analyzer. The relative standard deviations of organic carbon and total nitrogen are 7% and 8% in case of duplicate analysis with organic carbon and total nitrogen contents of 0.2wt.% and 0.02wt.%, respectively.
Opal values were detennined using a modification of the method developed by Mortlock and Froelich (1989). Samples of 10 to 20mg of dry bulk sediment after removing carbonate by acidification and organic matter with H2O2 were digested in 10ml of a 7% Na2CO3 solution at 85℃ in 20ml polyethylene bottles. Residues of selected samples were examined under an optical microscope to verify complete dissolution of the siliceous micro-organisms. Several giving unusual values were analyzed three times, providing a relative error of 3% in the measured values. The contribution of lithogenic matter was calculated as follows: Lithogenic = Total - Carbonate - Opal - 1.8 x Corg (± organic matter).
3. RESULTS AND DISCUSSION
3-l.Sinking particles along 175｡?
A total of nine records from different areas and water depths are available. Traps at Sites 3 and 4 were deployed in 1992/1993 while traps at Sites 5 through 8 were in 1993/1994. Sea surface temperatures (SST) compiled by Japanese Meteorological Agency show little interannual differences between both mooring periods, which suggests that sea surface conditions might be similar during trap experiments in spite of different mooring periods between equatorial sites and the other sites.
Site 3 (0｡?) in Equatorial region
Although the Site 3 was located at the eastern end of the equatorial upwelling area, relatively low OM fluxes (mean value of 4.36 mg m-2day-1) were found at the shallow trap (Fig. 1). One large OM flux maximum, October to November, and another small OM flux peak, June, were observed in 1992-1993 at both shallow and deep traps. The OM content varied from 4 to I6wt.%. The export organic carbon flux at 100m water depth was on average 23mg m-2day-1..
Site 4 (8｡?) in Equatorial region
Generally speaking, the lowest mean OM flux of 2.08 mg m -2day-1 was observed at Site 4 of all trap sites along 175｡? (Fig. 1). The OM flux at deep trap showed little seasonal variation. Carbonate was the dominant constituent (approximately 58wt.%) and was composed of coccolithophorids and planktonic foraminifera. The OM content was relatively low, 14 to 18wt.% in the shallow trap. The mean export organic carbon flux was 13mg m-2day-1
Site 6 (30｡?) in Subtropical gyre
One broad OM flux maximum with relatively intermediate rates was observed from December through March, when Kuroshio extension was shifted to the south of Site 6. On the other hand, nutrient poor surface water in Subtropical gyre covered Site 6 during the other period, when the mean OM was 2.12mg m-2day-1. The OM amounted to 7-9% of the total. The mean export organic carbon flux was 27mg m-2day-1, respectively.
Site 7 (37.5｡?) in Kuroshio extension
The OM flux at the shallow trap of Site 7 showed one large maximum in June (41.3mg m-2day-1) and two small maxima in late August and late March (10.9 and 22.9 mg m-2day-1, respectively) (Fig. 1). The pattern for OM fluxes at shallower depths was generally imprinted at deeper levels with little time-lags. The mean OM flux and export organic carbon flux were 11.6 and 65mg m-2 day-1, respectively.
Site 5 (34｡?, 178｡?) in Kuroshio extension
The OM flux at Site 5 exhibited similar seasonality to those observed at the Site 7 (Fig. 1). Two OM flux maxima in June and March were found at the shallow trap of Site 5. However, the OM fluxes at Site 5 were smaller than those observed at Site 7. The OM flux at shallow trap was in the range of 0.65 to 19.4 mg m -2day-1.The mean OM flux and export organic carbon flux were 5.24 and 27mg m -2day-1,respectively.
Site 8 (46｡?) in Subarctic area
By far, the highest OM fluxes were measured at the northernmost station of all the trap sites, where one large distinct peak in July to December was measured (Fig. 1). Large export fluxes in summer time characterized seasonality of sinking particles in the intermediate to relatively high latitude in the west Pacific. The OM
