The convexity of carbonate hilltops: 36Cl constraints on denudation and chemical weathering rates and implications for hillslope curvature

2021 ◽  
Author(s):  
Matan Ben-Asher ◽  
Itai Haviv ◽  
Onn Crouvi ◽  
Joshua J. Roering ◽  
Ari Matmon
Keyword(s):  
Mass Balance ◽  
Chemical Weathering ◽  
Airborne Lidar ◽  
Annual Rainfall ◽  
Deposition Flux ◽  
Soil Thickness ◽  
Denudation Rates ◽  
Soil Production ◽  
Mean Annual Rainfall ◽  
Dust Flux

Carbonate hillslopes are often soil mantled and display a classic convex morphology. In this study we examine controls on carbonate hillslope denudation and morphology using a modified regolith mass balance equation to account for chemical weathering and dust input—two fluxes that are commonly neglected in settings with silicate-dominated bedrock. We utilize seven study sites in the Eastern Mediterranean across a significant gradient in the mean annual rainfall and dust deposition flux. Combining cosmogenic 36Cl-derived hilltop denudation rates with an estimate of the regolith chemical depletion and the quantified fraction of dust in the regolith we predict hilltop curvature and compare our predictions with observations based on high-resolution airborne LiDAR (light detection and ranging). Denudation rates vary from 5 to 210 mm/k.y. and increase with mean annual rainfall. Less resistant carbonates (chalk) experience faster denudation rates relative to more resistant dolo-limestone and are less prone to chemical weathering. Soil production exhibits a humped dependency on soil thickness. The observed hilltop curvature varies as a function of rainfall and dust flux with a minimum at sub-humid sites. While trends in hilltop convexity are often solely attributed to variations in erosion rate, our results illustrate the additional effects of dust production and chemical depletion. Our mass balance model implies that drier sites in the south probably experienced a more intricate history of regolith production due to dust flux fluctuations. Thus, by incorporating dust flux and chemical weathering to the classic hillslope evolution model we are able to identify a complex relation between hilltop curvature, soil production, and climate.

The convexity of carbonate hillslopes: the influence of climate, chemical weathering and dust flux

2020 ◽  
Author(s):  
Matan Ben-Asher ◽  
Itai Haviv ◽  
Onn Crouvi ◽  
Josh J Roering ◽  
Ari Matmon
Keyword(s):  
Mass Balance ◽  
Carbonate Rocks ◽  
Chemical Weathering ◽  
Airborne Lidar ◽  
Annual Rainfall ◽  
Soil Thickness ◽  
Denudation Rates ◽  
Soil Production ◽  
Hillslope Evolution ◽  
Dust Flux

<p>Convex soil-covered hillslopes are ubiquitous in various tectonic and climatic settings and are often modeled based on a mass balance relating hillslope convexity to regolith transport and soil production. In order to account for chemical weathering of carbonate rocks and dust input to the regolith, two fluxes that are commonly neglected in settings with silicate-dominated bedrock,  we modify this mass balance.</p><p>We studied 7 study sites in carbonate rocks across an Eastern Mediterranean gradient in the mean annual rainfall (250 to 900 mm yr<sup>-1</sup>) and dust flux (150 to 40 g m<sup>-2</sup> yr<sup>-1</sup>). Combining cosmogenic <sup>36</sup>Cl-derived hilltops denudation rates with an estimate of the regolith chemical depletion and dust fraction based on immobile elements, we predict the hillslope curvature and compare our predictions with observations based on high-resolution airborne LiDAR.</p><p>Our results demonstrate that soft carbonates (chalk) experience faster denudation rates relative to resistant dolo-limestone. However, the harder carbonates are more prone to chemical weathering, which systematically constitutes around half of their total denudation.  Soil production rates exhibit a humped dependency on soil thickness, with an apparent maximum at a depth of 8-16 cm.</p><p>The observed hillslope curvature vary as function of rainfall and dust flux with a minimum at sub-humid sites with intermediate rainfall of  500-600 mm/yr. The predicted curvature based on our new mass balance is not far from the observed curvature, illustrating the prominent effects of dust flux and chemical weathering on hillslope morphology.  Our model also implies that drier sites in the south probably experienced a more complex history of regolith production due dust flux fluctuations.</p><p>By incorporating dust flux and chemical weathering to the classic hillslope evolution model we identify a complex relation between hillslope curvature, soil production, and climate. These two fluxes are not unique to carbonate bedrock and should be incorporated in hillslope evolution models.</p>

