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Anthropogenic stressors can alter the structure and functioning of infaunal communities, which are key drivers of the carbon cycle in marine soft sediments. Nonetheless, the compounded effects of anthropogenic stressors on carbon fluxes in soft benthic systems remain largely unknown. Here, we investigated the cumulative effects of ocean acidification (OA) and hypoxia on the organic carbon fate in marine sediments, through a mesocosm experiment. Isotopically labelled macroalgal detritus ( 13 C) was used as a tracer to assess carbon incorporation in faunal tissue and in sediments under different experimental conditions. In addition, labelled macroalgae ( 13 C), previously exposed to elevated CO 2 , were also used to assess the organic carbon uptake by fauna and sediments, when both sources and consumers were exposed to elevated CO 2 . At elevated CO 2 , infauna increased the uptake of carbon, likely as compensatory response to the higher energetic costs faced under adverse environmental conditions. By contrast, there was no increase in carbon uptake by fauna exposed to both stressors in combination, indicating that even a short-term hypoxic event may weaken the ability of marine invertebrates to withstand elevated CO 2 conditions. In addition, both hypoxia and elevated CO 2 increased organic carbon burial in the sediment, potentially affecting sediment biogeochemical processes. Since hypoxia and OA are predicted to increase in the face of climate change, our results suggest that local reduction of hypoxic events may mitigate the impacts of global climate change on marine soft-sediment systems., (© 2019 John Wiley & Sons Ltd.)

A 21-year time series of phytoplankton community structure was analysed in relation to Phaeocystis spp. to elucidate its contribution to the annual carbon budget at station L4 in the western English Channel (WEC). Between 1993-2014 Phaeocystis spp. contributed ∼4.6% of the annual phytoplankton carbon and during the March - May spring bloom, the mean Phaeocystis spp. biomass constituted 17% with a maximal contribution of 47% in 2001. Upper maximal weekly values above the time series mean ranged from 63 to 82% of the total phytoplankton carbon (∼42-137mg carbon (C)m -3 ) with significant inter-annual variability in Phaeocystis spp. Maximal biomass usually occurred by the end of April, although in some cases as early as mid-April (2007) and as late as late May (2013). The effects of elevated pCO 2 on the Phaeocystis spp. spring bloom were investigated during a fifteen-day semi-continuous microcosm experiment. The phytoplankton community biomass was estimated at ∼160mgCm -3 and was dominated by nanophytoplankton (40%, excluding Phaeocystis spp.), Phaeocystis spp. (30%) and cryptophytes (12%). The smaller fraction of the community biomass comprised picophytoplankton (9%), coccolithophores (3%), Synechococcus (3%), dinoflagellates (1.5%), ciliates (1%) and diatoms (0.5%). Over the experimental period, total biomass increased significantly by 90% to ∼305mgCm -3 in the high CO 2 treatment while the ambient pCO 2 control showed no net gains. Phaeocystis spp. exhibited the greatest response to the high CO 2 treatment, increasing by 330%, from ∼50mgCm -3 to over 200mgCm -3 and contributing ∼70% of the total biomass. Taken together, the results of our microcosm experiment and analysis of the time series suggest that a future high CO 2 scenario may favour dominance of Phaeocystis spp. during the spring bloom. This has significant implications for the formation of hypoxic zones and the alteration of food web structure including inhibitory feeding effects and lowered fecundity in many copepod species., (Crown Copyright © 2017. Published by Elsevier B.V. All rights reserved.)

