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Simple Summary The ocean absorbs large amounts of CO2 emitted by human activities, which leads to a decrease in seawater pH, and has the potential to cause damage to calcareous marine organisms. Planktic foraminifera are some of the most important calcareous marine organisms in the ocean, although the biological response of planktic foraminifera to the decline in seawater pH is still unknown. In this study, the biological response of planktic foraminifera to declining seawater pH was studied through a series of on-board experiments. The experimental results showed that the decrease in seawater pH adversely affected the biological processes of planktic foraminifera, resulting in weaker predation, slower growth, lighter shells, and more deformities. In addition, for the first time, we report that microalgae that live with planktic foraminifera were also killed under low-pH conditions. Several indices were established to quantify the relationships between the biological parameters of planktic foraminifera and seawater pH, which could be used to reconstruct the paleoceanographic seawater pH. This study provides experimental data to quantify the biological response of calcareous plankton to a decline in seawater pH. Abstract Understanding the way in which a decline in ocean pH can affect calcareous organisms could enhance our ability to predict the impacts of the potential decline in seawater pH on marine ecosystems, and could help to reconstruct the paleoceanographic events over a geological time scale. Planktic foraminifera are among the most important biological proxies for these studies; however, the existing research on planktic foraminifera is almost exclusively based on their geochemical indices, without the inclusion of information on their biological development. Through a series of on-board experiments in the western tropical Pacific (134°33′54″ E, 12°32′47″ N), the present study showed that the symbiont-bearing calcifier Trilobatus sacculifer—a planktic foraminifer—responded rapidly to a decline in seawater pH, including losing symbionts, bleaching, etc. Several indices were established to quantify the relationships between these biological parameters and seawater pH, which could be used to reconstruct the paleoceanographic seawater pH. We further postulated that the loss of symbionts in planktic foraminifera acts as an adaptive response to the stress of low pH. Our results indicate that an ongoing decline in seawater pH may hinder the growth and calcification of planktic foraminifera by altering their biological processes. A reduction in carbonate deposition and predation could have profound effects on the carbon cycle and energy flow in the marine food web.

acidification (OA), a global threat to the world’s oceans, is projected to significantly grow if CO2 continues to be emitted into the atmosphere at high levels. This will result in a slight decrease in pH. Since the latter is a logarithmic scale of acidity, the higher acidic seawater is expected to have a tremendous impact on marine living resources in the long-term. An 8-week laboratory experiment was designed to assess the impact of the projected pH in 2100 and beyond on fish survival, health, growth, and fish meat quality. Two projected scenarios were simulated with the control treatment, in triplicates. The control treatment had a pH of 8.10, corresponding to a pCO2 of 321.37 ± 11.48 µatm. The two projected scenarios, named Predict_A and Predict_B, had pH values of 7.80-pCO2 = 749.12 ± 27.03 and 7.40-pCO2 = 321.37 ± 11.48 µatm, respectively. The experiment was preceded by 2 weeks of acclimation. After the acclimation, 20 juvenile black sea breams (Acanthopagrus schlegelii) of 2.72 ± 0.01 g were used per tank. This species has been selected mainly due to its very high resistance to diseases and environmental changes, assuming that a weaker fish resistance will also be susceptibly affected. In all tanks, the fish were fed with the same commercial diet. The seawater’s physicochemical parameters were measured daily. Fish samples were subjected to physiological, histological, and biochemical analyses. Fish growth, feeding efficiency, protein efficiency ratio, and crude protein content were significantly decreased with a lower pH. Scanning electron microscopy revealed multiple atrophies of microvilli throughout the small intestine’s brush border in samples from Predict_A and Predict_B. This significantly reduced nutrient absorption, resulting in significantly lower feed efficiency, lower fish growth, and lower meat quality. As a result of an elevated pCO2 in seawater, the fish eat more than normal but grow less than normal. Liver observation showed blood congestion, hemorrhage, necrosis, vacuolation of hepatocytes, and an increased number of Kupffer cells, which characterize liver damage. Transmission electron microscopy revealed an elongated and angular shape of the mitochondrion in the liver cell, with an abundance of peroxisomes, symptomatic of metabolic acidosis.

