☆ 4.3 Article

Seasonal Change of Oceanographic Conditions and Chlorophyll a Vertical Distribution in the Southwestern Okhotsk Sea during the Non-Iced Season

JOURNAL OF OCEANOGRAPHY (2010)

Journal

JOURNAL OF OCEANOGRAPHY

Volume 66, Issue 1, Pages 13-26

Publisher

SPRINGER

DOI: 10.1007/s10872-010-0002-3

Keywords

Okhotsk Sea; chlorophyll a; subsurface chlorophyll a maximum; Intermediate Cold Water; Soya Warm Current

Funding

Seeds Study Grant in HNFRI/FRA

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Abstract

Seasonal changes in oceanographic conditions related to primary productivity was investigated in the southwestern Okhotsk Sea during non-iced seasons, using the observation data conducted in 2000-2006. Based on hydrographic characteristics, the studied area could be classified into two regions, the Coastal Region which is influenced under the Soya Warm Current and the Forerunner Water of the Soya Warm Current, and the Offshore Region where the Intermediate Cold Water was located in the subsurface layer. This study is the first report on seasonal change of nutrient and chlorophyll a concentrations in the offshore region of the southwestern Okhotsk Sea. Variability of concentrations of chlorophyll a and nutrients is temporally and regionally high in the Coastal Region. The maximum chlorophyll a concentration in April was observed at the surface layer of both regions. The most remarkable feature on the vertical structure in the Offshore Region was the consistent existence of the Intermediate Cold Water and the development of seasonal thermocline in the subsurface layer during summer and autumn. The stratification formed within the euphotic zone in the Offshore Region resulted in the formation of the subsurface chlorophyll a maximum (SCM) from May to October. Throughout the research period, although less amplitude of nutrients at the surface was observed in the Coastal Region than that in the Offshore Region, comparable amplitude of chlorophyll a concentration was observed between regions. These results suggested differences of environmental conditions for primary production between the two regions. Depending on the presence of SCM, relationships between chlorophyll a concentration at the sea surface and chlorophyll a standing stock within the euphotic layer were different. At most stations with SCM, the surface chlorophyll a concentration was lower than 0.6 mg m(-3). This suggests that the presence of SCM and the chlorophyll a standing stock within the euphotic layer may be estimated using the surface chlorophyll a concentration from spring to autumn in the studied area.

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Characteristics of subsurface chlorophyll maxima during the boreal summer in the South China Sea with respect to environmental properties

Wenlong Xu, Guifen Wang, Xuhua Cheng, Long Jiang, Wen Zhou, Wenxi Cao

Summary: Characterizing the vertical distribution of chlorophyll a in each oceanic region is crucial for accurate assessment of phytoplankton biomass. This study investigated the characteristics of the subsurface chlorophyll maximum (SCM) in the South China Sea during the boreal summer. The study found that the SCM layer was a prominent feature in the South China Sea during the boreal summer, with large spatial variability in its thickness, depth, and magnitude. The vertical position and magnitude of the SCM were influenced by light attenuation and physical processes. The study highlights the importance of considering ocean physical conditions and variability in accurately estimating primary production in the South China Sea.

SCIENCE OF THE TOTAL ENVIRONMENT (2022)