the dilution of riverine water discharge both contributed to the low CaCO3 saturation states.

Sea-ice melt CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;–carbonate chemistry in the western Arctic Ocean: meltwater contributions to air–sea CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; gas exchange, mixed-layer properties and rates of net community production under sea ice

Abstract. The carbon dioxide (CO2)-carbonate chemistry of sea-ice melt and co-located, contemporaneous seawater has rarely been studied in sea-ice-covered oceans. Here, we describe the CO2–carbonate chemistry of sea-ice melt (both above sea-ice as "melt ponds" and below sea-ice as "interface waters") and mixed-layer properties in the western Arctic Ocean in the early summer of 2010 and 2011. At 19 stations, the salinity (∼0.5 to &lt;6.5), dissolved inorganic carbon (DIC; ∼20 to &lt;550 μmol kg−1) and total alkalinity (TA; ∼30 to &lt;500 μmol kg−1) of above-ice melt pond water was low compared to the co-located underlying mixed layer. The partial pressure of CO2 (pCO2) in these melt ponds was highly variable (∼&lt;10 to &gt;1500 μatm) with the majority of melt ponds acting as potentially strong sources of CO2 to the atmosphere. The pH of melt pond waters was also highly variable ranging from mildly acidic (6.1 to 7) to slightly more alkaline than underlying seawater (&gt;8.2 to 10.8). All of the observed melt ponds had very low (&lt;0.1) saturation states (Ω) for calcium carbonate (CaCO3) minerals such as aragonite (Ωaragonite). Our data suggest that sea-ice generated alkaline or acidic type melt pond water. This melt water chemistry dictates whether the ponds are sources of CO2 to the atmosphere or CO2 sinks. Below-ice interface water CO2–carbonate chemistry data also indicated substantial generation of alkalinity, presumably owing to dissolution of CaCO3 in sea-ice. The interface waters generally had lower pCO2 and higher pH/Ωaragonite than the co-located mixed layer beneath. Sea-ice melt thus contributed to the suppression of mixed-layer pCO2, thereby enhancing the surface ocean's capacity to uptake CO2 from the atmosphere. Our observations contribute to growing evidence that sea-ice CO2–carbonate chemistry is highly variable and its contribution to the complex factors that influence the balance of CO2 sinks and sources (and thereby ocean acidification) is difficult to predict in an era of rapid warming and sea-ice loss in the Arctic Ocean.

Sodium Alginate Intercalated Zinc-Containing Layered Double Hydroxides for the Catalytic α-Pinene Oxidation

In this paper, the sodium alginate (SA) intercalated into a series of binary Mg-Al、Cu-Al, Zn-Al flaky layered double hydroxides (FLDH/SA) were fleetly prepared by the technology of the microwave-crystallization and low saturated state of coprecipitation. The purposed sample was characterized by XRD, IR and SEM. The result shows that the sample synthesized Zn-FLDH/SA with the flexible slice has the structure of LDHs, indicating the preparations are successful under microwave irradiation. The three types of CFLDH/SA were the calcined products of the three FLDH/SA under 673K for 4h, which were then applied to the catalytic α-pinene oxidation using 30 wt% hydrogen peroxide as oxidant. The effects of reaction time, catalyst type, reaction medium and so on were also investigated in details. The results show the Zn-CFLDH/SA is the best catalyst, α-pinene conversion and the selectivity of α-pinene epoxide , verbenol, verbenone can reach 69.6% and 29.1%, 39.6%, 12.0%, respectively, under optimized reaction conditions of acetone: water = 1:1 as reaction solvent, catalyst concentration of 0.431 g/L, reaction temperature 60 oC and reaction time 3 hours, Zn-CFLDH/SA as catalyst.

Seasonal and spatial variability in the CO2 system on the Scotian Shelf (Northwest Atlantic)

