Individual Microcystis colonies harbour distinct bacterial communities that differ by Microcystis oligotype and with time.

Interactions between bacteria and phytoplankton in the phycosphere have impacts at the scale of whole ecosystems, including the development of harmful algal blooms. The cyanobacterium Microcystis causes toxic blooms that threaten freshwater ecosystems and human health globally. Microcystis grows in colonies that harbour dense assemblages of other bacteria, yet the taxonomic composition of these phycosphere communities and the nature of their interactions with Microcystis are not well characterized.

C plant carbon isotope discrimination does not respond to CO concentration on decadal to centennial timescales.

Plant carbon isotope discrimination is complex, and could be driven by climate, evolution and/or edaphic factors. We tested the climate drivers of carbon isotope discrimination in modern and historical plant chemistry, and focus in particular on the relationship between rising [CO ] over Industrialization and carbon isotope discrimination. We generated temporal records of plant carbon isotopes from museum specimens collected over a climo-sequence to test plant responses to climate and atmospheric change over the past 200 yr (including Pinus strobus, Platycladus orientalis, Populus tremuloides, Thuja koraiensis, Thuja occidentalis, Thuja plicata, Thuja standishii and Thuja sutchuenensis).

Contrasting Controls on the Diel Isotopic Variation of Hg at Two High Elevation Sites in the Western United States.

The atmosphere is a significant global reservoir for mercury (Hg) and its isotopic characterization is important to understand sources, distribution, and deposition of Hg to the Earth's surface. To better understand Hg isotope variability in the remote background atmosphere, we collected continuous 12-h Hg samples for 1 week from two high elevation sites, Camp Davis, Wyoming (valley), and Mount Bachelor, Oregon (mountaintop). The samples collected at Camp Davis displayed strong diel variation in δHg values of Hg, but not in ΔHg or ΔHg values.

Carbon, Nitrogen, and Mercury Isotope Evidence for the Biogeochemical History of Mercury in Hawaiian Marine Bottomfish.

The complex biogeochemical cycle of Hg makes identifying primary sources of fish tissue Hg problematic. To identify sources and provide insight into this cycle, we combined carbon (δC), nitrogen amino acid (δN), and Hg isotope (ΔHg, ΔHg, δHg) data for six species of Hawaiian marine bottomfish. Results from these isotopic systems identified individuals within species that likely fed from separate food webs.

Isotopic Composition of Inorganic Mercury and Methylmercury Downstream of a Historical Gold Mining Region.

We measured total mercury (THg) and monomethyl mercury (MMHg) concentrations and mercury (Hg) isotopic compositions in sediment and aquatic organisms from the Yuba River (California, USA) to identify Hg sources and biogeochemical transformations downstream of a historical gold mining region. Sediment THg concentrations and δ(202)Hg decreased from the upper Yuba Fan to the lower Yuba Fan and the Feather River. These results are consistent with the release of Hg during gold mining followed by downstream mixing and dilution.

The effects of Porapak™ trap temperature on δ(18)O, δ(13)C, and Δ47 values in preparing samples for clumped isotope analysis.

Rationale: The clumped isotope paleothermometer, a new proxy widely applicable in studies of paleoclimate, tectonics, and paleontology, relates the abundance of doubly substituted isotopologues of carbonate-derived CO2 to the temperature of formation of the carbonate phase. As this technique becomes more widely used, more is discovered about the effects of everyday laboratory procedures on the clumped isotopic composition of CO2 gas.

Methods: Preparation of CO2 for clumped isotope analysis requires the removal of isobaric contaminants prior to measurement, achieved dynamically by passing the CO2 through a gas chromatography column using a helium carrier gas or cryogenically pumping CO2 through a static trap filled with Porapak™ Q (PPQ) material.

Mercury isotope study of sources and exposure pathways of methylmercury in estuarine food webs in the Northeastern U.S.

We measured mercury (Hg) isotope ratios in sediments and various estuarine organisms (green crab, blue mussel, killifish, eider) to investigate methylmercury (MMHg) sources and exposure pathways in five Northeast coast (U.S.) estuaries.

Mercury accumulation in sea lamprey (Petromyzon marinus) from Lake Huron.

We determined whole-fish total mercury (Hg) concentrations of 40 male and 40 female adult sea lampreys (Petromyzon marinus) captured in the Cheboygan River, a tributary to Lake Huron, during May 2011. In addition, bioenergetics modeling was used to explore the effects of sex-related differences in activity and resting (standard) metabolic rate (SMR) on mercury accumulation. The grand mean for Hg concentrations was 519 ng/g (standard error of the mean=46 ng/g).

A high-throughput system for boron microsublimation and isotope analysis by total evaporation thermal ionization mass spectrometry.

Rationale: Research on the ocean carbon cycle is vitally important due to the projected impacts of atmospheric CO2 on global temperatures and climate change, but also on ocean chemistry. The direct influence of this CO2 rise on the seawater pH can be evaluated from the boron isotopic composition in biogenic carbonates; however, conscientious laboratory techniques and data treatment are vital in obtaining accurate and precise results. A rapid-throughput boron purification and Total Evaporation Thermal Ionization Mass Spectrometry method was developed for high accuracy and precision boron isotopic analysis for small (ng) sample sizes.

Investigation of local mercury deposition from a coal-fired power plant using mercury isotopes.

Coal combustion accounts for approximately two-thirds of global anthropogenic mercury (Hg) emissions. Enhanced deposition of Hg can occur close to coal-fired utility boilers (CFUBs), but it is difficult to link specific point sources with local deposition. Measurement of Hg stable isotope ratios in precipitation holds promise as a tool to assist in the identification of local Hg deposition related to anthropogenic emissions.

Nanoscale manipulation of the properties of solids at high pressure with relativistic heavy ions.

High-pressure and high-temperature phases show unusual physical and chemical properties, but they are often difficult to 'quench' to ambient conditions. Here, we present a new approach, using bombardment with very high-energy, heavy ions accelerated to relativistic velocities, to stabilize a high-pressure phase. In this case, Gd(2)Zr(2)O(7), pressurized in a diamond-anvil cell up to 40 GPa, was irradiated with 20 GeV xenon or 45 GeV uranium ions, and the (previously unquenchable) cubic high-pressure phase was recovered after release of pressure.

Reporting of variations in the natural isotopic composition of mercury.

High-precision measurements of natural variations in the stable isotopic composition of mercury show great promise as a new tracer of mercury sources and chemical transformations in the environment. We strongly suggest that all laboratories adopt a common means of data correction, standardization, and nomenclature in order to ensure that data from various laboratories can be easily evaluated and compared. We make suggestions for mass bias correction, reporting of mass-dependent and mass-independent isotope variations, and a standard protocol for reporting analytical uncertainties.