Posts Tagged 'methods'

An alternative to static climatologies: robust estimation of open ocean CO2 variables and nutrient concentrations from T, S, and O2 data using Bayesian neural networks

This work presents two new methods to estimate oceanic alkalinity (AT), dissolved inorganic carbon (CT), pH, and pCO2 from temperature, salinity, oxygen, and geolocation data. “CANYON-B” is a Bayesian neural network mapping that accurately reproduces GLODAPv2 bottle data and the biogeochemical relations contained therein. “CONTENT” combines and refines the four carbonate system variables to be consistent with carbonate chemistry. Both methods come with a robust uncertainty estimate that incorporates information from the local conditions. They are validated against independent GO-SHIP bottle and sensor data, and compare favorably to other state-of-the-art mapping methods. As “dynamic climatologies” they show comparable performance to classical climatologies on large scales but a much better representation on smaller scales (40–120 d, 500–1,500 km) compared to in situ data. The limits of these mappings are explored with pCO2 estimation in surface waters, i.e., at the edge of the domain with high intrinsic variability. In highly productive areas, there is a tendency for pCO2 overestimation due to decoupling of the O2 and C cycles by air-sea gas exchange, but global surface pCO2 estimates are unbiased compared to a monthly climatology. CANYON-B and CONTENT are highly useful as transfer functions between components of the ocean observing system (GO-SHIP repeat hydrography, BGC-Argo, underway observations) and permit the synergistic use of these highly complementary systems, both in spatial/temporal coverage and number of observations. Through easily and robotically-accessible observations they allow densification of more difficult-to-observe variables (e.g., 15 times denser AT and CT compared to direct measurements). At the same time, they give access to the complete carbonate system. This potential is demonstrated by an observation-based global analysis of the Revelle buffer factor, which shows a significant, high latitude-intensified increase between +0.1 and +0.4 units per decade. This shows the utility that such transfer functions with realistic uncertainty estimates provide to ocean biogeochemistry and global climate change research. In addition, CANYON-B provides robust and accurate estimates of nitrate, phosphate, and silicate. Matlab and R code are available at https://github.com/HCBScienceProducts/.

Continue reading ‘An alternative to static climatologies: robust estimation of open ocean CO2 variables and nutrient concentrations from T, S, and O2 data using Bayesian neural networks’

Potential influence of ocean acidification on deep-sea Fe–Mn nodules and pelagic clays: an improved assessment by using artificial seawater

In order to assess the potential risk of metal release from deep-sea sediments in response to pH decrease in seawater, the mobility of elements from ferromanganese (Fe–Mn) nodules and pelagic clays was examined. Two geochemical reference samples (JMn-1 and JMS-2) were reacted with the pH-controlled artificial seawater (ASW) using a CO2-induced pH regulation system. Our experiments demonstrated that deep-sea sediments have weak buffer capacities by acid–base dissociation of surface hydroxyl groups on metal oxides/oxyhydroxides and silicate minerals. Element concentrations in the ASW were mainly controlled by elemental speciation in the solid phase and sorption–desorption reaction between the charged solid surface and ion species in the ASW. These results indicated that the release of heavy metals such as Mn, Cu, Zn and Cd should be taken into consideration when assessing the influence of ocean acidification on deep-sea environment.

Continue reading ‘Potential influence of ocean acidification on deep-sea Fe–Mn nodules and pelagic clays: an improved assessment by using artificial seawater’

Ocean acidification can interact with ontogeny to determine the trace element composition of bivalve shell

We sought to determine how pCO2 will affect the incorporation of trace elements into bivalve shell. This was to validate that under high pCO2 conditions reconstruction of animal movements is still viable; and to investigate potential trace element proxies for ocean carbonate chemistry. Here, we examined shell of the bivalve Perna canaliculus formed under current CO2 (pCO2 = 400 μatm) conditions and those predicted to exist in 2100 (pCO2 = 1050 μatm). Seventeen trace element:calcium ratios were examined at two locations within shells. Elements that are typically most useful in determining connectivity patterns (e.g., Sr, Mn, Ba, Mg, B) were not affected by pCO2 in shell produced early in individual’s lives. This suggests that the effects of ocean acidification on dispersal signatures may be dampened. However, cobalt, nickel, and titanium levels were influenced by pCO2 consistently across shells suggesting their role as potential indicators of CO2 level.

