Fine scale distribution of phytoplankton abundance along the cruise track of the icebreaker Shirase, from Tokyo to Fremantle, Australia in the 1991 season

Abstract

Water temperature, salinity, and in vivo fluorescence intensity were investigated using the Surface Water Monitoring System (SWMS) with five minute intervals along the first leg of the icebreaker Shirase cruise (Tokyo - Fremantle) from November 14 to 28, 1991 (Japan Antarctic Research Expedition (JARE) -33). Five prominent increases of in vivo fluorescence occurred during the period. Among them four were observed between islands in the coastal area of Southeast Asia, and were related to occurrence of low temperature water, suggesting local upwelling caused by the coast line and/or submarine topography. Average concentrations of chlorophyll a estimated from the in vivo fluorescence were consistent with those of previous observations based on sampling two to three times a day. However, the highest concentration detected by the SWMS in Lombok Strait was considerably more than the previous values. High resolution survey by the SWMS can easily reveal local increases of phytoplankton on a finer spatial scale than those with conventional observations. It is confirmed that the SWMS is a powerful tool to investigate local events in coastal waters.

1991年11月14日-28日の砕氷艦「しらせ」の第1レグ航路上(東京-フリマントル)で、表面水モニタリングシステム(SWMS)を用い、水温、塩分、クロロフィル現場蛍光値を5分間隔で調べた。この間、現場蛍光の急激な増加が5カ所においてみられた。その内4カ所は東南アジア沿岸水の島嶼間でみられ、いずれも低水温水塊と関連しており、海岸線や海底地形の変化により引き起こされる底層水の湧昇を示唆した。現場蛍光より見積ったクロロフィルα濃度は、過去の観測結果と平均的には一致した。しかしながら、ロンボク海峡でSWMSによって検出された最高濃度は、1日2-3回の観測にもとづく今までの結果よりかなり高かった。SWMSを用いた微細観測では、植物プランクトン群集の局所的増加における空間的規模やその最大量を容易に明らかにすることができる。沿岸域で起こる局所的現象の調査にはSWMSが威力を発揮することが確かめられた。