Numerical study for specifying the major origin of low salinity water associated with <Emphasis Type="Italic">Chattonella</Emphasis> (Raphidophyceae) blooms in Tachibana Bay,Japan

In both 2009 and 2010, massive Chattonella blooms occurred in Tachibana Bay. Observation results show that high cell densities of Chattonella were distributed in the central area of Tachibana Bay with low salinity water. Model results indicate that the low salinity water originated from the Ariake Sea and intruded into Tachibana Bay during the northerly or weak winds. It is suggested that low salinity water was mainly discharged from the northern area of the Ariake Sea. Northerly wind enhanced the horizontal advection of the low salinity water intruding into Tachibana Bay originating from the northern area of the Ariake Sea.     

Intraannual variability of sea level around Tosa Bay

Through analysis of monthly in situ hydrographic, tide gauge, altimetry and Kuroshio axis data for the years 1993–2001, the intraannual variability of sea level around Tosa Bay, Japan, with periods of 2–12 months is examined together with the intraannual variability of the Kuroshio south of the bay. It is shown that the intraannual variation of steric height on the slope in Tosa Bay can account for that of sea level at the coast around the bay as well as on this slope. It is found that the steric height (or sea level) variation on the slope in this bay is mainly controlled by the subsurface thermal variation correlated with the Kuroshio variation off Cape Ashizuri, the western edge of Tosa Bay. That is, when the nearshore Kuroshio velocity south of the cape is intensified [weakened] concurrently with the northward [southward] displacement of the current axis, temperature in an entire water column decreases [increases] simultaneously, mainly due to the upward [downward] displacement of isotherms, coincident with that of the main thermocline. It follows that the steric height (or sea level) decreases [increases].     

Wind effects on sub-tidal currents in Puget Sound

Wind effects on sub-tidal currents are studied using current meter records obtained at six moorings across the main basin of Puget Sound. High correlations between wind speeds and currents are found near the surface and at mid-depths of about 100 m. Empirical Orthogonal Function analysis applied to the axial currents in 1984 and 1985 shows that mode 1, containing over 60% of the variance, is highly correlated with wind speed even without any near surface current records. When near surface stratification is strong, direct wind effects are limited to the upper 30 m with counter currents in the lower layer indicating a baroclinic response. The transport in the lower layer almost balances the transport in the upper layer. When near surface stratification is weak, direct wind effects on currents can be detected to about 100 m. In this case, there is no clear and consistent depth at which one can separate the upper from the lower layer. Time series show that the acceleration in the surface layer initially increases in the same direction as the wind when the wind starts blowing, but it reaches a maximum, starts decreasing, and eventually changes to the opposite direction (decelerates) while the wind continues to blow in one direction. Results of a continuously stratified normal mode model and estimations from the observations suggest that friction at solid boundaries is a major cause of these phenomena. The model shows that modal currents of normal modes 2 and 3 are as important as mode 1, although the resultant vertical structure of total current shows a two-layer type pattern with only one zero crossing. The effect of the baroclinic pressure gradient is only apparent at low frequencies and among lower modes.     

Chemical studies of dissolved carbohydrates in seawater

Charcoal column chromatography and a dialysis system using a Visking tube were used for the concentration and separation of dissolved carbohydrates in seawater. Recoveries of mono-, oligo-, and polysaccharides were 46–74, 61–89 and 70%, respectively, relative to the total amount of sugars initially submitted to analysis. The combined charcoal column chromatography and dialysis system was used to separate dissolved carbohydrates in seawater samples from Mikawa Bay into mono-, oligo- and polysaccharide fractions. The polysaccharides are separated into two fractions with molecular weights of <4,000 and >4,000 using Sephadex G-25 column chromatography. Monosaccharides, oligosaccharides, polysaccharides with M.W.<4,000 and polysaccharides with M.W. >4,000 accounted for 7–9, 15–26, 7–13 and 20–33% of total dissolved carbohydrates, respectively. However, 32–38% of dissolved carbohydrates were lost during the analytical procedures. Glucose, galactose, mannose, xylose, arabinose, ribose, fucose, and rhamnose were found upon acid hydrolysis of the oligo- and polysaccharide fractions, while fucose and rhamnose were not present in the monosaccharide fraction. Possible sources of the carbohydrates in these fractions are discussed with reference to the monosaccharide composition of cellular carbohydrate in marine algae.     

