Posts Tagged 'review'

Using natural analogues to investigate the effects of climate change and ocean acidification on Northern ecosystems

Northern oceans are in a state of rapid transition. Still, our knowledge of the likely effects of climate change and ocean acidification on key species in the food web, functionally important habitats and the structure of Arctic and sub-Arctic ecosystems is limited and based mainly on short-term laboratory studies on single species. This review discusses how tropical and temperate natural analogues of carbonate chemistry drivers, such as CO2 vents, have been used to further our knowledge of the sensitivity of biological systems to predicted climate change, and thus assess the capacity of different species to show long-term acclimation and adaptation to elevated levels of pCO2. Natural analogues have also provided the means to scale-up from single-species responses to community and ecosystem level responses. However, to date the application of such approaches is limited in high latitude systems. A range of Arctic and sub-Arctic sites, including CO2 vents, methane cold seeps, estuaries, up-welling areas, and polar fronts, that encompass gradients of pH, carbonate saturation state, and alkalinity, are suggested for future high latitude, in-situ ocean acidification research. It is recommended that combinations of monitoring of the chemical oceanography, observational, and experimental (in situ and laboratory) studies of organisms around these natural analogues be used to attain better predictions of the impacts of ocean acidification and climate change on high latitude species and ecosystems.

Continue reading ‘Using natural analogues to investigate the effects of climate change and ocean acidification on Northern ecosystems’

The importance of natural acidified systems in the study of ocean acidification: what have we learned?

Human activity is generating an excess of atmospheric CO2, resulting in what we know as ocean acidification, which produces changes in marine ecosystems. Until recently, most of the research in this area had been done under small-scale, laboratory conditions, using few variables, few species and few life cycle stages. These limitations raise questions about the reproducibility of the environment and about the importance of indirect effects and synergies in the final results of these experiments. One way to address these experimental problems is by conducting studies in situ, in natural areas where expected future pH conditions already occur, such as CO2 vent systems. In the present work, we compile and discuss the latest research carried out in these natural laboratories, with the objective to summarize their advantages and disadvantages for research to improve these investigations so they can better help us understand how the oceans of the future will change.

Continue reading ‘The importance of natural acidified systems in the study of ocean acidification: what have we learned?’

Assessment of paleo-ocean pH records from boron isotope ratio in the Pacific and Atlantic ocean corals: Role of anthropogenic CO2 forcing and oceanographic factors to pH variability

Boron isotopes (δ11B) records from tropical ocean corals have been used to reconstruct paleo-pH of ocean for the past several decades to few centuries which are comparable to the resolution of instrumental records. In most of the studies, attempts have been made to decipher the role of anthropogenic CO2 forcing to recent trend of ocean acidification based on δ11B derived paleo-pH records. However, such attempts in past were often hindered by limited knowledge of oceanographic factors that contributed to past pH variability and changes. In this study, we have evaluated pH records reconstructed using δ11B records from the Pacific and the Atlantic Oceans corals and investigated major forcing factors that contributed to sub annual-decadal scale pH variability and changes since the industrial era ~1850AD.

To the best of our knowledge, total eight δ11B records from the Pacific and two from the Atlantic Oceans are available in published literatures. The compilations of these records show large variability; range between 26.27–20.82‰ which corresponds to pH range 8.40–7.63 respectively. Our investigation of pH records from the Pacific ocean based on principal component analysis (PCA) reveals that atmospheric CO2 can explains maximum up to ~26% of the total pH variability during 1950–2004AD, followed by the ocean-climate oscillations (i.e. ENSO and PDO) driven oceanographic factors up to ~17%. The remaining large variability (~57%) could not be explained by above forcing factors and hence we invoke possible influence of metabolic processes of corals and/or changes in micro-environments within the reefs which are often neglected in interpreting paleo-pH records. Therefore, we highlight the need for detailed investigation in future studies to understand about the exact mechanism, processes/factors that controlled boron isotope fractionations in coral reef environments. Further, our investigation reveals that amplitude of the ENSO driven pH variability shows fivefold increase during 1980–2000AD compared to the previous three decades (1950–1980AD). This observation is consistent with the historical records of global coral bleaching events and therefore underscores role of ENSO driven environmental stress responsible for coral bleaching events. Considering model based projections of increasing frequency and amplitude of extreme ENSO events in the backdrop of recent global warming, bleaching events are likely to increase in the next decades/centuries.

Continue reading ‘Assessment of paleo-ocean pH records from boron isotope ratio in the Pacific and Atlantic ocean corals: Role of anthropogenic CO2 forcing and oceanographic factors to pH variability’

Bio-buffering to combat ocean acidification?

