ALBERT

Description: We investigate the local seismotectonic of the Molucca Sea area using moment tensor calculations for the earthquakes that occurred in July 2019 at a depth of 10–55 km. The mainshock of Mw 6.8 occurred on July 7, followed by aftershocks until July 18, with magnitudes ranging from Mw 4.6 to Mw 5.8. Moment tensor solutions are calculated by applying Isolated Asperities (ISOLA) software using the full waveform data recorded at regional seismic stations. The analyzed frequency bands used in this study are 0.01–0.03 Hz and 0.04–0.05 Hz for the event with Mw ≥ 5 and Mw 

Description: Subsurface images of an area with a thick volcanic layer generally cannot be well-imaged with conventional seismic exploration (seismic reflection) due to seismic wave scattering. Another method is needed to obtain an accurate subsurface image in a thick volcanic layer area. In this study, we applied ambient noise tomography (ANT) to image the shear-wave velocity (Vs) structure in the Banyumas Basin, Central Java, Indonesia, which has relatively thick volcanic layers. We aimed to delineate the sediment deposits and the sedimentary thickness in this area through the utilization of ambient seismic noise. The application of cross-correlations from ambient seismic noise has been widely applied in numerous locations to obtain a greater understanding of subsurface structures. In this study, more than 1000 pairs of vertical component cross-correlations were used to estimate the Green's Function of the Rayleigh wave. The Neighbourhood Algorithm (NA) was utilized to invert the dispersion curves at 121 grid points which were used to obtain a vertical depth profile of 1D Vs. The Vs map results show that the low Vs tend to trend in a northwest–southeast direction associated with two areas: the Majenang low, and the Citanduy low. The presence of low Vs values corresponds with Middle Miocene–Pliocene sedimentary rocks. Meanwhile, the high Vs values in this area might correspond with Oligocene–Early Miocene volcanic products and Eocene sediment. Our study was also able to reveal the thickness of sedimentary rocks in the Banyumas sedimentary basin, which is believed to have hydrocarbon potential.

Description: Typhoon events have large impacts on marginal seas’ environmental conditions with implications for biological processes and carbon cycling. However, little is known about the responses of phytoplankton and particulate organic carbon (POC) to typhoon events in the Yellow-Bohai Sea (YBS). In this study, we utilized satellite-derived datasets of chlorophyll-a (Chl-a) and POC, together with key physical parameters, to analyze their responses to the Typhoon Lekima event induced heavy rainfall and strong winds. Overall, there were enhanced upwelling, strengthened currents, and increased terrestrial runoff during weakened Typhoon Lekima in the YBS. The basin-scale response of Chl-a showed large differences post the Typhoon Lekima event, with a decrease in the Bohai Sea (BS, 0.34 ± 3.0 mg m−3) but an increase in Yellow Sea (YS, 0.23 ± 1.7 mg m−3 in the south YS and 0.54 ± 0.8 mg m−3 in the north YS). The increase of Chl-a in the YS was attributed to increased nutrients, whereas the reduction of Chl-a in the BS was caused by dilution and water exchange with the North Yellow Sea. However, there was an overall increase in POC post-Typhoon Lekima in both BS and YS. The increase of POC in the majority of BS resulted largely from enhanced sediment resuspension and terrigenous input. The increase of POC in the nearshore waters of YS was attributable to enhanced biological production, sediment resuspension, and terrigenous input of POC, whereas the increase of POC in the central YS was partly due to transportation of high-POC waters from nearshore to offshore via strengthened current. Our study highlights the complex impacts of typhoon events on the carbon cycle in marginal seas.

Description: The Pacific Walker circulation (WC) is a major component of the global climate system. It connects the Pacific sea surface temperature (SST) variability to the climate variabilities from the other ocean basins to the mid- and high latitudes. Previous studies indicated that the ENSO-related atmospheric feedback, in particular, the surface wind response is largely underestimated in AMIP and CMIP models. In this study, we further investigate the responses in the WC stream function and the sea level pressure (SLP) to the ENSO-related SST variability by comparing the responses in 45 AMIP and 63 CMIP models and six reanalysis datasets. We reveal a diversity in the performances of simulated SLP and WC between different models. While the SLP responses to the El Niño-related SST variability are well simulated in most of the atmospheric and coupled models, the WC stream function responses are largely underestimated in most of these models. The WC responses in the AMIP5/6 models capture ~ 75% of those in the reanalysis, whereas the CMIP5/6 models capture ~ 58% of the responses. Further analysis indicates that these underestimated circulation responses could be partially attributed to the biases in the precipitation scheme in both the atmospheric and coupled models, as well as the biases in the simulated ENSO-related SST patterns in the coupled models. One should pay special attention to these biases when studying the WC or the tropical atmosphere–ocean interactions using numerical models.

Description: During the modern satellite era since 1979, the Pacific Walker circulation (PWC) experienced an intensification and a westward shift, which has broad impacts on the global climate variability. While the strengthening of the PWC has been shown to be driven by both the regional Pacific sea surface temperature (SST) and the remote forcing from other basins, its westward shift is primarily attributed to the phase change of the Atlantic Multidecadal variability. In this study, we investigate the potential effect of the remote SST forcing from the Atlantic and the Indian Oceans on the westward shift of the PWC, through statistical analysis and numerical experiments using atmospheric and coupled models. Results show that the tropical Atlantic warming plays a key (decisive) role in driving the PWC westward shift by triggering a Gill–Matsuno-type circulation anomaly in the tropics. This circulation response drives anomalous surface westerlies over the eastern Pacific and subsidence over the central Pacific that weakens the eastern part of the PWC, meanwhile generating easterly wind anomalies over the central-western Pacific and anomalous atmospheric convection over the western Pacific that intensifies the western part of the PWC. This direct forcing contributes ~ 32% of the observed PWC movement, while the Atlantic-induced inter-basin SST changes contribute another ~ 36% of its westward shift according to coupled model simulation results. Our results reinforce the importance of the inter-basin interactions in adjusting the tropical climate variabilities, and have broad implication for projecting the global climate.

