Eastern Sub-basin Research Articles

Tectonic evolution of the eastern margin of the Northern South Yellow Sea Basin in the Yellow Sea since the Late Cretaceous

The South Yellow Sea Basin is the largest sedimentary basin in the Yellow Sea. The Gunsan Basin in the central eastern part of the Northern South Yellow Sea Basin comprises the Western, Central, and Eastern Subbasins. The Eastern Subbasin marks the eastern margin of the South Yellow Sea Basin. Interpretation of multi-channel seismic profiles and balanced cross-section restoration of depth-converted seismic profiles reveal the structural characteristics and evolution of the Eastern Subbasin. The subbasin comprises three groups of faults: NW-SE, NE-SW, and NNE-SSW trending faults. The subsidence pattern of the subbasin, derived from the cross-section restoration analysis, indicates five distinguished evolution phases: (i) rapid subsidence in the Late Cretaceous, (ii) slow subsidence from the Paleocene to the Eocene, (iii) accelerated subsidence in the Oligocene, (iv) alternation of the uplift and subsidence in the Early Miocene, and (v) gradual subsidence since the Middle Miocene. The main and moderate subsidence can be explained by the combination of extension in the SE and NE-SW directions that formed double duplex structures. We suggest that the NW oblique subduction of the Pacific Plate under the NE Asia margin induced both extension toward the trench and dextral strike-slip parallel to the margin. The extension toward the trench caused SE transtension in a local pull-apart setting, whereas the dextral strike-slip parallel to the margin caused NE-SW extension, inducing more significant subsidence. The combined processes resulted in the progressive development of nested duplex structures. The evolution of the Eastern Subbasin is not compatible with previously suggested models for the western part of the South Yellow Sea Basin including foreland basin formation and transtension induced by branch faults of the Tan-Lu Fault.

Linkages between gully erosion susceptibility and hydrological connectivity in Tropical sub-humid river basin: Application of Machine learning algorithms and Connectivity Index

Hydrological connectivity from upslope to downslope of valley floor and main channel, triggered the gully initiation and associated land degradation continue occurring off-site erosion as considered most effective drivers on potential sediment detachment. Present study attempted to identify the linkage between gullies erosion susceptibility (GES) and hydrological connectivity pathway in sub-tropical humid river basin Kangsabati (KRB) using four machine-learning algorithms (MLALs) such as Random Forest (RF), Support Vector Machine (SVM), Extreme Gradient Boosting (XGB), Artificial Neural Network (ANN) for GES mapping, and connectivity index (IC) for hydrological connectivity mapping. Thirty-five controlling factors were selected using Boruta’s approach to produce GES mapping, while frequency ratio (FR) was applied to determine the significant role in each individual class of controlling factors on degree of gully susceptibility. To achieve the efficiency of using MLALs, AUC of ROC including sensitivity, specificity, accuracy, F, and Kappa index were employed to compare in each model. In testing datasets, AUC values reveals that RF (0.99) and XGB (0.99) were well performed and predicted to GES followed by ANN (0.97) and SVM (0.87). FR depicts the most contributing factors of barren land and laterite followed by rainfall erosivity, degraded forest, single crop, and elevation to GES. IC result showed that values range (−11.52 to 0.49) address the three connectivity categories i.e. not connected (NC), gully connected but not reach (CNR), and gully well connected (WC). Correlation analysis clarified that double crop (R = 0.82), topographical wetted index (R = 0.77) and slope (R = 0.0.44) are prolonged WC for large downslope in north-western sub-basins of upper catchment and western, eastern sub-basins of lower catchment, while dense forest (R = -0.71) and vegetation cover (R = -0.82) forms NC gullies and CNR to channel due to interrupted upslope in central sub-basins of upper and lower catchment. Finally, research findings could provide to take strategy for sustainable land uses policy.

Primeras huellas de tortugas terrestres gigantes del Cretácico Inferior (Soria, España): Testudopodus iberiae, nov. icnogen. nov. icnoesp.

