Earth's surface is subject to a complex interplay of tectonic, atmospheric, and biologic forcing and processes of chemical and physical weathering and erosion. In turn, surface processes can modulate climate, tectonics, and life by the cycling of sediments, water, nutrients, and carbon. Predicting the sensitivity of the Earth's surface to changes in climatic or tectonic forcing, therefore requires an understanding of individual processes as well as their interactions across spatial and temporal scales. Here we invite studies that use field, experimental, and modelling approaches to constrain the patterns and rates of erosion, weathering, and transport of solids and solutes across the Earth surface, and to assess their sensitivity to climatic, tectonic, or biologic change.
1:30pm - 1:45pm
Tectonic accretion controls erosional cyclicity in the Himalaya
1GFZ German Research Centre for Geosciences, Potsdam, Germany; 2Freie Universität Berlin, Berlin, Germany; 3Indian Institute of Science Education and Research Kolkata, Mohanpur, India
The evolution of Earth’s climate over geological timescales is linked to surface erosion by weathering of silicate minerals and burial of organic carbon. However, methodological difficulties in reconstructing erosion rates through time and feedbacks among tectonics, climate, and erosion spurred an ongoing debate on mountain erosion sensitivity to tectonic and climate forcing. A key question is whether late Cenozoic climate cooling has increased global erosion rates or not. The Himalaya plays a prominent role in this debate as its erosion produces a large fraction of global sediments delivered to ocean basins. We report a 6-Myr-long record of cosmogenic 10Be-derived erosion rates from the north-western Himalaya, which indicates that erosion rates in this region varied quasi-cyclically with a period of ~1 Myr and increased gradually towards the present. We hypothesize that the observed pattern of erosion rates occurred in response to the tectonic growth of the Himalaya by punctuated basal and frontal accretion of rocks from the underthrusting Indian plate and concomitant changes in topography. In this model, basal accretion episodically changes rock-uplift patterns, which brings landscapes out of equilibrium and results in quasi-cyclic variations in erosion rates. We used numerical landscape evolution simulations to demonstrate that this hypothesis is physically plausible. In addition, we suggest that the long-term increase in erosion rates was likely driven by successive basal accretion and the commensurate topographic growth in the interior of the Himalayan thrust wedge. Because tectonic accretion processes are inherent to collisional orogenesis, they likely confound climatic interpretations of erosion rate histories.
1:45pm - 2:00pm
A global rate of denudation from cosmogenic nuclides in the Earth’s largest rivers
1Helmholtz Centre Potsdam / Deutsches Geoforschungszentrum GFZ, Germany; 2Institut de Physique du Globe, Paris, France; 3Department of Earth and Environmental Sciences, Università di Milano-Bicocca, Milano, Italy; 4Institute of Geological Sciences, Freie Universität Berlin, Germany
Cosmogenic nuclide analysis in sediment from the Earth’s largest rivers yields mean denudation rates of the sediment-producing areas that average out local variations commonly found in small rivers. Using this approach, we measured in situ cosmogenic 26Al and 10Be in sand of >50 large rivers over a range of climatic and tectonic regimes covering 32% of the Earth’s terrestrial surface.
In 35% of the analyzed rivers, 26Al/10Be ratios are significantly lower than these nuclides´ surface-production-rate ratio of 6.75. We explain these low ratio by a combination of slow erosion and shielding in the source area, and we provide estimates of the buffering timescales of sediment transport using paired nuclides. In the other 65% of studied rivers, 26Al/10Be ratios are within uncertainty of their surface production-rate ratio, indicating cosmogenic steady state. For these rivers, we obtain a global source area denudation rate of 141 t/km2´yr (3.07 Gt/yr). By assuming that this sub-dataset is representative of the global land surface, we upscale to the total surface area for exorheic basins, thereby obtaining a global, millennial-scale denudation flux of 15.2 ± 2.8 Gt/yr. This value is slightly lower than published values from cosmogenic nuclides from small river basins (23 (+53/-16)) Gt/yr) upscaled using a global slope model, and also lower than modern sediment and dissolved loads exported to the oceans (24.0 Gt/yr). Our new approach confirms an estimate of global dissolved and solid matter transfer that converges to an encouragingly narrow range of within 35%.
2:00pm - 2:15pm
Rock slope failures along the Forkastningsfjellet coastline, Svalbard: characteristics and implications for controlling and triggering factors.
1Bundesanstalt für Geowissenschaften und Rohstoffe (BGR), Germany; 2Geological Survey of Norway (NGU), Norway
Climate warming and the related permafrost degradation are thought to influence slope stability, landscape evolution, and the natural hazard potential in polar- and high mountain regions. In this context, we investigate the coastal range of Forkastningsfjellet, Svalbard, which is affected by rock slope deformations of different magnitudes and age. Based on a detailed multidisciplinary investigation, we discuss the causes, kinematics and timing of rock slide activity.
The distinct stair-stepped morphostructural relief of the Forkastningsfjellet ridge is the result of a giant postglacial deep-seated rock slide, which involved a minimum rock mass volume of 0.10 km³ and was probably related to the deglaciation of Isfjorden. Rock failure and movement in the hanging wall of a NW-dipping listric sliding surface led to the fragmentation of the sliding mass into separated tilt blocks.
Since then mass wasting and seacliff erosion take place along the steep slopes of the coastal tilt blocks and on August 16th 2016 a coastal block of the postglacial Forkastningsfjellet rock slide was affected by a rotational rock slide comprising a volume of 175,000m³. As the reactivation of individual slide blocks could have severe consequences for the coastal regions of Longyearbyen by related displacement waves, a back analysis was carried out to derive potential controlling and triggering factors of the recent slope failure. Although the analysis suggests a structural control on the type and mechanism of slope failure, a significant impact of climate-related factors like permafrost degradation and increasing availability of water has to be considered.
