Johan Vellekoop^a, Appy Sluijs^a, Jan Smit^b, Stefan Schouten^c,d, Johan W. H. Weijers^c, Jaap S. Sinninghe Damsté^c,d, and Henk Brinkhuis^a

^aMarine Palynology, Department of Earth Sciences, Faculty of Geosciences, Laboratory of Palaeobotany and Palynology, Utrecht University, 3584 CD, Utrecht, The Netherlands;
^bEventstratigraphy, Sedimentology, Faculty of Earth- and Life Sciences, VU University Amsterdam, 1081 HV, Amsterdam, The Netherlands;
^cGeochemistry, Department of Earth Sciences, Faculty of Geosciences, Utrecht University, 3584 CD, Utrecht, The Netherlands; and
^dDepartment of Marine Organic Biogeochemistry, NIOZ Royal Netherlands Institute of Sea Research, 1790 AB, Den Burg, Texel, The Netherlands

Here, for the first time (to our knowledge), we are able to demonstrate unambiguously that the impact at the Cretaceous–Paleogene boundary (K–Pg, ∼66 Mya) was followed by a so-called “impact winter.” This impact winter was the result of the injection of large amounts of dust and aerosols into the stratosphere and significantly reduced incoming solar radiation for decades. Therefore, this phase will have been a key contributory element in the extinctions of many biological clades, including the dinosaurs. The K–Pg boundary impact presents a unique event in Earth history because it caused global change at an unparalleled rate. This detailed portrayal of the environmental consequences of the K–Pg impact and aftermath aids in our understanding of truly rapid climate change.

Reference
Vellekoop J, Sluijs A, Smit J, Schouten S, Weijers JWH, Damsté JSS and Brinkhuis H (2014) Rapid short-term cooling following the Chicxulub impact at the Cretaceous–Paleogene boundary.  Proceedings of the National Academy of Sciences of the United States of America 111:7537.
[doi:10.1073/pnas.1319253111]

Link to Article

M. Köhler, A. Jones and N. Ysard

Institut d’Astrophysique Spatiale (IAS), Université Paris-Sud & CNRS, Bât. 121, 91405 Orsay, France

Context. The depletion of iron and sulphur into dust in the interstellar medium and the exact nature of interstellar amorphous silicate grains is still an open question.
Aims. We study the incorporation of iron and sulphur into amorphous silicates of olivine- and pyroxene-types and their effects on the dust spectroscopy and thermal emission.
Methods. We used the Maxwell-Garnett effective-medium theory to construct the optical constants for a mixture of silicates, metallic iron, and iron sulphide. We also studied the effects of iron and iron sulphide in aggregate grains.
Results. Iron sulphide inclusions within amorphous silicates that contain iron metal inclusions show no strong differences in the optical properties of the grains. A mix of amorphous olivine- and pyroxene-type silicate broadens the silicate features. An amorphous carbon mantle with a thickness of 10 nm on the silicate grains leads to an increase in absorption on the short-wavelength side of the 10 μm silicate band.
Conclusions. The assumption of amorphous olivine-type and pyroxene-type silicates and a 10 nm thick amorphous carbon mantle better matches the interstellar silicate band profiles. Including iron nano-particles leads to an increase in the mid-IR extinction, while up to 5 ppm of sulphur can be incorporated as Fe/FeS nano inclusions into silicate grains without leaving a significant trace of its presence.

Reference
Köhler M, Jones A and Ysard N (2014) A hidden reservoir of Fe/FeS in interstellar silicates?.  Astronomy & Astrophysics 565:L9.
[doi:10.1051/0004-6361/201423985]
Reproduced with permission © ESO

Link to Article