En este trabajo se analizan las icnitas del yacimiento de “Valdelalosa III”, perteneciente a la subcuenca oriental de la Cuenca de Cameros (Cordillera Ibérica), Formación Huérteles, Berriasiense medio-superior (Cretácico basal), situado en los Valles de Valdelalosa, en el municipio de San Pedro Manrique (provincia de Soria, España). Las huellas de manos y pies son de diferente tamaño, tienen forma circular u ovalada y ocasionalmente marcan tres-cuatro uñas cortas y redondeadas. En el yacimiento se contabilizan 106 icnitas de las que 76 son huellas aisladas, 11 configuran un rastro, 15 son subhuellas y 4 son huellas parciales. En el rastro las impresiones de las extremidades del lado derecho del animal son paralelas a las del lado izquierdo y mantienen una distancia constante entre sí, carácter diagnóstico de los rastros de las tortugas. Las icnitas se han comparado morfológicamente y morfométricamente con otras icnitas de tortugas, con huellas de tortugas actuales, y con el pie y la mano de varios ejemplares de tortugas terrestres gigantes. Los resultados obtenidos de los análisis de las icnitas del yacimiento de “Valdelalosa III” permiten atribuirlas al paso de unas tortugas terrestres de gran tamaño y, debido a sus características se propone la creación del icnotaxon Testudopodus iberiae, nov. icnogen. nov icnosp.

Assessing the Vulnerability of Water Balance to Climate Change at River Basin Scale in Humid Tropics: Implications for a Sustainable Water Future

Sustainability in hydrology aims at maintaining a high likelihood of meeting future water demands without compromising hydrologic, environmental, or physical integrity. Therefore, understanding the local-scale impact of global climate change on hydrology and water balance is crucial. This study focuses on assessing the impact of climate change on water balance components (precipitation, surface runoff, groundwater flow, percolation, etc.) at the river basin scale in a humid tropical region. The Periyar river basin (PRB) in Kerala in India is considered as a case study and the SWAT hydrological model is adopted to obtain the water balance components. Three general circulation models are considered under two shared socioeconomic pathways (SSP 245 and SSP 585) emission scenarios assess the impact of climate change until 2100. For the PRB, the results demonstrate a significant increase in streamflow (>65%) and runoff (>40%) in the mid (2041–2070) and far (2071–2100) future under both the SSP scenarios, indicating a potential vulnerability to future floods. Conversely, in the near future under SSP 585, a decrease in runoff (−15%) and nominal changes in streamflow (−5%) are observed. Spatially, the eastern sub-basins and the west coast of the Periyar river basin are projected to experience higher precipitation events, while the central region faces reduced precipitation and low flow rates. The findings emphasize the need for proactive and sustainable management of water resources, considering irrigation requirements, groundwater discharge, and flood control measures, to mitigate the negative effects of climate change and prevent water stress/surplus situations in specific sub-basins. This study enhances our understanding of climate change impacts on water balance and emphasizes the significance of sustainable water resource management for an effective response. By integrating scientific knowledge into policy and management decisions, we can strive towards a resilient water future within a changing climate.

Bifurcation of mantle plumes by interaction with stagnant slabs in the mantle transition zone: Evidence from late Cenozoic basalts within Southeast Asia

Mantle plumes can encounter stagnant slabs in the mantle transition zone (MTZ) during their ascent from the lower mantle to Earth’s surface. However, the interactions between stagnant slabs and mantle plumes remain poorly understood. This study presents new data on the spatial thermal−lithological−chemical heterogeneity in the mantle over a vast area of Southeast Asia that reflects the variable influence of a late Cenozoic mantle plume. Site U1433 of International Ocean Discovery Program (IODP) Expedition 349 in the southwest sub-basin of the South China Sea (SCS) is located near the center of this seismically imaged mantle upwelling. This area also contains mid-ocean ridge basalt (MORB) derived from a peridotite-dominated and normal temperature mantle source with a depleted Nd-Hf and enriched 207Pb/206Pb isotopic composition. In contrast, MORB from Site U1431 of IODP Expedition 349 within the eastern sub-basin of the SCS and other intraplate basalts from the Hainan-Leizhou area, the eastern Indochina block, and elsewhere in the SCS are dominantly sourced from higher temperature pyroxenite-enriched mantle material that records mantle plume activity. These observations are in contrast with previous models involving a single plume rising from the lower mantle beneath the SCS that then tilted toward Hainan Island, China. Instead, it is likely that the observations from this region are indicative of plume-stagnant slab interaction. The shallow upper mantle beneath Site U1433 has not been influenced by a mantle plume as the presence of stagnant slabs within the MTZ prevented further upwelling of the plume. In contrast, a mantle plume passed through the weaker MTZ within the eastern sub-basin and circum-SCS areas, allowing plume-related magmatism to occur. The bifurcation of a deep-rooted mantle plume by stagnant slabs in the MTZ produced a cluster of small mantle upwellings that ascended to shallow depths, consistent with new multiscale global tomographic data for Southeast Asia.

