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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.

Johnson, KS, Jannasch HW, Coletti LJ, Elrod VA, Martz TR, Takeshita Y, Carlson RJ, Connery JG.  2016.  Deep-Sea DuraFET: A Pressure Tolerant pH Sensor Designed for Global Sensor Networks. Analytical Chemistry. 88:3249-3256.   10.1021/acs.analchem.5b04653   AbstractWebsite

Increasing atmospheric carbon dioxide is driving a long-term decrease in ocean pH which is superimposed on daily to seasonal variability. These changes impact ecosystem processes, and they serve as a record of ecosystem metabolism. However, the temporal variability in pH is observed at only a few locations in the ocean because a ship is required to support pH observations of sufficient precision and accuracy. This paper describes a pressure tolerant Ion Sensitive Field Effect Transistor pH sensor that is based on the Honeywell Durafet ISFET die. When combined with a AgCl pseudoreference sensor that is immersed directly in seawater, the system is capable of operating for years at a time on platforms that cycle from depths of several km to the surface. The paper also describes the calibration scheme developed to allow calibrated pH measurements to be derived from the activity of HCl reported by the sensor system over the range of ocean pressure and temperature. Deployments on vertical profiling platforms enable self-calibration in deep waters where pH values are stable. Measurements with the sensor indicate that it is capable of reporting pH with an accuracy of 0.01 or better on the total proton scale and a precision over multiyear periods of 0.005. This system enables a global ocean observing system for ocean pH.

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.   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
Takeshita, Y, Frieder CA, Martz TR, Ballard JR, Feely RA, Kram S, Nam S, Navarro MO, Price NN, Smith JE.  2015.  Including high-frequency variability in coastal ocean acidification projections. Biogeosciences. 12:5853-5870.   10.5194/bg-12-5853-2015   AbstractWebsite

Assessing the impacts of anthropogenic ocean acidification requires knowledge of present-day and future environmental conditions. Here, we present a simple model for upwelling margins that projects anthropogenic acidification trajectories by combining high-temporal-resolution sensor data, hydrographic surveys for source water characterization, empirical relationships of the CO2 system, and the atmospheric CO2 record. This model characterizes CO2 variability on timescales ranging from hours (e. g., tidal) to months (e. g., seasonal), bridging a critical knowledge gap in ocean acidification research. The amount of anthropogenic carbon in a given water mass is dependent on the age; therefore a density-age relationship was derived for the study region and then combined with the 2013 Intergovernmental Panel on Climate Change CO2 emission scenarios to add density-dependent anthropogenic carbon to the sensor time series. The model was applied to time series from autonomous pH sensors deployed in the surf zone, kelp forest, submarine canyon edge, and shelf break in the upper 100m of the Southern California Bight. All habitats were within 5 km of one another, and exhibited unique, habitat-specific CO2 variability signatures and acidification trajectories, demonstrating the importance of making projections in the context of habitat-specific CO2 signatures. In general, both the mean and range of pCO(2) increase in the future, with the greatest increase in both magnitude and range occurring in the deeper habitats due to reduced buffering capacity. On the other hand, the saturation state of aragonite (Omega(Ar)) decreased in both magnitude and range. This approach can be applied to the entire California Current System, and upwelling margins in general, where sensor and complementary hydrographic data are available.

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.

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.

Kapsenberg, L, Kelley AL, Shaw EC, Martz TR, Hofmann GE.  2015.  Near-shore Antarctic pH variability has implications for the design of ocean acidification experiments. Scientific Reports. 5:9638.: The Author(s)   10.1038/srep09638   AbstractWebsite
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
Matson, PG, Washburn L, Martz TR, Hofmann GE.  2014.  Abiotic versus biotic drivers of ocean pH variation under fast sea ice in McMurdo Sound, Antarctica. Plos One. 9   10.1371/journal.pone.0107239   AbstractWebsite

Ocean acidification is expected to have a major effect on the marine carbonate system over the next century, particularly in high latitude seas. Less appreciated is natural environmental variation within these systems, particularly in terms of pH, and how this natural variation may inform laboratory experiments. In this study, we deployed sensor-equipped moorings at 20 m depths at three locations in McMurdo Sound, comprising deep (bottom depth>200 m: Hut Point Peninsula) and shallow environments (bottom depth similar to 25 m: Cape Evans and New Harbor). Our sensors recorded high-frequency variation in pH (Hut Point and Cape Evans only), tide (Cape Evans and New Harbor), and water mass properties (temperature and salinity) during spring and early summer 2011. These collective observations showed that (1) pH differed spatially both in terms of mean pH (Cape Evans: 8.009 +/- 0.015; Hut Point: 8.020 +/- 0.007) and range of pH (Cape Evans: 0.090; Hut Point: 0.036), and (2) pH was not related to the mixing of two water masses, suggesting that the observed pH variation is likely not driven by this abiotic process. Given the large daily fluctuation in pH at Cape Evans, we developed a simple mechanistic model to explore the potential for biotic processes - in this case algal photosynthesis - to increase pH by fixing carbon from the water column. For this model, we incorporated published photosynthetic parameters for the three dominant algal functional groups found at Cape Evans (benthic fleshy red macroalgae, crustose coralline algae, and sea ice algal communities) to estimate oxygen produced/carbon fixed from the water column underneath fast sea ice and the resulting pH change. These results suggest that biotic processes may be a primary driver of pH variation observed under fast sea ice at Cape Evans and potentially at other shallow sites in McMurdo Sound.