scholarly journals Supplemental Material: The convexity of carbonate hilltops: 36Cl constraints on denudation and chemical weathering rates and implications for hillslope curvature

2020 ◽  
Author(s):  
Matan Ben-Asher
Keyword(s):  
Steady State ◽  
Numerical Modelling ◽  
Chemical Weathering ◽  
Annual Rainfall ◽  
State Table ◽  
Weathering Rates ◽  
Denudation Rates ◽  
Soil Creep ◽  
Mean Annual Rainfall ◽  
Study Sites

Figure S1: 36Cl denudation rates vs. mean annual rainfall of samples categorized by hillslope position and samples types; Figure S2: fd and CDF vs. mean annual rainfall, derived from immobile elements; Figure S3: Values of soil creep efficiency (K) vs. mean annual rainfall, estimated from numerical modelling and steady state, table with coordinates of study sites location; Figure S4: Photographs of hard dolo-limestone and soft chalk rocks; Figure S5: Mean hillslopes slope vs. mean relief.

scholarly journals Supplemental Material: The convexity of carbonate hilltops: 36Cl constraints on denudation and chemical weathering rates and implications for hillslope curvature

2020 ◽  
Author(s):  
Matan Ben-Asher
Keyword(s):  
Steady State ◽  
Numerical Modelling ◽  
Chemical Weathering ◽  
Annual Rainfall ◽  
State Table ◽  
Weathering Rates ◽  
Denudation Rates ◽  
Soil Creep ◽  
Mean Annual Rainfall ◽  
Study Sites

Figure S1: 36Cl denudation rates vs. mean annual rainfall of samples categorized by hillslope position and samples types; Figure S2: fd and CDF vs. mean annual rainfall, derived from immobile elements; Figure S3: Values of soil creep efficiency (K) vs. mean annual rainfall, estimated from numerical modelling and steady state, table with coordinates of study sites location; Figure S4: Photographs of hard dolo-limestone and soft chalk rocks; Figure S5: Mean hillslopes slope vs. mean relief.

Evaluating climate effects over long-term salts accumulation in hyperarid soils using stochastic modeling

2021 ◽  
Author(s):  
Lior Siman-Tov ◽  
Onn Crouvi ◽  
Efrat Morin ◽  
Rivka Amit ◽  
Yehouda Enzel ◽  
...  
Keyword(s):  
Late Pleistocene ◽  
Alluvial Fan ◽  
Sensitivity Analyses ◽  
Annual Rainfall ◽  
Soil Profiles ◽  
Sulfate Concentration ◽  
Climate Scenarios ◽  
Mean Annual Rainfall ◽  
Dust Flux

