Box model analysis of hydrography and behaviour of nitrogen and phosphorus in a eutrophic estuary

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.     

Ecologic and taxonomic diversification in the Mesozoic brackish-water bivalve faunas in Japan, with emphasis on infaunalization of heterodonts

Mesozoic brackish-water bivalve faunas in Japan diversified in three steps: at the beginning of the Early Jurassic, Early and Late Cretaceous. The Hettangian Niranohama Fauna in northeastern Honshu represents the establishment of a heterodont-dominated brackish-water fauna that persisted until the early Late Cretaceous. No similar composition is known from the Triassic. The infauna consists mostly of non-siphonate and some short-siphonate heterodonts, while the epifauna is represented by diverse pteriomorphian families. In the Early Cretaceous Tetori Group in central Honshu, the long-siphonate heterodonts Tetoria (Corbiculidae) and the semi-infaunal soft-bottom oyster Crassostrea appeared. The evolutionary diversification of the latter, known as the most important element of modern brackish-water faunas, may thus originate at that time. In the early Late Cretaceous (Cenomanian) of the Goshoura and Mifune Groups in west Kyushu, several euryhaline deep-burrowing heterodont families, such as Veneridae and Tellinidae, further diversified in the brackish and marine environments. The Late Cretaceous is characterized by massive shell biolithic beds in which large Crassostrea species are common, a feature common for Cenozoic brackish-water faunas. The long-term changes in the composition of the brackish-water faunas in Japan represents thus an evolutionary record, irrespective of the severe physiological and environmental conditions imposed on the highly conservative nature of the fauna.     

Modeling Arctic Ocean heat transport and warming episodes in the 20th century caused by the intruding Atlantic Water

This study investigates the Arctic Ocean warming episodes in the 20th century using both a high-resolution coupled global climate model and historical observations. The model, with no flux adjustment, reproduces well the Atlantic Water core temperature （AWCT） in the Arctic Ocean and shows that four largest decadalscale warming episodes occurred in the 1930s, 70s, 80s, and 90s, in agreement with the hydrographic observational data. The difference is that there was no pre-warming prior to the 1930s episode, while there were two pre-warming episodes in the 1970s and 80s prior to the 1990s, leading the 1990s into the largest and prolonged warming in the 20th century. Over the last century, the simulated heat transport via Fram Strait and the Barents Sea was estimated to be, on average, 31.32 TW and 14.82 TW, respectively, while the Bering Strait also provides 15.94 TW heat into the west- ern Arctic Ocean. Heat transport into the Arctic Ocean by the Atlantic Water via Fram Strait and the Barents Sea correlates significantly with AWCT （ C = 0.75 ） at 0- lag. The modeled North Atlantic Oscillation （NAO） index has a significant correlation with the heat transport （ C = 0.37 ）. The observed AWCT has a significant correlation with both the modeled AWCT （ C =0.49） and the heat transport （ C =0.41 ）. However, the modeled NAO index does not significantly correlate with either the observed AWCT （ C = 0.03 ） or modeled AWCT （ C = 0.16 ） at a zero-lag, indicating that the Arctic climate system is far more complex than expected.     

Empirical green's function corrected for source effect

One of the severe problems in the semi-empirical method for the prediction of strong ground motions is that there is no objective criterion for choosing empirical Green's functions. It is undesirable that synthesized strong ground motions are affected by the source process of an earthquake whose record is adopted as an empirical Green's function. Through the analysis of strong motion accelerograms of two aftershocks of the 1983 Japan Sea earthquakes, it is found that characteristics of the accelerograms are dependent on the moment rate function derived from teleseismic observations. A procedure is presented for removing the effect of the source process from observed strong motion accelerograms. The thus obtained empirical Green's function expresses approximately the impulse response of the medium between the earthquake source and the observation site.     

Ammonium uptake kinetics and interactions between nitrate and ammonium uptake inChattonella antiqua

Ammonium uptake kinetics and interactions between nitrate and ammonium uptake were examined inChattonella antiqua. After the addition of ammonium to the culture ofC. antiqua, the ammonium concentration decreased linearly with time. The ammonium uptake rate as a function of ammonium concentration followed the Michaelis-Menten equation; the maximal uptake rate was 2.0 pmol cell^–1hr^–1 and the half saturation constant, 2.2M. Although the ammonium uptake was not affected by nitrate, uptake of nitrate was rapidly (15min) suppressed by ammonium and a 50% reduction in nitrate uptake was observed at an ammonium concentration ofca. 2M.     

