Bones of recent mammals in the Amboseli Basin, southern Kenya, exhibit distinctive weathering characteristics that can be related to the time since death and to the local conditions of temperature, humidity and soil chemistry. A categorization of weathering characteristics into six stages, recognizable on descriptive criteria, provides a basis for investigation of weathering rates and processes. The time necessary to achieve each successive weathering stage has been calibrated using known-age carcasses. Most bones decompose beyond recognition in 10 to 15 yr. Bones of animals under 100 kg and juveniles appear to weather more rapidly than bones of large animals or adults. Small-scale rather than widespread environmental factors seem to have greatest influence on weathering characteristics and rates. Bone weathering is potentially valuable as evidence for the period of time represented in recent or fossil bone assemblages, in- cluding those on archeological sites, and may also be an important tool in censusing populations of animals in modern ecosystems.

Taphonomic and Ecologic Information Form Bone Weathering

Nutrient limitation to primary productivity and other biological processes is widespread in terrestrial ecosystems, and nitrogen (N) and phosphorus (P) are the most common limiting elements, both individually and in combination. Mechanisms that drive P limitation, and their interactions with the N cycle, have received less attention than mechanisms causing N limitation. We identify and discuss six mechanisms that could drive P limitation in terrestrial ecosystems. The best known of these is depletion-driven limitation, in which accumulated P losses during long-term soil and ecosystem development contribute to what Walker and Syers termed a "terminal steady state" of profound P depletion and limitation. The other mechanisms are soil barriers that prevent access to P; transactional limitation, in which weathering of P-containing minerals does not keep pace with the supply of other resources; low-P parent materials; P sinks; and anthropogenic changes that increase the supply of other resources (often N) relative to P. We distinguish proximate nutrient limitation (which occurs where additions of a nutrient stimulate biological processes, especially productivity) from ultimate nutrient limitation (where additions of a nutrient can transform ecosystems). Of the mechanisms that drive P limitation, we suggest that depletion, soil barriers, and low-P parent material often cause ultimate limitation because they control the ecosystem mass balance of P. Similarly, demand-independent losses and constraints to N fixation can control the ecosystem-level mass balance of N and cause it to be an ultimate limiting nutrient.

Terrestrial phosphorus limitation: mechanisms, implications, and nitrogen–phosphorus interactions

The Arctic climate is changing. Permafrost is warming, hydrological processes are chang- ing and biological and social systems are also evolving in response to these changing conditions. Knowing how the structure and function of arctic terrestrial ecosystems are responding to recent and persistent climate change is paramount to understanding the future state of the Earth system and how humans will need to adapt. Our holistic review presents a broad array of evidence that illustrates con- vincingly; the Arctic is undergoing a system-wide response to an altered climatic state. New extreme and seasonal surface climatic conditions are being experienced, a range of biophysical states and pro- cesses influenced by the threshold and phase change of freezing point are being altered, hydrological and biogeochemical cycles are shifting, and more regularly human sub-systems are being affected. Importantly, the patterns, magnitude and mechanisms of change have sometimes been unpredictable or difficult to isolate due to compounding factors. In almost every discipline represented, we show

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Evidence and implications of recent climate change in northern Alaska and other arctic regions.

Evidence and Implications of Recent Climate Change in Northern Alaska and Other Arctic Regions

