Posts Tagged 'methods'



Unifying biological field observations to detect and compare ocean acidification impacts across marine species and ecosystems: what to monitor and why

Approximately one quarter of the CO2 emitted to the atmosphere annually from human activities is absorbed by the ocean, resulting in a reduction of seawater pH and shifts in seawater carbonate chemistry. This multi-decadal process, termed “anthropogenic ocean acidification” (OA) has been shown to have detrimental impacts on marine ecosystems. Recent years have seen a globally coordinated effort to measure the changes in seawater chemistry caused by OA, with best practices now available for these measurements. In contrast to these substantial advances in observing physico-chemical changes due to OA, quantifying their biological consequences remains challenging, especially from in-situ observations under real-world conditions. Results from two decades of controlled laboratory experiments on OA have given insight into the likely processes and mechanisms by which elevated CO2 levels affect biological process, but the manifestation of these process across a plethora of natural situations has yet to be explored fully. This challenge requires us to identify a set of fundamental biological and ecological indicators that are i) relevant across all marine ecosystems, ii) have a strongly demonstrated link to OA, and iii) have implications for ocean health and the provision of ecosystem services with impacts on local marine management strategies and economies. This paper draws on the understanding of biological impacts provided by the wealth of previous experiments, as well as the findings of recent meta-analyses, to propose five broad classes of biological indicators that, when coupled with environmental observations, including carbonate chemistry, would allow the rate and severity of biological change in response to OA to be observed and compared. These broad indicators are applicable to different ecological systems, and the methods for data analysis suggested here would allow researchers to combine biological response data across regional and global scales by correlating rates of biological change with the rate of change in carbonate chemistry parameters. Moreover, a method using laboratory observation to design an optimal observing strategy (frequency and duration) and observe meaningful biological rates of change highlights the factors that need to be considered when applying our proposed observation strategy. This innovative observing methodology allows inclusion of a wide diversity of marine ecosystems in regional and global assessments and has the potential to increase the contribution of OA observations from countries with developing OA science capacity.

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Optimization and demonstration of in situ chemical sensors for marine waters

The importance of autonomous in situ chemical sensors for ocean observations has increased drastically over the last decades. Yet, the huge potentials of sensor-based data collection remain underutilized by the scientific and regulatory communities, despite wider than ever usage of sensors. This thesis is part of a growing body of work to extend the usability of sensors and is embedded in the Ocean Best Practice approach, which could improve data quality in ocean observation in general.

The here presented Ph.D. thesis covers multiple commercial sensors (LOC from ClearWater Sensors, Southampton, UK and OPUS from TriOS GmbH, Germany) for autonomous, high-resolution and in situ measurements of essential biogeochemical parameters (pH and nitrate) in marine waters. It was motivated by the necessity of improving the data quality of autonomous submersible optical sensors and broadening their utility. To achieve this, sensor deployments in various aquatic environments were conducted. Furthermore, the data obtained via sensors based on the same analytical principle was compared with each other, and with benchtop laboratory devices to assess the accuracy of the measurements.

The achievements are associated with the acquisition of accurate and temporally well-resolved real-time data. A more reliable sensor-based data collection and improved deployability promotes a broader usage of autonomous sensors in general. Thus, a financially more sustainable ocean monitoring approach can be achieved, since a broader adaptation of autonomous sensors in research yields a higher cost efficiency.

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Could a future ocean acidification scenario influence the photodegradation of microplastics?

Microplastics (MPs) in the marine environment are subject to photodegradation, a process in which they easily get fragmented and leach potentially dangerous compounds. Ocean acidification (OA), owing to the enrichment of carbon dioxide (CO 2 ), is one of the main chemical changes occurring in the marine environment and may be a factor that influences photodegradation. This study aims to investigate the influence of OA on the photodegradation of three types of MPs: polypropylene (PP), expanded polystyrene (EPS), and ethylene-vinyl acetate (EVA). MPs were weathered by exposing them simultaneously for 8 hours to accelerated ultraviolet (UV) radiation and to three pH levels ( i.e. , 8.1, 7.8, and 7.5), which were achieved by injecting CO 2 into a simulated marine medium. The acidification system reproduced the current environmental conditions and those calculated for the future. As expected, the higher the partial pressure of CO2 , total inorganic carbon, bicarbonate ion, and CO2 , the more acidic the pH, and the opposite is true for carbonate ion. Structural changes were assessed by Fourier transform infrared spectroscopy, differential scanning calorimetry, gel permeation chromatography, and scanning electron microscopy. All weathered samples showed a higher degradation rate than the virgin samples. The MPs of PP and EVA presented the highest degradation rates, indicating the development of oxygen-containing functional groups and an increase in crystalline fraction. The oxidation state and crystallinity were higher in samples exposed to the lowest pH. There was no significant difference (p > 0.05) in the degradation rate of EPS samples. The results allow us to infer that an increase in OA predicted for the future could interfere with the photodegradation of some types of MP polymers, accelerating this process.

