julilili42/papers huggingface dataset:
Does the Middle Miocene rise of the Greater Himalaya cause the slow down of Southern Tibet exhumation?
2023-02-25

The Himalaya is the highest and steepest mountain range on Earth and forms today efficient north-south barrier for moisture-bearing winds. 1D-thermokinematic modeling of new zircon (U-Th)/He bedrock-cooling ages and &gt;100 previously published mica 40Ar/39Ar, zircon and apatite fission track ages from the Sutlej Valley document a consistent rapid decrease in exhumation rates that initiated at ~17-15 Ma across the entire Greater and Tethyan Himalaya and the north-Himalayan Leo Pargil dome. We observe a rapid decrease from &gt;1 km/Myr to &lt;0.5 km/Myr. Simultaneous changes in the hanging and footwall of major Miocene shear zones suggest that cooling is associated to surface erosion and not due to tectonic unroofing such as due to E-W extension. We explain the middle Miocene deceleration of exhumation with major tectonic reorganization of the Himalayan orogen, probably coincident with the onset of basal accretion, which resulted in accelerated uplift of the Greater and Tethyan Himalaya above a mid-crustal ramp and the establishment of a new efficient orographic barrier. The period of slow exhumation in the upper Sutlej Valley coincides with a period of internal drainage in the south-Tibetan Zada Basin farther upstream, which we interpret to be a consequence of tectonic damming. Exhumation rates in the upper Sutlej Valley accelerate again at ~5-3 Ma, and allowed the Sutlej River to re-establish external drainage of the Zada Basin. Comparison with other data from the Himalaya and Southern Tibet along strike suggests that by ~15 Ma, southern Tibet was high, located in the rain shadow of the High Himalaya and eroding slowly for at least 10 Ma, before erosion accelerated again by ~5-3 Ma, most likely due to climatic changes. Our new finding document that the location of tectonic deformation processes controls the first order spatial pattern of both climatic zones and erosion across the orogen. Therefore, we think that the rise of Greater Himalaya is linked to the deceleration of exhumation in Southern Tibet.
Cenozoic Southwestern Tian Shan: Timing of Mountain Building, Intra-montane Basin Inversion, and Relation to Lithospheric Mantle Indentation
2023-02-25

Cenozoic reactivation of the Paleozoic thick-skinned fold-thrust belt of the southwestern Tian Shan has&amp;#8212;as the Afghan-Tajik Basin inversion&amp;#8212;been interpreted to reflect Indian mantle-lithosphere indentation underneath the Pamir. New low-temperature thermochronologic data, i.e. apatite fission-track (AFT), apatite (AHe), and zircon (ZHe) (U-Th)/He ages, reveal the exhumation history of the SW-Tajik Tian Shan along two N-S-transects. We date the reactivation and explore its temporal and spatial variations. Three domains emerged. In the Central Domain (Zeravshan-Gissar and Vashan), AFT data&amp;#8212;aided by Raman-spectroscopic chemical-composition discrimination of detrital apatite samples and vitrinite-reflectance temperature estimates&amp;#8212;record a ~10-13 Ma onset of shortening and &gt;4 km exhumation. The Northern Domain, where the N-Zeravshan Fault constitutes a major Cenozoic structural divide reactivating the Paleozoic Zirabulak Suture, exhumed from &lt;4 km, but apatite AHe ages outline a similar reactivation history as in the Central Domain. The synchronous structural reactivation implies rapid shortening propagation from the Pamir indenter across the Afghan-Tajik fold-thrust belt into and across the Tian Shan. In the Southern Domain (Gissar Batholith), ~7&amp;#8210;9 Ma AFT and ~4 Ma AHe ages suggest a southward shortening propagation from the northern Domains and anew thrust generation. In the hanging wall of major thrusts, ~3&amp;#8210;7 Ma-old AFT ages record significant and persistent exhumation but ZHe data limit it to &lt;6 km. Most of the Southern and Central Domains cooled monotonously but temperature-time models indicate northward-decreasing reheating by syn-orogenic deposition, consistent with stratigraphic data.
Ice rise evolution derived from radar investigations at a promontory triple junction, Dronning Maud Land, East Antarctica
2023-02-25

