Modification of Turbulence at the Air-Sea Interface Due to the Presence of Surfactants and Implications for Gas Exchange. Part II: Numerical Simulations

We conducted high-resolution non-hydrostatic numerical simulations to study the effect of surfactants on near-surface turbulence. Laboratory experiments at the UM RSMAS ASIST facility presented in a companion paper report a reduction of turbulence below the air-sea interface and an increase of the surface drift velocity in the presence of surfactants. We implement the effect of surfactants as a rheological, viscoelastic boundary condition at the surface. Our numerical experiments are consistent with the results of the laboratory experiments. We also simulated the effect of surfactants on the temperature difference across the thermal molecular sublayer (cool skin) and on gas transfer velocity. The numerical simulations demonstrate an increase in the temperature difference across the cool skin and reduction of the gas transfer velocity in the presence of surfactant. The results also reveal the effect of surfactants on the different types of molecular sublayers (viscous, thermal and diffusion), which is important for the development of proper parameterization of the interfacial component of air-sea gas exchange under low and moderate wind speed conditions.https://nsuworks.nova.edu/occ_facbooks/1052/thumbnail.jp

Hidden secrets of deformation: Impact-induced compaction within a CV chondrite

The CV3 Allende is one of the most extensively studied meteorites in worldwide collections. It is currently classified as S1—essentially unshocked—using the classification scheme of Stöffler et al. (1991), however recent modelling suggests the low porosity observed in Allende indicates the body should have undergone compaction-related deformation. In this study, we detail previously undetected evidence of impact through use of Electron Backscatter Diffraction mapping to identify deformation microstructures in chondrules, AOAs and matrix grains. Our results demonstrate that forsterite-rich chondrules commonly preserve crystal-plastic microstructures (particularly at their margins); that low-angle boundaries in deformed matrix grains of olivine have a preferred orientation; and that disparities in deformation occur between chondrules, surrounding and non-adjacent matrix grains. We find heterogeneous compaction effects present throughout the matrix, consistent with a highly porous initial material. Given the spatial distribution of these crystal-plastic deformation microstructures, we suggest that this is evidence that Allende has undergone impact-induced compaction from an initially heterogeneous and porous parent body. We suggest that current shock classifications (Stöffler et al., 1991) relying upon data from chondrule interiors do not constrain the complete shock history of a sample