Takahashi Kozo

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Takahashi
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Kozo
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  • Technical Report
    Two year time-series fluxes of Silicoflagellates and Actiniscus : size fractioned results from subarctic Pacific Station Papa, 1982-1984
    (Woods Hole Oceanographic Institution, 1985-12) Takahashi, Kozo
    A seasonal flux study of silicoflagellates and Actiniscus was conducted at subarctic Pacific Station PAPA (50°N, 145°W; water depth 4200 m) during September, 1982 through August, 1984 using PARFLUX time series sediment traps deployed at 1000 m and 3800 m depths. The time series sediment trap samples were collected for 4 to 16-day periods depending on the samples; most of the samples were collected for 14 to 16-day periods. A total of 47 continuous samples represents nearly a two-year record of the fluxes of silicoflagellate and Actiniscus taxa at 3800 m depth. An additional 12 samples from 1000 m represent a continuous 6-month period which provides a pair of samples from two depths of each time series. Analysis of the paired samples is essential to understand particle sinking processes. Seven silicoflagellate taxa, several additional variants of silicoflagellat.es, and Actiniscus pentasterias group were enumerated, based on a census of four wet sieved size fractions: 250-1000μm, 125-250μm, 63-125μm, and <63μm. A total of more than 32x103 specimens were identified to species level and counted in this study. Statistics of the counts are given. The fluxes of silicoflagellate taxa of all four size fractions are graphically presented. This report provides a detailed data base for further investigations of seasonal silicoflagellate fluxes in the area.
  • Book
    Radiolaria : flux, ecology, and taxonomy in the Pacific and Atlantic
    (Woods Hole Oceanographic Institution, 1991) Takahashi, Kozo ; Honjo, Susumu
    Radiolarians setting through the oceanic water column were recovered from three stations (western tropical Atlantic, Station E; central tropical Pacific, Station P1; and Panama Basin, Station PB) using PARFLUX sediment traps in moored arrays at several depths. The taxonomic diversity of the radiolarian assemblages in the sediment traps was very high. A total of 420 taxa (including 23 new taxa) were found at the three stations; of these 208 taxa were found at Station E. The polycystine radiolarians generally reach the sea floor with little change in abundance or species composition, although slight skeletal dissolution occurs during their descent through the water column. The phaeodarian radiolarians, on the other hand, are largely dissolved within the water column; only a few species reach the sea-floor and these dissolve rapidly at the sediment-water interface. Most radiolarian skeletons sink as individuals through deep water columns without being incorporated into large biogenic aggregates. Because significant numbers of nassellarian and phaeodarian species are deep-water dwelling forms, the diversity of radiolarians increases with increasing depth in the mesopelagic zone. The vertical flux of the total radiolarians arriving at the trap depths (in x 103 individuals/m2/day) ranged from 16-24 at Station E, 0.6-17 at Station Pl, and 29-53 at Station PB. On the average 25% and 69% of the total radiolarian flux is transported by Spumellaria and Nassellaria, respectively, while 5% is carried by Phaeodaria. The supply of radiolarian silica (mg Si02/m2/day) to each trap depth ranged from 2.5-4.0 at Station E, 0.9-3.2 at Station Pl, and 5.7-10.4 at Station PB. The Radiolaria appear to be a significantly large portion of the Si02 flux in the > 63 μm size fraction and thus play an important role in the silica cycle. When the radiolarian fluxes at the three stations are compared with Holocene radiolarian accumulation rates in the same areas it became apparent that several percent or less of the fluxes are preserved in the sediment in all cases and the rest must be dissolved on the sea-floor.
  • Thesis
    Vertical flux, ecology and dissolution of radiolaria in tropical oceans : implications for the silica cycle
    (Massachusetts Institute of Technology and Woods Hole Oceanographic Institution, 1981-11) Takahashi, Kozo
    Radiolarians which settle through the oceanic water column were recovered from three stations (western Tropical Atlantic-Station E, central Tropical Pacific-Pi and Panama Basin-PB) using PARLUX sediment traps in moored arrays at several depths. The taxonomic diversities of the radiolarian assemblages in the sediment traps were very high. A total of 420 taxa, including 23 newly identified taxa, were found at the three stations; of these, 208 taxa were found at station E. The polycystine radiolarians generally reach the sea floor with little change in abundance or species composition, although slight skeletal dissolution occurs throughout their descent. The phaeodarian radiolarians, on the other hand, are largely dissolved within the water column; only a few species reach the sea-floor and these dissolve rapidly at the sediment-water interface. Most radiolarian skeletons sink as individuals through deep water columns without being incorporated into large biogenic aggregates. Because significant numbers of nassellarian and phaeodarian species are deep-water dwelling forms the diversity index of radiolarians increases with increasing depth in the mesopelagic zone. The vertical flux of the total radiolarians arriving at the trap depths (in x 103 individuals/m2/day) ranged from 16-24 (E), 0.6-17 (Pl), and 29-53 (PB). Of these on the average 25% and 69% of the total radiolarian flux is transported by Spumellaria and Nassellaria, respectively, while 5% is carried by Phaeodaria. The measured Si02 content of the skeletons averaged 91, 98 and 71% of measured weight for Spumellaria, Nassellaria and Phaeodaria, respectively. The supply of radiolarian silica (mg Si02/m2/day) to each trap depth ranged from 