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Datasets of project "Paleo-climate Dynamics @ AWI"
Knorr, Gregor; Lohmann, Gerrit
During the Middle Miocene climate transition about 14 million years ago, the Antarctic ice sheet expanded to near-modern volume. Surprisingly, this ice sheet growth was accompanied by a warming in the surface waters of the Southern Ocean, whereas a slight deep-water temperature increase was delayed by more than 200 thousand years. Here we use a coupled atmosphere-ocean model to assess the relative effects of changes in atmospheric CO2 concentration and ice sheet growth on regional and global temperatures. In the simulations, changes in the wind field associated with the growth of the ice sheet induce changes in ocean circulation, deep-water...
Dietrich, Stephan; Werner, Martin; Spangehl, T; Lohmann, Gerrit
In this study we investigate the impact of mid- and late Holocene orbital forcing and solar activity on variations of the oxygen isotopic composition in precipitation. The investigation is motivated by a recently published speleothem d18O record from the well-monitored Bunker Cave in Germany. The record reveals some high variability on multi-centennial to millennial scales that does not linearly correspond to orbital forcing. Our model study is based on a set of novel climate simulations performed with the atmosphere general circulation model ECHAM5-wiso enhanced by explicit water isotope diagnostics. From the performed model experiments, we derive the following major results:...
Holstein, Jan M; Hensen, Christian
Pore water profiles from 24 stations in the South Atlantic (located in the Guinea, Angola, Cape, Guyana, and Argentine basins) show good correlations of oxygen and silicon, suggesting microbially mediated dissolution of biogenic silica. We used simple analytical transport and reaction models to show the tight coupling of the reconstructed process kinetics of aerobic respiration and silicon regeneration. A generic transport and reaction model successfully reproduced the majority of Si pore water profiles from aerobic respiration rates, confirming that the dissolution of biogenic silica (BSi) occurs proportionally to O2 consumption. Possibly limited to well-oxygenated sediments poor in BSi, benthic Si...
Holstein, Jan M; Hensen, Christian
Holstein, Jan M; Hensen, Christian
Laepple, Thomas; Schultz, Martin; Lamarque, J F; Madronich, S; Shetter, R E; Lefer, B L; Atlas, Elliot L