East Asian monsoon variation and climate changes in Jeju Island, Korea, during the latest Pleistocene to early Holocene

A 4.96-m-long sediment core from the Hanon paleo-maar in Jeju Island, Korea was studied to investigate the paleoclimatic change and East Asian monsoon variations during the latest Pleistocene to early Holocene (23,000-9000 cal yr BP). High-resolution TOC content, magnetic susceptibility, and major element composition data indicate that Jeju Island experienced the coldest climate around 18,000 cal yr BP, which corresponds to the last glacial maximum (LGM). Further, these multi-proxy data show an abrupt shift in climatic regime from cold and arid to warm and humid conditions at around 14,000 cal yr BP, which represents the commencement of the last major deglaciation. After the last major deglaciation, the TOC content decreased from 13,300 to 12,000 cal yr BP and from 11,500 to 9800 cal yr BP, thereby reflecting the weakening of the summer monsoon. The LGM in Jeju Island occurred later in comparison with the Chinese Loess Plateau. Such a disparity in climatic change events between central China and Jeju Island appears to be caused by the asynchrony between the coldest temperature event and the minimum precipitation event in central China and by the buffering effect of the Pacific Ocean.     

Assessment of uncertainties in the response of the African monsoon precipitation to land use change simulated by a regional model

Land use and land cover (LULC) over Africa have changed substantially over the last 60 years and this change has been proposed to affect monsoon circulation and precipitation. This study examines the uncertainties of model simulated response in the African monsoon system and Sahel precipitation due to LULC change using a set of regional model simulations with different combinations of land surface and cumulus parameterization schemes. Although the magnitude of the response covers a broad range of values, most of the simulations show a decline in Sahel precipitation due to the expansion of pasture and croplands at the expense of trees and shrubs and an increase in surface air temperature. The relationship between the model responses to LULC change and the climatologists of the control simulations is also examined. Simulations that are climatologically too dry or too wet compared to observations and reanalyses have weak response to land use change because they are in moisture or energy limited regimes respectively. The ones that lie in between have stronger response to the LULC changes, showing a more significant role in land–atmosphere interactions. Much of the change in precipitation is related to changes in circulation, particularly to the response of the intensity and latitudinal position of the African Easterly Jet, which varies with the changes in meridional surface temperature gradients. The study highlights the need for measurements of the surface fluxes across the meridional cross-section of the Sahel to evaluate models and thereby allowing human impacts such as land use change on the monsoon to be projected more realistically.     

Determination of perchlorate and iodide concentrations in edible seaweeds

Perchlorate and iodide concentrations were determined in brown (Undaria pinnatifida and Laminaria japonica) and red (Porphyra sp.) edible seaweeds, which are commonly consumed by Korean people, with the use of ion chromatography, coupled with a tandem mass spectrometer. Seaweeds (i.e., good sources of iodine) are among the most important plant life in the ocean and commonly consumed as food and nutritional supplement in South Korea. All seaweed samples were purchased from different regions in South Korea. The detected concentrations of perchlorate were as follows: 19.7–620.7 μg kg^?1 dry weight (n = 11, mean concentration = 149.2 μg kg^?1 dry weight) for L. japonica and 7.3–21.7 μg kg^?1 dry weight (mean concentration = 10.6 μg kg^?1 dry weight) for U. pinnatifida. Of the 11 samples of Porphyra sp., only 1 sample showed 6.7 μg kg^?1 dry weight perchlorate. The concentrations of iodide in all seaweed samples varied from 0.44 to 6,800 mg kg^?1 dry weight. L. japonica samples (n = 11) had significantly higher iodide concentrations, with a mean of 5,261 mg kg^?1 dry weight. The bioconcentration factor values for perchlorate and iodide in the three different seaweeds varied widely and showed similar variation trends. The trend for perchlorate and iodide was Porphyra sp. < U. pinnatifida < L. japonica. The results have provided growing evidence that perchlorate frequently occurs in food products.     

