Anomalous mid-twentieth century atmospheric circulation change over the South Atlantic compared to the last 6000 years

Determining the timing and impact of anthropogenic climate change in data-sparse regions is a considerable challenge. Arguably, nowhere is this more difficult than the Antarctic Peninsula and the subantarctic South Atlantic where observational records are relatively short but where high rates of warming have been experienced since records began. Here we interrogate recently developed monthly-resolved observational datasets from the Falkland Islands and South Georgia, and extend the records back using climate-sensitive peat growth over the past 6000 years. Investigating the subantarctic climate data with ERA-Interim and Twentieth Century Reanalysis, we find that a stepped increase in precipitation across the 1940s is related to a change in synoptic atmospheric circulation: a westward migration of quasi-permanent positive pressure anomalies in the South Atlantic has brought the subantarctic islands under the increased influence of meridional airflow associated with the Amundsen Sea Low. Analysis of three comprehensively multi-dated (using 14C and 137Cs) peat sequences across the two islands demonstrates unprecedented growth rates since the mid-twentieth century relative to the last 6000 years. Comparison to observational and reconstructed sea surface temperatures suggests this change is linked to a warming tropical Pacific Ocean. Our results imply 'modern' South Atlantic atmospheric circulation has not been under this configuration for millennia

Tephrochronology

Tephrochronology is the use of primary, characterized tephras or cryptotephras as chronostratigraphic marker beds to connect and synchronize geological, paleoenvironmental, or archaeological sequences or events, or soils/paleosols, and, uniquely, to transfer relative or numerical ages or dates to them using stratigraphic and age information together with mineralogical and geochemical compositional data, especially from individual glass-shard analyses, obtained for the tephra/cryptotephra deposits. To function as an age-equivalent correlation and chronostratigraphic dating tool, tephrochronology may be undertaken in three steps: (i) mapping and describing tephras and determining their stratigraphic relationships, (ii) characterizing tephras or cryptotephras in the laboratory, and (iii) dating them using a wide range of geochronological methods. Tephrochronology is also an important tool in volcanology, informing studies on volcanic petrology, volcano eruption histories and hazards, and volcano-climate forcing. Although limitations and challenges remain, multidisciplinary applications of tephrochronology continue to grow markedly

A Straightforward Method of Analysis for Direct Quantum Dynamics: Application to the Photochemistry of a Model Cyanine

We present in a new way of analyzing direct quantum dynamics simulations based on a Mulliken-type population analysis. This provides a straightforward interpretation of the wavepacket in much the same way as semiclassical trajectories are usually analyzed The result can be seen as a coupled set of quantum trajectories. We apply this to the study of the photochemistry of a 12-atom model cyanine to explore possibilities for intelligent optimal control The work presented here builds on previous semiclassical dynamics simulations [Hunt, P. A.; Robb, M. A J Am Chem. Soc. 2005 127, 5720] Those calculations suggested that, by controlling the distribution of momentum components in the initial wavepacket, it should be possible to drive the system to a specific region of the conical intersection seam and ultimately control the product distribution. This was confirmed experimentally by optimal control methods [Dietzek, B; Bruggemann, B, Pascher, T; Yartsev, A.J Ant. Chem. Soc 2007 129, 13014] This paper aims to demonstrate this in a quantum dynamics context and give further insight into the conditions required for control Our results show that directly addressing the trans-cis torsional modes is not efficient. Instead, one needs to decrease the momentum in the skeletal deformation coordinates to prompt radiationless decay near the minimum conical intersection at large twist angles