Insights from GO-SHIP hydrography data into the thermodynamic consistency of CO2 system measurements in seawater

Highlights
• The thermodynamic consistency of CO2 system measurements was investigated.

• Errors in CO2 measurements are unlikely to be the main cause of inconsistencies.

• There are likely systematic errors in K1, K2, and the total boron-salinity ratio.

• An unaccounted source of alkalinity may be present in the open ocean.

Abstract
Due to advances in technology, routine seawater pH measurements of excellent repeatability are becoming increasingly common for studying the ocean CO2 system. However, the accuracy of pH measurements has come into question due to a widespread observation, from a large number of carefully calibrated state-of-the-art CO2 measurements on various cruises, of there being a significant pH-dependent discrepancy between pH that was measured spectrophotometrically and pH calculated from concurrent measurements of total dissolved inorganic carbon (CT) and total alkalinity (AT), using a thermodynamic model of seawater

acid-base systems. From an analysis of four recent GO-SHIP repeat hydrography datasets, we show that a combination of small systematic errors in the dissociation constants of carbonic acid (K1 and K2), the total boron-salinity ratio, and in CT and AT measurements are likely responsible for some, but not all of the observed pH-dependent discrepancy. The residual discrepancy can only be fully accounted for if there exists a small, but meaningful amount (~4 μmol kg–1) of an unidentified and typically neglected contribution to measured AT, likely from organic bases, that is widespread in the open ocean. A combination of these errors could achieve consistency between measured and calculated pH, without requiring that any of the shipboard measurements be significantly in error. Future research should focus on establishing the existence of organic alkalinity in the open ocean and constraining the uncertainty in both CO2 measurements and in the constants used in CO2 calculations.

Fong M. B. & Dickson A. G., in press. Insights from GO-SHIP hydrography data into the thermodynamic consistency of CO2 system measurements in seawater. Marine Chemistry. Article.

0 Responses to “Insights from GO-SHIP hydrography data into the thermodynamic consistency of CO2 system measurements in seawater”



  1. Leave a Comment

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s

This site uses Akismet to reduce spam. Learn how your comment data is processed.




Subscribe to the RSS feed

Powered by FeedBurner

Follow AnneMarin on Twitter

Blog Stats

  • 1,211,604 hits

OA-ICC HIGHLIGHTS

Ocean acidification in the IPCC AR5 WG II

OUP book