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11.
Tatsuya?IwataEmail author Yoshiko?Shinomura Yuta?Natori Yasumasa?Igarashi Rumi?Sohrin Yoshimi?Suzuki 《Journal of Oceanography》2005,61(4):721-732
We investigated the water structure and nutrient distribution in the Suruga Bay from April 2000 to July 2002, especially the Offshore Water, which occupies a large part of the bay. The maximum salinity in the upper 200 m varied between 34.49 and 34.71, indicating a temporal change in the influence of Kuroshio Water on the Offshore Water. Seasonal variation in nutrient concentrations was largest from surface to 50 m. On the other hand, the variance in nutrient concentrations within each season was largest in the subsurface layer of 100–300 m in spring, summer and fall. In the Offshore Water, the change of nutrients was negatively correlated with that of salinity in each season. This suggests that an increasing intrusion of saline water brings about a lower nutrient concentration in the Offshore Water. Likewise, negative correlations were observed between the change of the maximum salinity and chlorophyll a (Δ [chl.a-int])/nutrients integrated in the upper 200 m. Δ[chl.a-int] was significantly correlated with the changes of nitrate and phosphorus, but there were no significant correlations between Δ[chl.a-int] and the change of silicate. These results suggest that the concentrations of chlorophyll a and nutrients in the Offshore Water were decreased due to the increasing intrusion of Kuroshio Water. The Offshore Water is likely to be related to the regulation of primary production by nitrate. 相似文献
12.
Mohamed?IsmailEmail author Tadashi?Kimura Yumiko?Suzuki Makoto?Tsuchiya 《Journal of Oceanography》2005,61(3):631-644
Total mass flux, size distribution of sediment particles and some chemical components such as total carbon (TC), total nitrogen (TN) and calcium carbonate (CaCO3) were monitored monthly using a multi-cup sediment traps at seven coral reef sites (6 reef flat and 1 reef slope) of the Marine Protected Areas around Ishigaki, Kohama, Kuroshima and Iriomote Islands in the southern Ryukyus, Japan from September 2000 to September 2001. The size distribution of trapped sediments revealed mostly uni-modal fine sand to mud in the reef flat and gravelly to coarse sand in the reef slope. The total mass flux ranged between 0.54 to 872 gm−2d−1, and showed a pronounced seasonality (high in summer-autumn and low in spring) at each site, which was consistent with the rainfall and typhoon regime. Exceptionally high values were observed on the reef slope (Iriomote) in February–March 2001 (1533 gm−2d−1) owing to a large amount of bottom sediment re-suspension. On the reef flat (Todoroki South and North; Ishigaki), values obtained in July–August 2001 (872 gm−2d−1) and August–September 2001 (800 gm− 2d−1) indicate the high terrestrial discharge from Todoroki River. Trapped sediment particles consist of CaCO3 (1.2–27.1%) and a non-carbonate fraction (98.8–72.9%), which contains total carbon (4.9–26%), carbonate carbon (CO2-C) (0.2–3.1%) and non-carbonate carbon (NC-C) (7.9–25.6%). Total nitrogen content was in the range 0.02–0.48%. TN is contained mainly in the carbonate fraction and NC-C may be contained in the non-carbonate fraction. The low TN/OC ratio of the trapped sediments suggests that they were mostly of terrestrial origin and that both fractions migrated. The high total mass flux derived from Todoroki River exceeded the threshold at which a lethal effect on coral community is caused. The results stress the importance of conducting seasonal studies of sedimentation over more than one year and at more than one location in south Japan coral reef ecosystems to gain an understanding of the processes controlling the total mass fluxes and their nutrients content, also to develop an awareness of how to prevent the damage of coral reef ecosystems and, if it does occur, to allow mitigation measures to be undertaken. 相似文献
13.
Joji Ishizaka Yasuhisa Kitaura Yasuharu Touke Hiroaki Sasaki Akihiko Tanaka Hiroshi Murakami Toshikazu Suzuki Kazumi Matsuoka Hideaki Nakata 《Journal of Oceanography》2006,62(1):37-45
High resolution SeaWiFS data was used to detect red tide events that occurred in the Ariake Sound, Japan, a small embayment
known as one of the most productive areas in Japan. SeaWiFS chlorophyll data clearly showed that a large red tide event, which
damaged seaweed (Nori) cultures, started early in December 2000 in Isahaya Bay, expanded to the whole sound and persisted
to the end of February 2001. The monthly average of SeaWiFS data from May 1998 to December 2001 indicated that the chlorophyll
peaks appeared twice a year, in early summer and in fall, after the peaks of rain and river discharge. The SeaWiFS data showed
that the red tide event during 2000–2001 winter was part of the fall bloom; however, it started later and continued significantly
longer than other years. Satellite ocean color data is useful to detect the red tide; however the algorithms require improvement
to accurately estimate chlorophyll in highly turbid water and in red tide areas. 相似文献
14.
