Geoscience

New Constraints on Climate in the Circum-Mediterranean Region

Eastern Mediterranean sapropels are organic-rich, dark-colored layers that are cyclically intercalated with organic-poor sediments and that have been deposited from the Late Miocene to Holocene. Sapropel formation was triggered by periodic (ca 22 kyr) changes in solar energy received in the northern tropics and mid-latitudes during summer insolation maxima, which correspond to precession minima. The formation of sapropels can be interrupted at the centennial-scale periods. However, it remains uncertain how centennial-scale interruptions in conditions that give rise to sapropels may reflect atmospheric circulation changes in low latitudes. Prof. Liu Qingsong of the Institute of Geology and Geophysics, CAS and his colleagues systematically investigated the fluctuations of the aeolian dust inputs from the Sahara deserts by integrating magnetic, geochemical, and diffuse reflectance spectroscopy data from three sapropels that are representative of glacial (S6) and interglacial (S1, S5) conditions in the eastern Mediterranean Sea to assess environmental changes associated with sapropel formation. Small variations in goethite contents across sapropels indicate additional aeolian entrainment of goethite that formed under previous wet phases in the NE Sahara or in subtropical savannahs located further south. We link short-lived dust abundance peaks within sapropels S1 and S6 to centennial-scale periods of enhanced bottom-water circulation reported previously for these sapropels. Although these sapropel interruptions are driven by high-latitude cooling events, our results indicate that such centennial-scale episodes of atmospheric reorganization affected not only the eastern Mediterranean and the northern borderlands, but also subtropical North Africa.Generally speaking, the results point to a dominant low-latitude forcing on sapropel formation via boreal summer insolation maxima and intensification of the African monsoon. Liu Q.S., Larrasoa?a J.C., Torrent J., Roberts A.P., Rohling E.J., Liu Z.F., and Jiang Z.X., Palaeogeography, Palaeoclimatology, Palaeoecology, 2012, 333-334: 1-12, doi:10.1016.

Method to Assess Debris Flow Hazard Risk

Comprehensive assessment of debris flow hazard risk is a challenging task due to the uncertainties and complexity of various related factors. Liang Wanjie, Zhuang Dafang, Jiang Dong, et. al from the Institute of Geographical Sciences and Natural Resources Research (IGSNRR-CAS) proposed a novel approach for assessing debris flow hazard risk based on BN (Bayesian Network). Based on multiple types of resources and environmental datasets from Resources and Environmental Scientific Data Center (RESDC), using knowledge representation and inference functions of BN for complex system, a novel method for assessing debris flow hazard risk on national scale was presented. According to the cross-validation conducted on two different sample datasets and the comparison with SVM (Support Vector Machine) and ANNs (Artificial Neural Networks), the results show that BN provides a higher probability (85.66%) of hazard detection, a better precision (89.63%), and a bigger AUC (area under the receiver operating characteristic curve) value (0.95) than SVM and ANNs. It indicates that the BN-based model is useful for mapping and assessing debris flow hazard risk on a national scale. The result has been recently published on Geomorphology (2012）.