Observation of chlorophyli-a distribution in the Suruga Bay using the underwater tow device-SCAN FISH

本项目的目的是研究骏河湾和日本东部开阔海域浮游植物的分布和春季开花机制。我们首先在东海大学的RV BOSEI-MARU （1777t）上，在日本附近的公海上使用水下拖曳装置- scan FISH观测系统（MACArtney A/S，丹麦），记录上层水柱的温度、盐度和叶绿素- A荧光的垂直剖面。后来，我们对系统进行了必要的操作修改，使其可以在骏河湾的渔船等较小的平台上使用。此外，利用Orb View2/Sea WiFS和NOAA/AVHRR卫星获取的1999-2001年3年的海洋颜色和海温数据，监测了Suruga湾海面热场的时空变化及其对近地表叶绿素-a浓度的影响。我们进一步发展了经验方法，从近地表色素浓度推导出叶绿素a的垂直剖面，以便在卫星数据上实现。为此，在100米范围内，在水面和不同深度处采集了原位水样，并利用高效液相色谱技术分析了叶绿素a浓度。从时间序列数据可以看出，2000年骏河湾的春华开始时间比1999年和2001年晚了一个月。研究结果表明，1999年和2001年2月下旬，骏河湾及周边海域开始出现水柱分层现象。但在2000年2月下旬，这种分层在局地风的强烈影响下被破坏，形成了深层混合层。这样的环境不允许浮游植物在春天开花。研究结果清楚地表明，垂直分层是海湾春华现象的一个重要参数。我们进一步利用SCAN FISH观测不同海洋参数的垂直剖面以及氯-a荧光，以了解水华现象的机理。海水盐度剖面对叶绿素-a垂直分布的影响比对水温的影响更大，特别是在海湾西段。盐度垂直剖面与叶绿素-a之间的密切关系强调了密度分层在海湾边春季水华现象中的重要性。这可归因于从西部边缘的四条主要河流流入海湾的大量淡水。少

Objective of our project was to develop appropriate methods to study phytoplankton distribution and spring bloom mechanism in the Suruga Bay as well as in open ocean waters off eastern Japan. We initially used the underwater tow device-SCAN FISH observation system (MACArtney A/S, Denmark) in the open ocean near Japan onboard RV BOSEI-MARU (1777t) of the Tokai University, to record vertical profile of temperature, salinity and chlorophyll-a fluorescence in the upper water column. Later we made necessary operational modification in the system to make it usable from smaller platforms such as fishing boats, in the Suruga Bay.Besides, we analyzed 3-year time series (1999-2001) of satellite derived ocean color and SST date respectively from Orb View2/Sea WiFS and NOAA/AVHRR to monitor spatial and temporal change in sea surface thermal field and its impact on near surface chlorophyll-a concentration in the Suruga Bay. We further developed empirical method to derive vertical profile of chlorop … More hyll a from the near surface pigment concentration for implementation on satellite data. For this purpose in situ water samples were collected during the cruises at surface and at different depths within 100m and chlorophyll a concentration was analyzed using HPLC technique.From the time series data it was noticed that beginning of the spring bloom in the Suruga Bay was delayed by one month during 2000 compared to 1999 and 2001. Our results based on different oceanographic and meteorological data in and around the Suruga Bay indicated that water column stratification started in the late-February in 1999 and 2001. However, during the late-February of 2000 such stratification got disrupted under strong influence of local wind creating deep mixed layer. Such condition did not allow phytoplankton to develop the spring bloom. Our results clearly indicated that vertical stratification is an important parameter in spring bloom phenomenon in the bay. We further used the SCAN FISH, to observe vertical profiles of different oceanographic parameters along with chlorohyll-a fluorescence to understand the mechanism of the bloom phenomenon. Vertical distribution of chlorophyll-a within upper 30m of the water column was noticed to be more strongly influenced by salinity profile than that of water temperature especially in the western sector of the bay. Strong relationship between vertical profile of salinity and chlorophyll-a underlines the importance of density stratification in the spring bloom phenomena in side the bay. This can be attrebuted to influx of plentiful freshwater into the bay from four major rivers along the western margin. Less