Terrestrial Water Storage Component Changes Derived from Multisource Data and Their Responses to ENSO in Nicaragua

Approximately 3.5 million people in Nicaragua have experienced food insecurity due to the El Niño-Southern Oscillation (ENSO)-induced drought from 2014 to 2016. It is essential to study terrestrial water storage component (TWSC) changes and their responses to ENSO to prevent the water crisis in Nicaragua influenced by ENSO. In this paper, we investigate the TWSC changes in Nicaragua and its sub-basins derived from the Gravity Recovery and Climate Experiment (GRACE)’s temporal gravity field, hydrological model, and water level data, and then determine the connection between the TWSC and ENSO from April 2002 to April 2021 by time series analysis. The research results show that: (1) The estimated TWSC changes in Nicaragua are in good agreement with the variation of precipitation and evaporation, and precipitation is the main cause of TWSC variation. (2) According to the cross-correlation analysis, there is a significant negative peak correlation between the interannual TWSC and ENSO in western Nicaragua, especially for interannual soil moisture (−0.80). The difference in peak correlation between the western and eastern sub-basins may be due to the topographic hindrance of the ENSO-inspired precipitation process. (3) The cross-wavelet analysis indicates that the resonance periods between TWSC and ENSO are primarily 2 and 4 years. These resonance periods are related to the two ENSO modes (the central Pacific (CP) mode with a quasi-2-year period and the eastern Pacific (EP) mode with a quasi-4-year period). Furthermore, their resonance phase variation may be due to the transition to ENSO mode. This study revealed the relationship between ENSO and TWSC in Nicaragua, which can provide a certain reference for water resources regulation.

Modelling the Mediterranean Sea ecosystem at high spatial resolution to inform the ecosystem-based management in the region

Cumulative pressures are rapidly expanding in the Mediterranean Sea with consequences for marine biodiversity and marine resources, and the services they provide. Policy makers urge for a marine ecosystem assessment of the region in space and time. This study evaluates how the whole Mediterranean food web may have responded to historical changes in the climate, environment and fisheries, through the use of an ecosystem modelling over a long time span (decades) at high spatial resolution (8 × 8 km), to inform regional and sub-regional management. Results indicate coastal and shelf areas to be the sites with highest marine biodiversity and marine resources biomass, which decrease towards the south-eastern regions. High levels of total catches and discards are predicted to be concentrated in the Western sub-basin and the Adriatic Sea. Mean spatial–temporal changes of total and commercial biomass show increases in offshore waters of the region, while biodiversity indicators show marginal changes. Total catches and discards increase greatly in offshore waters of the Western and Eastern sub-basins. Spatial patterns and temporal mean changes of marine biodiversity, community biomasses and trophic indices, assessed in this study, aim at identifying areas and food web components that show signs of deterioration with the overall goal of assisting policy makers in designing and implementing spatial management actions for the region.

Quantifying the changes in the runoff and its components across the Upper Indus River Basin under climate change

Abstract The runoff from the Upper Indus River Basin (UIB) is considered vital for sustainable water supply and agriculture. Climate change may alter the runoff and affect the availability of water. This study employs a hydrologic model and the climate projections of fine-resolution Meteorological Research Institute-Atmospheric General Circulation Model (MRI-AGCM) (0.1875°) to assess the impacts of climate change in the future (2075–2099) on the flows in the UIB and its sub-basins. The simulations have shown satisfactory results compared to the observed ones. Furthermore, simulated snow-cover was compared with estimated snow-cover by Moderate Resolution Imaging Spectroradiometer (MODIS). According to the results, meltwater from glaciers contributes to about two-thirds of the annual runoff from the UIB. According to the projections, the future temperature will increase by 5.3 °C and annual precipitation will increase by 17% across the UIB. Despite this increase, the annual river flows were projected to decrease by 14% in the future because of depleted glacier melt. Furthermore, the detailed hydrologic responses in selected sub-basins showed different patterns in the future depending on the climate and elevation. In an eastern sub-basin, flows will increase by 58% because of enhanced glacier melt and higher precipitation. Contrarily, two western sub-basins will experience the reduction of the flow by 30–70% because of the glacier retreat.

