Global ocean spectrophotometric pH assessment: Consistent inconsistencies

Details

• Journal Title:
  Environmental Science & Technology
• Personal Author:
  Álvarez, Marta ; Fajar, Noelia M. ; Carter , Brendan R. ; Guallart, Elisa F. ; Pérez, Fiz F. ; Woosley, Ryan J. ; Murataδ, Akihiko
• Corporate Authors:
  Instituto Español de Oceanografía ; Joint Institute for the Study of the Atmosphere and Ocean ; NOAA Pacific Marine Environmental Laboratory ; Instituto de Investigacións Mariñas ; Massachusetts Institute of Technology ; Center for Global Change Science ; Japan Agency for Marine-Earth Science and Technology ; Research Institute for Global Change
• NOAA Program & Office:
  OAR (Oceanic and Atmospheric Research) ; PMEL (Pacific Marine Environmental Laboratory) ; JISAO (Joint Institute for the Study of the Atmosphere and Ocean)
• Description:
  Ocean acidification (OA)—or the decrease in seawater pH resulting from ocean uptake of CO2 released by human activities—stresses ocean ecosystems and is recognized as a Climate and Sustainable Development Goal Indicator that needs to be evaluated and monitored. Monitoring OA-related pH changes requires a high level of precision and accuracy. The two most common ways to quantify seawater pH are to measure it spectrophotometrically or to calculate it from total alkalinity (TA) and dissolved inorganic carbon (DIC). However, despite decades of research, small but important inconsistencies remain between measured and calculated pH. To date, this issue has been circumvented by examining changes only in consistently measured properties. Currently, the oceanographic community is defining new observational strategies for OA and other key aspects of the ocean carbon cycle based on novel sensors and technologies that rely on validation against data records and/or synthesis products. Comparison of measured spectrophotometric pH to calculated pH from TA and DIC measured during the 2000s and 2010s eras reveals that (1) there is an evolution toward a better agreement between measured and calculated pH over time from 0.02 pH units in the 2000s to 0.01 pH units in the 2010s at pH > 7.6; (2) a disagreement greater than 0.01 pH units persists in waters with pH < 7.6, and (3) inconsistencies likely stem from variations in the spectrophotometric pH standard operating procedure (SOP). A reassessment of pH measurement and calculation SOPs and metrology is urgently needed.
• Keywords:
  Calibration Dissolved Organic Matter Organic Polymers PH Seawater
• Source:
  Environ. Sci. Technol., 54(18), 10977–10988
• Series:
  PMEL contribution   no. 2020-1071 ; PMEL contribution   no. 5109
• DOI:
  https://doi.org/10.1021/acs.est.9b06932
• ISSN:
  0013-936X ; 1520-5851
• Format:
  PDF
• Publisher:
  American Chemical Society
• Document Type:
  Journal Article
• Funding:
  Grant no. N8R3CEA-PDM
• Rights Information:
  Accepted Manuscript
• Rights Statement:
  The NOAA IR provides access to this content under the authority of the government's retained license to distribute publications and data resulting from federal funding. While users may legally access this content, the copyright owners retain rights that govern the reproduction, redistribution, and re-use of this work. The user is solely responsible for complying with applicable copyright law.
• Compliance:
  Submitted
• Main Document Checksum:
  urn:sha-512:ba6a40d827c03ecfd19b52320cacdfd77f442adbdf3c7fbdf1e83823f4f77489d3b200c76aff384196f2388522ce64db491b637f2ade3604bcf20bc6e75a0823
• Download URL:
  https://repository.library.noaa.gov/view/noaa/65858/noaa_65858_DS1.pdf
• File Type:
  [PDF - 6.20 MB ]