Fertilization Effects of Deep Ocean Water on Phytoplankton Community in Subtropical Surface Water

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  • 亜熱帯表層植物プランクトン群集に対する海洋深層水の肥沃化効果
  • アネッタイ ヒョウソウ ショクブツ プランクトン グンシュウ ニ タイスル カイヨウ シンソウスイ ノ ヒヨクカ コウカ

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Abstract

Acceleration of oceanic phytoplankton production by enriching oligotrophic surface seawater with eutrophic deep ocean water has becoming a recent desirable subject in order to achieve sustainable fisheries as well as contributing to possible absorption of carbon dioxide in the atmosphere to slow down global warming andefficient resource utilization of deep ocean water for multiple-purposes. Beforemaking actual operation of ocean fertilization, prior prediction of the probableeffects is required by means of field experiments and numerical simulation model. In this study, parameters and the applicable values for the model estimation of fertilization effects of deep ocean water on phytoplankton community in oligotrophic subtropical surface water were examined based on the data collected in out-door culture experiments using natural seawater samples. The addition of deep ocean water to surface seawater resulted 214-fold increase of chlorophyll aconcentration after several days of lag period. The specific growth constant of chlorophyll aconcentration increased at a rate of 0.3 days-1 perμM-nitrate and the yield of chlorophyll awas 1.48μg/μM-nitrate. These changes were resulted from the increase of phytoplankton, mainly diatoms. Due to the preferential growth of diatoms, the relative abundance of nano- and microphytoplankton increased from 20% or less to around 80%, and the Si/N ratio ofthe nutrients, consumed with the increase in chlorophyll a concentration, amounted to 0.87.

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