Radiolarians under the seasonally sea-ice covered conditions in the Okhotsk Sea

Flux and their implications for paleoceanography

Yusuke Okazaki, Kozo Takahashi, Hiroshi Yoshitani, Takeshi Nakatsuka, Minoru Ikehara, Masaaki Wakatsuchi

Research output: Contribution to journalArticle

59 Citations (Scopus)

Abstract

Four time-series sediment traps at two stations and three piston cores from the Okhotsk Sea were quantitatively examined for coarse-sized radiolarian shells (> 63 μm). Traps were deployed at 300 m and 1550 m at Station M4 (53°01′N, 145°30′E) and at 300 m and 700 m at Station M6 (49°30′N, 146°28′E) during August 1998 through May 2000. The chronologies of the piston cores were established applying δ 18O and paleomagnetic intensity variations; they provide records extending back to marine isotope stage (MIS) 5.51. The modern and past changes in radiolarian assemblages are associated with environmental and productivity changes. Radiolarian fluxes in the sediment traps exhibited significant summer to autumn flux peaks with suppressed values during the winter when sea-ice covered the sea surface at the trap sites. Total radiolarian accumulation rate (RAR) variations in each core tended to correspond to glacial-interglacial cycles and increased during the last deglaciation. In particular, the temporal RAR variation in Core XP98-PC1 (off Kamchatka) showed a similar trend with the climatic changes expressed by δ18O values during the glacial-interglacial cycles for the last 125 kyr. Regional differences were also apparent. RARs showed extremely low values during 12-40 kyr and 63-70 kyr in Core XP98-PC2 (central Okhotsk Sea), indicating the enhanced sea-ice impact. The sea-ice coverage might have continued for a significant part of the year during the intervals since radiolarians did not appear to increase even during the summer to autumn. RAR variations in Core XP98-PC4 (off Sakhalin) showed higher values than XP98-PC2 during MIS 2 and 4. Thus, in eastern Sakhalin around Site XP98-PC4, sea-ice coverage might have been seasonal, but not perennial even during MIS 2 and 4. Among the radiolarian taxa, Cycladophora davisiana was the most abundant species at the lower traps and in all cores. The fluxes of C. davisiana at lower traps showed much higher values than those of upper traps, and also showed similar temporal patterns with the fluxes of aluminum and terrigenous materials. Therefore, C. davisiana fluxes may be associated with terrigenous organic materials. Increased nutrient supply from the continental shelves, presumably transported by seasonal sea-ice and released by sea-ice melting, might be mainly responsible for the high production of C. davisiana in the Okhotsk Sea, especially during the last deglaciation.

Original languageEnglish
Pages (from-to)195-230
Number of pages36
JournalMarine Micropaleontology
Volume49
Issue number3
DOIs
Publication statusPublished - Jan 1 2003

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paleoceanography
sea ice
marine isotope stage
accumulation rate
last deglaciation
glacial-interglacial cycle
sediment trap
autumn
summer
sea
chronology
continental shelf
sea surface
aluminum
melting
time series
shell
productivity
climate change
nutrient

All Science Journal Classification (ASJC) codes

  • Oceanography
  • Palaeontology

Cite this

Radiolarians under the seasonally sea-ice covered conditions in the Okhotsk Sea : Flux and their implications for paleoceanography. / Okazaki, Yusuke; Takahashi, Kozo; Yoshitani, Hiroshi; Nakatsuka, Takeshi; Ikehara, Minoru; Wakatsuchi, Masaaki.

In: Marine Micropaleontology, Vol. 49, No. 3, 01.01.2003, p. 195-230.

Research output: Contribution to journalArticle

Okazaki, Yusuke ; Takahashi, Kozo ; Yoshitani, Hiroshi ; Nakatsuka, Takeshi ; Ikehara, Minoru ; Wakatsuchi, Masaaki. / Radiolarians under the seasonally sea-ice covered conditions in the Okhotsk Sea : Flux and their implications for paleoceanography. In: Marine Micropaleontology. 2003 ; Vol. 49, No. 3. pp. 195-230.
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