Low heavy-element photospheric abundance: a challenge for solar modeling

Recent spectroscopic data pointing to low heavy-element abundances Z pose a severe problem for solar-structure modeling. The low-Z abundances imply a lower opacity and a relatively shallow convective zone, both of which are in obvious contradiction with the observed helioseismic sound-speed profile. This paper presents a series of solar models with different heavy-element abundances. The SAHA-S equation of state and OPAL opacities properly take into account the respective heavy-element abundances. Diffusion of individual elements is also included in the models. Sound-speed profiles are compared with inversion results and it is shown that the models with low Z are in disagreement with the inversion data. Even combining the effect of diffusion, overshooting and mixing for the sound-speed profile did not lead to a solution of the low-Z problem. Models with varied neon abundance have also been computed. It turned out that a substantial increase of the neon abundance could produce a model in agreement with the sound-speed inversion but the required abundance increase would be unrealistic. The effect of the neon enhancement on the adiabatic exponent profile in the convection zone is also presented.     

Seasonal mortality rates of Oithona similis (Cyclopoida) in a large Arctic fjord

Instantaneous mortality rates of the common planktonic copepod Oithona similis were investigated for the first time in Kola Bay, a region of the Barents Sea that is influenced by freshwater discharge. The rates were estimated in different seasons (December, May, September 2005 and July 2006). A vertical life table approach (VLT) was used to assess mortality. The total abundance of O. similis (copepodites IV and V, and adults) was highest in autumn and lowest in winter. The maximum mortality of O. similis for the stage pair copepodite IV–copepodite V (0.005 ± 0.001 day^?1) occurred in December 2005, while the highest mortality rates for the pairs copepodite VM–adult male (0.453 ± 0.026 day^?1) and copepodite VF–adult female (0.228 ± 0.006 day^?1) occurred in summer 2006. Simple regression analyses showed that the total abundance of each stage and the mortality rates were positively significantly correlated with water temperature. The mortality rates for the stage pairs copepodite VM–adult male and copepodite VF–adult female were positively significantly correlated with chlorophyll a concentration. The abundance and mortality rate of O. similis in each season was determined by life cycle factors, and possibly by the dynamics of its food resources and potential predators.     

Distribution and changes of active layer thickness (ALT) and soil temperature (TTOP) in the source area of the Yellow River using the GIPL model

Active layer thickness (ALT) is critical to the understanding of the surface energy balance, hydrological cycles, plant growth, and cold region engineering projects in permafrost regions. The temperature at the bottom of the active layer, a boundary layer between the equilibrium thermal state (in permafrost below) and transient thermal state (in the atmosphere and surface canopies above), is an important parameter to reflect the existence and thermal stability of permafrost. In this study, the Geophysical Institute Permafrost Model (GIPL) was used to model the spatial distribution of and changes in ALT and soil temperature in the Source Area of the Yellow River (SAYR), where continuous, discontinuous, and sporadic permafrost coexists with seasonally frozen ground. Monthly air temperatures downscaled from the CRU TS3.0 datasets, monthly snow depth derived from the passive microwave remote-sensing data SMMR and SSM/I, and vegetation patterns and soil properties at scale of 1:1000000 were used as input data after modified with GIS techniques. The model validation was carried out carefully with ALT in the SAYR has significantly increased from 1.8 m in 1980 to 2.4 m in 2006 at an average rate of 2.2 cm yr^?1. The mean annual temperature at the bottom of the active layer, or temperature at the top of permafrost (TTOP) rose substantially from ?1.1°C in 1980 to ?0.6°C in 2006 at an average rate of 0.018°C yr^?1. The increasing rate of the ALT and TTOP has accelerated since 2000. Regional warming and degradation of permafrost has also occurred, and the changes in the areal extent of regions with a sub-zero TTOP shrank from 2.4×10⁴ to 2.2×10⁴ km² at an average rate of 74 km² yr^?1. Changes of ALT and temperature have adversely affected the environmental stability in the SAYR.