• Ocean and Polar Research
• /
• v.25 no.4
• /
• pp.625-631
• /
• 2003

While phytoplankton diversity and productivity in the Southern Ocean has been widely studied in recent years, most attention has been given to elucidating environmental factors that affect the dynamics of micro-plankton (mainly diatoms) and nano-plankton (mainly Phaeocystis antarctica). Only limited effects have been given to studying the occurrence and the potential risks associated with the blooming of dinoflagellates in the relevant waters. This study focused on the appearance and toxicological characteristics of a toxic dinoflagellate, Alexandrium tamarense, identified and isolated from the Drake Passage in a research cruise from November to December 2001 The appearance of A. tamarense in the Southern Ocean indicates the risk of a paralytic shellfish poisoning (PSP) outbreak there and is therefore of scientific concern. Results showed that while the overall quantity of A. tamarense in water samples from 30meters below the sea surface often comprised less than 0.1% of the total population of phytoplankton, the highest concentration of A. tamarense (20 cells $L^{-1}$) was recorded in the portion of the Southern Ocean between the southern end of South America and the Falkland Islands. Waters near the Polar Front contained the second highest concentrations of 10-15 cells $L^{-1}$. A. tamarense was however rarely found in waters near the southern side of the Polar Front, indicating that cold sea temperatures near the Antarctic ice does not favor the growth of this dinoflagellate. One strain of A. tamarense from this cruise was isolated and cultured for further study in the laboratory. Experiments showed that this strain of A. tamarense has a high tolerance to temperature variations and could survive at temperatures ranging from $5-26^{\circ}C$. This shows the cosmopolitan nature off. tamarense. With regard to the algal toxins produced, this strain of A. tamarense produced mainly C-2 toxins but very little saxitoxin and gonyailtoxin. The toxicological property of this A. tamarense strain coincided with a massive death of penguins in the Falkland Islands in December 2002 to January 2003.

• Journal of the Korean Society of Marine Environment & Safety
• /
• v.1 no.2
• /
• pp.53-60
• /
• 1995

We measured lagrangian currents in the coastal regions off east coast of Korea. The experiment sites are the Ulijin region where Polar Front of the East Sea is formed and the Ulgi region where coastal upwelling occurs frequently in summer. Each drifters are equipped with GPS receiver, and their trajectories are montiored by receiving the data transmitted from drifters through radio signal. The experiment with 'transmitting' GPS is very useful in monitering flows in coastal regions. Trajectories of drifters in the Uljin Polar Front region in October 1994 showed counterclockwise flow pattern. The flow pattern agrees with the SST distributions obtained from NOAA-11 AVHRR image for the same period. The lagrangian trajectories of drifters at 5m and 15m depths in the Ulgi region for normal period of April 1995 showed that the currents at the top 15m layer are almost uniform and their magnitude is 29cm/s. However, the currents, measured by KORDI, during the upwelling period of June 1994 showed that the currents at 5m depth were 1.2 times stronger than those at 15m depth. The current pattern in the Ulgi upwelling region agrees with the horizontal and vertical distributions of seawater temperature measured by NFRDA at the same period.

• Ocean and Polar Research
• /
• v.25 no.3
• /
• pp.303-314
• /
• 2003

The initiation of Cochlodinium polykrikoides blooming in the South Sea of Korea occurs in the sea near Naro-Do in late August. In this paper, the relationships of this annual occurrence with the environmental conditions are presented. In early summer, the winds in the sea near Naro-Do are southwesterly and the upwelling occurs in the near-shore area. The favorable winds to the upwelling are relaxed in August and the downwelling favorable northeasterly winds set in around late August. The change of wind direction causes the onshore transport of warm-and-fresh off-shore water into the sea near Naro-Do and a front between near-shore water and off·shore water is formed. Along the front, downwelling occurs and the environmental conditions for the diatom become unfavorable. When the typhoon and storm bring well-mixed East China Sea water into the sea near Naro-Do in September, the conditions for the dinoflagellates become unfavorable and blooming of C. polykrikoides disappears.

• Atmosphere
• /
• v.11 no.2
• /
• pp.6-12
• /
• 2001

The East Asian monsoon is generally accompanied with the quasi-stationary front along the northern and northwestern periphery of the subtropical anticyclone in the boundary zone of the polar cold air mass and the tropical warm air mass. The rainy season in Korea has been called as Changma since the middle of 1500s. In meteorology, the rainy season with the quasi-stationary front, the Changma front, during the early summer has been defined as the Changma since 1905. The difference of meaning on Changma between meteorologists and the general public sometime does give a confusion. For example, the heavy rainfall event after the retreat of Changma is recognized as Changma by the general public, but not by most of meteorologists. The decision of the onset and retreat dates of Changma among the meteorologists is also ambiguous because of different viewpoints on the definition of Changma. In this study we survey the etymology and definition of Changma.

