Biogeochemical, benthic and planktonic foraminiferal data of core MD01-2415 were investigated to compare variations of paleoproductivity and oxygen minimum zone (OMZ) intensity on the northern slope of the Okhotsk Sea during the Termination (T) I – marine iotope stage (MIS) 1 and TII – MIS 5e. We also estimated changes of the sea surface temperature (SST) based on the planktonic foraminiferal percentages. The IMAGES core MD01-2415 (53 57.09N; 149 57.52E) was collected on the northern slope at water depth 822 m during the WEPAMA 2001 cruise of the R/V Marion Dufresne. The 46.23 m-long core represents the last 1.1 million years (Nürnberg and Tiedemann, 2004). Our study focuses on two intervals 0-3.1 and 7.6-8.5 m, which correspond to the TI –
MIS 1 (the last 16 ka) and TII – MIS 5e (116-134 ka), respectively. The previous core age model (Nürnberg and Tiedemann, 2004) was improved basing on four AMS14C dates on foraminifers. Foraminifers were quantified in the size fraction 〉μm, For the SST estimation, planktonic foraminifers re-counted in the size fraction 〉150 μm. Faunal analysis were performed in 67 and 63 samples collected each 5 and 1-2 cm throughout the TI – MIS 1 and TII – MIS 5e sediments, respectively. It gives a temporal resolution about 300 years for the both studied intervals. The C/N Ratio, total organic carbon (TOC) and CaCO3 contents were obtained at 5 cm sample spacing that corresponds to a temporal resolution 300-600 years.
Benthic foraminiferal assemblages indicate that the Okhotsk Sea OMZ was intensified during the TI and TII – early MIS 5e (127-134 ka), whereas it was weakened during the MIS 1 and late MIS 5e. The increased marine (mainly coccoliths) productivity and terrestrial organic matter (OM) input from the submerged shelves occurred during the TI and TII in the Okhotsk Sea (Seki et al., 2009; Nürnberg and Tiedemann, 2004) that likely controlled the deglacial intensifications of the OMZ (Bubenshchikova et al., 2010). The stronger OMZ is reconstructed during the TI (i.e. Preboreal) based on maximum of the Dysoxic bolivinids: mainly Bolivina spissa. The less pronounced OMZ is recovered during the TII – early MIS 5e by the dominance of the Suboxic cassidulinids: Cassidulina laevigata/ carinata. The TOC and C/N Ratio values are found to be higher in the TI than in the TII – early MIS 5e. It suggests higher input of terrestrial OM and supports stronger OMZ during the TI.
Planktonic foraminiferal assemblages indicate that the summer SST increased during the TI and TII – early MIS 5e and decreased during the MIS 1 and late MIS 5e. It is evidenced from the higher contribution of temperate-to-subpolar
Globigerina bulloides up to 28% during the TI and up to 40% during the TII – early MIS 5e in the almost monospecies assemblages dominated by polar Neogloboquadrina pachyderma sinistral. The deglacial warmings of surface water could have caused stratification, inhibited diatom growth and stimulated coccolithophorid productivity in the Okhotsk Sea (Seki et al., 2009). It agrees with the reconstructed deglacial intensifications of the OMZ by benthic foraminiferal data.
Bubenshchikova, N.V., Nurnberg D., Gorbarenko, S.A., Lembke-Jene, L., 2010. Variations of the oxygen minimum zone of the Okhotsk Sea during the last 50 Kyr as indicated by benthic foraminiferal and biogeochemical data. Okeanologiya 50 (1), 93-106.
Nürnberg, D., Tiedemann, R., 2004. Environmental change in the Sea of Okhotsk during the last 1.1 million years. Paleoceanography 19, PA4011, doi:10.1029/2004Pa001023.
Seki, O., Sakamoto, T., Sakai, S., Schouten, St., Hopmans, E., Sinninghe Damste J.S., Pancost, R. D., 2009. Large changes in seasonal sea ice distribution and productivity in the Sea of Okhotsk during the deglaciations.
Geochemistry. Geophysics. Geosystems. 10 (10), Q 10007, doi:10.1029/2009GC002613
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