<p>Hyperarid (< 80 mm yr<sup>-1</sup>) soils in hot deserts are characterized by accumulations of soluble salts (gypsum and halite) in diagnostic horizons as a result of limited moisture availability. In most desert terrains, the source for pedogenic gypsum and halite is atmospheric dust and rainwater. The interplay between climatic properties such as frequency and intensity of rain events, rainfall composition, dust flux, and evaporation rates, govern the depth and concentration of these salts. Better understanding of these relationships can improve our estimation of regional paleoenvironmental and paleoclimate conditions. Up to date, only empirical correlations between annual rainfall and pedogenic salt horizons are available.</p><p>The goals of this study are to: 1) quantify rates of pedogenic gypsum accumulation with time and the role of controlling climatic conditions that govern its accumulation, 2) estimate the most likely climatic scenarios that led to the formation of the diagnostic gypsic horizon developed in late Pleistocene (~ 60 ka) abandoned alluvial fan surfaces in the hyperarid Negev desert,  southern Israel. To achieve these goals, we constructed a compartment model that simulates gypsum accumulation in soil and tests its sensitivity to various changes in the long-term climate properties. The model predicts gypsum content and depth of accumulation in the soil profile over thousands of years and more. The input parameters are stochastically simulated rainstorms, evaporation, dust flux, and sulfate concentration in rainwater, at daily time steps. The model was tested and calibrated using data of Holocene (< 11 ka) soil profiles developed on stable alluvial fans in the hyperarid Negev. With the assumption that the climate during the Holocene was not much different than today (i.e., mean annual rainfall < 50 mm). Sensitivity analyses indicate that gypsum accumulation is highly sensitive to mean annual rainfall and sulfate concentration in rainwater. Synthetic gypsum profiles were calculated using different climate scenarios and compared to late Pleistocene soils. Our results suggest that: (a) gypsum accumulation in late Pleistocene soils cannot occur simply by extending current climate conditions for a much longer duration. (b) The plausible climate scenarios for the late Pleistocene must include additional rain input (1.5 – 2.0 times than mean annual rainfall today) and increased sulfate concentration in rainwater (2.0 – 2.5 times than today) to successfully reconstruct the observed accumulated gypsum in mature (60 – 12 Ka) soil profiles.</p>

scholarly journals Erosion rates deduced from seasonal mass balance along the upper Urumqi River in Tianshan

Solid Earth ◽  
2011 ◽  
Vol 2 (2) ◽  
pp. 283-301 ◽  
Author(s):  
Y. Liu ◽  
F. Métivier ◽  
J. Gaillardet ◽  
B. Ye ◽  
P. Meunier ◽  
...  
Keyword(s):  
Mass Balance ◽  
Central Asia ◽  
Chemical Weathering ◽  
Annual Runoff ◽  
Mountain Stream ◽  
High Mountain ◽  
Mountain Range ◽  
Cosmogenic Dating ◽  
Denudation Rates ◽  
Sand And Gravel

Abstract. We report measurements performed during two complete flow seasons on the Urumqi River, a proglacial mountain stream in the northeastern flank of the Tianshan, an active mountain range in Central Asia. This survey of flow dynamics and sediment transport (dissolved, suspended and bed loads), together with a 25-year record of daily discharge, enables the assessment of secular denudation rates on this high mountain catchment of Central Asia. Our results show that chemical weathering accounts for more than one-third of the total denudation rate. Sediment transported as bed load cannot be neglected in the balance, given that sand and gravel transport accounts for one third of the solid load of the river. Overall, the mean denudation rates are low, averaging 46 t × km−2 × yr−1(17–18 m Myr−1). We furthermore analyse the hydrologic record to show that the long-term sediment budget is not dominated by extreme and rare events but by the total amount of rainfall or annual runoff. The rates we obtain are in agreement with rates obtained from the mass balance reconstruction of the Plio-Quaternary gravely deposits of the foreland but signicantly lower than the rates recently obtained from cosmogenic dating of the Kuitun River sands, west of the Urumqi River. We show that the resolution of this incompatibility may have an important consquence for our understanding of the interplay between erosion and tectonics in the semi-humid ranges of Central Asia.

scholarly journals Erosion rates deduced from Seasonal mass balance along an active braided river in Tianshan

2011 ◽  
Vol 3 (2) ◽  
pp. 541-589 ◽  
Author(s):  
Y. Liu ◽  
F. Métivier ◽  
J. Gaillardet ◽  
B. Ye ◽  
P. Meunier ◽  
...  
Keyword(s):  
Mass Balance ◽  
Central Asia ◽  
Chemical Weathering ◽  
Annual Runoff ◽  
Mountain Stream ◽  
High Mountain ◽  
Mountain Range ◽  
River Sand ◽  
Cosmogenic Dating ◽  
Denudation Rates