• Ocean and Polar Research
• /
• v.37 no.1
• /
• pp.23-35
• /
• 2015

A 450 m-long sediment section was recovered from Hole U1359D located at the eastern levee of the Jussieau submarine channel on the Wilkes Land continental rise (East Antarctica) during IODP Expedition 318. The age model for Hole U1359D was established by paleomagnetic stratigraphy and biostratigraphy, and the ages of core-top and core-bottom were estimated to be about 5 Ma and 13 Ma, respectively. Biogenic opal content during this period varied between 3% and 60%. In the Southern Ocean, high biogenic opal content generally represents warm climate characterized by the increased light availability due to the decrease of sea-ice distribution. The surface water productivity change in terms of biogenic opal content at about 10.2 Ma in the Wilkes Land continental rise was related to the development of Northern Component Water. After about 10.2 Ma, more production of Northern Component Water in the North Atlantic caused to increase heat transport to the Southern Ocean, resulting in the enhanced diatom production. Miocene isotope events (Mi4~Mi7), which are intermittent cooling intervals during the Miocene, appeared to be correlated to the low biogenic opal contents, but further refinement was required for precise correlation. Biogenic opal content decreased abruptly during 6 Ma to 5.5 Ma, which most likely corresponds to the Messinian salinity crisis. Short-term variation of biogenic opal content was related to the extent of sea-ice distribution associated with the location of Antarctic Polar Front that was controlled by glacial-interglacial paleoclimate change, although more precise dating and correlation will be necessary. Diatom production in the Wilkes Land continental rise increased during the interglacial periods because of the reduced sea-ice distribution and the southward movement of Antarctic Polar Front.

• Ocean and Polar Research
• /
• v.27 no.2
• /
• pp.231-235
• /
• 2005

The European Iron Fertilization Experiment EIFEX studied the growth and decline of a phytoplankton bloom stimulated by fertilising $10km^2$ in the core of a mesoscale $(80{\times}120km)$ cyclonic eddy south of the Antarctic Polar Front with about 2 times 7 tonnes of iron sulphate. The phytoplankton accumulation induced by iron fertilization did not exceed $3{\mu}g\;chl\;a\;l^{-1}$ despite a draw down of $5{\mu}M$ of nitrate that should have resulted in at least double to triple the amount of phytoplankton biomass assuming regular Redfield-ratios for draw down after phytoplankton growth in the Southern Ocean. During EIFEX the fertilized core of the mesoscale eddy evolved to a hotspot for a variety of small and medium sized mesozooplankton copepods. In contrast to copepods, the biomass of salps (Salpa thompson)) that dominated zooplankton biomass before the onset of our experiment decreased to nearly extinction. Most of the species of the rnosozooplankton community showed extremely hiか feeding rates compared to literature values from Southern Ocean summer communities. At the end of the experiment, massive phytoplankton sedimentation reached the sea floor at about 3800m water depth.

• Journal of the Mineralogical Society of Korea
• /
• v.19 no.3 s.49
• /
• pp.163-169
• /
• 2006

Mineralogy and geochemistry of the sediment core from the seamount (2710 m below the sea level) just south of the Antarctic Polar Front were examined to draw paleoceanographic information in glacial-interglacial cycles. Smectite was most abundant clay mineral associated with illite and chlorite. Its content was slightly higher below 170 cm, suggesting a boundary between isotope stage 4 and 5. Si, Zr, Cs, Th, REE, $K_{2}O$, and $Al_{2}O_{3}$ show complete antithetical distribution with respect to $CaCO_{3}$ through the core. $SiO_{2}$ maxima and $CaCO_{3}$ minima at depths of 24, 136, and 176 cm are probably correlated with massive influx of ice-rafted debris during the advance of Antarctic ice shelves. Ni, Cu, and Ba show rather little correlation with $SiO_{2}$, suggesting their relation to biogenic debris, precipitation from seawater, or hydrothermal input. Particularly, Ba maxima tend to lag $10{\sim}20cm$ after $SiO_{2}$ maxima, probably due to rapid increase of productivity following deglaciation.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.9 no.3
• /
• pp.105-114
• /
• 1997

