Increasing levels and biomagnification of persistent organic pollutants (POPs) in Antarctic biota

Representatives of the Antarctic food web (krill, cephalopod, fish, penguin, seal) of the area around Elephant Island and from the Weddell Sea were analysed for the most recalcitrant organochlorine compounds. Due to sorption of the compounds to sinking particles and accumulation in sediments, two benthic fish species (Gobionotothen gibberifrons, Chaenocephalus aceratus) feeding on benthos invertebrates and fish reflected significantly increasing concentrations within a decade (1987-1996), while a benthopelagic species (Champsocephalus gunnari) feeding on krill did not. In the pelagic food chain, lipid normalised concentrations of all compounds increased from Antarctic krill to fish proving that biomagnification of highly lipophilic pollutants (log octanol-water partition coefficient>5) occurs in water-breathing animals. As top predators Weddell and southern elephant seals (Leptonychotes weddellii, Mirounga leonina) biomagnified the persistent organic pollutants relative to krill 30-160 fold with the exception of hexachlorobenzene, the levels of which were lower than in fish indicating its intense specific elimination.     

Crustal transect from the North Atlantic Knipovich Ridge to the Svalbard Margin west of Hornsund

The crustal structure along a 312 km transect, stretching from the axial mountains of the North Atlantic Knipovich Ridge to the continental shelf of Svalbard, has been obtained using seismic reflection data and wide angle OBS data. The resulting seismic V_p and V_s models are further constrained by a 2-D-gravity model. The principal objective of this study is to describe and resolve the physical and compositional properties of the crust in order to understand the processes and creation of oceanic crust in this extremely slow-spreading counterpart of the North Atlantic Ridge Systems. V_p is estimated to be 3.50–6.05 km/s for the upper oceanic crust (oceanic layer 2), with a marked increase away from the ridge. The measured V_p of 6.55–6.95 km/s for oceanic layer 3A and 7.10–7.25 km/s for layer 3B, both with a V_p/V_s ratio of 1.81, except for slightly higher values at the ridge axis, does not allow a clear distinction between gabbro and mantle-derived peridotite (10–40% serpentized). The thickness of the oceanic crust varies a lot along the transect from the minimum of 5.6 km to a maximum of 8.1 km. The mean thickness of 6.7 km for the oceanic crust is well above the average thickness for slow-spreading ridges (<10 mm/year half-spreading rate). The areas of increased thickness could be explained by large magma production-rates found in the zones of axial highs at the ridge axis, which also have generated the off-axial highs adjacent the ridge. We suggest that these axial and off-axial highs along the ridge control the lithological composition of the oceanic crust. This approach suggests normal gabbroic oceanic crust to be found in the areas bound by the active magma segments (the axial and off-axial highs) and mantle-derived peridotite outside these zone.     

Assessing the Constrained Harmonic Mean Method for Deriving the Kinematics of ICMEs with a Numerical Simulation

In this study we use a numerical simulation of an artificial coronal mass ejection (CME) to validate a method for calculating propagation directions and kinematical profiles of interplanetary CMEs (ICMEs). In this method observations from heliospheric images are constrained with in-situ plasma and field data at 1 AU. These data are used to convert measured ICME elongations into distance by applying the harmonic mean approach, which assumes a spherical shape of the ICME front. We used synthetic white-light images, similar to those observed by STEREO-A/HI, for three different separation angles between remote and in-situ spacecraft of 30^°, 60^°, and 90^°. To validate the results of the method, the images were compared to the apex speed profile of the modeled ICME, as obtained from a top view. This profile reflects the “true” apex kinematics because it is not affected by scattering or projection effects. In this way it is possible to determine the accuracy of the method for revealing ICME propagation directions and kinematics. We found that the direction obtained by the constrained harmonic mean method is not very sensitive to the separation angle (30^° sep: ?=W7; 60^° sep: ?=W12; 90^° sep: ?=W15; true dir.: E0/W0). For all three cases the derived kinematics agree relatively well with the real kinematics. The best consistency is obtained for the 30^° case, while with growing separation angle the ICME speed at 1 AU is increasingly overestimated (30^° sep: ΔV _arr≈??50 km?s^?1, 60^° sep: ΔV _arr≈+?75 km?s^?1, 90^° sep: ΔV _arr≈+?125 km?s^?1). Especially for future L₄/L₅ missions, the 60^° separation case is highly interesting in order to improve space-weather forecasts.     

