Publications

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2018
Bresnahan, PJ, Martz TR.  2018.  Gas diffusion cell geometry for a microfluidic dissolved inorganic carbon analyzer. Ieee Sensors Journal. 18:2211-2217.   10.1109/jsen.2018.2794882   AbstractWebsite

Variable gas diffusion cell geometries were tested for the extraction of dissolved inorganic carbon (DIC) from a microfluidic (tens to hundreds of microliters) seawater sample. With a focus on optimization of diffusion cell geometry, we compare five unique diffusion cell designs. Using 3-D printing technology to streamline the prototyping and testing process, we were able to conceive, design, fabricate, and thoroughly evaluate each design over the course of about one month. In total, 1043 DIC measurements were carried out in 109 experiments for the five working manifolds. We find that a small diameter, cylindrical diffusion cell design offers several advantages over its planar counterparts and a larger diameter cylindrical cell, most notably the ability to increase the ratio of the exchange membrane's contact surface area to solution volume (the "aspect ratio") without sacrificing channel integrity. Multiple designs approached short-term repeatability of <1%, but only the cylindrical diffusion cell design allowed for <0.2% repeatability using less than 200 mu L of sample.

2017
Briggs, EM, Sandoval S, Erten A, Takeshita Y, Kummel AC, Martz TR.  2017.  Solid State Sensor for Simultaneous Measurement of Total Alkalinity and pH of Seawater. Acs Sensors. 2:1302-1309.   10.1021/acssensors.7b00305   AbstractWebsite

A novel design is demonstrated for a solid state, reagent-less sensor capable of rapid and simultaneous measurement of pH and Total Alkalinity (A(T)) using ion sensitive field effect transistor (ISFET) technology to provide a simplified means of characterization of the aqueous carbon dioxide system through measurement of two "master variables": pH and A(T). ISFET-based pH sensors that achieve 0.001 precision are widely used in various oceanographic applications. A modified ISFET is demonstrated to perform a nanoliter-scale acid base titration of A(T) in under 40 s. This method of measuring A(T), a Coulometric Diffusion Titration, involves electrolytic generation of titrant, through the electrolysis of water on the surface of the chip via a microfabricated electrode eliminating the requirement of external reagents. Characterization has been performed in seawater as well as titrating individual components (i.e., OH-, HCO3-, B(OH)(4)(-), PO43-) of seawater A(T). The seawater measurements are consistent with the design in reaching the benchmark goal of 0.5% precision in A(T) over the range of seawater A(T) of similar to 2200-2500 mu mol kg(-1) which demonstrates great potential for autonomous sensing.

2015
Nam, S, Takeshita Y, Frieder CA, Martz T, Ballard J.  2015.  Seasonal advection of Pacific Equatorial Water alters oxygen and pH in the Southern California Bight. Journal of Geophysical Research-Oceans. 120:5387-5399.   10.1002/2015jc010859   AbstractWebsite

Chemical properties of the California Undercurrent (CU) have been changing over the past several decades, yet the mechanisms responsible for the trend are still not fully understood. We present a survey of temperature, salinity, O-2, pH, and currents at intermediate depths (defined here as 50-500 m) in the summer (30 June to 10 July) and winter (8-15 December) of 2012 in the southern region of the Southern California Bight. Observations of temperature, salinity, and currents reveal that local bathymetry and small gyres play an important role in the flow path of the California Undercurrent (CU). Using spiciness (p) as a tracer, we observe a 10% increase of Pacific Equatorial Water (PEW) in the core of the CU during the summer versus the winter. This is associated with an increase in p of 0.2, and a decrease in O-2 and pH of 30 mu mol kg(-1) and 0.022, respectively; the change in pH is driven by increased CO2, while total alkalinity remains unchanged. The high-p, low-O-2, and low-pH waters during the summer are not distributed uniformly in the study region. Moreover, mooring observations at the edge of the continental shelf reveal intermittent intrusions of PEW onto the shelf with concomitant decreases in O-2 and pH. We estimate that increased advection of PEW in the CU could account for approximately 50% of the observed decrease in O-2, and between 49 and 73% of the decrease in pH, over the past three decades.

2012
Martz, T, Takeshita Y, Rolph R, Bresnahan P.  2012.  Tracer Monitored Titrations: Measurement of Dissolved Oxygen. Analytical Chemistry. 84:290-296.   10.1021/ac202537f   AbstractWebsite

The tracer monitored titration (TMT) technique is evaluated for measurement of dissolved oxygen. The TMT developed in this work uses a simple apparatus consisting of a low-precision pump for titrant delivery and an optical detector based on a white LED and two photodiodes with interference filters. It is shown that the classic Winkler method can be made free of routine volumetric and gravimetric measurements by application of TMT theory, which allows tracking the amounts of titrant and sample using a chemical tracer. The measurement precision of the prototype setup was 0.3% RSD.

