Development of the AUV ‘ISiMI’ and a free running test in an Ocean Engineering Basin

The Korea Ocean Research and Development Institute (KORDI) has developed a small AUV named ISiMI. The mission of ISiMI is to work as a test-bed AUV for the development and validation of various algorithms and instruments required to enhance the AUV's functions. The design concept of ISiMI is that of a vehicle small enough to cruise the Ocean Engineering Basin (OEB) of KORDI and to be handled by one or two people. The downsized design and the cruising ability in its tank enable fast experimental feedback on AUV technologies and a shorter development period for new technologies. This paper presents a review of our research work on the development of ISiMI, with a performance evaluation by simulation and an experimental test. After the design and implementation of ISiMI, including its positioning system in the OEB, are presented, a series of test results in the OEB and discussions of the results are presented, with comparisons of the simulation and experimental outputs.     

Dissolved organic phosphorus utilization and alkaline phosphatase activity of the dinoflagellate <Emphasis Type="Italic">Gymnodinium impudicum</Emphasis> isolated from the South Sea of Korea

This study investigated alkaline phosphatase (APase) activity and dissolved organic and inorganic phosphorus utilization by the harmful dinoflagellate Gymnodinium impudicum (Fraga et Bravo) Hansen et Moestrup isolated from the South Sea of Korea. Under conditions of limited phosphorus, observation of growth kinetics in batch culture yielded a maximum growth rate (μ_max) of 0.41 /day and a half saturation constant (Ks) of 0.71 μM. In time-course experiments, APase was induced as dissolved inorganic phosphorus (DIP) concentrations fell below 0.83 μM, a threshold near the estimated Ks; APase activity increased with further DIP depletion to a maximum of 0.70 pmol/cell/h in the senescent phase. Thus, Ks may be an important index of the threshold DIP concentration for APase induction. G. impudicum utilizes a wide variety of dissolved organic phosphorus compounds in addition to DIP. These results suggest that DIP limitation in the Southern Sea of Korea may have led to the spread of G. impudicum along with the harmful dinoflagellate Cochlodinium polykrikoides in recent years.     

Large seasonal changes in the recharge of seawater in a subterranean estuary revealed by a radon tracer

Activities of radon (²²²Rn) in groundwater were continuously monitored in a saline aquifer from September 2010 to July 2011. The activities of ²²²Rn ranged from 200 to 4300 Bq m^?3, with a large seasonal variation. Because the activity of ²²²Rn in seawater is low, ²²²Rn in saline groundwater must be produced in the aquifer from radium (²²⁶Ra) in rocks and sediments. The ²²²Rn activities were higher in the warm‐dry seasons (September–November 2010 and April–May 2011) when the saline aquifer was stable. In contrast, the lowest ²²²Rn activities were observed in the cold‐dry season (December 2010 and January–March 2011), because of the effective exchange between groundwater and seawater. In addition, sudden decreases of ²²²Rn activities coincided with episodic drops in groundwater temperatures. These results reveal that lower seawater temperature in winter may result in density‐driven seawater intrusion. During the wet season (June–July 2011), ²²²Rn activities were more clearly affected by semi‐monthly and diurnal tidal pumping, showing higher ²²²Rn activities during low and spring tides. Such a tidal effect was not clearly observed during the warm‐dry and cold‐dry seasons. This result implies that the residence time of SGD in coastal zones is significantly affected by seasonal changes in driving forces such as tidal pumping and seawater intrusion. Copyright © 2016 John Wiley & Sons, Ltd.     

Macrobenthos habitat mapping in a tidal flat using remotely sensed data and a GIS-based probabilistic model

This paper proposes and tests a method of producing macrofauna habitat potential maps based on a weights-of-evidence model (a probabilistic approach) for the Hwangdo tidal flat, Korea. Samples of macrobenthos were collected during field work, and we considered five mollusca species for habitat mapping. A weights-of-evidence model was used to calculate the relative weights of 10 control factors that affect the macrobenthos habitat. The control factors were compiled as a spatial database from remotely sensed data combined with GIS analysis. The relative weight of each factor was integrated as a species potential index (SPI), which produced habitat potential maps. The maps were compared with the surveyed habitat locations, revealing a strong correlation between the potential maps and species locations. The combination of a GIS-based weights-of-evidence model and remote sensing techniques is an effective method in determining areas of macrobenthos habitat potential in a tidal flat setting.     

