Sub-recent nitrogen-isotope trends in sediments from Skagerrak (North Sea) and Kattegat: Changes in N-budgets and N-sources?

We determined ¹⁵N/¹⁴N ratios of total nitrogen in surface sediments and dated sediment cores to reconstruct the history of N-loading of the North Sea. The isotopic N composition in modern surface sediments is equivalent to and reflects the isotopic mixture of oceanic nitrate on the one hand (δ¹⁵N = 5‰) and the imprint of river-borne nitrogen input into the SE North Sea (δ¹⁵N up to 12‰ in estuaries of the SE North Sea) on the other hand. We compare the results with δ¹⁵N records from pre-industrial sediment intervals in cores from the Skagerrak and Kattegat areas, which both constitute significant depositional centres for N in the North Sea and the Baltic Sea/North Sea transition. As expected, isotopically enriched anthropogenic nitrogen was found in the two records from the Kattegat area, which is close to eutrophication sources on land. Enrichment of δ¹⁵N in cores from the Skagerrak – the largest sediment sink for nitrogen in the entire North Sea – was not significant and values were similar to those found in sediment layers representing pre-industrial conditions. We interpret this isotopic uniformity as an indication that most riverine reactive nitrogen with its characteristic isotopic signature is removed by denitrification in shallow shallow-water sediments before reaching the main sedimentary basin of the North Sea.     

Future emissions of marine halogenated very-short lived substances under climate change

Halogenated Very Short-lived Substances (VSLS), such as bromoform, dibromomethane and methyl iodide, are naturally produced in the oceans and are involved in ozone depletion in the troposphere and the stratosphere. The effect of climate change on the oceanic emissions of these compounds is not well quantified. Based on present-day observed global oceanic and atmospheric concentrations, and historic and future data from three CMIP5 models, past and future sea-to-air fluxes of these VSLS are calculated. The simulations are used to infer possible effects of projected changes of physical forcing on emissions in different oceanic regimes. CMIP5 model output for 1979–2100 from the historical scenario and the RCP scenarios 2.6 and 8.5 are used as input data for the emission calculations. Of the parameters that have the main influence on the sea-to-air fluxes, the global sea surface temperatures show a steady increase during the twenty-first century, while the projected changes of sea surface wind speed is very small. The calculated emissions based on the historical CMIP5 model runs (1979–2005) increased over the 26 year period and agree well with the emissions based on ERA-Interim data. The future sea-to-air fluxes of VSLS generally increase during the twenty-first century under the assumption of constant concentration fields in the ocean and atmosphere. The multi-model mean global emissions of bromoform increase by 29.4% (9.0%) between 1986 and 2005 and 2081–2100 under RCP 8.5 (2.6) and dibromomethane and methyl iodide emissions increase by 23.3% (6.4%) and 5.5% (1.5%), respectively. Uncertainties of the future emission estimates, driven by ongoing environmental changes such as changing oceanic productivity (not considered in this study) are discussed.     

An Automated Iridium-Strip Heater for LA-ICP-MS Bulk Analysis of Geological Samples

In this paper we describe a flux‐free fusion technique for the highly precise LA‐ICP‐MS bulk analysis of geological samples. For this purpose we have developed an automated iridium‐strip heater with temperature and melt time control. To optimise the homogeneity of the fused glasses and to reduce possible depletion of volatile elements during melting, we undertook experiments with basaltic rock and glass powders using different melting temperatures (1300–1700 °C) and melting times (5‐80 s). Major and trace element microanalysis was performed using EPMA and LA‐ICP‐MS. Homogeneous glasses were obtained for temperatures ≥ 1500 °C and melting times ≥ 10 s. High loss (20‐90%) of highly volatile elements (e.g., Cs, Ge, Sn, Pb) was observed for high melting temperatures (≥ 1600 °C) and long melting times (80 s). Standard melting conditions (1600 °C, 10 s) represent a compromise, as the glasses were homogeneous with respect to major and trace elements and, at the same time, were not depleted in elements with condensation temperatures (at a pressure of 10^?4 bar) higher than about 900 K (e.g., Zr, Hf, Ba, Sr, REE, U, Mo, Ni, Rb, Ga). Several international geological reference materials with SiO₂ ranging between 47% m/m and 59% m/m were prepared using our standard melting conditions (1600 °C, 10 s) and subsequently analysed by LA‐ICP‐MS. These samples also include the new Brazilian basaltic reference material BRP‐1. Matrix‐matched calibration of the LA‐ICP‐MS data was performed using the basaltic reference glasses KL2‐G, ML3B‐G, BCR‐2G and BHVO‐2G. Most analytical data agreed within uncertainty at the 95% confidence level with the GeoReM preferred values published in the GeoReM database for reference materials of geological and environmental interest. To demonstrate routine bulk LA‐ICP‐MS analyses of geochemical and cosmochemical samples using the whole rock fusion technique, we also present trace element data for ocean island basalts from Lanai (Hawaii) and of Martian meteorites.     

APEX-SZ first light and instrument status

The apex-sz instrument is designed for the discovery and study of galaxy clusters at mm-wavelengths using the Sunyaev Zel’dovich effect. The receiver consists of 320 superconducting transition edge sensor (TES) bolometers cooled to 250 mK with the combination of a three stage He sorption fridge and mechanical pulse tube cooler. The detectors are instrumented with a frequency domain multiplexing readout system. The receiver is mounted on the 12 m apex telescope located at 5100 m on the Atacama plateau in Chile. For the first light engineering deployment of December 2005, the receiver was configured with a 55 element wedge of the bolometers and operating in the 150 GHz atmospheric window. During the engineering run we achieved significant milestones in our instrumentation development efforts, including celestial observations with a monolithically fabricated TES bolometer array cooled with a mechanical cooler and successful implementation of a SQUID-based MHz AC-biased readout. These technology demonstrations point the way toward future large TES bolometer array instruments. Here we describe the results of this deployment and future plans for the apex-sz instrument.     

