Bacteriohopanepolyol signatures of bacterial populations in Western Canadian soils

Bacteriohopanepolyols (BHPs) are naturally occurring compounds derived from bacteria. Their quantity and diversity in five Western Canadian soils, which vary mostly in vegetative cover, were examined using high performance liquid chromatography – atmospheric pressure chemical ionization – mass spectrometry (HPLC–APCI–MS). Eighteen BHP compounds including tetra-, penta- and hexa-functionalised components, as well as composite components, were identified. Concentrations were highest in the forest-grassland transition soil [515 μg/g organic carbon (OC)], followed by the forest soil (431 μg/g OC) and the grassland soils (333–306 μg/g OC). The distribution trends measured using HPLC–ACPI–MS agree with hopanoid measurements using gas chromatography–mass spectrometry (GC–MS) but intact BHPs were detected at a concentration that was an order of magnitude higher using HPLC–APCI–MS. Adenosylhopane was the most abundant BHP in all the samples and comprised on average 27% of total BHPs, supporting earlier work indicating that adenosylhopane is an excellent soil-specific biomarker. The soil samples vary in vegetative cover and this is likely one of the main reasons for observing variation in BHP composition, suggesting that BHP biomarkers may be a valuable tool for assessing bacterial community structure in soil when used in cooperation with other molecular microbial ecology methods (such as DNA genotyping).     

Structural diversity of diether lipids in carbonate chimneys at the Lost City Hydrothermal Field

The Lost City Hydrothermal Field hosts a distinctive microbial ecosystem that is supported by the products of serpentinization reactions. The calcium carbonate chimneys here contain abundant isoprenoidal and non-isoprenoidal ether lipids, the structural diversity of which is similar to that found in carbonate crusts at cold seeps where anaerobic oxidation of methane (AOM) is the dominant biogeochemical process. The microbial community at Lost City includes abundant archaea, which largely belong to a single phylotype within the methanogenic Methanosarcinales. Isoprenoidal diethers derived from these archaea have polar head groups comprising phosphatidylglycerol or monoglycosyl moieties, although many isoprenoidal diethers detected in these carbonates lack head groups.The non-isoprenoidal diether lipids at Lost City are largely glycolipids. Glycosydic non-isoprenoidal diethers have not previously been reported from any environments or bacterial isolates. Glycolipids are common in archaea where they contain isoprenoidal hydrocarbon cores ether linked to glycerol. Glycolipids also occur in some bacteria and in these non-isoprenoidal fatty acid chains are ester linked to glycerol. However, the glycosylated non-isoprenoidal diether lipids at Lost City contain a previously undetected combination of archaeal and bacterial traits that might be an adaptive response to the vent environment. We hypothesize that utilization of glycosyl head groups instead of phosphatidyl head groups is a strategy for conservation of phosphate by organisms growing in fluids low in this essential nutrient.     

Oscillations in the southern extent of the Indo-Pacific Warm Pool during the mid-Holocene

The Indo-Pacific Warm Pool (IPWP) is thought to play a key role in the propagation and amplification of climate changes through its influence on the global distribution of heat and water vapour. However, little is known about past changes in the size and position of the IPWP. In this study, we use a total of 48 modern and fossil coral records from the Mentawai Islands (Sumatra, Indonesia) and Muschu/Koil Islands (Papua New Guinea) to reconstruct oscillations in the extent of the IPWP since the mid-Holocene. We show that reliable estimates of mean sea surface temperature (SST) can be obtained from fossil corals by using low-resolution Sr/Ca analysis of a suite of corals to overcome the large uncertainties associated with mean Sr/Ca-SST estimates from individual coral colonies. The coral records indicate that the southeastern and southwestern margins of the IPWP were cooler than at present between 5500 and 4300 years BP (1.2 °C ± 0.3 °C) and were similarly cool before 6800 years BP. This mid-Holocene cooling was punctuated by an abrupt, short-lived shift to mean SSTs that were warmer than at present between 6600 and 6300 years BP (1.3 °C ± 0.3 °C), while similarly warm conditions may have also existed after 4300 years BP. We suggest that mid-Holocene cooling at our study sites was related to contractions of the southeastern and southwestern margins of the IPWP, associated with the more northerly position of the Inter-tropical Convergence Zone (ITCZ) that accompanied mid-Holocene strengthening of the Asian summer monsoon. Conversely, intervals of abrupt warming appear to correspond with widespread episodes of monsoon weakening and accompanying southward migrations of the ITCZ that caused the IPWP to expand beyond our coral sites. Intervals of a strengthened Asian monsoon and cooling in the southwestern IPWP during the mid-Holocene appear to correspond with a more positive Indian Ocean Dipole (IOD)-like mean configuration across the tropical Indian Ocean, suggesting that the Asian monsoon–IOD interaction that exists at interannual time scales also persists over centennial to millennial scales. Associated mean changes in the Pacific ENSO modes may have also occurred during the mid-Holocene. The dynamic and inter-connected behaviour of the IPWP with tropical climate systems during the mid-Holocene highlights the fundamental importance of the warm pool region for understanding climate change throughout the tropics and beyond.     

