Significant contribution of picoplankton size fraction to biogenic silica standing stocks in the Western Pacific Ocean
Yuqiu Wei, Jun Sun, Zhuo Chen, Zhaoyi Zhang, Guicheng Zhang, Xiaofang Liu
Abstract
The contribution of picoplankton size-fraction (<2 μm cells) to biogenic silica (bSi) stocks is likely to have not been included in previous analyses, making prior estimated budgets potentially underestimated. Based on size-fractionated bSi analysis in three size fractions (i.e., 0.2–2 µm; 2–20 µm; >20 µm), we observed picoplankton size class contributed a measurable and significant proportion of total bSi standing stocks in the Western Pacific Ocean (WPO). The depth-weighted average bSi stock in the < 2 μm size fraction averaged 65% of the total, indicating the magnitude of total bSi standing stocks was driven by the picoplankton fraction. While large diatoms had a relevant contribution to the > 20 μm bSi standing stock, this significant contribution of picoplankton size fraction to total bSi standing stocks was associated with marine picocyanobacteria. Interestingly, our estimated contributions of living Synechococcus alone to the < 2 μm bSi standing stock and total bSi standing stocks were small, only averaging 9% and 6%, respectively. Thus we suggested that these small but persistent contributions of living Synechococcus to the bSi standing stocks may be influenced by the detrital bSi or other siliceous organisms (e.g., Minidiscus comicus). Furthermore, water temperature had a potential effect on the variability of picoplankton bSi stock. Overall, these results provided some new insights into the various environmental and biological factors affecting the oceanic bSi standing stocks.