PALEOCEANOGRAPHIC CHANGES SINCE 50 kaBP INFERRED FROM RADIOLARIAN ASSEMBLAGES IN GULF OF ALASKA, SUBARCTIC PACIFIC

The paleoceanographic record of radiolarian assemblage for the past 50 ka is investigated using a box core (SO202-27-6) obtained from the Gulf of Alaska, subarctic Pacific during the R/V Sonne cruise SO202-INOPEX. Ten AMS¹⁴C data are used for establishing the stratigraphic age model.The study suggests that:(1) Cycladophora davisiana is the most dominant radiolarian specie in the Gulf of Alaska during the past 50 ka, followed by Siphocampe arachnea and Acanthodesmia micropora. (2) The Q-mode factor analysis obtains 4 maximum variance factors, which represent different radiolarian assemblages. Among them, C. davisiana can be used as a proxy for intermediate water of the Gulf of Alaska, which was sensitive to the rapid climate change of glacial-interglacial cycle, and the variable pattern reveals that the evolution of intermediate water was controlled by the formation and transportation of NPIW from subarctic Pacific. (3) Based on the indicative radiolarian species for environmental changes, such as Ceratospyris borealis, Actinomma boreale/leptodermum and Rhizoplegma boreal, we argue that the upper ocean conditions in the Gulf of Alaska underwent periodic changes during the past 50 ka. Before LGM, relatively stable surface productivity, sea-ice expansion and retreat, and melt-water pulse (MWP) responded clearly to the interstadial (GI) to stadial (GS) cycles. During LGM, under the conditions of complex ice sheet effects, atmospheric circulation and oceanic currents, there were rarely WMP,continuous sea-ice extension and limited productivity in the Gulf of Alaska. Since LGM, rapid increase and decrease in surface productivity was caused by rich-nutrient water from MWP and by rapid cooling event, respectively.