Source(s) and cycling of the nonhydrolyzable organic fraction of oceanic particles

A major fraction of particulate organic carbon (POC) in the deep ocean remains molecularly uncharacterized. In an effort to determine the chemical characteristics and source(s) of sinking POC, we studied a nonhydrolyzable fraction of sinking POC using ¹³C NMR (nuclear magnetic resonance) spectroscopy and analytical pyrolysis. ¹³C NMR spectra and products from analytical pyrolysis of the nonhydrolyzable fraction exhibit a strongly aliphatic character that is distinct from that of bulk POC. The aliphatic nature of this fraction is consistent with its low stable carbon isotope values. We hypothesize that the nonhydrolyzable fraction derives to a significant extent from a refractory component of organisms that selectively accumulates, resulting in its manifestation as a major part of POC sinking to the deep ocean and in underlying sediments.     

Polycyclic aromatic hydrocarbons in commercial fish and lobsters from the coastal waters of Madagascar following an oil spill in August 2009

Concentrations of polycyclic aromatic hydrocarbons were determined in species of commercial fish and lobsters following an oil-spill just off the protected Madagascan coastline. Samples were collected along the coastline within and outside the affected area. Summed PAH concentrations ranged from 1.9 μg kg⁻¹ to 63 μg kg⁻¹ wet weight, but with no higher molecular weight PAHs (>202 Da) being detected. All concentrations of benzo[a]pyrene, benz[a]anthracene and dibenz[a,h]anthracene were <0.1 μg kg⁻¹ wet weight, well within the EU and UK set limits for the protection of human health. Additionally, samples were calculated as the benzo[a]pyrene toxic equivalency quotient (TEQ) and found to be well below the level of concern in relation to health of human consumers. Evaluation of the biota PAH data indicated the origin of PAH was predominantly petrogenic with >80% arising from oil sources. Profile studies indicate a low-level multisource petrogenic contamination probably representing a pre-spill background for the area.     

Effects of bottom sediments on the survival of Enterobacter aerogenes in seawater

The survival of the coliform bacterium Enterobacter aerogenes in seawater was greatly affected by the underlying bottom sediments. The presence of sediments which contained higher concentrations of organic nutrients than the overlaying seawater prolonged the survival and even enabled growth of the bacterial cells. Results obtained from chemical analysis indicated that sediments of fine-grained, silt-clay type contained highest amounts of organic nutrients as compared with sediments with larger particle sizes such as silt and sand grains. Thus, nutrient contents of the sediments were found to be inversely proportional to sediment particle size. The degree of prolonged survival of E. aerogenes was also found to be inversely proportional to the size of the sediment particles presented. Release of the bound nutrients which became available to cells of E. aerogenes from sediments by action of waves and human activities can explain, at least in part, why high counts of coliform bacteria are obtained in coastal and beach waters.     

Couplage des équations de transfert de masse et des lois d''interactions solution-solide par l''utilisation des lanthanides comme traceurs — Approche expérimentale

In underground flow tracing studies, the estimation of the nature and the importance of interactions undergone by the substance used very often constitutes an obstacle to good modeling of mass-transfer processes in solution.

We propose a method to quantify these phenomena by the use of lanthanides as tracers.

For this study, we set up an analytical methodology adapted to routine measurements. The quality of five lanthanides as indicators has been examined. We have demonstrated the formation, by substitution, of a carbonate complex which is extremely stable in the natural environment. The field experiments carried out demonstrated the efficiency of those tracers and confirmed their great stability.

Tracer recovery graphs show that, in accord with our hypothesis, convection and dispersion are identical for all the lanthanide elements. Moreover, we have established a direct relation between their fixing rate on earth materials and the value of their stability constants.

Thus, we demonstrate the possibility of correlative multitracing, with known and quantifiable interelement relations.

Résumé

Dans les études de circulations souterraines par traceur, l'estimation de la nature et de l'importance des interactions subies par la substance utilisée constitue, bien souvent, un obstacle à une bonne modélisation des processus de transfert de masse en solution.

Nous proposons une méthode de quantification de ces phénomènes par l'utilisation des lanthanides comme traceurs.

Pour cette étude, nous avons mis au point une méthodologie analytique adaptée aux mesures de routine. Les qualités, en tant qu'indicateurs, de cinq lanthanides ont été examinées. Nous avons démontré la formation, par substitution, d'un complexe carbonaté extrèment stable en milieu naturel. Les expériences de terrain réalisées ont prouvé l'efficacité de ces traceurs et confirmé leur grande stabilité.

Les courbes de restitution obtenues ont montré que, conformément à nos hypothèses, la convection et la dispersion sont identiques pour l'ensemble de ces éléments. De plus, il a été établi une relation directe entre leurs taux de fixation sur le terrain et la valeur de leurs constantes de stabilité.

On dispose ainsi d'une possibilité de multitraçage corrélatif, avec des relations interélémentaires connues et quantifiables.     

Seasonal snowline instability in an energy balance model

The stability properties of a seasonal, one dimensional energy balance climate model are examined. The model contains idealized landsea geography, an interactive moving snowline and high space-time resolution. For a polar land cap surrounded by ocean we find a bifurcation in the seasonal cycle solutions as a function of solar constant leading to qualitatively different climate regimes: one with continental snow-free summers and the other with perennial snow cover over a large area surrounding the pole. In the parameterspace neighborhood of a bifurcation an infinitesimal change in any radiation budget parameter can cause the transition from one state to the other. Of special interest to those planning more elaborate numerical experiments (GCMs) is the result that 10s of seasonal cycles may be necessary for the model to damp out transient effects before settling upon a repeating seasonal cycle if parameter values are such that the solution is near a bifurcation. This latter finding is unexpected, since the longest time scale in the linear version of the energy balance model is about 5 years.     

