Assessment of autonomous pH measurements for determining surface seawater partial pressure of CO2

TitleAssessment of autonomous pH measurements for determining surface seawater partial pressure of CO2
Publication TypeJournal Article
Year of Publication2018
AuthorsTakeshita Y, Johnson K.S, Martz T.R, Plant J.N, Sarmiento J.L
JournalJournal of Geophysical Research-Oceans
Volume123
Pagination4003-4013
Date Published2018/06
Type of ArticleArticle
ISBN Number2169-9275
Accession NumberWOS:000440834100006
Keywordscresol purple; dissociation-constants; hot; inorganic carbon; internal consistency; marine carbonate system; networks; north pacific; oceanography; pCO2; ph; profiling float; Sensor; SOCCOM; southern-ocean; theta-s climatology; underway
Abstract

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.

DOI10.1029/2017jc013387
Short TitleJ Geophys Res-Oceans
Student Publication: 
No