Hothouse Hydrology: Evolving River Dynamics in the Eocene Montllobat and Castissent Formations, Southern Pyrenees

Slip slidin' away: A post-glacial environmental history of the Waipaoa River basin

Abstract. The sensitivity of fluvial systems to tectonic and climatic boundary conditions allows us to use the geomorphic and stratigraphic records as quantitative archives of past climatic and tectonic conditions. Thus, fluvial terraces that form on alluvial fans and floodplains as well as the rate of sediment export to oceanic and continental basins are commonly used to reconstruct paleoenvironments. However, we currently lack a systematic and quantitative understanding of the transient evolution of fluvial systems and their associated sediment storage and release in response to changes in base level, water input, and sediment input. Such knowledge is necessary to quantify past environmental change from terrace records or sedimentary deposits and to disentangle the multiple possible causes for terrace formation and sediment deposition. Here, we use a set of seven physical experiments to explore terrace formation and sediment export from a single, braided channel that is perturbed by changes in upstream water discharge or sediment supply, or through downstream base-level fall. Each perturbation differently affects (1) the geometry of terraces and channels, (2) the timing of terrace cutting, and (3) the transient response of sediment export from the basin. In general, an increase in water discharge leads to near-instantaneous channel incision across the entire fluvial system and consequent local terrace cutting, thus preserving the initial channel slope on terrace surfaces, and it also produces a transient increase in sediment export from the system. In contrast, a decreased upstream sediment-supply rate may result in longer lag times before terrace cutting, leading to terrace slopes that differ from the initial channel slope, and also lagged responses in sediment export. Finally, downstream base-level fall triggers the upstream propagation of a diffuse knickzone, forming terraces with upstream-decreasing ages. The slope of terraces triggered by base-level fall mimics that of the newly adjusted active channel, whereas slopes of terraces triggered by a decrease in upstream sediment discharge or an increase in upstream water discharge are steeper compared to the new equilibrium channel. By combining fill-terrace records with constraints on sediment export, we can distinguish among environmental perturbations that would otherwise remain unresolved when using just one of these records.

River discharge patterns are sensitive to changing precipitation as a result of evolving climates. In stratigraphy, the intermittency factor (If) of ancient rivers can help illuminate landscape dynamics in the past. The If is recorded in the geologic archive as the ratio of average transport rates (from long-term records of water or sediment flux) versus instantaneous maximum transport capacities if they were to be sustained over the same period, and applying intermittency calculations to stratigraphy can reveal how rivers and landscapes recorded and responded to external tectono-climatic forcings. Here we explore the Lower Eocene Castissent Formation of the Southern Pyrenees, Spain, a strongly progradational fluvio-deltaic succession deposited during the Early Eocene Climatic Optimum (EECO), an intense warm period analogous to potential future climate scenarios. We first reconstruct the depositional volumes of the Castissent Formation in the Tremp-Graus Basin and its equivalent marine successions in the Ainsa and Jaca Basins. We then compare these to estimates of instantaneous water and sediment fluxes using field-based quantitative palaeohydrology approaches.  From these reconstructions, we derive fluvial intermittency factors which we compare to river data for a range of climate conditions. Further, we present detailed reconstructions of morphodynamics in these lower Eocene rivers during the EECO. These results add to growing understanding of intermittency in the geologic past, and reveal the sensitivity of rivers and landscapes to climate forcing in a warm world analogue.  

Global suspended sediment and water discharge dynamics between 1960 and 2010: Continental trends and intra-basin sensitivity

