Limited release of previously-frozen C and increased new peat formation after thaw in permafrost peatlands

Permafrost stores globally significant amounts of carbon (C) which may start to decompose and be released to the atmosphere in form of carbon dioxide (CO 2 ) and methane (CH 4 ) as global warming promotes extensive thaw. This permafrost carbon feedback to climate is currently considered to be the most important carbon-cycle feedback missing from climate models. Predicting the magnitude of the feedback requires a better understanding of how differences in environmental conditions post-thaw, particularly hydrological conditions, control the rate at which C is released to the atmosphere. In the sporadic and discontinuous permafrost regions of north-west Canada, we measured the rates and sources of C released from relatively undisturbed ecosystems, and compared these with forests experiencing thaw following wildfire (well-drained, oxic conditions) and collapsing peat plateau sites (water-logged, anoxic conditions). Using radiocarbon analyses, we detected substantial contributions of deep soil layers and/or previously-frozen sources in our well-drained sites. In contrast, no loss of previously-frozen C as CO 2 was detected on average from collapsed peat plateaus regardless of time since thaw and despite the much larger stores of available C that were exposed. Furthermore, greater rates of new peat formation resulted in these soils becoming stronger C sinks and this greater rate of uptake appeared to compensate for a large proportion of the increase in CH 4 emissions from the collapse wetlands. We conclude that in the ecosystems we studied, changes in soil moisture and oxygen availability may be even more important than previously predicted in determining the effect of permafrost thaw on ecosystem C balance and, thus, it is essential to monitor, and simulate accurately, regional changes in surface wetness

Mapping the maze of assessment: an investigation into practice

“The final, definitive version of this article has been published in the Journal, Active Learning in Higher Education, 10 (2) pp.120-137, 2009, copyright SAGE Publications Ltd. on SAGE Journals Online: http://online.sagepub.com/ "This article presents the results of a preliminary survey of assessment tasks undertaken by students in higher education at a particular university. A key premise of the study was that the ability to handle assessment is central to the development of academic and professional literacy. Much of the current literature on assessment demonstrates a concern that it is not currently achieving this end. A grid of various features of assessment has been developed, onto which are mapped tasks used at all levels and within all disciplines in the institution. Considerable differences in the type and range of assessment tasks used across schools and disciplines are identified, and also a gap between the variation in tasks and the relatively narrow range of activities and techniques covered in most study skills manuals. It is argued that generic materials should broaden their base and that subject-specific material needs to be developed to accommodate the realities of lifelong learning.Peer reviewe

Record collectors: Hollywood record labels in the 1950s and 1960s

The affiliation between film and music is the cornerstone of modern entertainment industry synergy. This article examines one of the key chapters in that relationship: the period in the 1950s during which the major studios entered the record business. Ostensibly designed to capitalise on the emerging film soundtrack market, the flurry of mergers, acquisitions and the establishment of new record labels coincided with the rise of rock'n'roll and the explosion of the market for recorded popular music. The studios quickly found that in order to keep their record labels afloat, they needed to establish a foothold in popular music. The processes by which they achieved this transformed the marketing of recorded music, sparking a period of unprecedented commercial success for the record industry in the late 1960s. Simultaneously, from these record subsidiaries Hollywood learned how to market cinema to a youth audience, heralding the arrival of 'New Hollywood'

Late Holocene changes in ultraviolet radiation penetration recorded in an East Antarctic lake

Late Holocene changes in the ultraviolet radiation (UVR) penetration in a lake in the Larsemann Hills (East Antarctica) were reconstructed using sediment core proxies based on fossil pigments (scytonemins and its derivatives) and siliceous microfossils. The influence of changes in lake depth on the UVR proxy was excluded by applying a correction, based on the non-linear relation between modern scytonemin concentrations and lake depth in a regional reference data set, and the record of past lake depths inferred using a diatom based transfer function in the sediment core. Results showed four well-defined maxima in the UVR proxy during the last 1600–1800 years, centred around 1820–1780, 1580–1490, 790–580 and 680–440 AD. Several mechanisms may account for these observed changes in UVR penetration, including past variability in cloud cover, atmospheric turbidity, ozone column depth, snow cover on the lake ice, DOM concentrations and lake-ice thickness and transparency resulting from temperature fluctuations. Although some gaps remain in our knowledge of scytonemin production in relation to the limnology of Antarctic lakes, the results highlight the importance and potential of the sediments in these highly transparent water bodies as archives of changes in past UVR receipt at the Earth’s surface