As part of the Atlantic Zone Monitoring Program, dissolved inorganic carbon (DIC), total alkalinity, and nitrate measurements were made throughout the Scotian Shelf in 2007. A shelf-wide assessment of the spatio-temporal variability of the inorganic carbon system was made relying on observations in spring (April) and autumn (October). Over the 6-month period, a combination of biological production, surface dilution, and air–sea CO2 exchange resulted in seasonal decreases in surface DIC of up to 70μmolkg−1 and subsurface (between 50 and 100m) increases of DIC on the order of 50μmolkg−1 on the inner shelf. The regional mean surface water pH was roughly 7.8 in spring and increased to greater than 8.0 in autumn; subsurface pH was approximately 7.6 throughout the region and a seasonal decrease, attributed in part to the respiration of organic matter at depth, was observed. The surface aragonite saturation state increased from less than 2.0 to a maximum of 3.2 between spring and autumn; the region as a whole exhibited relatively low saturation states, however values approaching 1.0 were only observed in the Cabot Strait at depths below 100m. Winter-to-spring and winter-to-autumn deficits in surface inorganic carbon and nitrate were used to estimate net community production (NCP) throughout the region. The nitrate-based estimates of NCP using the autumn observations were significantly lower (0.1 to 0.3molCm−2month−1) than the carbon-based estimates (0.1 to 0.8molCm−2month−1) at most stations. The cumulative autumn NCP based on nitrate (0.4 to 1.9mol C m−2 over 6months) was up to 50% lower than the cumulative NCP based on inorganic carbon deficits (0.5 to 4.7molCm−2 over 6months), suggesting that continued biological production through the summer season occurs in nitrate-depleted waters.

Enhancement of struvite purity by re-dissolution of calcium ions in synthetic wastewaters

Although it is widely known that the presence of Ca ions inhibits the nucleation and growth of struvite, which consists of NH4+, PO43−, and Mg2+, there is a lack of knowledge on actual Ca contents in struvite co-precipitates at various N and P concentrations and the corresponding effects on the sizes of the precipitates. Therefore, to address this challenge, this study designed synthetic wastewaters including the variety of N and P concentrations, and conducted batch experimental reactions with each wastewater to investigate Ca precipitation and size distributions of the precipitates. The molar ratio of Mg:P:N was confined to 1:1:7, while the initial Ca2+ concentrations were chosen to be 30–60mg/L, which are typical Ca concentrations in real wastewaters. The result of the batch experiments confirmed that the presence of Ca caused smaller solids than struvite as indicated in previous studies, and there was competition between Ca-phosphate and Mg-N- PO4 (struvite) reactions, as expected. At the beginning of the experiment (∼1min), fast Ca-phosphate precipitation was dominant because free Ca and P ions were quickly removed while Mg and N concentrations gradually reduced. However, as the nucleation and crystal growth processes elapsed, dissolved Mg and N concentrations continuously decreased, but dissolved Ca concentrations could rise again at high N and P concentration conditions. The interesting phenomenon is that such increases of Ca concentrations probably results from the thermodynamic energy differences between struvite and Ca-phosphate formations. A high thermodynamic driving force of struvite precipitation could drive the re-dissolution of Ca-ions from the Ca-phosphate compounds with low saturation states. This result is expected to be applied for increasing the struvite purity by the Ca re-dissolution through the thermodynamic spontaneity without additional energy input.

Spatiotemporal Variability of Dimethylsulphoniopropionate on a Fringing Coral Reef: The Role of Reefal Carbonate Chemistry and Environmental Variability

Oceanic pH is projected to decrease by up to 0.5 units by 2100 (a process known as ocean acidification, OA), reducing the calcium carbonate saturation state of the oceans. The coastal ocean is expected to experience periods of even lower carbonate saturation state because of the inherent natural variability of coastal habitats. Thus, in order to accurately project the impact of OA on the coastal ocean, we must first understand its natural variability. The production of dimethylsulphoniopropionate (DMSP) by marine algae and the release of DMSP’s breakdown product dimethylsulphide (DMS) are often related to environmental stress. This study investigated the spatiotemporal response of tropical macroalgae (Padina sp., Amphiroa sp. and Turbinaria sp.) and the overlying water column to natural changes in reefal carbonate chemistry. We compared macroalgal intracellular DMSP and water column DMSP+DMS concentrations between the environmentally stable reef crest and environmentally variable reef flat of the fringing Suleman Reef, Egypt, over 45-hour sampling periods. Similar diel patterns were observed throughout: maximum intracellular DMSP and water column DMS/P concentrations were observed at night, coinciding with the time of lowest carbonate saturation state. Spatially, water column DMS/P concentrations were highest over areas dominated by seagrass and macroalgae (dissolved DMS/P) and phytoplankton (particulate DMS/P) rather than corals. This research suggests that macroalgae may use DMSP to maintain metabolic function during periods of low carbonate saturation state. In the reef system, seagrass and macroalgae may be more important benthic producers of dissolved DMS/P than corals. An increase in DMS/P concentrations during periods of low carbonate saturation state may become ecologically important in the future under an OA regime, impacting larval settlement and increasing atmospheric emissions of DMS.