Point defects and pre-dose requirements for sensitization of the 300°C TL peak in natural quartz

This paper discusses the structural features required to stimulate a strong thermoluminescence (TL) glow peak near 300°C in clear natural quartz. For that reason, fresh TL data taken from several specimens prepared from five single crystals with known impurity content are shown. The TL emission was measured with a test dose of 10 mGy of γ-rays in the readout intervals 50–160 and 160–320°C. The readings were carried out prior and after the administration of a pre-dose of 175 kGy of γ-rays followed by heat-treatments at 400°C. For each single specimen, the OH content and the population of inclusions were evaluated by infrared spectroscopy and optical microscopy, respectively. The darkening induced by high γ dose was evaluated by optical spectroscopy. It was observed that the absorption at 475 nm and TL responses decrease with increase of the OH. It was shown that both smoky darkening and TL signals were better explained in terms of Li/Al and Li/OH content ratios rather than the absolute values of aluminum and alkali concentrations. The sensitization with high γ dose and heating is essential to create and stabilize a class of defects sites with Li⁺ ions dislodged from [AlO₄/Li]⁰ and Li-dependent OH centers. It is suggested that the defect sites formed with Li⁺ act as electron traps during test dose irradiation, whereas electron-hole recombination occurs essentially at [AlO₄]⁰ centers during the TL output near 300°C.     

Placing racism in public health: a perspective from Aotearoa/New Zealand

This commentary reflects on Nancy Krieger’s thinking in light of the links between place, ‘race’ and public health from our vantage points as Maori (indigenous) and Pakeha (settler) researchers in Aotearoa New Zealand. We propose an addition to Krieger’s list of pathways through which racism impacts upon the health of indigenous peoples: the systematic alienation of indigenous lands and subsequent degradation of ecosystems that undermine traditional economies. We believe that this proposal, along with the forging of new community-based research partnerships, will increase the potency of Krieger’s challenge: to name and claim racism as a public health issue.     

Diagenesis and geochemistry of porites corals from Papua New Guinea: Implications for paleoclimate reconstruction

Coral proxy records of sea surface temperature (SST) and hydrological balance have become important tools in the field of tropical paleoclimatology. However, coral aragonite is subject to post-depositional diagenetic alteration in both the marine and vadose environments. To understand the impact of diagenesis on coral climate proxies, two mid-Holocene Porites corals from raised reefs on Muschu Island, Papua New Guinea, were analysed for Sr/Ca, δ¹⁸O, and δ¹³C along transects from 100% aragonite to 100% calcite. Thin-section analysis showed a characteristic vadose zone diagenetic sequence, beginning with leaching of primary aragonite and fine calcite overgrowths, transitional to calcite void filling and neomorphic, fabric selective replacement of the coral skeleton. Average calcite Sr/Ca and δ¹⁸O values were lower than those for coral aragonite, decreasing from 0.0088 to 0.0021 and −5.2 to −8.1‰, respectively. The relatively low Sr/Ca of the secondary calcite reflects the Sr/Ca of dissolving phases and the large difference between aragonite and calcite Sr/Ca partition coefficients. The decrease in δ¹⁸O of calcite relative to coral aragonite is a function of the δ¹⁸O of precipitation. Carbon-isotope ratios in secondary calcite are variable, though generally lower relative to aragonite, ranging from −2.5 to −10.4%. The variability of δ¹³C in secondary calcite reflects the amount of soil CO₂ contributing ¹³C-depleted carbon to the precipitating fluids. Diagenesis has a greater impact on Sr/Ca than on δ¹⁸O; the calcite compositions reported here convert to SST anomalies of 115°C and 14°C, respectively. Based on calcite Sr/Ca compositions in this study and in the literature, the sensitivity of coral Sr/Ca-SST to vadose-zone calcite diagenesis is 1.1 to 1.5°C per percent calcite. In contrast, the rate of change in coral δ¹⁸O-SST is relatively small (−0.2 to 0.2°C per percent calcite). We show that large shifts in δ¹⁸O, reported for mid-Holocene and Last Interglacial corals with warmer than present Sr/Ca-SSTs, cannot be caused by calcite diagenesis. Low-level calcite diagenesis can be detected through X-ray diffraction techniques, thin section analysis, and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions.     

'Lunch is for wimps': what drives parents to work long hours in 'successful' British and US cities?

This paper reflects on the impact of long working hours on home–work–family reconciliation from a household perspective. It focuses on discrete interactions between long working hours for households with two parents engaged in paid employment, raising awareness of the integrated nature of work–life balance. Attention is paid to the 'strong economy paradox' confronting dual earning households in 'successful' cities. Evidence is presented to suggest limited resistance to long hours as well as diverse ways one partner adapts their mode of employment to fit the constraints of the other.     

Trace metals in oysters from Knysna estuary

A preliminary survey of seven trace metals in three species of oyster from the Knysna estuary, South Africa, has been carried out. The results which were obtained indicate that this area is as yet unpolluted and provide base-line levels against which future trace-metal pollution can be measured. Two species of oyster are being grown at a number of sites as part of a long-term programme to monitor trace-metal levels in the estuary.