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The cold-water coral Solenosmilia variabilis as a paleoceanographic archive for the reconstruction of intermediate water mass temperature variability on the Brazilian continental margin

Recent oceanographic observations have identified significant changes of intermediate water masses characterized by increased temperatures, lowered pH and deoxygenation. In order to improve our understanding as to how these changes may impact deep-sea ecosystems one important strategy is to reconstruct past oceanic conditions. Here we examine the applicability of the scleractinian cold-water coral Solenosmilia variabilis as a marine archive for the reconstructions of past intermediate water mass temperatures by using Lithium (Li)/Magnesium (Mg) ratios. In particular, our study addresses 1) the calibration of Li/Mg ratios against in-situ temperature data, 2) the reconstruction of past intermediate water mass temperatures using scleractinian coral fossil samples from the Brazilian continental margin and 3) the identification of intraspecies variability within the coral microstructure. Results showed that Li/Mg ratios measured in the skeletons of S. variabilis fit into existing Li/Mg-T calibrations of other cold-water scleractinian. Furthermore, the coral microstructure exhibits interspecies variability of Li/Ca and Mg/Ca ratios were also similar to what has been observed in other cold-water scleractinian corals, suggesting a similar biomineralization control on the incorporation of Li and Mg into the skeleton. However, the Li/Mg based temperature reconstruction using fossil samples resulted in unexpectedly high variations >10°C, which might not be solely related to temperature variations of the intermediate water mass over the last 160 ka on the Brazilian continental margin. We speculate that such temperature variability may be caused by vertical movements of the aragonite saturation horizon and the associated seawater pH changes, which in turn influence the incorporation of Li and Mg into the coral skeleton. Based on these results it is recommended that future studies investigating past oceanic conditions need to consider the carbonate system parameters and how they might impact the mechanisms of Li and Mg being incorporated into skeletons of cold-water coral species such as S. variabilis.

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Planktonic foraminifera organic carbon isotopes as archives of upper ocean carbon cycling

The carbon cycle is a key regulator of Earth’s climate. On geological time-scales, our understanding of particulate organic matter (POM), an important upper ocean carbon pool that fuels ecosystems and an integrated part of the carbon cycle, is limited. Here we investigate the relationship of planktonic foraminifera-bound organic carbon isotopes (δ13Corg-pforam) with δ13Corg of POM (δ13Corg-POM). We compare δ13Corg-pforam of several planktonic foraminifera species from plankton nets and recent sediment cores with δ13Corg-POM on a N-S Atlantic Ocean transect. Our results indicate that δ13Corg-pforam of planktonic foraminifera are remarkably similar to δ13Corg-POM. Application of our method on a glacial sample furthermore provided a δ13Corg-pforam value similar to glacial δ13Corg-POM predictions. We thus show that δ13Corg-pforam is a promising proxy to reconstruct environmental conditions in the upper ocean, providing a route to isolate past variations in δ13Corg-POM and better understanding of the evolution of the carbon cycle over geological time-scales.

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Using biomimicry and bibliometric mapping to guide design and production of artificial coral reefs

Highlights

  • We created an artificial coral reef based on biomimicry using a bibliometric method.
  • We designed stage-gates to lead the innovation process.
  • Local community and government agencies were included in the conceptualization.
  • We demonstrate the recovery in natural marine ecosystems using 3D printed coral reefs.