Martz, T, Send U, Ohman MD, Takeshita Y, Bresnahan P, Kim HJ, Nam S.  2014.  Dynamic variability of biogeochemical ratios in the Southern California Current System. Geophysical Research Letters. 41:2496-2501.   10.1002/2014gl059332   AbstractWebsite

We use autonomous nitrate (NO3-), oxygen (O-2), and dissolved inorganic carbon (DIC) observations to examine the relationship between ratios of C:N:O at an upwelling site in the Southern California Current System. Mean ratios and 95% confidence intervals observed by sensors over 8 months were NO3-:O-2=-0.110.002, NO3-:DIC=0.140.001, and DIC:O-2=-0.830.01, in good agreement with Redfield ratios. Variability in the ratios on the weekly time scale is attributable to shifts in biological demand and nutrient availability and shown to exhibit a spectrum of values ranging from near 100% New Production to 100% Regenerated Production.

Bresnahan, PJ, Martz TR, Takeshita Y, Johnson KS, LaShomb M.  2014.  Best practices for autonomous measurement of seawater pH with the Honeywell Durafet. Methods in Oceanography.   10.1016/j.mio.2014.08.003  
Paytan, A, Crook ED, Cohen AL, Martz TR, Takeshita Y, Rebolledo-Vieyra M, Hernandez L.  2014.  Reply to Iglesias-Prieto et al.: Combined field and laboratory approaches for the study of coral calcification. Proceedings of the National Academy of Sciences. 3(111)   10.1073/pnas.1319572111  
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.

Takeshita, Y, Martz TR, Johnson KS, Plant JN, Gilbert D, Riser SC, Neill C, Tilbrook B.  2013.  A climatology-based quality control procedure for profiling float oxygen data. Journal of Geophysical Research-Oceans. 118:5640-5650.   10.1002/jgrc.20399   AbstractWebsite

Over 450 Argo profiling floats equipped with oxygen sensors have been deployed, but no quality control (QC) protocols have been adopted by the oceanographic community for use by Argo data centers. As a consequence, the growing float oxygen data set as a whole is not readily utilized for many types of biogeochemical studies. Here we present a simple procedure that can be used to correct first-order errors (offset and drift) in profiling float oxygen data by comparing float data to a monthly climatology (World Ocean Atlas 2009). Float specific correction terms for the entire array were calculated. This QC procedure was evaluated by (1) comparing the climatology-derived correction coefficients to those derived from discrete samples for 14 floats and (2) comparing correction coefficients for seven floats that had been calibrated twice prior to deployment (once in the factory and once in-house), with the second calibration ostensibly more accurate than the first. The corrections presented here constrain most float oxygen measurements to better than 3% at the surface.

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.

Frieder, CA, Nam SH, Martz TR, Levin LA.  2012.  High temporal and spatial variability of dissolved oxygen and pH in a nearshore California kelp forest. Biogeosciences. 9:4099-4132.   10.5194/bg-9-3917-2012  
Price, NN, Martz TR, Brainard RE, Smith JE.  2012.  Diel Variability in Seawater pH Relates to Calcification and Benthic Community Structure on Coral Reefs. Plos One. 7:e43843.: Public Library of Science   10.1371/journal.pone.0043843   AbstractWebsite

Community structure and assembly are determined in part by environmental heterogeneity. While reef-building corals respond negatively to warming (i.e. bleaching events) and ocean acidification (OA), the extent of present-day natural variability in pH on shallow reefs and ecological consequences for benthic assemblages is unknown. We documented high resolution temporal patterns in temperature and pH from three reefs in the central Pacific and examined how these data relate to community development and net accretion rates of early successional benthic organisms. These reefs experienced substantial diel fluctuations in temperature (0.78°C) and pH (>0.2) similar to the magnitude of ‘warming’ and ‘acidification’ expected over the next century. Where daily pH within the benthic boundary layer failed to exceed pelagic climatological seasonal lows, net accretion was slower and fleshy, non-calcifying benthic organisms dominated space. Thus, key aspects of coral reef ecosystem structure and function are presently related to natural diurnal variability in pH.

