Primary Production in Antarctic Sea Ice

A numerical model shows that in Antarctic sea ice, increased flooding in regions with thick snow cover enhances primary production in the infiltration (surface) layer. Productivity in the freeboard (sea level) layer is also determined by sea ice porosity, which varies with temperature. Spatial and temporal variation in snow thickness and the proportion of first-year ice thus determine regional differences in sea ice primary production. Model results show that of the 40 teragrams of carbon produced annually in the Antarctic ice pack, 75 percent was associated with first-year ice and nearly 50 percent was produced in the Weddell Sea.     

Genetic conversion of a fungal plant pathogen to a nonpathogenic, endophytic mutualist

The filamentous fungal ascomycete Colletotrichum magna causes anthracnose in cucurbit plants. Isolation of a nonpathogenic mutant of this species (path-1) resulted in maintained wild-type levels of in vitro sporulation, spore adhesion, appressorial formation, and infection. Path-1 grew throughout host tissues as an endophyte and retained the wild-type host range, which indicates that the genetics involved in pathogenicity and host specificity are distinct. Prior infection with path-1 protected plants from disease caused by Colletotrichum and Fusarium.Genetic analysis of a cross between path-1 and wild-type strains indicated mutation of a single locus.     

Stone tools from mid-pleistocene sediments in java

Two stone tools (a chopper and a retouched flake) were found in mid-Pleistocene channel fills at Sambungmachan (Java), which earlier yielded a hominid skull cap with characteristics of Solo man and a Trinil-like fauna. The artifacts are the first discovered in place in deposits on Java that are assigned to the mid-Pleistocene on faunal grounds.     

Transient floral change and rapid global warming at the Paleocene-Eocene boundary

Rapid global warming of 5 degrees to 10 degrees C during the Paleocene-Eocene Thermal Maximum (PETM) coincided with major turnover in vertebrate faunas, but previous studies have found little floral change. Plant fossils discovered in Wyoming, United States, show that PETM floras were a mixture of native and migrant lineages and that plant range shifts were large and rapid (occurring within 10,000 years). Floral composition and leaf shape and size suggest that climate warmed by approximately 5 degrees C during the PETM and that precipitation was low early in the event and increased later. Floral response to warming and/or increased atmospheric CO2 during the PETM was comparable in rate and magnitude to that seen in postglacial floras and to the predicted effects of anthropogenic carbon release and climate change on future vegetation.     

On the potential of documenting decadal-scale avifaunal change from before-and-after comparisons of museum and observational data across North America

Studies of biodiversity dynamics have been cast on either long(systematics)or short(ecology)time scales,leaving a gap in coverage for moderate time scales of de...