日本地球惑星科学連合2016年大会

講演情報

インターナショナルセッション(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-OS03] Marine ecosystem and biogeochemical cycles: theory, observation and modeling

2016年5月23日(月) 17:15 〜 18:30 ポスター会場 (国際展示場 6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)、Hofmann Eileen E.(Old Dominion University)、Charles Stock(Geophysical Fluid Dynamics Laboratory)

17:15 〜 18:30

[AOS03-P11] Optimality based models of phytoplankton size structure in the North Pacific

*Bingzhang Chen1Sherwood Lan Smith1 (1.Japan Agency for Marine-Earth Science and Technology)

キーワード:Phytoplankton, Size, Modeling

Phytoplankton size structure is an important factor determining trophic transferand export production in the ocean. To model phytoplankton size structure,conventional ocean models usually discretize the phytoplankton community intoa number of size classes, which is usually computing extensive. In addition, theflexible behaviors of phytoplankton physiology such as flexible intracellularnitrogen-to-carbon ratios and chlorophyll-to-carbon ratios should be alsoconsidered. Here we present a new ecosystem model which combines theflexible behavior of phytoplankton physiology and an innovative approach ofmodeling the mean and variance of a continuously distributed phytoplanktonsize. The key features of the new type of ecosystem model include: 1) A tradeoffexists phytoplankton photosynthesis and nitrogen uptake. Phytoplankton cellsare assumed to optimize the energy allocation between light harvesting andnitrogen uptake. 2) By assuming a continuous lognormal distribution ofphytoplankton size, key phytoplankton physiological parameters such asnutrient uptake rate, photosynthesis rate, minimal nutrient quota, etc. followvalidated size-scaling laws. Then the net growth rate of the bulk phytoplanktoncommunity can be expressed as a function of the net growth rate at mean log sizeand the second derivative of net growth rate evaluated at the mean log sizebased on moment closure approximations. 3) A killing-the-winner strategy isadopted to maintain phytoplankton size diversity. This model is coupled with a3D regional ocean circulation model (ROMS) in the North Pacific and canreproduce the large-scale patterns of oceanic circulation, temperature, andsalinity, nitrate and chlorophyll fields. As expected, nutrient concentration is themajor factor controlling distributions of phytoplankton mean size and sizevariance. Sensitivity analysis suggests that the ecosystem model is very sensitiveto the type of grazing functions and zooplankton mortality closure terms.