Publications

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2018
Du, N, Gholami P, Kline DI, Dupont CL, Dickson AG, Mendola D, Martz T, Allen AE, Mitchell BG.  2018.  Simultaneous quantum yield measurements of carbon uptake and oxygen evolution in microalgal cultures. Plos One. 13   10.1371/journal.pone.0199125   AbstractWebsite

The photosynthetic quantum yield (F), defined as carbon fixed or oxygen evolved per unit of light absorbed, is a fundamental but rarely determined biophysical parameter. A method to estimate Phi for both net carbon uptake and net oxygen evolution simultaneously can provide important insights into energy and mass fluxes. Here we present details for a novel system that allows quantification of carbon fluxes using pH oscillation and simultaneous oxygen fluxes by integration with a membrane inlet mass spectrometer. The pHOS system was validated using Phaeodactylum tricornutum cultured with continuous illumination of 110 mu mole quanta m(-2) s(-1) at 25 degrees C. Furthermore, simultaneous measurements of carbon and oxygen flux using the pHOS-MIMS and photon flux based on spectral absorption were carried out to explore the kinetics of F in P. tricornutum during its acclimation from low to high light (110 to 750 mu mole quanta m(-2) s(-1)). Comparing results at 0 and 24 hours, we observed strong decreases in cellular chlorophyll a (0.58 to 0.21 pg cell(-1)), Fv/Fm (0.71 to 0.59) and maximum Phi(CO2) (0.019 to 0.004) and Phi(O2) (0.028 to 0.007), confirming the transition toward high light acclimation. The Phi time-series indicated a non-synchronized acclimation response between carbon uptake and oxygen evolution, which has been previously inferred based on transcriptomic changes for a similar experimental design with the same diatom that lacked physiological data. The integrated pHOS-MIMS system can provide simultaneous carbon and oxygen measurements accurately, and at the time-resolution required to resolve highresolution carbon and oxygen physiological dynamics.

2017
McLaughlin, K, Dickson A, Weisberg SB, Coale K, Elrod V, Hunter C, Johnson KS, Kram S, Kudela R, Martz T, Negrey K, Passow U, Shaughnessy F, Smith JE, Tadesse D, Washburn L, Weis KR.  2017.  An evaluation of ISFET sensors for coastal pH monitoring applications. Regional Studies in Marine Science. 12:11-18.   10.1016/j.rsma.2017.02.008   AbstractWebsite

The accuracy and precision of ion sensitive field effect transistor (ISFET) pH sensors have been well documented, but primarily by ocean chemistry specialists employing the technology at single locations. Here we examine their performance in a network context through comparison to discrete measurements of pH, using different configurations of the Honeywell DuraFET pH sensor deployed in six coastal settings by operators with a range of experience. Experience of the operator had the largest effect on performance. The average difference between discrete and ISFET pH was 0.005 pH units, but ranged from -0.030 to 0.083 among operators, with more experienced operators within +/- 0.02 pH units of the discrete measurement. In addition, experienced operators achieved a narrower range of variance in difference between discrete bottle measurements and ISFET sensor readings compared to novice operators and novice operators had a higher proportion of data failing quality control screening. There were no statistically significant differences in data uncertainty associated with sensor manufacturer or deployment environment (pier-mounted, flowthrough system, and buoy-mounted). The variation we observed among operators highlights the necessity of best practices and training when instruments are to be used in a network where comparison across data streams is desired. However, while opportunities remain for improving the performance of the ISFET sensors when deployed by less experienced operators, the uncertainty associated with their deployment and validation was several-fold less than the observed natural temporal variability in pH, demonstrating the utility of these sensors in tracking local changes in acidification. (C) 2017 Elsevier B.V. All rights reserved.