Current climatic warming is causing accelerated melt of the Greenland Ice Sheet. Whilst the changing hydrological response is well known, the sediment export as well as the geomorphic changes in the proglacial area remain uncertain.  Here we present records of sediment transport from melt seasons 2022 and 2023 in the proglacial area of Leverett glacier, a land terminating glacier outlet on the Western part of the Greenland Ice Sheet. The proglacial area here is very well denifed by a waterfall cutting through bedrock functioning as terminal gauge, which allows for the installation of hydrological stations. These hydrological gauging stations, containing turbidity and pressure sensors, allow for estimation of discharge and suspended sediment concentrations over the melt season. Variations in bedload transport can be analysed using the sesimic data obtained from the geophones placed on the river bank close to the hydrological gauging stations. To convert the recorded seismic data into bedload flux, a Fluvial Inversion Model is used, which is calibrated using active seismics surveys and the water stage data from the hydrological gauging stations.The dataset allows us to investigate the relationships between bedload, suspended sediment, and water discharge from the Leverett glacier as well as sediment transport and deposition in the proglacial area. We observe several spring events in the first half of July, where suspended sediment concentration and water discharge increase simultaneously at the start of the melt season. During the first half of August, we observe a clear dilution signal, where increase in water discharge coincides with a decrease in suspended sediment concentration From insights about the relationship between water and sediment discharge from the ice sheet, we can speculate about the sediment export response to increased water discharge from the Ice Sheet.

Design and optimization of bilayer structure in metal foam flow field for proton exchange membrane fuel cell

Abstract. The Hoa Binh dam (HBD), located on a tributary of the Red River in Vietnam, has a capacity of 9.45 × 109 m3 and was commissioned in December 1988. Although it is important for flood prevention, electricity production and irrigation in northern Vietnam, the Hoa Binh dam has also highly influenced the suspended sediment distribution in the lower Red River basin, in the delta and in the coastal zone. Its impact was analysed from a 50-year data set of water discharge and suspended sediment concentration (1960–2010), and the distribution of water and sediment across the nine mouths of the delta was simulated using the MIKE11 numerical model before and after the dam settlement. Although water discharge at the delta inlet decreased by only 9%, the yearly suspended sediment flux dropped, on average, by 61% at Son Tay near Hanoi (from 119 to 46 × 106 t yr−1). Along the coast, reduced sedimentation rates are coincident with the lower sediment delivery observed since the impoundment of the Hoa Binh dam. Water regulation has led to decreased water discharge in the wet season (−14% in the Red River at Son Tay) and increased water discharge in the dry season (+12% at the same station). The ratios of water and suspended sediment flows, as compared to the total flows in the nine mouths, increased in the northern and southern estuaries and decreased in the central, main Ba Lat mouth. The increasing volume of dredged sediments in the Haiphong harbour is evidence of the silting up of the northern estuary of Cam–Bach Dang. The effect of tidal pumping on enhanced flow occurring in the dry season and resulting from changed water regulation is discussed as a possible cause of the enhanced siltation of the estuary after Hoa Binh dam impoundment.

We examined the connection between descent of European silver eels (Anguilla anguilla) and water discharge, water temperature, turbidity, photoperiod, light intensity, and moon phase based on 10 yr of field data and field experiments. The eel migration takes place between August and December, and mean water temperature for July–August and mean water discharge for August–October explained 91% of the total variation in the start of the yearly silver eel run. Low mean water temperatures during July–August and high mean water discharge during August–October resulted in an early start of the yearly silver eel run, whereas high mean water temperature and low water discharge gave the opposite effect. There was no significant correlation between the duration of the entire yearly silver eel run and the environmental variables investigated. But the duration of a part of the run, e.g. number of days from 5 to 25% cumulative eel descent, was significantly correlated with mean water temperature and increase in water discharge for the period in question (R2 = 0.84). Maximum silver eel descent was at a water temperature of 9 °C. Few silver eels descended at temperatures below 4 °C or above 18 °C. The migration speed of transplanted silver eels in the River Imsa was correlated with water discharge and water temperature (R2 = 0.88). Water discharge alone explained 85% of the total variation in migration speeds. The recapture rate of silver eels transplanted within the River Imsa was highest at 9 °C and decreased at higher and lower temperatures (R2 = 0.95). Illumination of 20 lx upon the river reduced the descent of silver eels.

