Weak Response of Biological Productivity and Community Structure of Phytoplankton to Mesoscale Eddies in the Oligotrophic Philippine Sea. Issue 12 (9th December 2020)

• Record Type: Journal Article
• Authors: Yun, Mi Sun; Kim, Yejin; Jeong, Yubeen; Joo, Hui Tae; Jo, Young‐Heon; Lee, Chang Hwa; Bae, Hyeonji; Lee, Dabin; Bhavya, P. S.; Kim, Dongseon; Sun, Jun; Lee, Sang H.
• Is Part Of: Journal of geophysical research. Volume 125:Issue 12(2020)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2020-12-09
• Subjects: community structure -- mesoscale eddies -- Philippine Sea -- phytoplankton -- primary production -- stable isotope; Oceanography -- Periodicals; 551.4605
• DOI: 10.1029/2020JC016436
• Languages: English
• ISSNs: 2169-9275

Abstract

Abstract: In the Philippine Sea, mesoscale eddies have been frequently observed, but little is known about their contributions to the biological productivity and community structure of phytoplankton in the region. In situ carbon and nitrogen uptake rates and phytoplankton community structure were investigated in the Philippine Sea based on the 13 C‐ 15 N dual‐tracer technique and photosynthetic pigment analysis from late August to September 2018. Based on the comparison of the phytoplankton community structure among the cold eddy, warm eddy, and outer area, we found that the phytoplankton composition was different in the warm eddy with relatively lower contributions of large phytoplankton. However, a distinct enhancement in phytoplankton biomass over the euphotic zone was not detected even in eddy occurrence. In terms of community, the picoplankton Prochlorococcus was persistently dominant, which was attributed to a low supply and chemical composition of nutrients. The average integrated primary productions (IPP) were 80.4, 75.9, and 76.3 mg C m −2 d −1 for the cold eddy, warm eddy, and outer area, respectively. The IPP under the eddy condition was not largely different from that in reference sites, even though the vertical distribution of productivity maximum was found to be different depending on eddy condition. These weak biological responses to mesoscale eddies might be attributed to the sustaining picoplankton‐dominant community structure and no substantial upward inputs of nutrients to the euphotic zone. Our findings represent an important contribution to understanding the biological response of mesoscale eddies in the oligotrophic Philippine Sea. Plain Language Summary: Eddies are ubiquitous in the ocean. Eddies play an important role in delivering nutrients to the euphotic zone and thus affect phytoplankton composition and biological activities. However, the different effects of eddy types (cold and warm eddies) on phytoplankton communities have not been well studied. In this study, the response of the phytoplankton community and biological productivity to mesoscale cold and warm eddies was studied in the Philippine Sea. The results indicate that primary production and phytoplankton biomass were not largely enhanced under mesoscale eddy conditions although cold eddies appear to have boosted productivity than warm eddies in the present study. Small phytoplankton‐dominant community structure stagnantly persisted even in the presence of mesoscale eddies, probably due to low nutrient supply and ratios. Key Points: No substantial phytoplankton production was found under mesoscale eddy conditions Insignificant response of phytoplankton community was also observed in this study Weak biological responses could be attributed to picoplankton‐dominant community structure and small upward nutrient flux