Promontory ice rises are locally grounded features adjacent to ice shelves that are still connected to the ice sheet. Ice rises are an archive for the atmospheric and ice dynamic history of the respective outflow regions where the presence, absence, or migration of Raymond arches in radar stratigraphy represents a memory of the ice-rise evolution. However, ice rises and their inferred dynamic history are not yet used to constrain large-scale ice flow model spin-ups because matching the arch amplitudes includes many unknown parameters, e.g., those pertaining to ice rheology. In particular, anisotropic ice flow models predict gradients in ice fabric anisotropy on either side of an ice divide. However, this has thus far not been validated with observations. &amp;#160; The ground-based phase-sensitive Radio Echo Sounder (pRES) has previously been used to infer ice fabric types for various flow regimes using the co-polarized polarimetric coherence phase as a metric to extract information from the&amp;#160;birefringent radar backscatter. Here, we apply this technique using quad-polarimetric radar data along a 5 km transect across a ridge near the triple junction of Hammarryggen Ice Rise at the Princess Ragnhild Coast. A comparison with ice core data collected at the dome shows that the magnitude of ice fabric anisotropy can reliably be reconstructed from the quad-polarimetric data. We use the combined dataset also to infer the spatial variation of ice fabric orientations in the vicinity of the triple junction. The observations are integrated with airborne radar profiles and strain rates based on the shallow ice approximation. We then discuss whether estimated anisotropy from radar polarimetry on ice rises, in general, can be another observational constraint to better ice rises as an archive of ice dynamics.
Layer-optimized SAR processing with a mobile pRES to illuminate the internal layering of an alpine glacier
2023-02-25

The internal, isochronous layering of glaciers is shaped by accumulation and ice deformation. Information about these processes can be inferred from observing the layers using radar sounding. The reflectivity of the layers depends on density (permittivity) and acidity (conductivity) contrasts which tend to decrease with depth. At places like alpine glaciers where logistic limitations often only allow the deployment of lightweight and power-constrained ground-penetrating radar systems, it can therefore be challenging to illuminate the deeper radio-stratigraphy.The phase-sensitive Radio Echo Sounder (pRES) is a lightweight frequency modulated continuous wave radar which allows the use of coherent&amp;#160;Synthetic Aperture Radar (SAR) processing techniques to improve the signal-to-noise ratio of internal reflection horizons. Using a mobile pRES we collected a radar profile on an alpine glacier (Colle Gnifetti, Italy/Switzerland). Here, we demonstrate how to apply layer-optimized SAR techniques to make deep internal layers visible, which could not be seen by a conventional pulsed radar. We evaluate the requirements on spatial resolution and positioning accuracy during data acquisition, necessary for applying layer-optimized SAR processing, as they constrain the feasibility of the method. We further discuss implications on how density and acidity contribute to decreasing dielectric contrasts.
Emulating internal and external components of global temperature variability with a stochastic energy balance model and Bayesian approach
2023-02-25

