Tidal correction of hydrographic measurements

Summary A simple procedure is presented to eliminate the influence of tidal oscillation from hydrographic measurements. This is done with a transformation from a co-ordinate system fixed in space to a co-ordinate system fixed in time using results of a numerical tidal model. The procedure is applied to a hydrographic survey in the German Bight. The hydrographic structure transformed onto a co-ordinate system fixed in time is much more similar to the structure obtained by satellite pictures and shows dynamical processes much clearer than in a co-ordinate system fixed in space.

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Gezeitenkorrektur von hydrographischen Messungen

Zusammenfassung In dieser Arbeit wird ein Verfahren vorgestellt, das hydrographische Messungen vom Einfluß periodischer Variationen durch die Gezeiten bereinigt. Dies geschieht unter Benutzung von Ergebnissen eines numerischen Modells durch eine Transformation einer gemessenen hydrographischen Struktur von einem ortsfesten in ein zeitfestes System. Dieses Verfahren wird auf eine hydrographische Aufnahme der Deutschen Bucht angewandt. Die auf ein zeitfestes Koordinatensystem transformierte hydrographische Messung zeigt sehr viel Ähnlichkeit mit einer synoptischen Messung, die bei einem Satellitenüberflug gewonnen wurde. Bestimmte dynamische Prozesse in der Deutschen Bucht lassen sich zudem im zeitfesten Koordinatensystem besser erkennen als im ortsfesten Koordinatensystem.

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Correction de l'influence de la marée sur les mesures hydrologiques

Résumé L'article présente une méthode simple pour éliminer l'influence de la marée sur les mesures hydrologiques. Cela est obtenu par le passage d'un système de coordonnées fixe dans l'espace à un système de coordonnées fixe dans le temps utilisant les résultats d'un modèle numérique de marée. La méthode est appliquée à un levé hydrologique dans la Baie Allemande. La structure hydrologique obtenue dans un système de coordonnées fixe dans le temps est beaucoup plus proche de celle qui est obtenue par les images satellites et décrit le processus dynamique beaucoup plus clairement que dans un système de coordonnées fixe dans l'espace.

     

Identification of a collapsing protostar

The globular molecular cloud B335 contains a single, deeply embedded, far-infrared source. Our recent observations of H₂CO and CS lines toward this source provide direct kinematic evidence for collapse. Both the intensity and detailed shape of the line profiles match those expected from inside-out collapse inside a radius of 0.036 pc. The collapse began about 1.5 × 10⁵ years ago, similar to the onset of the outflow. The mass accretion rate is about 10 times the outflow rate, and about 0.4M should have now accumulated in the star and disk. Because B335 rotates only very slowly, any disk would still be very small (about 3 AU). The accretion luminosity should be adequate to power the observed luminosity. Consequently, we believe that B335 is indeed a collapsing protostar.Paper presented at the Conference onPlanetary Systems: Formation, Evolution, and Detection held 7–10 December, 1992 at CalTech, Pasadena, California, U.S.A.     

A Global Dynamic Model for the Neolithic Transition

During the Holocene strong gradients in the distribution of technologyincluding subsistence ways emerged on a global scale.These patterns were further amplified in historic times and are stillvisible through worldwide differences in national wealth.In order to evaluate major factors responsible for the shift fromforaging to food production we here employ quantitative methods bydeveloping a deterministic but simple model. After compiling existing maps of potential vegetation at 5000 BP theinhabited world is split into 197 regions with homogeneous environmentalconditions. Suitable variables for the macro-economic and culturaldevelopment in the Neolithic period are found to be farming to hunting-gatheringratio, number of agricultural economies and a technological development index.The model explicitly describes economic adaptation, growth and migrationof human populations together with the spread of their cultural characteristics; it accounts for over-exploitation of natural resources, crowdingmortality and the climate variability on a millennium scale.In a thorough model validation region specific trajectories are compared toarchaeological evidence revealing a high correspondence. Major parts of the knownsequence of Neolithic centers including the timing differences are robustlyreproduced. A series of known problems in prehistory is discussedcomprising the lag between domestication and full scale farming, the off-levelingof the technological boost following the transition, the emergence ofdistinct migration waves and sensitivity to climate fluctuations.Not mere population pressure but continuous innovation and competition betweensubsistence strategies is identified as a prime mover of agricultural development.The results suggest that few aspects of biogeography may have determined theobserved continental gradients in the number of domesticable species ultimatelyleading to an increasing differentiation in technology and demography.     

