Late Quaternary paleoceanographic changes in the southwestern Okhotsk Sea: Evidence from geochemical, radiolarian, and diatom records

Yusuke Okazaki, Kozo Takahashi, Kota Katsuki, Ayumu Ono, Joichi Hori, Tatsuhiko Sakamoto, Masao Uchida, Yasuyuki Shibata, Minoru Ikehara, Kaori Aoki

Research output: Contribution to journalArticle

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Abstract

High-resolution analyses of geochemical parameters (biogenic opal, calcium carbonate, organic carbon, and nitrogen) and microfossil assemblages (diatoms and radiolarians) on Core MD01-2412 clarified detailed paleoceanographic changes such as sea-ice cover and biological production in the southwestern Okhotsk Sea during the last 115 kyr. An age model of Core MD01-2412 was established based on δ18O stratigraphy, accelerator mass spectrometer (AMS) 14C, and tephrochronology. Sea-ice history reconstructed by siliceous microplankton records indicated that the present sea-ice condition was formed during the last 8 kyr. Only during Marine Isotope Stage (MIS) 2 was the duration of sea-ice cover in this region much longer than that of today (4-5 months a year). Two diatom species, Thalassionema nitzschioides and Fragilariopsis doliolus, revealed that the Soya Warm Current Water (SWCW) flowed into the Okhotsk Sea near the site of Core MD01-2412 during the last 12-14 kyr and during MIS 5a, and was associated with sea-level rise. Biological productivity rapidly increased during MIS 1, associated with sea-ice retreat. Two major increases of organic carbon (OC) contents (wt%) and Corg/N ratios were observed, and the timings of these events were 15.8-16.7 ka (Event 1) and 13.1-13.6 ka (Event 2). Corresponding to these events, the abundance of Cycladophora davisiana, an intermediate water dwelling radiolarian species, increased. This high C. davisiana abundance can be correlated to the input of terrestrial organic matter from the submerged shelf to the intermediate water. Apart from the radiolarians, the production of diatoms in the surface waters was suppressed by the development of well-stratified surface water along with sea-ice melting during the early Holocene. Diatom production increased gradually during the last 10 kyr with enhanced vertical mixing.

Original languageEnglish
Pages (from-to)2332-2350
Number of pages19
JournalDeep-Sea Research Part II: Topical Studies in Oceanography
Volume52
Issue number16-18
DOIs
Publication statusPublished - Aug 1 2005
Externally publishedYes

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sea ice
diatom
marine isotope stage
intermediate water
ice cover
organic carbon
surface water
tephrochronology
ice retreat
biological production
microplankton
opal
vertical mixing
organic nitrogen
microfossil
calcium carbonate
sea
stratigraphy
spectrometer
melting

All Science Journal Classification (ASJC) codes

  • Oceanography

Cite this

Late Quaternary paleoceanographic changes in the southwestern Okhotsk Sea : Evidence from geochemical, radiolarian, and diatom records. / Okazaki, Yusuke; Takahashi, Kozo; Katsuki, Kota; Ono, Ayumu; Hori, Joichi; Sakamoto, Tatsuhiko; Uchida, Masao; Shibata, Yasuyuki; Ikehara, Minoru; Aoki, Kaori.

In: Deep-Sea Research Part II: Topical Studies in Oceanography, Vol. 52, No. 16-18, 01.08.2005, p. 2332-2350.

Research output: Contribution to journalArticle

Okazaki, Yusuke ; Takahashi, Kozo ; Katsuki, Kota ; Ono, Ayumu ; Hori, Joichi ; Sakamoto, Tatsuhiko ; Uchida, Masao ; Shibata, Yasuyuki ; Ikehara, Minoru ; Aoki, Kaori. / Late Quaternary paleoceanographic changes in the southwestern Okhotsk Sea : Evidence from geochemical, radiolarian, and diatom records. In: Deep-Sea Research Part II: Topical Studies in Oceanography. 2005 ; Vol. 52, No. 16-18. pp. 2332-2350.
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