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Culture experiments are uniquely suited for uncovering the fundamental factors controlling skeletal geochemistry because it is possible to explore conditions beyond what is found in the modern ocean and to decouple parameters that co-vary in nature. We cultured juvenile individuals of a cold-water coral (Balanophyllia elegans) in a set of experiments that decoupled carbonate chemistry parameters over a wide range of pH, DIC, and [CO32−] values. Using a multi-element mixed spike isotope dilution method we then analyzed cultured skeletons for U/Ca, which has been proposed as a potential proxy for seawater pH and [CO32−], as well as Sr/Ca, and Mg/Ca. We find that U/Ca and Sr/Ca ratios in cultured B. elegans are most strongly correlated with solution DIC and not pH or [CO32−]. We also confirm previous observations that Metal/Calcium (Me/Ca) ratios follow the same correlated relationships between and among individuals across different experimental conditions. Interpretation of these robust Me/Ca patterns within the framework of a geochemical model of biomineralization allows us to identify two “rules” of skeletal growth for B. elegans. First, changes in seawater exchange rates can explain variability in B. elegans Me/Ca ratios, correlations between these ratios, and sensitivity of Me/Ca to changes in seawater carbonate chemistry. Second, our model best fits our data if we assume that calcifying fluid pH for B. elegans remains constant across widely varying experimental seawater compositions. Our study has implications for the recently developed Sr-U paleothermometer because it refines our understanding of the environmental parameters affecting this proxy. Our model further demonstrates that U/Ca is not a robust indicator of seawater pH or [CO32−]. Instead, U/Ca may record how calcifying fluid [CO32−] responds to changes in the environment or calcification dynamics, which may be useful in evaluating how corals respond to changes like ocean acidification. Measurements of U/Ca and additional Me/Ca ratios in other coral species, evaluated within a similar framework, may elucidate how those species respond to environmental change.

International audience; Ocean acidification (OA) appears to have diverse impacts on calcareous coccolithophores, but the cellular processes underlying these responses are not well understood. Here we use stable boron and carbon isotopes, B/Ca ratios, as well as inorganic and organic carbon production rates to investigate the carbon utilization and the internal pH regulation at the site of calcification in Emiliania huxleyi, Calcidiscus leptoporus and Pleurochrysis carterae cultured over a wide pCO2 range (180–1000 μatm). Despite large variability, the geochemistry data indicate species-specific modes of pH control and differences in the utilization of inorganic carbon. Boron isotope data suggest that all three species generally upregulate the pH of the calcification fluid (pHCF) compared to surrounding seawater, which coincides with relatively constant growth rates and cellular ratios of inorganic to organic carbon. Furthermore, species exhibit different strategies in regulating their pHCF, i.e., two species maintain homeostasis (pHCF = ∼8.7), while one species shows a constant offset to the surrounding seawater (ΔpH = ∼0.6 units) over the entire tested pCO2 range. In addition to these different strategies, carbon isotope data suggests that high plasticity in the utilization of dissolved inorganic carbon might be an explanation for species-specific differences in coccolithophore responses to OA.

The Bering sea is susceptible to ocean acidification driven by both human activities (anthropogenic CO2) and distinctive natural processes. To assess the situation of ocean acidification, we investigated the spatial variability of aragonite saturation states (ΩAr) in July 2010 during the 4th Chinese National Arctic Research Expedition (CHINARE). The surface waters were all oversaturated with respect to aragonite (ΩAr > 1) due to high biological removal, and ΩAr ranged from 1.43 to 3.17. The relatively low ΩAr values were found in the western Bering Strait and eastern nearshore region of the Bering Sea Shelf, which were associated with the upwelling and riverine input, respectively. In the subsurface, the ΩAr decreased to generally low saturation states and were observed to be strongly undersaturated (ΩAr

This paper reviews the evidence on slow-onset events presented in the Special Report on Climate Change and Land (SRCCL) and the Special Report on the Ocean and Cryosphere in a Changing Climate (SROCC), both published in 2019. It analyses how the reports, and recent literature cited in them, deal with the eight types of slow-onset events, specified by the UNFCCC: increasing temperatures, sea level rise, salinization, ocean acidification, glacial retreat, land degradation, desertification and loss of biodiversity. The authors used qualitative data analysis software to analyse the reports, and for each of the SOEs, they coded and analysed information about the state, rate of change, timescale, geography, drivers, impacts, management responses, adaptation limits and residual losses and damages. The paper provides an overview of the state of the art on SOEs and helps to identify gaps and challenges in understanding the nature of SOEs, their impact and effective management approaches.

An important factor for predicting the effect of increased CO2 on future acidification of the ocean is a proper understanding of the interactions controlling production and dissolution of calcium carbonate minerals (CaCO3). The production and dissolution of CaCO3 in the ocean can be assessed over large spatial scales by measuring seawater calcium concentrations and total alkalinity (AT), yet past studies suggest that there could be large discrepancies between calcium and AT-based balances of the CaCO3 cycle in the North Pacific and Indian Oceans. Here, we analyse water column samples collected along transects in the North Pacific, Southern Ocean, tropical Indian Ocean and Red Sea for their concentrations of calcium, nutrients, and AT. We find that there is an excess calcium over AT anomaly in the top 1000 m of the tropical Indian Ocean water-column. The source of this anomaly is the dissolution of subsurface gypsum deposits in the Red Sea. We find no evidence for calcium-over-AT anomalies in the North Pacific, in contrast to previous studies. Our results show that, in most cases, calcium and AT data agree well and can be used to reconstruct the marine CaCO3 cycle.

Early Eocene hyperthermals are geologically short-lived global warming events and represent fundamental perturbations to the global carbon cycle and the Earth’s ecosystem due to massive additions of isotopically light carbon to the ocean-atmosphere system. They serve as ancient analogs for understanding how the oceanic carbonate system and surface-ocean ecosystem would respond to ongoing and future climate change. Here, we present a continuous carbonate record across the Eocene Thermal Maximum 2 (ETM2 or H1, ca. 54.1 ​Ma) and H2 (ca. 54 Ma) events from an expanded section at Ocean Drilling Program Site 1258 in tropical Atlantic. The abundant calcareous nannofossils and moderate carbonate content throughout the studied interval suggest this record was deposited above the calcite compensation depth (CCD), but below the lysocline and under the influence of terrestrial dilution. An Earth system model cGENIE is used to simulate the carbon cycle dynamics across the ETM2 and H2 to offer insights on the mechanism of the rapid warming and subsequent recovery in climate and ecosystem. The model suggests moderate changes in ocean pH (0.1–0.2 unit) for the two scenarios, biogenic methane from a rechargeable methane capacitor and organic matter oxidation from thawing of the permafrost. These pH changes are consistent with a recent independent pH estimate across the ETM2 using boron isotopes. The carbon emission flux during the ETM2 is at least an order of magnitude smaller than that during the Paleocene–Eocene Thermal Maximum (PETM) (0.015–0.05 ​Pg ​C yr−1 vs. 0.3–1.7 ​Pg ​C yr−1). The comparable pre- and post-event carbonate contents suggest the lysocline did not over deepen following the ETM2 at this tropical Atlantic site, indicating spatial heterogeneity in the carbonate system due to strong dilution influence from terrestrial weathering and riverine discharge at Site 1258.