Abstract

Worldwide, artificial reefs are being installed to simultaneously attract recreational divers and protect deteriorating natural reefs. This study uses a bibliometric review of artificial coral reefs to identify five clusters as gate criteria for artificial reef design. These clusters enable the conceptualization and testing of artificial reefs for optimum integration of sociotechnical requirements, biological integrity, and ecological marine health. The five clusters are: (1) applications, solutions, and performance; (2) management, technology, and science; (3) calcification, biomineralization, chemistry, and ocean acidification; (4) coral species survival, mortality, and photosynthesis; and (5) artificial reef development, and coral and fish recruitment. The six biomimicry design stages are: definebiologizediscoverabstractemulate, and evaluate. The 3D printing and hard corals design attracted a large number of planula larvae and different inhabitant corals, and a high species diversity in the surrounding waters. Practical implications include biomimicry-based means for coral reef restoration and recreational ecosystem services.

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Toward a decade of ocean science for sustainable development through acoustic animal tracking

The ocean is a key component of the Earth’s dynamics, providing a great variety of ecosystem services to humans. Yet, human activities are globally changing its structure and major components, including marine biodiversity. In this context, the United Nations has proclaimed a Decade of Ocean Science for Sustainable Development to tackle the scientific challenges necessary for a sustainable use of the ocean by means of the Sustainable Development Goal 14 (SDG14). Here, we review how Acoustic animal Tracking, a widely distributed methodology of tracking marine biodiversity with electronic devices, can provide a roadmap for implementing the major Actions to achieve the SDG14. We show that acoustic tracking can be used to reduce and monitor the effects of marine pollution including noise, light, and plastic pollution. Acoustic tracking can be effectively used to monitor the responses of marine biodiversity to human-made infrastructures and habitat restoration, as well as to determine the effects of hypoxia, ocean warming, and acidification. Acoustic tracking has been historically used to inform fisheries management, the design of marine protected areas, and the detection of essential habitats, rendering this technique particularly attractive to achieve the sustainable fishing and spatial protection target goals of the SDG14. Finally, acoustic tracking can contribute to end illegal, unreported, and unregulated fishing by providing tools to monitor marine biodiversity against poachers and promote the development of Small Islands Developing States and developing countries. To fully benefit from acoustic tracking supporting the SDG14 Targets, trans-boundary collaborative efforts through tracking networks are required to promote ocean information sharing and ocean literacy. We therefore propose acoustic tracking and tracking networks as relevant contributors to tackle the scientific challenges that are necessary for a sustainable use of the ocean promoted by the United Nations.

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Offshore extinctions: ocean acidification impacting interstitial fauna

As problematic as global warming, ocean acidification is a widespread problem, but the consequences of the interstitial fauna are still underrated. The biodiversity within sandy beaches is out of measurement, and its loss will be significantly felt. Estimations of the number of species are still vague. Acting as a key role in the trophic net, the interstitial organisms are threatened by pH value changes. Changing the pH values is already linked with less species richness and weakness of the sea community. The sediments may not be a sufficient buffer. Beyond this, there is another environmental problem aggravating the scenario. The decreasing complexity in the sand structure generated by the destruction of biological-generated sediments will impact the local biodiversity. Other environmental situations such as lack of sufficient O2 levels may be an aggravating combination. Here, I propose a protocol to observe if occur offshore extinctions, the veiled extinctions of interstitial fauna.

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Field application of automated spectrophotometric analyzer for high-resolution in situ monitoring of pH in dynamic estuarine and coastal waters

High quality pH measurements are required in estuarine and coastal waters to assess the impacts of anthropogenic atmospheric CO2 emissions on the marine carbonate system, including the resulting decrease in pH. In addition, pH measurements are needed to determine impacts on carbonate chemistry of phytoplankton blooms and their breakdown, following enhanced anthropogenic nutrient inputs. The spectrophotometric pH technique provides high quality pH data in seawater, and is advantageous for long-term deployments as it is not prone to drift and does not require in situ calibration. In this study, a field application of a fully automated submersible spectrophotometric analyzer for high-resolution in situ pH measurements in dynamic estuarine and coastal waters is presented. A Lab-on-Chip (LOC) pH sensor was deployed from a pontoon in the inner Kiel Fjord, southwestern Baltic Sea, for a total period of 6 weeks. We present a time-series of in situ pHT (total pH scale) and ancillary data, with sensor validation using discretely collected samples for pHT and laboratory analysis. The difference between the sensor and laboratory analyses of discrete samples was within ±0.015 pHT unit, with a mean difference of 0.001 (n=65), demonstrating that the LOC sensor can provide stable and accurate pHT measurements over several weeks.

