ALBERT

Description: Autoclaved natural seawater collected in the North Pacific Ocean was used as a reference material for nutrients in seawater (RMNS) during an inter-laboratory comparison (I/C) study conducted in 2008. This study was a follow-up to previous studies conducted in 2003 and 2006. A set of six samples was distributed to each of 58 laboratories in 15 countries around the globe, and results were returned by 54 of those laboratories (15 countries). The homogeneities of samples used in the 2008 I/C study, based on analyses for three determinants, were improved compared to those of samples used in the 2003 and 2006 I/C studies. Results of these I/C studies indicate that most of the participating laboratories have an analytical technique for nutrients that is sufficient to provide data of high comparability. The differences between reported concentrations from the same laboratories in the 2006 and 2008 I/C studies for the same batch of RMNS indicate that most of the laboratories have been maintaining internal comparability for two years. Thus, with the current high level of performance in the participating laboratories, the use of a common reference material and the adaptation of an internationally accepted nutrient scale system would increase comparability among laboratories worldwide, and the use of a certified reference material would establish traceability. In the 2008 I/C study we observed a problem of non-linearity of the instruments of the participating laboratories similar to that observed among the laboratories in the 2006 I/C study. This problem of non-linearity should be investigated and discussed to improve comparability for the full range of nutrient concentrations. For silicate comparability in particular, we see relatively larger consensus standard deviations than those for nitrate and phosphate.

Description: Flow cytometry was used to follow the diel variations in abundance of Synechococcus spp. and picoeukaryotes in subtropical western Pacific coastal waters in June 2017. A modified dilution method was also used to estimate diel changes in the effect of nanoflagellate and viruses on Synechococcus spp. and picoeukaryotes. Obvious diel patterns were found in changes in abundance in both Synechococcus spp. and picoeukaryotes, the highest values recorded at night. Synechococcus spp. and picoeukaryotic growth decreased significantly in more highly diluted samples incubated during the daytime, suggesting that picophytoplankton production is partially dependent on grazing- and virus-mediated nutrient cycling during the daytime. At nighttime, nanoflagellate grazing and viral lysis were responsible for Synechococcus spp. mortality at rates of 0.02 h−1 and 0.04 h−1, respectively, and nanoflagellate grazing was responsible for all picoeukaryotic mortality. The most important finding of this study was that nanoflagellate grazing exerts great control over picoeukaryotes at night in these subtropical western Pacific coastal waters.