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Molecular biomarkers preserved in lake sediments are increasingly used to develop records of past organism occurrence. When linked with traditional paleoecological methods, analysis of molecular biomarkers can yield new insights into the roles of herbivores and other animals in long-term ecosystem dynamics. We sought to determine whether fecal steroids in lake sediments could be used to reconstruct past ungulate use and dominant taxa in a small catchment in northern Yellowstone National Park. To do so, we characterized the fecal steroid profiles of a selection of North American ungulates historically present in the Yellowstone region (bison, elk, moose, mule deer, and pronghorn) and compared them with those of sediments from a small lake in the Yellowstone Northern Range. Analysis of a set of fecal steroids from herbivore dung (Δ5-sterols, 5α-stanols, 5β-stanols, epi5β-stanols, stanones, and bile acids) differentiated moose, pronghorn, and mule deer, whereas bison and elk were partially differentiated. Our results show that bison and/or elk were the primary ungulates in the watershed over the past c. 2300 years. Fecal steroid influxes reached historically unprecedented levels during the early and middle 20th century, possibly indicating high local use by ungulates. Comparison of fecal steroid influxes with pollen and diatom data suggests that elevated ungulate presence may have contributed to decreased forage taxa (Poaceae, Artemisia, and Salix), relative to long-term averages, and possibly increased lake production. Our results reflect past change within a single watershed, and extending this approach to a network of sites could provide much-needed information on past herbivore communities, use, and environmental influences in Yellowstone National Park and elsewhere. [ABSTRACT FROM AUTHOR]

The paleodiet evolution in a human community of Venetian Lagoon between the eighth and twelfth centuries has been reconstructed by the stable isotopes analysis of δ13C and δ15N found in collagen of teeth and bones from St. Mauro archaeological site (Jesolo, Venice). A total of 52 individuals of various ages, sex, chronologies, and pathological condition were included in this study. Our findings revealed the presence of two distinct dietary patterns influenced only by chronology. We observed that a more fish-based diet (30–60% of the overall diet) prevailed between the eighth and tenth centuries. However, between the tenth and twelfth centuries, fish consumption decreased (10–30% of the overall diet), and there was a shift towards a diet rich in terrestrial protein sources. We link this change in dietary habits to economic development also evidenced by the transformations of the site and increased trade with the hinterland. Furthermore, it was observed significantly higher δ15N values in individuals from 8th-10th compared to those from tenth-twelfth centuries. We proposed two potential explanations: a shift in child-rearing practices, such as delayed weaning during early middle age compared to late middle age, or a change in diet of breast feeders. [ABSTRACT FROM AUTHOR]

The effect of the insulating shield thickness on the steady-state diffusion-limiting current of sphere cap microelectrodes is investigated. Theoretical steady-state limiting currents are obtained by using a simulation procedure, which relies on the explicit finite difference method with a fixed time grid and an exponentially spatial grid. The results obtained indicate that the current increases by decreasing the thickness of the insulating sheath or by increasing the aspect ratio of the sphere cap (h/a, where h is the height of the sphere cap and a is the electrode basal radius), similarly to other types of microelectrodes with different electrode geometry, such as disks and finite cones. The simulated data are fitted to approximate analytical expressions to describe the dependence of the limiting current on both h/a and RG (RG = b/a, where b is the overall tip radius) parameter. Theoretical currents are also compared with experimental data, which are obtained with a range of mercury-coated platinum microelectrodes having different RG and h/a values. The measurements are performed by using cyclic voltammetry at 1 [mVs.sup.-1], in aqueous solutions containing Ru[([NH.sub.3]).sub.6-[Cl.sub.3] as electroactive species. A good agreement (within 3%) between theoretical and experimental steady-state currents is found. Finally, SECM operating in the feedback mode is used to assess the validity of the shape parameters found by voltammetry for sphere cap microelectrodes, whose insulating shields are of a thickness comparable to the electrode radius.

Biomass burning influences global atmospheric chemistry by releasing greenhouse gases and climate-forcing aerosols. There is controversy about the magnitude and timing of Holocene changes in biomass burning emissions from millennial to centennial time scales and, in particular, on the possible impact of ancient civilizations. Here we present a 5 kyr record of fire activity proxies levoglucosan, black carbon and ammonium measured in the RECAP ice core, drilled in the coastal East Greenland and therefore affected by processes occurring in the High North Atlantic Region. Levoglucosan and ammonium fluxes show high levels from 5 to 4.5 kyr followed by an abrupt decline, possibly due to monotonic decline in Northern Hemisphere summer insolation. Levoglucosan and black carbon show an abrupt decline at 1.1 kyr BP (before 2000 AD), suggesting a decline in wildfire regime in the Icelandic territory due to the extensive land clearing caused by Viking colonizers. A minimum is reached at 0.5 kyr BP for all fire proxies, after which levoglucosan and ammonium fluxes increase again, in particular over the last 200 years. We find that the fire regime reconstructed from RECAP fluxes seems mainly related to climatic changes, however over the last millennium human activities might have had a substantial influence controlling the occurrence of fire. [ABSTRACT FROM AUTHOR]