Effects of the Changjiang river discharge on sea surface warming in the Yellow and East China Seas in summer

This study explores the effects of the Changjiang (also called the Yangtze River) river discharge (CRD) on the density stratifications and associated sea surface temperature (SST) changes using a global ocean general circulation model with regional focus on the Yellow and East China Seas (YECS). It is found that CRD increases the SST in summer through a barrier layer (BL) formation that tends to enhance stratification at the mixed layer base, and thus reduces both vertical mixing and entrainment. This process is effective, particularly in August, after the CRD reaches its maximum in July. The SST difference between the composites of flood and drought years confirms that the surface warming is related to surface freshening by the CRD. This result suggests that the BL induced by the CRD is an important contributor to the surface heat budget in the YECS.     

Fossil wood diversity gradient and Far-East Asia palaeoclimatology during the Late Triassic – Cretaceous interval

Mesozoic fossil floras are distributed over eastern Asia (China, Mongolia, Siberia, Korea and Japan) according to a regular latitudinal pattern. Two floras are usually distinguished, a northern type and a southern type, the distribution of which oscillated during the Mesozoic. In Japan, this regular pattern is disrupted by a sharp inflexion of the boundary between the two floras. Two competing hypotheses have been proposed to explain this disruption. One hypothesis advocates later tectonic motion clouding the original pattern, while the other hypothesis proposes that a warm oceanic current allowed the southern flora to grow much further north in coastal areas. We used fossil wood, a biotic component that has not previously been used, for a palaeobiogeographical study of the region. The observed fossil wood diversity at the generic level does not fit with the hypothesis of a warm oceanic current, unless this hypothesis is modified to include alternating warm northbound and cold southbound oceanic currents. Our results provide new evidence for the palaeoecology of the Mesozoic continental biota in Far-East Asia.     

Sensitivity analysis for the GIS-based mapping of the ground subsidence hazard near abandoned underground coal mines

Ground subsidence around abandoned underground coal mines can cause much loss of life and property. We analyze factors that can affect ground subsidence around abandoned mines in Jeongahm in Kangwon-do by sensitivity analysis in geographic information system (GIS). Spatial data for the subsidence area, topography and geology and various ground engineering data were collected and used to make a factor raster database for a ground subsidence hazard map. To determine the importance of extracted subsidence-related factors, frequency ratio model and sensitivity analysis were employed. Sensitivity analysis is a method for comparing the combined effects of all factors except one. Sensitivity analysis and its verification showed that using all factors provided 91.61% accuracy. The best accuracy was achieved by not considering the groundwater depth (92.77%) and the worst by not considering the lineament (85.42%). The results show that the distance from the lineament and the distance from the drift highly affected the occurrence of ground subsidence, and the groundwater depth, land use and rock mass rating had the least effects. Thus, we determined causes of ground subsidence in the study area and this information could help in the prediction of ground subsidence in other areas.     

Valuing visitors' economic benefits of public beach access points

An increase in the population of coastal counties and popularity of coastal beaches as tourism destinations create difficulties for management agencies responsible for providing public beach access. The objective of this paper is to determine non-resident visitors to South Carolina beaches economic value for public beach access. Visitors are willing to pay an extra $6.60 per day for additional beach access points and parking or an aggregate of $93 million. Visitors' economic value of public beach access allows decision-makers the ability to better compare management policies in their efforts to provide sufficient public beach access through a target effective strategy.     

Acoustic tomography for monitoring the Sea of Japan: a pilot experiment

A pilot experiment was conducted in the Sea of Japan (also called the East Sea) in September-October 1999, to assess the possibility of using acoustic tomographic techniques for monitoring water mass structure and dynamics. Acoustic m-sequence signals at various frequencies between 250 and 634 Hz were transmitted from bottom-mounted acoustic sources in shallow water off the coast of Vladivostok to vertical-array receiving systems deployed off the north coast of Ulleung-Do island (S. Korea), 558 km to the south. The data are analyzed for temporal correlation, time spread, and transmission loss and are interpreted in terms of a tomographic system for monitoring the East Sea.