How depositional conditions control input, composition, and degradation of organic matter in sediments from the Chilean coastal upwelling region

In a comprehensive study, we compared depositional conditions, organic matter (OM) composition, and organic carbon turnover in sediments from two different depositional systems along the Chilean continental margin: at ∼23° S off Antofagasta and at ∼36° S off Concepción. Both sites lie within the Chilean coastal upwelling system and have an extended oxygen minimum zone in the water column. However, the northern site (23° S) borders the Atacama Desert, while the southern site (36° S) has a humid hinterland. Eight surface sediment cores (up to 30 cm long) from water depths of 126-1350 m were investigated for excess ²¹⁰Pb (²¹⁰Pb_xs) activity, total organic and total inorganic carbon concentrations (TOC and TIC, respectively), C/N-ratios, organic carbon isotopic compositions (δ¹³C), chlorin concentrations, Chlorin Indices (CI), and sulfate reduction rates (SRR). Sediment accumulation rates obtained from ²¹⁰Pb-analysis were similar in both regions (0.04-0.15 cm yr⁻¹ at 23° S, 0.10-0.19 cm yr⁻¹ at 36° S), although total ²¹⁰Pb_xs fluxes indicated that the vertical particle flux was higher at 36° S than at 23° S. We propose that sediment focusing in isolated deposition centers led to high sediment accumulation rates at 23° S. Furthermore, there were no indications for sediment mixing at 23° S, while bioturbation was intense at 36° S. δ¹³C-values (−24.5‰ to −20.1‰ vs. VPDB) and C/N-ratios (molar, 8.6-12.8) were characteristic of a predominantly marine origin of the sedimentary OM in both investigated areas. The extent of OM alteration in the water column was partly reflected in the surface sediments as chlorin concentrations decreased and C/N-ratios and CI increased with increasing water depth of the sampling site. SRR were lower at 23° S (areal SRR 0.12-0.60 mmol m⁻² d⁻¹) than at 36° S (areal SRR 0.82-1.18 mmol m⁻² d⁻¹), which was partly due to the greater water depth of most of the sediments investigated in the northern region and consistent with a lower quality of the sedimentary OM at 23° S. Reaction rate constants for TOC degradation that were obtained from measured SRR (k_SRR; 0.0004-0.0022 yr⁻¹) showed a good correspondence to k_TOC that were derived from the depth profiles of TOC (0.0003-0.0014 yr⁻¹). Both, k_SRR and k_TOC, reflect differences in OM composition. At 36° S they were related to the degradation state of bulk OM (represented by C/N-ratios), whereas near 23° S they were related to the freshness of a small fraction of labile OM (represented by CI). Our study shows that although rates of organic carbon accumulation were similar in both investigated sites, the extent and kinetics of organic carbon degradation were closely linked to differing depositional conditions.     