Abstract. We report measurements performed during two complete flow seasons on the Urumqi River, a proglacial mountain stream in the northeastern ank of the Tianshan, an active mountain range in Central Asia. This survey of flow dynamics and sediment transport (dissolved, suspended and bed loads), together with a 25-year record of daily discharge, enables the assessment of secular denudation rates on this high mountain catchment of Central Asia. Our results show that chemical weathering accounts for more than one third of the total denudation rate. Sediment transported as bed load cannot be neglected in the balance given that sand and gravel transport accounts for one third of the solid load of the river. Overall, the mean denudation rates are low, averaging 46 t × km−2 × yr−1 (17–18 m Myr−1). We furthermore analyse the hydrologic record to show that the long-term sediment budget is not dominated by extreme and rare events but by the total amount of rainfall or annual runoff. The rates we obtain are in agreement with rates obtained from the mass balance reconstruction of the Plio-Quaternary gravely deposits of the foreland but signicantly lower than the rates recently obtained from cosmogenic dating of river sand. We show that the resolution of this incompatibility has an important consequence for our understanding of the interplay between erosion and tectonics in the semi-humid ranges of Central Asia.

scholarly journals Vegetation and climate effects on soil production, chemical weathering, and physical erosion rates

2021 ◽  
Author(s):  
Mirjam Schaller ◽  
Todd Alan Ehlers
Keyword(s):  
Chemical Weathering ◽  
Mediterranean Climate ◽  
Annual Precipitation ◽  
Mean Annual Precipitation ◽  
Weathering Rates ◽  
Erosion Rates ◽  
Denudation Rates ◽  
Soil Production ◽  
Physical Erosion ◽  
Global Data

Abstract. Weathering of bedrock to produce regolith is essential for sustaining life on Earth and global biogeochemical cycles. The rate of this process is influenced not only by tectonics, but also by climate and biota. Here we investigate these interactions with new observations of soil production, chemical weathering, and physical erosion rates from the large climate and vegetation gradient of the Chilean Coastal Cordillera (26° to 38° S). These findings are compared to a global compilation of published data from similar settings. The four Chilean study areas span (from North to South): arid (Pan de Azúcar), semi-arid (Santa Gracia), mediterranean (La Campana) and temperate humid (Nahuelbuta) climate zones. We test the hypotheses that: 1) soil production as well as chemical weathering rates increase with increasing mean annual precipitation; 2) physical erosion rates stabilize as vegetation cover increases; and 3) the contribution of chemical weathering to total denudation is constant over the climate gradient.We find observed soil production rates range from ~7 to 290 t/(km2 yr) and are lowest in the sparsely vegetated and arid North, increase southward toward the vegetated mediterranean climate, and then decrease further South in the temperate humid zone. This trend is discussed and compared with global data from similar catchments underlain by granitic lithologies. Calculated chemical weathering rates range from zero in the arid North to a high value of 211 t/(km2 yr) in the mediterranean zone. Chemical weathering rates are comparable in the semi-arid and temperate humid zones (~20 t/(km2 yr). Physical erosion rates are low in the arid zone (~11 t/(km2 yr)) and increase towards the South (~ 40 t/(km2 yr)). Combined total chemical weathering and physical erosion rates indicate that denudation rates are lowest in the arid North and highest in the Mediterranean climate zone. The contribution of chemical weathering to total denudation rates increases and then decreases with increasing mean annual precipitation from North to South. The observation that the calculated chemical weathering rates in the southernmost location, with the highest mean annual precipitation and the highest chemical index of alteration, are not the highest of all four study areas is found to be consistent with the global data analysis.

