Session GM5.2

[Programme]

GM5.2 | Earth - Evolution at the Dry Limit

Earth - Evolution at the Dry Limit

Co-organized by BG7

Convener: Tibor J. Dunai | Co-conveners: Christine Heim, Dietmar Quandt, Tony Reimann, Martin Melles

Orals

| Fri, 19 Apr, 10:45–12:30 (CEST)

Room G1

Posters on site

| Attendance Fri, 19 Apr, 16:15–18:00 (CEST) | Display Fri, 19 Apr, 14:00–18:00

Hall X1

Water is the defining feature of the habitable Earth; it is essential for all life as we know it. Evolution and maintenance of life in extremely water limited environments, which cover significant portions of the Earth, is not well understood. Akin to life, water-driven processes leave unique marks on the Earth’s surface. Mars is the only other planet currently known to bear the marks of water-driven surface processes, albeit fossil and of great age. The slow biotic and abiotic surface processes that may operate even in the virtual absence of liquid water are still essentially unknown. What is evident is that transient episodes of increased water availability can leave long lasting traces in extremely water limited environments. Intriguingly, those traces of bursts in Earth surface evolution have rarely been related to bursts in biological colonization/evolution, and vice versa, although both relate to the same trigger: water.
The objective of this session is to showcase research on the mutual evolutionary relationships between Earth surface processes and biota in arid to hyper-arid systems, where both biota and Earth surface process are severely and predominantly limited by the availability of water (rather than by extreme temperatures). As the robust quantification of rates and fluxes in desert landscapes is one of the key challenges related to research at the Earth´s dry limit we highly welcome cutting-edge contributions from geochemistry, biogeosciences, geology, geomorphology and geochronology. We especially encourage contributions from early career scientists who work at the intersection of Earth surface processes and biological evolution.

Orals: Fri, 19 Apr | Room G1

Chairpersons: Tibor J. Dunai, Martin Melles, Christine Heim

10:45–10:50

5-minute convener introduction

10:50–11:10

EGU24-2204

solicited

Highlight

On-site presentation

On the tectonic and climatic controls to the evolutionary patterns of Andean plant groups

Esteban Acevedo-Trejos, Jean Braun, Benedikt Ritter, Tim Böhnert, Adeniyi Mosaku, and Hannah Davies

Life, climate, and landforms interact to shape the biodiversity patterns we observe in Earth’s Mountain regions. Plausible tectonic and climatic explanations have emerged to explain, for example, the evolutionary patterns of Andean plant groups. However, it remains unclear how different tectonic and climatic histories affect the evolution of Andean flora on geological time scales. Here we present the results of numerical experiments using our coupled speciation and landscape evolution model to investigate how tectonics and climate interact to produce distinct evolutionary histories in the Andes. To address this, we first calibrated our model using a Bayesian inversion algorithm with observations of present-day topography and precipitation, paleo-elevation reconstructions, and thermochronological data to calibrate three scenarios with different uplift histories, which were designed based on the literature and named as propagating and compound. The propagating scenario considers the west-to-east propagation of a Gaussian-shaped wave of uplift, which has been shown to adequately approximate the evolution of plateaus. The compound scenario divides the landscape into 6 geomorphic regions, each with its uplift history. Additionally, we tested a third scenario as a control, in which we maintained the present-day topography for the course of the simulation (ca. 80 Myr), which we named static. We ran the eco-evolutionary component of our model in these three distinct uplift scenarios, covering the mountain building of the Andes for the past 80 Myrs, and designed a series of ensemble simulations in which we randomly assigned dispersal and mutation variability to recreate different assemblages with distinct evolutionary histories and evaluate if the different scenarios produce any consistent speciation patterns comparable to reported time-calibrated phylogenies of various plant groups. We found that the uplift scenario with a more complex uplift history, i.e. compound, better agrees with the different observations. This scenario also showed increased diversification during the Miocene (23-4.5 Ma), a feature observed in several Andean plant groups. This demonstrates how diversification constraints obtained from phylogenetic studies can be used to discriminate between conflicting uplift scenarios for the Andes/Altiplano that have been suggested by paleo-altimetry estimates and other geological observations.

How to cite: Acevedo-Trejos, E., Braun, J., Ritter, B., Böhnert, T., Mosaku, A., and Davies, H.: On the tectonic and climatic controls to the evolutionary patterns of Andean plant groups, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2204, https://doi.org/10.5194/egusphere-egu24-2204, 2024.

11:10–11:20

EGU24-21791

On-site presentation

Water vapor transport into the Atacama desertsimulated with a high resolution atmospheric model

Jan H. Schween, Vera Schemann, and Ullrich Loehnert

The Atacama at the west coast of South America is one of the driest regions on earth. Any atmospheric transport of water vapor into this desert which may form fog or dew is accordingly important for its supply with freshwater. Within the CRC 'Earth Evolution at the dry Limit' a network of climate stations has been installed in the core of the Atacama (Schween et al 2020). This network shows a very regular circulation with strong winds from the west during day time and weaker winds from the east during night. These winds are part of a circulation pattern between the coast and the slopes of the Andes known as Rutllant cell. The daytime westerly winds in the desert are moister than the night-time easterlies but this day-night difference in moisture vanishes at the slope of the Andes. Accordingly there is a net transport of water vapor into the desert. But from these surface measurements it remains unclear whether this moisture remains in the surface layer or leaves the region at higher levels,
To get better insight in the circulation we performed simulations with the ICON-LEM model in a 300x300km domain centered around 20.75degS and 69.75W with a resolution of 624m. It covers the ocean as well the high Andes including the coastal mountain range and the central depression. A simulation of a typical winter day showed that the circulation is rather a complex movement of airmasses than a closed circulation. The moist air from the ocean reaches only partly up the slopes of the Andes before it switches to the night time pattern and flows back into the central depression of the desert. There the moist air collects as shallow pools in the basins and valleys where it eventually forms fog. When the following morning the breeze propagates into the desert, convergence at its head leads to injection of moist air into the free troposphere.
We use the model data to identify corridors in which moist air from the ocean enters the desert. In the regions where fog forms we calculate the horizontal transport of liquid (fog) water which can be used to estimate fog water deposition to the surface. We calculate a moisture budget for different layers of the atmosphere to identify where and when water vapor enters and leaves the desert.

Reference:
Schween, J. H., D. Hoffmeister, and U. Löhnert, 2020: Filling the Observational Gap in the Atacama Desert with a new Network of Climate Stations, Global and Planetary Change, 184, https://doi.org/10.1016/j.gloplacha.2019.103034

How to cite: Schween, J. H., Schemann, V., and Loehnert, U.: Water vapor transport into the Atacama desertsimulated with a high resolution atmospheric model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21791, https://doi.org/10.5194/egusphere-egu24-21791, 2024.

11:20–11:30

EGU24-3594

On-site presentation

Understanding a complex ecosystem: Tillandsiales in the hyperarid core of the Chilean Atacama Desert

Marcus Koch, Eric Stein, and Dietmar Quandt

Tillandsia landbeckii is a “core species” in the hyper arid parts of the Atacama Desert colonized by few vascular plants only and this species is totally depending on fog occurrence as the most important source of water. Tillandsia landbeckii is a key element of the most prominent vegetation type of the hyperarid Chilean Atacama core. Epiarenic growth, growing on bare sand and lacking any root system, evolved five times independently in the genus Tillandsia during the past 5 my in the Peruvian-Chilean Desert system and lay the ground to build up unique ecosystems, with Tillandsia purpurea representing the Peruvian vicariant species. The onset of this parallel evolution may be considered as a temporal land-mark for the evolution of those fog-dependent ecosystems of the hyperarid core Atacama. Footprints of evolutionary diversification of present-day gene pools of T. landbeckii go back roughly 500,000 years, and present-day biogeographic distribution pattern is mostly shaped due to environmental changes since the last 22,000 years and the Last Glacial Maximum (LGM). The genetic set-up is surprisingly characterized by ancestral gene pools, “frozen” hybrid genotypes and clonal propagation and dispersal. This observation feeds into our hypothesis that phenotypic plasticity - contributing to plant fitness and survival in space and time - is limited on individual level, but a genetic mosaic on population- and landscape level is compensating this by a mixture of different “frozen” geno- and phenotypes, thereby allowing to cope rapidly with environmental change at the extreme limits of plants´ life. A multi-disciplinary approach combining evidence from different disciplines (plant biology, evolutionary biology, microbiology, climatology, geology, geomorphology and remote sensing technology) aims to unravel the complex interplay of biotic and abiotic factors to elaborate on our understanding of life occuring at the limits of growth due to the lack of water. We introduce the complex phylogeographic history of the species in Chile and introduce a mechanistic/biological growth model exploring environmental - biotic and abiotic - parameters. For comparative analysis on metapopulation level three regions have been selected in Chile (North near Arica, Centre near Iquique, South near Caldera) for detailed comparative in-situ and ex-sito analyses.

