Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
  • Problem Description
• Data Files
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

Samples were collected from the CTD rosette following best practices (Dickson et al., 2007). Samples for single-step total alkalinity (TA) titrations were collected in 100-milliliter (mL) borosilicate glass bottles, and samples for open cell titrations were collected in 250-mL borosilicate glass bottles. Samples were poisoned with 0.04% HgCl2 and a precise headspace of ~1% was created using a pipette. Bottles were sealed with ground glass stopper, and apiezon L grease and a rubber band and plastic hose clamp were used to keep the stopper in place. The TA measured on board was measured by single-step titration with spectrophotometric endpoint detection using bromocresol green following the methods of Yao and Byrne (1998). The duplicate samples were shipped to the laboratory at Massachusetts Institute of Technology (MIT) in Cambridge, MA, USA for analysis using an open cell titration and non-linear least squares fitting as described in Dickson et al. (2003). DIC for both shipboard and land-based analysis was done by acidification and coulometric detection following best practices methods (Dickson et al. 2007).

Land-based pH on the total scale (pHt) at 20 degrees Celsius was done using a custom-built instrument similar to Carter et al. (2013) and purified meta-cresol purple indicator.

Instrumentation:
The shipboard TA analysis by single step titration was done using spectrophotometry with a single acid addition procedure using a custom-made system (Nippon ANS, Inc., Japan).

Land-based TA was performed with a custom-designed titration designed and built by the laboratory of Andrew G. Dickson (University of California, San Diego) as described in Dickson et al. (2003).

Shipboard DIC was determined using an automated TCO2 analyzer (Nippon ANS, Inc., Japan) with coulometric detection.

Land-based DIC was determined by a custom dissolved inorganic carbon extraction with coulometric detection built by the National Oceanographic and Atmospheric Administration Pacific Marine Laboratory and is a modern version of the original SOMMA system (Johnson et al. 1992).

Land-based pHt was measured at 20 degrees Celsius with a custom system designed and built by the Woosley laboratory consisting of a Kloehn syringe pump and Agilent 8453 spectrophotometer and controlled using LabView Software.

Certified reference material (CRM) provided by Andrew Dickson (UCSD) were used for all TA and DIC measurements. For shipboard analysis, Batch 209 was used. For laboratory analysis, batch 216 was used.

For single-step TA, the values were adjusted according to the ratio of the mean measured CRM value and the certified value. For open cell TA, no adjustment was made to the CRM.

For laboratory pHt, TRIS buffer made in house according to Paulsen and Dickson (2020) was used as an accuracy and precision check.

- Imported original file "TA Comparison Submit to BCODMO.xlsx" into the BCO-DMO system.
- Marked "-999", "-999.0000", and "-999.000" as missing data values (missing data are empty/blank in the final csv file).
- Renamed fields to comply with BCO-DMO naming conventions.
- Created date-time UTC column in ISO 8601 format.
- Saved final file as "957527_v1_ta_comparison.csv".

NSF Award Abstract
The oceans help to slow climate change by absorbing about a quarter of the carbon dioxide (CO2) produced by burning of fossil fuels and other human activities. The Pacific and Southern Oceans are known to take up and store significant amounts of anthropogenic CO2, but many questions regarding the amount, variability, and biogeochemical and ecological impacts remain unanswered. This research will focus on answering some of those questions in two areas of the Pacific by analyzing samples for total CO2, total alkalinity, and pH on two GEOTRACES cruises, GP17-OCE and GP17-ANT. The project will support several undergraduate student researchers and create educational modules on ocean acidification for general public and K-12 students.

On the GP17-OCE expedition in the south Pacific, sub-decadal scale variability in the uptake of CO2 and resulting decrease in pH (termed ocean acidification) will be examined by comparing data collected on this expedition with data from prior occupations of the line in 1991, 2005 and 2014. An extended multilinear regression technique will be used to separate natural variability from human induced changes. The second expedition, GP17-ANT, covers the Amundsen Sea, an area with few prior carbon measurements. This sea is perennially ice-covered with several seasonal polynyas (areas of open water surrounded by sea ice) and exhibits complex water circulation making the contribution to the global carbon cycle uncertain. The data collected from this expedition will examine several hypotheses regarding how carbon is taken up, mixed, and recirculated in the region, how glacial ice melt, sea ice, and biological productivity influence the carbon cycle, and provide baseline measurements against future data to determine changes in the carbon cycle of the region over time. Both expeditions will leverage the myriad of other parameters being measured, particularly trace metals such as iron and zinc, to examine how cycling of carbon and trace metals are interlinked through pH.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.