International audience; Measurements of seawater pH on the total scale, noted pHT, contribute to the assessment of ocean acidification and its impact on the marine environment if a sufficient data quality is achieved. In order to achieve this, reference materials known as TRIS buffers (equimolal buffer of 2-Amino-2-(hydroxymethyl)-1,3-propanediol (TRIS) and TRIS hydrochloride (TRIS.HCl) in artificial seawater of salinity 35) have been developed and commercialised in the last decades. This paper describes, for the first time, the production of this reference material according to the ISO guide 35 and ISO standard 17034 guidelines that includes a thorough uncertainty budget evaluation carried out following the Guide to the expression of Uncertainty in Measurement (GUM). Characterization with Harned Cell at three temperatures as well as homogeneity and long-term stability assessments were performed and taken into account in the final uncertainty budget. The global standard uncertainty budget of the produced reference material for seawater pHT measurements is of 0.0025, 0.0024 and 0.0022 at, respectively, 15°C, 25°C and 30°C for a shelf life of six months. The level of uncertainty obtained meets the requirements of the "climate" quality objective requested by the Global Ocean Acidification Observing Network (GOA-ON) for the monitoring of ocean acidification.

Climate change is altering marine biogeochemistry, thereby modifying factors affecting the formation and trophic transfer of the bioaccumulative neurotoxicant methylmercury (MeHg) in the global ocean. However, both the directionality and magnitude of future changes are unclear. Here we use a coupled 3-D atmosphere-ocean-ecology model to forecast how MeHg concentrations in the surface ocean will respond to changes in primary production and associated carbon export in 2100. Model results suggest a 68-93% increase in MeHg in the polar oceans and a 23% decrease in the high-latitude North Atlantic Ocean. Phytoplankton MeHg reservoirs will increase at high-latitudes and decrease in the mid- and low-latitude oceans due to a poleward shift in habitat. Ocean acidification is projected to increase phytoplankton MeHg reservoirs globally by promoting the growth of Synechococcus, a small phytoplankton species that efficiently accumulates MeHg. Changes in MeHg reservoirs in herbivorous zooplankton mimic their prey but with larger magnitudes due to non-linearity embedded in the food web structure. The effect of climate-driven shifts in marine biogeochemistry thus needs to be considered in evaluating future trajectories in biological MeHg concentrations.

Prey around the world experience the risk of predation, and most have evolved constitutive and phenotypically plastic defences in response. Phenotypically plastic defences often come with trade-offs related to foraging, such that the magnitude of defence is mediated by body condition and food availability. Such adaptive responses are beneficial to prey, and there is an increasing appreciation that they can be disrupted by chemical compounds resulting from human activities. We examined predator-induced behaviours in freshwater snails (Physa acuta) using 32 combinations of different concentrations of olfactory predator cues, body condition and food availability to understand how they respond to the trade-off between avoiding predators and obtaining food. Using a subset of these conditions (16 environments), we then examined how snail responses were altered by increases or decreases in pH. We found that snails responded to increased predator cue concentrations with a shape consistent with a saturating response curve and that low body condition and low food availability weakened these responses. When we increased pH (from 7.8 to 9.5), snails exhibited weaker predator avoidance responses, but only in the absence of food. When we decreased pH (from 7.8 to 6.0), snails exhibited stronger predator avoidance responses and stronger declines in foraging, but only in the presence of food. Collectively, these results suggest that changes in pH due to acid mine drainage, eutrophication and ocean acidification may substantially alter the adaptive responses of aquatic animals. Future work should determine whether such info-disruption is common in other taxa, determine the underlying mechanisms and quantify the consequences of info-disruption to predator–prey and prey–resource interactions.

Due to decreases in seawater pH resulting from ocean acidification, permeable calcium carbonate reef sands are predicted to be net dissolving by 2050. However, the rate of dissolution and factors that control this rate remain poorly understood. Experiments performed in benthic chambers predict that reefs will become net dissolving when the aragonite saturation state (Oa) in sea water falls below similar to 3, as underlying reef sediments start net dissolution due to lower saturation states in the pore water. We used flow-through reactors to investigate the rate of dissolution at various Omega(a) at the pore scale. The sediment became net dissolving at Omega(a) = 1.68-2.25, which is significantly greater than 1. This indicates that the bulk pore water does not represent conditions at the site of dissolution, and dissolution probably occurs in microniches inside porous sand grains. Measured dissolution rates were much higher under oxic conditions than anoxic conditions, but were not affected by the addition of carbonic anhydrase. Analysis of delta C-13-CO2 produced in the flow-through reactors revealed a bias in the conventional alkalinity anomaly method under anoxic conditions, showing that some of the CO2 attributed to metabolism by may actually be derived from carbonate dissolution. This deviation likely originates from alkalinity consumption by fermentation, which masks the alkalinity generated by dissolution. Therefore, dissolution rates determined by alkalinity changes in reef sands with anaerobic metabolisms may underestimate actual values. (C) 2020 Elsevier Ltd. All rights reserved.

Ocean acidification has long been framed by its epistemic community as a problem of carbon dioxide emissions that is concurrent to climate change. Framing ocean acidification in this way has been effective at garnering policy action at the domestic level in the United States. It is argued, however, in this paper that this framing has been counterproductive at the international level, resulting in two main impediments to the international governance of this issue. Firstly, defining ocean acidification as a concurrent problem to climate change, rather than as an impact of it, has resulted in the United Nations Framework Convention on Climate Change being interpreted as containing no obligation to address ocean acidification. Secondly, focussing almost solely on the reduction of global emissions of carbon dioxide as the only global solution to ocean acidification has resulted in ocean and biodiversity-related regimes that do not have the mandate to regulate CO2 emissions as being viewed as without the recourse to respond. Through an examination of the causes and consequences of ocean acidification and the general objectives of existing multilateral environmental agreements, a set of alternative problem frames are developed in this paper that could be deployed to mobilize action under existing environmental regimes.

Climate change is expected to cause significant changes to rocky shore diversity. This study used outdoor mesocosms to test the predictions that warming and ocean acidification will alter the responses of native Trichomya hirsuta and introduced Mytilus galloprovincialis mussels, and their associated communities of infauna. Experiments consisted of orthogonal combinations of temperature (ambient 22 °C or elevated 25 °C), pCO2 (ambient 400 μatm or elevated 1000 μatm), mussel species (T. hirsuta or M. galloprovincialis), and mussel configuration (native, introduced, or both), with n = 3 replicates. Elevated pCO2 reduced the growth of T. hirsuta but not that of M. galloprovincialis, and warming and pCO2 influenced the infauna that colonised both species of mussels. There was a reduction in infaunal molluscs and an increase in polychaetes; there was, however, no effect on crustaceans. Results from this study suggest that climate-driven changes from one mussel species to another can significantly influence infaunal communities.