Coral reef community composition, function, and resilience have been altered by natural and anthropogenic stressors. Future anthropogenic ocean and coastal acidification (together termed “acidification”) may exacerbate this reef degradation. Accurately predicting reef resilience requires an understanding of not only direct impacts of acidification on marine organisms but also indirect effects on species interactions that influence community composition and reef ecosystem functions. In this 28-day experiment, we assessed the effect of acidification on coral–algal, coral–sponge, and algal–sponge interactions. We quantified growth of corals (Siderastrea radians), fleshy macroalgae (Dictyota spp.), and sponges (Pione lampa) that were exposed to local summer ambient (603 μatm) or elevated (1105 μatm) pCO2 seawater. These species are common to hard-bottom communities, including shallow reefs, in the Florida Keys. Each individual was maintained in isolation or paired with another organism. Coral growth (net calcification) was similar across seawater pCO2 and interaction treatments. Fleshy macroalgae had increased biomass when paired with a sponge but lost biomass when growing in isolation or paired with coral. Sponges grew more volumetrically in the elevated seawater pCO2 treatment (i.e., under acidification conditions). Although these results are limited in temporal and spatial scales due to the experimental design, they do lend support to the hypothesis that acidification may facilitate a shift towards increased sponge and macroalgae abundance by directly benefiting sponge growth which in turn may provide more dissolved inorganic nitrogen to macroalgae in the Florida Keys.

Chemical changes in the diffusive boundary layer (DBL) generated by photosynthesising macroalgae are expected to play an important role in modulating the effects of ocean acidification (OA), but little is known about the effects on early life stages of marine invertebrates in modified DBLs. Larvae that settle to macroalgal surfaces and remain within the DBL will experience pH conditions markedly different from the bulk seawater. We investigated the interactive effects of seawater pH and DBL thickness on settlement and early post-settlement growth of the sea urchin Pseudechinus huttoni, testing whether coralline-algal DBLs act as an environmental buffer to OA. DBL thickness and pH levels (estimated from well-established relationships with oxygen concentration) above the crustose coralline algal surfaces varied with light availability (with photosynthesis increasing pH to as high as pH 9.0 and respiration reducing pH to as low as pH 7.4 under light and dark conditions, respectively), independent of bulk seawater pH (7.5, 7.7, and 8.1). Settlement success of P. huttoni increased over time for all treatments, irrespective of estimated pH in the DBL. Juvenile test growth was similar in all DBL manipulations, showing resilience to variable and low seawater pH. Spine development, however, displayed greater variance with spine growth being negatively affected by reduced seawater pH in the DBL only in the dark treatments. Scanning electron microscopy revealed no observable differences in structural integrity or morphology of the sea urchin spines among pH treatments. Our results suggest that early juvenile stages of P. huttoni are well adapted to variable pH regimes in the DBL of macroalgae across a range of bulk seawater pH treatments.

Increasing atmospheric CO2 concentrations are resulting in a reduction in seawater pH, with potential detrimental consequences for marine organisms. Improved efforts are required to monitor the anthropogenically driven pH decrease in the context of natural pH variations. We present here a high resolution surface water pH data set obtained in summer 2011 in North West European Shelf Seas. The aim of our paper is to demonstrate the successful deployment of the pH sensor, and discuss the carbonate chemistry dynamics of surface waters of Northwest European Shelf Seas using pH and ancillary data. The pH measurements were undertaken using spectrophotometry with a Lab-on-Chip pH sensor connected to the underway seawater supply of the ship. The main processes controlling the pH distribution along the ship&rsquo, s transect, and their relative importance, were determined using a statistical approach. The pH sensor allowed 10 measurements h&minus, 1 with a precision of 0.001 pH units and a good agreement with pH calculated from a pair of discretely sampled carbonate variables dissolved inorganic carbon (DIC), total alkalinity (TA) and partial pressure of CO2 (pCO2) (e.g., pHDICpCO2). For this summer cruise, the biological activity formed the main control on the pH distribution along the cruise transect. This study highlights the importance of high quality and high resolution pH measurements for the assessment of carbonate chemistry dynamics in marine waters.