Evolution of the Fine Structure of Magnetic Fields in the Quiet Sun: Observations from Sunrise/IMaX and Extrapolations

Observations with the balloon-borne Sunrise/Imaging Magnetograph eXperiment (IMaX) provide high spatial resolution (roughly 100 km at disk center) measurements of the magnetic field in the photosphere of the quiet Sun. To investigate the magnetic structure of the chromosphere and corona, we extrapolate these photospheric measurements into the upper solar atmosphere and analyze a 22-minute long time series with a cadence of 33 seconds. Using the extrapolated magnetic-field lines as tracer, we investigate temporal evolution of the magnetic connectivity in the quiet Sun’s atmosphere. The majority of magnetic loops are asymmetric in the sense that the photospheric field strength at the loop foot points is very different. We find that the magnetic connectivity of the loops changes rapidly with a typical connection recycling time of about 3±1 minutes in the upper solar atmosphere and 12±4 minutes in the photosphere. This is considerably shorter than previously found. Nonetheless, our estimate of the energy released by the associated magnetic-reconnection processes is not likely to be the sole source for heating the chromosphere and corona in the quiet Sun.     

Speeds and Arrival Times of Solar Transients Approximated by Self-similar Expanding Circular Fronts

The NASA Solar TErrestrial RElations Observatory (STEREO) mission offered the possibility to forecast the arrival times, speeds, and directions of solar transients from outside the Sun–Earth line. In particular, we are interested in predicting potentially geoeffective interplanetary coronal mass ejections (ICMEs) from observations of density structures at large observation angles from the Sun (with the STEREO Heliospheric Imager instrument). We contribute to this endeavor by deriving analytical formulas concerning a geometric correction for the ICME speed and arrival time for the technique introduced by Davies et al. (Astrophys. J., 2012, in press), called self-similar expansion fitting (SSEF). This model assumes that a circle propagates outward, along a plane specified by a position angle (e.g., the ecliptic), with constant angular half-width (λ). This is an extension to earlier, more simple models: fixed-Φ fitting (λ=0°) and harmonic mean fitting (λ=90°). In contrast to previous models, this approach has the advantage of allowing one to assess clearly if a particular location in the heliosphere, such as a planet or spacecraft, might be expected to be hit by the ICME front. Our correction formulas are especially significant for glancing hits, where small differences in the direction greatly influence the expected speeds (up to 100?–?200 km?s^?1) and arrival times (up to two days later than the apex). For very wide ICMEs (2λ>120°), the geometric correction becomes very similar to the one derived by Möstl et al. (Astrophys. J. 741, 34, 2011) for the harmonic mean model. These analytic expressions can also be used for empirical or analytical models to predict the 1 AU arrival time of an ICME by correcting for effects of hits by the flank rather than the apex, if the width and direction of the ICME in a plane are known and a circular geometry of the ICME front is assumed.     

Trace metal concentrations in Antarctic sea spiders (Pycnogonida, Pantopoda)

Trace metals were analysed in sea spiders collected on two Polarstern cruises in the Weddell Sea. We found a substantial interspecific heterogeneity of Cd, Cu, Ni, and Zn, indicating varying accumulation strategies and metabolic demands for essential elements. Means and 95%-confidence intervals for all 44 samples analysed are 26+/-7 mg Cd kg(-1), 38+/-22 mg Cu kg(-1), 62+/-13 mg Ni kg(-1) and 990+/-130 mg Zn kg(-1) DW. Only for Pb do we find values less than 1.0 mg kg(-1) for most collectives analysed, in good agreement with other Antarctic arthropods such as crustaceans. Our study provides further evidence for the frequently reported "Cd anomaly" in many polar arthropods. While Cu concentrations in pantopods are within the reported range for Antarctic amphipods and decapods, Ni concentrations are exceptionally high and might be part of predation defence mechanisms. These possibilities should be investigated in more detail in future studies.     

