How surface deformation within mountain ranges relates to tectonic processes at depth is not well understood. The upper crust of the Tibetan Plateau is generally thought to be poorly coupled to the underthrusting Indian crust because of an intervening low-viscosity channel. Here, however, we show that the contrast in tectonic regime between primarily strike-slip faulting in northern Tibet and dominantly normal faulting in southern Tibet requires mechanical coupling between the upper crust of southern Tibet and the underthrusting Indian crust. Such coupling is inconsistent with the presence of active ‘channel flow’ beneath southern Tibet, and suggests that the Indian crust retains its strength as it underthrusts the plateau. These results shed new light on the debates regarding the mechanical properties of the continental lithosphere, and the deformation of Tibet.

Evidence for mechanical coupling and strong Indian lower crust beneath southern Tibet (Invited)

https://research-information.bris.ac.uk/ws/files/256197550/1_s2.0_S2468265920300627_main.pdf

Cenozoic topography, monsoons and biodiversity conservation within the Tibetan Region: An evolving story.

The authors quantify the relationship between the location of the intertropical convergence zone (ITCZ) and the atmospheric heat transport across the equator (AHTEQ) in climate models and in observations. The observed zonal mean ITCZ location varies from 5.38S in the boreal winter to 7.28N in the boreal summer with an annual mean position of 1.658N while the AHTEQvaries from 2.1 PW northward in the boreal winter to 2.3 PW southward in the boreal summer with an annual mean of 0.1 PW southward. Seasonal variations in the ITCZ location and AHTEQ are highly anticorrelated in the observations and in a suite of state-of-the-art coupledclimatemodelswithregressioncoefficientsof22.78and22.48PW 21 respectively.Itisalsofoundthat seasonal variations in ITCZ location and AHTEQ are well correlated in a suite of slab ocean aquaplanet simulations with varying ocean mixed layer depths. However, the regression coefficient between ITCZ location and AHTEQ decreases with decreasing mixed layer depth as a consequence of the asymmetry that develops between the winter and summer Hadley cells as the ITCZ moves farther off the equator. The authors go on to analyze the annual mean change in ITCZ location and AHTEQ in an ensemble of climate perturbation experiments including the response to CO2 doubling, simulations of the Last Glacial Maximum, and simulations of the mid-Holocene. The shift in the annual average ITCZ location is also strongly anticorrelated with the change in annual mean AHTEQ with a regression coefficient of 23.28 PW 21 , similar to that found over the seasonal cycle.

The relationship between ITCZ location and cross equatorial atmospheric heat transport; from the seasonal cycle to the last glacial maximum

\n The theory of representative bureaucracy posits that citizens will view policy and service delivery more favorably if public servants share their background characteristics. However, automation is changing public service delivery, limiting human involvement in the process. We examine attitudes toward automated decision making through the lens of representative bureaucracy, generating expectations about how a lack of passive representation will affect views toward automated versus human decision making in government. Using a survey experiment, we find evidence that black citizens are more likely to rate automated decision making higher, compared with police officers, on fairness and preference when exposed to a lack of passive representation in a police agency. We do not find evidence of this relationship for white citizens. Our findings provide insight into the way in which passive representation conditions minority citizens’ views toward automation, highlighting the importance of considering representation, or lack thereof, as governments contemplate the adoption of automated services.

Representative Bureaucracy and Attitudes Toward Automated Decision Making

Abundant evidence from marine, ice-core and terrestrial records demonstrates that Earth’s climate has experienced co-evolution of orbital- and millennial-scale variability through the Pleistocene. The varying magnitude of millennial climate variability (MCV) was linked to orbitally paced glacial cycles over the past 800 kyr. Before this interval, global glaciations were less pronounced but more frequent, yet scarcity of a long-term integration of high-resolution continental and marine records hampers our understanding of the evolution and dynamics of MCV before the mid-Pleistocene transition. Here we present a synthesis of four centennial-resolved elemental time series, which we interpret as proxies for MCV, from North Atlantic, Iberian margin, Balkan Peninsula (Lake Ohrid) and Chinese Loess Plateau. The proxy records reveal that MCV was pervasive and persistent over the mid-latitude Northern Hemisphere during the past 1.5 Myr. Our results suggest that the magnitude of MCV is not only strongly modulated by glacial boundary conditions on Earth after the mid-Pleistocene transition, but also persistently influenced by variations in precession and obliquity through the Pleistocene. The combination of these four proxies into a new MCV stack offers a credible reference for further assessing the dynamical interactions between orbital and millennial climate variability. Orbital forcing consistently influenced the magnitude of millennial-scale climate variability through the Pleistocene, according to an analysis of four high-resolution Northern Hemisphere proxy records covering the past 1.5 Myr.