Water in its three ambient phases plays the central thermodynamic role in the terrestrial climate system. Clouds control Earth's radiation balance, atmospheric water vapour is the strongest "greenhouse" gas, and non-equilibrium relative humidity at the air-sea interface drives evaporation and latent heat export from the ocean. On climatic time scales, melting ice caps and regional deviations of the hydrological cycle result in changes of seawater salinity, which in turn may modify the global circulation of the oceans and their ability to store heat and to buffer anthropogenically produced carbon dioxide. In this paper, together with three companion articles, we examine the climatologically relevant quantities ocean salinity, seawater pH and atmospheric relative humidity, noting fundamental deficiencies in the definitions of those key observables, and their lack of secure foundation on the International System of Units, the SI. The metrological histories of those three quantities are reviewed, problems with their current definitions and measurement practices are analysed, and options for future improvements are discussed in conjunction with the recent seawater standard TEOS-10. It is concluded that the International Bureau of Weights and Measures, BIPM, in cooperation with the International Association for the Properties of Water and Steam, IAPWS, along with other international organisations and institutions, can make significant contributions by developing and recommending state-of-the-art solutions for these long standing metrological problems in climatology.

Coral reefs occupy only similar to 0.1 percent of the ocean's habitat, but are the most biologically diverse marine ecosystem. In recent decades, coral reefs have experienced a significant global decline due to a variety of causes, one of the major causes being widespread coral bleaching events. During bleaching, the coral expels its symbiotic algae, thereby losing its main source of nutrition generally obtained through photosynthesis. While recent coral bleaching events have been extensively investigated, there is no scientific data on historical coral bleaching prior to 1979. In this study, we employ high-resolution femtosecond Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) to demonstrate a distinct biologically induced decline of boron (B) isotopic composition (delta B-11) as a result of coral bleaching. These findings and methodology offer a new use for a previously developed isotopic proxy to reconstruct paleo-coral bleaching events. Based on a literature review of published delta B-11 data and our recorded vital effect of coral bleaching on the delta B-11 signal, we also describe at least two possible coral bleaching events since the Last Glacial Maximum. The implementation of this bleaching proxy holds the potential of identifying occurrences of coral bleaching throughout the geological record. A deeper temporal view of coral bleaching will enable scientists to determine if it occurred in the past during times of environmental change and what outcome it may have had on coral population structure. Understanding the frequency of bleaching events is also critical for determining the relationship between natural and anthropogenic causes of these events. BMBF/03V0956 National Science Foundation/0920572 SBM Minerva foundation

