Starting from traditional ideas on the climatic steering of fluvial system dynamics, it appears that there are different kinds of climatic influences on system dynamics. They vary from direct ...climatic forcing (like peak precipitation) to indirect (like permafrost) and partial forcing (like vegetation). Vegetation (or its absence), and not directly climate, is considered as the main cause of fluvial incision (or deposition) during temperate (or cold) periods. However, other external factors than climate and non-climatic factors, such as local basin characteristics (like subsoil lithology and relief), express their effects on the fluvial systems by their role in the energy balance of the river catchment. Finally, internal factors in fluvial system evolution (like thresholds and response time) should not be neglected.
A previously established non-linear theory of river cyclicity as a response to climate change states that short phases of fluvial instability occur both at the transition from relatively warm ...(temperate) to cold (periglacial) and from relatively cold to warm periods. Such instability typically starts with vertical erosion, successively followed by sedimentary fill of the erosive scar. In spite of frequent confirmation of this theory by geomorphological reconstructions, a few problems arise. First, there are fewer incision phases than climatic transitions. Secondly, remnants of erosion at ‘cold–warm’ transitions are scarce, in contrast to obvious erosion relics at ‘warm–cold’ transitions. Furthermore, it appears that the incision style is strikingly different at both kinds of climatic transitions. Similarly, the long stable phases are also expressed in terms of different floodplain development in cold and warm periods. These arguments require a modification of the general non-linear theory.
At the transition from relatively temperate to colder conditions, rivers transformed gradually from a regular, low-energy, single-channel course to a periodically high-energy, multi-channel type. The latter (braided) type is characterized by intense lateral movement, rather than by deep vertical erosion. This results in a well-expressed morphology of wide, extensive floodplains and terraces. In contrast, the linear and constrained, meandering channels incise with small width–depth ratio and build floodplains of limited lateral extent. Consequences are twofold: 1) the spatial limitation of the deeply incised, meandering valleys at the beginning of warm periods counts against their recognition; 2) relatively strong, lateral migration of the braided rivers removes most traces of previous (meandering) systems, which contrasts with the limited lateral activity of confined meandering channels. It means that in a ‘warm–cold–warm’ alternation generally only one phase of vertical erosion is preserved, the one that is caused by the high-energy, braided river at the start of the cold period.
The extent to which river processes and morphology are dependent on climate is an old question. When looking at large time scales climatic cyclicity seems to coincide with alternating events in ...fluvial development. However, the shorter the time scales at which fluvial development is considered, the more it is difficult to find a close correspondence with climate evolution. Ultimately, it appears that the response time of river processes to climatic change may restrict the sensitivity of the fluvial systems to adapt to short climatic oscillations. The impact of climate on fluvial systems is largely transferred to these systems by the climate-determined soil cohesion and peak discharges. The latter factors are especially related to vegetation cover and permafrost conditions. Finally, a number of basin characteristics are discussed that demonstrate that fluvial systems are not completely controlled by climate.
The strong present-day Asian monsoons are thought to have originated between 25 and 22 million years (Myr) ago, driven by Tibetan-Himalayan uplift. However, the existence of older Asian monsoons and ...their response to enhanced greenhouse conditions such as those in the Eocene period (55-34 Myr ago) are unknown because of the paucity of well-dated records. Here we show late Eocene climate records revealing marked monsoon-like patterns in rainfall and wind south and north of the Tibetan-Himalayan orogen. This is indicated by low oxygen isotope values with strong seasonality in gastropod shells and mammal teeth from Myanmar, and by aeolian dust deposition in northwest China. Our climate simulations support modern-like Eocene monsoonal rainfall and show that a reinforced hydrological cycle responding to enhanced greenhouse conditions counterbalanced the negative effect of lower Tibetan relief on precipitation. These strong monsoons later weakened with the global shift to icehouse conditions 34 Myr ago.
Gastric sensorimotor dysfunction, psychosocial factors and somatisation are all implicated in symptom generation in functional dyspepsia (FD).
To determine the relative contribution of each of these ...factors to overall dyspeptic symptom severity and weight loss in FD.