Seismic observations at an overstep of the western North Anatolian Fault (Abant–Sapanca region, Turkey)

The course of the active North Anatolian Fault system from Lake Abant to Lake Sapanca was traced by its high micro-earthquake activity. If approaching from the east this section includes a broad south to north overstep (fault offset) of the main fault. Local seismicity has been recorded in this area by a semi-permanent network of 8 stations since 1985 within the frame of the Turkish–German Joint Project for Earthquake Research. The effect of the overstep and its complex fracture kinematics are reflected by the seismicity distribution, the variations of composite fault-plane solutions, and by the spatial coda-Q distribution. Areas of different stress orientation can be distinguished and assigned to different groups of faults. The stresses and the tectonic pattern only in part correspond to a simple model of an extensional overstep and its correlative pull-apart basin. Other types of deformation involved are characterized by normal faulting on faults parallel to the general course of the main strike-slip fault and by synthetic strike-slip faults oriented similar to Riedel shears. Shear deformation by this fault group widely distributed in an area north and east of the main fault line may play an important role in the evolution of the overstep. The development of a pull-apart basin is inhibited along the eastern half of the overstep and compatibility of both strands of the main fault (Bolu–Lake Abant and Lake Sapanca– Izmit–Marmara Sea) seems to be achieved with the aid of the fault systems mentioned. The extension of the missing part of the pull-apart basin seems to be displaced to positions remote from the Lake Abant–Lake Sapanca main fault line, i.e. to the Akyaz?–Düzce basin tract. Highest Q-values (lowest attenuation of seismic waves) were found in the zone of highest seismicity north and west of the overstep which is the zone of strongest horizontal tension. If high coda-Q is an indicator for strong scattering of seismic waves it might be related to extensional opening of fractures.     

Recent trends in pre-monsoon daily temperature extremes over India

Extreme climate and weather events are increasingly being recognized as key aspects of climate change. Pre-monsoon season (March–May) is the hottest part of the year over almost the entire South Asian region, in which hot weather extremes including heat waves are recurring natural hazards having serious societal impacts, particularly on human health. In the present paper, recent trends in extreme temperature events for the pre-monsoon season have been studied using daily data on maximum and minimum temperatures over a well-distributed network of 121 stations for the period 1970–2005. For this purpose, time series of extreme temperature events have been constructed for India as a whole and seven homogeneous regions, viz., Western Himalaya (WH), Northwest (NW), Northeast (NE), North Central (NC), East coast (EC), West coast (WC) and Interior Peninsula (IP).     

Evidence from Ar/Ar Ages of Individual Hornblende Grains for Varying Laurentide Sources of Iceberg Discharges 22,000 to 10,500 yr B.P.

The abundance and lithic content of ice rafted detritus in glacial North Atlantic sediment cores vary abruptly on millennial time scales that have been correlated to Dansgaard-Oeschger cycles in the Greenland ice cores. There is growing evidence that various ice sheet outlets contributed increased iceberg fluxes at multiple discrete intervals, and the relative timing of iceberg discharges from different sources is important for understanding interactions between oceans and ice sheets. We present a provenance study based on ⁴⁰Ar/³⁹Ar dates of individual hornblende grains from 20 samples taken at 600 to 700 yr spacing between 10,500 and 22,000 yr B.P., from Orphan Knoll core EW9303-GGC31. Heinrich layers are characterized by a dominant Paleoproterozoic hornblende provenance consistent with published studies. A change in provenance between Heinrich events H2 and H1 indicates contributions of iceberg calving from the Newfoundland and southern Labrador margins. Between H1 and the Younger Dryas interval, Paleoproterozoic ice rafted grains remained dominant. The dominance of Baffin Island (or Greenland?) sources to the ice rafted detritus is ascribed to the retreat of the southern Laurentide ice sheet at about the time of H1—a retreat that isolated Newfoundland and southern Labrador ice from the shelf-slope boundary.     

ENSO,the IOD and the intraseasonal prediction of heat extremes across Australia using POAMA-2

The simulation and prediction of extreme heat over Australia on intraseasonal timescales in association with the El Niño–Southern Oscillation (ENSO) and the Indian Ocean Dipole (IOD) is assessed using the Bureau of Meteorology’s Predictive Ocean Atmosphere Model for Australia (POAMA). The analysis is based on hindcasts over 1981–2010 and focuses on weeks 2 and 3 of the forecasts, i.e. beyond a typical weather forecast. POAMA simulates the observed increased probabilities of extreme heat during El Niño events, focussed over south eastern and southern Australia in SON and over northern Australia in DJF, and the decreased probabilities of extreme heat during La Niña events, although the magnitude of these relationships is smaller than observed. POAMA also captures the signal of increased probabilities of extreme heat during positive phases of the IOD across southern Australia in SON and over Western Australia in JJA, but again underestimates the strength of the relationship. Shortcomings in the simulation of extreme heat in association with ENSO and the IOD over southern Australia may be linked to deficiencies in the teleconnection with Indian Ocean SSTs. Forecast skill for intraseasonal episodes of extreme heat is assessed using the Symmetric Extremal Dependence Index. Skill is highest over northern Australia in MAM and JJA and over south-eastern and eastern Australia in JJA and SON, whereas skill is generally poor over south-west Western Australia. Results show there are windows of forecast opportunity related to the state of ENSO and the IOD, where the skill in predicting extreme temperatures over certain regions is increased.