Impact of Poroelastic Response of Sandstones on Geothermal Power Production

During geothermal power production using a borehole doublet consisting of a production and injection well, the reservoir conditions such as permeability k, porosity φ and Skempton coefficient B at the geothermal research site Gross Schoenebeck/Germany will change. Besides a temperature decrease at the injection well and a change of the chemical equilibrium, also the pore pressure p _p will vary in a range of approximately 44 MPa ± 10 MPa in our reservoir at ?3850 to ?4258 m depth. This leads to a poroelastic response of the reservoir rocks depending on effective pressure p _eff (difference between mean stress and pore pressure), resulting in a change in permeability k, porosity φ and the poroelastic parameter Skempton coefficient B. Hence, we investigated the effective pressure dependency of Flechtinger sandstone, an outcropping equivalent of the reservoir rock via laboratory experiments. The permeability decreased by 21% at an effective pressure range from 3 to 30 MPa, the porosity decreased by 11% (p _eff = 6 to 65 MPa) and the Skempton coefficient decreased by 24% (p _eff = 4 to 25 MPa). We will show which mechanisms lead to the change of the mentioned hydraulic and poroelastic parameters and the influence of these changes on the productivity of the reservoir. The most significant changes occur at low effective pressures until 15 to 20 MPa. For our in situ reservoir conditions p _eff = 43 MPa a change of 10 MPa effective pressure will result in a change in matrix permeability of less than 4% and in matrix porosity of less than 2%. Besides natural fracture systems, fault zones and induced hydraulic fractures, the rock matrix its only one part of geothermal systems. All components can be influenced by pressure, temperature and chemical reactions. Therefore, the determined small poroelastic response of rock matrix does not significantly influence the sustainability of the geothermal reservoir.     

Recent Results from Studies of Electric Discharges in the Mesosphere

The paper reviews recent advances in studies of electric discharges in the stratosphere and mesosphere above thunderstorms, and their effects on the atmosphere. The primary focus is on the sprite discharge occurring in the mesosphere, which is the most commonly observed high altitude discharge by imaging cameras from the ground, but effects on the upper atmosphere by electromagnetic radiation from lightning are also considered. During the past few years, co-ordinated observations over Southern Europe have been made of a wide range of parameters related to sprites and their causative thunderstorms. Observations have been complemented by the modelling of processes ranging from the electric discharge to perturbations of trace gas concentrations in the upper atmosphere. Observations point to significant energy deposition by sprites in the neutral atmosphere as observed by infrasound waves detected at up to 1000 km distance, whereas elves and lightning have been shown significantly to affect ionization and heating of the lower ionosphere/mesosphere. Studies of the thunderstorm systems powering high altitude discharges show the important role of intracloud (IC) lightning in sprite generation as seen by the first simultaneous observations of IC activity, sprite activity and broadband, electromagnetic radiation in the VLF range. Simulations of sprite ignition suggest that, under certain conditions, energetic electrons in the runaway regime are generated in streamer discharges. Such electrons may be the source of X- and Gamma-rays observed in lightning, thunderstorms and the so-called Terrestrial Gamma-ray Flashes (TGFs) observed from space over thunderstorm regions. Model estimates of sprite perturbations to the global atmospheric electric circuit, trace gas concentrations and atmospheric dynamics suggest significant local perturbations, and possibly significant meso-scale effects, but negligible global effects.     

The volcanic acidification of glacial Lake Caviahue,Province of Neuquen,Argentina

Lake Caviahue (northern Patagonia, Argentina) is a large glacial lake acidified by volcanic fluids from Copahue volcano. The lake and the feeding rivers were sampled annually from 1997 till early 2006, including the eruptive period of 2000. Lake Caviahue waters evolved over time, with the most concentrated waters in 2000 during the eruptive period, followed by gradual dilution that was interrupted by renewed acidification in 2003–2004. Inversion of the lake water data and application of a dynamic non-steady state model for the lake provides our best quantitative estimates for the variation in element fluxes over the 9-year period. The model flux results agree well with most of the measured fluxes. The Copahue hydrothermal system had gently declining element fluxes between 1997 and mid-1999, although the lake was still becoming more concentrated. About 2–3 months before the 2000 eruption, element fluxes increased strongly, but the hydrothermal fluxes almost shutoff directly after the main eruptive events. The fluxes of several elements recovered post-2001, with an increase in element fluxes in 2003–2004; the lake became more dilute between 2004 and 2006. The intrusion of new magma into the hydrothermal system just prior to the 2000 eruption led to enhanced water rock interaction, with higher concentrations of the rock forming elements in the fluids, and the hot spring flow rate increased as a result of the higher pressure in the reservoir. The fluids became saturated in alunite and jarosite, and they were already saturated with anhydrite. Precipitation of these minerals possibly led to a decreased permeability of the hydrothermal reservoir, leading to the strongly reduced element fluxes just after the eruption. In addition, K, Al and S were retained in the newly precipitated minerals as well, further diminishing their export. The acidification in 2003–2004 may have resulted from a new small intrusion of magma or resulted from seismic activity that created new permeability and fresh rock surfaces for water rock interaction. The volcano is a significant source of toxic trace elements such as F, As, B and Li as well as a nutrient (P) for the local watershed. Monitoring of the hydrothermal fluids in the river that drains Copahue, especially the S/Cl, Mg/Cl and Mg/K values as well as the magnitude of the element fluxes would provide the best information for eruption forecasting for this volcano.