To characterize Earth&amp;#8217;s temperature variability, it is necessary to better understand underlying mechanisms and contributions from internal and externally forced components. Here, we utilize a stochastic two-box energy balance model to emulate internal and forced global mean surface temperature (GMST) variability [1]. As target data for the emulation, we employ observations and 20 last millennium simulations from climate models of intermediate to high complexity. We infer the parameters of the stochastic EBM using the target data and a Bayesian approach, as implemented with a Markov Chain Monte Carlo algorithm in our &amp;#8220;ClimBayes&amp;#8221; software package [2]. This yields the best estimates of the EBM&amp;#8217;s forced and forced + internal response. Applying spectral analysis, we contrast timescale-dependent variances of the EBM&amp;#8217;s forced and forced + internal variance with that of the GMST target. Our findings show that the simple two-box stochastic EBM reproduces the characteristics of simulated global temperature fluctuations, even from comprehensive climate models. Minor deviations occur mainly at interannual timescales and are related to the simplistic representation of internal variability in the EBM. Furthermore, the relative contribution of internal dynamics increases with model complexity and decreases with timescale. Altogether, we demonstrate that the combined use of simple stochastic climate models and Bayesian inference provides a valuable tool to emulate climate variability across timescales. [1] M. Schillinger, B. Ellerhoff, R. Scheichl, and K. Rehfeld: &amp;#8220;Separating internal and externally forced contributions to global temperature variability using a Bayesian stochastic energy balance framework,&amp;#8221; Chaos,&amp;#160; https://doi.org/10.1063/5.0106123 (2022).&amp;#160; [2] M. Schillinger, B. Ellerhoff, R. Scheichl, and K. Rehfeld, &amp;#8220;The ClimBayes package in R,&amp;#8221; Zenodo, V. 0.1.1, https://doi.org/10.5281/zenodo.7317984 (2022).&amp;#160;
Two methods on one stone: Integrating visual and analytical techniques to clarify lithic raw material utilization in the Middle and Later Stone Age at Umhlatuzana rockshelter (South Africa)
2023-02-26

&lt;p&gt; We develop a study protocol to efficiently and accurately identify the raw material categories constituting the lithic assemblages at Umhlatuzana rockshelter, South Africa. We combine visual and analytical methods to establish a raw material database and to provide a more accurate insight into raw material selection during the Pleistocene Middle and Later Stone Age occupational sequence of Umhlatuzana. The protocol combines petrological properties (as studied on micromorphological samples), elemental composition of the specimens (as measured with p-XRF) and visual characterization by lithic analysts. We tested the protocol by applying it to a sample of piece-plotted lithics from four spits across the stratigraphic sequence. We document the intensive use of sandstone accounting for 25% of the tested sample. We also report a larger importance of hornfels and lower proportion of quartz than was reported in previous analyses (Kaplan 1990). The combination of micromorphological and p-XRF analysis of the Umhlatuzana assemblages demonstrates that with only visual inspection, the variability of raw materials used may be misinterpreted. With accurate raw material datasets, we are better equipped to answer techno-economic questions of the southern African Stone Age. &lt;br&gt;&lt;/p&gt;
Mid-Pleistocene volcano-tectonic fragmentation of the Turkana-Suguta Megalake
2023-02-26

The East African Rift System (EARS) is a key location for studying Plio-Pleistocene paleoclimate and hominin inhabitance. The region experienced profound reorganization during this interval as a response to volcanism, tectonics and climate change, and arguably detailed spatiotemporally coherent climate datasets could provide evidence of causal links between geologic change and hominin evolution.&amp;#160; However, continued tectonism, erosion, burial and volcanism obscures much of this information. Despite its rich fossil record, the Turkana basin in the northern Kenya Rift is no exception. It has been hypothesized that Lake Turkana and paleo-Lake Suguta to its south formed one 530-650 km long mega-lake before 221 ka ago, and was a major barrier for E-W dispersal of hominids and other terrestrial fauna. Here we present new information on basin development based on paleolandscape modeling and 87Sr/86Sr analysis on microfossils of newly discovered paleo-lake sequences in the Suguta Valley, permitting reconstruction of volcano-tectonic processes 900-700 ka ago. Contrary to previous assumptions, results suggest that two to three lakes separated by tectono-volcanic barriers formed instead of one mega-lake. These results have implications for previously formulated hypotheses about mega-lakes preventing W-E migration and exchange and suggest that during the early Middle Pleistocene E-W migrations were possible.
Sustainable Pathways under Climate Variability
2023-02-26

