Skip to main content
eScholarship
Open Access Publications from the University of California

Scholarly Works (12 results)

  • Article
  • Peer Reviewed
UC San Diego Previously Published Works (2015)
Seawater CO2 measurements are being made with increasing frequency as interest grows in the ocean's response to changing atmospheric CO2 levels and to climate change. The ultimate usefulness of these measurements depends on the data quality and consistency. An inter-laboratory comparison was undertaken to help evaluate and understand the current reliability of seawater CO2 measurements. Two seawater test samples of different CO2 content were prepared according to the usual method for the creation of seawater reference materials in the Dickson Laboratory at Scripps Institution of Oceanography. These two test samples were distributed in duplicate to more than 60 laboratories around the world. The laboratories returned their measurement results for one or more of the following parameters: total alkalinity (AT), total dissolved inorganic carbon (CT), and pH, together with information about the methods used and the expected uncertainty of the measurements. The majority of laboratories reported AT and CT values for all their measurements that were within 10μmolkg-1 of the assigned values (i.e. within ±0.5%), however few achieved results within 2μmolkg-1 (i.e. within ±0.1%), especially for CT. Results for the analysis of pH were quite scattered, with little suggestion of a consensus value. The high-CO2 test sample produced results for both CT and pH that suggested in many cases that CO2 was lost during analysis of these parameters. This study thus documents the current quality of seawater CO2 measurements in the various participating laboratories, and helps provide a better understanding of the likely magnitude of uncertainties in these measurements within the marine science community at the present time. Further improvements will necessarily hinge on adoption of an improved level of training in both measurement technique and of suitable quality control procedures for these measurements.
    • Thesis
    • Peer Reviewed
    UC San Diego Electronic Theses and Dissertations (2021)

    As pH measurement technologies evolve and are increasingly used to study the ocean’s CO2 system, there is a need to assess the uncertainty of seawater pH measurements, particularly those based on the spectrophotometric method using an indicator dye, which is used to calibrate alternative pH measurement methods, including autonomous pH sensors. In this dissertation, I investigated methodological and instrumental contributions to uncertainty in spectrophotometric pH measurements, developed tools for their quality control, and evaluated their likely quality based on their consistency with other seawater CO2 parameters. The accuracy of seawater pH measurements has been questioned due to observations from open ocean cruises of a significant pH-dependent discrepancy between measured pH and pH calculated from dissolved inorganic carbon (CT) and total alkalinity (AT), using a thermodynamic model of seawater acid-base systems. Based on an analysis of high quality CO2 measurements on four open ocean cruises, I showed that a combination of plausible biases in the constants and assumptions used to calculate pH can explain the observed inconsistencies and that there is likely an unaccounted, possibly organic, contribution to the AT measured in the open ocean. Next, I developed methods for analyzing spectra to identify and possibly correct instrumental contributions to spectrophotometric pH measurement error, such as those that may arise from degradation of the spectrophotometer lamp. In another chapter, laboratory and chemical modeling experiments were conducted to evaluate how adjustments for effect of the indicator addition on the sample pH contribute to uncertainty in the final pH result. Assumptions about the indicator’s behavior can result in error in the pH correction, but is minor, except when using high dye concentrations in short pathlength cells. Finally, I evaluated the performance of pH measurements using impure m-cresol purple, which contains absorbing impurities that can bias pH measurements. Calibrated impure dye measurements can still be inconsistent with purified dye measurements depending on the assumptions about the impurity absorption behavior or the purity of the reference dye. This dissertation contributes to understanding of the uncertainty of spectrophotometric pH measurements and our ability to use ocean pH data to characterize the CO2 system.

      Cover page: Uncertainty of spectrophotometric pH measurements in seawater and implications for ocean carbon chemistry
      • Article
      • Peer Reviewed
      UC San Diego Previously Published Works (2019)
        • Article
        • Peer Reviewed
        UC San Diego Previously Published Works (2023)
          • Article
          • Peer Reviewed
          UC San Diego Previously Published Works (2022)
            • Article
            Scripps Institution of Oceanography Technical Report (2009)

            A large fraction of the carbon dioxide added to the atmosphere by human activity enters the sea, causing ocean acidification. We show that otoliths (aragonitic ear bones) of young fish grown under high CO2 (low pH) conditions are larger than normal, contrary to expectation. We hypothesize that CO2 moves freely through the epithelium around the otoliths in young fish, accelerating otolith growth while the local pH is controlled. This is the converse of the effect reported for structural biominerals.