Characteristics of tephra in Holocene lake sediments on King George Island, West Antarctica: implications for deglaciation and paleoenvironment

Several reworked tephra layers in gravity-flow deposits are present in lacustrine core sediments collected from Hotel and Rudy Lakes on King George Island, South Shetland Islands, maritime sub-Antarctica. This study tests the values of tephra for establishing regional tephrochronologies for lakes in ice-covered landscapes in the vicinity of volcanoes. The tephra record is more abundant in a long Hotel Lake core (515 cm long). This study uses volcanic glass samples from five tephra layers of Hotel Lake and from one tephra layer of Rudy Lake. Morphologically, tephras are mixtures of basaltic and pumice shards, both having various degrees of vesicularity. Major element analyses of glass shards reveal that the majority of the glass fragments belong to basic glass (<60 wt% SiO₂), compositionally ranging from basalt to low-silica andesite and subalkaline series medium-K tholeiites, probably sourced from Deception Island located 130 km southwest of King George Island. Less than 20% of tephra belongs to silicic glass and occurs in three tephra horizons E of Hotel Lake. However, source volcano(es) for about 10% of basic tephra and silicic tephra are not readily identified from nearby volcanic centers. Except for the studied tephra in Rudy Lake, all tephra samples in Hotel Lake are not ashfall deposits but reworked and redeposited pyroclasts derived from retreating ice sheet, resulting in the occurrence of geochemically equivalent tephra samples in different tephra horizons. The dating of the studied tephra horizons represents the timing of deglaciation rather than that of volcanic eruptions. The result of this study implies that combined with sedimentological information more chemical criterion is necessary to study tephrochronology and regional correlation and to understand paleoenvironmental changes using tephra.     

The Formation and Circulation of the Intermediate Water in the Japan Sea

In order to clarify the formation and circulation of the Japan/East Sea Intermediate Water (JESIW) and the Upper portion of the Japan Sea Proper Water (UJSPW), numerical experiments have been carried out using a 3-D ocean circulation model. The UJSPW is formed in the region southeast off Vladivostok between 41°N and 42°N west of 136°E. Taking the coastal orography near Vladivostok into account, the formation of the UJSPW results from the deep water convection in winter which is generated by the orchestration of fresh water supplied from the Amur River and saline water from the Tsushima Warm Current under very cold conditions. The UJSPW formed is advected by the current at depth near the bottom of the convection and penetrates into the layer below the JESIW. The origin of the JESIW is the low salinity coastal water along the Russian coast originated by the fresh water from the Amur River. The coastal low salinity water is advected by the current system in the northwestern Japan Sea and penetrates into the subsurface below the Tsushima Warm Current region forming a subsurface salinity minimum layer. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of wave amplitude on turbulent flow in a wavy channel by direct numerical simulation

The present study numerically investigates the characteristics of three-dimensional turbulent flow in a wavy channel. For the purpose of a careful observation of the effect of the wave amplitude on the turbulent flow, numerical simulations are performed at a various range of the wave amplitude to wavelength ratio (0.01?α/λ?0.05), where the wavelength is fixed with the same value of the mean channel height (H). The immersed boundary method is used to handle the wavy surface in a rectangular grid system, using the finite volume method. The Reynolds number (Re=U_bH/ν) based on the bulk velocity (U_b) is fixed at 6760. The present computational results for a wavy surface are well compared with those of references. When α/λ=0.02, the small recirculating flow occurs near the trough at the instant, but the mean reverse flow is not observed. In the mean flow field, the reverse flow appears from α/λ=0.03 among the wave amplitude considered in this study. The domain of the mean reverse flow defined by the locations of separation and reattachment depends strongly on the wave amplitude. The pressure drag coefficient augments with increasing the wave amplitude. The friction drag coefficient shows the increase and decrease behavior according to the wave amplitude. The quantitative information about the flow variables such as the distribution of pressure and shear stress on the wavy surface is highlighted.     