The geological storage of carbon dioxide (CO2) is expected to be an important component of future global carbon emission mitigation, but there is a need to understand the impacts of a CO2 leak on the marine environment and to develop monitoring protocols for leakage detection. In the present study, sediment cores were exposed to CO2-acidified seawater at one of five pH levels (8.0, 7.5, 7.0, 6.5 and 6.0) for 10 weeks. A bloom of Spirulina sp. and diatoms appeared on sediment surface exposed to pH 7.0 and 7.5 seawater. Quantitative PCR measurements of the abundance of 16S rRNA also indicated an increase within the pH 7.0 and 7.5 treatments after 10 weeks incubation. More detailed analysis of the microbial communities from the pH 7.0, 7.5 and 8.0 treatments confirmed an increase in the relative abundance of Spirulina sp. and Navicula sp. sequences, with changes in the relative abundance of major archaeal and bacterial groups also detected within the pH 7.0 treatment. A decreased flux of silicate from the sediment at this pH was also detected. Monitoring blooms of microphytobenthos may prove useful as an indicator of CO2 leakage within coastal areas., (© FEMS 2015. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The Arctic Ocean already experiences areas of low pH and high CO2, and it is expected to be most rapidly affected by future ocean acidification (OA). Copepods comprise the dominant Arctic zooplankton; hence, their responses to OA have important implications for Arctic ecosystems, yet there is little data on their current under-ice winter ecology on which to base future monitoring or make predictions about climate-induced change. Here, we report results from Arctic under-ice investigations of copepod natural distributions associated with late-winter carbonate chemistry environmental data and their response to manipulated pCO2 conditions (OA exposures). Our data reveal that species and life stage sensitivities to manipulated OA conditions were correlated with their vertical migration behavior and with their natural exposures to different pCO2 ranges. Vertically migrating adult Calanus spp. crossed a pCO2 range of >140 μatm daily and showed only minor responses to manipulated high CO2. Oithona similis, which remained in the surface waters and experienced a pCO2 range of <75 μatm, showed significantly reduced adult and nauplii survival in high CO2 experiments. These results support the relatively untested hypothesis that the natural range of pCO2 experienced by an organism determines its sensitivity to future OA and highlight that the globally important copepod species, Oithona spp., may be more sensitive to future high pCO2 conditions compared with the more widely studied larger copepods.

Some planktonic groups suffer negative effects from ocean acidification (OA), although copepods might be less sensitive. We investigated the effect of predicted CO2 levels (range 480-750ppm), on egg production and hatching success of two copepod species, Centropages typicus and Temora longicornis. In these short-term incubations there was no significant effect of high CO2 on these parameters. Additionally a very high CO2 treatment, (CO2=9830ppm), representative of carbon capture and storage scenarios, resulted in a reduction of egg production rate and hatching success of C. typicus, but not T. longicornis. In conclusion, reproduction of C. typicus was more sensitive to acute elevated seawater CO2 than that of T. longicornis, but neither species was affected by exposure to CO2 levels predicted for the year 2100. The duration and seasonal timing of exposures to high pCO2, however, might have a significant effect on the reproduction success of calanoid copepods., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Further steps are needed to establish feasible alleviation strategies that are able to reduce the impacts of ocean acidification, whilst ensuring minimal biological side-effects in the process. Whilst there is a growing body of literature on the biological impacts of many other carbon dioxide reduction techniques, seemingly little is known about enhanced alkalinity. For this reason, we investigated the potential physiological impacts of using chemical sequestration as an alleviation strategy. In a controlled experiment, Carcinus maenas were acutely exposed to concentrations of Ca(OH)2 that would be required to reverse the decline in ocean surface pH and return it to pre-industrial levels. Acute exposure significantly affected all individuals' acid-base balance resulting in slight respiratory alkalosis and hyperkalemia, which was strongest in mature females. Although the trigger for both of these responses is currently unclear, this study has shown that alkalinity addition does alter acid-base balance in this comparatively robust crustacean species., (Copyright © 2013 Elsevier Ltd. All rights reserved.)

Surface ocean carbon dioxide (CO2) measurements are used to compute the oceanic air–sea CO2 flux. The CO2 flux component from rivers and estuaries is uncertain due to the high spatial and seasonal heterogeneity of CO2 in coastal waters. Existing high-quality CO2 instrumentation predominantly utilises showerhead and percolating style equilibrators optimised for open-ocean observations. The intervals between measurements made with such instrumentation make it difficult to resolve the fine-scale spatial variability of surface water CO2 at timescales relevant to the high frequency variability in estuarine and coastal environments. Here we present a novel dataset with unprecedented frequency and spatial resolution transects made at the Western Channel Observatory in the south-west of the UK from June to September 2016, using a fast-response seawater CO2 system. Novel observations were made along the estuarine–coastal continuum at different stages of the tide and reveal distinct spatial patterns in the surface water CO2 fugacity (fCO2) at different stages of the tidal cycle. Changes in salinity and fCO2 were closely correlated at all stages of the tidal cycle and suggest that the mixing of oceanic and riverine endmembers partially determines the variations in fCO2. The correlation between salinity and fCO2 was different in Cawsand Bay, which could be due to enhanced gas exchange or to enhanced biological activity in the region. The observations demonstrate the complex dynamics determining spatial and temporal patterns of salinity and fCO2 in the region. Spatial variations in observed surface salinity were used to validate the output of a regional high-resolution hydrodynamic model. The model enables a novel estimate of the air–sea CO2 flux in the estuarine–coastal zone. Air–sea CO2 flux variability in the estuarine–coastal boundary region is influenced by the state of the tide because of strong CO2 outgassing from the river plume. The observations and model output demonstrate that undersampling the complex tidal and mixing processes characteristic of estuarine and coastal environment biases quantification of air–sea CO2 fluxes in coastal waters. The results provide a mechanism to support critical national and regional policy implementation by reducing uncertainty in carbon budgets. [ABSTRACT FROM AUTHOR]

