Toshiro Saino

Geographical variation of the water column distrubution of suspended particulate organic nitrogen and its 15N natural abundance in the Pacific and its marginal seas

The water column distribution of suspended particulate organic nitrogen (PON) and its natural abundance ratio of 15N: 14N were investigated to a depth of ∼4000 m at 13 stations in the North Pacific, and the South China, Philippine and Bering seas. At two stations in the northern North Pacific, sediment trap experiments were also carried out. The δ15N of PON ranged from −1.5 to 23.3 per mil. The 15N natural abundance of PON increased with depth between 0 and 200 m, while the PON concentration decreased sharply in the same depth range. In the vertical profiles, the PON in the deep water was, on an average, enriched with 15N by approximately 6 per mil as compared with that in the euphotic zone. These findings imply that the vertical transport of organic matter is mediated primarily by rapidly sinking particles, and that most of the decomposition of organic matter takes place in the shallow layer beneath the bottom of the euphotic zone (<200 m) in a similar manner at all locations. n nThe average 15N abundance of PON in the water column was higher in the eastern tropical and central gyre portions of the Pacific than in the western Pacific, the South China Sea, the Philippine Sea, and the Bering Sea. Year-round stratification, the influence of 15N enriched nitrate produced during denitrification and the lack of significant nitrogen fixation in the surface layer probably caused the 15N enrichment in the eastern tropical Pacific.

Diel variation in nitrogen fixation by a marine blue-green alga, Trichodesmium thiebautii

Abstract A diel variation was demonstrated with respect to nitrogen fixing capacity of a marine blue-green alga, Trichodesmium thiebautii, collected from subtropical waters of the western North Pacific. A 200-fold difference was observed between day and night activities when measured at a light intensity of 12,000 lx. The pattern and extent of variation were different from diel variations reported for photosynthesis, nutrient uptake, and nitrogen fixation of natural populations of marine phytoplankton.

Trace metal contamination in Tokyo Bay, Japan

Concentrations of seven trace metals (Cr, Ni, Cu, Zn, Ag, Cd and Pb) in the Tokyo Bay surface sediment were determined for samples collected at 42 points in 1984–1985 and at 7 points in 1989. Significant metal accumulations were observed in the northern half part of the bay. The distribution profile indicated that majority of these metals are principally discharged from rivers located at the north-west end of the bay. However, the trace metal concentrations in sediments were relatively low around the river mouth regions, whereas they were considerably high in the upper reaches of the rivers, showing a discontinuity along the estuaries. The stable carbon isotope ratio, δ13C, of the sedimentary organic matter in dicated that metals in the river/estuarine sediments were deposited together with terrestrial plants debris. Meanwhile, metals in the bay sediments were primarily associated with authigenic planktonic organic matter. Possible factors controlling such dissemination of trace metals onto the bay sediments were ascribed to both the formation of the bay water/open seawater front and the loop current within the semi-closed bay. The bay-water/open seawater front (thermohaline front) developed at the mouth of the bay hinders advection of both terrigeneous and bay-born materials to the open ocean. The landward residual flow of the open seawater as well as the loop current in the bay was thought to be responsible for transportation and accumulation of the trace metal-rich fine particles at around the northern central part of the bay.

Upwelling plumes in sagami bay and adjacent water around the Izu Islands, Japan

Water plumes, 20 km long or less, identified by low temperature, high salinity and high nutrient concentrations, were observed on the eastern side of Izu Islands where the Kuroshio Current or its branch flowed eastward. The T-S diagrams and the vertical profiles of oceanographic variables indicated that the water plumes resulted from the upwelling of subsurface water. A newly formed plume, characterized by a sharp temperature front and high nutrient concentrations, contained less chlorophyll than did old plumes. It is suggested that the upwelling plumes are maintained for a period long enough to allow luxuriant growth of phytoplankton.

Subsurface ammonium maximum in the northern North Pacific and the bering sea in summer

Abstract Ammonium data collected on three summer cruises of the R.V. Hakuho Maru , University of Tokyo, in offshore shallow waters (200 m or less) of the northern North Pacific and the Bering Sea are summarized. Three types can be distinguished with respect to vertical distribution of ammonium: (1) the maximum concentration of ammonium appears in subsurface layer of 30 to 50 m, (2) the maximum appears near the sea floor, and (3) ammonium concentration is low throughout the water column and shows no vertical trend. The subsurface ammonium maximum is commonly observed in the areas where the depth is > 100 m. It is associated with a sharp pycnocline near the bottom of the euphotic zone. The regeneration of ammonium by zooplankaton and/or bacteria together with the stratification of the water column in summer are responsible for the formation of the subsurface ammonium maximum. Even with the utilization of this ammonium by phytoplankaton, the supply is sufficient for the maximum to persist. The second type of ammonium distribution is found in the midshelf region of the eastern Bering Sea. Different processes are responsible for the formation of the subsurface and sea-floor ammonium maxima. The ammonium near the sea floor is probably produced by benthic organisms. Implications of the subsurface ammonium ammonium to the fertility of the subarctic Pacific and the Bering Sea are discussed.