How to cite: Koch, M., Stein, E., and Quandt, D.: Understanding a complex ecosystem: Tillandsiales in the hyperarid core of the Chilean Atacama Desert, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3594, https://doi.org/10.5194/egusphere-egu24-3594, 2024.

11:30–11:40

EGU24-2118

ECS

On-site presentation

The entanglement of microorganisms and mineral matrices in a hyperarid environment – observations by SEM imaging and biomarker analysis from the Atacama Desert

Isabel Prater, Helge Mißbach-Karmrodt, Kathrin König, Daniel Friedrich, and Christine Heim

In hyperarid deserts like the Atacama Desert, biota face additional aggravations beside the dryness, e.g. high UV radiation and often high surface temperatures. However, even under these extreme conditions, diverse microbial communities thrive on and within the sediment and interact strongly with their mineral substrate. Common habitats for microbial communities in this environment are fog-receiving surfaces and endolithic zones within evaporite crusts. Endolithic microorganisms are highly adapted to both the substrate and severe water limitations and colonize protected cracks, niches, and caverns within translucent rocks and crusts. They have the potential to alter mineral components and stimulate the formation of secondary minerals as they redistribute moisture and potentially extract crystal water. Processes like these are the starting point of pedogenesis and, even if proceeding extremely slowly, affect the shape of the surface.

To elucidate the relationship of microbial communities with the mineral matrix, we investigated the biogeochemical traces of microbial communities and their spatial distribution on and within gypsum and halite crusts from different regions within the Atacama Desert in Northern Chile. We combined imaging techniques (scanning electron microscopy, SEM) and biomolecular methods (gas chromatography-mass spectrometry, GC-MS/MS and nuclear magnetic resonance, NMR) to obtain a deeper insight into the entanglement of microorganisms and evaporitic crusts. Tight interactions of bacteria and fungi with the mineral matrix were revealed by SEM. Short-chain membrane fatty acids (C₁₄-C₁₈) indicated recent bacterial activity in all samples analyzed. Extracellular short-chain acids (C₆-C₁₂) and carbohydrates of the extracellular polymeric substances (EPS) make up to 75% of the total biomass within evaporites which point to efficient desiccation buffers and protection mechanisms against UV radiation. Furthermore, the sticky EPS leads to the biochemical stabilization of mineral aggregates by agglutination, which was also visible with SEM.

How to cite: Prater, I., Mißbach-Karmrodt, H., König, K., Friedrich, D., and Heim, C.: The entanglement of microorganisms and mineral matrices in a hyperarid environment – observations by SEM imaging and biomarker analysis from the Atacama Desert, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2118, https://doi.org/10.5194/egusphere-egu24-2118, 2024.

11:40–11:50

EGU24-12681

ECS

On-site presentation

The coevolution of life and landscape in the Atacama Desert

Ariane Binnie, Kathrin Lampert, Pia Victor, Klaus Reicherter, Ambrosio Vega Ruiz, Laura Evenstar, Gabriel González, and Steven Binnie

The evolution of landscapes has often been inferred from the phylogenetic records of species that inhabit them, but it is rare to have a sufficiently detailed record of landscape evolution to be able to test the validity of links between bio- and geochronometers. Here we derive the history of fluvial incision of the Tiliviche River in the Central Depression of the northern Atacama Desert, Chile, using cosmogenic nuclide exposure dating of fluvial terraces and nearby paleochannels. We compare this to the timing of speciation from molecular clock dating of Ephemeroptera (Mayflies), collected from both the Tiliviche and proximal Camerones Rivers. Both these drainages source their discharge in the Western Cordillera of the Andes Mountains and drain westwards to the Pacific Ocean. Where they pass through the low relief Central Depression between the Andes and Coastal Cordillera they have formed steeply incised canyons. Our exposure dating shows that notable incision of the Tiliviche River into the Central Depression began around 2 Myr ago. The timing of the divergence of Ephemeroptera species from the Tiliviche and Camerones Rivers is coeval with the onset of Tiliviche incision at 2 Myr. Furthermore, this history of river incision and speciation is consistent with the timing of abandonment of smaller streams that used to flow across the pampa between the Tiliviche and Camerones rivers (Binnie et al., 2020). Our results imply that the downcutting of the Tiliviche as a deep canyon and the contemporaneous drying out of smaller drainages between Tiliviche and Camerones were sufficient to isolate the Ephemeroptera clades. This provides a positive test of a coupled bio- geochronometer approach for unravelling relationships between life and landscape. Whether the controls of river incision and consequently speciation are predominantly climatic, tectonic, or autogenous in nature is still to be resolved.

Binnie S. A, Reicherter K. R., Victor P., González G., Binnie A., Niemann K., Stuart F.M., Lenting C., Heinze S., Freeman S.P.H.T. and Dunai T. J. (2020)
The origins and implications of paleochannels in hyperarid, tectonically active regions: The northern Atacama Desert, Chile. Global and Planetary Change, Volume 185. https://doi.org/10.1016/j.gloplacha.2019.103083

How to cite: Binnie, A., Lampert, K., Victor, P., Reicherter, K., Vega Ruiz, A., Evenstar, L., González, G., and Binnie, S.: The coevolution of life and landscape in the Atacama Desert, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12681, https://doi.org/10.5194/egusphere-egu24-12681, 2024.

11:50–12:00

EGU24-13512

ECS

On-site presentation

Depositional environment of upper Miocene to lower Pliocene diatom-rich deposits of the Bahía Inglesa Formation inferred from benthic foraminiferal assemblages

Fatima Zohra Bouhdayad, Tiago Menezes Freire, Laura Schneider, Daniel Herwartz, Stephanie Scheidt, Jassin Petersen, Sven Nielsen, Marcelo Rivadeneira, and Patrick Grunert

Neogene diatom-rich deposits of north-central Chile represent fundamental archives for studying the dynamic relationship between sea surface temperatures and paleoclimatic fluctuations in the Atacama Desert. To ensure a reliable correlation between the (often discontinuous) marine and terrestrial archives, a well-calibrated stratigraphic framework is needed. In this sense, this study presents microfossil and sedimentological data from a c. 9m-thick diatomaceous mudstone deposit cropping out at the Quebrada Tiburón (27°42' S, 70°59' W, Bahía Inglesa Formation) for paleoenvironment investigations. Biostratigraphy, chemostratigraphy, and tephrochronometry correlated the diatomaceous mudstones with the upper Messinian and Zanclean (c. 6.1-3.6 Ma). To further improve the paleoceanographic interpretations and stratigraphic framework of the sequence, we also measured stable oxygen isotopes (δ¹⁸O) from two shallow infaunal benthic foraminifera species (Bulimina falconensis and Uvigerina striata/peregrina). However, the diatom-rich succession shows distinctive horizons of bioturbation, often associated with overlaying sandstones of variable thicknesses which are intercalated with the diatomaceous mudstones. These repetitive bioturbation cycles warrant caution when interpreting δ¹⁸O data, as they may imply potential hiatuses in sedimentation. At the same time, the observed cycles may provide the opportunity to establish a sequence stratigraphic framework for the deposition of the diatomaceous mudstones.

Benthic foraminiferal assemblages from the mudstones indicate high export productivity and limited oxygen supply at the seafloor related to a coastal upwelling setting. The low-diversity fauna is mostly dominated by individuals < 150 μm of Bolivina granti/pacifica, Epistominella obesa, and Eubuliminella bassendorfensis. Across the Miocene/Pliocene boundary, the relative abundances of Bolivina granti/pacifica and Epistominella obesa respectively increase and decrease, and Bolivina aenariensis disappears. This faunal shift may be explained by changes in the amount and/or frequency of organic matter input. In the intercalated sandstones, Bolivina granti/pacifica, Eubuliminella bassendorfensis, and Epistominella obesa are still the most abundant species, with variable minor contributions of uvigerininds, Bolivina advena and shallow-water taxa such as Buccella peruviana. Notably, the faunal composition of these sandstones differs from neritic upper Tortonian to lower Messinian and upper Pliocene sandstones below and above the studied section, respectively, in which cibicids and Buccella spp. are dominant. In further steps, increased resolution of the assemblage data and statistical analysis combined with sedimentological data will provide more insights into the depositional processes to explain the observed sedimentary cycles. Understanding these processes will help to interpret the δ¹⁸O record and potentially establish a sequence stratigraphic framework for the section.