Seasonal Variation of Space/Time Statistics of Short-Term Sea Surface Temperature Variability in the Kuroshio Region

Spatial and temporal scales of sea surface temperature (SST) variations in the Kuroshio region have been investigated using a satellite-based one-year merged SST product. Targeting short-term variations with temporal scales of less than a year, decorrelation scales, which are defined as the e-folding scale of SST variability, have been derived as functions of regional positions and calendar months. We assumed that the autocorrelation function of SST has anisotropic Gaussian characteristics in the space-time domain. Resultant spatial and temporal decorrelation scales range from 1 to 3° and 2 to 3 days, respectively. They are strongly inhomogeneous, anisotropic and time-dependent. These characteristics are attributed to the oceanic and atmospheric disturbances. Spatial decorrelation scales are determined mainly by strong atmospheric forcing in the study region. In the area with dominant atmospheric forcing, the spatial scales are larger than those in the other regions. Those in the regions with dynamical oceanographic disturbances are as small as 1°. Signal-to-noise ratios are also large where the atmospheric forcing is strong, while they are small where the oceanic signals are active.     

Estimating the Kuroshio Axis South of Japan Using Combination of Satellite Altimetry and Drifting Buoys

By tracking the locally strongest part of the sea-surface velocity field, which was obtained by integrating data of satellite altimeters and surface drifting buoys, we extracted the Kuroshio axis south of Japan every 10 days from October 1992 to December 2000. The obtained axes clearly express the effect of the bottom topography; three modes were observed when the Kuroshio ran over the Izu Ridge. The axis was very stable to the south of ‘Tosa-bae,’ off the Kii Channel. Mean current speed at the Kuroshio axis gradually increased from 0.65 m/s south of Kyushu to 1.45 m/s off Enshu-nada. This revised version was published online in July 2006 with corrections to the Cover Date.     

Seasonal Variation in Host Utilization of Epiphytic Lacuna Species in Mixed Algal and Surfgrass Stands in Japan

Abstract.  On the subtidal rocky shore of Akkeshi Bay, Hokkaido, Japan, the congeneric phytal gastropods, Lacuna uchidai and L. decorata , inhabit the multispecific vegetation consisting of the surfgrass, Phyllospadix iwatensis and the brown alga, Cystoseira hakodatensis . We studied the phenologies of Phyllospadix and Cystoseira , host utilization patterns and life histories of Lacuna spp. to examine how these gastropods accommodate the seasonal fluctuations of the habitat. The preferences for macrophyte by Lacuna spp. were examined by laboratory experiments. The phenologies of macrophytes, the seasonal and between-substrata variations of Lacuna spp. were examined by monthly sampling from Phyllospadix and Cystoseira beds between May 1999 and May 2000. Lacuna uchidai showed significant preference for Phyllospadix , whereas L. decorata had no preference for a particular substratum. Most L. uchidai were collected from the Phyllospadix bed, however L. decorata appeared in both Phyllospadix and Cystoseira beds. The peak of new recruit of L. uchidai coincided with that of Phyllospadix biomass. The synchronization of life cycle with the phenology of the host may be adaptive for using the limited habitat. Seasonal variation in density of L. decorata coincided with neither patterns for Phyllospadix nor Cystoseira . Seasonal variation in density and size frequency distribution suggested L. decorata migrated among adjacent macrophytes. Although it was a little vague, this hypothesis was probably the best explanation of our results. Our study shows that two co-occurring Lacuna species utilize the macrophytes as habitats by the different life histories and utilization patterns and, may be alternatively accommodated to the seasonal fluctuations of their habitats.