              Cover page: Elevated CO2 Enhances Otolith Growth in Young Fish (Supplementary Data)
              • Article
              • Peer Reviewed
              UC San Diego Previously Published Works (2023)
              Abstract: Long-term ocean time series have proven to be the most robust approach for direct observation of climate change processes such as Ocean Acidification. The California Cooperative Oceanic Fisheries Investigations (CalCOFI) program has collected quarterly samples for seawater inorganic carbon since 1983. The longest time series is at CalCOFI line 90 station 90 from 1984–present, with a gap from 2002 to 2008. Here we present the first analysis of this 37- year time series, the oldest in the Pacific. Station 90.90 exhibits an unambiguous acidification signal in agreement with the global surface ocean (decrease in pH of −0.0015 ± 0.0001 yr−1), with a distinct seasonal cycle driven by temperature and total dissolved inorganic carbon. This provides direct evidence that the unique carbon chemistry signature (compared to other long standing time series) results in a reduced uptake rate of carbon dioxide (CO2) due to proximity to a mid-latitude eastern boundary current upwelling zone. Comparison to an independent empirical model estimate and climatology at the same location reveals regional differences not captured in the existing models.
                Cover page: A 37-year record of ocean acidification in the Southern California currentCreative Commons 'BY-ND' version 4.0 license
                • Article
                • Peer Reviewed
                UC San Diego Previously Published Works (2018)
                  • Article
                  • Peer Reviewed
                  UC San Diego Previously Published Works (2012)
                  The California Current System (CCS) is expected to experience the ecological impacts of ocean acidification (OA) earlier than most other ocean regions because coastal upwelling brings old, CO2-rich water relatively close to the surface ocean. Historical inorganic carbon measurements are scarce, so the progression of OA in the CCS is unknown. We used a multiple linear regression approach to generate empirical models using oxygen (O 2), temperature (T), salinity (S), and sigma theta (sq) as proxy variables to reconstruct pH, carbonate saturation states, carbonate ion concentration ([CO32-]), dissolved inorganic carbon (DIC) concentration, and total alkalinity (TA) in the southern CCS. The calibration data included high-quality measurements of carbon, oxygen, and other hydrographic variables, collected during a cruise from British Columbia to Baja California in May-June 2007. All resulting empirical relationships were robust, with r2 values >0.92 and low root mean square errors. Estimated and measured carbon chemistry matched very well for independent data sets from the CalCOFI and IMECOCAL programs. Reconstructed CCS pH and saturation states for 2005-2011 reveal a pronounced seasonal cycle and inter-annual variability in the upper water column. Deeper in the water column, conditions are stable throughout the annual cycle, with perennially low pH and saturation states. Over sub-decadal time scales, these empirical models provide a valuable tool for reconstructing carbonate chemistry related to ocean acidification where direct observations are limited. However, progressive increases in anthropogenic CO2 content of southern CCS water masses must be carefully addressed to apply the models over longer time scales. © Copyright 2012 by the American Geophysical Union.
                    Cover page: Robust empirical relationships for estimating the carbonate system in the southern California Current System and application to CalCOFI hydrographic cruise data (2005–2011)
                    • Article
                    • Peer Reviewed
                    UC San Diego Previously Published Works (2017)
                    Accurate pH measurements in polar waters and sea ice brines require pH indicator dyes characterized at near-zero and below-zero temperatures and high salinities. We present experimentally determined physical and chemical characteristics of purified meta-Cresol Purple (mCP) pH indicator dye suitable for pH measurements in seawater and conservative seawater-derived brines at salinities (S) between 35 and 100 and temperatures (T) between their freezing point and 298.15 K (25 °C). Within this temperature and salinity range, using purified mCP and a novel thermostated spectrophotometric device, the pH on the total scale (pHT) can be calculated from direct measurements of the absorbance ratio R of the dye in natural samples as[Formula: see text] Based on the mCP characterization in these extended conditions, the temperature and salinity dependence of the molar absorptivity ratios and - [Formula: see text] of purified mCP is described by the following functions: e 1 = -0.004363 + 3.598 × 10-5 T, e 3/e 2 = -0.016224 + 2.42851 × 10-4 T + 5.05663 × 10-5(S - 35), and - [Formula: see text] = -319.8369 + 0.688159 S -0.00018374 S 2 + (10508.724 - 32.9599 S + 0.059082S 2) T-1 + (55.54253 - 0.101639 S) ln T -0.08112151T. This work takes the characterisation of mCP beyond the currently available ranges of 278.15 K ≤ T ≤ 308.15 K and 20 ≤ S ≤ 40 in natural seawater, thereby allowing high quality pHT measurements in polar systems.
                      Cover page: Characterization of meta-Cresol Purple for spectrophotometric pH measurements in saline and hypersaline media at sub-zero temperatures
                      Top