Assessing and mapping human well-being for sustainable development amid drought and flood hazards: Dadu River Basin of China.

Drought and flood are two of the most destructive natural disasters with the most significant impact and greatest losses in the Dadu River basin (DRB). However, their impacts on people's life have not attracted enough attention from scholars. In this study, the Standardized Precipitation Index (SPI) describing the drought/flood situation and the Composite Index of Human Well-being (CIHW) are calculated, and a framework is further constructed to assess the impacts of drought and flood disasters on human well-being in the DRB. The results show that the annual and seasonal SPI in the DRB generally exhibit an increasing trend in fluctuations during 2000-2009, indicating a wetting climate in this basin. Overall, the upper reaches of the DRB have experienced an evolution of flood-drought-flood state transition, where the variation amplitude of the SPI in the western sub-basin is greater than that in the eastern sub-basin. In addition, the lower reaches of the DRB have suffered more dramatic and periodic changes from the drought/flood disasters in terms of the SPI. For human well-being during 2000-2019, Maerkang City in the upper reaches, Kangding City in the middle reaches, and Shimian County in the lower reaches of the DRB are at a relatively higher level, with the CIHW decreasing from administrative centers to the around. Moreover, the CIHW over the whole basin increases gradually from 2000 to 2019. The SPI has significantly negative effects on different capitals, following a descending order of financial, social, physical, human and natural capitals. The counties of the basin are divided into four groups, namely the group with high disaster risks and high human well-being, the group with high disaster risks and low human well-being, the group with low disaster risks and high human well-being, and the group with low disaster risks and low human well-being. The panel regression results suggest that the construction of water conservancy facilities, the financial inputs in agriculture and meteorology, and the educational level have positive impacts on human well-being, but the impacts differ from different groups. The construction of water conservancy facilities has highly significant impacts on human well-being in all groups; the education level has no significant impact on the group with high disaster risk and high human well-being, which has not passed the significance test; while the financial inputs in agriculture and meteorology have relatively higher impacts on the whole basin and on the group with low disaster risk and low human well-being compared with other groups. Therefore, it is suggested that the negative impacts of drought and flood disasters can be mitigated through strengthening infrastructure construction, responding appropriately to climate change, avoiding disasters at the source of major projects and improving the disaster prevention and mitigation systems.

Evaluation of climate change effects on flood frequency in arid and semi-arid basins

Abstract Climate change (CC) will increase the intensity of extreme phenomena such as drought and flood in arid and semi-arid regions. This will cause the water supply of these areas to become very difficult in times of crisis. This study identifies sub-basins with high flood potential in the baseline period (1982–2005) and the future period (2025–2048) in the Hablehroud basin, north-central Iran. It uses the soil and water assessment tool (SWAT) and 23 coupled model intercomparison project 5 (CMIP5) general circulation models (GCMs). It estimates the instantaneous peak flow (IPF) and uses a flood index (FI) to determine the contributions of each sub-basin to the floods. The rainfall of the basin will increase by 11.5% under representative concentration pathway (RCP) 4.5 and 12.6% under RCP 8.5. The minimum daily temperature (Tmin) of the basin will increase by 0.8 °C under RCP 4.5 and 1.1 °C under RCP 8.5 in the future period. In addition, the maximum daily temperature (Tmax) will rise by 1 °C under RCP 4.5 and 1.2 °C under RCP 8.5. Moreover, basin runoff will increase by 6.4% under RCP 4.5 and 11.6% under RCP 8.5. The results indicate that the central and southern sub-basins made the most significant contribution to floods in the baseline period, while the eastern sub-basins will make the most considerable contribution to future floods.

