The effects of horizontal advection on the spring bloom of phytoplankton in the central Southern Huanghai Sea
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The effects of horizontal advection on the spring bloom of phytoplankton in the central Southern Huanghai Sea HAN Jun1,2 , WEI Hao1,3 , ZHAO Liang1∗ , SHI Yao2 , SHI Jie1 , ZHANG Guosen4 1
2 3 4
Key Lab of Physical Oceanography of Ministry of Education, Ocean University of China, Qingdao 266100, China Mailbox 5111, Beijing 100094, China Tianjin University of Science and Technology, Tianjin 300222, China State Key Laboratory of Estuarine and Coastal Research, East China Normal University, Shanghai 200062, China
Received 8 April 2010; accepted 8 October 2010 ©The Chinese Society of Oceanography and Springer-Verlag Berlin Heidelberg 2011
Abstract An algal bloom is defined as a relatively rapid increase in the biomass of phytoplankton in an aquatic system. During 30 March to 24 April 2007, a cruise was conducted in the central Southern Huanghai Sea to investigate the spring bloom processes. The spatial and temporal variations of phytoplankton are discussed based on the in-situ observations and simultaneous remote sensing data. The explosive algal blooming varied quickly in temporal and spatial scales, due to the highly patchy distribution. Data obtained at the 2 anchor stations (BM1 and BM2) were analyzed in the present study. Horizontal advection is speculated to be responsible for the abrupt decrease in the concentration of chlorophyll-a at stations BM1 and BM2. At station BM2, the intermediate high chlorophyll-a concentration, coinciding with the low temperature, was found to be advected from the inshore colder water mass located to the east of the site. Key words: chlorophyll-a, algal bloom, horizontal advection, remote sensing, Southern Huanghai Sea
1 Introduction An algal bloom is a relatively rapid increase in the biomass of phytoplankton in an aquatic system. This phenomenon has attracted the interest of ocean scientists during the last century. The spring bloom is important to the primary production of the sea. In the late senescent stage of the bloom, a large part of the accumulated phytoplankton biomass sinks out of the euphotic zone. Thus, the spring bloom dynamics has an impact on the pelagic and benthic ecology, fisheries and carbon fluxes in coastal areas (Kudo and Matsunaga, 1999). Much of the overall productivity at higher trophic levels in temperate latitude oceans is dependent on the relatively short period of time associated with the spring phytoplankton bloom (Townsend et al., 1994). In the spring, the timing of the phytoplankton bloom is variable every year in coastal waters where
the depth of the mixed layer extends to the bottom, and abundant nutrients could not be a limitation to algal growth. Thus, bloom initiation is triggered by the increase in water temperature and solar radiation in spring (Townsend et al., 1994). Sverdrup (1953) gave a quantitative description of the spring bloom of deep waters, demonstrating how the timing of the onset of the bloom was controlled by the relation between the depth of water column mixing and the available light. The Huanghai Sea is a semi-enclosed shelf
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