No abstract

At high altitudes (Ͼ1000 m) throughout the Dry Valleys, Antarctica, liquid water is rare, yet ground ice, which may be millions of years old, is pervasive in glacial sediments and bedrock. The origin of this ice is different from its arctic and alpine counterparts and may be similar to water on Mars. We present chemical and isotopic analyses of Antarctic ground ice from cores of Sirius Group sediments at Table Mountain in the Dry Valleys. These data, together with the presence of diagenetic calcite and chabazite in the frozen sediments, indicate that the ice and minerals accumulated over long periods of time from atmospheric water vapor and brine films formed on the surface of the ground. This analogy indicates that ferric-bearing minerals could precipitate under present conditions in the Martian soil.

[1] Concentrations of 10 Be, 9 Be, and salt in a soil profile from the lower Wright Valley reveal two distinct climatic regimes. In the upper horizon of the soil profile, a thin gravel lag overlies the Hart ash (3.9 ± 0.3 Ma), and this sits on the surface of a well-developed paleosol, which makes up the lower horizon of the profile. The surface lag has a smaller inventory of 10 Be than predicted from the fallout rate at nearby Taylor Dome. Below the gravel, the Hart ash is virtually devoid of 10 Be and the calculated erosion rate for the gravel-ash horizon is 2.8 m Ma À1 . The paleosol, which has been sealed by the overlying ash, has a relatively high inventory of 10 Be, and this gives it a significantly lower erosion rate (0.5 m Ma À1 ) than the gravel-ash horizon. Beryllium-10 migrates into a soil profile either by solution transport or by fine-particle translocation. The lack of 10 Be in the Hart ash indicates that neither of these processes have been active at this site for the past 3.9 Ma. However, enrichment of 10 Be in the paleosol indicates they were active prior to deposition of the ash. The most likely reason these processes were active is that there was more water, which could translocate fine particles with attached 10 Be. Thus, the gravel-ash horizon developed in climatic conditions similar to the present, while the paleosol developed in wetter and possibly warmer conditions during the early Pliocene and possibly before that time.

[1] We present the first dedicated study of the thermal properties of perennially frozen, ice-cemented, subsurface Dry Valley permafrost. From time series analysis of 14 months' temperature measurements, we resolve depth and seasonal variations in the thermal properties at two nearby sites at Table Mountain with different origin, composition, and polygonal ground patterning. We determine apparent thermal diffusivity (ATD) profiles directly from thermistor array measurements at 13.5-cm-depth intervals and 4-hour time intervals in the top 2 m. We treat the system as purely conductive year round due to the cold temperatures and compare the performance of several common analysis schemes with a graphical finite difference method that we present in detail. This comparison is facilitated by one site showing strong depth variations including an abrupt twofold increase in ATD across a sharp compositional boundary. We characterize the composition of the inhomogeneous ground from recovered cores and estimate an ice-fractiondependent heat capacity in the range C = 1.7 ± 0.1 to 1.8 ± 0.1 MJ m À3°CÀ1 . We calculate apparent thermal conductivity profiles that correlate very well with the core compositions. The conductivity generally lies in the range 2.5 ± 0.5 W m À1°CÀ1 but is as high as 4.1 ± 0.4 W m À1°CÀ1 for a quartose Sirius sandstone unit at one site. The seasonal variation in the ATD is consistent with its expected temperature dependence.

No abstract