Effect of filtration on the total alkalinity of open-ocean seawater

Total alkalinity (TA) of filtered and unfiltered samples was measured during the P16N 2006 cruise in the Pacific Ocean and the 19N 2007 cruise in the Indian Ocean. Although filtering coastal water samples may be important to remove the contributions of phytoplankton and bacteria on the measured TA, it is not the case for open ocean samples. In this study, our results show that the at-sea measured total alkalinity of filtered and unfiltered samples were not statistically different. Measurements of 180 samples of surface, oxygen minimum, and deep waters in the Pacific and Indian oceans for unfiltered and filtered agreed to ±2 μmol kg^-1 Therefore, the findings of this article show that it is not necessary to filter seawater samples when measuring total alkalinity in the open ocean.