Persistent orbital influence on millennial climate variability through the Pleistocene

The Tibetan Plateau exerts a major influence on Asian climate, but its long-term environmental history remains largely unknown. We present a detailed record of vegetation and climate changes over the past 1.74 million years in a lake sediment core from the Zoige Basin, eastern Tibetan Plateau. Results show three intervals with different orbital- and millennial-scale features superimposed on a stepwise long-term cooling trend. The interval of 1.74–1.54 million years ago is characterized by an insolation-dominated mode with strong ~20,000-year cyclicity and quasi-absent millennial-scale signal. The interval of 1.54–0.62 million years ago represents a transitional insolation-ice mode marked by ~20,000- and ~40,000-year cycles, with superimposed millennial-scale oscillations. The past 620,000 years are characterized by an ice-driven mode with 100,000-year cyclicity and less frequent millennial-scale variability. A pronounced transition occurred 620,000 years ago, as glacial cycles intensified. These new findings reveal how the interaction of low-latitude insolation and high-latitude ice-volume forcing shaped the evolution of the Tibetan Plateau climate.

Evolution of vegetation and climate variability on the Tibetan Plateau over the past 1.74 million years

The X-ray fluorescence (XRF) core-scanned Rb/Sr ratios of lake sediments have been widely used as a proxy for chemical weathering intensity and past climate change. However, some factors could affect Rb/Sr ratios, causing misinterpretation and limiting its application. In this study, we present a high-resolution XRF core-scanned Rb/Sr record of core ZB13-C1 from the Zoige Basin in the eastern Tibetan Plateau. To validate its application, we correlated this record with the chemical index of alteration (CIA) and other paleoclimatic proxies. Our results showed that (1) the core-scanned Rb/Sr ratios and CIA were reliable proxies of chemical weathering intensity in fine-grained sedimentary sequences; (2) the low values of core-scanned Rb/Sr ratios and CIA were significantly correlated with high total organic carbon content, arboreal pollen content, carbonate content, and C/N ratios, confirming its reliability as a proxy for the Asian summer monsoon intensity; (3) the core-scanned Rb/Sr ratios at core depths of 25–0.3 and 56–17 m were unable to reliably reflect chemical weathering intensity due to both the grain-size effect and the low test accuracy. Our study highlights the need for mutual verification of multiple indicators before accurately applying Rb/Sr as a paleoclimatic proxy in other similar study areas.

Paleoclimatic indication of X-ray fluorescence core-scanned Rb/Sr ratios: A case study in the Zoige Basin in the eastern Tibetan Plateau

A promising method of reconstructing past vegetation from pollen records uses mathematical models of the relationship between pollen and vegetation. These can be calibrated using the extended R-value (ERV) approach on datasets of modern pollen assemblages and related vegetation surveys. This study presents the results of calibrating the pollen-vegetation models for non-arboreal pollen types in alpine meadow habitats on the Tibetan Plateau. Surface soil samples were analysed for pollen and the surrounding vegetation was recorded at 30 randomly located sites in the Zoige basin, northeastern Tibetan Plateau. ERV analysis found that the most reliable results were obtained when using ERV sub-models 1 and 2, and distance-weighting the vegetation data by applying the taxon-specific Prentice–Sutton method. The relevant source area of pollen for these soil samples was found to be ca. 200 m. Relative pollen productivities (RPP) of 15 non-arboreal taxa were estimated relative to Cyperaceae (RPPCyp). The taxa can be divided into three groups according to their RPPs, those with high RPPCyp values > 1.68 (Thalictrum, Artemisia, Caryophyllaceae, Chenopodiaceae and Plantago), those with moderate values (0.42–0.62) (Taraxacum-type, Apiaceae, Polygonum and Aster-type), and those with low values < 0.4 (Gentianaceae, Potentilla, Brassicaceae, Saussurea-type and Poaceae). The RPP values obtained from our study differ from those of previous studies in other parts of China, and form the basis for future reconstruction of palaeovegetation on the Tibetan Plateau through model-based methods, such as the Landscape Reconstruction Algorithm, or Multiple Scenario Approach.

/pdf/relative-pollen-productivity-estimates-for-alpine-meadow-3gb1pp6jrl.pdf

Relative pollen productivity estimates for alpine meadow vegetation, northeastern Tibetan Plateau

Knowledge of historical changes in moisture within semi-arid and arid regions is the basis of climatic change predictions and strategies in response to long-term drought. In this study, a multiproxy peat record with high-resolution from Sichanghu in the northern Tianshan was used to document the changes in vegetation and climate over the past 450 years in the arid Central Asia. The pollen, grain size, and loss on ignition (LOI) records indicate that the productivity of local peat began to increase at ∼1730 AD. The vegetation in the Sichanghu area experienced several transitions, from temperate desert to dense desert, marsh meadow, and steppe desert vegetation. The climate in the study area was extremely dry during the early stages of the Little Ice Age (LIA) (before 1730 AD) and relatively wet during the late stages (1730–1880 AD). The inferred changes in the moisture conditions of the Sichanghu peatland since the LIA may have been controlled by the extent of Arctic sea ice, the North Atlantic Oscillation, and the Siberian High via the connections of large-scale atmospheric circulations such as the Westerlies.

Weihe Ren

Papers

Evolution of vegetation and climate variability on the Tibetan Plateau over the past 1.74 million years

Paleoclimatic indication of X-ray fluorescence core-scanned Rb/Sr ratios: A case study in the Zoige Basin in the eastern Tibetan Plateau

Relative pollen productivity estimates for alpine meadow vegetation, northeastern Tibetan Plateau

Changes in vegetation and moisture in the northern Tianshan of China over the past 450 years