There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

The planetary boundaries framework defines a safe operating space for humanity based on the intrinsic biophysical processes that regulate the stability of the Earth system. Here, we revise and update the planetary boundary framework, with a focus on the underpinning biophysical science, based on targeted input from expert research communities and on more general scientific advances over the past 5 years. Several of the boundaries now have a two-tier approach, reflecting the importance of cross-scale interactions and the regional-level heterogeneity of the processes that underpin the boundaries. Two core boundaries—climate change and biosphere integrity—have been identified, each of which has the potential on its own to drive the Earth system into a new state should they be substantially and persistently transgressed.

/pdf/planetary-boundaries-guiding-human-development-on-a-changing-5gmf909etg.pdf

Planetary boundaries: Guiding human development on a changing planet

THE major active ingredient of marijuana, Δ9-tetrahydrocannabi-nol (Δ9-THC), has been used as a psychoactive agent for thousands of years. Marijuana, and Δ9-THC, also exert a wide range of other effects including analgesia, anti-inflammation, immunosuppression, anticonvulsion, alleviation of intraocular pressure in glaucoma, and attenuation of vomiting1. The clinical application of cannabinoids has, however, been limited by their psychoactive effects, and this has led to interest in the biochemical bases of their action. Progress stemmed initially from the synthesis of potent derivatives of δ9-THC4,5, and more recently from the cloning of a gene encoding a G-protein-coupled receptor for cannabinoids6. This receptor is expressed in the brain but not in the periphery, except for a low level in testes. It has been proposed that the non-psychoactive effects of cannabinoids are either mediated centrally or through direct interaction with other, non-receptor proteins1,7,8. Here we report the cloning of a receptor for cannabinoids that is not expressed in the brain but rather in macrophages in the marginal zone of spleen.

Molecular characterization of a peripheral receptor for cannabinoids

This paper contrasts the natural and anthropogenic controls on the conversion of unreactive N2 to more reactive forms of nitrogen (Nr). A variety of data sets are used to construct global N budgets for 1860 and the early 1990s and to make projections for the global N budget in 2050. Regional N budgets for Asia, North America, and other major regions for the early 1990s, as well as the marine N budget, are presented to highlight the dominant fluxes of nitrogen in each region. Important findings are that human activities increasingly dominate the N budget at the global and at most regional scales, the terrestrial and open ocean N budgets are essentially dis- connected, and the fixed forms of N are accumulating in most environmental reservoirs. The largest uncertainties in our understanding of the N budget at most scales are the rates of natural biological nitrogen fixation, the amount of Nr storage in most environmental reservoirs, and the production rates of N2 by denitrification.

/pdf/nitrogen-cycles-past-present-and-future-1zdbw0976r.pdf

Nitrogen cycles: past, present, and future

Relationships between wind speed and gas transfer, combined with knowledge of the partial pressure difference of CO2 across the air-sea interface are frequently used to determine the CO2 flux between the ocean and the atmosphere. Little attention has been paid to the influence of variability in wind speed on the calculated gas transfer velocities and the possibility of chemical enhancement of CO2 exchange at low wind speeds over the ocean. The effect of these parameters is illustrated using a quadratic dependence of gas exchange on wind speed which is fit through gas transfer velocities over the ocean determined by the natural-14C disequilibrium and the bomb-14C inventory methods. Some of the variability between different data sets can be accounted for by the suggested mechanisms, but much of the variation appears due to other causes. Possible causes for the large difference between two frequently used relationships between gas transfer and wind speed are discussed. To determine fluxes of gases other than CO2 across the air-water interface, the relevant expressions for gas transfer, and the temperature and salinity dependence of the Schmidt number and solubility of several gases of environmental interest are included in an appendix.

Relationship between wind speed and gas exchange over the ocean

Biotic enhancement of weathering, atmospheric oxygen and carbon dioxide in the Neoproterozoic

Geomorphological evidence and associated stratified ‘open’ sites have enabled a reconstruction to be made of fluctuations in palaeoclimate and prehistoric activity during the Late Pleistocene over an area of Africa south of the Zambezi exceeding one million square kilometres. Radiocarbon dates from relevant sites in Swaziland suggest that the Middle Stone Age flourished over a large part of the interior of southern Africa between 30,000 and 20,000 years b.p., during which time the south‐eastern part of Africa was experiencing climates considerably more arid than at present.