During the Early Toarcian, volcanic gases released by the Karoo-Ferrar large igneous province are widely believed to have caused severe environmental disturbances, including ocean acidification. Here we show records of δ Ca and δ Sr through the Early Toarcian, as recorded in three groups of biogenic calcite: Megateuthididae belemnites, Passaloteuthididae belemnites, and brachiopods of the species Soaresirhynchia bouchardi. We evaluate the data to eliminate the influence on isotopic composition of varying temperature, calcification rate, and salinity, through the section that may mask the environmental signals. Neither δ Ca nor δ Sr show negative isotope excursions across the suggested acidification interval as would be expected had acidification occurred. A profile of δ B, re-interpreted from a published study, shows no variation through the interval. Taken together, these data provide little support for ocean acidification at this time. In our belemnites, values of δ Sr are independent of temperature or Sr/Ca. For brachiopods, too few data are available to determine whether such dependences exist. Values of δ Ca show a weak temperature control of magnitude +0.020 ± 0.004 ‰/°C (2 s.d.). In belemnites, δ Ca also correlates positively with Mg/Ca and Sr/Ca. 44/40 88/86 44/40 88/86 11 88/86 44/40 44/40

This paper present the effects of ocean acidification on growth and domoic acid (DA) content of several strains of the toxic Pseudo-nitzschia australis and the non-toxic P. fraudulenta. Three strains of each species (plus two subclones of P. australis) were acclimated and grown in semi-continuous cultures at three pH levels: 8.07, 7.77, and 7.40, in order to simulate changes of seawater pH from present to plausible future levels. Our results showed that lowering pH from current level (8.07) to predicted pH level in 2100 (7.77) did not affect the mean growth rates of some of the P. australis strains (FR-PAU-17 and L3-100), but affected other strains either negatively (L3-30) or positively (L3.4). However, the growth rates significantly decreased with pH lowered to 7.40 (by 13% for L3-100, 43% for L3-30 and 16% for IFR-PAU-17 compared to the rates at pH 8.07). In contrast, growth rates of the non-toxic P. fraudulenta strains were not affected by pH changing from 8.07 to 7.40. The P. australis strains produced DA at all pH levels tested, and the highest particulate DA concentration normalized to cell abundance (pDA) was found at pH 8.07. Total DA content (pDA and dissolved DA) was significantly higher at current pH (8.07) compared to pH (7.77), exept for one strain (L 3.4) where no difference was found. At lower pH levels 7.77–7.40, total DA content was similar, except for strains IFR-PAU-17 and L3-100 which had the lowest content at the pH 7.77. The diversity in the responses in growth and DA content highlights the inter- and intra-specific variation in Pseudo-nitzschia species in response to ocean acidification. When exploring environmental responses of Pseudo-nitzschia using cultured cells, not only strain-specific variation but also culturing history should be taken into consideration, as the light levels under which the subclones were cultured, afterwards affected both maximum growth rates and DA content.

Accurate and precise marine CO2 system measurements are important for marine carbon cycle research and investigations of ocean acidification. Seawater pH is important because it can be used to characterize a wide range of chemical and biogeochemical processes. Saturation states of calcium carbonate minerals, which are directly proportional to carbonate ion concentration ([CO32-]), influence biogenic calcification and rates of carbonate dissolution. Spectrophotometric pH and carbonate ion measurements can both benefit greatly from the high sensitivity, stability, consistency and processing speed made possible through automation. Spectrophotometric methods are well-suited for shipboard, underway and in situ deployments under harsh conditions. Spectrophotometric pH measurements typically have a reproducibility of 0.0004-0.001 for shipboard and laboratory measurements and 0.0014-0.004 for in situ measurements. Shipboard spectrophotometric measurements of [CO32-] are becoming common on research expeditions. This review highlights the development of methods and instrumentation for spectrophotometric pH and [CO32-] measurements, and discusses the pros and cons of current technology. A comprehensive summary of the analytical merits of different flow analysis instruments is given. Aspects of measurement protocols that bear on the quality of pH and [CO32-] measurements, such as indicator purification, sample pretreatment, etc., are also described. Based on three decades of experience with seawater analysis, this review includes method recommendations and perspectives directly applicable or potentially applicable to pH and [CO32-] analysis of seawater.

Marine biofouling by the swiftly spreading invasive mussel (Musculista senhousia) has caused serious ecological and economic consequences in the global coastal waters. However, the fate of this highly invasive fouling species in a rapidly acidifying ocean remains unknown. Here, we demonstrated the impacts of ocean acidification within and across generations, to understand whether M. senhousia has the capacity to acclimate to changing ocean conditions. During the gonadal development, exposure of mussels to elevated pCO2 caused significant decreases of survival, growth performance and condition index, and shifted the whole-organism energy budget by inflating energy expenses to fuel compensatory processes, eventually impairing the success of spawning. Yet, rapid transgenerational acclimation occurred during the early life history stage and persisted into adulthood. Eggs spawned from CO2-exposed mussels were significantly bigger compared with those from non-CO2-exposed mussels, indicating increased maternal provisioning into eggs and hence conferring larvae resilience under harsh conditions. Larvae with a prior history of transgenerational exposure to elevated pCO2 developed faster and had a higher survival than those with no prior history of CO2 exposure. Transgenerational exposure significantly increased the number of larvae completing metamorphosis. While significant differences in shell growth were no longer observed during juvenile nursery and adult grow-out, transgenerationally exposed mussels displayed improved survival in comparison to non-transgenerationally exposed mussels. Metabolic plasticity arose following transgenerational acclimation, generating more energy available for fitness-related functions. Overall, the present study demonstrates the remarkable ability of M. senhousia to respond plastically and acclimate rapidly to changing ocean conditions.