Atmospheric carbon dioxide (CO2) concentration is rising faster than ever before, due to continuous surge in burning fossil fuel. According to the ‘State of the Climate in 2017’ report from the National Oceanic and Atmospheric Administration (NOAA) and the American Meteorological Society, the global growth rate of atmospheric CO2 concentration was approximately 0.6 ± 0.1 ppm/year in the 1960s [3]. However, in the last decade, the growth rate has jumped to 2.3 ppm/year. The estimated atmospheric CO2 concentration is expected to reach 800–1000 ppm by the end of this century [6]. Oceans absorb nearly 30% of the global CO2 emissions [8], resulting in decrease in ocean pH, known as ocean acidification (OA). While atmospheric CO2 is the major contributor to OA globally, other anthropogenic activities influence OA on a local level. These include acid rain from vehicle emissions and industry in urban areas, inflow of organic carbon to the oceans in the form of sewage, and nutrient loading into the oceans from agricultural runoff; all of which contribute to OA [7].

Ocean acidification not only lowers the pH of ocean water, but also decreases dissolved carbonate ion (CO32−) concentration and alters the saturation states of calcium carbonate minerals. Calcifying organisms, such as corals, mollusks, and shellfishes, which use CO32− ions along with calcium ions to produce their calcium carbonate skeletons and shells, are negatively impacted by decreased CO32− levels. In addition, OA causes changes in habitat quality and nutrient cycling, which have numerous effects on food web interactions. Overall, complex changes occur in populations, communities, and the entire ecosystem; the scope of which is yet to be fully understood.

Continue reading ‘Bio-buffering to combat ocean acidification?’

Evidences of CO2 leakage during the last deglaciation: the need to understand deep-ocean carbonate chemistry of the Arabian Sea

It is generally accepted view that the ventilation of Southern Ocean during the last deglaciation was the key factor in atmospheric CO2 rise. Further, other sites were identified, like the western equatorial Pacific, the Sub-Antarctic Atlantic and the eastern equatorial Pacific. Now there are evidences that CO2 was also released from the eastern Arabian Sea. The Arabian Sea is unique in characteristic, being land locked from the North and affected by monsoon winds and seasonal reversing circulations. Furthermore, the CO2 outgassing noticed during deglaciation makes it an interesting region to understand if the outgassing occurred from the deeper waters and hence led to any rise in deepwater [CO3 2−]. 

Continue reading ‘Evidences of CO2 leakage during the last deglaciation: the need to understand deep-ocean carbonate chemistry of the Arabian Sea’

AMAP assessment 2018: Arctic ocean acidification

Ocean acidification, resulting from changes in ocean chemistry induced by increasing seawater carbon dioxide concentrations, is one of the growing challenges to marine organisms, ecosystems and biogeochemical cycling. Some of the fastest rates of ocean acidification currently observed are in the Arctic Ocean, with important physiological and geochemical thresholds already surpassed. Projections indicate that large parts of the Arctic Ocean are undergoing marine carbonate system changes that will incur significant shifts in ecological status over the coming decades unless global carbon emissions are drastically curtailed. These changes in water chemistry and biology will have significant socio-ecological and economic consequences at the local to global level.

The first AMAP Arctic Ocean acidification report (AMAP, 2013) presented a scientific assessment on the changing state of ocean acidification in the Arctic and provided an Arctic-wide perspective on the rapid increase in seawater acidity. The report concluded that ocean acidification was affecting the Arctic marine environment and ecosystems.

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Complexity of marine CO2 system highlighted by seasonal asymmetries

The complexities of the marine carbon cycle continue to be uncovered. In this issue, Fassbender et al (2018) combined measured surface ocean partial pressure of carbon dioxide (pCO2) with model predictions of increases in dissolved inorganic carbon (DIC) to explore seasonal pCO2 changes. They find that when seasonal cycles of other variables (temperature, salinity, total alkalinity, and DIC) are maintained to climatological means, seasonal amplitudes of pCO2 are affected asymmetrically. Thus, even ignoring other natural or climate change factors, the assumption that the seasonal cycle of pCO2 will be preserved may not be valid. Fassbender et al. (2018) intentionally ignore the influence of other variables such as a global warming signal in order to hone in explicitly on carbon system dynamics. The results show that when studying CO2 fluxes, especially into the future, the full seasonal cycle must be investigated, as what happens at one time of year may not translate to the rest of the year. Practically, this means that in order to fully understand the marine carbon cycle and its control over atmospheric CO2 levels, there is an urgent need for more surface pCO2 data covering more months of the year particularly in the polar oceans which are highly seasonally biased.

Continue reading ‘Complexity of marine CO2 system highlighted by seasonal asymmetries’

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Ocean acidification in the IPCC AR5 WG II

OUP book