Vertical and seasonal characteristics of biogenic silica (BSi) dissolution in seawater were investigated by multiple dissolution experiments using seawater collected from surface and mesopelagic layers in Suruga Bay during the period 2002–2004. The dissolution rate coefficients calculated based on temporal changes of BSi concentration varied with the season of sample collection. They ranged from 0.023–0.057 day− 1 for surface samples and 0.0018–0.0025 day− 1 for mesopelagic samples for temperatures approaching in situ conditions. Experiments at various temperatures confirmed that BSi dissolution depends on temperature in natural seawater. Dissolution rate coefficient (day− 1) of BSi correlated significantly with temperature (°C), and Q10 was 2.6. Addition of bioavailable organic matter to low-bioactivity seawater enhanced the protease activity and abundance of bacteria, and increased BSi dissolution rate by a factor of 1.4–2.0. There is clear evidence that BSi dissolution is accelerated by bacterial activity and potentially limited by bioavailable organic matter in natural seawater. Dissolution rates and total decreases of BSi concentration were lower during experiments using mesopelagic samples than in those using surface samples. This suggests that dissolution of BSi varies with depth and that BSi in the mesopelagic water is more resistant to the dissolution than that in the surface water. This lower dissolution rate was caused by lower temperature and lower bacterial activity due to less bioavailable organic matter in mesopelagic water. Our results provide a mechanistic understanding of variations in silica cycling within the seasonally and vertically differing marine environment. 相似文献
15.
In order to investigate the mechanism of eutrophication in Atsumi Bay which is a shallow and partially mixed estuary, distributions of temperature, salinity and concentrations of nitrogen and phosphorus in all their chemical forms were observed once a month throughout a year. Supplies of freshwater and nutrients are estimated and balances of salt and nutrients are examined using a modified box model. The deduced estuarine hydrography and calculated values of photosynthesis, decomposition, deposition and sedimentation are compared with those obtained byin situ observations and laboratory experiments. It is found that the factors responsible for the appearance of heavy eutrophication include not only the general increase of nutrient supply from land but also nutrient accumulation in the rainy season just before summer, the N/P ratio of the supply from land being favourable for uptake by phytoplankton, formation of semi-closed circulations of the nutrients associated with stratification and vertical circulation of estuarine water, and possibly the inorganic turnover of phosphorus (PO4-P) under aerobic and anaerobic conditions. The usefulness of the modified box model for obtaining a synoptic understanding of the estuarine system is also demonstrated. 相似文献
16.
Gymnodinium mikimotoi, a senior synonym ofGymnodinium nagasakiense often causes red tides in coastal waters of the western part of Japan. The photosynthetic pigment composition of two strains ofG. mikimotoi were analyzed by HPLC. They contain chlorophyllc
3 which has not been reported from dinoflagellates. They also contain fucoxanthin, 19'-hexanoyloxyfucoxanthin and 19'-butanoyloxyfucoxanthin as major carotenoides, which are anomalous in dinoflagellates. The pigment composition ofG. mikimotoi is compared with that ofGyrodinium aureolum which occur in European waters and is thought as a conspecific species withG. mikimotoi by several authors. 相似文献
17.
18.
Metal-organic complexes of transition elements removed by Amberlite XAD-2 resin from seawater pumped up from under the ground were determined. The proportions of iron, copper and zinc retained on the resin to dissolved forms of these metals were about 70, 40 and 5%, respectively, while manganese, cobalt and nickel were not retained on the resin. These results suggest that although iron may be retained in colloidal form, a significant fraction of copper is present in some organic form(s). 相似文献
19.
20.
Temporal change of clustered distribution in vertical profiles of three nutritional groups of planktonic ciliates, e.g. heterotrophic
naked ciliates, mixotrophic naked ciliates and heterotrophic loricated ciliates, was investigated by following a drifting
buoy in Toyama Bay on the Japan Sea coast of central Japan in summers of 1989 and 1990. Clustered distribution, represented
as the mode of population density in the vertical plane, occurred mainly in the oligotrophic upper layer (0–50 m depth) above
the subsurface chlorophyll-a maximum layer. Its clustered degree was stronger when the mode of population density in the vertical plane was formed at
shallower depth, while its longevity was shorter as mentioned above. Vertical distribution of ciliates during summer in Toyama
Bay is characterized by ephemeral clustered distribution, or in other wards, by rapid alternations of appearance and disappearance
of the clustered distribution. 相似文献