2011
Matson, PG, Martz TR, Hofmann GE.  2011.  High-frequency observations of pH under Antarctic sea ice in the southern Ross Sea. Antarctic Science. 23:607-613.   10.1017/s0954102011000551   AbstractWebsite

Although predictions suggest that ocean acidification will significantly impact polar oceans within 20-30 years, there is limited information regarding present-day pH dynamics of the Southern Ocean. Here, we present novel high-frequency observations of pH collected during spring of 2010 using SeaFET pH sensors at three locations under fast sea ice in the southern Ross Sea. During these deployments in McMurdo Sound, baseline pH ranged between 8.019-8.045, with low to moderate overall variation (0.043-0.114 units) on the scale of hours to days. The variation was predominantly in the direction of increased pH relative to baseline observations. Estimates of aragonite saturation state (Omega(Ar)) were > 1 with no observations of subsaturation. Time series records such as these are significant to the Antarctic science community; this information can be leveraged towards framing more environmentally relevant laboratory experiments aimed at assessing the vulnerability of Antarctic species to ocean acidification. In addition, increased spatial and temporal coverage of pH datasets may reveal ecologically significant patterns. Specifically, whether such variation in natural ocean pH dynamics may drive local adaptation to pH variation or provide refugia for populations of marine calcifiers in a future, acidifying ocean.

Kroeker, KJ, Micheli F, Gambi MC, Martz TR.  2011.  Divergent ecosystem responses within a benthic marine community to ocean acidification. Proceedings of the National Academy of Sciences of the United States of America. 108:14515-14520.   10.1073/pnas.1107789108   AbstractWebsite

Ocean acidification is predicted to impact all areas of the oceans and affect a diversity of marine organisms. However, the diversity of responses among species prevents clear predictions about the impact of acidification at the ecosystem level. Here, we used shallow water CO(2) vents in the Mediterranean Sea as a model system to examine emergent ecosystem responses to ocean acidification in rocky reef communities. We assessed in situ benthic invertebrate communities in three distinct pH zones (ambient, low, and extreme low), which differed in both the mean and variability of seawater pH along a continuous gradient. We found fewer taxa, reduced taxonomic evenness, and lower biomass in the extreme low pH zones. However, the number of individuals did not differ among pH zones, suggesting that there is density compensation through population blooms of small acidification-tolerant taxa. Furthermore, the trophic structure of the invertebrate community shifted to fewer trophic groups and dominance by generalists in extreme low pH, suggesting that there may be a simplification of food webs with ocean acidification. Despite high variation in individual species' responses, our findings indicate that ocean acidification decreases the diversity, biomass, and trophic complexity of benthic marine communities. These results suggest that a loss of biodiversity and ecosystem function is expected under extreme acidification scenarios.

2009
Martz, TR, Jannasch HW, Johnson KS.  2009.  Determination of carbonate ion concentration and inner sphere carbonate ion pairs in seawater by ultraviolet spectrophotometric titration. Marine Chemistry. 115:145-154.   10.1016/j.marchem.2009.07.002   AbstractWebsite

We describe a novel method for determination of carbonate ion concentration in seawater by acidimetric titration with UV detection. Because CO(3)(2-) absorbs light at wavelengths of less than similar to 250 nm, it is feasible to titrate most carbonate-containing natural waters with acid and observe an increase in %Transmittance. The observed signal is proportional to the concentration of carbonate ion in the original sample. Present technology permits a theoretical precision in the determination of [CO(3)(2-)] in natural seawater background of similar to 0.5% (at 10 cm pathlength, 200 mu M CO(3)(2-), +/- 0.0001 AU). The procedure has been tested at 1 and 10 cm pathlengths using single and multipoint titration methods, respectively. Results using natural seawater test solutions indicate a resolution in [CO(3)(2-)] of 3.6% in a standard I cm cuvette using a very simple manual method, and 0.7% using a custom-built 10 cm closed titration cell. Estimates of the relative distribution of CO(3)(2-) between inner and outer sphere complexes with Mg(2+) and Na(+) were also determined and the equilibrium constants agree with published values. This method provides a new tool for studies of several fundamental aspects CO(2) chemistry, including the second dissociation constant of carbonic acid, CO(3)(2-) ion pairing, and can be used to directly measure the distribution of carbonate ion in seawater and many other types of natural waters. (C) 2009 Elsevier B.V. All rights reserved.