Takeshita, Y, Martz TR, Coletti LJ, Dickson AG, Jannasch HW, Johnson KS.  2017.  The effects of pressure on pH of Tris buffer in synthetic seawater. Marine Chemistry. 188:1-5.   10.1016/j.marchem.2016.11.002   AbstractWebsite

Equimolar Tris (2-amino-2-hydroxymethyl-propane-1,3-diol) buffer prepared in artificial seawater media is a widely accepted pH standard for oceanographic pH measurements, though its change in pH over pressure is largely unknown. The change in volume (Delta V) of dissociation reactions can be used to estimate the effects of pressure on the dissociation constant of weak acid and bases. The Delta V of Tris in seawater media of salinity 35 (Delta V-Tris*) was determined between 10 and 30 degrees C using potentiometry. The potentiometric cell consisted of a modified high pressure tolerant Ion Sensitive Field Effect Transistor pH sensor and a Chloride-Ion Selective Electrode directly exposed to solution. The effects of pressure on the potentiometric cell were quantified in aqueous HCl solution prior to measurements in Tris buffer. The experimentally determined Delta V-Tris* were fitted to the equation Delta V-Tris*= 4528 +0.04912t where t is temperature in Celsius; the resultant fit agreed to experimental data within uncertainty of the measurements, which was estimated to be 0.9 cm(-3) mol(-1). Using the results presented here, change in pH of Tris buffer due to pressure can be constrained to better than 0.003 at 200 bar, and can be expressed as: DpH(Tris) = -(4.528 + 0.04912t)p/ln(10)RT. where T is temperature in Kelvin, R is the universal gas constant (83.145 cm(3) bar K-1 mol(-1)), and Pis gauge pressure in bar. On average, pH of Tris buffer changes by approximately -0.02 at 200 bar. (C) 2016 Elsevier B.V. All rights reserved.

2016
Bresnahan, PJ, Wirth T, Martz TR, Andersson AJ, Cyronak T, D’Angelo S, Pennise J, Melville KW, Lenain L, Statom N.  2016.  A sensor package for mapping pH and oxygen from mobile platforms. Methods in Oceanography. 17:1-13.   http://dx.doi.org/10.1016/j.mio.2016.04.004   AbstractWebsite

A novel chemical sensor package named “WavepHOx” was developed in order to facilitate measurement of surface ocean pH, dissolved oxygen, and temperature from mobile platforms. The system comprises a Honeywell Durafet pH sensor, Aanderaa optode oxygen sensor, and chloride ion selective electrode, packaged into a hydrodynamic, lightweight housing. The WavepHOx has been deployed on a stand-up paddleboard and a Liquid Robotics Wave Glider in multiple near-shore settings in the Southern California Bight. Integration of the WavepHOx into these mobile platforms has enabled high spatiotemporal resolution pH and dissolved oxygen data collection. It is a particularly valuable tool for mapping shallow, fragile, or densely vegetated ecosystems which cannot be easily accessed by other platforms. Results from three surveys in San Diego, California, are reported. We show pH and dissolved oxygen variability >0.3 and >50% saturation, respectively, over tens to hundreds of meters to highlight the degree of natural spatial variability in these vegetated ecosystems. When deployed during an extensive discrete sampling program, the WavepHOx pH had a root mean squared error of 0.028 relative to pH calculated from fifty six measurements of total alkalinity and dissolved inorganic carbon, confirming its capacity for accurate, high spatiotemporal resolution data collection.

Takeshita, Y, McGillis W, Briggs EM, Carter A, Donham E, Martz TR, Price NN, Smith JE.  2016.  Assessment of net community production and calcification of a coral reef using a boundary layer approach. Journal of Geophysical Research: Oceans.   10.1002/2016JC011886   Abstract
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2015
Martz, TR, Daly KL, Byrne RH, Stillman JH, Turk D.  2015.  Technology for ocean acidification research: Needs and availability. Oceanography. 28:40-47.   10.5670/oceanog.2015.30   AbstractWebsite

Diverse instruments, both custom built and commercially available, have been used to measure the properties of the aqueous CO2 system in seawater at differing levels of autonomy (automated benchtop, continuous underway, autonomous in situ). In this I review, we compare the capabilities of commercially available instruments with the needs of oceanographers in order to highlight major shortfalls in the state-of-the art instrumentation broadly available to the ocean acidification (OA) scientific community. In addition, we describe community surveys that identify needs for continued development and refinement of sensor and instrument technologies, expansion of programs that provide Certified Reference Materials, development of best practices documentation for autonomous sensors, and continued and expanded sensor intercomparison experiments.

