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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.

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.

Takeshita, Y, Johnson KS, Martz TR, Plant JN, Sarmiento JL.  2018.  Assessment of autonomous pH measurements for determining surface seawater partial pressure of CO2. Journal of Geophysical Research-Oceans. 123:4003-4013.   10.1029/2017jc013387   AbstractWebsite

The Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) program currently operates >80 profiling floats equipped with pH sensors in the Southern Ocean. Theoretically, these floats have the potential to provide unique year-around estimates of pCO(2) derived from pH measurements. Here, we evaluate this approach in the field by comparing pCO(2) estimates from pH sensors to directly measured pCO(2). We first discuss data from a ship's underway system which covered a large range in temperature (2-30 degrees C) and salinity (33.6-36.5) over 43 days. This pH sensor utilizes the same sensing technology but with different packaging than those on SOCCOM floats. The mean residual varied between -4.64.1 and 8.64.0 (1 sigma) atm, depending on how the sensor was calibrated. However, the standard deviation of the residual, interpreted as the ability to track spatiotemporal variability, was consistently <5 atm and was independent of the calibration method. Second, we assessed the temporal stability of this approach by comparing pCO(2) estimated from four floats over 3 years to the Hawaii Ocean Time-series. Good agreement of -2.110.4 (1 sigma) mu atm was observed, with coherent seasonal cycles. These results demonstrate that pCO(2) estimates derived from profiling float pH measurements appear capable of reproducing spatiotemporal variations in surface pCO(2) measurements and should provide a powerful observational tool to complement current efforts to understand the seasonal to interannual variability of surface pCO(2) in underobserved regions of the open ocean.

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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Takeshita, Y, Cyronak T, Martz TR, Kindeberg T, Andersson AJ.  2018.  Coral reef carbonate chemistry variability at different functional scales. Frontiers in Marine Science. 5   10.3389/fmars.2018.00175   AbstractWebsite

There is a growing recognition for the need to understand how seawater carbonate chemistry over coral reef environments will change in a high-CO2 world to better assess the impacts of ocean acidification on these valuable ecosystems. Coral reefs modify overlying water column chemistry through biogeochemical processes such as net community organic carbon production (NCR) and calcification (NCC). However, the relative importance and influence of these processes on seawater carbonate chemistry vary across multiple functional scales (defined here as space, time, and benthic community composition), and have not been fully constrained. Here, we use Bermuda as a case study to assess (1) spatiotemporal variability in physical and chemical parameters along a depth gradient at a rim reef location, (2) the spatial variability of total alkalinity (TA) and dissolved inorganic carbon (DIC) over distinct benthic habitats to infer NCC:NCP ratios [< several km(2); rim reef vs. seagrass and calcium carbonate (CaCO3) sediments] on diel timescales, and (3) compare how TA-DIC relationships and NCC:NCP vary as we expand functional scales from local habitats to the entire reef platform (10's of km(2)) on seasonal to interannual timescales. Our results demonstrate that TA-DIC relationships were strongly driven by local benthic metabolism and community composition over diel cycles. However, as the spatial scale expanded to the reef platform, the TA-DIC relationship reflected processes that were integrated over larger spatiotemporal scales, with effects of NCC becoming increasingly more important over NCR. This study demonstrates the importance of considering drivers across multiple functional scales to constrain carbonate chemistry variability over coral reefs.

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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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.