Impacts of elevated CO2 on phytoplankton community composition and organic carbon dynamics in nutrient-depleted Okhotsk Sea surface waters

• Main Authors: Yoshimura, T., Nishioka, J., Suzuki, K., Hattori, H., Kiyosawa, H., Watanabe, Y. W.
• Format: Text
• Language: English
• Published: 2018
• Subjects: Okhotsk; Ocean acidification; okhotsk sea
• Online Access: https://doi.org/10.5194/bgd-6-4143-2009; https://www.biogeosciences-discuss.net/bg-2009-65/

Impacts of the increasing CO 2 in seawater (i.e. ocean acidification) on phytoplankton physiology may have various and potentially adverse effects on phytoplankton dynamics and the carbon cycle. We conducted a CO 2 manipulation experiment in the Sea of Okhotsk in summer 2006 to investigate the response of the phytoplankton assemblage and dynamics of organic carbon. During the 14-day incubation of nutrient-depleted surface water with a natural phytoplankton assemblage under 150, 280, 480, and 590 μatm p CO 2 , the relative abundance of fucoxanthin-containing phytoplankton such as diatoms and prymnesiophytes decreased with increasing p CO 2 . The amount of DOC accumulation also decreased with increasing p CO 2 , while differences in POC accumulation between the treatments were small and did not show a clear trend with the p CO 2 . Change in the phytoplankton community composition under different CO 2 conditions will alter the organic carbon dynamics as found in the present experiment. Compared to results in the literature from nutrient-replete conditions indicating a potential enhancement of phytoplankton production with elevated CO 2 , the present results indicated a different physiological response of phytoplankton under nutrient-depleted conditions. These results indicate that the continuing increase in atmospheric CO 2 can significantly affect the structure of marine ecosystems and carbon cycle in nutrient-depleted subpolar surface waters.