Posts Tagged 'review'

Acidification in aquatic systems

Aquatic acidification is a proven phenomenon principally caused by human carbon dioxide emissions. Important changes in pH and on carbonate chemistry in conjunction with other anthropogenic impacts are seriously affecting aquatic communities. Nowadays, there is substantial evidence that acidification has an important impact on marine, coastal, and freshwater habitats. Calcifying organisms, juvenile stages, and coral reefs ecosystems are particularly vulnerable to this process. Species diversity and ecosystem resilience are expected to decrease in the near future. The amplitude of future acidification levels will depend on actual and future carbon dioxide emissions. Immediate actions are needed to limit the negative ecological and socioeconomic effects.

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Boron isotopes in foraminifera: systematics, biomineralisation, and CO2 reconstruction

The boron isotope composition of foraminifera provides a powerful tracer for CO2 change over geological time. This proxy is based on the equilibrium of boron and its isotopes in seawater, which is a function of pH. However while the chemical principles underlying this proxy are well understood, its reliability has previously been questioned, due to the difficulty of boron isotope (δ11B) analysis on foraminferal samples and questions regarding calibrations between δ11B and pH. This chapter reviews the current state of the δ11B-pH proxy in foraminfera, including the pioneering studies that established this proxy’s potential, and the recent work that has improved understanding of boron isotope systematics in foraminifera and applied this tracer to the geological record. The theoretical background of the δ11B-pH proxy is introduced, including an accurate formulation of the boron isotope mass balance equations. Sample preparation and analysis procedures are then reviewed, with discussion of sample cleaning, the potential influence of diagenesis, and the strengths and weaknesses of boron purification by column chromatography versus microsublimation, and analysis by NTIMS versus MC-ICPMS. The systematics of boron isotopes in foraminifera are discussed in detail, including results from benthic and planktic taxa, and models of boron incorporation, fractionation, and biomineralisation. Benthic taxa from the deep ocean have δ11B within error of borate ion at seawater pH. This is most easily explained by simple incorporation of borate ion at the pH of seawater. Planktic foraminifera have δ11B close to borate ion, but with minor offsets. These may be driven by physiological influences on the foraminiferal microenvironment; a novel explanation is also suggested for the reduced δ11B-pH sensitivities observed in culture, based on variable calcification rates. Biomineralisation influences on boron isotopes are then explored, addressing the apparently contradictory observations that foraminifera manipulate pH during chamber formation yet their δ11B appears to record the pH of ambient seawater. Potential solutions include the influences of magnesium-removal and carbon concentration, and the possibility that pH elevation is most pronounced during initial chamber formation under favourable environmental conditions. The steps required to reconstruct pH and pCO2 from δ11B are then reviewed, including the influence of seawater chemistry on boron equilibrium, the evolution of seawater δ11B, and the influence of second carbonate system parameters on δ11B-based reconstructions of pCO2. Applications of foraminiferal δ11B to the geological record are highlighted, including studies that trace CO2 storage and release during recent ice ages, and reconstructions of pCO2 over the Cenozoic. Relevant computer codes and data associated with this article are made available online.

Continue reading ‘Boron isotopes in foraminifera: systematics, biomineralisation, and CO2 reconstruction’

Larval ecology in the face of changing climate – impacts of ocean warming and ocean acidification

Ocean warming and acidification are major climate change stressors for marine invertebrate larvae, and their impacts differ between habitats and regions. In many regions species with pelagic propagules are on the move, exhibiting poleward trends as temperatures rise and ocean currents change. Larval sensitivity to warming varies among species, influencing their invasive potential. Broadly distributed species with wide developmental thermotolerances appear best able to avail of the new opportunities provided by warming. Ocean acidification is a multi-stressor in itself and the impacts of its covarying stressors differ among taxa. Increased pCO2 is the key stressor impairing calcification in echinoid larvae while decreased mineral saturation is more important for calcification in bivalve larvae. Non-feeding, non-calcifying larvae appear more resilient to warming and acidification. Some species may be able to persist through acclimatization/adaptation to produce resilient offspring. Understanding the capacity for adaptation/acclimatization across generations is important to predicting the future species composition of marine communities.