We provide a brief synopsis of the unique physical and ecological attributes of sandy beach ecosystems and review the main anthropogenic pressures acting on the world's single largest type of open shoreline. Threats to beaches arise from a range of stressors which span a spectrum of impact scales from localised effects (e.g. trampling) to a truly global reach (e.g. sea-level rise). These pressures act at multiple temporal and spatial scales, translating into ecological impacts that are manifested across several dimensions in time and space so that today almost every beach on every coastline is threatened by human activities. Press disturbances (whatever the impact source involved) are becoming increasingly common, operating on time scales of years to decades. However, long-term data sets that describe either the natural dynamics of beach systems or the human impacts on beaches are scarce and fragmentary. A top priority is to implement long-term field experiments and monitoring programmes that quantify the dynamics of key ecological attributes on sandy beaches. Because of the inertia associated with global climate change and human population growth, no realistic management scenario will alleviate these threats in the short term. The immediate priority is to avoid further development of coastal areas likely to be directly impacted by retreating shorelines. There is also scope for improvement in experimental design to better distinguish natural variability from anthropogenic impacts. Sea-level rise and other effects of global warming are expected to intensify other anthropogenic pressures, and could cause unprecedented ecological impacts. The definition of the relevant scales of analysis, which will vary according to the magnitude of the impact and the organisational level under analysis, and the recognition of a physical–biological coupling at different scales, should be included in approaches to quantify impacts. Zoning strategies and marine reserves, which have not been widely implemented in sandy beaches, could be a key tool for biodiversity conservation and should also facilitate spillover effects into adjacent beach habitats. Setback and zoning strategies need to be enforced through legislation, and all relevant stakeholders should be included in the design, implementation and institutionalisation of these initiatives. New perspectives for rational management of sandy beaches require paradigm shifts, by including not only basic ecosystem principles, but also incentives for effective governance and sharing of management roles between government and local stakeholders.

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Threats to sandy beach ecosystems: A review

Two pistons corers are described which are successful in cuting the wood or undecomposed fibrous peat that characterizes many peat deposits. These modified corers are equipped with a serrated cutting edge, along with modifications to permit the core tube to be rotated back and forth, so that undecomposed fibers and roots can be cut. Complete sections of peat and even the underlying silt or sand can be acquired to a depth of several meters. The 10-cm diameter corer provides sufficient material for close-interval macrofossil and chemical analysis and for radiocarbon dating. The 5-cm corer is more portable and more convenient.

Piston corers for peat and lake sediments

Late Pleistocene and Holocene paleoenvironments of the North Pacific coast

Fire is the keystone disturbance in the Alaskan boreal forest and is highly influenced by summer weather patterns. Records from the last 53 years reveal high vari- ability in the annual area burned in Alaska and corresponding high variability in weather occurring at multiple spatial and temporal scales. Here we use multiple linear regression (MLR) to systematically explore the relationships between weather variables and the annual area burned in Alaska. Variation in the seasonality of the atmospheric circulation-fire linkage is addressed through an evaluation of both the East Pacific teleconnection field and a Pacific Decadal Oscillation index keyed to an annual fire index. In the MLR, seven explanatory variables and an interaction term collectively explain 79% of the variability in the natural logarithm of the number of hectares burned annually by lightning-caused fires in Alaska from 1950 to 2003. Average June temperature alone explains one-third of the variability in the logarithm of annual area burned. The results of this work suggest that the Pacific Decadal Oscillation and the East Pacific teleconnection indices can be useful in determining a priori an estimate of the number of hectares that will burn in an upcoming season. This information also provides insight into the link between ocean-atmosphere interactions and the fire disturbance regime in Alaska.

Impacts of large‐scale atmospheric–ocean variability on alaskan fire season severity

Oil stranded by the 1989 Exxon Valdez spill has persisted in subsurface sediments of exposed shores for 16 years. With annualized loss rates declining from approximately 68% yr(-1) prior to 1992 to approximately 4% yr(-1) after 2001, weathering processes are retarded in both sediments and residual emulsified oil ("oil mousse"), and retention of toxic polycyclic aromatic hydrocarbons is prolonged. The n-alkanes, typically very readily oxidized by microbes, instead remain abundant in many stranded emulsified oil samplesfrom the Gulf of Alaska. They are less abundant in Prince William Sound samples, where stranded oil was less viscous. Our results indicate that, at some locations, remaining subsurface oil may persist for decades with little change.

Daniel H. Mann

Papers

Piston corers for peat and lake sediments

Late Pleistocene and Holocene paleoenvironments of the North Pacific coast

Impacts of large‐scale atmospheric–ocean variability on alaskan fire season severity

Slightly weathered Exxon Valdez oil persists in Gulf of Alaska beach sediments after 16 years.

Extent and Timing of the Last Glacial Maximum in Southwestern Alaska