WOS:000426917500003; International audience; The boron isotope composition (delta B-11) of marine biogenic carbonates has been predominantly studied as a proxy for monitoring past changes in seawater pH and carbonate chemistry. However, a number of assumptions regarding chemical kinetics and thermodynamic isotope exchange reactions are required to derive seawater pH from delta B-11 biogenic carbonates. It is also probable that delta B-11 of biogenic carbonate reflects seawater pH at the organism's site of calcification, which may or may not reflect seawater pH. Here, we report the development of methodology for measuring the delta B-11 of biogenic carbonate samples at the multicollector inductively coupled mass spectrometry facility at Ifremer (Plouzane, France) and the evaluation of delta(BCaCO3)-B-11 in a diverse range of marine calcifying organisms reared for 60 days in isothermal seawater (25 degrees C) equilibrated with an atmospheric pCO(2) of ca. 409 mu atm. Average delta(BCaCO3)-B-11 composition for all species evaluated in this study range from 16.27 to 35.09 %, including, in decreasing order, coralline red alga Neogoniolithion sp. (35.89 +/- 3.71 %), temperate coral Oculina arbuscula (24.12 +/- 0.19 %), serpulid worm Hydroides crucigera (19.26 +/- 0.16 %), tropical urchin Eucidaris tribuloides (18.71 +/- 0.26 %), temperate urchin Arbacia punctulata (16.28 +/- 0.86 %), and temperate oyster Crassostrea virginica (16.03 %). These results are discussed in the context of each species' proposed mechanism of biocalcification and other factors that could influence skeletal and shell delta B-11, including calcifying site pH, the proposed direct incorporation of isotopically enriched boric acid (instead of borate) into biogenic calcium carbonate, and differences in shell/skeleton polymorph mineralogy. We conclude that the large inter-species variability in delta(BCaCO3)-B-11 (ca. 20%) and significant discrepancies between measured delta(BCaCO3)-B-11 and delta(BCaCO3)-B-11 expected from established relationships between abiogenic delta(BCaCO3)-B-11 and seawater pH arise primarily from fundamental differences in calcifying site pH amongst the different species. These results highlight the potential utility of delta B-11 as a proxy of calcifying site pH for a wide range of calcifying taxa and underscore the importance of using species-specific seawater-pH-delta(BCaCO3)-B-11 calibrations when reconstructing seawater pH from delta B-11 of biogenic carbonates.

International audience; Research assessing the biological impacts of global ocean change often requires a burdensome characterization of seawater carbonate chemistry. For laboratory-based ocean acidification research, this impedes the scope of experimental design. Honeywell Durafet ® III pH electrodes provide precise and continuous seawater pH measurements. In addition to use in oceanographic sensor packages, Durafets can also be used in the laboratory to track and control seawater treatments via Honeywell Universal Dual Analyzers (UDAs). Here we provide performance data, instructions, and step-by-step recommendations for use of multiple UDA-Durafets. Durafet pH measurements were within ±0.005 units pH T of spectrophotometric measurements and agreement among eight Durafets was better than ±0.005 units pH T. These results indicate equal performance to Durafets in oceanographic sensor packages, but methods for calibration and quality control differ. Use of UDA-Durafets vastly improves time-course documentation of experimental conditions and reduces person-hours dedicated to this activity. Due to the versatility of integrating Durafets in laboratory seawater systems, this technology opens the door to advance the scale of questions that the ocean acidification research community aims to address.

Current global trends will lead to large-scale changes in climate patterns, ocean circulation and stratification; increased atmospheric CO2 levels will cause acidification of the oceans, with significant impacts on marine biogeochemical cycles and calcareous organisms. In the Mediterranean area, the northern Adriatic Sea is one of the most suitable sites for studying the responses of marine pH to such occurrences because it is the northernmost basin affected by dense water formation during winter, and is also one of the most productive areas in the Mediterranean. The first comparison between two sets of data relating to the dense cold waters of the northern Adriatic, formed in the winters of 1982–1983 and 2007–2008, is presented here. pH values on the Nation Bureau Standard scale from the old dataset have been converted to the ‘total hydrogen ion concentration scale’ adopted for the new dataset, and are expressed as μmol H . Results at 25 °C show acidification (−0.063 pHT units) and a decrease in carbonat...

Water dissolves many substances with which it comes into contact, leading to a variety of aqueous solutions ranging from simple and dilute to complex and highly concentrated. Of the multiple chemical species present in these solutions, the hydrogen ion, H+, stands out in importance due to its relevance to a variety of chemical reactions and equilibria that take place in aquatic systems. This importance, and the fact that its presence can be assessed by reliable and inexpensive procedures, are the reasons why pH is perhaps the most measured chemical parameter. In this paper, while examining climatologically relevant ocean pH, we note fundamental problems in the definition of this key observable, and its lack of secure foundation on the International System of Units, the SI. The metrological history of seawater pH is reviewed, difficulties arising from its current definition and measurement practices are analysed, and options for future improvements are discussed in conjunction with the recent TEOS-10 seawater standard. It is concluded that the International Bureau of Weights and Measures (BIPM), in cooperation with the International Association for the Properties of Water and Steam (IAPWS), along with other international organisations and institutions, can make significant contributions by developing and recommending state-of-the-art solutions for these long standing metrological problems.

