Taphonomic bias in the transition from life to death assemblages of marine phytoplanktor

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Four sets of a time-series of thirteen consecutive 27 to 28 days-long samples representing one sediment trapping interval (Mar. 5,1991-Mar. 2,1992) were collected from four deferent depths in the northwest Pacific at station JT (34ﾟ9.802'N,141ﾟ59.268'E ; 916m, 3422m, 5429m and 8430m), and provided material to evaluate information loss in the transition from life to death assemblages of diatoms. Two sediment samples also provided material to evaluate the loss on sediment-water interface. Comparison in flux records among the four sets of trap samples distinguishes one high flux period found in two different dephts as conspicuous flux peaks ; 3442m and 5429m. A sinking velocity of diatom flux is calculated from a time lag between the two peaks ; more than 71m/day. Differences in diatom assemblages among the two peaks and the underlying sediments suggest that dissolution on sediment-water interface appears to be the prime factor in determining diatom assemblages preserved in sediments, and the following three diatom groups are distinguished as most susceptible forms to value dissolution in the Kuroshio water ; Nitzschia bicapitata-bifulcata complex, Neodelphineis indica, Chaetoceros species. These forms together comprise 55% to 60% of total sediment-trap floras which suggests that information loss from water column to sediments is at least 50%.