This study contributes to CRC 1211 “Earth-Evolution at the dry limit”, funded by the Deutsche Forschungsgemeinschaft (DFG).

How to cite: Bouhdayad, F. Z., Menezes Freire, T., Schneider, L., Herwartz, D., Scheidt, S., Petersen, J., Nielsen, S., Rivadeneira, M., and Grunert, P.: Depositional environment of upper Miocene to lower Pliocene diatom-rich deposits of the Bahía Inglesa Formation inferred from benthic foraminiferal assemblages, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13512, https://doi.org/10.5194/egusphere-egu24-13512, 2024.

12:00–12:10

EGU24-20073

On-site presentation

Miocene to recent precipitation history of the central Atacama Desert as reconstructed from a clay pan record in the Coastal Cordillera, northern Chile.

Volker Wennrich, Julia Diederich-Leicher, Stephanie Scheidt, Benedikt Ritter, Niklas Leicher, Richard Albert, Barbara Blanco-Arrue, Pritam Yogeshwar, Rafael Carballeira, Roberto Bao, Dominik Brill, Alicia Medialdea, Melanie Bartz, Eduardo Campos Sepúlveda, Tibor Dunai, and Martin Melles

Hyperaridity is the major limiting factor of Earth-surface processes and biological activity in the Atacama Desert of northern Chile, one of the oldest and driest deserts on Earth. On geological timescales, however, the general aridity, which is thought to have onset during the Oligocene to Miocene, has been punctuated by distinct pluvial periods. Also nowadays sporadic but severe rainfall events, like during the flood in 2015, occur within the hyperarid core of the Atacama Desert. During the Miocene and Pliocene, such wetter conditions caused lake formation in parts of the Central Depression and Coastal Cordillera, but also amplified surface processes as well as changes in vegetation dynamics. Unfortunately, due to the limited number and heterogeneity of suitable paleoclimate archives, the long-term precipitation history of the central Atacama Desert and its drivers are still a matter of controversy.

Here we present a first quasi-continuous (on time periods of 10-100 kyr) record of the Mid-Miocene to present paleoclimatic and environmental history of the central Atacama Desert obtained from an endorheic clay pan. Due to its location in the Coastal Cordillera, the investigated clay pan is assumed to have been decoupled from Andean ground and surface-water inflow, and thus to have recorded only local and regional precipitation variations on different timescales.

The investigated 52 m-long sediment sequence exhibits significant changes in the sedimentological, geochemical paleontological, and mineralogical properties. Preliminary data from the recovered Mid-Miocene sediments imply permanent lacustrine conditions with alternating evaporation cycles that point to significantly different hydrological and/or climatic conditions in Coastal Cordillera than today. A major lithological shift, accompanied by a well-preserved paleosol, documents a significant local groundwater lowering, probably due to fault activation during the mid-Miocene. Subsequent high sedimentation of coarse-grained alluvial deposits indicates alternating periods of wetter than present precipitation, though still arid, conditions with episodic shallow lake phases during the Miocene. A distinct drop in the sedimentation rate and a synchronous transition to fine-grained distal alluvial deposits highlights a significant change in the moisture availability in the Coastal Cordillera during the Pliocene and Pleistocene, probably marking the final onset of hyperarid conditions in the central Atacama Desert.

How to cite: Wennrich, V., Diederich-Leicher, J., Scheidt, S., Ritter, B., Leicher, N., Albert, R., Blanco-Arrue, B., Yogeshwar, P., Carballeira, R., Bao, R., Brill, D., Medialdea, A., Bartz, M., Campos Sepúlveda, E., Dunai, T., and Melles, M.: Miocene to recent precipitation history of the central Atacama Desert as reconstructed from a clay pan record in the Coastal Cordillera, northern Chile. , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20073, https://doi.org/10.5194/egusphere-egu24-20073, 2024.

12:10–12:20

EGU24-20672

On-site presentation

Triple oxygen isotopes in Atacama Desert waters since the late Miocene

Michael Staubwasser, Claudia Voigt, Daniel Herwartz, Carsten Münker, and Guillermo Chong

Utilizing H and triple O isotopes, the main hydrologic variables from the Craig-Gordon model (CGM) of isotope evaporation from a lake, i.e. inflow composition (R_i), the atmosphere’s vapor composition (R_v), and relative humidity (h_r) can now be accurately constrained by measurements from differently evaporated subset lakes within the basin, if they fall on a single isotope evaporation trajectory in a diagram of ¹⁷O-excess or d-excess over δ¹⁸O. We demonstrate here, that this approach can be applied also to paleo-lakes by sampling subsets of lacustrine hydrous mineral deposits - e.g. gypsum (CaSO₄ • 2H₂O) – from the same geologic unit representing a narrowly constrained interval of time. This allows for the reconstruction of the above variables for the past. We conducted a proof-of-concept study in the Atacama Desert on modern and U-Pb dated paleo-gypsum lacustrine deposits. We tested the principles of the above approach on gypsum and lake water from the present-day Salar de Llamara. We verified signal preservation in a 1.8 Ma old – R_i constrained – marine lagoon gypsum outcrop situated on the tectonically uplifted Mejillones Peninsula that has been exposed to meteoric water for the last ~1 Ma. Finally, we applied the method to a 9 Ma old gypsum outcrop from the paleo-lake system of Tilliviche, which existed during the late Miocene / early Pliocene between ~ 11 Ma and 5 Ma. The CGM is applied to nine sub-samples with a ~ +13 to -10 per meg range in ¹⁷O-excess (~ +15 to -16 ‰ in d-excess). The model yields a paleo-R_i equal within model uncertainty to the present-day water flowing down Tilliviche ravine with a δ¹⁸O ~ -9 ‰ reflecting its high altitude source in the Andes. Paleo-R_v has a δ¹⁸O ~ -20 ‰, which is ~ 5 ‰ lower than the present-day atmosphere. Average modelled annual paleo-h_r is 66 % (44 to 84 % range), which is considerably more humid than at present (30 to 40 %). The data suggests that rainfall in the late Miocene Atacama Desert had an annual distribution equal to the present time and was likely as scarce. The more depleted past vapor composition can plausibly be explained only by higher subtropical rain-out prior to moisture advection into the desert. The higher paleo-h_r implies a much lower late Miocene evaporation rate, and must have been the prime cause of the lake’s existence. Thus, the late Miocene Atacama was likely already hyper-arid in terms of rainfall, but its atmosphere was more humid and less evaporative. The desert’s hyper aridity trend since the late Miocene fits with the global subtropical aridity trend beginning ~ 8 Ma ago and widely recorded by the expansion of drought-resistant C4 plants.

How to cite: Staubwasser, M., Voigt, C., Herwartz, D., Münker, C., and Chong, G.: Triple oxygen isotopes in Atacama Desert waters since the late Miocene, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20672, https://doi.org/10.5194/egusphere-egu24-20672, 2024.

12:20–12:30

EGU24-21353

On-site presentation

Late Neogene terrestrial climate reconstruction of the central Namib Desert derived by the combination of U–Pb silcrete and terrestrial cosmogenic nuclide exposure dating

Richard Albert, Benedikt Ritter, Aleksandr Rakipov, Frederik M. van der Wateren, Tibor J. Dunai, and Axel Gerdes

The Cenozoic “Namib Group” of the Namib Desert relies on relative chronology and lacks direct radiometric dating. Therefore, the landscape evolution and paleoclimate of the central Namib Desert remains imprecise, hindering the detailed search for global and/or local forcing factors for the aridification of the Namib. The broad presence of silcretes and calcretes in the Namib Desert allows the application of the of the U–Pb laser ablation dating technique on silcretes and calcretes to date important phases of landscape stability and to retrieve crucial paleoclimatic and environmental information on desertification and its paleoclimatic variability. Microscale silcrete formation (maximum of 8 mm), as a result of pressure solution by expanding calcrete cementation, grants the opportunity to date multiple phases (multiple generations of silcrete as growing layers) of silcrete formation. Groundwater silcrete and calcrete formation took place at our study site during the Pliocene, an epoch of relatively stable climate and landscape evolution under semi-arid to arid conditions. Terrestrial cosmogenic nuclide (TCN) exposure dates from flat canyon rim surfaces show the remission of groundwater calcrete formation due to river incision during Late Pliocene–Early Pleistocene. This incision is a consequence of a large-scale landscape rejuvenation caused by a climate shift towards more arid conditions in the Pleistocene, which can be connected to global climate patterns. This study shows the feasibility of applying U–Pb laser ablation to groundwater calcretes and silcretes, discusses important issues associated with this technique, and opens up the possibility of dating numerous sedimentary sequences with silcretes and calcretes in arid environments. Our study redefines and improves the generally accepted Late Cenozoic chronostratigraphy of the Namib Desert (Miller, 2008).