A simple procedure for mass spectrometric microanalysis of 15N in particulate organic matter with special reference to 15N-tracer experiments

Abstract A simple procedure for mass spectrometric analysis of 15N with a small amount of organic nitrogen is described. Particulate organic nitrogen is converted into N2 by a modified Dumas method, using a catalyst-packed vessel consisting of three concentric quartz tubes. The N2 gas produced is then purified, collected on a molecular sieve, and introduced into a mass spectrometer. Using this method, the 15N abundance (δ15N) can be determined with a precision of ± 1.0‰ at a level of 2.5 μg atoms N, or a change in excess 15N as small as 3.6 × 10−11 g atoms N can be detected.

Phytoplankton Pigment Distributions in Regional Upwelling around the Izu Peninsula Detected by Coastal Zone Color Scanner on May 1982

Phytoplankton pigment (chlorophylla+pheopigments) distributions in a regional upwelling around the Izu Peninsula obtained by the Coastal Zone Color Scanner (CZCS) on May 23, 1982, were compared with ship-observed pigment and satellite sea-surface-temperature distributions. Pigment concentrations detected by the CZCS were positively correlated with the ship-observed pigment concentrations. However, they were about factor of 5 smaller when atmospheric correction parameters known for typical oceanic and land aerosol were used and when the parameters were estimated with the “clear water algorithm”. When the atmospheric correction parameters were adjusted so that a pigment concentration derived by CZCS was equivalent to a concentration obtained by the ship at a coincide location, the pattern and magnitudes of the CZCS-derived pigment distributions showed remarkable agreement with ship-observed pigment distributions. Thus, the normal atmospheric correction algorithm may not be suitable for waters around Japan, and the development of better atmospheric correction methods combined with more verification programs is required. The pigment distributions showed patterns that were similar to those observed in sea-surface-temperature distributions. Cold water showed higher pigment concentrations, and warm water showed lower pigment concentrations. The Kuroshio, which can be identified by generally warm, low pigment water, showed a large meander which flowed offshore at Shiono-misaki, looped back onshore from Hachijo Island to Omaezaki and then flowed northeast along the Izu and Boso Peninsulas. Locally upwelled water along the Izu Peninsula was seen clearly in the sea-surface-temperature and CZCS pigment distributions as a region of cold water and high pigment concentrations. Cold upwelled waters were also found at the eastern side of the Izu Islands, but pigment concentrations in these waters was not always high. This difference in the two upwelling regions may be caused by different physical and biological interactions.

OCTOPUS, an octo parameter underwater sensor, for use in biological oceanography studies

A realtime monitoring system for observing physical, biological, and optical oceanographic parameters in shallow waters was developed. It consists of a CTD with oxygen sensor, anin situ fluorometer, anin situ transmissometer, and anin situ quanta meter together with an on-deck quanta meter. The system is also equipped with a water sampling device. Water sampling can be done during the upward cast on the basis of depth profiles of temperature, salinity, oxygen,in situ fluorescence, transmittance, and underwater irradiance taken during the downward cast.

13C/12C and 15N/14N ratios of vesicomyid clams and a vestimentiferan tube worm in the subduction zone east of Japan

Abstract The 13 C/ 12 C and 15 N/ 14 N ratios were measured for a vesicomyid clam, Calyptogena phaseoliformis collected at a depth of 5960 m in the Japan Trench, and the vesicomyid clam C. soyoae and a vestimentiferan tube worm Lamellibrachia sp. collected at a depth of 1170 m in Sagami Bay. The 13 C/ 12 C of clams varied from −35.9 to − 38.7% in C. phaseoliformis and from − 34.3 to − 35.5% in C. soyoae . 13 C/ 12 C of the tube worm (−19.9% in tube, and −25.8% in trophosome) differed markedly from that of C. soyoae collected at the same location. 15 N/ 14 N of the clams varied from −3.3 to + 0.8% in C. phaseoliformis and from −4.1 to +9.6% in C. soyoae . 15 N/ 14 N of the tube worm were −3.6% in tube, and − 4.1% in trophosome. In Calyptogena , gills showed the lowest 13 C/ 12 C and 15 N/ 14 N ratios. The 15 N/ 14 N of the gill of C. soyoae reported here was the lowest (−9.6%) ever reported for animals in hydrothermal vents and cold seeps. A possibility of seepage of isotopically depleted ammonium is briefly discussed.

Tidal pump at the shelf edge

Material transport through the shelf edge to the deep ocean determines the fate of particulate matter generated in productive coastal seas. In stratified estuaries, onshore flow in the bottom layer generally keeps particulate matter generated in the upper layer and settled down to the bottom layer within the estuaries. AT the shelf edge of Tokyo Bay under the condition of average onshore flow in the bottom layer, we observed higher vertical sediment flux during ebb than flood tidal currents. The on-shelf and off-shelf differences in turbulent mixing and water depth mainly cause such difference in sediment flux. We propose to call this export process of particulate matter “the tidal pump” at the shelf edge.