Variations are found in the shape and the steepness of wind-generated surface gravity waves between very young waves, such as seen in a laboratory tank, and larger waves of various wave ages encountered at sea as the result of wind stress over larger fetches. These differences in the characteristic shape of wind waves are presented as a function of the wave age. The wave steepness is also expressed as a function of wave age, the measurement of which is consistent with the 3/2-power law connecting wave height and characteristic period, normalized by the air friction velocity.
In order to determine quantitatively the reason for the high productivity in the Oyashio Region, which is the southwest part of the Pacific Subarctic Region, the annual-mean vertical circulation of nitrogen in the region was estimated from the vertical profiles of nitrate, dissolved oxygen and salinity, and sediment-trap data by adapting them to the balance equations. Estimates of the upwelling velocity (1.7×10-5cm sec-1) and the vertical diffusivity (2.1 cm2 sec-1) in the abyssal zone and the primary and secondary productivities (44 and 4mgN m-2day-1, respectively) in the euphotic zone were close to those of previous works. The estimated vertical circulation of nitrogen strongly suggested that, since the divergence (5 mgN m-2day-1) is caused by the abyssal convergence (6 mgN m-2day-1) and the positive precipitation, the local new production (22 mgN m -2day -1) necessarily exceeds not only the sinking flux (10 mgN m -2day -1) itself but also the sum of the sinking flux and the downward diffusion of dissolved and particulate organic matter (7mgN m-2day-1) produced probably in the euphotic zone. The important roles of the abyssal circulation, the winter convection, and the metabolic activity in the bathyal zone to support the high productivity in the euphotic zone were clarified quantitatively.
Large amorphous aggregates (NUTA) observed in coastal areas after spring and autumn phytoplankton blooms and red tide outbreaks were collected using NUTA traps which we devised. These particles become thickly attached to mooring ropes and/or fishing nets. The variation of the collection of materials by NUTA traps was about 23% in organic carbon and 25% in organic nitrogen (n=29). The chemical nature and vertical distribution pattern of NUTA were significantly different from those of suspended particles collected by water samplers. Since C/ATP and C/Chl α ratios in NUTA were very high compared with those of suspended particles, NUTA seems to consist of a small amount of phytoplankton but much detritus. These values suggest that NUTA has characteristics intermediate between suspended particles and sinking particles. The standing stock of NUTA was also estimated to be no more than 10% suspended particles from a calculation of the trapping efficiency of the NUTA trap.
The beam attenuation coefficient, organic carbon (POC) and organic nitrogen (PON) contents of suspended materials in Etauchi Bay, which has little inflow of river water as well as very weak tidal current (maximum speed: 6.5cm·sec-1), were measured as a function of depth for all seasons to understand a seasonal variation of bottom turbidity layer. In spring and summer, the beam attenuation coefficient in bottom layer and POC and PON contents of suspended materials in the surface water layer increased with time, which brought the occurrence of the bottom turbidity layer. From autumn to winter, however, their concentrations became low and constant over the whole depth almost independent of time. As a result, the bottom turbidity layer disappeared in winter and beam attenuation coefficient became constant over the whole depth. From these results, it may be considered that the bottom turbidity layer was produced by phytodetritus brought from surface water layer, rather than by resuspension of bottom sediment in Etauchi Bay.
During the concentrated observation (April-May 1988) conducted as a part of the Ocean Mixed Layer Experiment (OMLET) in the sea area south of Japan, a conspicuous outbreak of warm water occurred from the large-meander region of the Kuroshio toward the southwest in the direction of the former Ocean Weather Station “T”. A series of NOAA-AVHRR infrared images clearly showed the process of this event. A surface buoy-mooring system deployed in this experiment recorded the arrival of this outbreak of water, in terms of the rise of sea-surface temperature (SST) of 1.5°C and the flow of warm water of 1.5kt toward the northwest at “T”. We studied this phenomenon by combining time series of infrared SST images with the oceanographic data obtained by two research vessels. The warm water was about 100 m deep in the section at 137°E along the edge of the Off-Shikoku Warm Water. It was estimated that about twenty outbreaks of this kind in a year can compensate a large heat loss to the atmosphere above this ocean region.