Roles of Biogeochemical Processes in the Oceanic Carbon Cycle Described with a Simple Coupled Physical-Biogeochemical Model

To evaluate the contribution of biogeochemical processes to the oceanic carbon cycle and to calculate the ratio of calcium carbonate to organic carbon downward export, we have incorporated biological and alkalinity pumps in the yoked high-latitude exchange/interior diffusion-advection (YOLDA) model. The biogeochemical processes are represented by four parameters. The values of the parameters are tuned so that the model can reproduce the observed phosphate and alkalinity distributions in each oceanic region. The sensitivity of the model to the biogeochemical parameters shows that biological production rates in the euphotic zone and decomposition depths of particulate matters significantly influence horizontal and vertical distributions of biogeochemical substances. The modeled vertical fluxes of particulate organic phosphorus and calcium carbonate are converted to vertical carbon fluxes by the biological pump and the alkalinity pump, respectively. The downward carbon flux from the surface layer to the deep layer in the entire region is estimated to be 3.36 PgC/yr, which consists of 2.93 PgC/yr from the biological pump and 0.43 PgC/yr from the alkalinity pump, which is consistent with previous studies. The modeled rain ratio is higher with depth and higher in the Pacific and Indian Oceans than in the Atlantic Ocean. The global rain ratio at the surface layer is calculated to be 0.14 to 0.15. This value lies between the lower and higher ends of the previous estimates, which range widely from 0.05 to 0.25. This study indicates that the rain ratio is unlikely to be higher than 0.15, at least in the surface waters.     

Ecological and physiological features of the mesopelagic mysid,Meterythrops microphthalma,in the Japan Sea

The abundance and vertical distribution pattern of a mysidMeterythrops microphthalma were investigated in the Japan Sea. Results from vertical hauls from 602–982 m depth to the surface around Yamato Rise in April 1987 indicated that the dominance (by biomass) ofM. microphthalma was third to fifth of major zooplankton taxa. Vertical distribution investigated at a single station in Toyama Bay in June, September and December 1986 showed that the most part of population of this mysid inhabited consistently below 250 m depth. No marked diurnal vertical migration was evident. Data on body composition and oxygen consumption rate ofM. microphthalma are presented. Water content of the body was 75.6–83.8% of wet weight, and ash was 11.4–20.4% of dry weight. Carbon, hydrogen and nitrogen were 37.9–47.5%, 6.2–7.4% and 9.4–10.1%, respectively, of dry weight. Oxygen consumption rates were 2.2–11.0µl O₂ individual^–1 hr^–1 at 0.5°C, and were directly proportional to body mass. From the comparison with the published data on epipelagic and bathypelagic mysids it is revealed that both body nitrogen composition and oxygen consumption rate expressed as adjusted metabolic rate [AMR₀₂,µl O₂ (mg body N)^–0.85 hr^–1] ofM. microphthalma are intermediate between high epipelagic and low bathypelagic levels, indicating typical mesopelagic features.     

Nitrogen budget in Tokyo Bay with special reference to the low sedimentation to supply ratio

In order to determine why the sedimentation to supply ratio of nutrients in Tokyo Bay is markedly small, the nitrogen budget was investigated for 1979, when a systematic and continuous observation of flow and salinity was carried out. The data were analyzed by use of a simple advective-diffusive box model and dissolved oxygen balance in the lower layer was also examined. The calculated values of two-layer flow, settling, primary production, mineralization, denitrification, and dissolved oxygen consumption were comparable to those observed.The factors making the sedimentation to supply ratio makedly small were summarized as: 1) a strong and stable two-layer flow generated by a large freshwater supply, 2) further intensification of this two-layer flow by the northern winter monsoon, 3) coincidence of the discharge region with the supply region of nutrients caused by the transverse inclination of the interface, probably due to the earth's rotation. 4) effective discharge of nutrients from the bay due to a strong tidal flow and a possible cyclonic tidal residual circulation in the inner bay mouth, 5) incomplete consumption of nutrient salts by phytoplankton in the upper layer even in the most productive season, and 6) possible denitrification in the anaerobic bottom water in summer and in the bottom sediment itself throughout the year in the inner bay.