Via the valuable opportunity of the Three Gorges Reservoir (TGR) 135-m filling in June 2003, the Yangtze discharge and suspended sediment concentration (SSC) entering the estuary during the period from 15 May to 15 July 2003 were analyzed to examine the instant effects of the filling on them. The Yangtze discharge and SSC entering the estuary in the periods before, during and after the filling clearly indicated three phases: 1) the pre-storage phase characterized by natural conditions, in which the SSC increased with increasing water discharge; 2) the storage phase, during which the SSC decreased dramatically with decreasing water discharge; and 3) the post-storage phase, during which both the SSC and water discharge remained at relatively low levels first until the end of June, then the SSC increased gradually with increasing water discharge. It seems that the times for the instant effects of the decreasing discharge downstream from the upper Yangtze on the Yangtze discharge and SSC entering the estuary due to the TGR 135-m filling to take place were about 5 d and 1 d respectively, while both were about 18 d for those of the increasing discharge. This probably reflects the buffering and resultantly hysteresis of the 1800-km stretch from the upper Yangtze to the estuary. The results are helpful for scientific and hydrological investigation of the Yangtze mainstream downstream from the TGR Dam and of the estuarine and adjacent coastal waters.

The sediment detachment-transport coupling concept is widely used in soil erosion prediction models including WEPP (Water Erosion Prediction Project), EUROSEM (European Soil Erosion Model), LISEM (Limburg Soil Erosion Model) and KINEROS2 (Kinematic Wave Overland Flow, Channel, Routing and Erosion Model). Sediment transport capacity is one of the key values in this concept, which impacts the prediction of sediment detachment, transport, and deposition. Therefore, it is essential to obtain more reliable transport capacity predictions for better soil erosion modeling based on the sediment detachment-transport coupling concept. Sediment transport capacity is the equilibrium sediment transport rate under steady-state conditions. When measuring transport capacities in the lab, most previous studies considered surface hydrologic impacts alone. However, the impacts of subsurface hydrology on sediment transport cannot be ignored in the real world. The downward infiltration under drainage conditions and the upward exfiltration under seepage conditions introduce opposite forces on sediment particles, and influence soil strength and water discharge which may affect transport capacity. A series of experiments were carried out with a relatively uniform sand and an Opal clay soil using four water discharges at three slope gradients. The flume contained four rills with slope lengths of 0.5, 1.0, 2.0 and 3.0 m (Figure 1). Four different subsurface hydrologic conditions were studied including free drainage, saturation, 5 cm seepage head and 10 cm seepage head. By introducing sediment at the top of the flume at different rates, sediment transport capacities were measured under both detachment-limited and transport-limited conditions. The determination of transport capacity was based on the spatial changes of sediment transport as slope length increased and the elevation changes of the erodible bed surface. The results indicated that there was only one equilibrium sediment transport value for a given surface and subsurface hydrologic condition, given similar observations were obtained under detachment-limited and transport-limited conditions. The critical shear stress decreased 20% from the drainage to the saturation condition, and decreased slightly from saturation to the seepage condition. Measured transport capacities increased from drainage to saturation conditions (Figure 2), and increased slightly from saturation to seepage conditions, which was the result of decreased soil strength and increased water discharge. The impacts of subsurface hydrology on transport capacity increased as water discharge and slope steepness increased. Dramatic increases of transport capacities were obtained for the greatest water discharge and steepest slope in this study when subsurface hydrologic condition changed from free drainage to saturation. The differences in transport capacities between saturation and seepage conditions were relatively stable for all considered water discharges and slopes. This study improves the estimation of transport capacity by introducing the subsurface hydrologic impacts, and the sediment transport capacity predictions were examined with various water discharges, slopes, and subsurface hydrologic conditions.