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Tough, armed and omnivorous: Hermodice carunculata (Annelida: Amphinomidae) is prepared for ecological challenges

The bearded fireworm, Hermodice carunculata, is a common species in the marine annelid taxon Amphinomidae. It has a widespread distribution throughout the Atlantic, Gulf of Mexico, the Caribbean, Mediterranean and Red Seas. We review its environmental tolerances, defence mechanisms and feeding habits to evaluate its potential to survive in changing ocean conditions, to increasingly emerge as a nuisance species and to invade new geographic areas. Hermodice carunculata tolerates a wide range of environmental conditions, including temperature, salinity, oxygen saturation and various types of pollution. It has few natural predators because it is protected by its sharp chaetae and probably by toxins. Hermodice carunculata is best known for consuming live cnidarians, and has been implicated in transmitting coral pathogens, but it also feeds non-selectively on detritus. In the short term, we predict that H. carunculata will be able to withstand many future ecological challenges and possibly contribute to coral reef decline. In the long term, ocean acidification may negatively impact its defence mechanisms and survival. Its invasive potential may be significant. We highlight the gaps in our knowledge about the reproduction and development of this species, the nature and origin of its toxins and role of microbes in their feeding behaviour and defensive strategies.

Continue reading ‘Tough, armed and omnivorous: Hermodice carunculata (Annelida: Amphinomidae) is prepared for ecological challenges’

Adaptation strategies to climate change in marine systems

The world’s oceans are highly impacted by climate change and other human pressures, with significant implications for marine ecosystems and the livelihoods that they support. Adaptation for both natural and human systems is increasingly important as a coping strategy due to the rate and scale of ongoing and potential future change. Here, we conduct a review of literature concerning specific case studies of adaptation in marine systems, and discuss associated characteristics and influencing factors, including drivers, strategy, timeline, costs, and limitations. We found ample evidence in the literature that shows that marine species are adapting to climate change through shifting distributions and timing of biological events, while evidence for adaptation through evolutionary processes is limited. For human systems, existing studies focus on frameworks and principles of adaptation planning, but examples of implemented adaptation actions and evaluation of outcomes are scarce. These findings highlight potentially useful strategies given specific social–ecological contexts, as well as key barriers and specific information gaps requiring further research and actions.

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Climate conditions, and changes, affect microalgae communities… should we worry?

Microalgae play a pivotal role in the regulation of Earth’s climate and its cycles, but are also affected by climate change, mainly by changes in temperature, light, ocean acidification, water stratification, and precipitation‐induced nutrient inputs. The changes and impacts on microalgae communities are difficult to study, predict, and manage, but there is no doubt that there will be changes. These changes will have impacts beyond microalgae communities, and many of them will be negative. Some actions are currently ongoing for the mitigation of some of the negative impacts, such as harmful algal blooms and water quality, but global efforts for reducing CO2 emissions, temperature rises, and ocean acidification are paramount for reducing the impact of climate change on microalgae communities, and eventually, on human well‐being.

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Phytoplankton as key mediators of the biological carbon pump: their responses to a changing climate

The world’s oceans are a major sink for atmospheric carbon dioxide (CO2). The biological carbon pump plays a vital role in the net transfer of CO2 from the atmosphere to the oceans and then to the sediments, subsequently maintaining atmospheric CO2 at significantly lower levels than would be the case if it did not exist. The efficiency of the biological pump is a function of phytoplankton physiology and community structure, which are in turn governed by the physical and chemical conditions of the ocean. However, only a few studies have focused on the importance of phytoplankton community structure to the biological pump. Because global change is expected to influence carbon and nutrient availability, temperature and light (via stratification), an improved understanding of how phytoplankton community size structure will respond in the future is required to gain insight into the biological pump and the ability of the ocean to act as a long-term sink for atmospheric CO2. This review article aims to explore the potential impacts of predicted changes in global temperature and the carbonate system on phytoplankton cell size, species and elemental composition, so as to shed light on the ability of the biological pump to sequester carbon in the future ocean.

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Ocean acidification in the IPCC AR5 WG II

OUP book