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.

Hofmann, GE, Smith JE, Johnson KS, Send U, Levin LA, Micheli F, Paytan A, Price NN, Peterson B, Takeshita Y, Matson PG, Crook ED, Kroeker KJ, Gambi MC, Rivest EB, Frieder CA, Yu PC, Martz TR.  2011.  High-Frequency Dynamics of Ocean pH: A Multi-Ecosystem Comparison. Plos One. 6   10.1371/journal.pone.0028983   AbstractWebsite

The effect of Ocean Acidification (OA) on marine biota is quasi-predictable at best. While perturbation studies, in the form of incubations under elevated pCO(2), reveal sensitivities and responses of individual species, one missing link in the OA story results from a chronic lack of pH data specific to a given species' natural habitat. Here, we present a compilation of continuous, high-resolution time series of upper ocean pH, collected using autonomous sensors, over a variety of ecosystems ranging from polar to tropical, open-ocean to coastal, kelp forest to coral reef. These observations reveal a continuum of month-long pH variability with standard deviations from 0.004 to 0.277 and ranges spanning 0.024 to 1.430 pH units. The nature of the observed variability was also highly site-dependent, with characteristic diel, semi-diurnal, and stochastic patterns of varying amplitudes. These biome-specific pH signatures disclose current levels of exposure to both high and low dissolved CO2, often demonstrating that resident organisms are already experiencing pH regimes that are not predicted until 2100. Our data provide a first step toward crystallizing the biophysical link between environmental history of pH exposure and physiological resilience of marine organisms to fluctuations in seawater CO2. Knowledge of this spatial and temporal variation in seawater chemistry allows us to improve the design of OA experiments: we can test organisms with a priori expectations of their tolerance guardrails, based on their natural range of exposure. Such hypothesis-testing will provide a deeper understanding of the effects of OA. Both intuitively simple to understand and powerfully informative, these and similar comparative time series can help guide management efforts to identify areas of marine habitat that can serve as refugia to acidification as well as areas that are particularly vulnerable to future ocean change.

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.

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.

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.

Yu, PC, Matson PG, Martz TR, Hofmann GE.  2011.  The ocean acidification seascape and its relationship to the performance of calcifying marine invertebrates: Laboratory experiments on the development of urchin larvae framed by environmentally-relevant pCO(2)/pH. Journal of Experimental Marine Biology and Ecology. 400:288-295.   10.1016/j.jembe.2011.02.016   AbstractWebsite

Variation in ocean pH is a dynamic process occurring naturally in the upwelling zone of the California Current Large Marine Ecosystem. The nearshore carbonate chemistry is under-characterized and the physiology of local organisms may be under constant challenge from cyclical changes in pH and carbonate ion concentration of unexpectedly high magnitude. We looked to environmental pH conditions of coastal upwelling and used those values to examine effects of low pH on 4-arm larvae of purple sea urchin Strongylocentrotus purpuratus. We deployed a pH sensor at a nearshore shallow benthic site for 3 weeks during summer 2010 to assess the changes in pH in the Santa Barbara Channel, a region considered to have relatively less intense upwelling along the US Pacific Coast. Large fluctuations in pH of up to 0.67 pH units were observed over short time scales of several days. Daily pH fluctuations on a tidal pattern followed temperature fluctuations over short time scales, but not over scales greater than a day. The lowest pH values recorded (similar to 7.70) are lower than some of those pH values predicted to occur in surface oceans at the end of the century. In the context of this dynamic pH exposure, larvae were raised at elevated pCO(2) levels of 1000 ppm and 1450 ppm CO(2) (pH 7.7 and 7.5 respectively) and measured for total larval length (from the spicule tip of the postoral arm to the spicule tip of the aboral point) along the spicules, to assess effects of low pH upwelling water on morphology. Larvae in all treatments maintained normal development and developmental schedule to day 6, and did not exhibit significant differences in larval asymmetry between treatments. At day 3 and day 6, larvae in the 1450 ppm CO(2) treatment were significantly smaller (p<0.001) than the control larvae by only 7-13%. The observation of smaller larvae raised under high pCO(2) has an as yet undetermined physiological mechanism, but has implications for locomotion and feeding. These effects of small magnitude in these urchin larvae are indicative of a potential resilience to near-future levels of ocean acidification. Using environmental monitoring of pH to inform experimental parameters provides a means to improve our understanding of acclimatization of organisms in a dynamic ecosystem. (C) 2011 Elsevier B.V. All rights reserved.