Posts Tagged 'methods'

Evaluation of a new carbon dioxide system for autonomous surface vehicles

Current carbon measurement strategies leave spatiotemporal gaps that hinder the scientific understanding of the oceanic carbon biogeochemical cycle. Data products and models are subject to bias because they rely on data that inadequately capture mesoscale spatiotemporal (kilometers and days to weeks) changes. High-resolution measurement strategies need to be implemented to adequately evaluate the global ocean carbon cycle. To augment the spatial and temporal coverage of ocean-atmosphere carbon measurements, an Autonomous Surface Vehicle CO2 (⁠⁠) system was developed. From 2011 to 2018, ASVCO2 systems were deployed on seven Wave Glider and Saildrone missions along the U.S. Pacific and Australia’s Tasmanian coastlines and in the tropical Pacific to evaluate the viability of the sensors and their applicability to carbon cycle research. Here we illustrate that the ASVCO2 systems are capable of long-term oceanic deployment and robust collection of air and seawater pCO2 within ± 2 µatm based on comparisons with established ship-board underway systems, with previously described MAPCO2 systems, and with companion ASVCO2 systems deployed side-by-side.

Continue reading ‘Evaluation of a new carbon dioxide system for autonomous surface vehicles’

Reversible and high accuracy pH colorimetric sensor array based on a single acid-base indicator working in a wide pH interval

Highlights

• Reversible pH CSA working within 7 pH units by using only one pH indicator.

• Use of a suitable surfactant to vary the pKa of the indicator over 7 pH units.

• Error minimization (0.01 pH units) with a model computing the optimal spots number.

• A pH CSA with analytical performance comparable to the glass electrode.

Abstract

A pH colorimetric sensor array (CSA) with fast response time (<1 min) using only one acid-base indicator, Bromothymol Blue (BB), was prepared and characterized by modulating the amount, C, of the surfactant Hexadecyltrimethylammonium p-toluenesulfonate between 0 and 0.3725 gCTApTs/gprecursor with a constant amount of the OrMoSil precursors. The effect of the C increase is a continuous acidic shift of the calibration position, i.e. a huge variation of the pKa value of BB in the pH range 5.80-13.50. The precision error decreased with increasing C from 0.096 pH units (lower C values) to 0.023 pH units (larger C values). This result led to the development of a model to determine the number of spots with suitable C values required for having a similar value of precision in the entire working interval of the CSA. By selecting only 4 spots the precision error is < 0.100 pH units in the pH range 5.80–13.50. With 256 spots (diameter of each spot ≈ 3 mm), the model predicted an error almost constant (≈0.010) in the entire pH range.

Continue reading ‘Reversible and high accuracy pH colorimetric sensor array based on a single acid-base indicator working in a wide pH interval’

Calcification of planktonic foraminifer Pulleniatina obliquiloculata controlled by seawater temperature rather than ocean acidification

Highlights

• A method is provided to correct the dissolution effect on foraminiferal SNW

• Core-top ISNWP. obli is positively correlated with calcification temperature

• ISNWP. obli linked to seawater temperature, but not atmospheric pCO2, since 250 ka

• Temperature is the dominant factor controlling P. obliquiloculata calcification

Abstract

Planktonic foraminifera represent a major component of global marine carbonate production, and understanding environmental influences on their calcification is critical to predicting marine carbon cycle responses to modern climate change. The present study investigated the effects of different environmental influences on calcification of the planktonic foraminifer Pulleniatina obliquiloculata. By correcting the dissolution effect on the size-normalized weight (SNW) of P. obliquiloculata from deep-sea sediments, we provide a means of estimating initial size-normalized weight (ISNW) from which to assess secular changes in the degree of calcification of P. obliquiloculata. Core-top ISNW in P. obliquiloculata from the global tropical oceans is significantly positively correlated with calcification temperature, suggesting that temperature is the dominant control on calcification. Using Neogloboquadrina dutertrei SNW as an independent deep-water Δ[CO32−] proxy, we present an ISNW record for P. obliquiloculata from the western tropical Pacific since 250 ka. The response of ISNW to past seawater temperature variations further confirms the dominant influence of temperature on P. obliquiloculata calcification. A potential increase in calcification as a result of ocean warming may have reduced oceanic uptake of CO2 from the atmosphere and increased atmospheric pCO2, generating a positive feedback for global warming.