Description: An electrical resistivity survey was carried out using the pole–pole configuration around the Sayanokami spring area in the northern part of Ito Campus (Kyushu University, Fukuoka, Japan) to study the groundwater aquifer and its electrical characteristics. A Code Division Multiple Transmission (CDMT) system was used. The CDMT system transmits 24 currents simultaneously and measures 24 potential responses with monitoring of actual current waveforms. The system can inject current from multiple electrodes into the underground environment simultaneously using different individual current waveforms. The two-dimensional (2-D) inversion results of the electrical resistivity data indicate three layers from top to bottom, as follows: (a) a thin layer with a thickness of 3 m and a low resistivity (

Description: Identification of periodicities in hydrological time series and evaluation of their statistical significance are not only important for water-related studies, but also challenging issues due to the complex variability of hydrological processes. In this article, we develop a “Moving Correlation Coefficient Analysis” (MCCA) method for identifying periodicities of a time series. In the method, the correlation between the original time series and the periodic fluctuation is used as a criterion, aiming to seek out the periodic fluctuation that fits the original time series best, and to evaluate its statistical significance. Consequently, we take periodic components consisting of simple sinusoidal variation as an example, and do statistical experiments to verify the applicability and reliability of the developed method by considering various parameters changing. Three other methods commonly used, harmonic analysis method (HAM), power spectrum method (PSM) and maximum entropy method (MEM) are also applied for comparison. The results indicate that the efficiency of each method is positively connected to the length and amplitude of samples, but negatively correlated with the mean value, variation coefficient and length of periodicity, without relationship with the initial phase of periodicity. For those time series with higher noise component, the developed MCCA method performs best among the four methods. Results from the hydrological case studies in the Yangtze River basin further verify the better performances of the MCCA method compared to other three methods for the identification of periodicities in hydrologic time series.

Description: Past sea-level change represents the large-scale state of global climate, reflecting the waxing and waning of global ice sheets and the corresponding effect on ocean volume. Recent developments in sampling and analytical methods enable us to more precisely reconstruct past sea-level changes using geological indicators dated by radiometric methods. However, ice-volume changes alone cannot wholly account for these observations of local, relative sea-level change because of various geophysical factors including glacio-hydro-isostatic adjustments (GIA). The mechanisms behind GIA cannot be ignored when reconstructing global ice volume, yet they remain poorly understood within the general sea-level community. In this paper, various geophysical factors affecting sea-level observations are discussed and the details and impacts of these processes on estimates of past ice volumes are introduced.

Description: Signals of Opportunity Reflectometry (SoOp-R) employs the communication system, GNSS (Global Navigation Satellite System) constellation and other potential Signals of Opportunity (SoOp) as the transmitters. In recent years, it has gained increased interests. Several experiments have been carried out, however it is still in the initial development stage. Theoretical predictions of SoOp Reflectometry for land surface parameters detection, such as soil moisture and vegetation biomass, should be carried out simultaneously. Meanwhile, at present less works are paid attention to the polarization study of the polarizations. The first-order radiative transfer equation models are employed here and they are developed according to the wave synthesis technique to get the various polarization combinations. Using the two models as analysis tools, we simulate the bistatic scattering at all potential SoOp Reflectometry bands, i.e., P-, L-, C- and X-band for circular polarizations and linear polarizations. While the original commonly used microwave scattering models are linear polarizations, here we compare the difference. Although the models can simulate bistatic scattering at any incident angles and scattering angles. Four special observation geometry are taken into considerations during the analysis. Using the developed models as tools, the developed models establish the relationship between the land surface parameters (such as soil moisture, soil roughness and vegetation water content, diameters et al.) and bistatic radar cross section. The forward scattering models developed here enables the understanding of the effects of different geophysical parameters and transmitter–receiver observation scenarios on the bisatic scattering at any polarization combinations for any potential SoOP reflectometry bands. Robust retrieval methods for soil moisture and vegetation biomass can benefit from the forward scattering models.

Description: The Pearl River Delta (PRD) is a densely populated special economic zone in South China where rapid development since the late 1990s coincided with an increase of many environmental problems in recent years. One of these concerns is the high concentration of arsenic (As; up to 300 μg/L in groundwater) that has been documented in the PRD. Likewise, in surface water and soils, As levels are comparatively higher than in other places in China. Arsenic is discharged from various geogenic sources and anthropogenic activities along the river courses before it drains into the Pearl River Estuary. In general, relatively low As concentrations in the river are due to the limited input from weathering of parent rocks. In contrast, where mining is an important industry, As levels in the surroundings are higher, exceeding the national and international standards for drinking water and soil. The presence of sulfide ores and mining operations, such as extraction of heavy metals and disposal of mine tailings, are most likely responsible for the sharp increase of As above background levels in several tributaries draining into the Pearl River. Besides, in the middle and lower reaches of the tributaries, other anthropogenic sources, e.g., industrial effluents and domestic sewage discharge play an important role in increasing As levels. Finally, rice cultivated in the contaminated areas accumulates As and poses a health risk to the local people in the watershed.