ALBERT

Description: Water tracks are zones of high soil moisture that route water downslope over the ice table in polar environments. We present physical, hydrological, and geochemical evidence collected in Taylor Valley, McMurdo Dry Valleys, Antarctica, which suggests that previously unexplored water tracks are a significant component of this cold desert land system and constitute the major flow path in a cryptic hydrological system. Geological, geochemical, and hydrological analyses show that the water tracks are generated by a combination of infiltration from melting snowpacks, melting of pore ice at the ice table beneath the water tracks, and melting of buried segregation ice formed during winter freezing. The water tracks are enriched in solutes derived from chemical weathering of sediments as well as from dissolution of soil salts. The water tracks empty into ice-covered lakes, such as Lake Hoare, resulting in the interfingering of shallow groundwater solutions and glacier-derived stream water, adding complexity to the geochemical profile. Approximately four orders of magnitude less water is delivered to Lake Hoare by any given water track than is delivered by surface runoff from stream flow; however, the solute delivery to Lake Hoare by water tracks equals or may exceed the mass of solutes delivered from stream flow, making water tracks significant geochemical pathways. Additionally, solute transport is two orders of magnitude faster in water tracks than in adjacent dry or damp soil, making water tracks "salt superhighways" in the Antarctic cold desert. Accordingly, water tracks represent a new geological pathway that distributes water, energy, and nutrients in Antarctic Dry Valley, cold desert, soil ecosystems, providing hydrological and geochemical connectivity at the hillslope scale.

Description: The oxidation state of Fe in garnets in a garnet peridotite xenolith from the Wesselton kimberlite (South Africa) was quantitatively mapped using X-ray absorption near edge structure (XANES) spectroscopy. Maps of Fe 3+ /Fe were produced by recording the fluorescence intensity at discrete energies rather than recording the full spectrum at each point. The intensity at each point in the map was quantitatively converted to Fe 3+ /Fe with reference to a linear calibration derived from garnet standards for which Fe 3+ /Fe had been determined previously by Mössbauer spectroscopy. The resolution of these maps approaches that of elemental maps obtained using an electron microprobe. The maps reveal zoning in Fe 3+ /Fe between the core (0.075) and rim (0.125) that correlates with zoning of other elements. The rims record an oxidizing metasomatic event in the lithospheric mantle. The oxygen fugacity ( f O 2 ) of this metasomatism is considerably higher than expected from studies of homogeneous garnets that exhibit metasomatic signatures; such garnets may represent a re-equilibrated average of the original (core) and metasomatic (rim) f O 2 values. Metasomatism of the lithospheric mantle may thus have a greater impact on diamond stability than previously thought.

Description: The Middle to early Late Devonian transition from diminutive plants to the first forests is a key episode in terrestrialization. The two major plant groups currently recognized in such "transitional forests" are pseudosporochnaleans (small to medium trees showing some morphological similarity to living tree ferns and palms) and archaeopteridaleans (trees with woody trunks and leafy branches probably related to living conifers). Here we report a new type of "transitional" in-situ Devonian forest based on lycopsid fossils from the Plantekløfta Formation, Munindalen, Svalbard. Previously regarded as very latest Devonian (latest Famennian, 360 Ma), their age, based on palynology, is early Frasnian (ca. 380 Ma). In-situ trees are represented by internal casts of arborescent lycopsids with cormose bases and small ribbon-like roots occurring in dense stands spaced ~15–20 cm apart, here identified as Protolepidodendropsis pulchra Høeg. This plant also occurs as compression fossils throughout most of the late Givetian–early Frasnian Mimerdalen Subgroup. The lycopsids grew in wet soils in a localized, rapidly subsiding, short-lived basin. Importantly, this new type of Middle to early Late Devonian forest is paleoequatorial and hence tropical. This high-tree-density tropical vegetation may have promoted rapid weathering of soils, and hence enhanced carbon dioxide drawdown, when compared with other contemporary and more high-latitude forests.