9 páginas, 4 figuras.-- Proyecto Carbochange, Ocean acidification is directly related to increasing atmospheric CO2 levels due to human activities and the active role of the global ocean in absorbing part of this anthropogenic CO2. Here we present an assessment of the pH changes that have occurred along 24.5°N in the subtropical North Atlantic through comparison of pH observations conducted in 1992 and 2011. It reveals an overall decline in pH values in the first 1000 dbar of the water column. The deconvolution of the temporal pH differences into anthropogenic and nonanthropogenic components reveals that natural variability, mostly owed to a decrease in oxygen levels in particular regions of the section, explains the vertical distribution of the larger pH decreases (up to −0.05 pH units), which are found within the permanent thermocline. The detection of long-term trends in dissolved oxygen in the studied region gains importance for future pH projections, as these changes modulate the anthropogenically derived acidification. The anthropogenic forcing explains significant acidification deeper than 1000 dbar in the western basin, within the Deep Western Boundary Current., We acknowledge funding from the Spanish Ministry of Economy and Competitiveness through grants CSD2008-00077 (Circumnavigation Expedition MALASPINA 2010 Project), CTM2009-08849 (ACDC Project), and CTM2012-32017 (MANIFEST Project) and from the Seventh Framework Programme FP7 CARBOCHANGE (grant agreement 264879). E.F. Guallart was funded by CSIC through a JAE-Pre grant.

This thesis studies the impacts of ocean acidification on an ecologically and economically important invertebrate of the Nordic waters: the green sea urchin Strongylocentrotus droebachiensis. Acidification affects the different life stages and transitions composing the life-cycle. Paper I establishes the robustness of the larval stage to a broad range of acidification (-1.5 pHT units) covering present, projected near-future variability and beyond. Development of normal, although showing morphological plasticity, swimming larvae was possible as low as pHT ≥ 7.0. Acidification increased mortality and respiration and decreased growth rate. Paper II focuses on the impacts of a decreased pH (-0.4 and -0.8 units) on the transitions phases between the larval and juvenile stages and on juveniles’ survival. Lowered pH induced both direct effects of (e.g. juvenile spine amount) and carry-over effects (e.g. increased settlement rates). Paper III deals with juvenile and adult stages. While adult fecundity was reduced after a 4-months exposure to low pH (-0.4 units), it was not affected anymore after 16-months. On the other hand, juveniles experienced a 95% mortality when grown at low pH since fertilization. Paper IV is a meta-analysis based on the available experimental data available on echinoderms in 2010 revealing differing sensitivities of the stages and processes studied to near-future predictions. Paper V reveals, from in vivo measurements on S. droebachiensis pluteus larvae, that the extracellular compartment surrounding the calcifying cells conforms to the surrounding seawater with respect to pH. Under ocean acidification, maintaining constant intracellular pH for calcium precipitation probably causes enhanced metabolic costs.

