Posts Tagged 'methods'

Boron isotopes as a proxy for pH in siliceous and calcareous marine algae

Rising CO2 in the atmosphere has directly led to a reduction in surface ocean pH -a process known as ocean acidification. There is a need to understand past climates in terms of ocean pH change in order to be able to relate these to the current effects of climate change on marine organisms. One way of doing this is by measuring boron isotopes in marine carbonates, such as foraminifera and corals, to estimate past ocean pH, and thus to infer past pCO2. Key regions of atmospheric-ocean CO2 exchange are the Southern Ocean and subarctic North Pacific, and they are also areas where modern ocean acidification is occurring fastest. The current application of the boron isotope proxy is restricted in these high latitude regions due to lack of calcareous organisms preserved in the sediment here. Therefore, there is a need to expand the boron isotope proxy into novel materials, such as diatoms and coralline algae, which are found in these key high latitude habitats in abundance.
This thesis aims to investigate whether the hard parts of marine algae (siliceous: di-atoms; calcareous: coralline algae) are suitable archives for the boron isotope pH proxy. This is achieved by examining: (i) which boron species could be incorporated into the frustule/skeleton; (ii) the relationship between boron isotopic composition and seawater pH, and hence the sensitivity of boron isotopes in each organism to changes in seawater pH; (iii) the palaeo-archive potential of each organism. These aims are addressed by developing a method to measure boron isotopes and boron content of diatoms by MC-ICP-MS, calibrating the boron-pH relationships in a species of diatom using culturing experiments, applying this calibration to sedimentary diatoms collected from a core in the subarctic North Pacific, and also by investigating the relationship between boron isotopes and seawater pH in a species of coralline algae.

Continue reading ‘Boron isotopes as a proxy for pH in siliceous and calcareous marine algae’

MWCNT/polyaniline nanocomposites used for pH nanosensors of marine waters

Polymer nanocomposites of conductive polymer, polyaniline (PANI) with multi-walled carbon nanotubes (MWCNTs), have gained a great interest for their application in environmental and water quality monitoring (where pH value becomes one of the reliable data). Compared to the inorganic counterparts, conducting polymers have advantage in achieving high sensitivity and selectivity by virtue of their chemical and structural diversity. In the framework of FP7 project COMMON SENSE (OCEAN 2013.2-614155), screen-printed electrodes as a pH nanosensors based on nanocomposites of conductive polymer matrix-PANI and MWCNT were prepared by electrochemical polymerization. Characterization was performed by several spectroscopic techniques and electrical measurements. Electrochemical synthesis of the PANI-based composites was performed at 0.75 V vs. saturated calomel electrode (SCE) for 40 and 60 minutes. The working conditions were determined using electrochemical steady-state polarization measurements. Morphology of the produced composites was observed using scanning electron microscope (SEM), structural characteristics were studied using Raman spectroscopy, while thermal stability was determined using thermal gravimetric analysis (TGA/DTA). The results point out on fibrous and porous structure of PANI-based composites, with strong interaction between quinoidal structure of PANI with carbon nanostructures via p–p stacking according to Raman spectroscopy measurements. TGA coupled with DTA showed the increased thermal stability of the studied composites. The obtained nanocomposites exhibited a high value of conductivity which attributed to the synergy effect of the conductive polymer matrix and carbon nanostructure. Resistivity (i.e., conductivity) changes were measured at different pHs (4 to 10) as well as in different marine regions.

Continue reading ‘MWCNT/polyaniline nanocomposites used for pH nanosensors of marine waters’

Updated methods for global locally interpolated estimation of alkalinity, pH, and nitrate

We have taken advantage of the release of version 2 of the Global Data Analysis Project data product (Olsen et al. 2016) to refine the locally interpolated alkalinity regression (LIAR) code for global estimation of total titration alkalinity of seawater (AT), and to extend the method to also produce estimates of nitrate (N) and in situ pH (total scale). The updated MATLAB software and methods are distributed as Supporting Information for this article and referred to as LIAR version 2 (LIARv2), locally interpolated nitrate regression (LINR), and locally interpolated pH regression (LIPHR). Collectively they are referred to as locally interpolated regressions (LIRs). Relative to LIARv1, LIARv2 has an 18% lower average AT estimate root mean squared error (RMSE), improved uncertainty estimates, and fewer regions in which the method has little or no available training data. LIARv2, LINR, and LIPHR produce estimates globally with skill that is comparable to or better than regional alternatives used in their respective regions. LIPHR pH estimates have an optional adjustment to account for ongoing ocean acidification. We have used the improved uncertainty estimates to develop LIR functionality that selects the lowest-uncertainty estimate from among possible estimates. Current and future versions of LIR software will be available on GitHub at https://github.com/BRCScienceProducts/LIRs.

Continue reading ‘Updated methods for global locally interpolated estimation of alkalinity, pH, and nitrate’

Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment (update)

