לוח שנה משולב

Earth climate varies on long and short time scales and its patterns have been derived by a variety of geochemical proxies. The most commonly used paleoclimate proxy is the oxygen isotopic composition in carbonates (δ18O). δ18O, however, is not a direct paleo-thermometer, and temperature reconstructions rely on independent estimates of water isotopic compositions. This caveat is particularly challenging on land, due to the complexity of hydrological variations that control the δ18O of the relevant waters. Carbonate clumped isotope (Δ47) thermometry is a new method for estimating paleo-temperatures that is independent of water isotopic compositions. It is therefore particularly useful as a temperature proxy in terrestrial environments. When combined with carbonate δ18O, it can also serve as a hydrological indicator. Here I will show the application of this method to the study of Late Pleistocene climate in terrestrial settings in the Levant and East Africa.
Glacial-Interglacial climate in the Northern Jordan Rift Valley (Israel) was examined by applying the clumped isotope thermometer to modern and fossil fresh water snails from water bodies in the region. The observed Glacial-Interglacial temperature change is similar to regional records but absolute temperatures are warmer. Paleo-water δ18O values have an opposite trend for the last glacial termination compared to the global ocean trends and regional records that reflects a change in the snow-rain dominance of the region’s rivers and changes in evaporation. An integration of Δ47 and δ18O measurements of land and freshwater mollusks from Lake Victoria, East Africa, provide information on past climatic conditions in the region. Results show no significant increase in precipitation for a time interval during which lake levels were significantly higher than in modern-day. These findings support non-climatic mechanisms for the lake level increase, such as tectonically driven change in lake drainage.

The design and synthesis of molecules that operate like microscopic machines is of fundamental importance. Such systems can be modeled theoretically by stochastic dynamics in which the system makes thermally activated transitions between a finite set of coarse-grained states. Artificial molecular machines can be driven away from thermal equilibrium in ways not found in biological molecular motors, in particular by time variation of external parameters. Such systems are often termed stochastic pumps. We demonstrate that a seemingly natural protocol of driving such systems does not lead to directed motion. We argue that this result holds also for systems of several particles with zero range interactions. We then consider the hydrodynamic limit of systems with many particles and states and show how the same no-go result can be derived from the non linear diffusion equation that describes the dynamics