The combined effects of elevated pCO2 and temperature were investigated during an experimentally induced autumn phytoplankton bloom in vitro sampled from the western English Channel (WEC). A full factorial 36-day microcosm experiment was conducted under year 2100 predicted temperature (+4.5 °C) and pCO2 levels (800 μatm). Over the experimental period total phytoplankton biomass was significantly influenced by elevated pCO2. At the end of the experiment, biomass increased 6.5-fold under elevated pCO2 and 4.6-fold under elevated temperature relative to the ambient control. By contrast, the combined influence of elevated pCO2 and temperature had little effect on biomass relative to the control. Throughout the experiment in all treatments and in the control, the phytoplankton community structure shifted from dinoflagellates to nanophytoplankton . At the end of the experiment, under elevated pCO2 nanophytoplankton contributed 90% of community biomass and was dominated by Phaeocystis spp. Under elevated temperature, nanophytoplankton comprised 85% of the community biomass and was dominated by smaller nanoflagellates. In the control, larger nanoflagellates dominated whilst the smallest nanophytoplankton contribution was observed under combined elevated pCO2 and temperature (~40 %). Under elevated pCO2, temperature and in the control there was a significant decrease in dinoflagellate biomass. Under the combined effects of elevated pCO2 and temperature, dinoflagellate biomass increased and was dominated by the harmful algal bloom (HAB) species, Prorocentrum cordatum. At the end of the experiment, chlorophyll a (Chl a) normalised maximum photosynthetic rates (PmB) increased >6- fold under elevated pCO2 and >3-fold under elevated temperature while no effect on PmB was observed when pCO2 and temperature were elevated simultaneously. The results suggest that future increases in temperature and pCO2 simultaneously do not appear to influence coastal phytoplankton productivity but significantly influence community composition during autumn in the WEC. [ABSTRACT FROM AUTHOR]

The geological storage of carbon dioxide (CO2) is expected to be an important component of future global carbon emission mitigation, but there is a need to understand the impacts of a CO2 leak on the marine environment and to develop monitoring protocols for leakage detection. In the present study, sediment cores were exposed to CO2-acidified seawater at one of five pH levels (8.0, 7.5, 7.0, 6.5 and 6.0) for 10 weeks. A bloom of Spirulina sp. and diatoms appeared on sediment surface exposed to pH 7.0 and 7.5 seawater. Quantitative PCR measurements of the abundance of 16S rRNA also indicated an increase within the pH 7.0 and 7.5 treatments after 10 weeks incubation. More detailed analysis of the microbial communities from the pH 7.0, 7.5 and 8.0 treatments confirmed an increase in the relative abundance of Spirulina sp. and Navicula sp. sequences, with changes in the relative abundance of major archaeal and bacterial groups also detected within the pH 7.0 treatment. A decreased flux of silicate from the sediment at this pH was also detected. Monitoring blooms of microphytobenthos may prove useful as an indicator of CO2 leakage within coastal areas. [ABSTRACT FROM AUTHOR]

