The effect of seasonality in phytoplankton community composition on CO2 uptake on the Scotian Shelf

• Published in: Journal of marine systems 2015-07, Vol.147, p.52-60
• Main Authors: Craig, Susanne E., Thomas, Helmuth, Jones, Chris T., Li, William K.W., Greenan, Blair J.W., Shadwick, Elizabeth H., Burt, William J.
• Format: Article
• Language: English
• Subjects: Abundance; Carbon; Carbon dioxide; Cell abundance; CO2 drawdown; Communities; Marine; Phytoplankton; Seasonal variations; Shelves; Small phytoplankton; Uptakes
• ISSN: 0924-7963; 1879-1573
• DOI: 10.1016/j.jmarsys.2014.07.006

We characterise seasonal patterns in phytoplankton community composition on the Scotian Shelf, northwest Atlantic Ocean, through a study of the numerical abundance of different cell sizes — pico-, nano- and microphytoplankton. Cell abundances of each size class were converted to cellular carbon and their seasonal patterns compared with the partial pressure of carbon dioxide (pCO2) also measured at the study site. We observed a persistent drawdown of CO2 throughout the summer months, despite nutrient depleted conditions and apparent low biomass suggested by the chlorophyll record. This drawdown was associated with a summertime phytoplankton assemblage numerically dominated by small phytoplankton that reach their peak abundance during this period. It was found that phytoplankton carbon during this period accounted for approximately 10% of spring bloom phytoplankton carbon and pointed to the importance role that small cells play in annual CO2 uptake. •The seasonal abundance of phytoplankton in large and small size classes was studied.•Phytoplankton abundance was converted to carbon to study its relationship with pCO2.•An assemblage dominated by small cells is associated with drawdown of summer pCO2.•Summer small cell dominated assemblage accounts for 10% of spring bloom carbon uptake.