How to cite: Albert, R., Ritter, B., Rakipov, A., van der Wateren, F. M., Dunai, T. J., and Gerdes, A.: Late Neogene terrestrial climate reconstruction of the central Namib Desert derived by the combination of U–Pb silcrete and terrestrial cosmogenic nuclide exposure dating, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21353, https://doi.org/10.5194/egusphere-egu24-21353, 2024.

Posters on site: Fri, 19 Apr, 16:15–18:00 | Hall X1

Display time: Fri, 19 Apr 14:00–Fri, 19 Apr 18:00

Chairpersons: Martin Melles, Christine Heim, Tony Reimann

X1.114

EGU24-1472

Minimum duration of a Miocene lake phase in the hyperarid core of the Atacama Desert, Chile

Stephanie Scheidt, Stefanie Koboth-Bahr, Volker Wennrich, Richard Albert, Julia L. Diederich-Leicher, Barbara N. Blanco-Arrué, Niklas Leicher, Lena Wallbrecht, Pritam Yogeshwar, and Martin Melles

In 2017, sediment cores were drilled in the PAG clay pan in the hyperarid core of the Atacama Desert as part of CRC1211 (Earth - Evolution at the Dry Limit). The aim of the endeavour was to deduce the climate history of this region from the sedimentary record. The core composite established from the individual core runs goes down to a depth of approx. 52 metres. The core is composed of three major lithological facies. Below 29.2 metre composite depth (mcd), the core consists of fine-grained silty-clayey sediments, which are cyclically interspersed with layers of gypsum. These sediments are interpreted as lacustrine strata. They are overlain by coarse sediments with clasts up to several centimetre in size, which are referred to as colluvial sediments. The upper around seven metre are formed by fine-grained clay pan sediments. The geochronological framework of the core was investigated using various dating methods, most of which were unable to provide reliable ages. For the lake sediments no absolute ages could be obtained. However, U-Pb ages of zircons of a tephra layers, at the transition between the lake and coarse-grained facies suggest a Miocene age for the lake deposits. To constrain the age framework of the lake phase, magnetic polarity stratigraphy was combined with an analysis of gypsum cyclicity that is interpreted as an orbital signal. Here, we present and discuss the results of the study, which provides a new age model for this lacustrine part of the core and thus, sheds new light on an extended pluvial phase in the Atacama Desert.

How to cite: Scheidt, S., Koboth-Bahr, S., Wennrich, V., Albert, R., Diederich-Leicher, J. L., Blanco-Arrué, B. N., Leicher, N., Wallbrecht, L., Yogeshwar, P., and Melles, M.: Minimum duration of a Miocene lake phase in the hyperarid core of the Atacama Desert, Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1472, https://doi.org/10.5194/egusphere-egu24-1472, 2024.

X1.115

EGU24-3506

Paleocene surface exposure ages imply an early development of hyperaridity in the Atacama Desert

Benedikt Ritter, Steven A. Binnie, Finlay M. Stuart, Derek Fabel, Richard Albert, Volker Wennrich, and Tibor J. Dunai

X1.116

EGU24-6493

ECS

Dating of upwelling archives in the eastern South Pacific: a multiproxy approach in the Late Neogene Bahía Inglesa Formation, North-Central Chile

Tiago Freire, Fatima Zohra Bouhdayad, Gerald Auer, Rafael Carballeira, Fabrizio Lirer, Niklas Leicher, Volker Wennrich, Richard Albert, Axel Gerdes, Bárbara Blanco-Arrué, Pritam Yogeshwar, Stephanie Scheidt, Jassin Petersen, Sven Nielsen, Marcelo Rivadeneira, and Patrick Grunert

In modern oceans, upwelling processes are responsible for high biological productivity and low sea surface temperatures at coastal zones. Upwelling may have intensified during the late Neogene in the eastern South Pacific due to the strengthening of the Humboldt Current System. Records of Neogene coastal upwelling are preserved in outcrops along the coast of north-central Chile (~ 26°S to 28°S) as diatomaceous mudstone deposits of the Neogene Bahía Inglesa Formation. To place such records in a broader paleoceanographic context, however, their stratigraphic assessment still needs refinements. Our work presents a multiproxy dataset to provide a stratigraphic framework for the Bahía Inglesa Formation at Quebrada Tiburón (27°42' S, 70°59' W), one of the southernmost outcrops of diatomaceous mudstone. Our approach is based on tephrochronometry, strontium isotope chronology (mollusk shells ⁸⁷Sr/⁸⁶Sr), and calcareous nannoplankton, diatom, and planktonic foraminifera biostratigraphy. Zircon crystals separated from a volcanic ash layer at the base of the sequence were analyzed by laser ablation ICP-MS for U-Pb dating. The youngest cluster of five concordant zircon crystallization ages indicates a tephra deposition after 8.68 ± 0.15 Ma. The ⁸⁷Sr/⁸⁶Sr analyses were performed on an oyster and a pectinid from sandstones underlying the diatomaceous mudstone using high-precision MC-ICP-MS measurements. The corrected and adjusted ⁸⁷Sr/⁸⁶Sr ratios resulted in 8.12 ± 0.40 Ma and 6.10 ± 0.25 Ma ages. The microfossil biostratigraphy was based on First (FAD) and Last Appearance (LAD) datums of biostratigraphic markers from the diatomaceous mudstone. The presence of mainly Miocene diatoms (e.g., Actinocyclus ingens, Cavitatus joseanus, and Nitzschia fossilis) and the planktonic foraminifera Neogloboquadrina acostaensis (sinistral) indicate a Tortonian age for the base of the diatomaceous mudstone. The Messinian-Zanclean boundary was identified in the middle interval of the mudstone by the disappearance of the calcareous nannoplankton species Calcidiscus pataecus and the appearance of Helicosphaera sellii and Umbilicosphaera sibogae. This interpretation is supported by the continuity and limit of the diatoms Actinocyclus ellipticus, Azpeitia nodulifer, and Coscinodiscus plicatus overlapping with Hemidiscus cuneiformis. A Zanclean age was attributed to the upper part of the mudstone sequence due to the co-occurrence of the calcareous nannoplankton species Reticulofenestra pseudoumbilicus and Sphenolithus moriformis, the diatoms Actinocyclus ellipticus, the co-occurrence of the diatoms Nitzschia fossilis and Shionodiscus oestrupii, and the planktonic foraminifera Globoconella miotumida and Sphaeroidinellopsis seminulina. The following sandstones contain Pliocene mollusks. Although inconsistencies between biostratigraphic data of taxa from different microfossil groups were observed (likely due to the lack of a local biozonation appropriate for the upwelling context), our dataset suggests a late Tortonian to Zanclean (8.68 to 3.5 Ma) age constraint for the succession and late Messinian to Zanclean (6.09 to 3.5 Ma) age for the diatomaceous mudstone. Further studies will apply our stratigraphic constraints for paleoenvironmental reconstructions. This research is part of the CRC 1211 “Earth-Evolution at the dry limit” project, funded by the German Research Foundation (DFG).

How to cite: Freire, T., Bouhdayad, F. Z., Auer, G., Carballeira, R., Lirer, F., Leicher, N., Wennrich, V., Albert, R., Gerdes, A., Blanco-Arrué, B., Yogeshwar, P., Scheidt, S., Petersen, J., Nielsen, S., Rivadeneira, M., and Grunert, P.: Dating of upwelling archives in the eastern South Pacific: a multiproxy approach in the Late Neogene Bahía Inglesa Formation, North-Central Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6493, https://doi.org/10.5194/egusphere-egu24-6493, 2024.