2.5-4.0 (E), 0.9-3.2 (Pl), and 5.7-10.4 (PB). The Radiolaria appear to be a significantly large portion of the Si02 flux in >63 pm size fraction and thus play an important role in the silica cycle. When the radiolarian fluxes at the three Stations are compared with Holocene radiolarian accumulation rates in the same areas it became apparent that several percent or less of the fluxes are preserved in the sediments in all cases and the rest is dissolved on the sea-floor. Estimated excess Si which is derived from Si02 dissolution on the sea-floor is fairly small relative to advective Si in the western North Atlantic and thus it appears to be insignificant to show any deviation in a simple mixing curve of deep water masses. Weight, length, width, projected area and volume of 58 radiolarian taxa were measured. The density contrast of radiolarians, relative to seawater, generally falls between 0.01 and 0.5 g/cm3. The sinking speed of 55 radiolarian taxa, measured in the laboratory at 3°C, ranged from 13 to 416 m/day. Despite the wide variety of morphology between the species, sinking speeds were best correlated with weight/shell among all the possible combinations of the examined variables. The estimated residence times of these taxa in the 5 km pelagic water column ranged from 2 weeks to 14 months. Large phaeodarians reached the water-sediment interface relatively quickly and ultimately dissolved on the sea floor. Small-sized taxa dissolved en route during sinking. The standing stock of 26 examined abundant taxa is on the order of 1 to 100 shells/m3. Total radiolarian standing stock ranges from about 450 shells/m3 at Stations Pl and E to 1200 shells/m3 at Station PB. The rate of production of total Radiolaria is calculated to be 77 to 225 shells/m3 /day. The turnover time for these species ranges from several days to one month depending on the species and the assumption of the depth interval used for the estimation.
  • Technical Report
    Pelagic diatom fluxes I : size fractioned time-series results from subarctic Pacific Station Papa during 1982-1983
    (Woods Hole Oceanographic Institution, 1985-12) Takahashi, Kozo ; Povio, Danielle N. ; Billings, John D. ; Manganini, Steven J.
    A time series vertical flux assessment of pelagic diatoms was conducted during September, 1982 through September, 1983 at subarctic Pacific Station PAPA (50°N, 145°W; water depth 4200 m) using PARFLUX sediment traps deployed at 1000 and 38000 m. The time series sediment trap samples were collected for 11 to 16-day periods during the year; a total of 24 samples represent a full year's record of flux. Eighteen taxonomic groups of diatoms were enumerated, based on a census of four wet-sieved size fractions: 250-1000μm, 125-250μm, 63-125μm, and < 63μm. In order to study the sinking processes of diatoms, detailed information on frustule integrity was acquired. For example , counts of single valves were separated from frustules. Size-fractioned fluxes of all the counting groups are graphically presented, which provides a data base for further investigations.
  • Book
    Silicoflagellates and Actiniscus : vertical fluxes at Pacific and Atlantic sediment trap stations
    (Woods Hole Oceanographic Institution, 1991) Takahashi, Kozo ; Honjo, Susumu
    Vertical fluxes of silicoflagellate skeletons were measured in meso- and bathypelagic zones at four PARFLUX sediment trap stations located in the Pacific and Atlantic oceans. The average flux measured at several depths ranged from 35 X 103 skeletons/m2/day at the Pacific gyre (P1) station to 424 X 103 skeletons/m2/day at the Panama Basin (PB1) station. The skeletal fluxes at these stations constituted a few weight percent or less of the total biogenic opal flux. The fluxes measured at Station P1, as well as the relative abundance of different assemblages, were fairly constant with depth. At Station PB1, while relative abundance of assemblages was constant with depth, the flux measured at mesopelagic depths was threefold greater than that in the bathypelagic zone. At equatorial Atlantic Station E a slight increase toward the bathypelagic zone is correlated with gradual change in the relative abundance of two predominant taxa, suggesting seasonality in the production of each taxa. Aggregate forms of vertical settling were observed at Station E; the number of skeletons in the aggregates was more than one-half of the total number in the mesopelagic zone and it decreased with increasing depth. The percent abundances of Dictyocha messanensis messanensis and Distephanus pulchra are correlated with organic carbon flux at four stations. Preservation of the skeletons in Holocene sediment at Station P1 is less than one percent of the silicoflagellate flux.
  • Technical Report
    Dimensions and sinking speeds of tropical radiolarian skeletons from the parflux sediment traps : technical report
    (Woods Hole Oceanographic Institution, 1982-05) Takahashi, Kozo
    Length, width and projected area (58 species) and weight (53 species) of radiolarian. skeletons, mainly from the Panama Basin PARFLUX sediment trap (5°21.8'N, 82°01.4'W) samples, were measured. Volume and density contrast were computed. The measured mean weight values for the examined species range from 0.05 pg/shell to 24 μg/shell. The weight is best correlated with projected area among the studied size dimensions of Radiolaria as a whole group. The density contrast of the radiolarian skeletons, relative to seawater, generally falls between 0.01 and 0.5 g/cm3 and appear to be constant with an order of magnitude increase of the shell diameter. The sinking speeds of specimens of 55 radiolarian species measured in 3, 10 and 20°C seawater range from 13 to 416 m/day. Despite the wide variety of morphology between the species, the sinking speed is best correlated with weight/shell with reasonably small deviations from a regression line. Using the sinking speeds residence times of the 55 species in the 5 Krn pelagic water column range from 2 weeks to 14 months.