Continue reading ‘Calcification of planktonic foraminifer Pulleniatina obliquiloculata controlled by seawater temperature rather than ocean acidification’

Global ocean spectrophotometric pH assessment: consistent inconsistencies

Ocean Acidification (OA)—or the decrease in seawater pH resulting from ocean uptake of CO2 released by human activities—stresses ocean ecosystems and is recognized as a Climate and Sustainable Development Goal Indicator that needs to be evaluated and monitored. Monitoring OA related pH changes requires a high level of precision and accuracy. The two most common ways to quantify seawater pH are to measure it spectrophotometrically or to calculate it from Total Alkalinity (TA) and Dissolved Inorganic Carbon (DIC). However, despite decades of research, small but important inconsistencies remain between measured and calculated pH. To date, this issue has been circumvented by examining changes only in consistently-measured properties. Currently, the oceanographic community is defining new observational strategies for OA and other key aspects of the ocean carbon cycle based on novel sensors and technologies, that rely on validation against data records and/or synthesis products. Comparison of measured spectrophotometric pH to calculated pH from TA and DIC measured during the 2000s and 2010s eras, reveals that: 1) there is an evolution towards a better agreement between measured and calculated pH over time from 0.02 pH units in the 2000s to 0.01 pH units in the 2010s at pH>7.6; 2) a disagreement greater than 0.01 pH units persists in waters with pH<7.6, and 3) inconsistencies likely stem from variations in the spectrophotometric pH standard operating procedure (SOP). A reassessment of pH measurement and calculation SOPs and metrology is urgently needed.

Continue reading ‘Global ocean spectrophotometric pH assessment: consistent inconsistencies’

The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii) (update)

The high-latitude oceans are key areas of carbon and heat exchange between the atmosphere and the ocean. As such, they are a focus of both modern oceanographic and palaeoclimate research. However, most palaeoclimate proxies that could provide a long-term perspective are based on calcareous organisms, such as foraminifera, that are scarce or entirely absent in deep-sea sediments south of 50 S in the Southern Ocean and north of 40 N in the North Pacific. As a result, proxies need to be developed for the opal-based organisms (e.g. diatoms) found at these high latitudes, which dominate the biogenic sediments recovered from these regions. Here we present a method for the analysis of the boron (B) content and isotopic composition (δ11B) of diatom opal. We apply it for the first time to evaluate the relationship between seawater pH, δ11B and B concentration ([B]) in the frustules of the diatom Thalassiosira weissflogii, cultured across a range of carbon dioxide partial pressure (pCO2) and pH values. In agreement with existing data, we find that the [B] of the cultured diatom frustules increases with increasing pH (Mejía et al., 2013). δ11B shows a relatively well defined negative trend with increasing pH, completely distinct from any other biomineral previously measured. This relationship not only has implications for the magnitude of the isotopic fractionation that occurs during boron incorporation into opal, but also allows us to explore the potential of the boron-based proxies for palaeo-pH and palaeo-CO2 reconstruction in high-latitude marine sediments that have, up until now, eluded study due to the lack of suitable carbonate material.

Continue reading ‘The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii) (update)’

Mid-infrared sensor system based on tunable laser absorption spectroscopy for dissolved carbon dioxide analysis in the South China Sea: system-level integration and deployment

System-level integration of a mid-infrared carbon dioxide (CO2) sensor system based on tunable laser absorption spectroscopy (TLAS) was realized for the analysis of dissolved CO2 in seawater employing an interband cascade laser (ICL) centered at 4319 nm and a multi-pass cell (MPC) with an optical path length of 29.8 m. At low measurement pressure of 30 Torr, three absorption lines of 12CO2 were selected to realize different measurement ranges, and a 13CO2 absorption line was targeted for simultaneous isotopic abundance analysis of δ13CO2. The sensor system was compactly integrated into a standalone system with automatic operation for underwater field deployment, and the working process was controlled by a specially-designed electrical system. A gas-liquid separator system was developed for CO2 extraction from water, and a pressure-control mechanism with two operation modes (i.e. static and dynamic mode) was proposed to make the sensor system applicable under deep-sea environment. Series of experiments were carried out in laboratory for performance assessment of the developed sensor system employed for the analysis of dissolved CO2 in water. The sensor was deployed for a field test for natural gas hydrates exploration at an underwater depth of 0−2000 m in the South China Sea, with the sensor operating normally during the deployment.

Continue reading ‘Mid-infrared sensor system based on tunable laser absorption spectroscopy for dissolved carbon dioxide analysis in the South China Sea: system-level integration and deployment’

Technical note: Seamless gas measurements across Land-Ocean Aquatic Continuum – corrections and evaluation of sensor data for CO2, CH4 and O2 from field deployments in contrasting environments