External forcings and feedback processes of the Earth system lead to timescale and state-dependent climate variability, causing substantial surface climate fluctuations in the past. Particularly relevant for future livelihoods, changing variability patterns could also modify the occurrence of extreme events. However, spatiotemporal mechanisms of climate variability are poorly understood. Likewise, the societal implications are weakly constrained, particularly variability&amp;#8217;s potential to drive sustainable transformation. The SPACY project investigates climate variability from past cold and warm periods to future scenarios. One research focus is how forcing mediates climate fluctuations. Bridging the gap between Earth system models and palaeoclimate proxies, we study vegetation and water isotope changes. A second focus is exploring sustainable pathways under climate variability, addressing potential interactions between artificial carbon dioxide removal and surface climate, among others.&amp;#160;In particular, we validate the ability of climate models to represent potential climate variability changes. Here, we focus on isotope-enabled simulations with dynamic vegetation. We find that models exhibit less local temperature and water isotope variability than paleoclimate proxies on decadal and longer timescales. Simulations with natural forcing agree much better with proxy records than unforced ones. The mean local temperature variability decreases with warming. Furthermore, we analyze potentials and limitations of terrestrial hydroclimate proxies. This includes water isotopes in speleothems and ice cores and vegetation indicators derived from pollen assemblages.Transferring our understanding to the future, we contribute to mitigation and sustainable transitions. Weather and climate extremes determine losses and damages, but their impact on socioeconomic development is poorly examined. We scrutinize damage parametrization of economic models regarding the ability to consider variability. While large-scale sequestration of atmospheric carbon dioxide is paramount to mitigation targets, its representation in climate models is insufficient. Accounting for feedbacks of carbon dioxide removal (CDR) requires model experiments with modified land surfaces. We develop CDR representations of &amp;#8220;artificial photosynthesis&amp;#8221; in Earth system models. Pollen records benchmark the simulated climate&amp;#8211;carbon dioxide&amp;#8211;vegetation interactions. This supports modeling endogenous societal land use decisions in the future.Our work continues to improve the understanding of long-term climate predictability. The combined knowledge from past climate studies and comprehensive modeling for future scenarios underlines the relevance of changing boundary conditions for a future within planetary boundaries.&amp;#160;&amp;#160;
Drought increases the relative contribution of mycorrhiza-mediated mineral N uptake of Sorghum bicolor
2023-02-26

Climate change scenarios forecast increasing droughts in large areas globally with significant effects on food production. Nutrient availability is an imperative factor for plant growth and it is greatly modulated by water availability. Nitrogen (N) availability extensively constrains plant growth in most terrestrial ecosystems especially in sub-Saharan Africa, where soils are unfertile and often degraded. How rhizosphere traits at the plant soil-interface affect N uptake in response to drought in N poor tropical soils remains elusive. We used 15N, and 13C pulse labelling to trace and quantify N transport from a root-restricted compartment by AMF across an air gap to the host plants coupled with quantifying the allocation of carbon to below-ground pools. Three sorghum genotypes were grown under optimal and water deficit conditions. By tracer analysis in the plant tissues, we assessed that drought enlarged uptake and delivery 15N by arbuscular mycorrhizal fungi (AMF) from the root restricted compartment across the air gap to the host plant. In addition, drought induced enhanced below-ground incorporation of recently assimilated carbon (C) into the microbial biomass pool both in rhizo-hyphosphere and hyphosphere. Enzyme assays revealed that whereas potential enzymatic reaction (Vmax) of chitinase was reduced under drought, that of leucine amino peptidase (LAP) was upregulated by water scarcity suggesting that N input from protein mineralization was relatively enhanced to that of chitin following moisture limitation. Michaelis-Menten constant (Km) of LAP strongly increased by drought compared to that of chitinase which displayed genotype-specific shifts in rhizosphere enzyme systems. We conclude that in addition to AMF symbiosis, enzyme regulation and enhanced belowground C allocation are key strategies to enhance nitrogen uptake under adverse conditions of resource limitations.
On the global synchronicity of glacial vegetation changes
2023-02-26