Geochemistry of mantle source during the initial expansion and its implications for the opening of the South China Sea

The South China Sea (SCS) is the largest extensional basin in the western Pacific. Due to the lack of sampling appropriate seafloor rocks, few studies focused on magma evolution in the initial expansion of the SCS, which limits the understanding of the tecto-magmatic evolution of the SCS. Here, we analyzed whole-rock Sr-Nd-Pb-Hf isotopic compositions as well as major and trace element concentrations of basalts recovered from the International Ocean Discovery Program (IODP) Expedition 367 Site U1500B in the northern margin of the SCS, which represents the early-stage formed oceanic crust. Combining with published oceanic crust basalts (e.g., IODP Expedition 349 Site U1431 in the eastern sub-basin, Sites U1433 and U1434 in the southwestern sub-basin) formed in the late spreading, the mantle nature and its evolution during the expansion of the SCS were evaluated. Although Sr-Nd-Pb-Hf isotope compositions of these basalts from the SCS suggest an Indian-type mid-ocean ridge basalts (MORB) mantle, the northern margin basalts from Site U1500B show moderate Pb isotopic compositions between those from the eastern and southwestern sub-basin, suggesting a heterogeneous mantle source beneath the SCS. Modeling calculations based on Sr-Nd-Pb-Hf isotopic compositions show that different amounts of lower continental crust and Hainan plume can account for the heterogeneity of such Indian-type MORB mantle in the SCS. The difference in the involved enriched components in the mantle source might be related to the periodic expansion of the SCS. Based on the geochemical imprints of Hainan plume on the SCS basalts that formed in the initial and late spreading stage, we propose that Hainan plume has a great effect in triggering the opening of the SCS.

Fingerprinting the spatial sources of fine-grained sediment deposited in the bed of the Mehran River, southern Iran

Accurate information on the sources of suspended sediment in riverine systems is essential to target mitigation. Accordingly, we applied a generalized likelihood uncertainty estimation (GLUE) framework for quantifying contributions from three sub-basin spatial sediment sources in the Mehran River catchment draining into the Persian Gulf, Hormozgan province, southern Iran. A total of 28 sediment samples were collected from the three sub-basin sources and six from the overall outlet. 43 geochemical elements (e.g., major, trace and rare earth elements) were measured in the samples. Four different combinations of statistical tests comprising: (1) traditional range test (TRT), Kruskal–Wallis (KW) H-test and stepwise discriminant function analysis (DFA) (TRT + KW + DFA); (2) traditional range test using mean values (RTM) and two additional tests (RTM + KW + DFA); (3) TRT + KW + PCA (principle component analysis), and; 4) RTM + KW + PCA, were used to the spatial sediment source discrimination. Tracer bi-plots were used as an additional step to assess the tracers selected in the different final composite signatures for source discrimination. The predictions of spatial source contributions generated by GLUE were assessed using statistical tests and virtual sample mixtures. On this basis, TRT + KW + DFA and RTM + KW + DFA yielded the best source discrimination and the tracers in these composite signatures were shown by the biplots to be broadly conservative during transportation from source to sink. Using these final two composite signatures, the estimated mean contributions for the western, central and eastern sub-basins, respectively, ranged between 10–60% (overall mean contribution 36%), 0.3–16% (overall mean contribution 6%) and 38–77% (overall mean contribution 58%). In comparison, the final tracers selected using TRT + KW + PCA generated respective corresponding contributions of 1–42% (overall mean 20%), 0.5–30% (overall mean 12%) and 55–84% (overall mean 68%) compared with 17–69% (overall mean 41%), 0.2–12% (overall mean 5%) and 29–76% (overall mean 54%) using the final tracers selected by RTM + KW + PCA. Based on the mean absolute fit (MAF; ≥ 95% for all target sediment samples) and goodness-of-fit (GOF; ≥ 99% for all samples), GLUE with the final tracers selected using TRT + KW + PCA performed slightly better than GLUE with the final signatures selected by the three other combinations of statistical tests. Based on the virtual mixture tests, however, predictions provided by GLUE with the final tracers selected using TRT + KW + DFA and RTM + KW + DFA (mean MAE = 11% and mean RMSE = 13%) performed marginally better than GLUE with RTM + KW + PCA (mean MAE = 14% and mean RMSE = 16%) and GLUE with TRT + KW + PCA (mean MAE = 17% and mean RMSE = 19%). The estimated source proportions can help watershed engineers plan the targeting of conservation programmes for soil and water resources.

