Use of cyanobacterial pigments to characterize the ocean surface mixed layer in the western Pacific warm pool |
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| Authors: | Kazuhiko Matsumoto Kentaro Ando |
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| Affiliation: | 1. Research Institute for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka, Japan;2. Department of Earth Science and Bjerknes Centre of Climate Research, University of Bergen, Allegaten 55, Bergen, N-5007, Norway;3. Department of Oceanography and Center for Oceanographic Research in the Eastern South Pacific (COPAS), University of Concepción, Casilla 160-C, Concepción, Chile;4. Department of Zoology, University of Concepción, Casilla 160-C, Concepción, Chile;5. Kochi Institute for Core Sample Research, Japan Agency for Marine-Earth Science and Technology, Nankoku, Japan;1. Central Laboratory, Marine Ecology Research Institute (MERI), 300 Iwawada, Onjuku-machi, Isumi-gun, Chiba 299-5105, Japan;2. Natural History Museum, Department of Geology, University of Oslo, P.O. Box 1172, Blindern, 0318 Oslo, Norway;3. Dennigkofenweg 33, 3073 Guemligen, Switzerland;4. Section for Genetics and Evolutionary Biology, Department of Biosciences, University of Oslo, P.O box 1066, N-0316 Oslo, Norway;5. Research and Development Center for Global Change, JAMSTEC, Natsushima-cho 2-15, Yokosuka 237-0061, Japan;6. Arctic Environment Research Center, National Institute of Polar Research, 10-3 Midori-cho, Tachikawa, Tokyo 190-8518, Japan;1. V.I. Il''ichev Pacific Oceanological Institute, Far East Branch of Russian Academy of Science, (FEB of RAS), Vladivostok 690041, Russian Federation;2. Far Eastern Geological Institute, FEB of RAS, Vladivostok 690022, Russian Federation;3. North-Eastern Interdisciplinary Scientific Research Institute, FEB of RAS, Magadan, Russian Federation |
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| Abstract: | We collected biological and physical oceanographic data simultaneously from shipboard observations and mooring buoys in the Pacific equatorial warm pool during the 2002–2003 El Niño event and found that the vertical profiles of cyanobacterial pigments reflected the turbulent kinetic energy (TKE) better than did analyses of the mixed layer by temperature and salinity profiling. Zeaxanthin, an accessory pigment of cyanobacteria, was abundant and almost homogeneous in the warm pool within the surface mixed layer, although chlorophyll a concentrations were low. The intracellular content of chlorophyll a increases with increasing depth and decreasing light in a photoprotective response, but the zeaxanthin content does not change with depth. Hence, we hypothesized that the profile of the ratio of zeaxanthin to chlorophyll a would decrease with increasing depth if the water column were stable, without vertical mixing. On the contrary, vertically constant ratios would indicate vertical mixing. Our analysis using a numerical model showed a good agreement between profiles of these ratios and the profiles of TKE and supported the hypothesis. However, a comparative analysis of the zeaxanthin:chlorophyll a ratio profiles with mixed layer depth based on temperature and salinity data revealed two distinct patterns. In the first pattern, the ratio was uniform in the mixed layer when TKE was strong. In the second, the ratio decreased with increasing depth, even in the mixed layer, because of reduced TKE. |
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