We report high-resolution, high-precision δ44/40Ca, δ88/86Sr, and 87Sr/86Sr records spanning the Permian-Triassic boundary (PTB) from the Meishan and Dajiang carbonate successions in south China. The goal of the study was to understand the behavior of Ca and Sr isotopes during a time period in Earth history characterized by severe biological and environmental perturbations, including a major mass extinction, flood basalt volcanism, ocean acidification, and sea level fluctuations. Dajiang displays negative δ44/40Ca and δ88/86Sr excursions and invariant 87Sr/86Sr ratios in the

Ocean acidification and warming, fueled by excess atmospheric carbon dioxide, can impose stress on marine organisms. Most studies testing the effects of climate change on marine organisms, however, use extreme climate projection scenarios, despite moderate projections scenarios being most likely to occur. Here, we examined the interactive effects of warming and acidification on reproduction, respiration, mobility and metabolic composition of polyps of the Irukandji jellyfish, Carukia barnesi, to determine the responses of a cubozoan jellyfish to moderate and extreme climate scenarios in Queensland, Australia. The experiment consisted two orthogonal factors: temperature (current 25 °C and future 28 °C) and pH (current (8.0) moderate (7.9) and extreme (7.7)). All polyps survived in the experiment but fewer polyps were produced in the pH 7.7 treatment compared to pH 7.9 and pH 8.0. Respiration rates were elevated in the lowest pH treatment throughout most of the experiment and polyps were approximately half as mobile in this treatment compared to pH 7.9 and pH 8.0, regardless of temperature. We identified metabolites occurring at significantly lower relative abundance in the lowest pH (i.e. glutamate, acetate, betaine, methylguanidine, lysine, sarcosine, glycine) and elevated temperature (i.e. proline, trigonelline, creatinine, mannose, acetate, betaine, methylguanidine, lysine, sarcosine) treatments. Glycine was the only metabolite exhibiting an interactive effect between pH and temperature. Our results suggest that C. barnesi polyps are unaffected by the most optimistic climate scenario and may tolerate even extreme climate conditions to some extent.

The West Coast rock lobster (WCRL), Jasus lalandii, inhabits highly variable environments frequented by upwelling events, episodes of hypercapnia and large temperature variations. Coupled with the predicted threat of ocean acidification and temperature change for the coming centuries, the immune response in this crustacean will most likely be affected. We therefore tested the hypothesis that chronic exposure to hypercapnia and elevated seawater temperature will alter immune function of the WCRL. The chronic effects of four combinations of two stressors (seawater pCO2 and temperature) on the total number of circulating haemocytes (THC) as well as on the lobsters’ ability to clear (inactivate) an injected dose of Vibrio anguillarum from haemolymph circulation were assessed. Juvenile lobsters were held in normocapnic (pH 8.01) or hypercapnic (pH 7.34) conditions at two temperatures (15.6 and 18.9 °C) for 48 weeks (n = 30 lobster per treatment), after which a subsample of lobsters (n = 8/treatment), all at a similar moult stage, were selected from each treatment for the immune challenge. Baseline levels of haemocytes (THC ml−1) and bacteria (CFU ml−1) in their haemolymph were quantified 24 h prior to bacterial challenge. Lobsters were then challenged by injecting 4 × 104 V. anguillarum per g body weight directly into the cardiac region of each lobster and circulating haemocyte and culturable bacteria were measured at 20 min post challenge. No significant differences in THC ml−1 (p normocapnia/high temperature > normocapnia/low temperature > hypercapnia/high temperature. This study demonstrated that despite chronic exposure to combinations of reduced seawater pH and high temperature, the WCRL was still capable of rapidly rendering an injected dose of bacteria non-culturable.

The physiological consequences of exposing marine organisms to predicted future ocean scenarios, i.e. simultaneous increase in temperature and p CO 2 , have only recently begun to be investigated. Adult American lobster ( Homarus americanus ) were exposed to either current (16 °C, 47 Pa p CO 2 , pH 8.10) or predicted year 2300 (20 °C, 948 Pa p CO 2 , pH 7.10) ocean parameters for 14–16 days prior to assessing physiological changes in their hemolymph parameters as well as whole animal ammonia excretion and resting metabolic rate. Acclimation of lobster simultaneously to elevated p CO 2 and temperature induced a prolonged respiratory acidosis that was only partially compensated for via accumulation of extracellular HCO 3 – and ammonia. Furthermore, acclimated animals possessed significantly higher ammonia excretion and oxygen consumption rates suggesting that future ocean scenarios may increase basal energetic demands on H. americanus . Enzyme activity related to protein metabolism (glutamine dehydrogenase, alanine aminotransferase, and aspartate aminotransferase) in hepatopancreas and muscle tissue were unaltered in future ocean scenario exposed animals; however, muscular citrate synthase activity was reduced suggesting that, while protein catabolism may be unchanged, the net energetic output of muscle may be compromised in future scenarios. Overall, H. americanus acclimated to ocean conditions predicted for the year 2300 appear to be incapable of fully compensating against climate change-related acid-base challenges and experience an increase in metabolic waste excretion and oxygen consumption. Combining our study with past literature on H. americanus suggests that the whole lifecycle from larvae to adult stages is at risk of severe growth, survival and reproductive consequences due to climate change.

Aquatic and terrestrial organisms are being exposed to a number of anthropogenically-induced environmental stresses as a consequence of climate change. In addition, climate change is altering various linkages that exist between ecosystems on land and in water. Here we compare and contrast how climate change is altering aquatic and terrestrial environments and address some of the ways that the organisms in these ecosystems, especially the primary producers, are being affected by climate change factors, including changes in temperature, moisture, atmospheric carbon dioxide and solar UV radiation. Whereas there are some responses to climate change in common between terrestrial and aquatic ecosystems (e.g., changes in species composition and shifting geographic ranges and distributions), there are also responses that fundamentally differ between these two (e.g., responses to UV radiation). Climate change is also disrupting land-water connections in ways that influence biogeochemical and hydrologic cycles, and biosphere-atmosphere interactions in ways that can modify how aquatic and terrestrial ecosystems are affected by climate change and can influence climate change. The effects of climate change on these ecosystems are having wide-ranging effects on ecosystem biodiversity, structure and function and the abilities of these systems to provide essential services.

The impact of climate changes on corals living in naturally extreme environments is poorly understood but crucial to longer-term sustainability of coral reefs. Here we report century-long temperature (Sr/Ca and Li/Mg) and calcifying fluid (CF) carbonate chemistry (δ11B and B/Ca) records for a long-lived (1919 to 2016) Porites coral from the high thermally variable Kimberley region of northwestern Australia. We investigate how increasing temperatures and ocean acidification are manifested in the carbonate chemistry of coral's CF and impacts of climate change on calcification. Using Sr/Ca and Li/Mg multiproxy we show that annual temperature in the nearshore Kimberley exhibited a gradual increase (0.009 ± 0.003 °C/yr) from the 1920s onward. However for the most recent years (2000–2015) more rapid summer warming (0.05 ± 0.01 °C/yr) are registered, indicative of intensified warming. Despite that, we find no significant trend for calcification rate of this coral over the past century, as well as ‘normal’ seasonal variability in coral's CF carbonate chemistry. Importantly, the coral's ability to concentrate inorganic carbon seems to be affected by recent warming, with reduced DICcf observed during 2008 to 2015, while the minimally-affected pHcf acts to compensate the decreases of DICcf with the calcification rate showing only slight decrease. Additionally, we also find that ocean acidification has clearly led to the long-term reduction in the pH of the CF.