2014
Takeshita, Y, Martz TR, Johnson KS, Dickson AG.  2014.  Characterization of an Ion Sensitive Field Effect Transistor and Chloride Ion Selective Electrodes for pH Measurements in Seawater. Analytical Chemistry. 86:11189-11195.: American Chemical Society   10.1021/ac502631z   AbstractWebsite
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2013
Ohman, MD, Rudnick DL, Chekalyuk A, Davis RE, Feely RA, Kahru M, Kim HJ, Landry MR, Martz TR, Sabine CL, Send U.  2013.  Autonomous ocean measurements in the California Current ecosystem. Oceanography. 26:18-25. AbstractWebsite

Event-scale phenomena, of limited temporal duration or restricted spatial extent, often play a disproportionately large role in ecological processes occurring in the ocean water column. Nutrient and gas fluxes, upwelling and downwelling, transport of biogeochemically important elements, predator-prey interactions, and other processes may be markedly influenced by such events, which are inadequately resolved from infrequent ship surveys. The advent of autonomous instrumentation, including underwater gliders, profiling floats, surface drifters, enhanced moorings, coastal high-frequency radars, and satellite remote sensing, now provides the capability to resolve such phenomena and assess their role in structuring pelagic ecosystems. These methods are especially valuable when integrated together, and with shipboard calibration measurements and experimental programs.

2011
Strutton, PG, Martz TR, DeGrandpre MD, McGillis WR, Drennan WM, Boss E.  2011.  Bio-optical observations of the 2004 Labrador Sea phytoplankton bloom. Journal of Geophysical Research-Oceans. 116   10.1029/2010jc006872   AbstractWebsite

A unique time series of moored bio-optical measurements documented the 2004 spring-summer bloom in the southern Labrador Sea. In situ and satellite chlorophyll data show that chlorophyll levels in the 2004 bloom were at the upper end of those typically observed in this region. Satellite chlorophyll and profiling float temperature/salinity data show that the main bloom, which typically peaks in June/July, is often preceded by ephemeral mixed layer shoaling and a lesser, short-lived bloom in May; this was the case ;in 2004. The particulate backscatter to beam attenuation ratio (b(bp)[470 nm]/C(p)[660 nm]) showed peaks in the relative abundance of small particles at bloom initiation and during the decline of the bloom, while larger particles dominated during the bloom. Chlorophyll/C(p) and b(bp)/chlorophyll were correlated with carbon export and dominated by changes in the pigment per cell associated with lower light levels due to enhanced attenuation of solar radiation during the bloom. An NPZ (nutrients, phytoplankton, zooplankton) model captured the phytoplankton bloom and an early July peak in zooplankton. Moored acoustic Doppler current profiler (ADCP) data showed an additional mid-June peak in zooplankton biomass which was attributed to egg-laying copepods. The data reported here represent one of the few moored time series of C(p), b(bp) and chlorophyll extending over several months in an open ocean region. Interpretation of data sets such as this will become increasingly important as these deployments become more commonplace via ocean observing systems. Moreover, these data contribute to the understanding of biological-physical coupling in a biogeochemically important, yet poorly studied region.

Gray, SEC, DeGrandpre MD, Moore TS, Martz TR, Friederich GE, Johnson KS.  2011.  Applications of in situ pH measurements for inorganic carbon calculations. Marine Chemistry. 125:82-90.   10.1016/j.marchem.2011.02.005   AbstractWebsite