The sediment detachment-transport coupling concept is widely used in soil erosion prediction models including WEPP (Water Erosion Prediction Project), EUROSEM (European Soil Erosion Model), LISEM (Limburg Soil Erosion Model) and KINEROS2 (Kinematic Wave Overland Flow, Channel, Routing and Erosion Model). Sediment transport capacity is one of the key values in this concept, which impacts the prediction of sediment detachment, transport, and deposition. Therefore, it is essential to obtain more reliable transport capacity predictions for better soil erosion modeling based on the sediment detachment-transport coupling concept. Sediment transport capacity is the equilibrium sediment transport rate under steady-state conditions. When measuring transport capacities in the lab, most previous studies considered surface hydrologic impacts alone. However, the impacts of subsurface hydrology on sediment transport cannot be ignored in the real world. The downward infiltration under drainage conditions and the upward exfiltration under seepage conditions introduce opposite forces on sediment particles, and influence soil strength and water discharge which may affect transport capacity. A series of experiments were carried out with a relatively uniform sand and an Opal clay soil using four water discharges at three slope gradients. The flume contained four rills with slope lengths of 0.5, 1.0, 2.0 and 3.0 m (Figure 1). Four different subsurface hydrologic conditions were studied including free drainage, saturation, 5 cm seepage head and 10 cm seepage head. By introducing sediment at the top of the flume at different rates, sediment transport capacities were measured under both detachment-limited and transport-limited conditions. The determination of transport capacity was based on the spatial changes of sediment transport as slope length increased and the elevation changes of the erodible bed surface. The results indicated that there was only one equilibrium sediment transport value for a given surface and subsurface hydrologic condition, given similar observations were obtained under detachment-limited and transport-limited conditions. The critical shear stress decreased 20% from the drainage to the saturation condition, and decreased slightly from saturation to the seepage condition. Measured transport capacities increased from drainage to saturation conditions (Figure 2), and increased slightly from saturation to seepage conditions, which was the result of decreased soil strength and increased water discharge. The impacts of subsurface hydrology on transport capacity increased as water discharge and slope steepness increased. Dramatic increases of transport capacities were obtained for the greatest water discharge and steepest slope in this study when subsurface hydrologic condition changed from free drainage to saturation. The differences in transport capacities between saturation and seepage conditions were relatively stable for all considered water discharges and slopes. This study improves the estimation of transport capacity by introducing the subsurface hydrologic impacts, and the sediment transport capacity predictions were examined with various water discharges, slopes, and subsurface hydrologic conditions.

The El Niño Southern Oscillation (ENSO) during the Early Eocene Climatic Optimum (EECO, 56–48 million years ago) is investigated using a multi-model ensemble of deep-time climate simulations. We reveal that ENSO sea surface temperature variability during the EECO had significantly longer periodicity and stronger amplitude than present-day conditions. These changes are attributed to intensified ocean-atmosphere feedback processes and enhanced in-phase tropical inter-basin interactions within a broader ocean basin compared to the present-day. Sensitivity experiments in coupled ocean-atmosphere models suggest that tectonic changes, particularly the expansion of the tropical ocean basin, play a dominant role in amplifying ENSO variability and extending its periodicity, while stronger inter-basin connections further enhance ENSO amplitude. Elevated atmospheric CO2 levels, though driving substantial mean-state changes, partially offset the tectonic influence on ENSO variability by modifying feedback processes. These findings underscore the role of tropical ocean basin geometry and atmospheric CO2 levels in shaping ENSO variability, offering insights into past climate dynamics and implications for future projections under sustained global warming.

Fluvial-system response to climate change: The Paleocene-Eocene Tremp Group, Pyrenees, Spain