Sea urchin larvae reduce developmental rates accompanied by changes in their energy budget when exposed to acidified conditions. The necessity to maintain highly alkaline conditions in their digestive systems led to the hypothesis that gastric pH homeostasis is a key trait affecting larval energy budgets leading to distinct tipping points for growth and survival. To test this hypothesis, sea urchin (Strongylocentrotus purpuratus) larvae were reared for 10 days in different pH conditions ranging from pH 7.0 to pH 8.2. Survival, development and growth rates were determined demonstrating severe impacts < pH 7.2. To test the effects of pH on midgut alkalization we measured midgut pH and monitored the expression of acid-base transporters. While larvae were able to maintain their midgut pH at 8.9-9.1 up to an acidification level of pH 7.2, midgut pH was decreased in the lower pH treatments. The maintenance of midgut pH under low pH conditions was accompanied by dynamic changes in the expression level of midgut acid-base transporters. Metabolic rates of the larvae increased with decreasing pH and reached a threshold between pH 7.0 and pH 7.3 where metabolic rates decreased again. Methylation analyses on promoter CpG islands were performed for midgut acid-base transporter genes to test for possible epigenetic modifications after 10-day exposure to different pH conditions. This analysis demonstrated no correlation between methylation level and pH treatments suggesting low potential for epigenetic modification of acid-base transporters upon short-term exposure. Since a clear tipping point was identified at pH 7.2, which is much lower than near-future ocean acidification (OA) scenarios, this study suggests that the early development of the purple sea urchin larva has a comparatively high tolerance to seawater acidification with substantial acclimation capacity and plasticity in a key physiological trait under near-future OA conditions.

The combined effects of seawater acidification and the non-steroidal anti-inflammatory drug diclofenac on haemocyte parameters of the mussel Mytilus galloprovincialis and the clam Ruditapes philippinarum were investigated for the first time. Animals were maintained for one week (T0) in natural pH condition (8.1) and two reduced pH values (pH −0.4 units and pH −0.7 units). Bivalves were then exposed for additional 14 days (T1 and T2) to the three experimental pH values in both the presence and absence of environmentally realistic concentrations of diclofenac (0.05 and 0.50 μg/L). To assess potential impairment in immunosurveillance, haemocyte parameters (total haemocyte count, haemocyte volume and diameter, Neutral Red uptake, haemocyte proliferation and lysozyme activity) were measured after 7, 14 and 21 days of exposure to differing pH value or pH/diclofenac combinations. In both species, pH affected the whole haemocyte data set at all sampling times, influencing most of the parameters measured at T0 and T1 in clams, and at T2 in mussels. Conversely, in both species diclofenac affected the overall haemocyte response at T2 only. However, in R. philippinarum a higher number of haemocyte parameters were significantly influenced even at T1. A significant interaction between pH and diclofenac was mainly evident in mussels, affecting haemocyte size and lysozyme activity at both T1 and T2. Overall, the results obtained demonstrated that the experimental conditions tested can alter markedly haemocyte parameters in marine bivalves.

Diatoms and other phytoplankton groups are exposed to abrupt changes in pCO2, in waters in upwelling areas, near CO2 seeps, or during their blooms; or to more gradual pCO2 rise through anthropogenic CO2 emissions. Gradual CO2 rises have, however, rarely been included in ocean acidification (OA) studies. We therefore compared how small (Thalassiosira pseudonana) and larger (Thalassiosira weissflogii) diatom cell isolates respond to gradual pCO2 rises from 180 to 1000 μatm in steps of ~40 μatm with 5–10 generations at each step, and whether their responses to gradual pCO2 rise differ when compared to an abrupt pCO2 rise imposed from ambient 400 directly to 1000 μatm. Cell volume increased in T. pseudonana but decreased in T. weissflogii with an increase from low to moderate CO2 levels, and then remained steady under yet higher CO2 levels. Growth rates were stimulated, but Chl a, particulate organic carbon (POC) and cellular biogenic silica (BSi) decreased from low to moderate CO2 levels, and then remained steady with further CO2 rise in both species. Decreased saturation light intensity (Ik) and light use efficiency (α) with CO2 rise in T. pseudonana indicate that the smaller diatom becomes more susceptible to photoinhibition. Decreased BSi/POC (Si/C) in T. weissflogii indicates the biogeochemical cycles of both silicon and carbon may be more affected by elevated pCO2 in the larger diatom. The different CO2 modulation methods resulted in different responses of some key physiological parameters. Increasing pCO2 from 180 to 400 μatm decreased cellular POC and BSi contents, implying that ocean acidification to date has already altered diatom contributions to carbon and silicon biogeochemical processes.

The effects of ocean acidification, a major anthropogenic impact on marine life, have been mainly investigated in laboratory/mesocosm experiments. We used the CO2 vents at Ischia as a natural laboratory to study the long-term effects of ocean acidification on the sea urchin Paracentrotus lividus population resident in low-pH (7.8 ± 0.2) compared to that at two control sites (pH 8.02 ± 0.00; 8.02 ± 0.01). The novelty of the present study is the analysis of the sea urchin immune cells, the sentinels of environmental stress responses, by a wide-ranging approach, including cell morphology, biochemistry and proteomics. Immune cell proteomics showed that 311 proteins were differentially expressed in urchins across sites with a general shift towards antioxidant processes in the vent urchins. The vent urchin immune cells showed higher levels of total antioxidant capacity, up-regulation of phagosome and microsomal proteins, enzymes of ammonium metabolism, amino-acid degradation, and modulation of carbon metabolism proteins. Lipid-hydroperoxides and nitric oxide levels were not different in urchins from the different sites. No differences in the coelomic fluid pH, immune cell composition, animal respiration, nitrogen excretion and skeletal mineralogy were observed. Our results reveal the phenotypic plasticity of the immune system of sea urchins adapted to life at vent site, under conditions commensurate with near-future ocean acidification projections.

Ocean acidification (OA) has the potential to alter the bioavailability of pH sensitive metals contaminating coastal sediments, particularly copper, by changing their speciation in seawater. Hence OA may drive increased toxicity of these metals to coastal biota. Here, we demonstrate complex interactions between OA and copper on the physiology and toxicity responses of the sediment dwelling polychaete Alitta virens. Worm coelomic fluid pCO2 was not increased by exposure to OA conditions (pHNBS 7.77, pCO2 530 μatm) for 14 days, suggesting either physiological or behavioural responses to control coelomic fluid pCO2. Exposure to 0.25 μM nominal copper caused a decrease in coelomic fluid pCO2 by 43.3% and bicarbonate ions by 44.6% but paradoxically this copper-induced effect was reduced under near-future OA conditions. Hence OA appeared to ‘buffer’ the copper-induced acid-base disturbance. DNA damage was significantly increased in worms exposed to copper under ambient pCO2 conditions, rising by 11.1% compared to the worms in the no copper control, but there was no effect of OA conditions on the level of DNA damage induced by copper when exposed in combination. These interactions differ from the increased copper toxicity under OA conditions reported for several other invertebrate species. Hence this new evidence adds to the developing paradigm that species’ physiology is key in determining the interactions of these two stressors rather than it purely being driven by the changes in metal chemistry under lower seawater pH.