Five tropical seaweeds,Kappaphycus alvarezii(Doty) Doty ex P.C. Silva,Padina australisHauck,Sargassum binderiSonder ex J. Agardh (syn.S. aquifolium(Turner) C. Agardh),Sargassum siliquosumJ. Agardh andTurbinaria conoides(J. Agardh) Kützing, were incubated in seawater of pH 8.0, 7.8 (ambient), 7.6, 7.4 and 7.2, to study the effects of changing seawater pH on halocarbon emissions. Eight halocarbon species known to be emitted by seaweeds were investigated: bromoform (CHBr3), dibro­momethane (CH2Br2), iodomethane (CH3I), diiodomethane (CH2I2), bromoiodomethane (CH2BrI), bromochlorometh­ane (CH2BrCl), bromodichloromethane (CHBrCl2), and dibro­mochloromethane (CHBr2Cl). These very short-lived halocarbon gases are believed to contribute to stratospheric halogen concentrations if released in the tropics. It was observed that the seaweeds emit all eight halocarbons assayed, with the exception ofK. alvareziiandS. binderifor CH2I2and CH3I respectively, which were not measurable at the achievable limit of detection. The effect of pH on halocarbon emission by the seaweeds was shown to be species-specific and compound specific. The highest percentage changes in emissions for the halocarbons of interest were observed at the lower pH levels of 7.2 and 7.4 especially inPadina australisandSargassumspp., showing that lower seawater pH causes elevated emissions of some halocarbon compounds. In general the seaweed least affected by pH change in terms of types of halocarbon emission, wasP. australis. The commercially farmed seaweedK. alvareziiwas very sensitive to pH change as shown by the high increases in most of the compounds in all pH levels relative to ambient. In terms of percentage decrease in maximum quantum yield of photosynthesis (Fv∕Fm) prior to and after incubation, there were no significant correlations with the various pH levels tested for all seaweeds. The correlation between percentage decrease in the maximum quantum yield of photosynthesis (Fv∕Fm) and halocarbon emission rates, was significant only for CH2BrCl emission byP. australis(r = 0.47;p ≤ 0.04), implying that photosynthesis may not be closely linked to halocarbon emissions by the seaweeds studied. Bromine was the largest contributor to the total mass of halogen emitted for all the seaweeds at all pH. The highest total amount of bromine emitted byK. alvarezii(an average of 98% of total mass of halogens) and the increase in the total amount of chlorine with decreasing seawater pH fuels concern for the expanding seaweed farming activities in the ASEAN region.

International audience; Boron isotopic and elemental systematics are used to define the vital effects for the temperate shallow water Mediterranean coral Cladocora caespitosa. The corals are from a range of seawater pH conditions (pH(T) similar to 7.6 to similar to 8.1) and environmental settings: (1) naturally living colonies harvested,from normal pH waters offshore Levanto, (2) colonies transplanted nearby a subsea volcanic vent system, and (3) corals cultured in aquaria exposed to high (700 mu atm) and near present day (400 mu atm) pCO(2) levels. BiCa compositions measured using laser ablation inductively coupled mass spectrometry (LA-ICPMS) show that boron uptake by C caespitosa cultured at different pCO(2) levels is independent of ambient seawater pH being mainly controlled by temperature-dependent calcification. In contrast, the boron isotope compositions (delta(11)B(carb)) of the full suite of corals determined by positive thermal ionisation mass spectrometry (PTIMS) shows a clear trend of decreasing delta(11) B(carb) (from 26.7 to 22.2%.) with decreasing seawater pH. reflecting the strong pH dependence of the boron isotope system. The delta(11)B(carb) compositions together with measurements of ambient seawater parameters enable calibration of the boron pH proxy for C caespitosa, by using a new approach that defines the relationship between ambient seawater pH (pH,) and the internally controlled pH at the site of calcification (pH(biol)). C. caespitosa exhibits a linear relationship between pH(sw) and the shift in pH due to physiological processes (Delta pH = pH(biol) - pH(sw)) giving the regression Delta pH(clad) = 4.80 - 0.52 x pH(sw) for this species. We further apply this method (''Delta pH-pH(sw)'') to calibrate tropical species of Porites, Acropora, and Stylophora reported in the literature. The temperate and tropical species calibrations are all linearly correlated (r(2)> 0.9) and the biological fractionation component (pH) between species varies within similar to 0.2 pH units. Our ``Delta pH-pH(sw)'' approach provides a robust and accurate tool to reconstruct palaeoseawater pH, for both temperate and tropical corals, further validating the boron fractionation factor (alpha(B3)-(B4) = 1.0272) determined experimentally by Klochko et al. (2006) and the boron isotope pH proxy, both of which have been the foci of considerable debate. (C) 2011 Elsevier B.V. All rights reserved.