Modeling Carbon Budgets and Acidification in the Mediterranean Sea Ecosystem Under Contemporary and Future Climate

We simulate and analyze the effects of a high CO2 emission scenario on the Mediterranean Sea biogeochemical state at the end of the XXI century, with a focus on carbon cycling, budgets and fluxes, within and between the Mediterranean sub-basins, and on ocean acidification. As a result of the overall warming of surface water and exchanges at the boundaries, the model results project an increment in both the plankton primary production and the system total respiration. However, productivity increases less than respiration, so these changes yield to a decreament in the concentrations of total living carbon, chlorophyll, particulate organic carbon and oxygen in the epipelagic layer, and to an increment in the DIC pool all over the basin. In terms of mass budgets, the large increment in the dissolution of atmospheric CO2 results in an increment of most carbon fluxes, including the horizontal exchanges between eastern and western sub-basins, in a reduction of the organic carbon component, and in an increament of the inorganic one. The eastern sub-basin accumulates more than 85% of the absorbed atmospheric CO2. A clear ocean acidification signal is observed all over the basin, quantitatively similar to those projected in most oceans, and well detectable also down to the mesopelagic and bathypelagic layers.

Modified hydrologic regime of upper Ganga basin induced by natural and anthropogenic stressors

Climate change and anthropogenic activities pose serious threats to river basin hydrology worldwide. The Ganga basin is home to around half a billion people and has been significantly impacted by hydrological alterations in the last few decades. The increasing high-intensity rainfall events often create flash flooding events. Such events are frequently reported in mountainous and alluvial plains of the Ganga basin, putting the entire basin under severe flood risk. Further, increasing human interventions through hydraulic structures in the upstream reaches significantly alter the flows during the pre-and post-monsoon periods. Here, we explore the hydrological implications of increasing reservoir-induced and climate-related stressors in the Upper Ganga Basin (UGB), India. Flow/sediment duration curves and flood frequency analysis have been used to assess pre-and post-1995 hydrological behaviour. Our results indicate that low and moderate flows have been significantly altered, and the flood peaks have been attenuated by the operation of hydraulic structures in the Bhagirathi (western subbasin). The Alaknanda (eastern subbasin) has experienced an increase in extreme rainfall and flows post-1995. The downstream reaches experience reservoir-induced moderate flow alterations during pre-and post-monsoon and increasing extreme flood magnitudes during monsoon. Furthermore, substantial siltation upstream of the reservoirs has disrupted the upstream–downstream geomorphologic linkages.

Characterization of precipitation and recharge in the peripheral aquifer of the Salar de Atacama

To reduce uncertainty in the identification of the recharge areas in the Peripheral Aquifer of the Salar de Atacama (SdA), a few studies have investigated the isotopic characteristics and moisture sources of precipitation in the SdA basin. In the present study, the seasonal cycle of meteorological parameters and the relationships of this cycle with sea surface temperature anomalies are shown, the sources of humidity are identified, and the types of clouds producing precipitation are defined. Finally, the isotopic compositions of precipitation, surface water and groundwater in the SdA basin and the Altiplano-Puna Plateau basins are analysed to identify the area recharging the northern, eastern and southern subbasins of the SdA. In summer, when the highest temperature, relative humidity and precipitation values of the year are recorded, the precipitation is due to deep convection. The trajectories of the arriving air masses can be classified into three groups: from the North Atlantic Ocean across the Amazon basin, from the South Atlantic Ocean across the La Plata River basin and the Gran Chaco, and from the Pacific Ocean. In winter, when the temperature, relative humidity and precipitation are lower, the moisture masses come from the Pacific Ocean. Winter precipitation is more depleted in heavy isotopes than summer precipitation. The isotopic analysis of precipitation, surface water and groundwater shows that recharge of the eastern subbasins of the SdA occurs by diffuse infiltration of precipitation and concentrated infiltration of surface water, both within the hydrographic basin of the SdA. The meteoric source of the waters in the Altiplano-Puna Plateau basins is isotopically lighter than the waters found in the side basins of the SdA, so there is no significant water quantity transfer to the peripheral aquifers of the SdA from outside the hydrographic basin.

