Sedimentary Features of Tsunami Deposits in Carbonate-Dominated Beach Environments: A Case Study from the 25 October 2010 Mentawai Tsunami

This study provides a case history of tsunami deposition in a carbonate-dominated environmental setting. We present the results of a sedimentological investigation conducted on deposits formed by the 25 October 2010 Mentawai Island Tsunami and report on deposits analyzed at three sites on North Pagai Island: Sabeu Gunggung, Macaroni Resort, and Tumalei. The deposits are mainly composed of medium to coarse sand-sized fragments of corals, shells and foraminifera, with thickness ranging from 3 to 26 cm. The deposits consist of two to five layers, with fining-upward trends dominating. Local topography noticeably affects the thickness, number of layers, and distribution of tsunami deposits. The foraminiferal assemblage and diversity vary at each sample point, along transect and between different transects. Based on the foraminiferal content, most of the deposit material likely came from shallower depths. In addition, density distribution of the tsunami deposit material exhibits some degree of variability in terms of the range of densities in each sample and the trend of the overall density along each transect. In contrast to heavy mineral-dominated deposits, the density of carbonate grains as a function of size may be an important consideration when carbonate-dominated deposits are used to interpret hydraulic conditions that created a particular tsunami deposit. Since there are relatively few studies of tsunami deposits in carbonate-dominated environmental settings such as the Mentawai Islands, our study provides a useful case history of tsunami deposition in such an environmental setting.     

Optimal primary production model and parameterization in the eastern East China Sea

Integrated primary production (IPP) datasets from the eastern East China Sea (ECS) were used to validate the depth dependent and time integrated model (TIM), the empirical model (EM), and the vertically generalized production model (VGPM). Employing constant maximum chlorophyll-a (Chl-a) specific carbon fixation rate (P _opt ^B ), the original TIM could not explain measured IPP variance, while the low P _opt ^B estimated using P _opt ^B models originally embedded in the EM were responsible for original EM low estimations. The disparity between P _opt ^B expressions originally embedded in the VGPM and that observed in this study was responsible for the low accuracy of the original VGPM. After locally tuning on the P _opt ^B model, TIM and VGPM could predict well, whereas EM still gave low estimates. This was probably due to the fact that, unlike TIM and VGPM, EM employs a constant factor instead of a light dependent function in describing the depth of light-saturation primary production. The high accuracy of TIM was limited by the complexity of estimating many variable inputs. EM, as a simplest model, should be used with caution in the eastern ECS. Global VGPM with locally adjusted P _opt ^B seemed to be an effective model for estimating IPP in the eastern ECS.     

Development of drain hole design optimisation: a conceptual model for open pit mine slope drainage system with fractured media using a multi-stage genetic algorithm

High rainfall in equatorial regions leads to high groundwater levels or pore pressures and a high risk of landslides on the slopes of open pit mines, hindering mining operations. To lower the groundwater level surrounding a slope, a drainage system is needed. A drain hole is a part of a drainage system which utilises gravity to drain groundwater. Drain hole installation in fractured media requires the determination of the number, location, length and other parameters of the drain holes. Drain holes are frequently installed in uniform configurations or in layouts with uniform spacing, which are often ineffective and uneconomical, as some holes are not in the right positions or directions within the fractured media. This paper attempts to develop a conceptual model of an optimised configuration of drain holes by setting the drain hole parameters, or decision variables, such as number, location and length, in such a way that it produces the most effective and efficient outcome by maximising groundwater lowering and minimising cost. The optimisation is supported by the multi-stage genetic algorithm method in combination with a groundwater simulator, hereafter called the multi-stage GWSim-GA SO method. The procedure of the conceptual model will be further developed and used as a framework in the groundwater management of fractured media of an open pit mine slope.     

Spatial and temporal hydrochemistry variations of karst water in Gunung Sewu,Java, Indonesia