Studying geological carbon cycle disruption helps to further understand modern carbon cycle and to better apprehend the consequences of the current increase in atmospheric CO2. Specifically, geological crisis highlight the reaction ability of the environment to stressful situation. We used a multi‐proxy approach to study the Triassic‐Jurassic (TJ) boundary events. This transition period is characterized by a succession of two carbon isotopes negative excursions (CINEs) in sections from Tethyan realm. Through GEOCLIM modeling, we show that the Central Atlantic Magmatic Province (CAMP) likely generated the carbonate production crisis observed during the first CINE provided that emplacement is modeled as a succession of intense short‐lived pulses (, L'étude des perturbations géologiques du cycle du carbone permet d'améliorer la compréhension du cycle moderne du carbone et de mieux appréhender les effets des perturbations de la teneur en CO2 atmosphérique. En particulier, les crises géologiques fournissent un objet d'étude permettant de mieux connaître les capacités de réactions de l'environnement en situation de stress. Nous avons étudié la crise de la limite Trias‐Jurassique (TJ) selon une approche combinée entre modélisation et étude multi‐traceur centrée sur les isotopes du carbone de la matière organique et des carbonates. La limite TJ est caractérisée dans les coupes téthysiennes par la succession de deux excursions négatives de la composition isotopique du carbone organique. La première est associée à une extinction de masse et une crise de la production carbonatée. Nous montrons grâce au modèle GEOCLIM que la mise en place de la Province Magmatique de l'Atlantique Central (CAMP) a pu engendrer la crise de la production carbonatée en prenant en compte les observations selon lesquelles cette mise en place s'est faite sous forme de pulses intenses (

Special issue Paleoclimatology research in Catalonia.-- 10 pages, 6 figures, [EN] Since the Industrial Revolution, the CO2 concentration in the atmosphere has increased substantially, enhancing the greenhouse effect, which is very much related to current global warming. Fortunately, the Earth has a series of reservoirs, especially its oceans, which trap a significant amount of the excess CO2. This marine absorption of CO2, however, results in progressive acidification of the oceans, which has detrimental and possibly devastating effects for marine organisms, particularly those that construct a skeleton of calcium carbonate (corals, mussels, clams, etc.). To understand the magnitude of this problem, it is crucial to know how seawater pH has oscillated in the past, particularly during those periods of time that are not covered by instrumental measurements, which are restricted to the last decade. For this purpose, the isotopic composition of boron in fossil biogenic carbonates provides a geochemical indicator, or proxy, which allows reconstruction of the past variations in seawater pH. In this review, we explain the theoretical grounds of this proxy, show the empirical calibrations carried out so far, briefly comment on some aspects of boron isotope analysis, and list the results of paleo-pH reconstructions published so far, [CAT] Des de la revolució industrial, la concentració de CO2 a l'atmosfera ha augmentat de manera molt significativa, amb el consegüent augment de l'efecte d'hivernacle, molt relacionat amb l'actual escalfament global. Per sort, la Terra disposa d'una sèrie de reservoris, sobretot els oceans, que atrapen una quantitat significativa d'aquest excés de CO2. No obstant això, com a resultat de l'absorció marina de CO2, les aigües s'estan acidificant progressivament i comprometran, potser de manera devastadora, el desenvolupament d'organismes marins, sobretot d'aquells que construeixen un esquelet de carbonat (coralls, musclos, cloïsses, etc.). Per entendre l abast d'aquest problema, és molt important conèixer com ha variat el pH al llarg del temps, sobretot durant aquells períodes de què no disposem de dades instrumentals, les quals es limiten a la darrera dècada. Amb aquesta finalitat, disposem d'un indicador indirecte o proxy, la composició isotòpica de bor en carbonats fòssils biogènics, que ens permet reconstruir la variació del pH marí al llarg del temps. En aquesta revisió expliquem els fonaments d'aquest proxy, mostrem els calibratges que s'han fet fins al moment, comentem breument els requeriments analítics per a la mesura dels isòtops de bor i exposem els resultats que s'han obtingut fins ara, This work has been supported by the Generalitat de Catalunya through funding of the Catalan Research Group of Marine Biogeochemistry and Global Change (grant 2005SGR00021) and by the Spanish Ministry of Education and Science (MEC) through project ROMIAT (CTM2006-01957/MAR). E.C. acknowledges a Ramón y Cajal contract from the MEC and C.P. acknowledges a contract as a research professor from Institució Catalana de Recerca i Estudis Avançats (ICREA)

