Aridity-driven decoupling of δ¹³C between pedogenic carbonate and soil organic matter

Pedogenic carbonate is an invaluable archive for reconstructing continental paleoclimate and paleoecology. The δ¹³C of pedogenic carbonate (δ¹³C_c) has been widely used to document the rise and expansion of C₄ plants over the Cenozoic. This application requires a fundamental presumption that in soil pores, soil-respired CO₂ dominates over atmospheric CO₂ during the formation of pedogenic carbonates. However, the decoupling between δ¹³C_c and δ¹³C of soil organic matter (δ¹³C_(SOM)) have been observed, particularly in arid regions, suggesting that this presumption is not always valid. To evaluate the influence of atmospheric CO₂ on soil δ¹³C_c, here we performed systematic δ¹³C analyses of paleosols across the Chinese Loess Plateau, with the sample ages spanning three intervals: the Holocene, the Late Pleistocene, and the mid-Pliocene warm period. Our paired δ¹³C_c and δ¹³C_(SOM) data reveal broadly divergent trending patterns. Using a two-component CO₂-mixing model, we show substantial incorporations of atmospheric CO₂ (up to 60%) into soil pore space during carbonate precipitation. This result readily explains the enrichment of δ¹³C_c and its divergence from δ¹³C_(SOM). As a consequence, δ¹³C of pedogenic carbonates formed under semiarid and/or arid conditions are largely driven by regional aridity through its control on soil CO₂ composition, and thus cannot be used to evaluate the relative abundance of C₃ versus C₄ plants. Nonetheless, these carbonates can be applied for atmospheric CO₂ reconstructions, even for periods with low CO₂ levels

Aridity-driven decoupling of δ¹³C between pedogenic carbonate and soil organic matter

Pedogenic carbonate is an invaluable archive for reconstructing continental paleoclimate and paleoecology. The δ¹³C of pedogenic carbonate (δ¹³C_c) has been widely used to document the rise and expansion of C₄ plants over the Cenozoic. This application requires a fundamental presumption that in soil pores, soil-respired CO₂ dominates over atmospheric CO₂ during the formation of pedogenic carbonates. However, the decoupling between δ¹³C_c and δ¹³C of soil organic matter (δ¹³C_(SOM)) have been observed, particularly in arid regions, suggesting that this presumption is not always valid. To evaluate the influence of atmospheric CO₂ on soil δ¹³C_c, here we performed systematic δ¹³C analyses of paleosols across the Chinese Loess Plateau, with the sample ages spanning three intervals: the Holocene, the Late Pleistocene, and the mid-Pliocene warm period. Our paired δ¹³C_c and δ¹³C_(SOM) data reveal broadly divergent trending patterns. Using a two-component CO₂-mixing model, we show substantial incorporations of atmospheric CO₂ (up to 60%) into soil pore space during carbonate precipitation. This result readily explains the enrichment of δ¹³C_c and its divergence from δ¹³C_(SOM). As a consequence, δ¹³C of pedogenic carbonates formed under semiarid and/or arid conditions are largely driven by regional aridity through its control on soil CO₂ composition, and thus cannot be used to evaluate the relative abundance of C₃ versus C₄ plants. Nonetheless, these carbonates can be applied for atmospheric CO₂ reconstructions, even for periods with low CO₂ levels

Low CO_2 levels of the entire Pleistocene epoch

Quantifying ancient atmospheric pCO_2 provides valuable insights into the interplay between greenhouse gases and global climate. Beyond the 800-ky history uncovered by ice cores, discrepancies in both the trend and magnitude of pCO_2 changes remain among different proxy-derived results. The traditional paleosol pCO_2 paleobarometer suffers from largely unconstrained soil-respired CO_2 concentration (S(z)). Using finely disseminated carbonates precipitated in paleosols from the Chinese Loess Plateau, here we identified that their S(z) can be quantitatively constrained by soil magnetic susceptibility. Based on this approach, we reconstructed pCO_2 during 2.6–0.9 Ma, which documents overall low pCO_2 levels (<300 ppm) comparable with ice core records, indicating that the Earth system has operated under late Pleistocene pCO_2 levels for an extended period. The pCO_2 levels do not show statistically significant differences across the mid-Pleistocene Transition (ca. 1.2–0.8 Ma), suggesting that CO_2 is probably not the driver of this important climate change event

Efficient subspace skyline query based on user preference using MapReduce

Subspace skyline, as an important variant of skyline, has been widely applied for multiple-criteria decisions, business planning. With the development of mobile internet, subspace skyline query in mobile distributed environments has recently attracted considerable attention. However, efficiently obtaining the meaningful subset of skyline points in any subspace remains a challenging task in the current mobile internet. For more and more mobile applications, subspace skyline query on mobile units is usually limited by big data and wireless bandwidth. To address this issue, in this paper, we propose a system model that can support subspace skyline query in mobile distributed environment. An efficient algorithm for processing the Subspace Skyline Query using MapReduce (SSQ) is also presented which can obtain the meaningful subset of points from the full set of skyline points in any subspace. The SSQ algorithm divides a subspace skyline query into two processing phases: the preprocess phase and the query phase. The preprocess phase includes the pruning process and constructing index process which is designed to reduce network delay and response time. Additionally, the query phase provides two filtering methods, SQM-filtering and ε-filtering, to filter the skyline points according to user preference and reduce network cost. Extensive experiments on real and synthetic data are conducted and the experimental results indicate that our algorithm is much efficient, meanwhile, the pruning strategy can further improve the efficiency of the algorithm

Pluripotent Transcription Factors Possess Distinct Roles in Normal versus Transformed Human Stem Cells

Cancer and normal stem cells (SCs) share proliferative properties of self-renewal and expression of key transcription factors (TFs). Despite similar TF identities, the functional role of specific TFs responsible for retaining SC state has yet to be examined in cancer.Here, we compare the role of Oct4 and Nanog, two-core pluripotent TFs, in transformed (t-hPSCs), and normal human pluripotent stem cells (hPSCs). Unlike normal SCs, self-renewal and survival of t-hPSCs were found to be independent of Oct4. In contrast, t-hPSCs exhibit hypersensitivity to reduction in Nanog and demonstrate complete loss of self-renewal coupled with apoptosis. Dual and sequential knockdown of Oct4 and Nanog revealed that sensitivity of t-hPSCs to Nanog was Oct4 dependent.Our study indicates a bifurcation for the role of two-core SC and cancer related TFs in self-renewal and survival processes. We suggest that the divergent roles of these TFs establish a paradigm to develop novel therapeutics towards selective destruction of aggressive tumors harboring cancer stem cells (CSCs) with similar molecular signatures