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OceanSODA-MDB: a standardised surface ocean carbonate system dataset for model-data intercomparisons

In recent years, large datasets of in situ marine carbonate system parameters (partial pressure of CO2 (pCO2), total alkalinity, dissolved inorganic carbon and pH) have been collated, quality controlled and made publicly available. These carbonate system datasets have highly variable data density in both space and time, especially in the case of pCO2, which is routinely measured at high frequency using underway measuring systems. This variation in data density can create biases when the data are used, for example for algorithm assessment, favouring datasets or regions with high data density. A common way to overcome data density issues is to bin the data into cells of equal latitude and longitude extent. This leads to bins with spatial areas that are latitude and projection dependent (e. g. become smaller and more elongated as the poles are approached). Additionally, as bin boundaries are defined without reference to the spatial distribution of the data or to geographical features, data clusters may be divided sub-optimally (e. g. a bin covering a region with a strong gradient).

To overcome these problems and to provide a tool for matching surface in situ data with satellite, model and climatological data, which often have very different spatiotemporal scales both from the in situ data and from each other, a methodology has been created to group in situ data into ‘regions of interest’: spatiotemporal cylinders consisting of circles on the Earth’s surface extending over a period of time. These regions of interest are optimally adjusted to contain as many in situ measurements as possible. All surface in situ measurements of the same parameter contained in a region of interest are collated, including estimated uncertainties and regional summary statistics. The same grouping is applied to each of the non-in situ datasets in turn, producing a dataset of coincident matchups that are consistent in space and time. About 35 million in situ data points were matched with data from five satellite sources and five model and re-analysis datasets to produce a global matchup dataset of carbonate system data, consisting of ~286,000 regions of interest spanning 54 years from 1957 to 2020. Each region of interest is 100 km in diameter and 10 days in duration. An example application, the reparameterisation of a global total alkalinity algorithm, is shown. This matchup dataset can be updated as and when in situ and other datasets are updated, and similar datasets at finer spatiotemporal scale can be constructed, for example to enable regional studies. The matchup dataset provides users with a large multiparameter carbonate system dataset containing data from different sources, in one consistent, collated and standardised format suitable for model-data intercomparisons and model evaluations. The OceanSODA-MDB data can be downloaded from https://doi.org/10.12770/0dc16d62-05f6-4bbe-9dc4-6d47825a5931 (Land and Piollé, 2022).

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Coral bleaching from a nutrient perspective is understudied: a bibliometric survey

How coral–Symbiodiniaceae mutualistic symbiosis is established, maintained, and disrupted is arguably the most fundamental and central area of coral research. The breakdown of this symbiosis, and consequent coral bleaching, have been frequently attributed to thermal stress, although microbial attack and pollution have also been blamed. Despite the perceived intense and broad research, it is unclear whether all the potential causes have been given adequate attention and whether some important areas have been overlooked. This work aims to comprehensively review the literature on coral and Symbiodiniaceae research and provide a portrait of the current coral research landscape, hence identifying areas that require more research effort. Data of publication output were extracted from the Web of Science (WoS) from 1986 to 2022 by using the keywords “coral” and “Symbiodiniaceae.” A total of 43,089 and 3,191 papers in the coral and Symbiodiniaceae were identified, mostly published after 2002. The journal Coral Reefs was ranked first regarding the total number of publications on coral or Symbiodiniaceae. The USA, Australia, and China were the top three countries in the number of publications. The network co-occurrence analysis of all keywords in coral and Symbiodiniaceae using VOSviewer showed that biodiversity, climate change, nutrient, and survival were the central research areas in coral and Symbiodiniaceae. Among them, climate change was the most invested research field, as revealed by the high proportion of published literature, while nutrient was the most understudied area. Thematic evolution analysis revealed that nutrient enrichment combined with elevated temperature was an emerging research field about coral and Symbiodiniaceae. Besides, nitrogen is currently the most studied nutrient. The findings from this study shed light on the trends of coral and Symbiodiniaceae research in the past 36 years, current research hotspots in the field, and areas that need more research investment going forward.

