Carbonate chemistry measurements

Study of the marine CO₂ system is critical for understanding global carbon cycling and the impacts of changing ocean chemistry on marine ecosystems. A complete resolution of the marine CO₂ system requires measurement of two out of four parameters: partial pressure (pCO₂) or fugacity of CO₂ (fCO₂), dissolved inorganic carbon (DIC), total alkalinity (TA), and pH. Traditional bottle sample titrations for DIC and TA are slow, constraining studies by speed and cost of both sample collection and laboratory methods. Only pH and pCO₂ sensors are commercially available for autonomous, in-situ deployments; however, the strong covariance of this pair results in a system with greater calculation errors than a choice of any two other parameters, and high quality pH measurements in turbid coastal environments can be difficult to achieve.

To address the need for autonomous in-situ DIC sampling, we are developing the Channelized Optical System (CHANOS) II, a high-resolution DIC and fCO₂ sensor with a targeted precision of ± 2 µmol/kg (DIC) and ± 1 µatm (pCO₂) (e.g. laboratory quality measurements). The original CHANOS, described by Wang et al. (2015), could simultaneously measure DIC and pH, but due its size and power requirements was only suitable for time-series measurements from fixed platforms. CHANOS II is designed for near-continuous, high temporal and spatial resolution DIC measurements from both stationary and mobile platforms including CTD Rosettes, ROVs, and AUVs.