ALBERT

Description: Lower Cretaceous pedogenic carbonates exposed in SE China have been dated by U–Pb isotope measurements on single zircons taken from intercalated volcanic rocks, and the ages integrated with existing stratigraphy. 13 C values of calcretes range from –7.0 to –3.0 and can be grouped into five episodes of increasing–decreasing values. The carbon isotope proxy derived from these palaeosol carbonates suggests p CO 2 mostly in the range 1000–2000 parts per million by volume (ppmV) at S ( z ) (CO 2 contributed by soil respiration) = 2500 ppmV and 25°C during the Hauterivian–Albian interval ( c . 30 Ma duration). Such atmospheric CO 2 levels are 4–8 times pre-industrial values, almost double those estimated by geochemical modelling and much higher than those established from stomatal indices in fossil plants. Rapid rises in p CO 2 are identified for early Hauterivian, middle Barremian, late Aptian, early Albian and middle Albian time, and rapid falls for intervening periods. These episodic cyclic changes in p CO 2 are not attributed to local tectonism and volcanism but rather to global changes. The relationship between reconstructed p CO 2 and the development of large igneous provinces (LIPs) remains unclear, although large-scale extrusion of basalt may well be responsible for relatively high atmospheric levels of this greenhouse gas. Suggested levels of relatively low p CO 2 correspond in timing to intervals of regional to global enrichment of marine carbon in sediments and negative carbon isotope ( 13 C) excursions characteristic of the oceanic anoxic events OAE1a (Selli Event), Kilian and Paquier events (constituting part of the OAE 1b cluster) and OAE1d. Short-term episodes of high p CO 2 coincide with negligible carbon isotope excursions associated with the Faraoni Event and the Jacob Event. Given that episodes of regional organic carbon burial would draw down CO 2 and negative 13 C excursions indicate the addition of isotopically light carbon to the ocean–atmosphere system, controls on the carbon cycle in controlling p CO 2 during Early Cretaceous time were clearly complex and made more so by atmospheric composition also being affected by changes in silicate weathering intensity.

Description: The electronic and magnetic properties of tetravalent-ion-doped La 0.85 Zr 0.15 MnO 3 (LZMO) thin films that were epitaxially grown on SrTiO 3 (STO) and MgO substrates were studied using temperature-dependent x-ray diffraction (XRD), x-ray absorption near-edge structure, x-ray linear dichroism, and x-ray magnetic circular dichroism at the Mn L 3,2 - and K -edge. XRD studies reveal that the LZMO thin films have compressive and tensile strains (along the c -axis) on the STO and MgO substrates, respectively. As the temperature is reduced from room temperature to below magnetic transition temperature, the preferentially occupied Mn majority-spin e g orbital changes from the in-plane d x 2 -y 2 to the out-of-plane d 3 z 2 -r 2 orbital for LZMO/STO, and vice versa for LZMO/MgO. Experimental results suggest that the new hopping path that is mediated by the Mn 2+ ions triggers a stronger d 3 z 2 -r 2 orbital ordering of Mn 3+ ions and enhances the ferromagnetic coupling between the Mn spin moments of t 2g electrons in LZMO/STO, whereas the strong tensile strain stabilizes the d x 2 -y 2 orbital by inducing lattice distortions of the MnO 6 octahedra in LZMO/MgO.