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pH trends and seasonal cycle in the coastal Balearic Sea reconstructed through machine learning

The decreasing seawater pH trend associated with increasing atmospheric carbon dioxide levels is an issue of concern due to possible negative consequences for marine organisms, especially calcifiers. Globally, coastal areas represent important transitional land-ocean zones with complex interactions between biological, physical and chemical processes. Here, we evaluated the pH variability at two sites in the coastal area of the Balearic Sea (Western Mediterranean). High resolution pH data along with temperature, salinity, and also dissolved oxygen were obtained with autonomous sensors from 2018 to 2021 in order to determine the temporal pH variability and the principal drivers involved. By using environmental datasets of temperature, salinity and dissolved oxygen, Recurrent Neural Networks were trained to predict pH and fill data gaps. Longer environmental time series (2012–2021) were used to obtain the pH trend using reconstructed data. The best predictions show a rate of  −0.0020 ± 0.00054 − 0.0020 ± 0.00054 pH units year−1, which is in good agreement with other observations of pH rates in coastal areas. The methodology presented here opens the possibility to obtain pH trends when only limited pH observations are available, if other variables are accessible. Potentially, this could be a way to reliably fill the unavoidable gaps present in time series data provided by sensors.

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Ocean acidification in the western Pacific: boron isotopic composition recorded in a tropical massive coral core from Lanyu Islet SE Taiwan

Boron (B) and B isotopic compositions (δ11B) in biogenic carbonates are useful proxies for pH reconstruction in the ocean. However, high-resolution archives are scarce due to associated sampling and analytical difficulty. In this study, a modern long-lived massive coral skeleton (Porites lobata) from Lanyu Islet off southeast Taiwan was drilled and used for high-resolution major/trace element analyses, including trace elements B and δ11B, as well as oxygen and carbon isotopes, to investigate the associated environmental changes during 1991–1997. To avoid complicated biological influence, the top-most tissue layer was excluded in this study. The coralline records show a clear temporal trend in metal/Ca-based sea surface temperatures (SSTs) on annual and monthly timescales. In particular, the Mg/Ca-SSTs, the most sensitive temperature proxy at the site, show a significant warming trend (+0.2°C year−1) during the study period. On the other hand, subtle changes in the annual δ11B record were identified, corresponding to ~0.2 pH unit, which is comparable with other coral records in the Pacific, e.g., the South China Sea (SCS), Guam Island, Flinders, and Arlington Reef, as well as the in-situ seawater pH measurement at Hawaii station. This corresponds to an acidification rate of ~0.25 pH unit 100 year−1, similar to other coralline data, in-situ pH/pCO2 measurement, or model predictions, and emphasizes the importance of ocean acidification due to anthropogenic activities. Combined with the Mg/Ca-SST, the intra-annual data show a clear seasonal cycle with higher pH in winter, consistent with the pCO2 at the oceanic surface. These chemical and isotopic results in corals conclude that marine biogenic carbonates are informative for oceanic pH reconstruction and can provide new insights into the relationships between climate changes and environmental responses on the coast of Taiwan.

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Gaining insights into the seawater carbonate system using discrete fCO2 measurements

Understanding the ocean carbon sink and its future acidification-derived changes requires accurate and precise measurements with good spatiotemporal coverage. In addition, a deep knowledge of the thermodynamics of the seawater carbonate system is key to interconverting between measured and calculated variables. To gain insights into the remaining inconsistencies in the seawater carbonate system, we assess discrete water column measurements of carbon dioxide fugacity (fCO2), dissolved inorganic carbon (DIC), total alkalinity (TA), and pH measured with unpurified indicators, from hydrographic cruises in the Atlantic, Pacific, and Southern Oceans included in GLODAPv2.2020 (19,013 samples). An agreement of better than ± 3% between fCO2 measured and calculated from DIC and pH is obtained for 94% of the compiled dataset, while when considering fCO2 measured and calculated from DIC and TA, the agreement is better than ± 4% for 88% of the compiled dataset, with a poorer internal consistency for high-CO2 waters. Inspecting all likely sources of uncertainty from measured and calculated variables, we conclude that the seawater carbonate system community needs to (i) further refine the thermodynamic model of the seawater carbonate system, especially K2, including the impact of organic compounds and other acid-base systems on TA; (ii) update the standard operating procedures for the seawater carbonate system measurements following current technological and analytical advances, paying particular attention to the pH methodology that is the one that evolved the most; (iii) encourage measuring discrete water column fCO2 to further check the internal consistency of the seawater carbonate system, especially given the new era of sensor-based seawater measurements; and (iv) develop seawater Certified Reference Materials (CRMs) for fCO2 and pH together with seawater CRMs for TA and DIC over the range of values encountered in the global ocean. Our conclusions also suggest the need for a re-evaluation of the adjustments applied by GLODAPv2 to pH, which were based on DIC and TA consistency checks but not supported by fCO2 and DIC consistency.

