Paleoecology of a Middle Wisconsin Deposit from Southern California

Analysis of a buried deposit in the Diamond Valley of southern California has revealed well-preserved pollen, wood, and diatom remains. Accelerator mass spectrometry dates of 41,200±2100 and 41,490±1380 ¹⁴C yr B.P. place this deposit in marine isotope stage 3. Diatoms suggest a shallow lacustrine environment. Pollen data suggest that several plant communities were present near the site, with grassland, scrub, chaparral, forest, and riparian communities represented. Comparison with modern pollen suggests similarities with montane forests in the nearby San Bernardino and San Jacinto ranges, indicating vegetation lowering by at least 900 m elevation and temperatures 4°–5°C cooler than today. An increase in high-elevation conifer pollen documents climatic cooling near the profile top. Early-profile diatoms are typical of warm water with high alkalinity and conductivity, whereas later diatoms suggest a higher flow regime and input of cooler water into the system. We suggest that the sequence is part of the cooling phase of an interstadial Dansgaard–Oeschger cycle. Records of the middle Wisconsin period are rare in southern California, but the Diamond Valley site is similar to records from Tulare Lake in the San Joaquin Valley and the ODP Site 893A record from Santa Barbara Basin. It is probable that the Diamond Valley assemblage is a local expression of a vegetation type widespread in the ranges and basins of southwestern California during the middle Wisconsin.     

Isotope variations in a Sierra Nevada snowpack and their relation to meltwater

Isotopic variations in melting snow are poorly understood. We made weekly measurements at the Central Sierra Snow Laboratory, California, of snow temperature, density, water equivalent and liquid water volume to examine how physical changes within the snowpack govern meltwater δ¹⁸O. Snowpack samples were extracted at 0.1 m intervals from ground level to the top of the snowpack profile between December 1991 and April 1992. Approximately 800 mm of precipitation fell during the study period with δ¹⁸O values between −21.35 and −4.25‰. Corresponding snowpack δ¹⁸O ranged from −22.25 to −6.25‰. The coefficient of variation of δ¹⁸O in snowpack levels decreased from −0.37 to −0.07 from winter to spring, indicating isotopic snowpack homogenization. Meltwater δ¹⁸O ranged from −15.30 to −8.05‰, with variations of up to 2.95‰ observed within a single snowmelt episode, highlighting the need for frequent sampling. Early snowmelt originated in the lower snowpack with higher δ¹⁸O through ground heat flux and rainfall. After the snowpack became isothermal, infiltrating snowmelt displaced the higher δ¹⁸O liquid in the lower snowpack through a piston flow process. Fractionation analysis using a two-component mixing model on the isothermal snowpack indicated that δ¹⁸O in the initial and final half of major snowmelt was 1.30‰ lower and 1.45‰ higher, respectively, than the value from simple mixing. Mean snowpack δ¹⁸O on individual profiling days showed a steady increase from −15.15 to −12.05‰ due to removal of lower δ¹⁸O snowmelt and addition of higher δ¹⁸O rainfall. Results suggest that direct sampling of snowmelt and snow cores should be undertaken to quantify tracer input compositions adequately. The snowmelt sequence also suggests that regimes of early lower δ¹⁸O and later higher δ¹⁸O melt may be modeled and used in catchment tracing studies.     

Alpine medicinal plant trade and Himalayan mountain livelihood strategies

Commercial alpine medicinal plants are collected from the wild by local rural households throughout the Himalaya and sold in order to increase household incomes. Recent studies indicate that this annual trade amounts to thousands of tonnes of roots, rhizomes, tubers, leaves, etc., worth millions of US dollars. The main market is in India. Based on a national survey, including the most commonly traded species, and a village study this paper investigates the importance of the alpine medicinal plant trade at national and local levels in Nepal. The national survey included standardized open-ended interviews with 232 harvesters, 64 local traders, 66 central wholesalers, 47 regional wholesalers, and 16 production companies. The village survey is based on the daily records of household activities in 15 households in a one-year period. The annual Nepalese alpine and sub-alpine medicinal plant trade is conservatively estimated to vary from 480 to 2500 t with a total harvester value of US$0.8–3.3 million; the average harvester value is estimated at US$66.0 ± 99.0. The trade in 1997/98 amounted to 1600 t with a harvester value of US$2.3 million and an export value equivalent to 2.5% of total export from Nepal. Medicinal plant harvesting was found to constitute an integrated part of local livelihood strategies, contributing from 3 to 44% (average of 12%) of the annual household income. Importance at household level depended on land and animal holdings, and the availability of adult male labour. The validity and reliability of methods and analyses is evaluated, and issues of conservation and management of alpine medicinal plant species under the community forestry scheme are discussed.     

Aspects of the loss-on-ignition (LOI) technique in the context of clay-rich, glaciolacustrine sediments

The loss‐on‐ignition (LOI) technique for organic matter determination is evaluated with reference to clay‐rich, glaciolacustrine sediments. Examples of the use of LOI in glaciolacustrine literature are inconsistent in their methodology, and standardisation is called for. Problems with application of the technique to glaciolacustrine sediments stem mainly from the effects of additional weight loss due to release of structurally bound water and exposure time to ignition temperatures. Exposure time should be increased from 1 hour to 2.5 hours in the light of significant additional weight loss occurring between 2 and 2.5 hours in clay‐rich samples. The reason for this sudden increase in LOI after 2 hours (up to 86% of total LOI in some cases) appears to be the build‐up of a distinct surface crust during heating that insulates the core of the sample from ignition temperatures. Some time between 2 and 2.5 hours, the crust breaks down and exposes the sample core to ignition temperatures, increasing weight loss significantly. Overestimation of LOI due to loss of structural water is thought to be insignificant. Replicates of LOI at 550 and 1000°C in non‐calcareous, clay‐rich (>40%) sediments, show differences of <0.25%, which, for the purpose of inferring broad changes in glacier extent in lake catchments, is an acceptable error.     