Continue reading ‘Ocean acidification can interact with ontogeny to determine the trace element composition of bivalve shell’

A simple colorimetric method for determining seawater alkalinity using bromophenol blue

The development of small portable USB‐spectrophotometer systems makes monitoring alkalinity and pH possible in the field and remote locations. Here, we present a method utilizing purified bromophenol blue (BPB) as an end‐point indicator for making simple one‐point alkalinity measurements with spectrophotometric detection. The approach utilizes purified BPB dye whose absorbance characteristics have been determined over a range of temperatures and salinities. The end‐point pH for titrated samples was determined using the BPB absorbance ratio (R(t) = 25 A590/A436) for the acid and base forms via the following equation: urn:x-wiley:15415856:media:lom310253:lom310253-math-0001, where, e1 = 0.00533, e2 = 2.232, e3 = 0.0319. A pKa of 3.513 was determined for the dissociation of the second proton from the BPB dye. The temperature (t) dependence of R can be expressed using the following relationship: urn:x-wiley:15415856:media:lom310253:lom310253-math-0002. The dependence of the pKa on salinity (S) was weak and can be expressed as urn:x-wiley:15415856:media:lom310253:lom310253-math-0003. Application of the method for determining the alkalinity of in‐house and certified standards typically produced an uncertainty of ± 1.5 μmol kg−1 for purified BPB dye. When the impure BPB dye was used as an end‐point indicator the uncertainty for alkalinity measured was slightly higher at approximately ± 3–4 μmol kg−1. Hence, if high‐precision alkalinity measurements are not required (≥ 4 μmol kg−1) then utilization of the unpurified BPB maybe suitable. We also compared the use of BPB to two other dyes: bromocresol purple (BCP) and bromocresol green (BCG). The utilization of all three dyes for end‐point determination produced comparable results with an overall precision of ± 4 μmol kg−1. The one‐point titration method using BPB was utilized at a remote field location, One Tree Island, Australia and was found to be suitable for producing accurate and precise alkalinity data in a timely manner; ∼ 10–15 samples can be determined per hour. When combined with seawater pH measurements, the one‐point titration method allows the full marine carbonate system to be fully constrained without the need for high‐tech spectrophotometric equipment and comprehensive laboratory facilities.

Continue reading ‘A simple colorimetric method for determining seawater alkalinity using bromophenol blue’

A strain gauge monitor (SGM) for continuous valve gape measurements in bivalve molluscs in response to laboratory induced diel-cycling hypoxia and pH

An inexpensive, laboratory-based, strain gauge valve gape monitor (SGM) was developed to monitor the valve gape behavior of bivalve molluscs in response to diel-cycling hypoxia. A Wheatstone bridge was connected to strain gauges that were attached to the shells of oysters (Crassostrea virginica). The recorded signals allowed for the opening and closing of the bivalves to be recorded continuously over two-day periods of experimentally-induced diel-cycling hypoxia and diel-cycling changes in pH. Here, we describe a protocol for developing an inexpensive strain gauge monitor and describe, in an example laboratory experiment, how we used it to measure the valve gape behavior of Eastern oysters (C. virginica), in response to diel-cycling hypoxia and cyclical changes in pH. Valve gape was measured on oysters subjected to cyclical severe hypoxic (0.6 mg/L) dissolved oxygen conditions with and without cyclical changes in pH, cyclical mild hypoxic (1.7 mg/L) conditions and normoxic (7.3 mg/L) conditions. We demonstrate that when oysters encounter repeated diel cycles, they rapidly close their shells in response to severe hypoxia and close with a time lag to mild hypoxia. When normoxia is restored, they rapidly open again. Oysters did not respond to cyclical pH conditions superimposed on diel cycling severe hypoxia. At reduced oxygen conditions, more than one third of the oysters closed simultaneously. We demonstrate that oysters respond to diel-cycling hypoxia, which must be considered when assessing the behavior of bivalves to dissolved oxygen. The valve SGM can be used to assess responses of bivalve molluscs to changes in dissolved oxygen or contaminants. Sealing techniques to better seal the valve gape strain gauges from sea water need further improvement to increase the longevity of the sensors.