This study examines the utility of combining pH measurements with other inorganic carbon parameters for autonomous mooring-based carbon cycle research. Determination of the full suite of inorganic carbon species in the oceans has previously been restricted to ship-based studies. Now with the availability of autonomous sensors for pH and the partial pressure of CO(2) (pCO(2)), it is possible to characterize the inorganic carbon system on moorings and other unmanned platforms. The indicator-based pH instrument, SAMI-pH, was deployed with an autonomous equilibrator-infrared pCO(2) system in Monterey Bay. California USA from June to August 2007. The two-month time-series show a high degree of short-term variability, with pH and pCO(2) changing by as much as 0.32 pH units and 240 mu atm, respectively, during upwelling periods. The pH and salinity-derived alkalinity (A(Tsalin)) were used to calculate the other inorganic carbon parameters, including pCO(2), total dissolved inorganic carbon (DIC) and CaCO(3) saturation states. The calculated pCO(2) was within 2 mu atm of the measured pCO(2) during the first day of the deployment and within 8 mu atm over the first month. The DIC calculated from pH-A-Ban and pCO(2)-A(Tsalin) were within 5 mu mol kg(-1) of each other during the first month. However, DIC calculated from pH-pCO(2) differed by similar to 50 mu mol kg(-1) from the other estimates over the same period, reflecting the sensitivity of the pH-pCO(2) calculation to measurement error. The data continued to diverge during the final month and this difference was likely driven by extensive biofouling. Because of the relative insensitivity of CO(3)(2-) concentration to these errors, aragonite saturation calculated from the pH-pCO(2) pair was within 0.15 of the pH-A(Tsalin) values over the entire deployment. These results show that in situ pH, when combined with other CO(2) parameters, can provide valuable insights into both data quality and inorganic carbon cycling. (C) 2011 Elsevier B.V. All rights reserved.

DeGrandpre, MD, Martz TR, Hart RD, Elison DM, Zhang A, Bahnson AG.  2011.  Universal Tracer Monitored Titrations. Analytical Chemistry. 83:9217-9220.   10.1021/ac2025656   AbstractWebsite

Titrations, while primarily known as the chemical rite of passage for fledgling science students, are still widely used for chemical analysis. With its many years of existence and improvement, the method would seem an unlikely candidate for innovation, yet it is desirable, in this age of autonomous sensing where analyzers may be sent into space or to the bottom of the ocean, to have a simplified titrimetric method that does not rely upon volumetric or gravimetric measurement of sample and titrant. In previous work on the measurement of seawater alkalinity, we found that use of a tracer in the titrant eliminates the need to measure mass or volume. Here, we show the versatility of the method for diverse types of titrations and tracers. The results suggest that tracers may be employed in all types of titrations, opening the door for greatly simplified laboratory and field-based chemical analysis.

2010
Byrne, RH, DeGrandpre MD, Short T, Martz TR, Merlivat L, McNeil C, Sayles F, Bell R, Fietzek P.  2010.  Sensors and Systems for Observations of Marine CO2 System Variables. Proceedings of OceanObs’09: Sustained Ocean Observations and Information for Society . 2( Hall J, Harrison DE, Stammer D, Eds.)., Venice, Italy: ESA Publication WPP-306   10.5270/OceanObs09.cwp.13   Abstract
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2009
Martz, TR, DeGrandpre MD, Strutton PG, McGillis WR, Drennan WM.  2009.  Sea surface pCO(2) and carbon export during the Labrador Sea spring-summer bloom: An in situ mass balance approach. Journal of Geophysical Research-Oceans. 114   10.1029/2008jc005060   AbstractWebsite

We report depth-resolved in situ time series of the partial pressure of CO(2) (pCO(2)) and other carbon-related parameters spanning the development and decline of a high-latitude phytoplankton bloom. A suite of sensors was deployed on a mooring in the Labrador Sea from June to August 2004. The study became quasi-Lagrangian when the mooring broke free in late June. Measured parameters included pCO(2), chlorophyll a fluorescence, beam c, optical backscatter, and photosynthetically active radiation. During the bloom, the pCO(2) was drawn down from 330 to 260 mu atm, corresponding to a 70 mu mol kg(-1) decrease of dissolved inorganic carbon (DIC). One-dimensional model results suggest that the observed drawdown was primarily driven by local processes and contributions from horizontal advection were minimal. A mass balance using the DIC and particulate organic carbon found that 47 mmol C m(-2) d(-1) of DIC was assimilated into biomass. The bloom biomass was not remineralized in the mixed layer but was rapidly exported below 35 m within 15 days of the bloom. As a consequence, the large air-sea pCO(2) gradient persisted, and approximately 30% of the DIC was regained through air-sea exchange by the end of the study. It is likely that all of the exported organic matter, corresponding to 5.4 +/- 1.9 Tg of carbon, was replaced by atmospheric CO(2) prior to the onset of deep convective mixing.

