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1. Assessment of pH dependent errors in spectrophotometric pH measurements of seawater

   https://doi.org/10.1016/j.marchem.2020.103801  

   Takeshita, Yuichiro; Johnson, Kenneth S.; Coletti, Luke J.; Jannasch, Hans W.; Walz, Peter M.; Warren, Joseph K. (June 2020, Marine Chemistry)
2. The effects of pressure on pH of Tris buffer in synthetic seawater

   https://doi.org/10.1016/j.marchem.2016.11.002  

   Takeshita, Yuichiro; Martz, Todd R.; Coletti, Luke J.; Dickson, Andrew G.; Jannasch, Hans W.; Johnson, Kenneth S. (January 2017, Marine Chemistry)
3. Technical note: Stability of tris pH buffer in artificial seawater stored in bags

   https://doi.org/10.5194/os-17-819-2021  

   Wolfe, Wiley H.; Shipley, Kenisha M.; Bresnahan, Philip J.; Takeshita, Yuichiro; Wirth, Taylor; Martz, Todd R. (January 2021, Ocean Science)

   null (Ed.)

   Abstract. Equimolal tris (2-amino-2-hydroxymethyl-propane-1,3-diol) buffer in artificialseawater is a well characterized and commonly used standard for oceanographic pH measurements. We evaluated the stability of tris pH when stored in purportedly gas-impermeable bags across a variety of experimental conditions, including bag type and storage in air vs. seawater over300 d. Bench-top spectrophotometric pH analysis revealed that the pH of tris stored in bags decreased at a rate of 0.0058±0.0011 yr−1 (mean slope ±95 % confidence interval of slope). The upper and lower bounds of expected pH change att=365 d, calculated using the averages and confidence intervals of slope and intercept of measured pH change vs. time data, were −0.0042 and −0.0076 from initial pH. Analyses of total dissolved inorganic carbonconfirmed that a combination of CO2 infiltration and/or microbialrespiration led to the observed decrease in pH. Eliminating the change in pH of bagged tris remains a goal, yet the rate of pH change is lower than many processes of interest and demonstrates the potential of bagged tris for sensor calibration and validation of autonomous in situ pH measurements. 

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4. Consistency and stability of purified meta-cresol purple for spectrophotometric pH measurements in seawater

   https://doi.org/10.1016/j.marchem.2021.104018  

   Takeshita, Yuichiro; Warren, Joseph K.; Liu, Xuewu; Spaulding, Reggie S.; Byrne, Robert H.; Carter, Brendan R.; DeGrandpre, Michael D.; Murata, Akihiko; Watanabe, Shu-ichi (November 2021, Marine Chemistry)

   null (Ed.)
5. Synthetic and practical reconstructions of SST and seawater pH using the novel multiproxy SMITE method

   https://doi.org/10.1371/journal.pone.0305607  

   Hughes, Hunter P; Thompson, Diane; Foster, Gavin L; Lees, Jonathan; Surge, Donna; Standish, Christopher D (June 2024, PLOS ONE)

   Pokkathappada, Abdul Azeez (Ed.)

   Geochemical proxies of sea surface temperature (SST) and seawater pH (pH_sw) in scleractinian coral skeletons are valuable tools for reconstructing tropical climate variability. However, most coral skeletal SST and pH_swproxies are univariate methods that are limited in their capacity to circumvent non-climate-related variability. Here we present a novel multivariate method for reconstructing SST and pH_swfrom the geochemistry of coral skeletons. Our Scleractinian Multivariate Isotope and Trace Element (SMITE) method optimizes reconstruction skill by leveraging the covariance across an array of coral elemental and isotopic data with SST and pH_sw. First, using a synthetic proxy experiment, we find that SMITE SST reconstruction statistics (correlation, accuracy, and precision) are insensitive to noise and variable calibration period lengths relative to Sr/Ca. While SMITE pH_swreconstruction statistics remain relative toδ¹¹B throughout the same synthetic experiment, the magnitude of the long-term trend in pH_swis progressively lost under conditions of moderate-to-high analytical uncertainty. Next, we apply the SMITE method to an array of seven coral-based geochemical variables (B/Ca,δ¹¹B, Li/Ca, Mg/Ca, Sr/Ca, U/Ca & Li/Mg) measured from two BermudanPorites astreoidescorals. Despite a <3.5 year calibration period, SMITE SST and pH_swestimates exhibit significantly better accuracy, precision, and correlation with their respective climate targets than the best single- and dual-proxy estimators. Furthermore, SMITE model parameters are highly reproducible between the two coral cores, indicating great potential for fossil applications (when preservation is high). The results shown here indicate that the SMITE method can outperform the most common coral-based SST and pH_swreconstructions methods to date, particularly in datasets with a large variety of geochemical variables. We therefore provide a list of recommendations and procedures for users to begin implementing the SMITE method as well as an open-source software package to facilitate dissemination of the SMITE method. 

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