Particulate inorganic carbon in the ocean: Evaluation of discrete sampling protocols

This study evaluates the impact of sampling protocols on the measurement of particulate inorganic carbon (PIC) in ocean waters, an essential component for understanding the global carbon cycle and climate regulation. The study compares four protocols for estimating PIC in discrete water column samples, focusing on the effects of filter pore size (0.4 vs. 0.8 μm) and rinsing agents (pH-adjusted MilliQ water with NH₄OH vs. potassium tetraborate buffer). Five coccolithophore strains were selected to represent variations in PIC content resulting from species-specific differences in coccolith mass, coccolith number per cell, and life cycle phase. Discrete samples were analyzed using inductively coupled plasma mass spectrometry. Statistical analyses show no significant differences in PIC concentrations between protocols, filter types, or rinsing agents, confirming the robustness and precision of the measurement method. In addition, the non-calcifying strain provided insights into the measurement uncertainty and enabled us to quantify the precision of the sampling method. These results suggest that researchers can use any tested protocol without compromising data quality. This will improve the reliability and comparability of PIC measurements and contribute to a more precise understanding of ocean carbon dynamics and climate regulation.