In 201 consecutive tertiary care patients with FD (mean age 40.1 (SD 12.6) years), gastric sensorimotor function was studied using barostat (sensitivity, compliance and accommodation). Psychosocial factors (depression and anxiety disorders, positive and negative affect, perceived stress, alexithymia and history of abuse), somatisation and co-morbid irritable bowel syndrome (IBS) and chronic fatigue symptoms were assessed using self-report questionnaires. Variables were correlated with dyspepsia symptom severity (DSS) and weight loss. Hierarchical multiple linear regression was used to identify determinants of DSS and weight loss.
Multiple linear regression identified the following determinants of DSS: gastric sensitivity (beta = 0.77, p = 0.25), depression (beta = 0.12, p = 0.06) and somatisation (beta = 0.48, p<0.0001) (controlling for age and occupation, R(2) = 0.29, p<0.0001). The effect of depression on DSS is partially mediated by somatisation. Gastric sensitivity (beta = 2.87, p = 0.08), history of childhood sexual abuse (beta = 9.37, p = 0.0006), depression (beta = 0.19, p = 0.24) and somatisation (beta = 0.67, p = 0.01) are independent determinants of weight loss (controlling for gender and occupation, R(2) = 0.42, p<0.0001). The effect of depression on weight loss is fully mediated by somatisation.
Symptom severity and weight loss in FD are determined by psychosocial factors (depression, abuse history) and somatisation, and only to a lesser extent by gastric sensorimotor function. The importance of psychosocial factors and somatisation compared to gastric sensorimotor function is most pronounced in hypersensitive patients.
The aim of this paper is to investigate the morphological implications of the interplay between tectonic movements at different rates, timescales, and spatial extent in a catchment of intermediate ...size, the Huang Shui River (a main tributary of the Yellow River in the NE Tibet Plateau). River incision started from a peneplain-like surface that developed in post-Miocene–Pliocene times. At the end of the Tertiary, a general tectonic uplift of the Tibetan Plateau initiated river incision. This general uplift also caused local fragmentation of the Huang Shui catchment into blocks (kilometers or maximally, a few tens of kilometers) of local extent that have subsided and/or uplifted relative to one another. Fluvial deposition of >
30
m in the subsiding blocks contrasts with erosion and formation of gorges in the uplifted blocks. Incision into the former peneplain was not continuous but a staircase of terraces developed under climatic influences. Terrace deposits are sometimes capped by interglacial soils or soil-derived material. Apparently, terrace incision occurred at the transition to the next cold period. The different rates of uplift and subsidence of the individual blocks resulted in the simultaneous development of erosion and accumulation terraces of different sizes within the same catchment, even within the same tectonic block. This makes it impossible to connect the terraces of the different blocks, except for the three youngest terraces (representing the last 300,000
years), thus illustrating the uniform tectonic history of the catchment since that time.
► Complex morphological impact of tectonic fragmentation in one drainage basin. ► Thick fluvial deposits in subsided blocks contrast with gorges in uplifted blocks. ► Main terrace incision occurs at interglacial–glacial transition. ► The general uplift of the Tibetan Plateau induced overall river incision. ► A terrace staircase, due to climate change, overprints general tectonic uplift.