Wind is one of the main forcing contributing the circulation of the East Sea. By using 1.5-layer and 2.5-layer reduced gravity models, circulation in the East Sea is simulated. The bifurcation of the Tsushima Warm Current (TWC), the separation of East Korea Warm Current (EKWC) from the east coast of Korea, the Nearshore Branch of TWC, and the cyclonic gyres stretched from the East Korea Bay to the northern half of the East Sea are compared well with the schematic map. The features of the upper and the lower layer are very similar except for those of the central region. The Polar Front is the separating line of two different features. The main feature of northern part of the East Sea, north of the Polar Front is cyclonic gyres, which are composed of three cyclonic gyres in most seasons. North Korean Cold Current (NKCC) and Liman Cold Current (LCC) are the nearshore part of these cyclonic gyres. In the south of the Polar Front the current systems of both layers are anticyclonic in most seasons, except that those of the upper layer in winter and spring are not anticyclonic. Along the coast of Korea and Russia, the velocity structure is barotropic, while that of the central region is baroclinic. The effects due to the seasonal variations of wind stress and local Ekman suction/pumping are studied by imposing the domain with modified wind stress. which is spatial mean with temporal variations and temporal mean with spatial variations. It is found that the local Ekman suction/pumping due to wind stress curl is important to the formation of the cyclonic gyres in the western and the northwestern region of the East Sea.

• Korean Journal of Fisheries and Aquatic Sciences
• /
• v.24 no.4
• /
• pp.237-247
• /
• 1991

To characterize the community structure and spatial distribution of phytoplankton, observations on seawater temperature, salinity, nutrients, primary productivity and abundance and species composition of phytoplankton were made in the polar front region and its neighborhood off the east coast of Korea in summer 1990. Among the 96 taxa identified, Rhizosolenia setigera and Thalassionema nitzschioides were the most dominant species. The assemblage at the surface and 50 m depth was quite different in the northern inshore part of the study area but similar in the southern and offshore part. Principal component analysis by the species abundance showed that the phytoplankton consisted of the communities representing the surface of the northern inshore part with the neritic-warm dinoflagellates, the Northern Korean Cold Water with the cold water diatoms and the southern and offshore part, which seems to represent the Eastern Korean Warm Water, with the warm water diatoms. At the frontal region, diatoms were mixed with warm and cold water species. Primary productivity and phytoplankton standing crops were higher at the front than the neighboring waters. Nutrients were markedly high at the Northern Korean Cold Water. Horizontal advection of the Northern Korean Cold Water accompanied by nutrient supply seems to contribute to the high phytoplankton biomass at the front.

• Fisheries and Aquatic Sciences
• /
• v.5 no.3
• /
• pp.219-228
• /
• 2002

Based on the five-year (October 1992 through September 1997) Topex/Poseidon altimeter measurements, we describe the statistical characteristics of the eddy variability in the East Sea in terms of sea surface height anomaly, slope variability, and eddy kinetic energy (EKE). The sea surface height anomalies in the East Sea are produced with standard corrections from Topex/Poseidon measurements. In order to eliminate the high frequency noise in the sea surface height anomaly data, the alongtrack height anomaly data was filtered by about 40 km low-pass Lanczos filter based on Strub et al. (1997) and Kelly et a1. (1998). We find that there exists a distinct spatial contrast of high eddy variability in the south and low eddy energy in the north, bordering the Polar Front. In the northwestern area $(north\;of\;39^{\circ}N\;and\;west\;of\;133^{\circ}E)$ from the Polar Front where the eddies frequently appear, the EKE is also considerabel. The high kinetic energy in the southern East Sea reveals a close connection with the paths of the Tsushima Warm Current, suggesting that the high variability in the south is mainly generated by the baroclinic instability process of the Tsushima Warm Current. This finding is supported by other studies (Fu and Zlontnicki, 1989; Stammer, 1997) wh.ch have shown the strong eddy energy coupled in the major current system. The monthly variation of the EKE in both areas of high and low eddy variability shows a strong seasonality of a high eddy kinetic energy from October to February and a relatively low one from March to September. The sequential pattern of wind stress curl shows resemblance with those of monthly and seasonal EKE and the two sequences have a correlation of 0.82 and 0.67, respectively, providing an evidence that wind stress curl can be the possible forcing for the monthly and seasonal variation of the EKE in the East Sea. The seasonality of the EKE also seems to correlate with the seasonality of the Tsushima Warm Current. There also exists the large spatial and interannual variabilities in the EKE.