scholarly journals Long term precipitation chemistry and wet deposition in a remote dry savanna site in Africa (Niger)

2009 ◽  
Vol 9 (5) ◽  
pp. 1579-1595 ◽  
Author(s):  
C. Galy-Lacaux ◽  
D. Laouali ◽  
L. Descroix ◽  
N. Gobron ◽  
C. Liousse
Keyword(s):  
Wet Deposition ◽  
Ph Value ◽  
Precipitation Chemistry ◽  
Annual Rainfall ◽  
Deposition Flux ◽  
Air Concentration ◽  
Ionic Charge ◽  
Rainfall Gradient ◽  
The Mean

Abstract. Long-term precipitation chemistry have been recorded in the rural area of Banizoumbou (Niger), representative of a semi-arid savanna ecosystem. A total of 305 rainfall samples ~90% of the total annual rainfall) were collected from June 1994 to September 2005. From ionic chromatography, pH major inorganic and organic ions were detected. Rainwater chemistry is controlled by soil/dust emissions associated with terrigeneous elements represented by SO42−, Ca2+, Carbonates, K+ and Mg2+. It is found that calcium and carbonates represent ~40% of the total ionic charge. The second highest contribution is nitrogenous, with annual Volume Weighed Mean (VWM) for NO3− and NH4+ concentrations of 11.6 and 18.1 μeq.l−1, respectively. This is the signature of ammonia sources from animals and NOx emissions from savannas soil-particles rain-induced. The mean annual NH3 and NO2 air concentration are of 6 ppbv and 2.6 ppbv, respectively. The annual VWM precipitation concentration of sodium and chloride are both of 8.7 μeq.l−1 which reflects the marine signature of monsoonal and humid air masses. The median pH value is of 6.05. Acidity is neutralized by mineral dust, mainly carbonates, and/or dissolved gases such NH3. High level of organic acidity with 8μeq.l−1 and 5.2 μeq.l−1 of formate and acetate were also found. The analysis of monthly Black Carbon emissions and Fraction of Absorbed Photosynthetically Active Radiation (FAPAR) values show that both biogenic emission from vegetation and biomass burning could explain the rainfall organic acidity content. The interannual variability of the VWM concentrations around the mean (1994–2005) is between ±5% and ±30% and mainly due to variations of sources strength and rainfall spatio-temporal distribution. From 1994 to 2005, the total mean wet deposition flux in the Sahelian region is of 60.1 mmol.m−2.yr−1 ±25%. Finally, Banizoumbou measurements are compared to other long-term measurements of precipitation chemistry in the wet savanna of Lamto (Côte d'Ivoire) and in the forested zone of Zoétélé (Cameroon). The total chemical loading presents a maximum in the dry savanna and a minimum in the forest (from 143.7, 100.2 to 86.6 μeq.l−1), associated with the gradient of terrigeneous sources. The wet deposition fluxes present an opposite trend, with 60.0 mmol.m−2.yr−1 in Banizoumbou, 108.6 mmol.m−2.yr−1 in Lamto and 162.9 mmol.m−2.yr−1 in Zoétélé, controlled by rainfall gradient along the ecosystems transect.

scholarly journals Quantification of southwest China rainfall during the 8.2 ka BP event with response to North Atlantic cooling

2016 ◽  
Vol 12 (7) ◽  
pp. 1583-1590 ◽  
Author(s):  
Yuhui Liu ◽  
Chaoyong Hu
Keyword(s):  
High Resolution ◽  
Southwest China ◽  
East Asian Monsoon ◽  
Moving Average ◽  
Ice Core ◽  
Scale Model ◽  
Annual Rainfall ◽  
Transport Pathway ◽  
Mean Annual Rainfall ◽  
Monsoon Area