A hydrogeochemical study was conducted in the Gunung Sewu Karst, Java Island, Indonesia. The main objective of this study is to describe the spatial and temporal variations of hydrochemistry that occur in the central and western parts of Gunung Sewu. Discharge measurements for a one-year period are taken in some karst springs or underground rivers to define their discharge hydrograph. Furthermore, baseflow separation analysis was conducted to determine the base flow percentage throughout the year. Water sampling for hydrogeochemical analysis was taken every month to represent the dry and rainy season conditions. To describe the hydrogeochemical processes, a scatter plot analysis with a small sample size was conducted. The results showed that the hydrochemistry of karst water in the study area has different characteristics spatially and temporally. Within the dry season, the dominant hydrogeochemical process is water–rock interaction (precipitation of calcite mineral), indicated by achieving the maximum level of Ca²⁺, HCO₃ ^?, electrical conductivity, base flow percentage, and SI calcite, with the lowest level of log \(P_{{{\text{CO}}_{2} }}\) in the water. In addition, the dry season hydrochemistry is characterized by a strong relationship between electrical conductivity–calcium/bicarbonate, base flow percentage-discharge, base flow percentage-SI calcite, and SI calcite-log \(P_{{{\text{CO}}_{2} }}\). Spatially, the different level of correlations between these parameters depended on the sampling location, flow recharge, and the conduit development. Conversely, in the rainy season, the hydrogeochemical process shifted from water–rock interaction to dilution of rainwater as a result of rain water supply through a conduit system channel, which is characterized by declining Ca²⁺, HCO₃ ^?, electrical conductivity, base flow percentage, and SI calcite, with the highest level of log \(P_{{{\text{CO}}_{2} }}\) in the water. The dilution of rainwater process also caused a decline in the correlation of some hydrogeochemical parameters.     

Tsunami Source of the 2010 Mentawai, Indonesia Earthquake Inferred from Tsunami Field Survey and Waveform Modeling

The 2010 Mentawai earthquake (magnitude 7.7) generated a destructive tsunami that caused more than 500 casualties in the Mentawai Islands, west of Sumatra, Indonesia. Seismological analyses indicate that this earthquake was an unusual “tsunami earthquake,” which produces much larger tsunamis than expected from the seismic magnitude. We carried out a field survey to measure tsunami heights and inundation distances, an inversion of tsunami waveforms to estimate the slip distribution on the fault, and inundation modeling to compare the measured and simulated tsunami heights. The measured tsunami heights at eight locations on the west coasts of North and South Pagai Island ranged from 2.5 to 9.3 m, but were mostly in the 4–7 m range. At three villages, the tsunami inundation extended more than 300 m. Interviews of local residents indicated that the earthquake ground shaking was less intense than during previous large earthquakes and did not cause any damage. Inversion of tsunami waveforms recorded at nine coastal tide gauges, a nearby GPS buoy, and a DART station indicated a large slip (maximum 6.1 m) on a shallower part of the fault near the trench axis, a distribution similar to other tsunami earthquakes. The total seismic moment estimated from tsunami waveform inversion was 1.0 × 10²¹ Nm, which corresponded to M_w 7.9. Computed coastal tsunami heights from this tsunami source model using linear equations are similar to the measured tsunami heights. The inundation heights computed by using detailed bathymetry and topography data and nonlinear equations including inundation were smaller than the measured ones. This may have been partly due to the limited resolution and accuracy of publically available bathymetry and topography data. One-dimensional run-up computations using our surveyed topography profiles showed that the computed heights were roughly similar to the measured ones.     

Verification of vertically generalized production model and estimation of primary production in Sagami Bay,Japan

The Vertically Generalized Production Model (VGPM) was verified by the primary production data of the Sagami Bay, Japan. The VGPM with open ocean parameters including P ^B _opt , maximum primary production per unit of chlorophyll a in the water column, explained only 40% of the variability of integrated primary production. Formulations of the open ocean P ^B _opt showed no correlation with in situ P ^B _opt . Adjustment of the parameters of chlorophyll a and temperature dependent P ^B _opt improved the estimation of integrated primary production to 47% of the variation. Vertical integration parameters of VGPM also have to be adjusted to improve the estimation. Integrated primary production calculated with a stronger light dependency and with the adjusted P ^B _opt model can explain 74% of the variation. This model was used to estimate primary production of the Sagami Bay during 2003 with satellite data. In situ measurements on cloudy days indicate that the use of satellite data from sunny days only overestimates primary production.     

Molecular identification of anisakid nematodes third stage larvae isolated from common squid (Todarodes pacificus) in Korea

The occurrence of Genus Anisakis nematode larvae in marine fishes and cephalopods is epidemiologically important because Anisakis simplex larval stage can cause a clinical disease in humans when infected hosts are consumed raw. Common squid (Todarodes pacificus) from Korean waters were investigated for anisakid nematodes infection during 2009～2011. In total, 1,556 larvae were collected from 615 common squids and 732 of them were subsequently identified by PCR-RFLP analysis of ITS rDNA. Depending on the sampling locations, the nematode larvae from common squid showed different prevalence, intensity and species distribution. A high prevalence (P) and mean intensity (MI) of infection were observed in the Yellow Sea (n = 250, P = 86.0%, MI = 5.99 larvae/host) and the southern sea of Korea (n = 126, P = 57.1%, MI = 3.36 larvae/host). Anisakis pegreffii was dominantly found in common squid from the southern sea (127/ 140, 90.7%) and the Yellow Sea (561/565, 98.9%). In contrast, the P and MI of infection were relatively low in the East Sea (n = 239, P = 8.37%, MI = 1.25 larvae/host). A. pegreffii was not found from the East Sea and 52.0% (13/25) of the nematodes were identified as A. simplex. Most of them were found in the body cavity or digestive tract of common squid, which are rarely consumed raw by humans. Considering the differenences in anisakid nematode species distribution and their microhabitat in common squid, it remains unclear whether common squid plays an important role in the epidemiology of human anisakis infection in Korea. Further extensive identification of anisakid nematodes in common squid, with geographical and seasonal information will be necessary.     

