We are developing the “Micro-Rosette,” an instrument that will be deployed on an Argo-style profiling float. The Micro-Rosette is capable of capturing and storing a vertical profile of submilliliter sea­water samples and then performing chemical analyses of the samples during a profiling float’s park cycle. The prototype Micro-Rosette was designed to measure dissolved inorganic carbon (DIC) based on the method of Hall and Aller (1992) and refined by Sayles and Eck (2009). This technique involves placing an acidified seawater sample in a gas diffusion manifold where the CO₂ is quantitatively transferred to a receiving solution (NaOH). CO₂ reacts with OH^– to form carbonate and bicarbonate, thereby decreasing the solution’s conductivity. The carbonate-loaded NaOH is eluted through a custom capacitively coupled contactless conductivity detector (C⁴D), where the decrease in conductivity is quantified in order to determine the seawater’s initial DIC content.

Bresnahan, P., T. Martz, J. de Almeida, B. Ward­, and P. Maguire. 2017. Looking ahead: A profiling float Micro-Rosette. Oceanography 30(2):32, https://doi.org/​10.5670/oceanog.2017.215.

Bresnahan, P.J. 2015. Development and application of in situ marine inorganic carbon sensors: Quantifying change at high spatiotemporal resolution in the anthropocene. PhD thesis, University of California, San Diego.
1. Hall, P.J., and R.C. Aller. 1992. Rapid, small-volume, flow injection analysis for ΣCO₂, and NH₄⁺ in marine and freshwaters. Limnology and Oceanography 37:1,113–1,119, https://doi.org/10.4319/lo.1992.37.5.1113.
2. Sayles, F.L., and C. Eck. 2009. An autonomous instrument for time series analysis of TCO₂ from oceanographic moorings. Deep Sea Research Part I 56:1,590–1,603, https://doi.org/10.1016/j.dsr.2009.04.006.

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