High-frequency measurements of total CO2: Method development and first oceanographic observations

We developed a system to accurately, precisely, and rapidly measure total dissolved carbon dioxide (TCO2) in a continuously flowing seawater stream. The system is based on a gas-permeable membrane contactor, through which CO2 evolved from an acidified seawater stream is continuously and quantitatively stripped by a flowing gas stream. The CO2 content of this strip-gas stream, which is proportional to the TCO2 of the seawater stream via a simple mass balance, is then analyzed using a non-dispersive infra-red (NDIR) gas analyzer. Laboratory results have shown that the system has an e-folding response time of 6 s and is able to resolve changes in signal with better than ± 0.1% precision. Independent coulometric analyses of check samples collected in the field, analyses of internal check samples, and analyses of certified reference materials have shown the accuracy of the system to be reliable to ± 0.1%. Coupled with the Lamont Pumping SeaSoar system, the TCO2 system has yielded high spatial resolution distributions of TCO2 across the New England shelfbreak front. These TCO2 data, in conjunction with collocated PCO2 measurements of similar resolution, allowed us to calculate total alkalinity (TALK) at the high spatial resolution of the TCO2 and PCO2 measurements. While we cannot rule out or fully constrain the effects of mixing or variations in fresh water input, distributions of TALK relative to TCO2, in the context of several independent lines of reasoning, indicated that biogenic calcium carbonate production may play an important role in shaping the TALK and TCO2 distributions in waters across the New England shelfbreak front.