日本地球惑星科学連合2019年大会

講演情報

[E] ポスター発表

セッション記号 A (大気水圏科学) » A-OS 海洋科学・海洋環境

[A-OS12] Marine ecosystems and biogeochemical cycles: theory, observation and modeling

2019年5月27日(月) 17:15 〜 18:30 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:伊藤 進一(東京大学大気海洋研究所)、平田 貴文(北海道大学地球環境科学研究院)、Enrique N Curchitser(Rutgers University New Brunswick)、Eileen E Hofmann(Old Dominion University)

[AOS12-P08] Impacts of cyclonic eddies on phytoplankton biomass and phenology in the Kuroshio Extension region

*Eko Siswanto1Yoshikazu Sasai1 (1.Japan Agency for Marine-Earth Science and Technology)

キーワード:Ocean color, Phytoplankton, Bloom onset, Upwelling

Two-decade ocean color chlorophyll-a concentration (CHL, a metric of phytoplankton biomass) data from 1997 to 2017 were used to comprehend the impact of cyclonic eddies on phytoplankton biomass and phenology in the Kuroshio Extension region (KE) of the western North Pacific Ocean. The CHL data have 4-km and 8-day spatiotemporal resolution and were acquired from the ESA Ocean Colour-Climate Change Initiative (http://www.esa-oceancolour-cci.org/). Prior to defining spring bloom onset, spatiotemporal gaps in CHL data were filled by applying empirical orthogonal function-based interpolation. The analysis was mainly focused on the winter season (January-March) as oceanographic conditions during the winter largely control phytoplankton spring bloom in terms of both magnitude and onset. Based on winter sea surface height anomaly (SSHa), cyclonic eddies (negative SSHa) were dominant mainly within the periods from 1998 to 2001 and from 2005 to 2009, whereas anti-cyclonic eddies (positive SSHa) were dominant mainly within the periods from 2002 to 2004 and from 2011 to 2015. Based on datasets from all seasons, the concurrences of negative SSHa and positive phytoplankton chlorophyll anomaly (CHLa) were observed, albeit not always. This indicates an eddy-induced upwelling supplies nutrients to the near-surface layer. Upwelled nutrients eventually promote phytoplankton growth. Such a concurrence of low SSHa and high CHLa was less obvious during the winter indicating that another factor (such as intense winter vertical mixing) also non-trivially controlled nutrient input to the surface layer, and hence CHLa variability. Overall temporal mean indeed showed that the active cyclonic eddy area (approximately south of the Kuroshio Current main axis) was characterized by high CHLa, low SSHa, and shoaled mixed layer. In this study, a Cumulative Sum method was applied to find phytoplankton spring bloom onset. Correlation between SSHa and spring bloom onset time was investigated, and it was found that approximately over the active cyclonic eddy area, positive correlation between winter/late winter SSHa and time of spring bloom onset was observed. Such a positive correlation indicates that cyclonic eddies during the winter likely tended to advance phytoplankton spring bloom onset.