Continue reading ‘A strain gauge monitor (SGM) for continuous valve gape measurements in bivalve molluscs in response to laboratory induced diel-cycling hypoxia and pH’

Carbon sequestration via enhanced weathering of peridotites and basalts in seawater

Highlights

• Enhanced weathering of ultrafine peridotites and basalts in seawater was studied.
• Open system experiments were performed in batch reactors at ambient conditions.
• Peridotites induced CO2 drawdown directly from the atmosphere via mineralization.
• The basalt did not yield any significant changes in seawater composition.
• The precipitation of sepiolite could reduce the carbon sequestration efficiency.

Abstract

Enhanced weathering of mafic and ultramafic rocks has been suggested as a carbon sequestration strategy for the mitigation of climate change. This study was designed to assess the potential drawdown of CO2 directly from the atmosphere by the enhanced weathering of peridotites and basalts in seawater. Pulverized, and ball milled dunite, harzburgite and olivine basalt were reacted in artificial seawater in batch reactor systems open to the atmosphere for two months. The results demonstrate that the ball-milled dunite and harzburgite changed dramatically the chemical composition of the seawater within a few hours, inducing CO2 drawdown directly from the atmosphere and ultimately the precipitation of aragonite. In contrast, pulverized but unmilled rocks, and the ball-milled basalt, did not yield any significant changes in seawater composition during the two-month experiments. As much as 10 wt percent aragonite was precipitated during the experiment containing the finest-grained dunite. These results demonstrate that ball milling can substantially enhance the weathering rate of peridotites in marine environments, promoting the permanent storage of CO2 as environmentally benign carbonate minerals through enhanced weathering. The precipitation of Mg-silicate clay minerals, however, could reduce the efficiency of this carbon sequestration approach over longer timescales.

 

Continue reading ‘Carbon sequestration via enhanced weathering of peridotites and basalts in seawater’

A versatile optode system for oxygen, carbon dioxide, and pH measurements in seawater with integrated battery and logger

Herein, we present a small and versatile optode system with integrated battery and logger for monitoring of O2, pH, and pCO2 in seawater. Three sensing materials designed for seawater measurements are optimized with respect to dynamic measurement range and long‐term stability. The spectral properties of the sensing materials were tailored to be compatible with a commercially available laboratory oxygen logger that was fitted into a pressure housing. Interchangeable sensor caps with appropriate “sensing chemistry” are conveniently attached to the end of the optical fiber. This approach allows using the same instrument for multiple analytes, which offers great flexibility and minimizes hardware costs. Applications of the new optode system were demonstrated by recording depth profiles for the three parameters during a research cruise in the Baltic Sea and by measuring surface water transects of pH. The optode was furthermore used to monitor the concentration of dissolved oxygen in a seagrass meadow in the Limfjord, Denmark, and sensor packages consisting of pO2, pH, and pCO2 were deployed in the harbors of Kiel, Germany, and Southampton, England, for 6 d. The measurements revealed that the system can resolve typical patterns in seawater chemistry related to spatial heterogeneities as well as temporal changes caused by biological and tidal activity.

Continue reading ‘A versatile optode system for oxygen, carbon dioxide, and pH measurements in seawater with integrated battery and logger’


Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,113,444 hits

OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book