Comparatively the ocean and inland waters are two separate worlds, with concentrations in greenhouse gases having orders of magnitude in difference between the two. Together they create the Land-Ocean Aquatic Continuum (LOAC), which comprises itself largely of areas with little to no data in regards to understanding the global carbon system. Reasons for this include remote and inaccessible sample locations, often tedious methods that require collection of water samples and subsequent analysis in the lab, as well as the complex interplay of biological, physical and chemical processes. This has led to large inconsistencies, increasing errors and inevitably leading to potentially false upscaling. Here we demonstrate successful deployment in oceanic to remote inland regions, over extreme concentration ranges with multiple pre-existing oceanographic sensors combined set-up, allowing for highly detailed and accurate measurements. The set-up consists of sensors measuring pCO2pCH4 (both flow-through, membrane-based NDIR or TDLAS sensors), O2, and a thermosalinograph at high-resolution from the same water source simultaneously. The flexibility of the system allowed deployment from freshwater to open ocean conditions on varying vessel sizes, where we managed to capture day-night cycles, repeat transects and also delineate small scale variability. Our work demonstrates the need for increased spatiotemporal monitoring, and shows a way to homogenize methods and data streams in the ocean and limnic realms.

Continue reading ‘Technical note: Seamless gas measurements across Land-Ocean Aquatic Continuum – corrections and evaluation of sensor data for CO2, CH4 and O2 from field deployments in contrasting environments’

Subsurface Automated Samplers (SAS) for ocean acidification research

Ocean acidification (OA) is the process whereby anthropogenic carbon dioxide is absorbed into seawater, resulting in altered carbonate chemistry and a decline in pH. OA will negatively impact numerous marine organisms, altering the structure and function of entire ecosystems. The progression of OA, while faster than has occurred in recent geological history, has been subtle and detection may be complicated by high variability in shallow-water environments. Nevertheless, comprehensive monitoring and characterization is important given the scale and severity of the problem. Presently, technologies used to measure OA in the field are costly and limited by their detection of only one carbonate chemistry parameter, such as pH. Discrete water samples, by contrast, offer a means of measuring multiple components of the carbonate system, including parameters of particular explanatory value (e.g., total alkalinity, dissolved inorganic carbon), for which field-based sensors do not presently exist. Here we describe the design, use, and performance of a low-cost (<$220 USD) Subsurface Automated Sampler (SAS), suitable for the collection of water for carbonate chemistry analysis. Each sampler is field-programmable using a remote control, performs in depths up to 55 m seawater, collects two separately preserved samples, and logs temperature at the time of collection. SASs are designed from the ground up to be open source with respect to physical design and sampling components, electronic hardware, and software. Build instructions, parts lists, and printable 3D files are provided along with code to ultimately lower the cost of OA monitoring, facilitate further research, and encourage application-specific customization.

Continue reading ‘Subsurface Automated Samplers (SAS) for ocean acidification research’

A high precision method for calcium determination in seawater using ion chromatography

Calcium (Ca2+) is an important major cation in seawater, which is closely related to the oceanic biogeochemistry cycle. Direct and accurate determination of Ca2+ concentration is required for a more comprehensive study of the carbonate system in seawater. Due to the high background concentration of Ca2+ in seawater and small variances of Ca2+ during CaCO3 precipitation and dissolution process, a precision of better than 0.1% (of approximately ± 10 μmol/kg) is very much desired for carbonate chemistry related studies. In this study, a simple, non-toxic and labor-saving technique using ion chromatography (IC) has been developed to determine Ca2+ in seawater with an overall precision of better than 0.1%. Due to lack of available commercial calcium standard in seawater matrix, IAPSO seawater was selected as the reference after calibration. This proposed method can get a result within 15 min and only requires a small sample volume (∼1 ml). The concentrations and flow rates of the eluent have been optimized to achieve the best chromatographic separation (20 mmol/L and 1.0 mL/min were selected in this study). Our work suggests that sample dilutions by weighing have no discernible effect on Ca2+ determinations. However, the measured Ca2+ concentration shows a linear decrease with the increasing Mg/Ca ratio in samples, which could be corrected by a derived formula to achieve high accuracy within 0.1%. This optimized method has been applied to the analysis of Ca2+ distribution in Southwest Indian Ocean and the laboratory study on the calcite precipitation in seawater.

Continue reading ‘A high precision method for calcium determination in seawater using ion chromatography’

Pressure compensated pH sensor (United States Patent)

Inventors: Daryl Allen Carlson, Jesse John Bauman, David Dahl Walter, Matthew Eric D’Asaro

An embodiment a pressure compensated pH sensor apparatus, including: a pH sensing component comprising a sensing portion that is exposed to a fluid source when in use; a pressure chamber located in a position under the sensing portion and that envelopes all of the sensing portion not exposed to the fluid source when in use; and a pressure compensation mechanism located within the pressure chamber, wherein the pressure compensation mechanism reacts to pressure from an environment outside the apparatus, thereby support the sensing portion.

Continue reading ‘Pressure compensated pH sensor (United States Patent)’


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OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book