Abstract. The 8.2 ka BP event could provide important information for predicting abrupt climate change in the future. Although published records show that the East Asian monsoon area responded to the 8.2 ka BP event, there is no high-resolution quantitative reconstructed climate record in this area. In this study, a reconstructed 10-year moving average annual rainfall record in southwest China during the 8.2 ka BP event is presented by comparing two high-resolution stalagmite δ18O records from Dongge cave and Heshang cave. This decade-scale rainfall reconstruction is based on a central-scale model and is confirmed by inter-annual monitoring records, which show a significant positive correlation between the regional mean annual rainfall and the drip water annual average δ18O difference from two caves along the same monsoon moisture transport pathway from May 2011 to April 2014. Similar trends between the reconstructed rainfall and the stalagmite Mg ∕ Ca record, another proxy of rainfall, during the 8.2 ka BP period further increase the confidence of the quantification of the rainfall record. The reconstructed record shows that the mean annual rainfall in southwest China during the central 8.2 ka BP event is less than that of present (1950–1990) by  ∼  200 mm and decreased by  ∼  350 mm in  ∼  70 years experiencing an extreme drying period lasting for  ∼  50 years. Comparison of the reconstructed rainfall record in southwest China with Greenland ice core δ18O and δ15N records suggests that the reduced rainfall in southwest China during the 8.2 ka BP period was coupled with Greenland cooling with a possible response rate of 110 ± 30 mm °C−1.

scholarly journals Modelling monthly runoff generation processes following land use changes: groundwater–surface runoff interactions

2004 ◽  
Vol 8 (5) ◽  
pp. 903-922 ◽  
Author(s):  
M. Bari ◽  
K. R. J. Smettem
Keyword(s):  
Land Use ◽  
Water Balance ◽  
Surface Runoff ◽  
Land Use Changes ◽  
Annual Rainfall ◽  
Rainfall Runoff ◽  
Runoff Generation ◽  
Mean Annual Rainfall ◽  
Monthly Runoff ◽  
Stream Bed

Abstract. A conceptual water balance model is presented to represent changes in monthly water balance following land use changes. Monthly rainfall–runoff, groundwater and soil moisture data from four experimental catchments in Western Australia have been analysed. Two of these catchments, "Ernies" (control, fully forested) and "Lemon" (54% cleared) are in a zone of mean annual rainfall of 725 mm, while "Salmon" (control, fully forested) and "Wights" (100% cleared) are in a zone with mean annual rainfall of 1125 mm. At the Salmon forested control catchment, streamflow comprises surface runoff, base flow and interflow components. In the Wights catchment, cleared of native forest for pasture development, all three components increased, groundwater levels rose significantly and stream zone saturated area increased from 1% to 15% of the catchment area. It took seven years after clearing for the rainfall–runoff generation process to stabilise in 1984. At the Ernies forested control catchment, the permanent groundwater system is 20 m below the stream bed and so does not contribute to streamflow. Following partial clearing of forest in the Lemon catchment, groundwater rose steadily and reached the stream bed by 1987. The streamflow increased in two phases: (i) immediately after clearing due to reduced evapotranspiration, and (ii) through an increase in the groundwater-induced stream zone saturated area after 1987. After analysing all the data available, a conceptual monthly model was created, comprising four inter-connecting stores: (i) an upper zone unsaturated store, (ii) a transient stream zone store, (ii) a lower zone unsaturated store and (iv) a saturated groundwater store. Data such as rooting depth, Leaf Area Index, soil porosity, profile thickness, depth to groundwater, stream length and surface slope were incorporated into the model as a priori defined attributes. The catchment average values for different stores were determined through matching observed and predicted monthly hydrographs. The observed and predicted monthly runoff for all catchments matched well with coefficients of determination (R2) ranging from 0.68 to 0.87. Predictions were relatively poor for: (i) the Ernies catchment (lowest rainfall, forested), and (ii) months with very high flows. Overall, the predicted mean annual streamflow was within ±8% of the observed values. Keywords: monthly streamflow, land use change, conceptual model, data-based approach, groundwater

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