X1.117

EGU24-6736

Early Pliocene coastal upwelling off central Chile (Coquimbo Formation, Tongoy)

Patrick Grunert, Rafael Carballeira, Stephanie Scheidt, Tiago Menezes Freire, Sven N. Nielsen, Marcelo M. Rivadeneira, Fatima Zhora Bouhdayad, and Jassin Petersen

Diatom-rich sediments exposed along the coastline of northern and central Chile are prominent archives of coastal upwelling properties in the Neogene. Unlocking these archives is fundamental to evaluate the potential significance of changing sea surface temperatures for landward moisture transport and palaeoclimatic fluctuations in the Atacama Desert. One of the southernmost occurrences of Neogene diatom-rich sediments is known from a series of quebradas, i.e. seaward ravines, on the Tongoy Pensinsula (30.3°S). The diatomaceous muds, previously correlated with the Middle to Upper Miocene, have been deposited in the Tongoy Paleobay. Here we present new bio- and magnetostratigraphic data from a 3.5 m-thick section of diatomaceous muds in the Quebrada Las Salinas together with a preliminary assessment of the depositional environment.

While calcareous microfossils are absent, the sample material is rich in silicious microfossils. Diatoms are the predominant group, while silicoflagellates, ebridians, radiolarians, and sponge spicules contribute to a lesser extent. Co-occurrences of the diatom species Nitzschia fossilis and Shionodiscus oestrupii constrain the diatomaceous muds to an age < 5.7-5.9 Ma. Together with normal magnetic polarity at the base of the section, the lowermost age limit is further refined to an Early Pliocene age < 5.23 Ma (base of the Thvera subchron). Occurrences of the diatom species Rouxia californica in the upper part of the diatomaceous muds suggest an upper age limit within the Zanclean. The results demonstrate for the first time that diatomaceous muds in the Tongoy Paleobay extend well into the Pliocene. Comparison with previous studies suggests that diatom-rich deposits in the study area may be highly diachronous within and between quebradas.

The microfossil assemblages suggest that coastal upwelling was prevalent in the Tongoy Paleobay during the Early Pliocene. Diatom assemblages are dominated by planktonic and meroplanktonic taxa that prefer cold, nutrient-rich surface waters of coastal upwelling such as Chaetoceros and its resting spores, Thalassionema nitzschoides, Coscinodiscus spp., and Actinoptychus senarius. Cold surface waters are also indicated by high abundances of Distephanus spp. in the silicoflagellate assemblages. Benthic taxa are very rare, suggesting water depths of 100-150 meters. The Early Pliocene diatom assemblages more closely resemble those of today’s upwelling in Eastern equatorial Pacific and off the northern Peruvian continental margin than off central Chile. This may suggest a range of surface temperatures at least comparable to or even warmer than off central Chile today, and significantly enhanced primary productivity. This preliminary assessment will be further evaluated through detailed statistical analysis.

This study is part of the CRC 1211 “Earth-Evolution at the dry limit” project, funded by the Deutsche Forschungsgemeinschaft (DFG).

How to cite: Grunert, P., Carballeira, R., Scheidt, S., Menezes Freire, T., Nielsen, S. N., Rivadeneira, M. M., Bouhdayad, F. Z., and Petersen, J.: Early Pliocene coastal upwelling off central Chile (Coquimbo Formation, Tongoy), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6736, https://doi.org/10.5194/egusphere-egu24-6736, 2024.

X1.118

EGU24-8271

ECS

Quantifying processes in Earth’s Critical Zone in the Atacama Desert by combined luminescence and sedimentological approaches

Linda Maßon, Svenja Riedesel, Simon Matthias May, Johanna Steiner, Stephan Opitz, and Tony Reimann

The central Atacama Desert is generally considered the driest non-polar desert on Earth. Given the fog-related moisture availability along the northern Chilean Coastal Cordillera and the increasing precipitation towards the Andean Cordillera, it is an ideal area to explore the transition of biotically to abiotically driven subsurface soil processes (e.g., soil turbation and weathering) in the Earth’s Critical Zone (ECZ). So far, no geochronological framework exists for these subsurface soil processes, and the factors controlling these processes are still unknown. Here we combine feldspar single grain luminescence dating with detailed sedimentological and geochemical analyses to improve our understanding of factors, processes, and time scales involved in subsurface soil processes in the Atacama Desert, ultimately contributing to decipher geomorphodynamics and landscape evolution under hyper arid conditions. While single-grain luminescence dating has successfully been applied to infer sediment transport and mixing processes in various geological settings [e.g., Reimann et al., 2017], luminescence dating of Atacama Desert sediments has proven to be challenging and time-consuming. It has been shown that establishing a standardised growth curve (SGC) for single-grain feldspar post-infrared infrared stimulated luminescence measurements reduces the measurement time considerably [Li et al., 2018]. In this regard, we previously showed that SGCs are only suitable for Atacama Desert feldspars if special modifications are made [Maßon et al., under review].

Based on a combination of the sedimentological and geochemical analyses of samples from nine sediment profiles of 35-180 cm depth, four dust traps and luminescence dating techniques using the modified SGC approach of Maßon et al. [under review] we explore biotic and abiotic subsurface soil processes in the ECZ along two W-E-oriented climatic transects in the north and south of the central Atacama Desert. The northern transect focusses on the transition from the Central Depression to the Precordillera, where biotic components in the ECZ increase with increasing humidity and elevation. The southern transect reflects the transition from the fog-influenced Coastal Cordillera to the Central Depression, where biotic components in the ECZ decrease with decreasing fog-frequency and increasing elevation. We present first results of the successful combination of the refined SGC method from Maßon et al. [under review] and detailed sedimentological and geochemical results to disentangle and infer the processes and rates of sediment deposition and surface evolution, as well as post-depositional subsurface soil processes in both transects. Furthermore, we test if different soil formation processes (e.g., incorporation of aeolian dust vs. in-situ weathering), identified using a combination of sedimentological and geochemical analysis of samples from both sediment profiles and dust traps, can be traced by specific luminescence vs. depth fingerprints. Our preliminary results indicate surface and soil activity during the Late Pleistocene and Holocene even in the abiotic sections of the transects. This suggests that Earth surface dynamics and soil processes such as vertical particle transport and the incorporation of aeolian dust in the most hyperarid parts of the Atacama Desert – virtually independent from flowing water and plant activity - are more active than previously expected, although acting on long time and subtle spatial scales.

How to cite: Maßon, L., Riedesel, S., May, S. M., Steiner, J., Opitz, S., and Reimann, T.: Quantifying processes in Earth’s Critical Zone in the Atacama Desert by combined luminescence and sedimentological approaches, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8271, https://doi.org/10.5194/egusphere-egu24-8271, 2024.

X1.119

EGU24-8995

ECS

Alluvial deposition at the Skeleton Coast, northern Namibia: chronology and spatial patterns

Joel Mohren, Janek Walk, Dominik Brill, Julian Krieger, Wolfgang Römer, Alicia Medialdea, Anna Nguno, and Frank Lehmkuhl

Quaternary topography sculpting along the Skeleton Coast of northern Namibia has predominantly been governed by long-term (hyper-)aridity and a rather absence of tectonic activity. The long-term prevalence of such environmental conditions has been favoured by the overall geographical setting, as the Skeleton Coast is situated at the western passive continental margin of the African continent, close to the southern tropic. As a consequence, the main episode of denudation and relief building in this region is usually believed to have taken place during the Cretaceous. However, Quaternary sediment successions and modern records on flash floods hold proof for a highly active environment post-dating the Mesozoic. Given the important role climate and its variability are presumed to play for sediment redistribution during the Quaternary, alluvial deposits found along this coast-parallel stretch may be regarded as valuable paleoclimate archives, potentially reflecting indications for climate-controlled pulses of sediment aggradation. The present-day environmental conditions limit the decay of such landforms, while promoting the persistence of a long-stretched, coast-parallel dune belt obstructing fluvial sediment conveyance towards the Pacific. The dune belt, termed Skeleton Coast erg, represents aeolian, coast-parallel sediment transport, and covers older alluvial surfaces. Altogether, this special setting bears the potential to investigate linkages between pulses of wetter episodes, the different modes of erosion, and spatiotemporal patterns of alluvial deposition.

