Light dependence of [H-3]leucine incorporation in the oligotrophic North Pacific ocean

The influence of irradiance on bacterial incorporation of [H-3] leucine was evaluated at Station ALOHA in the oligotrophic North Pacific subtropical gyre. Six experiments were conducted on three cruises to Station ALOHA to examine how [H-3]leucine incorporation varied as a function of irradiance. Two experiments were also conducted to assess the photoautotrophic response to irradiance (based on photosynthetic uptake of [C-14] bicarbonate) in both the upper and lower photic zones. Rates of [H-3]leucine incorporation responded to irradiance in a photosynthesis-like manner, increasing sharply at low light and then saturating and sometimes declining with increasing light intensity. The influence of irradiance on bacterial growth was evaluated in both the well-lit (5 to 25 m) and dimly lit regions of the upper ocean (75 to 100 m) to determine whether the bacterial response to irradiance differed along the depth-dependent light gradient of the photic zone. [H-3] leucine incorporation rates were analyzed with a photosynthesis-irradiance model for a quantitative description of the relationships between [H-3] leucine incorporation and irradiance. Maximum rates of [H-3] leucine incorporation in the upper photic zone increased 48 to 92% relative to those of dark-incubated samples, with [H-3]leucine incorporation saturating at light intensities between 58 and 363 mumol of quanta m(-2) s(-1). Rates of [H-3]Ieucine incorporation in the deep photic zone were photostimulated 53 to 114% and were susceptible to photoinhibition, with rates declining at light intensities of \u3e100 mumol of quanta m(-2) s(-1). The results of these experiments revealed that sunlight directly influences bacterial growth in this open-ocean ecosystem

Application of mineral magnetism in Atlantic Scotland archaeology 1: techniques, magnetic enhancement and the identification of fuel sources

Natural and archaeological deposits tend to contain mixtures of magnetic grains of differing 1) concentrations, 2) domain states (linked to grain size) and 3) mineralogies. Many laboratory based magnetic measurements are available to study these attributes. Fire ash is a significant component in the formation of archaeological deposits in Atlantic Scotland and its magnetic enhancement means it is easily identified and traced. Several magnetic techniques were developed from which different types of fuel ash could be identified. The techniques were successfully applied to archaeological samples from the Western and Northern Isles of Scotland. The results show a uniformity in the use of well-humified peat as the major fuel source on Lewis, whereas considerable variability in fuel types was observed at Cladh Hallan, South Uist and Old Scatness Broch, Shetland

Multiyear increases in dissolved organic matter inventories at station ALOHA in the North Pacific Subtropical Gyre

The inventories and dynamics of dissolved organic matter (DOM) in the surface water at Station ALOHA were analyzed from the Hawaii Ocean Time-series (HOT) data set for the period 1989-1999. Euphotic zone, depth-integrated (0-175 m) concentrations of dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) were temporally variable. In particular, during the period 1993-1999, concentrations of DOC and DON increased while inventories of DOP remained unchanged. DOC inventories increased by 303 mmol C m(-2) yr(-1), a value equivalent to approximately 2% of measured primary production (C-14 method) at this site. DON increased at 11 mmol N m(-2) yr(-1), resulting in a mean molar DOC : DON ratio of 27.5 for the accumulated DOM. Accumulation of DOC and DON without corresponding accumulation of DOP resulted in changes to the bulk organic C : N : P stoichiometry; bulk DOC : DOP ratios increased 16% and DON: DOP ratios increased by 17%. These results indicate that a small fraction of the annually produced organic matter escaped biological utilization on time scales of months to years. More importantly, the accumulated DOM inventories grew progressively enriched in C and N relative to P. Fundamental changes in the North Pacific Subtropical Gyre (NPSG) habitat appear to have altered microbial processes that regulate organic matter fluxes. Considered together, the long-term increases in DOC and DON inventories are consistent with previous observations, indicating that a recent reorganization of plankton community dynamics may have altered organic matter cycling in this ecosystem

Firewood, food and niche construction: the potential role of Mesolithic hunter-gatherers in actively structuring Scotland's woodlands

Over the past few decades the potential role of Mesolithic hunter–gatherers in actively constructing their own niches, through the management of wild plants, has frequently been discussed. It is probable that Mesolithic hunter–gatherers systematically exploited specific woodland resources for food and fuel and influenced the ‘natural’ abundance or distribution of particular species within Mesolithic environments. Though there has been considerable discussion of the pollen evidence for potential small-scale human-woodland manipulation in Mesolithic Scotland, the archaeobotanical evidence for anthropogenic firewood and food selection has not been discussed in this context. This paper assesses the evidence for the active role of Mesolithic hunter–gatherer communities in systematically exploiting and managing woodlands for food and fuel in Scotland. While taphonomic factors may have impacted on the frequency of specific species in archaeobotanical assemblages, it is suggested that hunter–gatherers in Mesolithic Scotland were systematically using woodland plants, and in particular hazel and oak, for food and fuel. It is argued that the pollen evidence for woodland management is equivocal, but hints at the role of hunter–gatherers in shaping the structure of their environments, through the maintenance or creation of woodland clearings for settlement or as part of vegetation management strategies. It is proposed that Mesolithic hunter–gatherers may have actively contributed to niche construction and that the systematic use of hazel and oak as a fuel may reflect the deliberate pruning of hazel trees to increase nut-yields and the inadvertent – or perhaps deliberate – coppicing of hazel and oak during greenwood collection

Seeds, fruits and nuts in the Scottish Mesolithic

Over the past few decades, the potential importance of plants within European Mesolithic economies has frequently been discussed, but there has been little systematic consideration of the archaeobotanical evidence for Mesolithic plant consumption in Scotland. This paper assesses the use of plants in the Scottish Mesolithic economy using the archaeobotanical evidence from 48 sites. It is argued that plants were systematically, and, in some cases, intensively exploited in Mesolithic Scotland. Though plant remains were extremely sparse at most sites, it is suggested that uneven archaeological sampling and taphonomic factors, together with the relatively short duration of occupation of many sites, may be responsible for the restricted range and frequency of edible taxa in most assemblages