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Recent ocean acidification trends from boron isotope (δ11B) records of coral: role of oceanographic processes and anthropogenic CO2 forcing

Abstract

Anthropogenic CO2 emission has resulted in lowering of surface ocean pH referred as ‘Ocean acidification (OA)’ which posed a serious threat to calcifying marine organisms. Several attempts have been made to assess the role of anthropogenic CO2 forcing against oceanographic factors/processes contributing to the recent OA trend; however, such attempts were hindered by the dearth of long-term pH records. Boron isotopic composition (δ11B) of corals has been used as a robust proxy for seawater pH records. In the present study, we have compiled available coral δ11B-pH records from the Indian, Pacific and Atlantic oceans and assessed regional trends, variability, forcing factors and their relative roles. Most of these δ11B-pH records show a discernable decline trend in recent decades with large variability. Our assessment of the Pacific records reveals that atmospheric CO2 forcing explains maximum pH variability followed by physical oceanographic factors/processes modulated by Pacific oscillations, e.g., ENSO and PDO. In addition, coral metabolic processes might control a large portion of the pH variability; however, they require detailed laboratory-based studies. Further, our investigation reveals a significant increase in pH variability (pH extremes) since ~1970s associated with ENSO events which might be critical for the resilience and adaptability of corals and other calcifiers.

Research Highlights

  • Since the industrial era (~1850), Coral δ11B-pH records show a discernible decreasing trend and a rapid decline since 1970.
  • Oceanographic processes control large inter-annual pH variability, whereas the long-term declining trend is driven by atmospheric CO2 forcing.
  • The pH extremes are predicted to increase in future warming scenarios, a threat to coral ecosystem.
Continue reading ‘Recent ocean acidification trends from boron isotope (δ11B) records of coral: role of oceanographic processes and anthropogenic CO2 forcing’

Physiological control on carbon isotope fractionation in marine phytoplankton

One of the great challenges in biogeochemical research over the past half a century has been to quantify and understand the mechanisms underlying stable carbon isotope fractionation (εp) in phytoplankton in response to changing CO2 concentrations. This interest is partly grounded in the use of fossil photosynthetic organism remains as a proxy for past atmospheric CO2 levels. Phytoplankton organic carbon is depleted in 13C compared to its source because of kinetic fractionation by the enzyme RubisCO during photosynthetic carbon fixation, as well as through physiological pathways upstream of RubisCO. Moreover, other factors such as nutrient limitation, variations in light regime as well as phytoplankton culturing systems and inorganic carbon manipulation approaches may confound the influence of aquatic CO2 concentrations [CO2] on εp. Here, based on experimental data compiled from the literature, we assess which underlying physiological processes cause the observed differences in εp for various phytoplankton groups in response to C-demand/C-supply, i.e., particulate organic carbon (POC) production  [CO2]) and test potential confounding factors. Culturing approaches and methods of carbonate chemistry manipulation were found to best explain the differences in εp between studies, although day length was an important predictor for εp in haptophytes. Extrapolating results from culturing experiments to natural environments and for proxy applications therefore require caution, and it should be carefully considered whether culture methods and experimental conditions are representative of natural environments.

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Visualizing a field of research with scientometrics: climate change associated with major aquatic species production in the world

Climate change research on major aquatic species assists various stakeholders (e.g. policymakers, farmers, funders) in better managing its aquaculture activities and productivity for future food sustainability. However, there has been little research on the impact of climate change on aquatic production, particularly in terms of scientometric analyses. Thus, using the bibliometric and scientometric analysis methods, this study was carried out to determine what research exists on the impact of climate change on aquatic production groups. We focused on finfish, crustaceans, and molluscs. Data retrieved from Web of Science was mapped with CiteSpace and used to assess the trends and current status of research topics on climate change associated with worldwide aquatic production. We identified ocean acidification as an important research topic for managing the future production of aquatic species. We also provided a comprehensive perspective and delineated the need for: i) more international collaboration for research activity focusing on climate change and aquatic production in order to achieve the United Nations Sustainable Development Goal by 2030; ii) the incorporation of work from molecular biology, economics, and sustainability.