We seek to identify these patterns on a regional scale and hence apply a combined, spatially extensive approach including geochronological and (hydro-)morphometric analyses of mapped alluvial fans (n = 52) along the Skeleton Coast and catchments draining the hinterland (n = 67). The drainage is mostly confined by the Great Escarpment to the east, providing similar (modern) rainfall regimes of less than ~150 mm yr^-1 on average. Preliminary results obtained from the morphometric analyses indicate that typical power-law correlations between catchment and fan metrics exist, providing evidence for intact source-sink communication pathways for climate signals from the feeding catchments towards the coast. However, significant spatial fan confinement, e.g. caused by the coastal erg, is very likely to affect the morphometric relationships and landscape reconstruction efforts based on these data. Hence, establishing a regional geochronological framework integrating over timescales relevant for major episodes of alluvial deposition is crucial for our study aims. First results obtained from optically stimulated luminescence (OSL) dating provide indications for significant Holocene and Late Pleistocene sediment conveyance, as previously reported for other study areas across Namibia. Additionally, preliminary ¹⁰Be exposure dating yields Middle Pleistocene ages for alluvial surfaces in the vicinity of the Skeleton Coast erg. Such old ages could reflect the impact of orbital forcing on fan activity and may imply that landscape formation processes temporally integrating over timescales relevant for our analyses are archived in both the fan and catchment morphology. Investigating polyphase fans will help to further increase the spatiotemporal resolution of alluvial deposition patterns to unravel Quaternary climatic conditions and climate variability along the Skeleton Coast of Namibia.

How to cite: Mohren, J., Walk, J., Brill, D., Krieger, J., Römer, W., Medialdea, A., Nguno, A., and Lehmkuhl, F.: Alluvial deposition at the Skeleton Coast, northern Namibia: chronology and spatial patterns, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8995, https://doi.org/10.5194/egusphere-egu24-8995, 2024.

X1.120

EGU24-10039

ECS

Model Characterization of Hydrological and Fluvial Sediment Transport Processes in Present-day and Mid-Pliocene Climate Conditions

Cong Jiang and Yaping Shao

The Atacama Desert, known for its hyper-arid climate, occasionally experiences extreme rainfall events, significantly impacting desert hydrology and land-surface evolution. Climate records suggest past interruptions of hyper-aridity, notably during the mid-Pliocene. Understanding hydrological changes during the wet phases is hindered by data scarcity. To address this, we use dynamically downscaled precipitation data from a regional climate model (WRF) and offline Atmospheric and Hydrological-Sediment Modeling Systems (AHMS-SED) to analyze water and sediment discharge during extreme rainfall events under the present-day and mid-Pliocene conditions. Calibration and validation were performed for the Salado River Basin and Paranal clay pan, where relatively more data were recorded. Using AHMS-SED simulations, we explore the long-term land-surface responses to extreme precipitation events and examine the impacts of flash floods on sediment transport under different climate scenarios. This study also provides insights into the effects of extreme rainfall events on desert hydrology and land-surface evolution in a future warmer climate.

How to cite: Jiang, C. and Shao, Y.: Model Characterization of Hydrological and Fluvial Sediment Transport Processes in Present-day and Mid-Pliocene Climate Conditions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10039, https://doi.org/10.5194/egusphere-egu24-10039, 2024.

X1.121

EGU24-10679

ECS

Mechanisms and timing of haloturbation in the northern Atacama Desert derived from a subsurface network of calcium sulphate wedges

Aline Zinelabedin, Svenja Riedesel, Benedikt Ritter, Joel Mohren, Steven A. Binnie, Maria Wierzbicka-Wieczorek, Simon M. May, Tibor J. Dunai, Stefan Heinze, and Tony Reimann

The presence of subsurface wedges and polygonal patterned grounds on the Earth’s surface is usually associated with cycles of cryogenic subsurface processes in periglacial environments. However, similar though calcium sulphate-dominated structures are found at numerous sites in the central Atacama Desert (N Chile), including particularly well-developed wedges in the subsurface of the Aroma alluvial fan in the Central Depression. Here, the subsurface wedges are covered by a ~20 cm thick, gypsum‑dominated surface crust, impeding the detection of the polygonal structures on the present-day Aroma fan surface. Due to high salt contents in the local alluvial fan deposits, the wedges are thought to be preliminary formed by haloturbation and may represent a hyperarid equivalent to periglacial wedge structures. The dominance of calcium sulphate phases in the vertical lamination of the wedges, accompanied by clastic minerals, is revealed by X-ray diffraction analysis. Hence, haloturbation is likely to be the key driver of wedge formation, caused by significant volumetric changes in the deposits and soil cracking induced by swelling and shrinking during calcium sulphate phase transitions.

Geochronological information on subsurface wedge growth under conditions of extreme water scarcity is crucial for using these laminated wedges as an additional terrestrial palaeoclimate archive for arid to hyperarid environments in the northern Atacama Desert. Information on the processes and timing of wedge-polygon formation may also be important for interpreting wedge-polygon formation in other water-limited environments such as on Mars. Therefore, in order to unravel the mechanisms and governing environmental conditions of calcium sulphate wedge and crust formation at the Aroma site, we here present mineralogical, geochemical, and sedimentological data of wedge and crust material. In addition, our chronological investigations aimed at constraining the age of wedge growth activity by using a combination of feldspar luminescence dating and meteoric ¹⁰Be dating techniques as well as ²³⁹Pu concentration measurements. Based on a minimum age model of our luminescence dating results, wedge growth was last active at the Pleistocene-Holocene boundary. The presence of the overlying gypsum-dominated surface crust could reflect an environmental change from slightly marginally ‘wetter’ conditions to present-day hyperaridity, which ultimately inhibited wedge-polygon formation during the Holocene. However, ²³⁹Pu concentrations measured in surface crust samples indicate recent downward migration of soil fines through the crust body. Therefore, it remains an open question whether surface sediments and/or moisture can penetrate the surface crust to promote processes of wedge-polygon formation even under present hyperarid conditions, leading to wedge growth over longer time scales.

How to cite: Zinelabedin, A., Riedesel, S., Ritter, B., Mohren, J., Binnie, S. A., Wierzbicka-Wieczorek, M., May, S. M., Dunai, T. J., Heinze, S., and Reimann, T.: Mechanisms and timing of haloturbation in the northern Atacama Desert derived from a subsurface network of calcium sulphate wedges , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10679, https://doi.org/10.5194/egusphere-egu24-10679, 2024.

X1.122

EGU24-11939

ECS

Assessing the last “large scale fluvial modification” across the hyperarid Atacama Desert, northern Chile

Janek Walk, Joel Mohren, Ariane Binnie, Dominik Brill, Helmut Brückner, Viktor Schaubert, Andrés Quezada, and Frank Lehmkuhl

During the last decade, a consensus has been widely established about an Early Miocene onset of hyperaridity characterizing the Atacama Desert located in the Andean forearc region in northern Chile. Prevailing hyperarid conditions were interrupted by many pluvial episodes of varying duration and spatial extent. In contrast to the onset of hyperaridity, highly discrepant interpretations persist regarding the last “large scale fluvial modification” (Ritter et al., 2018) of the Atacama Desert. While terminal aggradation of the coastal alluvial fans is constrained at several sites to the Last Glacial Maximum (MIS 2), followed by Holocene progradation to the shore, chronological constraints for last major fluvial activity throughout the inland desert scatter between the Late Miocene and Middle Pleistocene. The types of investigated sedimentary archives differ and many studies have a local focus. Instead, a systematic assessment from the hyperarid coast (W) to the footslopes of the Precordillera (E) is yet lacking. We therefore mapped 84 alluvial fan systems with small (<25 km²) source areas along a latitudinal transect at ~21°S. The last-abandoned, widely distinguishable fan surface generations (S1) and subrecent incised channels of five alluvial fan systems was further systematically sampled for ¹⁰Be cosmogenic nuclide exposure dating of surface pebbles. Morphometric results indicate a significant positive dependence of both fan area and fan slope on the catchment area and can further be interpreted as the result of (palaeo)climatic effects on the fan systems. Initial ¹⁰Be exposure dating reveals Middle Pleistocene terminal aggradation of the S1 fan generation, confirming the younger interpretations of the last “large scale fluvial modification” of the Atacama Desert. Forthcoming additional ¹⁰Be results will provide further insights into the function of the alluvial fans as buffers in the sediment cascade under prevailing hyperaridity, spatial patterns in Pleistocene fan morphodynamics and implications for a potential spatio-temporal gradient in (palaeo‑)precipitation.

