Exploring spatial heterogeneity of Antarctic sea ice algae using an autonomous underwater vehicle mounted irradiance sensor

Sea ice algae represent a key energy source for many organisms in polar food webs, butestimating their biomass at ecologically appropriate spatiotemporal scales remains achallenge. Attempts to extend ice-core derived biomass to broader scales using remotesensing approaches has largely focused on the use of under-ice spectral irradiance.Normalized difference index (NDI) based algorithms that relate the attenuation ofirradiance by the snow-ice-algal ensemble at specific wavelengths to biomass havebeen used to explain up to 79% of the biomass of algae in limited areas. Application ofthese algorithms to datasets collected using tethered remotely operated vehicles (ROVs)has begun, generating methods for spatial sampling at scales and spatial resolutionnot achievable with ice-core sampling. Successful integration of radiometers withuntethered autonomous underwater vehicles (AUVs) offers even greater capability tosurvey broader regions to explore the spatial heterogeneity of sea ice algal communities.This work describes the pilot use of an AUV fitted with a multispectral irradiance sensorto estimate ice-algal biomass along transects beneath land-fast sea ice (~2 m thick withminimal snow cover) in McMurdo Sound, Antarctica. The AUV obtained continuous,repeatable, multi-band irradiance data, suitable for NDI-type approaches, over transectsof 500 m, with an instrument footprint of 4 m in diameter. Algorithms were developedusing local measurements of ice algae biomass and spectral attenuation of sea iceand were able to explain 40% of biomass variability. Relatively poor performance of thealgorithms in predicting biomass limited the confidence that could be placed in biomassestimates from AUV data. This was attributed to the larger footprint size of the opticalsensors integrating small-scale biomass variability more effectively than the ice core inthe platelet-dominated ice algal habitat. Our results support continued development ofremote-sensing of sea ice algal biomass at m–km spatial scales using optical methods,but caution that footprint sizes of calibration data (e.g., coring) must be compatible withoptical sensors used. AUVs offer autonomous survey techniques that could be appliedto better understand the horizontal variability of sea ice algae from nearshore ice out tothe marginal ice zone

Warming Can Boost Denitrification Disproportionately Due to Altered Oxygen Dynamics

Background: Global warming and the alteration of the global nitrogen cycle are major anthropogenic threats to the environment. Denitrification, the biological conversion of nitrate to gaseous nitrogen, removes a substantial fraction of the nitrogen from aquatic ecosystems, and can therefore help to reduce eutrophication effects. However, potential responses of denitrification to warming are poorly understood. Although several studies have reported increased denitrification rates with rising temperature, the impact of temperature on denitrification seems to vary widely between systems. Methodology/Principal Findings: We explored the effects of warming on denitrification rates using microcosm experiments, field measurements and a simple model approach. Our results suggest that a three degree temperature rise will double denitrification rates. By performing experiments at fixed oxygen concentrations as well as with oxygen concentrations varying freely with temperature, we demonstrate that this strong temperature dependence of denitrification can be explained by a systematic decrease of oxygen concentrations with rising temperature. Warming decreases oxygen concentrations due to reduced solubility, and more importantly, because respiration rates rise more steeply with temperature than photosynthesis. Conclusions/Significance: Our results show that denitrification rates in aquatic ecosystems are strongly temperature dependent, and that this is amplified by the temperature dependencies of photosynthesis and respiration. Our result

Energy services

Energy consumers are driven by their demand for energy services (such as space and water heating, cooking, transportation, lighting, entertainment and computing). This piece introduces the reader to the concept of energy services, and explains why it is important to analyze energy markets and climate policies from the perspective of energy services. The paper discusses the theoretical foundations and empirical evidence, particularly related to the rebound effect and the demand in developing economies. The paper concludes that governments should encourage the collection of statistical information about energy services in order to help economists analyse markets and policies through this lens. Most importantly, governments should formulate more integrated policies that focus explicitly on energy services, connecting markets for energy and for energy-using equipment with the development of technologies. Careful and balanced energy service policies are especially important as economies industrialise because they can help reduce economic, political and environmental vulnerability

Diploids in the Cryptococcus neoformans Serotype A Population Homozygous for the α Mating Type Originate via Unisexual Mating