Abundance and distribution of Nemopilema nomurai (Scyphozoa,Rhizostomeae), in Korean waters in 2005–2013

Nemopilema nomurai have appeared massively since 2003 in Korean waters, and regular offshore monitoring has been performed since 2005 in the eastern Yellow Sea (YS), northwestern East China Sea (ECS), Korean southern waters (Ksw), and western East Sea (ES). Korea Jellyfish Monitoring Network (KoJEM) was established in 2006 for coastal jellyfish monitoring. From these, sight survey monitoring data were gathered and analyzed to extract the yearly and seasonal fluctuation of N. nomurai’s abundance and distribution. The first massive annual appearance of N. nomurai occurred in the northwestern ECS, off Shanghai, China, in mid May of 2005–2008 and of 2012–2013. In other years or concurrently with the appearance in the northwestern ECS in the same year, several individuals were found in the mid-eastern YS and Ksw, and southwestern ES. The population of N. nomurai at the northwestern ECS moved to the southeastern YS and Jeju Strait in June, and from the July to August it extended its distribution all around the Korean peninsula and persisted till October. Since October, the distribution was retracted into the southern YS and Ksw, and disappeared slowly. N. nomurai’s yearly abundance varied a lot, from nearly 0 inds 10^?4m^?2 in 2010 to 62.4 inds 10^?4m^?2 in 2005. The highest abundance was recorded in 2005, followed by 2007 and 2009, and the least abundance was in 2008 and 2010–2013. The results were compared with those of the Liaoning Bay, Bohai Sea, which led to speculation about a new seeding place of N. nomurai, and mortality during the early planktonic phase of N. nomurai was proposed as the determinant of the yearly variation in abundance.     

Estimation of the minimum food requirement using the respiration rate of medusa of Aurelia aurita in Sihwa Lake

We examined the respiration rate of Aurelia aurita medusae at 20 °C and 28 °C to evaluate minimum metabolic demands of medusae population in Sihwa Lake, Korea during summer. While weight specific respiration rates of medusae were constant and irrespective to the wet weight (8?C220 g), they significantly varied in respect to temperatures (p<0.001, 0.11±0.03 mg C g^?1 of medusa d^?1 at 20°C and 0.28±0.11 mg C g^?1 of medusa d^?1 at 28 °C in average, where Q ₁₀ value was 2.62). The respiration rate of medusae was defined as a function of temperature (T, °C) and body weight (W, g) according to the equation, R=0.13×2.62^(T-20)/10 W ^0.93. Population minimum food requirement (PMFR) was estimated from the respiration rate as 15.06 and 4.86 mg C m^?3 d^?1 in June and July, respectively. During this period, increase in bell diameter and wet weight was not significant (p=1 in the both), suggesting that the estimated PMFR closely represented the actual food consumption in the field. From July to August, medusae grew significantly at 0.052 d-1, thus the amount of food ingested by medusae population in situ was likely to exceed the PMFR (1.27 mg C m^?3 d^?1) during the period. In conclusion, the medusae population of higher density during June and July had limited amount of food, while those of lower in July and August ingested enough food for growth.     

Numerical simulation of nearshore circulation on field topography under random wave environment

In order to investigate surf zone hydrodynamics through two-dimensional numerical simulations of nearshore circulation under random wave environment, a nearshore circulation model, SHORECIRC, and a random wave model, SWAN, were combined and utilized. Using this combined model, a numerical simulation of the October 2, 1997 SandyDuck field experiment was performed. For this simulation, field topography and an input offshore spectrum were constructed using observed data sets synchronized with the experiment. The wave-breaking model in SWAN was modified by using breaker parameters varied according to bottom slope. The simulation results were compared with the experimental data, which revealed a well-developed longshore current, as well as with results using other combinations which were SHORECIRC and its original monochromatic wave-driver, and SHORECIRC and the default of SWAN. The results from the novel combined model agreed well with the experimental data. The results of the present simulation also indicate that alongshore field topography influences shear fluctuation of longshore currents.