Reference
Ritter, B., Stuart, F.M., Binnie, S.A., Gerdes, A., Wennrich, V., Dunai, T.J. (2018). Neogene fluvial landscape evolution in the hyperarid core of the Atacama Desert. Scientific Reports 8, 13952. doi:10.1038/s41598-018-32339-9

How to cite: Walk, J., Mohren, J., Binnie, A., Brill, D., Brückner, H., Schaubert, V., Quezada, A., and Lehmkuhl, F.: Assessing the last “large scale fluvial modification” across the hyperarid Atacama Desert, northern Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11939, https://doi.org/10.5194/egusphere-egu24-11939, 2024.

X1.123

EGU24-12220

ECS

Significance of millennial-scale coastal upwelling and Rio Loa variability forAtacama paleoclimate during MIS 2

Jessica Fabritius, Andrea Jaeschke, Jassin Petersen, Volker Wennrich, and Patrick Grunert

The Atacama Desert located in northern Chile is one of the driest places on earth. The factors determining recent hyperarid climate conditions and their interplay and variability on interannual and decadal time scales are generally understood. Evidence for wetter (yet arid) conditions in the Atacama’s past is mostly provided by ephemeral lacustrine and fluvial deposits. The main watercourse of the Atacama Desert is the Rio Loa sourced by rainfall in the Andean mountains. Information on changes in the terrestrial supply to the ocean is recorded in marine sediments off the Rio Loa mouth.

Sediment core SO-104-52KL has been collected on the upper continental slope (∼340 m water depth, 21°S) off the Rio Loa during cruise 104, Leg 3 by RV Sonne in 1995. The preliminary chronology of the core based on ¹⁴C datings constrains the top and base of the core to 16 and 42 ka, respectively, with a mean sedimentation rate of 30-40 cm kyr^-1. These very high average sedimentation rates allow reconstructions of the paleoceaonographic and paleoclimatic conditions during marine isotope stages (MIS) 3 and 2 on millennial to centennial time scales. The location of the core on the continental slope off the Rio Loa mouth allows for the parallel evaluation of the Humboldt Current System and Andean rainfall as moisture sources for the Atacama Desert.

Proxy data for upwelling properties are established from microfossil assemblages and lipid biomarkers. Preliminary results show that foraminifera are abundant and well-preserved in the upper 4 m of the core. While planktonic foraminifera are rare, benthic assemblages are rich. In total, 24 genera and 49 species of benthic foraminifera were distinguished. The three taxa Bolivina, Bulimina, and Suggrunda, which indicate hypoxic to dysoxic conditions at the seafloor, make up most of the individuals. The dominance of hypoxia tolerating taxa indicates strong upwelling conditions via the presence of a pronounced Oxygen Mimimum Zone impinging on the upper continental slope. These data are put into context with relatively warm sea surface temperatures of average 21 °C as derived from alkenone data. Together with XRF data and grain-size analyses, both applied to characterize the terrestrial input by the Rio Loa, the expected proxy data will provide new insights into the dynamics of land-ocean coupling between the Atacama Desert and the eastern Pacific Ocean.

This study is part of the CRC 1211 “Earth-Evolution at the dry limit” project, funded by the German Research Foundation (DFG).

How to cite: Fabritius, J., Jaeschke, A., Petersen, J., Wennrich, V., and Grunert, P.: Significance of millennial-scale coastal upwelling and Rio Loa variability forAtacama paleoclimate during MIS 2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12220, https://doi.org/10.5194/egusphere-egu24-12220, 2024.

X1.124

EGU24-9660

Highlight

Terracettes in the hyperarid Atacama Desert – fog-driven landforms of Holocene age?

Simon Matthias May, Dirk Hoffmeister, Dominik Brill, Stephan Opitz, and Olaf Bubenzer

Terracettes are quasi-contour parallel step-like microtopographic features consisting of repetitious platform-type benches and slope-type risers and are documented from hillslopes in a range of climates. While a number of studies emphasize their formation by trampling of livestock and grazing animals (cat steps or stock trails), it has been shown that terracette formation may be explained by a number of natural processes, including solifluction or freeze-thaw processes, slumping, soil creep, or vegetation control. Despite this variability and the controversy about their origin, these micro-terraces may alter hillslope soil moisture and vegetation patterns, infiltration and surface hydrology, as well as downslope sediment flux, potentially disconnecting downslope conveyance processes of surface runoff. Given the process mechanisms discussed in these previous studies, the extremely hyperarid climate of the central Atacama Desert in northern Chile may be regarded as unfavourable for terracette formation; here, livestock and grazing animals are absent, moisture availability is extremely limited, and frost processes in elevations below ~1000 m asl are rare. Nevertheless, here we report on terracette-covered slopes in the central Atacama Desert located close to the Rio Loa canyon in the Coastal Cordillera that represents an important inland pathway for coastal fog. Based on sedimentological, geochemical (e.g., micro-X-ray fluorescence) and geomorphological investigations, thin section analyses, UAV-derived aerial photos, soil moisture monitoring as well as post-infrared infrared stimulated luminescence (post-IR IRSL) dating, we present geomorphological, chronostratigraphical and soil hydrological characteristics of the terracettes and discuss potential drivers of terracette formation. Our observations suggest a combination of wind and fog-related moisture supply, particularly during several day-long periods of sustained high relative humidity and fog occurrence, as the key driver for terracette formation, adding to the various processes discussed in previous studies. Post-IR IRSL dating of terracette platform sediments suggests a late Pleistocene to Holocene formation of the terracettes, thereby illustrating the role of fog in driving hillslope dynamics and shaping the desert landscape in the Atacama under past and present hyperaridity.

How to cite: May, S. M., Hoffmeister, D., Brill, D., Opitz, S., and Bubenzer, O.: Terracettes in the hyperarid Atacama Desert – fog-driven landforms of Holocene age?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9660, https://doi.org/10.5194/egusphere-egu24-9660, 2024.

X1.125

EGU24-13141

ECS

U-Pb LA-ICP-MS in situ dating of chrysocolla in copper deposits in Coastal Cordillera, northern Chile

Juan Ríos-Contesse

The study of supergene minerals has been used as a proxy to unravel the palaeoclimatic conditions that prevailed when it occurred. The youngest age of supergene mineralisation is interpreted as the last time with sufficient moisture; therefore, it will reflect the transition from semi-arid towards hyperarid conditions.

The history of dating supergene minerals, mainly alunite and far less common copper-bearing minerals such as atacamite and pseudomalachite, in the Atacama Desert is mainly restricted to the Central Depression and Precordillera indicating that supergene processes were active from 44 to 6 Ma. In contrast, there are only four ages in the Coastal Cordillera, one reported by Sillitoe & McKee, 1996, and three obtained by Reich et al., 2009. This lack of information makes it impossible to constrain the onset of hyperaridity in the Coastal Cordillera and how it relates with the previously mentioned physiographic units.

The Coastal Cordillera in northern Chile correspond to a Jurassic-Early Cretaceous magmatic arc consisting mainly of andesites and basaltic andesites intruded by numerous plutonic bodies. It hosts the metallogenic belt with the largest number of mineral deposits in the Antofagasta Region, the majority of which are copper deposits.

We test for the first time, the potential of the LA-ICP-MS in situ U-Pb technique to date the deposition of the copper deposits in the Coastal Cordillera and use it as a new proxy to understand its palaeoclimatic evolution. For this purpose, we selected chrysocolla samples from manto- and vein-type deposits hosted in the west side of the Coastal Cordillera.

Chrysocolla is an amorphous hydrated copper silicate that precipitate from gel-like material. Furthermore, the chrysocolla may occurs as a replacement of other copper minerals such as malachite and atacamite. Macroscopically it is possible found it in crust, in veins filling cracks along the host rock or in amygdales of andesites. The second most common mineral is atacamite which presents a complex textural relationship with chrysocolla.

The amorphous structure of chrysocolla makes difficult that the U and Pb concentrations will be consistent along the same sample. Due to this, we apply a pre-scan with the laser to measure the U-Pb ratio in the sample. After that, the laser spots were defined in tree main areas: highest, intermediate and lowest U-Pb ratio to be secure that we will get a dispersion of the ratios that can help to obtain an isochron.