Effects of Reduced Carbonate Saturation State on Early Development in the Common Edible Sea Urchin Lytechinus variegatus: Implications for Land-Based Aquaculture

Land-based aquaculture facilities often utilize additional bicarbonate sources such as commercial sea salts that are designed to boost alkalinity in order to buffer seawater against reductions in pH. Despite these preventative measures, many facilities are likely to face occasional reductions in pH and corresponding reductions in carbonate saturation states due to the accumulation of metabolic waste products. We investigated the impact of reduced carbonate saturation states (ΩCa, ΩAr) on embryonic developmental rates, larval developmental rates, and echinoplutei skeletal morphometrics in the common edible sea urchin Lytechinus variegatus under high alkalinity conditions. Commercial artificial seawater was bubbled with a mixture of air and CO2 gas to reduce the carbonate saturation state. Rates of embryonic and larval development were significantly delayed in both the low and extreme low carbonate saturation state groups relative to the control at a given time. Although symmetry of overall skeletal body lengths was not affected, allometric relationships were significantly different between treatment groups. Larvae reared under ambient conditions had significantly greater postoral arm and overall body lengths relative to body lengths than larvae grown under extreme low carbonate saturation state conditions, indicating that extreme changes in the carbonate system affected not only developmental rates but also larval skeletal shape. Reduced rates of embryonic development and delayed and altered larval skeletal growth are likely to negatively impact larval culturing of L. variegatus in land-based, intensive culture situations where calcite and aragonite saturation states are lowered by the accumulation of metabolic waste products.

Arctic microbial community dynamics influenced by elevated CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; levels

Abstract. The Arctic Ocean ecosystem is particularly vulnerable to ocean acidification (OA) related alterations due to the relatively high CO2 solubility and low carbonate saturation states of its cold surface waters. Thus far, however, there is only little known about the consequences of OA on the base of the food web. In a mesocosm CO2-enrichment experiment (overall CO2 levels ranged from ~ 180 to 1100 μatm) in Kongsfjorden off Svalbard, we studied the consequences of OA on a natural pelagic microbial community. OA distinctly affected the composition and growth of the Arctic phytoplankton community, i.e. the picoeukaryotic photoautotrophs and to a lesser extent the nanophytoplankton thrived. A shift towards the smallest phytoplankton as a result of OA will have direct consequences for the structure and functioning of the pelagic food web and thus for the biogeochemical cycles. Besides being grazed, the dominant pico- and nanophytoplankton groups were found prone to viral lysis, thereby shunting the carbon accumulation in living organisms into the dissolved pools of organic carbon and subsequently affecting the efficiency of the biological pump in these Arctic waters.

Robust empirical relationships for estimating the carbonate system in the southern California Current System and application to CalCOFI hydrographic cruise data (2005–2011)

The California Current System (CCS) is expected to experience the ecological impacts of ocean acidification (OA) earlier than most other ocean regions because coastal upwelling brings old, CO2‐rich water relatively close to the surface ocean. Historical inorganic carbon measurements are scarce, so the progression of OA in the CCS is unknown. We used a multiple linear regression approach to generate empirical models using oxygen (O2), temperature (T), salinity (S), and sigma theta (σθ) as proxy variables to reconstruct pH, carbonate saturation states, carbonate ion concentration ([CO32−]), dissolved inorganic carbon (DIC) concentration, and total alkalinity (TA) in the southern CCS. The calibration data included high‐quality measurements of carbon, oxygen, and other hydrographic variables, collected during a cruise from British Columbia to Baja California in May–June 2007. All resulting empirical relationships were robust, withr2values &gt;0.92 and low root mean square errors. Estimated and measured carbon chemistry matched very well for independent data sets from the CalCOFI and IMECOCAL programs. Reconstructed CCS pH and saturation states for 2005–2011 reveal a pronounced seasonal cycle and inter‐annual variability in the upper water column. Deeper in the water column, conditions are stable throughout the annual cycle, with perennially low pH and saturation states. Over sub‐decadal time scales, these empirical models provide a valuable tool for reconstructing carbonate chemistry related to ocean acidification where direct observations are limited. However, progressive increases in anthropogenic CO2 content of southern CCS water masses must be carefully addressed to apply the models over longer time scales.