The ubiquitous environmental human pathogen Cryptococcus neoformans is traditionally considered a haploid fungus with a bipolar mating system. In nature, the α mating type is overwhelmingly predominant over a. How genetic diversity is generated and maintained by this heterothallic fungus in a largely unisexual α population is unclear. Recently it was discovered that C. neoformans can undergo same-sex mating under laboratory conditions generating both diploid intermediates and haploid recombinant progeny. Same-sex mating (α-α) also occurs in nature as evidenced by the existence of natural diploid αADα hybrids that arose by fusion between two α cells of different serotypes (A and D). How significantly this novel sexual style contributes to genetic diversity of the Cryptococcus population was unknown. In this study, ∼500 natural C. neoformans isolates were tested for ploidy and close to 8% were found to be diploid by fluorescence flow cytometry analysis. The majority of these diploids were serotype A isolates with two copies of the α MAT locus allele. Among those, several are intra-varietal allodiploid hybrids produced by fusion of two genetically distinct α cells through same-sex mating. The majority, however, are autodiploids that harbor two seemingly identical copies of the genome and arose via either endoreplication or clonal mating. The diploids identified were isolated from different geographic locations and varied genotypically and phenotypically, indicating independent non-clonal origins. The present study demonstrates that unisexual mating produces diploid isolates of C. neoformans in nature, giving rise to populations of hybrids and mixed ploidy. Our findings underscore the importance of same-sex mating in shaping the current population structure of this important human pathogenic fungus, with implications for mechanisms of selfing and inbreeding in other microbial pathogens

Solution ripening of hydroxyapatite nanoparticles: Effects on electrophoretic deposition

Electrophoretic deposition is a low-cost, simple, and flexible coating method for producing hydroxyapatite (Hap) coatings on metal implants. However, densification requires heating the coated metal to high temperatures, which, for commercial HAp powders, generally means at least 1200°C. At such temperatures, the metal tends to react with the HAp coating, inducing decomposition, and the strength of titanium and stainless steel implants is severely degraded. With the use of raw uncalcined nanoparticulate HAp, densification can occur at 900°-1050°C; however, such coatings are prone to cracking due to the high drying shrinkage. This problem was solved by precipitating nanoparticulate HAp by the metathesis process [10Ca(NO3)2 + 6NH4H2PO4 + 8NH4OH] and optimizing the ~30 nm of nanoprecipitates by an Ostwald ripening approach, that is, by boiling and/or ambient aging in the mother liquor. While the as-precipitated nanoparticles produced severely cracked coatings, 2 h of boiling or 10 days of ambient aging ripened the 'gel-like' mass into unagglomerated nanoparticles, which produced crack-free coatings. Since boiling enhanced particle size but ambient aging did not, crack elimination probably was due to the transition from the highly agglomerated gel-like state to the dispersed nanoparticulate state rather than to particle growth. Furthermore, boiling only reduced the amount of cracking whereas aging completely eliminated cracking

Precipitation of hydroxyapatite nanoparticles: Effects of precipitation method on electrophoretic deposition

Electrophoretic deposition is a low-cost, simple, and flexible coating method for producing hydroxyapatite (HA) coatings on metal implants with a broad range of thicknesses, from 500 μ m. As for many other HA coating techniques, densification of electrophoretically deposited coatings involves heating the coated metal to temperatures above 1000°C. Metal substrates tend to react with HA coatings at such temperatures inducing decomposition at temperatures below 1050°C (decomposition for pure HA normally occurs above 1300°C). Therefore, densification of these coatings needs to be conducted at temperatures lower than 1050°C, and this necessitates the use of high-surface-area HA nano-precipitates, rather than commercially available pre-calcined powders, which densify at temperatures typically higher than 1200°C. HA nano-precipitates were prepared by three methods and deposited on metal substrates by electrophoresis: (1) the acid base method, which produced plate-like nano-particles with a 2.5:1 aspect ratio, and severely cracked coatings; (2) the calcium acetate method, which produced needle-like nano-particles with a 10:1 aspect ratio, and slightly cracked coatings; (3) the metathesis method, which produced rounded nano-particles with a 2:1 aspect ratio, and high-quality crack-free coatings. The results suggested that the less equiaxed the nano-particles, the more cracked the coatings obtained by the electrophoretic deposition technique. © 2005 Springer Science + Business Media, Inc