Institute of Earth Sciences

The influence of hydrosol nonsphericity on the polarization characteristics of light under water is investigated by combining accurate single-scattering models for randomly oriented spheroidal scatterers with a radiative transfer model that employs Stokes formalism and considers refraction of direct unpolarized solar radiation and 100% linearly polarized radiation at the air–water interface followed by single scattering. Variations in what we call the “linear polarization phase function” (the degree of linear polarization as a function of scattering angle and the angle of linear polarization as a function of scattering angle) are examined for a wide range of spheroid aspect ratios and complex refractive indices of hydrosols. Implications for polarization-sensitive marine organisms and for remote sensing of the marine environment are discussed.

A new paper by our graduate student Yonathan Keinan (with co-authors Miryam Bar-Matthews, Avner Ayalon, and Tami Zilberman (Geological Survey of Israel) and Amotz Agnon and Amos Frumkin (the Institute of Earth Sciences, Hebrew University) analyzes speleothems from the Zalmon Cave, located at the current rain shadow zone in the northern Upper Jordan River Valley, Israel. The speleothm data indicate a humid phase with increased precipitation during the last glacial, borne out from a change in the storm track over the eastern Mediterranean. Zalmon precipitation was probably somewhat lower than in the higher altitudes in the Upper Galilee and the central Judean Mountains of Israel. This conclusion supports earlier views of increased precipitation in the headwaters of the Dead Sea basin during that interval. Furthermore, the new paper indicates that unlike the spelothems from the Ma'ale Efrayim cave, which are impacted by the rain shadow of the Samaria Mountains, and show no speleothm activity during the interglacial and possibly dry vadose zone, these Zalmon Cave speleothm data indicate permanent water in the vadose zone during both glacial and interglacials. 

The isotopic composition of Thorium in marine sediment cores from east of Africa shows that Sahara dust fluxes decreased by at least 50% between the last deglaciation and the mid Holocene, while the Northern Sector of the Red Sea remained unchanged. This constrains the African Humid Period impact to have extended up to ca. 22°N, across a more limited region than previously thought.