Cycladophora davisiana (Radiolaria) in the Okhotsk Sea: A key for reconstructing glacial ocean conditions |
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| Authors: | Yusuke Okazaki Osamu Seki Takeshi Nakatsuka Tatsuhiko Sakamoto Minoru Ikehara Kozo Takahashi |
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| Institution: | (1) Institute of Observational Research for Global Change, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka 237-0061, Japan;(2) Graduate School of Environmental Science, Hokkaido University, Kita-ku, Sapporo 060-0810, Japan;(3) Institute of Low Temperature Science, Hokkaido University, Kita-ku, Sapporo 060-0819, Japan;(4) Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Natsushima-cho, Yokosuka 237-0061, Japan;(5) Center for Advanced Marine Core Research, Kochi University, Monobe, Nankoku 783-8502, Japan;(6) Department of Earth and Planetary Sciences, Graduate School of Sciences, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan |
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| Abstract: | Cycladophora davisiana, a radiolarian species dwelling at mesopelagic depths, is known as a representative glacial fauna due to its unique distribution
during glacial periods. In the present ocean, abundant production of C. davisiana is only observed in the Okhotsk Sea, indicating an adaptation of C. davisiana for seasonal sea-ice covered conditions. We found pronounced abundant production of C. davisiana during the early to middle Holocene in the Okhotsk Sea, suggesting more favorable conditions for C. davisiana than the present Okhotsk Sea. In order to clarify the reason, oceanographic conditions during the Holocene were reconstructed
based on biomarkers, lithogenic grains including ice-rafted debris (IRD), biogenic opal, and total organic carbon (TOC) in
two sediment cores from the Okhotsk Sea. These indicators suggest that the pronounced C. davisiana production may be attributed to: 1) a supply to mesopelagic depths under intensified stratification of fine organic particles
derived from coccolithophorids, bacteria, and detrital materials; and 2) cold, well-ventilated intermediate water formation. |
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| Keywords: | Radiolaria intermediate water sea-ice stratification export production Okhotsk Sea |
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