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Characteristics of alkenone distributions in suspended and sinking particles in the northwestern North Pacific |
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| Authors: | Naomi Harada Miyako Sato Aya Shiraishi |
| Institution: | a Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology, 2-15 Natsushima-cho, Yokosuka 237-0061, Japan b Department of Marine Science, Marine Works Japan Ltd. 2-16-32, Kamariya-higashi, Kanazawa-ku, Yokohama 236-0042, Japan c Mutsu Institute for Oceanography, Japan Agency for Marine-Earth Science and Technology, 690 Kitasekine, Sekine, Mutsu 035-0022, Japan |
| Abstract: | We investigated alkenones recorded in suspended particles and a settling particle time series collected at three stations, 40N (40°N, 165°E), KNOT (44°N, 155°E), and 50N (50°N, 165°E), in the northwestern North Pacific from December 1997 to May 1999. Emiliania huxleyi, the most abundant alkenone producer in this area, is present in surface to subsurface (to ∼50 m depth) waters. The alkenone concentrations recorded in the suspended particles indicated that the seasonal alkenone particle distribution differed significantly interannually. Alkenone export fluxes at the three sediment-trap stations ranged from 0.16 to 49.3 μg m−2 day−1, and the maximum export flux, which occurred in summer to fall (July-November), was associated with a high organic carbon export flux. The amount of alkenone produced during the maximum export season accounted for 60-80% of the total annual amount of alkenone, and the alkenones accumulated in the sediment below the traps had characteristics corresponding to subsurface waters during the summer-autumn season. Alkenone-derived temperatures recorded in suspended particles corresponded to the in situ temperature within ∼2 °C. Although alkenone-derived temperatures corresponded approximately to the temperatures observed in the stratified subsurface waters at the three trap stations during the high-export season, large differences were observed during the low-export (winter-spring) period. For example, the alkenone-derived temperatures observed at stations KNOT and 50N were much higher than the in situ subsurface temperatures reported in the World Ocean Atlas 2001. Relatively large differences between alkenone-derived temperatures and in situ temperatures in the subarctic might be due to (1) a low-light limitation or (2) contributions of allochthonous alkenones in particulate material transported from subtropical areas within a warm-core ring. |
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