The Southern Ocean provides a vital service by absorbing about one-sixth of humankind’s annual emissions of CO2. This comes with a cost – an increase in ocean acidity that is expected to have negative impacts on ocean ecosystems. The reduced ability of phytoplankton and zooplankton to precipitate carbonate shells is a clearly identified risk. The impact depends on the significance of these organisms in Southern Ocean ecosystems, but there is very little information on their abundance or distribution. To quantify their presence, we used coulometric measurement of particulate inorganic carbonate (PIC) on particles filtered from surface seawater into two size fractions: 50–1000 µm to capture foraminifera (the most important biogenic carbonate-forming zooplankton) and 1–50 µm to capture coccolithophores (the most important biogenic carbonate-forming phytoplankton). Ancillary measurements of biogenic silica (BSi) and particulate organic carbon (POC) provided context, as estimates of the biomass of diatoms (the highest biomass phytoplankton in polar waters) and total microbial biomass, respectively. Results for nine transects from Australia to Antarctica in 2008–2015 showed low levels of PIC compared to Northern Hemisphere polar waters. Coccolithophores slightly exceeded the biomass of diatoms in subantarctic waters, but their abundance decreased more than 30-fold poleward, while diatom abundances increased, so that on a molar basis PIC was only 1 % of BSi in Antarctic waters. This limited importance of coccolithophores in the Southern Ocean is further emphasized in terms of their associated POC, representing less than 1 % of total POC in Antarctic waters and less than 10 % in subantarctic waters. NASA satellite ocean-colour-based PIC estimates were in reasonable agreement with the shipboard results in subantarctic waters but greatly overestimated PIC in Antarctic waters. Contrastingly, the NASA Ocean Biogeochemical Model (NOBM) shows coccolithophores as overly restricted to subtropical and northern subantarctic waters. The cause of the strong southward decrease in PIC abundance in the Southern Ocean is not yet clear. The poleward decrease in pH is small, and while calcite saturation decreases strongly southward, it remains well above saturation ( > 2). Nitrate and phosphate variations would predict a poleward increase. Temperature and competition with diatoms for limiting iron appear likely to be important. While the future trajectory of coccolithophore distributions remains uncertain, their current low abundances suggest small impacts on overall Southern Ocean pelagic ecology.

Continue reading ‘Distribution of planktonic biogenic carbonate organisms in the Southern Ocean south of Australia: a baseline for ocean acidification impact assessment (update)’

Viewpoints in bioerosion research—are we really disagreeing? A reply to the comment by Silbiger and DeCarlo (2017)

A recent literature review by Schönberg et al. (2017) on bioerosion under ocean acidification and global change led to a detailed comment by Silbiger and DeCarlo (2017). We use the opportunity to reply to this comment, to correct misinterpreted data and to further stimulate the discussion in bioerosion science. We still believe that our paper and the included method discussion were timely. Most discussed studies captured only a partial bioeroder community, for which upscaling and generalization remains difficult. However, after re-visiting Silbiger et al. (2014) we would like to propose a new interpretation: Their net bioerosion/accretion did not change along a natural gradient, but may have responded to localized pH “anomalies”.

Continue reading ‘Viewpoints in bioerosion research—are we really disagreeing? A reply to the comment by Silbiger and DeCarlo (2017)’

Past and future evolution of the carbonate system in a coastal zone of the Northern Antarctic Peninsula

Highlights

• Anthropogenic carbon concentrations are estimated within the mixed layer using three different methods.
• There is a large increasing rate of anthropogenic carbon penetration in the deep waters.
• Undersaturated aragonite saturation state at sea surface could be reached before year 2060.
• An alternative method for calculating anthropogenic carbon is purposed for regions with low carbonate system datasets.

Abstract

It is arduous to gather a good spatial and temporal dataset of marine carbonate properties, especially in the Southern Ocean. In this study, we have reconstructed the carbonate system in the Gerlache Strait, a coastal zone of the Northern Antarctic Peninsula. We also analyzed the impact of ocean acidification by calculating the tipping points of the calcium carbonate saturation states and pH (i.e., when saturation state and pH goes below one and 7, respectively). Hydrographic and carbonate data from three distinct data sets (GOAL – 2013 to 2016, FRUELA – 1996, and World Ocean Database – 1965 to 2004) have been joined and used to reconstruct the carbonate system from the past 50 years. Temporal annual mean trends were determined depending on the water column depth-layer. The northern Gerlache Strait showed a significant increasing trend of CT concentrations (1.0024 ± 0.34 µmol kg–1) and related pH decreasing trend (–0.0026 ± 0.0009 sws) in the surface mixed layer (> 60 m). The properties variability is relatively different (magnitudes and signs) between the northern and southern sectors of the Gerlache Strait, which indicate that adjacent regions to the Gerlache Strait to the southwest and north, respectively, may major influence the regional carbonate dynamics. Results also show that episodic under-saturation conditions, in relation to aragonite within the surface mixed layer, may already occur, especially in regions close to large glaciers.

Continue reading ‘Past and future evolution of the carbonate system in a coastal zone of the Northern Antarctic Peninsula’

Repeated measurement of MO2 in small aquatic organisms: a manual intermittent flow respirometer using off-the-shelf components

Measurement of rates of oxygen consumption (MO2) in small aquatic embryos or larvae (< 1mm) in response to altered environmental conditions has traditionally been challenging. Here, using modifications of a commercially available fluorescent optode flow-through cell (FTC: PreSens{trade mark, serif} FTC-PSt3) and routine laboratory supplies (syringes, stopcocks, tubing), we have constructed a manual intermittent flow respirometer (MIFR) that allows measurement of MO2 in small numbers of individuals when sequentially exposed to different environmental conditions (e.g. changes in seawater pH) through a gravity-driven media replacement perfusion system. We first show that the FTC can be used in ‘static’ mode while incubating small numbers of embryos/larvae contained within the planar oxygen sensor (POS) chamber with Nitex filters. We then demonstrate the use of the MIFR by exposing larval echinoderms (Fellaster zelandiae, Evechinus chloroticus, Centrostephanus rodgersii) to seawater equilibrated with elevated CO2, and measured MO2 during acute and chronic exposure to hypercapnia. This MIFR method will allow investigators to address questions regarding the respiratory physiology of small aquatic animals, such as the thresholds for metabolic depression in embryonic and larval forms.

Continue reading ‘Repeated measurement of MO2 in small aquatic organisms: a manual intermittent flow respirometer using off-the-shelf components’


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Ocean acidification in the IPCC AR5 WG II

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