New observations on the prehistory and palaeoclimate of the Late Pleistocene in southern Africa

Atmospheric impacts of the space industry require oversight

The technique of reverse transcription-PCR for mRNA phenotyping was applied to total RNA isolated from the two compartments of cancellous bone, namely trabecular bone and hematopoitic tissue or marrow. The pattern of gene expression for ten different growth factor ligands and five growth factor receptors was examined in total RNA isolated from the two compartments of cancellous bone of the female rat distal femur. Our results show that transcripts encoding IGF-I, IGF-II, transforming growth factor-beta 1 (TGF-beta 1), TGF-alpha, basic fibroblast growth factor, platelet-derived growth factor A and osteocalcin are detectable in samples from both trabeculae and marrow. Expression of epidermal growth factor (EGF) was confined to samples from trabeculae while nerve growth factor expression was only detected in marrow. Transcipts encoding insulin were not detected in any of the bone-derived samples in this study. Samples from cancellous bone trabeculae and marrow both showed evidence of expression of the genes encoding receptors for IGF-I, parathyroid hormone (PTH)/PTH-related protein and insulin. Neither compartment of cancellous bone contained transcripts encoding the receptor for IGF-II. Transcripts encoding the EGF receptor were detected in samples from cancellous bone marrow and not trabeculae as has been previously reported. These patterns of growth factor ligand and receptor gene expression suggest that it is likely that both autocrine and paracrine regulatory circuits are established in cancellous bone. This study also demonstrated the feasibility of assessing the expression of multiple genes from the small samples of total RNA obtained from separated tissues of cancellous bone. This is the first time that growth factor gene expression has been examined in separated trabeculae and marrow from cancellous bone and this approach will allow a more detailed analysis of molecular events in cancellous bone as opposed to whole bone or extracts of isolated and cultured bone cells.

Expression of growth factor ligand and receptor genes in rat cancellous bone trabeculae and marrow

The Lagrangian Southern Ocean Iron Release Experiment (SOIREE) allowed study of a gradually evolving iron-mediated phytoplankton bloom in water labelled with the inert tracer sulfur hexafluoride, SF 6 . This article describes a pelagic carbon budget for the mixed layer in SOIREE and assesses the extent to which closure of the budget is achieved. Net community production (NCP) converted 837 mmol m −2 of inorganic carbon to organic carbon in 12.0 d after the first iron addition. A large fraction (41%) of NCP remained as particulate organic carbon in the mixed layer of the iron-enriched patch, while 23% was lost by horizontal dispersion and 0–29% was exported. The closure of the carbon budget is hampered by the lack of measurements of dissolved organic carbon (DOC), by a major uncertainty in carbon export, and by use of empirical conversion factors in estimates of carbon biomass and metabolic rates. Lagrangian carbon-budget studies may be improved by direct measurement of all major carbon parameters and conversion factors. Carbon cycling in the SOIREE bloom resembled that in ‘natural’ algal blooms in the open Southern Ocean in some respects, but not in all. Daily NCP in the SOIREE bloom (70 mmol m −2  d −1 ) was higher than in natural blooms, partly because other studies did not account for horizontal dispersion, were for longer periods or included less productive areas. The build-up of POC stock and carbon export as a fraction of NCP in SOIREE were in the lower range of observations elsewhere.

/pdf/matching-carbon-pools-and-fluxes-for-the-southern-ocean-iron-mkasqgw1w2.pdf

Andrew J. Watson

Papers

Biotic enhancement of weathering, atmospheric oxygen and carbon dioxide in the Neoproterozoic

New observations on the prehistory and palaeoclimate of the Late Pleistocene in southern Africa

Atmospheric impacts of the space industry require oversight

Expression of growth factor ligand and receptor genes in rat cancellous bone trabeculae and marrow

Matching carbon pools and fluxes for the Southern Ocean Iron RElease Experiment (SOIREE)