Comparison of carbon cycle between the western Pacific subarctic and subtropical time-series stations: highlights of the K2S1 project

A comparative study of ecosystems and biogeochemistry at time-series stations in the subarctic gyre (K2) and subtropical region (S1) of the western North Pacific Ocean (K2S1 project) was conducted between 2010 and 2013 to collect essential data about the ecosystem and biological pump in each area and to provide a baseline of information for predicting changes in biologically mediated material cycles in the future. From seasonal chemical and biological observations, general oceanographic settings were verified and annual carbon budgets at both stations were determined. Annual mean of phytoplankton biomass and primary productivity at the oligotrophic station S1 were comparable to that at the eutrophic station K2. Based on chemical/physical observations and numerical simulations, the likely “missing nutrient source” was suggested to include regeneration, meso-scale eddy driven upwelling, meteorological events, and eolian inputs in addition to winter vertical mixing. Time-series observation of carbonate chemistry revealed that ocean acidification (OA) was ongoing at both stations, and that the rate of OA was faster at S1 than at K2 although OA at K2 is more critical for calcifying organisms.     

Meridional and seasonal footprints of the Pacific Decadal Oscillation on phytoplankton biomass in the northwestern Pacific Ocean

We used 16 years of multiplatform-derived biophysical data to reveal the footprint of the Pacific Decadal Oscillation (PDO) on the phytoplankton biomass of the northwestern Pacific Ocean in terms of chlorophyll a concentration (Chl), and to discern the probable factors causing the observed footprint. There were meridional differences in the response of phytoplankton to changes of environmental conditions associated with deepening of the mixed layer during the positive phase of the PDO. In general, deepening of the mixed layer increased phytoplankton biomass at low latitudes (increase of Chl due to increase of nutrient supply), but lowered phytoplankton at high latitudes (decrease of Chl due to reduction of average irradiance and temperature in the mixed layer). The areas where Chl increased or decreased changed meridionally and seasonally in accord with regulation of nutrient and light/temperature limitation by changes of mixed layer depth. The observed PDO footprint on Chl in the northwestern Pacific is likely superimposed on the high-frequency component of the PDO excited by El Niño/Southern Oscillation interannual variability. On a decadal time scale, however, Chl in the northwestern Pacific were more strongly associated with the recently discovered North Pacific Gyre Oscillation.     

Relationships of interannual variability in SST and phytoplankton blooms with giant jellyfish (Nemopilema nomurai) outbreaks in the Yellow Sea and East China Sea

Giant jellyfish (Nemopilema nomurai) outbreaks in relation to satellite sea surface temperature (SST) and chlorophyll-a concentrations (Chl-a) were investigated in the Yellow Sea and East China Sea (YECS) from 1998 to 2010. Temperature, eutrophication, and match–mismatch hypotheses were examined to explain long-term increases and recent reductions of N. nomurai outbreaks. We focused on the timing of SST reaching 15 °C, a critical temperature enabling polyps to induce strobilation and enabling released ephyra to grow. We analyzed the relationship of the timing with interannual variability of SST, Chl-a, and the timing of phytoplankton blooms. Different environmental characteristics among pre-jellyfish years (1998–2001), jellyfish years (2002–2007, 2009), and non-jellyfish years (2008, 2010) were assessed on this basis. The SST during late spring and early summer increased significantly from 1985 to 2007. This indicated that high SST is beneficial to the long-term increases in jellyfish outbreaks. SST was significantly lower in non-jellyfish years than in jellyfish years, suggesting that low SST might reduce the proliferation of N. nomurai. We identified three (winter, spring, and summer) major phytoplankton bloom regions and one summer decline region. Both Chl-a during non-blooming periods and the peak increased significantly from 1998 to 2010 in most of the YECS. This result indicates that eutrophication is beneficial to the long-term increases in jellyfish outbreaks. Timing of phytoplankton blooms varied interannually and spatially, and their match and mismatch to the timing of SST reaching 15 °C did not correspond to long-term increases in N. nomurai outbreaks and the recent absence.