The fossil record is the primary source of data used to study predator-prey interactions in deep time and to evaluate key questions regarding the evolutionary and ecological importance of predation. Here, we review the types of paleontological data used to infer predation in the marine fossil record, discuss strengths and limitations of paleontological lines of evidence used to recognize and evaluate predatory activity, assess the influence of environmental gradients on predation patterns, and review fossil evidence for predator behavior and prey defense. We assembled a predation database from the literature that documents a steady increase in the number of papers on predation since the 1960s. These studies have become increasingly quantitative and have expanded in focus from reporting cases of predation documented by fossils to using the fossil record of predation to test ecological and evolutionary hypotheses. The data on the fossil record of predation amassed so far in the literature primarily come from trace fossils, mostly drill holes and, to a lesser extent, repair scars, derived predominantly from the Cenozoic of Europe and North America. Mollusks are the clade most often studied as prey and inferred predators. We discuss how to distinguish biotic from abiotic damage and predatory from parasitic traces, and how to recognize failed predation. Our data show that identifying the predator is easiest when predator and prey are preserved in the act of predation or when predators were fossilized with their gut contents preserved. However, determining the culprits responsible for bite traces, drill holes, and other types of predation traces can be more problematic. Taphonomic and other factors can distort patterns of predation, but their potential effects can be minimized by careful study design. With the correct identification and quantification of fossilized traces of predation, ecological trends in predator-prey interactions may be discerned along environmental gradients in water depth, habitat, and oxygen and nutrient availability. However, so far, these trends have not been explored adequately for the fossil record. We also review the effects of climate change and ocean acidification on predator-prey interactions, but, again, few studies consider those factors from a deep-time perspective. Finally, fossils have been used successfully to infer the behavior of ancient predators and identify and interpret active and passive defense strategies employed by their prey. The marine fossil record of predation has become a major field of research over the last 50 years, but many critical gaps remain in our understanding of the evolutionary history of predator-prey interactions.

The carbonate system is a vital buffering system that controls the pH of seawater and maintains a healthy environment for marine organisms. As concerns regarding the fate of anthropogenic CO2 in the oceans are rising, it is becoming increasingly urgent to systematically quantify and understand this system's parameters, particularly in heavily human-impacted areas, such as the Mediterranean Sea. To date, the paucity of time-series stations adopted to monitor the carbonate system in this sea has precluded characterizing the region at an adequate spatial resolution. Here, we present and study the seasonal and annual variability and drivers of the first carbonate system dataset collected for the Lebanese waters, monthly at the upper 80 m between 2012 and 2017 in two time-series stations offshore the North of Lebanon-Levantine Sub-basin, Eastern Mediterranean Sea. Annual trends were calculated for the non-adjusted and the adjusted carbonate system parameters (an adjustment that reduces the influence of simple-dilution-concentration [SDC] processes on the trends). Our results show high carbonate system inventory [total alkalinity (AT), total dissolved inorganic carbon (CT), and pH] compared to other Mediterranean areas. The obtained trends reflect increasing rates for both AT and CT, only significant at surface for CT (+5 ± 2 μmol kg−1.yr−1; p Highlights • The first carbonate system dataset collected for the Lebanese waters, -Levantine Sub-basin, Eastern Mediterranean Sea, are presented in this study. • Our results show high carbonate system inventory compared to other Mediterranean areas with increasing rates of both AT and CT. • Annual acidification rates have been document (i.e. from −0.009 ± 0.004 to −0.0021 ± 0.001 pH units.yr−1 at 0 m and in the upper 80 m respectively for pHT25adj. • Decreasing trends of the saturation states for both CaCO3 minerals were calculated. • Simple-dilution-concentration processes, together with CO2 release/invasion and the active overturning circulation, are controlling this system in our study area. • The increasing trend of total alkalinity may be buffering the observed acidification rate, which could have been worst in case AT in our area was lower.

This study investigates the immediate and mid-term effects of the biogeochemical variables input into the Reloncavi fjord (41°40′S; 72°23′O) as a result of the eruption of Calbuco volcano. Reloncavi is an estuarine system supporting one of the largest mussels farming production within Northern Chilean-Patagonia. Field-surveys were conducted immediately after the volcanic eruption (23–30 April 2015), one month (May 2015), and five months posterior to the event (September 2015). Water samples were collected from three stations along the fjord to determine greenhouse gases [GHG: methane (CH4), nitrous oxide (N2O)], nutrients [NO3−, NO2−, PO43−, Si(OH)4, sulphate (SO42−)], and carbonate systems parameters [total pH (pHT), temperature, salinity, dissolved oxygen (O2), and total alkalinity (AT)]. Additionally, the impact of physicochemical changes in the water column on juveniles of the produced Chilean blue mussel, Mytilus chilensis, was also studied. Following the eruption, a large phytoplankton bloom led to an increase in pHT, due to the uptake of dissolved-inorganic carbon in photic waters, potentially associated with the runoff of continental soil covered in volcanic ash. Indeed, high surface SO42− and GHG were observed to be associated with river discharges. No direct evidence of the eruption was observed within the carbonate system. Notwithstanding, a vertical pattern was observed, with an undersaturation of aragonite (ΩAr 10 m), and saturated values in subsurface waters (3 to 7 m). Simultaneously, juvenile mussel shells showed maximized length and weight at 4 m depth. Results suggest a localized impact of the volcanic eruption on surface GHG, nutrients and short-term effects on the carbonate system. Optimal conditions for mussel calcification were identified within a subsurface refuge in the fjord. These specific attributes can be integrated into adaptation strategies by the mussel aquaculture industry to confront ocean acidification and changing runoff conditions.

A solid understanding of global oceanic change throughout Holocene time is needed to contextualize and interpret recent observations of rapid warming (Moore, 2016), ocean acidification (Popova et al., 2014; Qi et al., 2017), increasing meltwater input (Halfar et al., 2013; Notz and Stroeve, 2016) and circulation changes (Liu et al., 2017; Rahmstorf et al., 2015; Yang et al., 2016) in the Arctic and subarctic Oceans. Precisely reconstructing acidification and temperature variations throughout the Holocene will provide a vital context for interpreting current environmental changes and future climate projections in the region. However, existing paleoenvironmental reconstructions are sparse and uncertain, largely owing to limited availability of high fidelity paleoceanographic archives, such as marine carbonates, in high latitude waters. Coralline algae of the genus Clathromorphum have emerged as key candidates for reconstructing high-latitude environmental variability at annual to sub-annual resolution. Here, we present the first empirical calibrations of boron isotope-pH and Mg/Li-temperature relationships within the long-lived, crustose coralline red alga Clathromorphum compactum. Calibration experiments were performed in triplicate, growing wild-collected specimens for four months at three controlled temperatures (6.4 – 12.4 oC) and four pCO2 conditions (352 - 3230 ppm), to test the effects of these environmental parameters on the isotopic and elemental composition of the algal skeleton. We find that boron isotopes within the skeleton of C. compactum (δ11Bcc) are well correlated with δ11B of seawater borate (δ11Βborate), defining the following equation: δ11Βcc (2σ) = 1.46 (0.06) δ11Βborate + 6.91 (0.72). This equation can be used to reconstruct δ11Βborate of the coralline alga’s ambient seawater, from which past seawater pH can be calculated. We also identified a strong correlation between skeletal Mg/Li ratio and seawater temperature, defined by the equation: Mg/Li (2σ) = 0.17 (0.02) temperature (oC) + 1.02 (0.16). Therefore, despite the strong biological control that this species appears to exert on calcification site pH (elevated 1.0-1.6 pH units above seawater pH, inferred from δ11Bcc > δ11Βborate), and the apparent relationship between skeletal extension rate and skeletal Li/Ca and Mg/Ca, the δ11Bcc and Mg/Li ratios of the coralline alga’s skeleton strongly and significantly respond to ambient seawater pH and temperature, respectively. These results support the use of δ11B and Mg/Li within C. compactum for pH and temperature reconstructions of northern high-latitude oceans.