With the Arctic summer sea-ice extent in decline, questions are arising as to how changes in sea-ice dynamics might affect biogeochemical cycling and phenomena such as carbon dioxide (CO2) uptake and ocean acidification. Recent field research in these areas has concentrated on biogeochemical and CO2 measurements during spring, summer or autumn, but there are few data for the winter or winter–spring transition, particularly in the High Arctic. Here, we present carbon and nutrient data within and under sea ice measured during the Catlin Arctic Survey, over 40 days in March and April 2010, off Ellef Ringnes Island (78° 43.11′ N, 104° 47.44′ W) in the Canadian High Arctic. Results show relatively low surface water (1–10 m) nitrate (<1.3 µM) and total inorganic carbon concentrations (mean±SD=2015±5.83 µmol kg−1), total alkalinity (mean±SD=2134±11.09 µmol kg−1) and under-ice pCO2sw (mean±SD=286±17 µatm). These surprisingly low wintertime carbon and nutrient conditions suggest that the outer Canadian Arctic Archipelago region is nitrate-limited on account of sluggish mixing among the multi-year ice regions of the High Arctic, which could temper the potential of widespread under-ice and open-water phytoplankton blooms later in the season. [ABSTRACT FROM AUTHOR]

Abstract: The Arctic Ocean and its associated ecosystems face numerous challenges over the coming century. Increasing atmospheric CO2 is causing increasing warming and ice melting as well as a concomitant change in ocean chemistry (“ocean acidification”). As temperature increases it is expected that many temperate species will expand their geographic distribution northwards to follow this thermal shift; however with the addition of ocean acidification this transition may not be so straightforward. Here we investigate the potential impacts of ocean acidification and climate change on populations of an intertidal species, in this case the barnacle Semibalanus balanoides, at the northern edge of its range. Growth and development of metamorphosing post-larvae were negatively impacted at lower pH (pH 7.7) compared to the control (pH 8.1) but were not affected by elevated temperature (+4 °C). The mineral composition of the shells did not alter under any of the treatments. The combination of reduced growth and maintained mineral content suggests that there may have been a change in the energetic balance of the exposed animals. In undersaturated conditions more mineral is expected to dissolve from the shell and hence more energy would be required to maintain the mineral integrity. Any energy that would normally be invested into growth could be reallocated and hence organisms growing in lowered pH grow slower and end up smaller than individuals grown in higher pH conditions. The idea of reallocation of resources under different conditions of pH requires further investigation. However, there could be long-term implications on the fitness of these barnacles, which in turn may prevent them from successfully colonising new areas. [Copyright &y& Elsevier]

The article presents a study which investigates the effects of carbon dioxide induced acidification on the shell mineralogy, embryonic development and survival of the intertidal barnacle Semibalanus balanoides through the use of intrtidal micorcosm system. It mentions that embryonic development rate was slower in the high-carbon dioxide conditions which resulted in a 60% reduction in the number of hatched eggs. The authors conclude that ocean acidification could potentially develop compromise embyonic development in a certain specie.

Improving our ability to monitor ocean carbonate chemistry has become a priority as the ocean continues to absorb carbon dioxide from the atmosphere. This long-term uptake is reducing the ocean pH; a process commonly known as ocean acidification. The use of satellite Earth Observation has not yet been thoroughly explored as an option for routinely observing surface ocean carbonate chemistry, although its potential has been highlighted. We demonstrate the suitability of using empirical algorithms to calculate total alkalinity (A T) and total dissolved inorganic carbon (C T), assessing the relative performance of satellite, interpolated in situ , and climatology datasets in reproducing the wider spatial patterns of these two variables. Both A T and C T in situ data are reproducible, both regionally and globally, using salinity and temperature datasets, with satellite observed salinity from Aquarius and SMOS providing performance comparable to other datasets for the majority of case studies. Global root mean squared difference (RMSD) between in situ validation data and satellite estimates is 17 μmol kg−1 with bias < 5 μmol kg−1 for A T and 30 μmol kg−1 with bias < 10 μmol kg−1 for C T. This analysis demonstrates that satellite sensors provide a credible solution for monitoring surface synoptic scale A T and C T. It also enables the first demonstration of observation-based synoptic scale A T and C T temporal mixing in the Amazon plume for 2010–2016, complete with a robust estimation of their uncertainty. • Satellite salinity measurements enable estimation of surface carbonate parameters. • Uncertainties within these observation-based estimates are well characterized. • Monthly satellite salinity and temperature allows synoptic monitoring. • Satellite observations allow study of seasonal, interannual and episodic variations. [ABSTRACT FROM AUTHOR]