2:15pm - 2:30pm
Relict permafrost features identification in landscape and deposits of Borisoglebsk Upland, Central European Russia
1Lomonosov Moscow State University, Russian Federation; 2Institute of Geography, Russian Academy of Sciences, Russian Federation
Relict permafrost features (RPF) indicated by specific patterns of soil, sedimentary and landform structure are characteristic of Central Russian Plain watersheds. Paleocryogenic polygonal networks appear in a pattern of semi-regular spots, blocks and polygons on the surface usually associated with pseudomorphs of ice wedges or sand casts in correlated deposits. This research aimed at distinguishing RPF in sedimentary structure and its correlation with the modern and paleolandscape structure of 3 ha watershed area exposed in constantly expanding trenches. Interpretation of multi-temporal UAV-photography, lithological investigation of 21 sections and apparent magnetic susceptibility measurements allowed to reconstruct spatial organization of the postglacial sedimentary sequence of the key site. Eight sedimentary beds were distinguish starting with Late Saalian limnoglacial base followed by lacustrine (pond-like) facies of the Pleniglacial and solifluction-colluvial lenses of the Late Pleniglacial and Late Glacial up to Holocene colluvial and agrogenic slope facies. At least three generations of inherited wedge-like deformations have been revealed in these stratified thicknesses preliminary attributed to the onset of the last glaciation and its maximum and to one of the Late Glacial coolings. It is established that established are contrastingly displayed in the sedimentary structure, paleolandscapes and modern soil and vegetative cover, however, are rarely or almost not shown in the actual microtopography. Established relationship of ice wedge pseudomorphs and shallow dry gullies allowed interpreting the origin of the latter as initially cryogenic dells infilled by colluvial, incl. agrogenic, deposits and partially incised by agrogenically instigated slope erosion of the last century.
2:30pm - 2:45pm
Multi-proxy, localised reconstructions of climate and weathering from cave speleothem samples
1University of Oxford, United Kingdom; 2Johannes Gutenberg University, Mainz, Germany; 3University of Bern, Switzerland; 4Geological Institute, ETH Zurich, Switzerland
Speleothems (secondary calcium carbonate formations) offer significant potential for recording environmental processes above caves, an area increasingly referred to as the Critical Zone. Speleothems grow for hundreds to millions of years, with absolute chronology from U-Th and U-Pb chronometers. The solution properties of rainwater infiltrating the soil and underlying caves respond to environmental controls. These environmental signals can be preserved within speleothem carbonates. Recent efforts to calibrate, model and interpret this complex geochemistry has progressed along multiple paths. Here we bring together recent examples, including: i) calibrating and using Li isotopes for reconstructing weathering intensity [1,2]; ii) the use of Ca isotopes for reconstructing changes in rainfall amount ; iii) the combined use of d13C, 14C and d44Ca to demonstrate changes in soil respiration . Combining these proxies provides the potential of regional-scale input into climate, weathering and the chemical cycling of elements, on timescales from thousands to millions of years.
 C.C. Day et al. Lithium isotopes and partition coefficients in inorganic carbonates: proxy calibration for weathering reconstruction. GCA.  P.A.E. Pogge von Strandmann et al. 2017. Lithium isotopes in speleothems: Temperature-controlled variation in silicate weathering during glacial cycles. EPSL. 469, 64–74.  R.A. Owen et al. 2016. Calcium isotopes in caves as a proxy for aridity: Modern calibration and application to the 8.2 kyr event. EPSL, 443, 129–138.  F.A. Lechleitner et al. (in review). Stalagmite carbon isotopes suggest deglacial increase in soil respiration in Western Europe driven by temperature change. Climate of the Past.
2:45pm - 3:00pm
How minerals govern the advance of weathering: comparison of a shallow and a deep weathering profile in different climatic zones (Chilean Coastal Cordillera)
1Department of Applied Geochemistry, Technische Universität Berlin, Germany; 2GFZ German Research Centre for Geosciences, Potsdam, Germany; 3Chair of Ecohydrology and Landscape Evaluation, Technische Universität Berlin, Germany
Weathering is the fundamental precondition for erosion and soil formation which sculpture Earth´s surface. It is a complex interplay of minerals, rock fabric, tectonical fractures, climate, and organic activity.
To explore the dependences between these factors two weathering profiles on magmatic bedrock were compared using six-meter-deep soil pits and drill cores in both a humid and a Mediterranean climate regime of Chile. Detailed mineralogical and geochemical investigations of soil and saprolite were combined with spatially highly resolved geochemical analyses of fracture-related rock weathering.
The maximum saprolite depth in the humid climate turned out to be much shallower (approx. 6 m) than in the Mediterranean climate (almost 30 m). However, the entire soil-pit profile in the humid climate is characterized by distinct chemical depletion and intense mineral weathering (predominantly chemical weathering), whereas the Mediterranean profile only shows weak chemical and mineral weathering but high degrees of fracturing (predominantly physical weathering). This study suggests that surface inputs (water, O2) initially enter the subsurface via tectonical fractures and trigger reactions such as iron-oxidation in Fe(II)-bearing silicates which induces fracturing or the transformation of feldspars which can hamper the weathering advance by porosity reduction. The higher content of Fe(II)-bearing silicates in the bedrock of the Mediterranean climate is thus considered the critical factor for the different developments of the two profiles.
This study stresses the magnitude of control the mineralogical composition has on weathering processes and that surface processes like erosion cannot be fully understood without a thorough investigation of the subsurface.