Coral reefs occupy only similar to 0.1 percent of the ocean's habitat, but are the most biologically diverse marine ecosystem. In recent decades, coral reefs have experienced a significant global decline due to a variety of causes, one of the major causes being widespread coral bleaching events. During bleaching, the coral expels its symbiotic algae, thereby losing its main source of nutrition generally obtained through photosynthesis. While recent coral bleaching events have been extensively investigated, there is no scientific data on historical coral bleaching prior to 1979. In this study, we employ high-resolution femtosecond Laser Ablation Multiple Collector Inductively Coupled Plasma Mass Spectrometry (LA-MC-ICP-MS) to demonstrate a distinct biologically induced decline of boron (B) isotopic composition (delta B-11) as a result of coral bleaching. These findings and methodology offer a new use for a previously developed isotopic proxy to reconstruct paleo-coral bleaching events. Based on a literature review of published delta B-11 data and our recorded vital effect of coral bleaching on the delta B-11 signal, we also describe at least two possible coral bleaching events since the Last Glacial Maximum. The implementation of this bleaching proxy holds the potential of identifying occurrences of coral bleaching throughout the geological record. A deeper temporal view of coral bleaching will enable scientists to determine if it occurred in the past during times of environmental change and what outcome it may have had on coral population structure. Understanding the frequency of bleaching events is also critical for determining the relationship between natural and anthropogenic causes of these events.

10 páginas, 4 figuras, 1 tabla, [EN] Acidification of the oceans is one of the consequences of ongoing increasing atmospheric CO2 concentrations. The effects on organisms that build their shells of calcium carbonate are not sufficiently studied and might be detrimental. Simulating ocean acidification scenarios in the laboratory is a reasonable way to study their response to decreased pH and carbonate ion concentrations. In this study we describe in detail an experimental system to carry out ocean acidification experiments with non-symbiotic benthic foraminifera. We test the performance of the designed experimental set up by running a long-term experiment (90 days) using a potentially suitable benthic foraminiferal species for culturing (Miliolinella spp.). Although foraminifera did not survive the experimental period likely due to ciliates infestation, seawater pH measurement results indicate that the design is suitable for carrying out ocean acidification experiments, [ES] La acidificación oceánica es una de las consecuencias del aumento progresivo de la concentración de CO2 en la atmósfera. Los efectos en los organismos que construyen sus conchas con carbonato cálcico no están suficientemente estudiados, pero podrían ser perjudiciales. La simulación en laboratorio de diferentes escenarios de acidificación oceánica es una forma de estudiar la respuesta de esos organismos al descenso de pH y de la concentración del ion carbonato. En este estudio se describe minuciosamente un sistema experimental diseñado para realizar experimentos de acidificación oceánica con foraminíferos bentónicos sin simbiontes. La viabilidad del diseño experimental se ha probado con un experimento de larga duración (90 días) utilizando una especie de foraminífero bentónico potencialmente apta para ser cultivada (Miliolinella spp.). Aunque los foraminíferos no sobrevivieron durante todo el experimento debido a contaminación por ciliados, los resultados de las medidas del pH marino ponen de manifiesto que el diseño es adecuado para llevar a cabo experimentos de acidificación oceánica, This research leading to these results was supported by the Spanish Ministry of Sciences and Innovation and co-founded by the Fondo Europeo de Desarrollo Regional 2007-2012 (FEDER) through the CATARINA Project (CTM2010-17141/MAR) and GRACCIE