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Quality control of potentiometric pH measurements with a combination of NBS and Tris buffers at salinities from 20 to 40 and pH from 7.2 to 8.6

Seawater pH is a valuable parameter to describe ocean acidification. However, pH measurements are often subject to large uncertainty and the results of the pH comparison from different laboratories are not convincing. We assessed the potentiometric method for pH measurement on seawater samples with salinities from 20 to 40 and pH ranging from 7.2 to 8.6. pH glass electrodes were calibrated using both commercially available NBS buffers and the equimolal Tris (2‐amino‐2‐hydroxymethyl‐1,3‐propanediol) buffer (prepared in synthetic seawater at a salinity of 35). The results demonstrated that the uncertainty in pH measurements was within ± 0.01 in the entire salinity range and was better than ± 0.003, when the sample salinity was close to that of equimolal Tris buffer (salinity difference within ± 2.5), regardless of the sample pH. This study suggests that if the electrode calibration is performed properly, the potentiometric method can fulfill the “weather” goal (± 0.02) of the Global Ocean Acidification Observing Network in pH measurements; it might even meet the “climate” goal (± 0.003) if the difference between the salinity of the samples and the Tris buffer is small.

Continue reading ‘Quality control of potentiometric pH measurements with a combination of NBS and Tris buffers at salinities from 20 to 40 and pH from 7.2 to 8.6’

How to measure pHT in biological experiments

Research on ocean acidification requires following best practices. The OA-ICC contributes to the development of teaching material for the implementation of simplified methodologies for laboratories with limited finances or infrastructure.

Authors: Sanja Grđan, University of Dubrovnik & Sam Dupont, University of Gothenburg

Translation: Celeste Sánchez Noguera (Spanish) and Sam Dupont (French)

Description: Measuring pH in seawater using a glass electrode is not trivial and requires TRIS buffer. TRIS buffers are commercially available from Dr. Andrew Dickson’s laboratory at the Scripps Institution of Oceanography, California. However, access to this buffer can be difficult due to a continuously increasing demand as well as costs including shipping, customs fees, and taxes, making them less available for countries and laboratory with limited funds.

A simplified buffer preparation method is described in Paulsen & Dickson (2020) making the use of TRIS buffers available to a wider range of researchers.

The aim of this document and associated material (xls sheets and videos) is to help experimentalists entering the field of ocean acidification to make their own TRIS buffer, calibrate their glass electrodes for pH measurement on the total scale, take water samples and calculate pH on the total scale (pHT).

English Language Materials

French Language Materials

Spanish Language Materials

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Carbonate parameter estimation and its application in revealing temporal and spatial variation in the South and Mid-Atlantic Bight, USA

Abstract

To overcome the limitations due to sporadic carbonate parameter data, this study developed and evaluated empirical multiple linear regression (MLR) models for dissolved inorganic carbon (DIC), pHT (in total scale), and aragonite carbonate saturation state (ΩAr) using hydrographic data (temperature, salinity, and oxygen) measured during 2007 – 2018 in the South Atlantic Bight (SAB) and Mid-Atlantic Bight (MAB) along the U.S. East Coast. We first reviewed the assumptions and routines of MLR models and then generated MLR models for each cruise for all three carbonate parameters in each region and assessed model performance. Models derived from measured spectrophotometric pH have smaller uncertainties than pHT models based on pH calculated from total alkalinity (TA) and DIC. The regional differences of carbonate parameters between MAB and SAB are reflected in the coefficients of the empirical models. The MLR model temporal consistency indicates the effect of the atmospheric CO2 increase on the carbonate parameters cannot be unequivocally resolved for the period of this study in the regions. Therefore, we combined different cruises to build concise and composite models for each region. The composite models can capture the key features in the SAB and MAB. To further assess the model applicability, we applied our models to Biogeochemical-Argo data to reconstruct carbonate parameters. The algorithm in this study helps to reconstruct seawater carbonate chemistry using proxy data of high spatial and temporal resolution, which will enhance our understanding of physical and biological processes on carbon cycle and the long-term anthropogenic carbon inputs in coastal oceans.

Key Points

  • pH estimation models based on measured pH have smaller uncertainties than those based on pH calculated from other carbonate parameters
  • Models differ between the Mid and South Atlantic Bights, and their temporal changes due to atmospheric CO2 are limited over 10 years
  • Multiple linear regression models provide a promising tool for reconstructing carbonate parameters using data from autonomous platforms
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