Measurements of dissolved methane (CH4) and carbonate system parameters were conducted in shelf and slope waters off Baffin Island and northern Labrador during September 2012 and August 2016 in order to investigate potential cold seeps and their influence on the marine carbonate system. Evidence of a strong near-bottom methane source was found at two sites along the Baffin Island Shelf (Scott Inlet and Cape Dyer) and above a pair of reported sea floor mounds in the Saglek Basin between Baffin Island and northern Labrador. Stable carbon isotope measurements of dissolved methane made at the Cape Dyer site give an estimated δ13C value of −71.2‰ for the source, consistent with microbial methanogenesis. The distributions of pCO2, pH and aragonite and calcite saturation states showed no evidence of enhanced ocean acidification in the vicinity of these sites, so it would seem that these seeps were not significant local sources of carbon dioxide, either as a component in the seep fluid or produced subsequent to release by water column microbial methane oxidation, nonetheless, aragonite saturation states of one or less were seen along the Baffin Island Shelf suggesting that ecosystems here may be vulnerable to further acidification. Spectrophotometric pH measurements of fresh samples in 2012 revealed a bottom water spike in pH at two seep sites that were not replicated by measurements of preserved seawater samples. We hypothesise that this was due to an unstable anionic compound present in seep fluid that can locally increase total alkalinity, pH and calcium carbonate saturation with HS− being a likely candidate, possibly to the benefit of calcifying organisms in an environment bordering on aragonite under-saturation.

Ocean acidification (OA) is already impacting marine organisms and may fundamentally alter marine ecosystems in the coming decades, with major implications for ocean services, such as food provision. Though OA is an emerging concern in coastal zone management, current actions are limited to monitoring and knowledge production. This article presents a framework for addressing coastal zone OA in local-level policy agendas through workshops, and lessons learned and outcome from the implementation of this framework in two cases in southern and northern Norway. The framework includes four components: 1) facilitating knowledge exchange and identify challenges and opportunities relating to OA; 2) ensuring legitimacy of new knowledges; 3) building capacity through learning and skill development; and 4) raise awareness about OA among local decisionmakers. The case studies include local and regional coastal zone management stakeholders and, using OA measurements and modelling, illustrate co-production of new knowledge of coastal ocean acidification and its potential local impacts. Through two rounds of workshops, we demonstrate that the level of OA awareness markedly increases among stakeholders. This awareness manifests in vocal interest for looming projected impacts and their necessary mitigative measures. This concern is compounded by stakeholders who recognize that OA should be treated as a component of water-quality, implying that OA is gaining salience as a local policy issue. However, it is evident that local management faces challenges in addressing such an issue, combined with expectations that higher levels of government take responsibility for mitigative and adaptive actions in response to OA.

CO2 atmospheric pressure is increasing since industrial revolution, leading to a lowering of the ocean surface water pH, a phenomenon known as ocean acidification, with several reported effects on individual species and cascading effects on marine ecosystems. Despite the great amount of literature on ocean acidification effects on calcifying organisms, the response of their reproductive system still remains poorly known. In the present study, we investigated the histopathological effects of low pH on the gonads of three key macroinvertebrates of the Terra Nova Bay (Ross Sea) littoral area: the sea urchin Sterechinus neumayeri, the sea star Odontaster validus and the scallop Adamussium colbecki. After 1 month of exposure at control (8.12) and reduced (7.8 and 7.6) pH levels, we dissected the gonads and performed histological analyses to detect potential differences among treatments. Results showed significant effects on reproductive conditions of A. colbecki and S. neumayeri, while O. validus did not show any kind of alteration. Present results reinforce the need to focus on ocean acidification effects on soft tissues, particularly the gonads, whose damage may exert large effects on the individual fitness, with cascading effects on the population dynamic of the species.

Ocean acidification and warming represent major environmental threats to kelp mariculture. In this study, sporophytic photochemical efficiency and gametophytic growth of Saccharina japonica and Undaria pinnatifida were evaluated under different pCO2 levels (360, 720, and 980 ppmv) and temperatures (5, 10, 15, and 20 °C for sporophytes; 15 and 20 °C for gametophytes). Sporophytic photochemical efficiencies of both kelps were significantly greater at 720 ppmv than at 360 and 980 ppmv. Female gametophytes of both kelps grew significantly better at 360 ppmv than at higher pCO2 levels. The growth of U. pinnatifida gametophytes was significantly greater at 20 °C than at 15 °C, while no significant difference was observed for the growth of S. japonica. These results indicate that increased pCO2 stimulated sporophytic photochemical efficiency while inhibited gametophytic growth of these kelps, which might negatively affect their seedling cultivation. U. pinnatifida exhibited higher productivity in warmer ocean than S. japonica.

Mangrove soil carbon stocks are known to decrease following forest loss due to respiration and enhanced soil CO2 emissions. However, changes in carbon outwelling to the coastal ocean due to mangrove forest disturbance have not been considered. In December 2015, an extremely large mangrove dieback event (∼7000 hectares, spanning 1000 km of coastline) occurred in the Gulf of Carpentaria, Australia. To assess the effect this dieback event had on carbon outwelling, we used radium isotopes and dissolved carbon measurements (dissolved organic carbon, DOC, dissolved inorganic carbon, DIC, and total alkalinity, TAlk) to estimate cross-shelf carbon transport from living and dead mangrove areas and to calculate the carbon losses from living and dead forest soils via SGD. Radium distributions imply cross shelf eddy diffusivity of 107.5 ± 26.9 and 104.6 ± 23.9 m−2 s−1 from dead and living areas and radium water ages reveal that mangrove carbon reaches 10 km offshore within 7 days. Outwelling rates from living and dead areas were explained by soil carbon losses via SGD. This study suggests a decrease in carbon outwelling to the ocean from dead forest areas compares to living areas by 0–12% for DOC, 50–52% for DIC and by 37–51% for TAlk ∼8 months after the dieback event occurred. Changes to oceanic carbon outwelling rates following mangrove loss are likely driven by a gradual depletion of carbon stocks from the sediment profile.