The study of Eocene deposits from the Dinaric foreland basin (Outer Dinarides, eastern Adriatic coast) documents a 300 m thick sequence of shallow-water carbonates originated on ramps that formed intermittently during the tectonic evolution of the basin. During the intense tectonic activity in this area, global sea-level changes, and warming events occurred (Early Eocene Climatic Optimum, EECO, Late Lutetian Thermal Maximum, LLTM and Middle Eocene Climatic Optimum, MECO). Up to 60% of all skeletal debris in these carbonates are larger benthic foraminifera (LBF). Ramp successions are rarely complete in terms of inner-, mid- and outer-ramp environments (availability of suitable benthic habitats for different LBF group) and very often stratigraphically incomplete. The LBF rich deposits document three distinctive groupings: i) the post - PETM phase (SBZ4 - SBZ10); ii) the EECO phase (from pre - to post - EECO phase, SBZ 10/11 - SBZ12/13); and iii) the late post - EECO phase including short-lived LLTM (SBZ13 - SBZ17). The studies of the dominant LBF (Drobne & Ćosović, 2009, 2010; Drobne et al., 2011; Pavlovec, 2012), showed no significant generic and species diversity across the foreland basin, from SBZ4 to SBZ17, but differences in species richness were found. The LBF assemblages included representatives of alveolinids, nummulitids, complex miliolids, conical agglutinated foraminifera, orthophragiminids, encrusting foraminifera and larger rotaliids. For this study, the diversity of the genera Alveolina, Assilina, Nummulites and conical foraminifera and complex miliolids was compared. The post-PETM stage showed similar species diversity of Alveolina, Nummulites, and Assilina (14-18-16) in contrast to the presence of three species of complex miliolids. In the EECO stage, representatives of Nummulites (32 species) were preferred over eighteen species of Alveolina, while the low species diversity showed conical foraminifera (8 species), Assilina (5 species) and complex miliolids (4 species). In the post - EECO and LLTM stages, Nummulites species were most abundant (39 species), Assilina less abundant (16 species), while the diversity of other groups decreased sharply (3 species of Alveolina and six species of complex miliolids). From the Ypresian to the Bartonian, LBF maintained high species diversity, with differences in species richness most likely due to competition (e.g., alveolinids vs. complex miliolids), local shifts in the paleoenvironment and long-term evolution, rather than global atmospheric or oceanic conditions.The study was funded by the Croatian Science Foundation (HRZZ) through Project IP-2019-04-5775 (BREEMECO).Drobne K., Ćosović V., 2009, Palaeobiogeography of the Late Cretaceous to Paleogene larger Miliolids from topical to subtropical sea belts (Neotethys to Caribbean). Bull. Soc. Geol. Fr., 180/4, 317-331.Drobne K., Ćosović V., 2010, Paleogene conical agglutinated walls foraminifera in the Tethyan realm. Abstract book, Forams2010, 78-79, Bonn.Drobne K., Ćosović V., Moro A., Bucković D., 2011, The role of the Paleogene Adriatic platform in the spatial distribution of alveolinids. Turkish Journal of Earth Sciences, 20/6, 721-751.Pavlovec R., 2012, The Nummulitins from the Outer Dinarids. Folia Biologica and Geologica, 53/3, 85-109. 

The topographic history of an orogen, a key element to study the interactions of the climate and tectonic conditions that drove it, can be reconstructed by inverting the sedimentary record of its adjacent basins. Previous tectono-stratigraphic studies, including flexural models, and sparse stable oxygen and carbon isotope data from the South-Pyrenean foreland basin suggest a major topographic rise occurred in the late Paleocene-early Eocene. To further test this hypothesis, we present a stack of 658 stable isotope measurements on whole-rock marine carbonate mudstone from a 4800-m-thick composite sedimentary succession which provides a 12 Ma continuous record of environmental conditions during the early to middle Eocene (54 to 42 Ma). From the base of this record (at 54 Ma), oxygen isotopes (δ18O values) show a faster decrease rate than the coeval global negative excursion associated with the Early Eocene Climatic Optimum (EECO). This local alteration of the global δ18O signal indicates that topographic growth during this period, associated with significant tectonic activity, perturbed the oxygen isotopic composition of foreland waters. Thus, our data suggest that significant topographic uplift of the Pyrenean orogen started from at least 54 Ma and continued until ca. 49 Ma, reaching the maximum elevations of 2000 ± 500 m in this phase from previous isotope and flexural studies. In addition, our record shows that the long-term carbon stable isotope composition during this period remained relatively stable with no similarity to the global bell-shaped long-term trend of the EECO. This is consistent with the restricted physiography of the South-Pyrenean foreland basin, mainly influenced by local sedimentary and water inputs. Overall, the Pyrenean topographic growth from the late Cretaceous to the Miocene displays several growth stages that seem to be primarily determined by episodes of increased rate of tectonic plate convergence. The duration of these growth stages (several millions of years) is a possible documentation of the response time of mountain ranges to tectonic perturbations. The results of this work, therefore, demonstrate that stable isotope measurements on whole-rock sediments in foreland basins can provide key information for tectono-climatic and topographic reconstructions of mountain ranges.