Recent morpho-sedimentary processes in Dove Basin, southern Scotia Sea, Antarctica: A basin-scale case of interaction between bottom currents and mass movements

Multibeam bathymetric imagery and acoustic sub-bottom profiles are used to reveal distribution patterns of sub-surface sedimentation in Dove Basin (Scotia Sea). The goals of the study are to determine the imprint of the inflow of deep Antarctic water masses from the Weddell Sea into the Scotia Sea, to establish the factors driving the styles of contourite deposition and to discern the relative contribution of alongslope versus downslope processes to the construction of the uppermost late Quaternary sedimentary record in the basin.The most significant morpho-sedimentary features in Dove Basin are linked to contouritic processes and to mass movements. Plastered drifts on the flanks of the basin constitute the most common contouritic deposits. Basement-controlled drifts on top of structural elevations are common along the central ridge, the central basin plain and scattered along the basin flanks. Sheeted drifts occur on top of adjacent banks or are restricted to the deep basin. In contrast, mounded drifts are poorly represented in Dove basin. A laterally extensive contouritic channel runs along the central ridge. Contouritic channels are also identified in the upper parts of the lateral banks and slopes. Numerous slide scars along the upper parts of the slopes evolve downslope into semitransparent lens-shaped bodies, with occasional development of across-slope channels. Semitransparent lenses occur intercalated within stratified deposits in the slopes of the basin, in the central ridge and in the deepest basin plain.The spatial arrangement of contouritic morphologies points to the influence of the water column structure and the basin physiography. In the eastern sub-basin, two different fractions (lower and upper) of Weddell Sea Deep Water (WSDW) leave an imprint on contourite deposits owing to the sloping interface between the two fractions. Contouritic influence is more subdued in the western sub-basin, and limited to the imprint of the lower WSDW. The upper parts of the surrounding banks are under the influence of deep-reaching Circumpolar waters (i.e., Lower Circumpolar Deep Water), which develops both depositional and erosional morphologies. The cross-section V-shaped morphology of the basin and the common occurrence of structural highs drive the predominance of plastered and basement-controlled drifts in the sediment record. The frequent alternation between contourites and downslope gravity-flow deposits is likely due to different processes associated with over-steepening in the basin, such as basement-controlled steep slopes, deformed drifts atop basement elevations, and the development of thick contouritic piles. Dove Basin is an example of a basin without mounded, plastered or mixed hybrid drifts in the transition between the lower slope and the deep basin, because the upper boundary of the deepest water mass —the Weddell Sea Deep Water— flows shallower along the middle slope. This fact underlines the relevance of the position and depth of water masses in shaping the morphology of the feet of slopes along continental margins.

Contrasted Chemical Weathering Rates in Cratonic Basins: The Ogooué and Mbei Rivers, Western Central Africa

Despite the absence of tectonic activity, cratonic environments are characterized by strongly variable, and in places significant, rock weathering rates. This is shown here through an exploration of the weathering rates in two inter-tropical river basins from the Atlantic Central Africa: the Ogooué and Mbei River basins, Gabon. We analyzed the elemental and strontium isotope composition of 24 water samples collected throughout these basins. Based on the determination of the major element sources we estimate that the Ogooué and Mbei rivers total dissolved solids (TDS) mainly derive from silicate chemical weathering. The chemical composition of the dissolved load and the area-normalized solute fluxes at the outlet of the Ogooué are similar to those of other West African rivers (e.g., Niger, Nyong, or Congo). However, chemical weathering rates (TZsil+rate expressed as the release rate of the sum of cations by silicate chemical weathering) span the entire range of chemical weathering intensities hitherto recorded in worldwide cratonic environments. In the Ogooué-Mbei systems, three regions can be distinguished: (i) the Eastern sub-basins draining the Plateaux Batéké underlain by quartz-rich sandstones exhibit the lowestTZsil+rates, (ii) the Northern sub-basins and the Mbei sub-basins, which drain the southern edge of the tectonically quiescent South Cameroon Plateau, show intermediateTZsil+rates and (iii) the Southern sub-basins characterized by steeper slopes record the highestTZsil+rates. In region (ii), higher DOC concentrations are associated with enrichment of elements expected to form insoluble hydrolysates in natural waters (e.g., Fe, Al, Th, REEs) suggesting enhanced transport of these elements in the colloidal phase. In region (iii), we suggest that a combination of mantle-induced dynamic uplift and lithospheric destabilization affecting the rim of the Congo Cuvette induces slow base level lowering thereby enhancing soil erosion, exhumation of fresh primary minerals, and thus weathering rates. The study points out that erosion of lateritic covers in cratonic areas can significantly enhance chemical weathering rates by bringing fresh minerals in contact with meteoric water. The heterogeneity of weathering rates amongst cratonic regions thus need to be considered for reconstructing the global, long-term carbon cycle and its control on Earth climate.

