to Subarctic region. However, little is known about the present annual flux and
seasonality in sinking particles in this area. To understand carbon cycling andseasonality
of associated compounds in the Western Pacific, we deployed a total of six time-series
sediment trap moorings for one year. The sites were mainly located along 175｡? between
the Equatorial region and Subarctic region. We here compare the results from the various
latitude with respect to organic matter fluxes and to estimate organic carbon removal
rates in this area.
2.FIELD WORK AND ANALYSIS
2-1. Areas of investigation and oceanographic setting
Six deep ocean moorings were mainly deployed along 175｡?. Site 3 and Site 4 were
located at 0｡? and 8｡?, respectively. Sites 5, 6, 7, and 8 were located at 30｡?, 34｡?
(178｡?), 37.5｡?, and 46｡?, respectively. According to seawater temperature distribution
in the 300m thick surface seawater measured with CTD instruments in summer of 1994, the
surface water in the Western Pacific of the northern hemisphere is divided into four
zones: 1) Equatorial region, 2) Subtropical gyre, 3) Kuroshio extension, 4) Subarctic
area. 'Three currents are important in the equatorial region: 1) North Equatorial Current,
2) Equatorial Counter Current, 3) South Equatorial Current. North Equatorial Current is a
westbound flow and it is observed between 10 and 16｡?. The east-bound Equatorial Counter
Current is predominant between 3 and 10｡?. To the uth of Equatorial Counter Current,
South Equatorial Current is a westbound flow. The Subtropical gyre, extending from the
Equatorial Water to about 31｡?, is the most aline of the central water masses of the
oceans. North of the North Pacific Central Water is a Kuroshio extension and Pacific
Subarctic Water Mass which extends across the greater part of the ocean. In the North
Pacific the Subarctic Convergence is only clear in the western part of the North Pacific
where the Subarctic Water must be formed by mixing between the warm, saline waters of the
Kuroshio Extension and the cold, less saline waters of the Oyashio. The Convergence is
located around 40｡? at 175｡?.
2-2. Sampling methods and analytical methods
The water depths of the northern hemisphere of the Western Pacific are usually 4-5km
except Hess Rise. Four PARFLUX Mark 7G-21 and five SMD2I-6000 time-series sediment traps
with the 21 rotary collectors on each were deployed. The same cone apes were adopted for
attaining the same collection efficiency. The sample bottles, 21 for each trap, were
filled with filtered seawater collected in the Caroline Basin. Analytical grade formalin
was added to make a 3% solution buffered with sodium boric acid. Sample bottles were
mechanically sealed from he ambient water except for each 14 days collecting periods.
Recovered sample bottles were immediately refrigerated on board at approximately 2 to 4℃
Particle samples in 250ml polyethylene sample bottles were transported to Geological
Survey of Japan under refrigeration at 2℃. Samples were passed through 1mm sieves and
the <1mmfraction was split into aliquots with a rotaing splitter.
We used a desalted and homogenized split from each sample for the bulk analysis.
Organic carbon was determined with a Yanako MT-S CHN analyzer after removing carbonate by
acidification within ceramic sample boats using HCI vapor. Samples were weighed out into
precombusted ceramic boats and 100ml ultra-pure water was pipetted into each sample boat.
The samples were reacted with HCl vapor at room temperature for 24 hours in a glass
desiccator which contained 500ml of 12N HCI. Then the samples were dried up to drive off
HCI and water at 50 for at least 3 hours until the determination of carbon with Yanako
MT-S analyzer. The combustion condition was 950℃ for five minutes. Silver granules were
aided to the reduction tube to remove halogen. The bridge current for the detector was set
at 100mA for carbon dioxide. Antipyrine was used as a calibration standard. At least 6
concentrates were measured to obtain a linear calibration (r2>0.99 (Yamamuro and
Kayanne, 1995). Total nitrogen measurements were also preformed from dried and ground bulk
sediment samples with the CHN