2006
Martz, TR, Dickson AG, DeGrandpre MD.  2006.  Tracer monitored titrations: measurement of total alkalinity. Analytical Chemistry. 78:1817-1826.   10.1021/ac0516133   AbstractWebsite

We introduce a new titration methodology, tracer monitored titration (1741), in which analyses are free of volumetric and gravimetric measurements and insensitive to pump precision and reproducibility. Spectrophotometric monitoring of titrant dilution, rather than volume increment, lays the burden of analytical performance solely on the spectrophotometer. In the method described here, the titrant is a standardized mixture of acid-base indicator and strong acid. Dilution of a pulse of titrant in a titration vessel is tracked using the total indicator concentration measured spectrophotometrically. The concentrations of reacted and unreacted indicator species, derived from Beer's law, are used to calculate the relative proportions of titrant and sample in addition to the equilibrium position (pH) of the titration mixture. Because the method does not require volumetric or gravimetric additions of titrant, simple low-precision pumps can be used. Here, we demonstrate application of TMT for analysis of total alkalinity (AT). High-precision, high-accuracy seawater AT measurements are crucial for understanding, for example, the marine CaCO3 budget and saturation state, anthropogenic CO2 penetration into the oceans, calcareous phytoplankton blooms, and coral reef dynamics. We present data from 286 titrations on three types of total alkalinity standards: Na2CO3 in 0.7 mol kg(.)soln(-1) NaCl, NaOH in 0.7 mol kg(.)soln(-1) NaCl, and a seawater Certified Reference Material (CRM). Based on Na2CO3 standards, the accuracy and precision are +/- 0.2 and +/- 0.1% (4 and 2 mu mol kg-soln(-1) for A(T) similar to 2100-2500 mu mol kg(.)soln(-1), n = 242), using low-precision solenoid pumps to introduce sample and titrant. Similar accuracy and precision were found for analyses run 42 days after the initial experiments. Excellent performance is achieved by optimizing the spectrophotometric detection system and relying upon basic chemical thermodynamics for calculating the equivalence point. Although applied to acid-base titrations in this paper, the approach should be generally applicable to other types of titrations.

2003
Martz, TR, Carr JJ, French CR, DeGrandpre MD.  2003.  A submersible autonomous sensor for spectrophotometric pH measurements of natural waters. Analytical Chemistry. 75:1844-1850.   10.1021/ac020568l   AbstractWebsite

An autonomous sensor for long-term in situ measurements of the pH of natural waters is described. The system is based upon spectrophotometric measurements of a mixture of sample and sulfonephthalein indicator. A simple plumbing design, using a small, low-power solenoid pump and valve, avoids the need for quantitative addition of indicator. A similar to50-muL slug of indicator is pulled into the sample stream by the pump, and subsequent pumping and mixing results in a section of indicator and sample where absorbance measurements can be made. The design also permits direct determination of the indicator pH perturbation. Absorbances are recorded at three wavelengths (439, 579, and 735 nm) using a custom-built 1.7-cm path length fiber-optic flow cell. Solution blanks are obtained by periodically flushing the cell with sample. Field tests were performed in a local river over an 8-day period. The in situ accuracy, based on comparison with laboratory spectrophotometric pH measurements, was -0.003 pH unit (n = 16), similar to the measurement precision. No drift was observed during the 8-day period. The absorbance ratio used to calculate pH, in combination with a simple and robust optical design, imparts an inherent stability not achievable with conventional potentiometric methods, making the design feasible for long-term autonomous pH measurements.