(Re)surveying the uses of Geographical Information Systems in Health Authorities 1991–2001

This paper provides a comparative analysis of two separate national surveys of the uptake and use of Geographical Information Systems (GIS) by Health Authorities (HAs) in England and Wales. The surveys were undertaken at two different time points (1991 and 2001), and the intervening period has been characterized by major (and continuing) health sector restructuring. The substantial number of HA mergers between 1991 and 2001 provide a methodological challenge in attempting to make comparisons. A pragmatic approach is adopted and the presentation of results has to be restricted solely to English and Welsh HA data. Our findings show that there has been a considerable increase in the use of GIS since the early 1990s, and there is some evidence of more sophisticated uses for a wider range of policy-related and application tasks. However, we conclude that there is still considerable scope for the wider uptake and use of GIS within the NHS. In addition, our findings provide a baseline with which to monitor the impacts of future organizational restructuring on the uses of GIS within the NHS. We suggest that this is important given the replacement of 95 English HAs with 28 new Strategic HAs (StHAs) from April 2002, and the repercussions of the anticipated shift in GIS responsibility to Primary Care Trusts.     

Recent temperature and precipitation increases in West Siberia and their association with the Arctic Oscillation

Surface air temperature and precipitation records for the years 1958-1999 from ten meteorological stations located throughout West Siberia are used to identify climatic trends and determine to what extent these trends are potentially attributable to the Arctic Oscillation (AO). Although recent changes in atmospheric variability are associated with broad Arctic climate change, West Siberia appears particularly susceptible to warming. Furthermore, unlike most of the Arctic, moisture transport in the region is highly variable. The records show that West Siberia is experiencing significant warming and notable increases in precipitation, likely driven, in part, by large-scale Arctic atmospheric variability. Because this region contains a large percentage of the world's peatlands and contributes a significant portion of the total terrestrial freshwater flux to the Arctic Ocean, these recent climatic trends may have globally significant repercussions. The most robust patterns found are strong and prevalent springtime warming, winter precipitation increases, and strong association of non-summer air temperatures with the AO. Warming rates for both spring (0.5-0.8 °C/decade) and annual (0.3-0.5°C/decade) records are statistically significant for nine often stations. On average, the AO is linearly congruent with 96% (winter), 19% (spring), 0% (summer), 67% (autumn) and 53% (annual) of the warming found in this study. Significant trends in precipitation occur most commonly during winter, when four of ten stations exhibit significant increases (4-13 %/decade). The AO may play a lesser role in precipitation variability and is linearly congruent with only 17% (winter), 13% (spring), 12% (summer), 1% (autumn) and 26% (annual) of precipitation trends.     

Infiltration on mountain slopes: a comparison of three environments

Water is well established as a major driver of the geomorphic change that eventually reduces mountains to lower relief landscapes. Nonetheless, within the altitudinal limits of continuous vegetation in humid climates, water is also an essential factor in slope stability. In this paper, we present results from field experiments to determine infiltration rates at forested sites in the Andes Mountains (Ecuador), the southern Appalachian Mountains (USA), and the Luquillo Mountains (Puerto Rico). Using a portable rainfall simulator–infiltrometer (all three areas), and a single ring infiltrometer (Andes), we determined infiltration rates, even on steep slopes. Based on these results, we examine the spatial variability of infiltration, the relationship of rainfall runoff and infiltration to landscape position, the influence of vegetation on infiltration rates on slopes, and the implications of this research for better understanding erosional processes and landscape change.Infiltration rates ranged from 6 to 206 mm/h on lower slopes of the Andes, 16 to 117 mm/h in the southern Appalachians, and 0 to 106 mm/h in the Luquillo Mountains. These rates exceed those of most natural rain events, confirming that surface runoff is rare in montane forests with deep soil/regolith mantles. On well-drained forested slopes and ridges, apparent steady-state infiltration may be controlled by the near-surface downslope movement of infiltrated water rather than by characteristics of the full vertical soil profile. With only two exceptions, the local variability of infiltration rates at the scale of 10° m overpowered other expected spatial relationships between infiltration, vegetation type, slope position, and soil factors. One exception was the significant difference between infiltration rates on alluvial versus upland soils in the Andean study area. The other exception was the significant difference between infiltration rates in topographic coves compared to other slope positions in the tabonuco forest of one watershed in the Luquillo Mountains. Our research provides additional evidence of the ability of forests and forest soils to preserve geomorphic features from denudation by surface erosion, documents the importance of subsurface flow in mountain forests, and supports the need for caution in extrapolating infiltration rates.     

Mantle plumes: heat-flow near Iceland

In the first of four pieces arising from Gill Foulger's challenge to the mantle plume hypothesis (last issue), Carol Stein and Seth Stein join the debate with some data and comment on heat-flow around Iceland.