Posts Tagged 'methods'

The role of natural variability in shaping the response of coral reef organisms to climate change

Purpose of Review

We investigate whether regimes of greater daily variability in temperature or pH result in greater tolerance to ocean warming and acidification in key reef-building taxa (corals, coralline algae).

Recent Findings

Temperature and pH histories will likely influence responses to future warming and acidification. Past exposure of corals to increased temperature variability generally leads to greater thermotolerance. However, the effects of past pH variability are unclear. Variability in pH or temperature will likely modify responses during exposure to stressors, independent of environmental history. In the laboratory, pH variability often limited the effects of ocean acidification, but the effects of temperature variability on responses to warming were equivocal.


Environmental variability could alter responses of coral reef organisms to climate change. Determining how both environmental history as well as the direct impacts of environmental variability will interact with the effects of anthropogenic climate change should now be high priority.

Continue reading ‘The role of natural variability in shaping the response of coral reef organisms to climate change’

Methods for reconstruction of paleo-seawater pH based on boron isotopes in evaporative depositional sequences: case study using the Cambrian–Lower Ordovician evaporite sequence in the Tarim Block, NW China

Evaluation of paleo-seawater pH is an important aspect to study the paleo-ocean environment. The Paleozoic strata lack foraminiferal shells; therefore, reconstruction of paleo-seawater pH is difficult. In this paper, the Cambrian–Lower Ordovician evaporate sequence present in the Tarim Basin is used as an example to work out methods for reconstruction of paleo-seawater pH for evaporate sequences through study of boron isotopes. Analysis of diagenetically unaltered samples yields δ11B values for normal seawater in an open environment ranging from 7.5 to 12.6‰ (average = 9.4‰) and those of evaporative salt-lake facies ranging from − 4.7 to − 1.8‰ (average = − 3.3‰). With increase in the rate of evaporation of seawater, its pH decreases gradually and the δ11B values of tricoordinated and tetracoordinated compounds decrease synchronously. Using a salt-lake brine with pH 7, δ11B value in sedimentary rock of − 3.3‰ and unfractionated δ11B in tetracoordinated B(OH)4 in solution, the average δ11B of the Middle Cambrian–Early Ordovician paleo-seawater came to be 16.2‰. It establishes a workable relationship between δ11B in sedimentary rock and seawater pH. The Middle Cambrian–Early Ordovician normal paleo-seawater pH estimated using the δ11B value of sedimentary rock representing the weakest evaporation intensity is ~ 9.1 that is 0.9 higher than pH of modern seawater. In these calculations, it is assumed that the total dissolved inorganic carbon is unchanged between the Cambrian–Early Ordovician paleo-seawater and modern seawater and the [CO32−] content in the paleo-seawater is greater by a factor of 2–3 than that in modern seawater. This increase in [CO32−] content is inferred to be one of the main factors for the widespread development of dolomite.

Continue reading ‘Methods for reconstruction of paleo-seawater pH based on boron isotopes in evaporative depositional sequences: case study using the Cambrian–Lower Ordovician evaporite sequence in the Tarim Block, NW China’

Assessment of the suitability of Durafet-based sensors for pH measurement in dynamic estuarine environments


• We deployed a SeapHOx sensor package in a dynamic estuarine environment.
• We evaluated Durafet performance over a wide salinity range (S = 3.25 to 29.33).
• We evaluated Durafet performance over rapid pH fluctuations of >1 pH unit.
• The sensor performed well (pH RMSE = 0.011 to 0.036) relative to discrete samples.
• We highlighted aspects of electrode response in estuaries requiring further study.


The suitability of the Honeywell Durafet to the measurement of pH in productive, high-fouling, and highly-turbid estuarine environments was investigated at the confluence of the Murderkill Estuary and Delaware Bay (Delaware, USA). Three different flow configurations of the SeapHOx sensor equipped with a Honeywell Durafet and its integrated internal (Ag/AgCl reference electrode containing a 4.5 M KCl gel liquid junction) and external (solid-state chloride ion selective electrode, Cl-ISE) reference electrodes were deployed for four periods between April 2015 and September 2016. In this environment, the Honeywell Durafet proved capable of making high-resolution and high-frequency pH measurements on the total scale between pH 6.8 and 8.4. Natural pH fluctuations of >1 pH unit were routinely captured over a range of timescales. The sensor pH collected between May and August 2016 using the most refined SeapHOx configuration exhibited good agreement with multiple sets of independently measured reference pH values. When deployed in conjunction with rigorous discrete sampling and calibration schemes, the sensor pH had a root-mean squared error ranging between 0.011 and 0.036 pH units across a wide range of salinity relative to both pHT calculated from measured dissolved inorganic carbon and total alkalinity and pHNBS measured with a glass electrode corrected to pHT at in situ conditions. The present work demonstrates the viability of the Honeywell Durafet to the measurement of pH to within the weather-level precision defined by the Global Ocean Acidification Observing Network (GOA-ON, ≤ 0.02 pH units) as a part of future

Continue reading ‘Assessment of the suitability of Durafet-based sensors for pH measurement in dynamic estuarine environments’

Spectrophotometric pH measurements from river to sea: calibration of mCP for 0 ≤ S ≤ 40 and 278.15 ≤ T ≤ 308.15 K


• Need for a spectrophotometric model using purified mCP across the estuarine salinity range is described.
• Estuarine pH data using unpurified mCP are corrected for impurity absorbances.
• A new model is presented to characterize behavior of purified mCP across the range of temperatures and salinities for temperate estuaries.
• New estuarine model corroborates models of purified mCP in pure water and seawater and bridges the salinity gap between them.