Vegetation responds to local climate and carbon dioxide changes with response times ranging from decades to millennia, depending on location, spatial scale, and vegetation characteristic. Here, we focus on orbital timescales, for which all available estimates suggest an equilibrium of vegetation and climate. Over the course of the last glacial period, global mean temperature varied between minima during Marine Isotope Stage (MIS) 4 and MIS2, and a maximum in MIS3. If orbital-scale climate changes followed this global trend across most of the globe, we would expect vegetation changes to feature a similar temporal evolution.Leveraging a global compilation of pollen records, we quantify the synchronicity of orbital-scale vegetation changes within and across regions during the last glacial period. We use the arboreal pollen fraction, statistical mode decompositions, and key taxa as indicators for forest cover changes. Our results suggest that a globally coherent forest cover minimum occurred during MIS2. However, we do not find evidence for other periods of coherent forest cover trends across the globe or either hemisphere. This indicates that vegetation changes were more regionally confined during earlier parts of the last glacial. As chronologies become more uncertain further back in time, we examine the likelihood of dating errors to explain the absence of globally coherent vegetation changes during MIS4 and MIS3. Finally, we compare our results with simulations of climate and vegetation to assess if models capture the diagnosed forest cover trends found in the pollen records. Moreover, this comparison allows us to infer the influence of temperature, moisture availability, and carbon dioxide on vegetation variations during the last glacial period.
Past and future changes of temperature and precipitation variability in climate model projections and transient simulations of the Last Deglaciation
2023-02-26

Reliable projections of future climate change are vital for mitigation and adaptation efforts. Such efforts require not only projections of mean changes but of changes in variability, too, since those directly affect the occurrence of extremes. The evaluation of climate models regarding their ability to simulate expected changes in variability of temperature and precipitation relies on the comparison of observations with simulations of past and present-day climate. As such, studying past periods of warming furthers the understanding of the climate system and its projected changes. However, the response of the climate system to forcings depends on the background state. Thus, understanding how insights from studies of the past transfer to future projections and the limitations of this transfer is vital.Here, we present an analysis of temperature and precipitation variability in transient simulations of the Last Deglaciation and projected future climate. To this end, we analyze how the distributions of temperature and precipitation change as exemplified by the moments of the distribution, i.e. variance, skewness and kurtosis. We identify trends in the projections and compare them to results for the Last Deglaciation and present commonalities and differences between the responses in these climate states. We further present how these changes relate to differences in the background state, forcings, and the timescales on which these forcings act as well as the limitations imposed by these differences. Based on this analysis of the state-dependency of variability and its change with a warming mean state, we present conclusions on how past climates can inform and support studies of future climate change.
Climate change, landscapes and human impacts during the 4.2kyr event in Mesopotamia and beyond
2023-02-26

The 4.2kyr event saw major changes in civilizations across the world, often attributed to climate change and widespread drought. Indeed, there are high quality palaeohydrological proxies that seem to document a significant drying at this time in Egypt, the Indus Valley and in the Near East. In Mesopotamia, settlements were abandoned, agricultural practices shifted and the Akkadian Empire ended. Climate model simulations covering 5000-3000 years ago are able to reproduce much of the evidence for Holocene climate change and some of the key reductions in mid-late Holocene precipitation. However, unlike some other regions, the annual mean rainfall in Mesopotamia at 4.2kyr is similar to the adjoining millennia. The climate model simulates significant droughts during this time, but these are within the range seen both before and after.The end of the middle Holocene saw rapid population growth in Mesopotamia, with significant urban centres putting pressure on local resources. Although the models suggest no significant change in climate, the archaeological evidence shows the exploitation of a dryer landscape, both in existing sites and new urban centres in dryer regions. This time also sees changing agricultural practices and the loss of available sources of wood. Vegetation models suggest little impact of climate change on the natural landscape, although drought years bring major losses in net primary productivity. However, human activities in Mesopotamia could have affected the landscape and exacerbated the impacts of existing drought cycles. We suggest that an unexceptional drought, combined with a large population and anthropogenic impacts on the landscape contributed to significant societal change in Mesopotamia at 4.2kyr.