We aimed to show how the predicted pH decrease in the ocean would alter the toxicity, bioconcentration and dietary transfer of trace metal copper on seagrass ecosystems, on a short-term basis. Seagrass Zostera noltei was exposed to two pH levels (8.36 and 8.03) and three copper levels (nominal concentrations, < 3, 30 and 300 mu g Cu L-1) in a factorial design during 21 days, while Gammarus Iocusta amphipods were continuously fed with the treated seagrass leaves. We found that the toxicity and bioconcentration of copper in seagrasses were not affected by pH, yet complex copper-pH interactions were observed in the seagrass photosynthesis. We demostrated that seagrasses can act as a copper source in the food web via direct consumption by herbivores. Future research need to investigate the interactive effects on a long-term basis, and to include biochemical and molecular endpoints to provide additional insights to the complex phisiological interactions observed. project "Ecological risk assessment of oils and hazardous and noxious substances in the NW Portuguese coast (ECORISK)" - North Portugal Regional Operational Programme (ON.2-O Novo Norte), under the National Strategic Reference Framework (NSRF) [NORTE-07-0124-FEDER-000054] European Regional Development Fund (ERDF)European Union (EU) Portuguese Science and Technology FoundationPortuguese Foundation for Science and Technology [SFRH/BPD/119344/2016, SFRH/BPD/77912/2011] ARCOPOL plus - Improving maritime safety and pollution response through technology transfer, training & innovation project [2011-1/150]

One of the effects of the atmospheric CO2 increase is ocean acidification. Over the past 20 years, accurate measurements of the seawater carbonate system have become a high priority because this is the main system controlling seawater acidity. However, this phenomenon has not been widely studied in estuaries, even if they are among the most productive natural habitats in the world, lodging some of the highest biotic diversity and production. Due to that lack of information, this work aims to develop and discuss new strategies for the determination of total alkalinity (TA), one of the most measured parameters in the study of acidification, in estuarine waters in the wide range of salinities that can be found in these systems. For that purpose, a new set of stability constants for the carbonate system was established and compared with those most widely used up to date. For the determination of TA, different approaches were studied for the data treatment of the potentiometric titration data.

In response to the accelerating processes of marine natural gas hydrate exploration and gas production from hydrate-bearing sediments, their potential impacts on the environment have been attracting extensive attention from international academia as well as from industry, especially in recent years. Methane seeps related to gas hydrate degradation on the seafloor are ubiquitous on continental slopes in both active and passive continental margins. A previous series of articles suggest that hydrate dissociation (gas release or ebullition at large scale) mainly occurs as a result of faulting or decreased lithostatic pressure triggered by many external driving forces (mainly including tectonic activities, overpressure zone, earthquake and tides), and temperature change. These frequently affect methane inputs into the atmosphere, fueling seafloor oxygen consumption or ocean acidification, and even posing submarine geohazards. Gas hydrate-related areas are usually estimated from indirect biochemical indications (cold-seep communities, element and isotopic anomalies in pore water) and geophysical indications (surface morphology, gas plumes and pathways). Therefore, appropriate application of monitoring and detection methods is of crucial significance for assessing the temporal and spatial variability of related environmental indicators in gas hydrate reservoirs. Monitoring is also as an essential support for harvesting this potential alternative energy in ways that are safer, more economical, and more environmentally friendly. Following the three structural elements of a hydrocarbon seep pumping system (gas/fluid source, fluid migration pathway, and seeping structures at or near the seafloor), this paper sets forth the significance of indicators for dynamics resulting from the destabilization of reservoirs of natural gas hydrates, reviews the corresponding monitoring or detection methods and integrated monitoring systems; and especially, expatiates the in situ observation networks regarding gas hydrate reservoirs and gas hydrate production tests. In the closing section, we discuss and draw conclusions regarding the challenges for future development of hydrate environmental monitoring and significant environmental issues requiring special attention. We intend this paper to provide references and to set the scene for future research activities about gas hydrates, so as to ignite the interest of more research groups around the world.

With increasing levels of atmospheric pCO2 the oceans are becoming progressively more acidic, with the impact of a lowered pH beginning to affect the calcification of numerous invertebrate groups, including foraminifers, pteropods, heteropods and calcareous nannoplankton. Research on the ecology of foraminifera in the Mediterranean Sea, Gulf of California, Caribbean Sea and elsewhere has shown how modern assemblages are responding to acidification. Experimental work in mesocosms and laboratory cultures are also adding to our knowledge of the response to pH changes. Near Ischia (Italy), natural CO2 vents amongst sea grass meadows are creating low pH environments in which it is possible to observe the response of benthic foraminifera. At a pH of 7.8 the foraminiferal assemblages are already becoming less diverse and below pH 7.6 there are often no calcite-secreting benthic foraminifera. In the Gulf of California, in a deeper-water setting, natural CO2 (and methane) vents are also lowering sea floor pH. The foraminifera show the impact of this change, although the relatively high carbonate saturation ensures that calcite-secreting foraminifers are able to live and reproduce in these relatively low pH environments, only becoming impacted by dissolution effects once dead. Using data from the Cretaceous–Paleogene boundary in Texas, Alabama and north-west Europe it is clear that the plankton was severely impacted by surface water acidification while the relatively shallow water benthic foraminifera show little change and no visible signs of post-mortem dissolution due to ocean acidification.

The boron (B) isotope-pH proxy for marine carbonates has been widely used to reconstruct past ocean pH values. Unlike seawater, the apparent dissociation constant of boric acid (KB) and the δ11B values of brines from the terrestrial salt lakes in western China vary. However, relevant studies concerning the B isotope geochemistry of brine-carbonate systems in terrestrial salt lakes are limited. In this study, thirty-nine clastic samples from a sediment core (ISL1A) from the Qarhan Salt Lake in the Qaidam Basin were collected. These carbonates were analyzed for δ11B, B, Mg, Sr and Ca. Using our new data as well as published pH values, total dissolved solids (TDS), element concentrations, and δ11B values of brines in western China, we reached the following conclusions. (1) During evaporation process, salinity increases, the δ11B values of brines in salt lakes increase, and the pKB (−logKB) and pH values simultaneously decrease. (2) The large heterogeneity in the δ11B values of the carbonates (−2.74‰ to +7.64‰) from core ISL1A is mainly due to the δ11B values of the brines, rather than pKB and pH. (3) B isotopic fractionation with a small αcarbonate-brine of 0.997 in a brine-carbonate system conforms to the Rayleigh fractionation model. (4) Our comparison of the δ11B values of these carbonates with other records from core ISL1A suggests that the δ11B values of the carbonates in the arid Qaidam Basin can be used as a new proxy for the salinity of paleo-lake water.