The indicator meta-cresol purple (mCP) has been widely used for spectrophotometric pH measurements in seawater and has been recently used in freshwater as well. Previous works have not, however, provided the comprehensive characterization of purified mCP (equilibrium and spectral behavior) required for pH measurements across the full ranges of temperature (T) and salinity (S) found in temperate estuaries. This work provides, for the first time, a comprehensive S– and T-dependent model for spectrophotometric pH measurements appropriate to freshwater, estuarine water, and seawater. Our model combines previous characterizations of the behavior of (a) purified mCP in pure water (S = 0), (b) purified mCP in seawater (20  S  40), and (c) unpurified mCP at 298.15 K and 0  S  40, herein corrected for the effects of impurities. Using the ratio (R) of mCP absorbances at 578 nm and 434 nm, the summary equations for calculations of pH on the total proton concentration scale for the conditions of 0  S  40 and 278.15  T  308.15 K are as follows:


where e1 =  0.007762 + 4.5174 10 5 T


This new model, appropriate for use with purified mCP, produces pH values that are within ± 0.004 of those obtained using previously published data and purified-mCP models for pure water and seawater.

Continue reading ‘Spectrophotometric pH measurements from river to sea: calibration of mCP for 0 ≤ S ≤ 40 and 278.15 ≤ T ≤ 308.15 K’

Fluctuating seawater pH/pCO2 regimes are more energetically expensive than static pH/pCO2 levels in the mussel Mytilus edulis

Ocean acidification (OA) studies typically use stable open-ocean pH or CO2 values. However, species living within dynamic coastal environments can naturally experience wide fluctuations in abiotic factors, suggesting their responses to stable pH conditions may not be reflective of either present or near-future conditions. Here we investigate the physiological responses of the mussel Mytilus edulis to variable seawater pH conditions over short- (6 h) and medium-term (2 weeks) exposures under both current and near-future OA scenarios. Mussel haemolymph pH closely mirrored that of seawater pH over short-term changes of 1 pH unit with acidosis or recovery accordingly, highlighting a limited capacity for acid–base regulation. After 2 weeks, mussels under variable pH conditions had significantly higher metabolic rates, antioxidant enzyme activities and lipid peroxidation than those exposed to static pH under both current and near-future OA scenarios. Static near-future pH conditions induced significant acid–base disturbances and lipid peroxidation compared with the static present-day conditions but did not affect the metabolic rate. These results clearly demonstrate that living in naturally variable environments is energetically more expensive than living in static seawater conditions, which has consequences for how we extrapolate future OA responses in coastal species.

Continue reading ‘Fluctuating seawater pH/pCO2 regimes are more energetically expensive than static pH/pCO2 levels in the mussel Mytilus edulis’

Advancing ocean acidification biology using Durafet® pH electrodes

Research assessing the biological impacts of global ocean change often requires a burdensome characterization of seawater carbonate chemistry. For laboratory-based ocean acidification research, this impedes the scope of experimental design. Honeywell Durafet® III pH electrodes provide precise and continuous seawater pH measurements. In addition to use in oceanographic sensor packages, Durafets can also be used in the laboratory to track and control seawater treatments via Honeywell Universal Dual Analyzers (UDAs). Here we provide performance data, instructions, and step-by-step recommendations for use of multiple UDA-Durafets. Durafet pH measurements were within ±0.005 units pHT of spectrophotometric measurements and agreement among eight Durafets was better than ±0.005 units pHT. These results indicate equal performance to Durafets in oceanographic sensor packages, but methods for calibration and quality control differ. Use of UDA-Durafets vastly improves time-course documentation of experimental conditions and reduces person-hours dedicated to this activity. Due to the versatility of integrating Durafets in laboratory seawater systems, this technology opens the door to advance the scale of questions that the ocean acidification research community aims to address.

Continue reading ‘Advancing ocean acidification biology using Durafet® pH electrodes’

Comment on “Bioerosion: the other ocean acidification problem”: on field studies and mechanisms

In a recent review, “Bioerosion: the other ocean acidification problem,” Schönberg et al. claim that studies of bioerosion across natural chemical gradients are “flawed” or “compromised” by co-variation among environmental factors. Their discussion falls largely on two publications, Silbiger et al. and DeCarlo et al. Here, we demonstrate that critical errors in plotting, statistical analysis, and data selection in Schönberg et al.’s reanalysis, result in a gross misrepresentation of these studies. Further, we argue three key points regarding field-based studies that require broader discussion within the bioerosion community and marine scientists in general: (1) that natural variability in field studies is not a flaw, (2) interpretations must be supported by mechanistic understanding, and (3) field-based studies play an essential role in elucidating interactions between OA and natural variability that is not captured by laboratory CO2-manipulation experiments. Our goal with this comment is to encourage open discussion of the advantages and caveats of field-based studies in general, and ultimately, advance our understanding of bioerosion patterns observed in nature.

Continue reading ‘Comment on “Bioerosion: the other ocean acidification problem”: on field studies and mechanisms’

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Ocean acidification in the IPCC AR5 WG II

OUP book