A refined numerical model to precisely simulate the biological and physical cycle in muddy tidal flat was developed by improving an existing model constructed for the tidal flat extending on the Shiota river mouth (Shiota tidal flat) in Ariake Sea in past years. For the newly developed model, the relationships of water quality including suspended solids to tidal change was formulated based on in situ data, and calibrated with observation results in multiple years to universalise it. The model could simulate well the concentrations of NH4–N, NOx–N and suspended solids in sea water, which were strongly associated with denitrification, compared with the existing model. The nitrogen transportation in the Shiota tidal flat calculated with this model clarified that the generation of organic nitrogen on the tidal flat was especially significant, and the tidal flat was considered to be a source of organic matter for Ariake Sea.
Ventilations and behaviors of large juvenile or adult Japanese flounder Paralichthys olivaceus were investigated at 16 decremental steps of dissolved oxygen (DO) ranging from 6.00 to 0.50 mg O2/L. The frequency of opercular movements increased with the decrease in DO from 4.00 mg O2/L to 1.00 mg O2/L. On the other hand, when DO was below 1.25 mg O2/L, flounders often moved horizontally at the bottom, and opened their mouths and opercula extremely. These behaviors suggest that it is difficult for Japanese flounders to maintain their metabolisms by opercular movement. Below 0.75 mg O2/L, off-bottom swimming behaviors that are considered to be escape behaviors were observed. A rapid decrease of the frequency of opercular movements at 0.50 mg O2/L might indicate a lethal effect of low DO on Japanese flounders.
Conventional methods determining solute fluxes across the sediment–water interface have limitations in terms of the reproducibility of hydrodynamic forcing and the representativeness of spatially-heterogeneous biological processes. The newly developed eddy-covariance technique overcomes these limitations. The eddy-covariance technique is based on the principle that vertical flux is expressed by an average of the product of fluctuating vertical velocity and passive scalar, such as dissolved oxygen. Here I review previous studies using the eddy-covariance technique and two case studies on in-situ measurement of benthic oxygen exchange rates.
Passive acoustic monitoring (PAM) has been widely used as the standard method to observe small cetaceans. Recent drastic improvement of monitoring device makes PAM more convenient, cost-effective monitoring method. Also, improvement of analysis methods of acoustic data enables us to estimate habitat range, density, behavior of animals using PAM. However, most previous studies focus on one species and select the data that the observed species were confirmed visually. In order to extend the application of PAM to the field that several species appear simultaneously, species identification method is essential. Especially, PAM plays a key role of environmental assessment on marine development such as offshore wind farm in recent years. In that case, it is important to observe each species which appear in the construction area separately for effective conservation. This paper reviewed the recently developed species identification methods. Basically, many identification methods focused on one of two types of animal call, whistles used for communications or biosonar signals used for echolocation. We introduce the advantage and disadvantage of the method using whistles or biosonar signals, and discuss the current issues and future works we need to resolve them.
Drag coefficient is an important parameter when estimating the air-sea momentum flux correctly. The drag coefficient, however, hasn’t been accurately established due to variations in the data from field observation. Thus, a number of drag coefficient models have been formulated. Since these models define an effective low wind speed range (e.g., 6 m/s), it is important to correctly estimate the air-sea momentum flux in such an effective low wind speed range. Nevertheless, with regard to such models, the air-sea momentum flux is commonly extrapolated out of the effective low wind speed range that is defined for each model. Therefore, such an estimated drag coefficient is not always correct, and the difference in the drag coefficient is reflected by the particular model that is used. In this study, we investigated the effect of the various drag coefficient models concerning the air-sea momentum for the low wind speed range in two processes: (1) calculating the drag coefficient in the effective low wind speed range, and (2) extrapolating the drag coefficient out of the range. Six drag coefficient models were used (Charnock, 1955; Smith, 1980; Large and Pond, 1981; Yelland and Taylor, 1996; Large and Yeager, 2004; Takagaki et al., 2012). We found the largest difference between the maximum and the minimum annual mean global air-sea momentum flux on the estimated data in the effective low wind speed range at 98.5% while 19.1% was observed on the extrapolated data. When taking into consideration both the 10-degree latitude and the proposed seven sea areas, we also found that significant impact on the air-sea momentum flux was apparent when the occurrence frequency of low wind speed was high. These results show that the parametrization of the drag coefficient is imperative for the low wind speed range.
Air-sea CO2 gas transfer velocity is used to estimate the air-sea CO2 gas flux and is generally expressed as a function of wind speed. There has been considerable research on the air-sea CO2 gas transfer velocity including wind speeds due to the fact that the difference in wind speeds impacts the air-sea CO2 gas flux. On the other hand, CO2 solubility to estimate the air-sea CO2 gas flux and the Schmidt number to measure the air-sea CO2 gas transfer velocity are expressed as a function of sea surface temperature. Given this, different data sets of global sea surface temperature have been proposed. Therefore, it is imperative to evaluate the effect of the air-sea CO2 gas flux caused by the difference in sea surface temperature. In this study, we estimated and then investigated the global air-sea CO2 gas flux using wind and wave data sets by ECMWF, as well as seven kinds of sea surface temperature data sets (ERA40, JRA-25, JRA-55, NCEP R1, NCEP R2, ERA-interim-high, and ERA-interim-low). Our findings show that the largest difference of the data sets in annual global air-sea CO2 gas flux was 13.2%, and the largest difference by 10-degree latitude was 0.11 (PgC/year) at 60–70 degrees south latitude. To conclude, these results clearly demonstrate that the difference in sea surface temperature has a significant effect on the air-sea CO2 gas flux.