The preliminary results show that the chrysocolla is extremely young (<1 Ma). The oldest age obtained is 7 Ma. It is possible that these ages are the consequence of a reset of the system. We need to consider the possibility that the amorphous structure of chrysocolla allows U- and Pb-loss that can give a younger age than the real deposition age.

How to cite: Ríos-Contesse, J.: U-Pb LA-ICP-MS in situ dating of chrysocolla in copper deposits in Coastal Cordillera, northern Chile, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13141, https://doi.org/10.5194/egusphere-egu24-13141, 2024.

X1.126

EGU24-18984

Enhancing AMS measurement precision with the incorporation of 𝛿13C data measured with IRMS

Martina Gwozdz, Andrea Jaeschke, Stefan Heinze, Janet Rethemeyer, Dennis Mücher, and Markus Schiffer

Within the CRC1211 project-Evolution at the Dry Limit, there is a need for precise dating analysis on soil samples extracted from the Atacama Desert. These samples have a characteristically low carbon content. Consequently, ultra-small samples containing approximately 2-20 𝜇g of carbon, need to be measured reliably. For this reason an elemental analyser (EA) and an isotope ratio mass spectrometer (IRMS) have been coupled to the 6 MV AMS system of CologneAMS as well as an existing gas interface (GIS). This provides a fully automated, online-analysis of ¹⁴C/¹²C, and it delivers precise values for 𝛿¹³C. We investigated whether this set-up improves the fractionation correction which is used in the ¹⁴C data evaluation. 𝛿¹³C values from multiple standard materials are measured quasi-simultaneously at the AMS and at the IRMS. Within these measurements we determined that the 𝛿¹³C values form both AMS and IRMS agree with each other within their respective errors. While the 𝛿¹³C AMS values scatter multiple orders higher than the IRMS values we concluded that the 𝛿¹³C IRMS values can be used for a reliable and more precise AMS measurements.

How to cite: Gwozdz, M., Jaeschke, A., Heinze, S., Rethemeyer, J., Mücher, D., and Schiffer, M.: Enhancing AMS measurement precision with the incorporation of 𝛿13C data measured with IRMS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18984, https://doi.org/10.5194/egusphere-egu24-18984, 2024.

X1.127

EGU24-10611

ECS

Fog controls biological cycling of soil phosphorus in the Coastal Cordillera of the Atacama Desert

Xiaolei Sun, Wulf Amelung, Erwin Klumpp, Janek Walk, Ramona Mörchen, Christoph Böhm, Simon Matthias May, Federica Tamburini, and Roland Bol

Soils in hyper-arid climates, such as the Chilean Atacama Desert, show indications of past and present forms of life despite extreme water limitations. We hypothesize that fog plays a key role in sustaining life. In particular, we assume that fog water is incorporated into soil nutrient cycles, with the inland limit of fog penetration corresponding to the threshold for biological cycling of soil phosphorus (P). We collected topsoil samples (0‒10 cm) from each of 54 subsites, including sites in direct adjacency (< 10 cm) and in 1 m distance to plants, along an aridity gradient across the Coastal Cordillera. Satellite-based fog detection revealed that Pacific fog penetrates up to 10 km inland, while inland sites at 10‒23 km from the coast rely solely on sporadic rainfall for water supply. To assess biological P cycling we performed sequential P fractionation and determined oxygen isotope of HCl-extractable inorganic P (δ¹⁸O_HCl-Pi). Total P (P_t) concentration exponentially increased from 336 mg kg^-1 to a maximum of 1021 mg kg^-1 in inland areas ≥ 10 km. With increasing distance from the coast, soil δ¹⁸O_HCl-_Pi values declined exponentially from 16.6‰ to a constant 9.9‰ for locations ≥ 10 km inland. Biological cycling of HCl-P_i near the coast reached a maximum of 76‒100%, which could only be explained by the fact that fog water predominately drives biological P cycling. In inland regions, with minimal rainfall (< 5 mm) as single water source, only 24±14% of HCl-P_i was biologically cycled. We conclude that biological P cycling in the hyper-arid Atacama Desert is not exclusively but mainly mediated by fog, which thus controls apatite dissolution rates and related occurrence and spread of microbial life in this extreme environment.

How to cite: Sun, X., Amelung, W., Klumpp, E., Walk, J., Mörchen, R., Böhm, C., May, S. M., Tamburini, F., and Bol, R.: Fog controls biological cycling of soil phosphorus in the Coastal Cordillera of the Atacama Desert, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10611, https://doi.org/10.5194/egusphere-egu24-10611, 2024.

X1.128

EGU24-11773

Plant evolution and diversity at the dry limit

(withdrawn)

Dietmar Quandt, Marcus Koch, Julia Bechteler, and Alexandra Stoll

X1.129

EGU24-9360

Studies of Nitrate Deposits in the Atacama Desert, Chile: Insights from Triple Oxygen Isotopes and Strontium Isotopes

Camila Riffo Contreras, Guillermo Chong, Swea Klipsch, Kathi Deußen, Carsten Münker, and Michael Staubwasser

The Atacama Desert in northern Chile is the oldest and driest place on Earth, characterized by continuous arid conditions since mid-Tertiary times and hyperarid since the Pliocene. These extreme aridity conditions make this region an ideal environment for the accumulation of highly soluble salts, including the Nitrate Deposits which are of economic importance and scientific research. Despite almost two centuries of exploitation and research, a comprehensive generic model fitting the extremely variable settings and types of Nitrate Deposits has not been universally accepted.

Geochemical and isotopic evidence suggests predominant atmospheric deposition of sea salt and ozone oxidation products with diagnostic Δ¹⁷O anomalies in the nitrates and sulfates deposition. Current models invoke two genesis scenarios: (1)episodic rains and salts washing-down from the soil surface followed by reprecipitation due to evaporation that is assumed to concentrate nitrates and associated salts in sedimentary continental sequences, and (2)salts dissolution in low-O₂ groundwater with subsequent precipitation after capillary activity and evaporation. However, certain Nitrate Deposits, like pure nitrate veins and manto-type up to 1m thick cutting through sedimentary or volcanic rocks at depths of 25m, cannot be easily explained through these two mechanisms. They are too thick and deep to be easily related to capillarity evaporitic concentration from dilute groundwater because the capillary fringe in sediments rarely exceeds 2m. On the other hand, in some cases they are related to gypsum veins, suggesting the possibility of redissolution of primary nitrate deposits by hydrothermal, seismic activity, or precipitations, and brines emplaced into fracture systems, fault planes and stratigraphic boundaries.

This study investigates a possible origin of Nitrate Deposits by analyzing triple oxygen isotopes in nitrates and sulfates. The triple oxygen isotope values in nitrates offer constraints on the formation processes, such as bacterial denitrification and atmospheric photochemical reactions, thereby giving clues to interpret the possible origin and evolution of these deposits.

Sulfates are the dominating salt in soils of the Atacama Desert and are present in Nitrate Deposits. Thenardite and mirabilite appear in several stratigraphic sequences of saline soils between 5-65 cm below the surface. Gypsum is present in continental sequences mainly as gypsysols, but our main interest is when it occurs in groups of sulfate veins associated with nitrates cutting volcanic rocks. Triple oxygen isotope analysis of sulfate veins helps to distinguish between secondary atmospheric sulfate, deposition of sea spray, biological sulfate reduction, and reoxidation. For thenardites, appear to fall on a unique trend in the multi-isotope plots, tending towards zero in ∆¹⁷O_SO4 and very low δ¹⁸O_SO4 and δ³⁴S_SO4, extrapolating this trend to ∆¹⁷O_SO4=0‰ yields a hypothetical hydrothermal end member.

Additionally, the strontium isotopes (⁸⁷Sr/⁸⁶Sr) in Nitrate Deposits offer further insights. The strontium isotope composition reflects interactions between nitrate-bearing fluids (high and low temperature) and host rocks. Comparing these isotopic ratios with known geological formations aids in detecting potential nitrate sources.

The combination of these isotopic systems offers a comprehensive approach to understanding and provides new ideas about the origin and evolution of these still enigmatic deposits in the Atacama Desert.

How to cite: Riffo Contreras, C., Chong, G., Klipsch, S., Deußen, K., Münker, C., and Staubwasser, M.: Studies of Nitrate Deposits in the Atacama Desert, Chile: Insights from Triple Oxygen Isotopes and Strontium Isotopes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9360, https://doi.org/10.5194/egusphere-egu24-9360, 2024.