The Continental Intercalaire groundwaters of the Tidikelt (In-Salah region, Algeria). Hydrochemical and isotopic features

ABSTRACT The Continental Intercalaire (CI) groundwaters of the Tidikelt (In-Salah region) are characterized by a high salinity and ion concentrations higher than the maximum standards for drinkability. The total dissolved solids range from 850 to 3390 mg L–1 for conductivities ranging from 1470 to 6780 μS cm–1. Their chemical facies is dominated by Cl–, SO4 2– and Na+, respectively. Alkali ions, Cl– and SO4 2– are acquired through the dissolution of Halite (NaCl) and Gypsum (CaSO4, 2H2O). CI waters have depleted δ values for 18O and 2H, corresponding to a cold end-member. This is an indication of a very homogeneous aquifer which is similar to what was observed for the CI in the eastern sub-basin (Great Oriental Erg) and for palaeowaters elsewhere in the Middle-East and Libya. Tritium analyses show that these waters are all very weakly tritiated, which is a testimony of the non-renewed character for these waters. Both δ 13C and 14C measured on more than a dozen of samples also show that CI groundwaters are old, with ages comprised between 19,000 and 35,000 years with an average δ 13C of –10 ‰. This means that these waters are derived from old precipitation whose features were totally different from the very scarce prevailing ones.

Response of non-point source pollution to landscape pattern: case study in mountain-rural region, China.

Landscape patterns have a substantial effect on non-point source (NPS) pollution in watersheds. Facilitating sustainable development of mountain-rural areas is a major priority for China. Knowledge of the impacts of various landscapes on water quality in these areas is critical to meeting environmental goals. This study applied the Soil and Water Assessment Tool (SWAT) to create a hydrologic and water quality model of the study watershed; then, the relationship between water quality and landscape patterns was investigated using multiple linear regression and redundancy analysis. The results show that the western sub-basins had higher nitrogen pollution loads, and the total nitrogen concentration reached a maximum value of 3.91 mg/L; the eastern sub-basins had a higher pollution load of phosphorous featured by maximum total phosphorous concentration of 2.15 mg/L. The water quality of the entire watershed in all scenarios tended to deteriorate over time. Landscape metrics accounted for 81.7% of the total variation in pollutant indicators. The percentage of forest landscape was negatively correlated with NPS pollution, while other types of landscape showed a positive correlation. The patch density, landscape shape index, and largest patch index of urban and agricultural lands were negatively correlated with pollutant concentrations. Upland landscapes contributed more pollutants than paddy fields. Some measures, e.g., returning grassland and farmland to forest in steep regions and replacing upland crops with paddy fields, were recommended for mitigating NPS pollution in the study watershed.

Structural interpretation of the Beetaloo Sub-basin, NT from nonseismic geophysical data

The Beetaloo Sub-basin is known for its vast unconventional hydrocarbon resources even though it is relatively underexplored. There is reasonably good coverage of 2D seismic within the sub-basin which is used as the basis for most structural interpretations. However, seismic quality varies, and it is occasionally deteriorated by the presence of basalts from the Kalkarindji suite and the karstic nature of the Gum Ridge formation. Aeromagnetic data, constrained by petrophysical logs are used, to map faults in the basalts of the Kalkarindji suite and their lateral extent to the South and the East of the sub-basin. The same structural elements are identified in the full tensor gravity gradiometry data. The top of this unit is observed in the electrical conductivity profiles, derived from Tempest data, in the NW part of the eastern sub-basin.