報告書番号

U00010

タイトル（和文）

東部北太平洋亜寒帯域における生物的な炭素移送量評価のための海洋プランクトン生態系モデルの構築

タイトル（英文）

Modelling of biological carbon transport processes in the subarctic northeast Pacific Ocean

概要 （図表や脚注は「報告書全文」に掲載しております）

高栄養塩低生産海域では、鉄不足が植物プランクトンの増殖制限要因の一つになっている。地球規模の炭素循環に果たす海洋プランクトン生態系の役割と、鉄肥沃化による炭素固定効果と環境影響を定量的に評価するには、鉄濃度と植物プランクトン増殖の関係を表す数値モデルを開発する必要がある。 本研究では、鉄添加培養実験および沿岸メソコスム実験を行い、鉄供給の少ない東部北太平洋亜寒帯域のプランクトン生態系の特徴を明らかにし、海洋プランクトン生態系モデルの構築を行った。 東部北太平洋亜寒帯域の特徴をモデルに反映させるため、アンモニアを利用する再生循環型と、鉄・硝酸を利用する新生産型のプランクトン生態系に分けてモデルを構築した。鉄濃度のミハエリスーメンテン型の式を用いることによって、鉄濃度の変化に伴う植物プランクトンの増殖の変動を表現可能にした。

概要 （英文）

To investigate the role of plankton ecosystem in CO2 dynamics and the effect of iron fertilization on the growth of phytoplankton and CO2 transportation through oceanic plankton ecosystem at subarctic northeast Pacific Ocean being a typical high nutrients and low chlorophyll region (HNLC), onboard bottle incubation experiments and controlled ecosystem enclosure (mesocosms) experiments were conducted. Major results obtained are as follows:1. Small size phytoplankton which uses ammonium is dominant at HNLC region. The iron addition induce the bloom of large size phytoplankton (diatom) with utilization of ambient nitrate at subarctic northeast Pacific Ocean during summer.2. A large amount of particulate organic carbon was kept in surface layer during diatom bloom. Once nitrate was exhausted by diatom at the end of bloom, particulate organic carbon was transported to deep layer by particle precipitation process. However organic carbon produced by small size phytoplankton is easily decomposed at the surface and negligible amount is transported to the deep layer. Based on these results, fundamental biological carbon transport model was constructed. In this model, the carbon flow which is regenerated by small size phytoplankton is expressed by four compartments (small size phytoplankton, micro-zoo plankton, ammonium, detritus). In addition, the carbon flow during the large size phytoplankton blooming which is regulated by nitrate and iron concentration is expressed by two compartments (large phytoplankton, nitrate). And a formula of iron concentration versus large phytoplankton growth rate is used to phytoplankton ecosystem model for estimate the effect of iron fertilization to phytoplankton growth and carbon transportation.

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