Potential microbial bioinvasions via ships' ballast water, sediment, and biofilm

A prominent vector of aquatic invasive species to coastal regions is the discharge of water, sediments, and biofilm from ships' ballast-water tanks. During eight years of studying ships arriving to the lower Chesapeake Bay, we developed an understanding of the mechanisms by which invasive microorganisms might arrive to the region via ships. Within a given ship, habitats included ballast water, unpumpable water and sediment (collectively known as residuals), and biofilms formed on internal surfaces of ballast-water tanks. We sampled 69 vessels arriving from foreign and domestic ports, largely from Western Europe, the Mediterranean region, and the US East and Gulf coasts. All habitats contained bacteria and viruses. By extrapolating the measured concentration of a microbial metric to the estimated volume of ballast water, biofilm, or residual sediment and water within an average vessel, we calculated the potential total number of microorganisms contained by each habitat, thus creating a hierarchy of risk of delivery. The estimated concentration of microorganisms was greatest in ballast water>sediment and water residuals>biofilms. From these results, it is clear microorganisms may be transported within ships in a variety of ways. Using temperature tolerance as a measure of survivability and the temperature difference between ballast-water samples and the water into which the ballast water was discharged, we estimated 56% of microorganisms could survive in the lower Bay. Extrapolated delivery and survival of microorganisms to the Port of Hampton Roads in lower Chesapeake Bay shows on the order of 10(20) microorganisms (6.8 x 10(19) viruses and 3.9 x 10(18) bacteria cells) are discharged annually to the region.     

Magnetic fields and the dynamics of spiral galaxies

We investigate the dynamics of magnetic fields in spiral galaxies by performing 3D magnetohydrodynamics simulations of galactic discs subject to a spiral potential using cold gas, warm gas and a two-phase mixture of both. Recent hydrodynamic simulations have demonstrated the formation of interarm spurs as well as spiral arm molecular clouds, provided the interstellar medium model includes a cold H  i phase. We find that the main effect of adding a magnetic field to these calculations is to inhibit the formation of structure in the disc. However, provided a cold phase is included, spurs and spiral arm clumps are still present if β≳ 0.1 in the cold gas. A caveat to the two-phase calculations though is that by assuming a uniform initial distribution, β≳ 10 in the warm gas, emphasizing that models with more consistent initial conditions and thermodynamics are required. Our simulations with only warm gas do not show such structure, irrespective of the magnetic field strength.
Furthermore, we find that the introduction of a cold H  i phase naturally produces the observed degree of disorder in the magnetic field, which is again absent from simulations using only warm gas. Whilst the global magnetic field follows the large-scale gas flow, the magnetic field also contains a substantial random component that is produced by the velocity dispersion induced in the cold gas during the passage through a spiral shock. Without any cold gas, the magnetic field in the warm phase remains relatively well ordered apart from becoming compressed in the spiral shocks. Our results provide a natural explanation for the observed high proportions of disordered magnetic field in spiral galaxies and we thus predict that the relative strengths of the random and ordered components of the magnetic field observed in spiral galaxies will depend on the dynamics of spiral shocks.     

A simple model for the relationship between star formation and surface density

We investigate the relationship between the star formation rate per unit area and the surface density of the interstellar medium (ISM; the local Kennicutt–Schmitt law) using a simplified model of the ISM and a simple estimate of the star formation rate based on the mass of gas in bound clumps, the local dynamical time-scales of the clumps and an efficiency parameter of around  ε≈ 5  per cent. Despite the simplicity of the approach, we are able to reproduce the observed linear relation between star formation rate and surface density of dense (molecular) gas. We use a simple model for the dependence of H₂ fraction on total surface density to argue why neither total surface density nor the H  i surface density is a good local indicator of star formation rate. We also investigate the dependence of the star formation rate on the depth of the spiral potential. Our model indicates that the mean star formation rate does not depend significantly on the strength of the spiral potential, but that a stronger spiral potential, for a given mean surface density, does result in more of the star formation occurring close to the spiral arms. This agrees with the observation that grand design galaxies do not appear to show a larger degree of star formation compared to their flocculent counterparts.     

New Sediment Cores Reveal Environmental Changes Driven by Tectonic Processes at Ancient Helike,Greece

According to various historical sources an earthquake and an associated tsunami wiped out the Greek city of Helike on the Gulf of Corinth in 373 B.C. This study combines stratigraphical data from a new series of sediment cores with archaeological findings of the Helike Project to better assess the fate of Helike. Abrupt lithological changes, for example, from coarse‐grained littoral facies at the base to fine‐grained lagoonal deposits, in three of the new cores suggest sudden formation of lagoonal or lacustrine conditions in the central delta during tectonic events of subsidence due to fault‐slip. These events date before c. 2550 B.C., before 348 cal. B.C.–64 cal. A.D. (probably 373 B.C.), and before 1437–1634 cal. A.D. (probably A.D. 1402). Vertically displaced isochronic surfaces between two neighboring cores may be related to active faulting of the fan‐delta north of the Western Helike Fault Zone in 373 B.C. and A.D. 1402. Although the Helike Project reported possible tsunami evidence in earlier cores and trenches, no unequivocal sedimentary traces of a tsunami were identified in the Classical horizons of the new cores.