High-resolution continuous core material, geophysical measurements, and hundreds of archived core descriptions enabled to identify 13 Late Pleistocene Rhine-Meuse sedimentary units in the infill of ...the southern part of the North Sea basin (the Netherlands, northwestern Europe). This sediment record and a large set of Optical Stimulated Luminescence dates, 14C dates and biostratigraphical data, allowed to establish detailed relationships between climate change, sea-level oscillation, glaciation history and the sedimentary development of the Rhine fluvial system during the last glacial cycle (Marine Isotope Stages 5e-2, Eemian-Weichselian). A well-preserved Eemian sediment record was encountered as the infill of a Late Saalian (MIS6) subglacial basin. Part of this record reflects groundwater rise controlled (fine-grained) sedimentation as a result of postglacial (early) Eemian sea-level rise. It shows strong analogy to developments known from the Holocene Rhine-Meuse delta. Outside of the glacial depressions near coastal deposits are only fragmentarily preserved. The Early Glacial Rhine sediment record is dominated by organic debris and peat layers, marking landscape stability and low fluvial activity. Part of this record may have been formed under near coastal conditions. Significant amounts of reworked marine biomarkers in the lag-deposits of Early Pleniglacial (MIS4) fluvial systems indicate that this period is characterized by extensive reworking of older (MIS5) near-coastal sediments. Despite the marked Early Pleniglacial climatic cooling, input of new sediment from the drainage basin was relatively low, a feature that is related to the presence of regolith protective relic soil complexes in the basin. During the early Middle Pleniglacial, a major Rhine avulsion indicates the system was in an aggrading mode and that sediment supply into the lower reaches of the Rhine had strongly increased. This increase in sediment supply coincided with the timing of major climate cooling that occurred from ∼50 to 45ka onwards. The increase in sediment supply is related to final breakup of the soil complexes in the drainage basin. After ∼24ka, a strong input of coarse-grained gravelly sediments was observed which indicates a strong increase in physical weathering processes and periglacial-controlled supply of bedload sediment in the catchment. A time delay between climate change (∼30ka) and channel belt aggradation (<24ka), is explained as a result of transport path length between source and sink and/or effects of higher continental runoff rates after 22ka. The Late Middle Pleniglacial, Late Pleniglacial and Lateglacial Rhine-Meuse record testifies for strong influence of glacio-isostatic-controlled differential upwarping of the study area. Glacio-isostatic-controlled forebulge upwarping and lateral valley tilting is shown to have deflected Rhine-Meuse channel belts after 35ka. Glacio-isostatic upwarping is seen as the main cause for strong incision during the first phase of the Late Pleniglacial (30–24ka). At later stage glacio-isostatic-controlled incision was overruled due to high climate-controlled sediment input from the catchment and probably initial glacio-isostatic subsidence. Migration of channel belts towards the direction of the former centre of glacio-isostatic uplift indicates that glacio-isostacy influenced Rhine-Meuse paleogeography until far into the Lateglacial.
Background Previous work indicated that psychosocial factors (depression and somatization) are more strongly associated with symptom severity and weight loss in functional dyspepsia (FD) than ...gastric sensorimotor function. However, there is conflicting evidence regarding the association of these etiopathogenetic factors with Rome III symptom‐based subgroups in FD epigastric pain syndrome (EPS), postprandial distress syndrome (PDS). We aimed to test whether gastric sensitivity and emptying, depression, and somatization are differentially associated with empirically derived functional gastroduodenal disorders (FGD) symptom factors in one comprehensive model.
Methods In 259 tertiary care FD patients, we studied gastric sensorimotor function with barostat and gastric emptying breath test. Depression, somatization, and FGD symptoms were measured using self‐report questionnaires. Confirmatory factor analysis (CFA) on 7 FGD symptoms was used to determine the fit of a latent variable structure based on Rome III symptom‐based subgroups. Structural equation modeling (SEM) was used to test the putative relationships of the symptom factors with gastric sensorimotor function, depression, and somatization.
Key Results The results of the CFA show a good fit Cmin/DF = 1.54, CFI(comparative fit index) = 0.97 for the three‐factor solution based on Rome III subgroups. The SEM also fitted the data well (Cmin/DF = 1.24, CFI = 0.98) and demonstrated that gastric sensitivity and depression are associated with PDS and nausea and vomiting. Gastric emptying is uniquely associated with EPS and somatization is strongly associated with all three symptom factors.
Conclusions & Inferences Confirmatory factor analysis confirms the existence of three FGD symptom factors, corresponding to Rome III symptom‐based subgroups. The SEM results suggest that different psychobiological mechanisms may play a role in these subgroups.
In the long term (glacial/interglacial sequences), river development follows general climatic evolution. However, at the scale of one cold-warm cycle, it appears that the geomorphological effect of ...river activity is best expressed at times of climatic change. Such periods of pronounced fluvial action last only a short time. In more detail, the internal evolution in a drainage basin after a climatic event results in a delayed response of the morphology and sedimentation pattern. Finally, on the shortest timescale local thresholds may play a decisive role in the reactions of river systems. It is concluded that the relation between fluvial development and climate is not a simple one, but is fundamentally dependant on the timescale.
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