Sources and fate of amino sugars in coastal Peruvian sediments

Amino sugars are involved in the marine carbon and nitrogen cycles and comprise a geochemically significant fraction of marine organic material (OM). However, information on abundance and distribution of these compounds in marine sediments is scarce. Three sediment cores (<50 cm) from the coastal region off Peru were investigated for concentrations of glucosamine (GlcN), galactosamine (GalN), mannosamine (ManN), and muramic acid (Mur). The sum of the four amino sugars accounted for 1.0-2.4% of organic carbon and 1.9-3.8% of nitrogen in the sediments. At the shallowest (102 m) and the deepest site (1278 m), carbon-normalized concentrations decreased down-core, suggesting preferential degradation of amino sugars compared to bulk sedimentary OM. At the site from the center of the oxygen minimum zone (238 m), amino sugar concentrations were high throughout the core, pointing to enhanced preservation of amino sugars under anoxic conditions. GlcN (44-56 mol%) and GalN (33-42 mol%) were the dominant amino sugars in all investigated samples, while ManN (6-14 mol%) and Mur (1-4 mol%) were significantly less abundant. Mur was predominantly associated with cell wall remains rather than with living bacteria, since bacterial abundances estimated based on Mur concentrations were up to 500 times higher than cell counts reported for sediments from this area. GlcN/GalN-ratios (1.1-1.7) indicated that chitin, a polymer of GlcN, was not a major contributor to the amino sugar pool of the investigated sediments. Furthermore, GlcN/Mur-ratios (13-68) are inconsistent with a predominant contribution of intact peptidoglycan, which exhibits a 1:1-ratio. The present study includes a compilation of previously published information on distribution and abundance of amino sugars in the marine environment. Both concentrations and ratios observed in the Peruvian sediments fall in the range of values reported for OM in water column and sediments from different oceanic regions and water depths. Although specific sources for the majority of sedimentary amino sugars remain unidentified, there are indications for a major prokaryotic origin. As suggested in previous studies, the uniform amino sugar compositions of altered marine OM and particularly the close association of GlcN and GalN, which is similar to the ratio observed in living bacteria, are consistent with a transformation of planktonic into bacterial OM.     

High-Spatial-Resolution Imaging Combining High-Order Adaptive Optics,Frame Selection,and Speckle Masking Reconstruction

We present, for the first time, high-spatial-resolution observations combining high-order adaptive optics (AO), frame selection, and post-facto image correction via speckle masking. The data analysis is based on observations of solar active region NOAA 10486 taken with the Dunn Solar Telescope (DST) at the Sacramento Peak Observatory (SPO) of the National Solar Observatory (NSO) on 29 October 2003. The high Strehl ratio encountered in AO corrected short-exposure images provides highly improved signal-to-noise ratios leading to a superior recovery of the object’s Fourier phases. This allows reliable detection of small-scale solar features near the diffraction limit of the telescope. Speckle masking imaging provides access to high-order wavefront aberrations, which predominantly originate at high atmospheric layers and are only partially corrected by the AO system. In addition, the observations provided qualitative measures of the image correction away from the lock point of the AO system. We further present a brief inspection of the underlying imaging theory discussing the limitations and prospects of this multi-faceted image reconstruction approach in terms of the recovery of spatial information, photometric accuracy, and spectroscopic applications.The editors apologize to the authors: due to a misunderstanding during the editorial process, the publication of this paper has been delayed.     

High-Resolution Hα Observations of Proper Motion in NOAA 8668: Evidence for Filament Mass Injection by Chromospheric Reconnection

There have been two different kinds of explanations for the source of cool material in prominences or filaments: coronal condensations from above and cool plasma injections from below. In this paper, we present observational results which support filament mass injection by chromospheric reconnection. The observations of an active filament in the active region NOAA 8668 were performed on 17 August 1999 at a wavelength of H–0.6 Å using the 65 cm vacuum reflector, a Zeiss H birefringent filter, and a 12-bit SMD digital camera of Big Bear Solar Observatory. The best image was selected every 12 s for an hour based on a frame selection algorithm. All the images were then co-aligned and corrected for local distortion due to the seeing. The time-lapse movie of the data shows that the filament was undergoing ceaseless motion. The H flow field has been determined as a function of time using local correlation tracking. Time-averaged flow patterns usually trace local magnetic field lines, as inferred from H fibrils and line-of-sight magnetograms. An interesting finding is a transient flow field in a system of small H loops, some of which merge into the filament. The flow is associated with a cancelling magnetic feature which is located at one end of the loop system. Initially a diverging flow with speeds below 10 km s^–1 is visible at the flux cancellation site. The flow is soon directed along the loops and accelerated up to 40 km s^–1 in a few minutes. Some part of the plasma flow then merges into and moves along the filament. This kind of transient flow takes place several times during the observations. Our results clearly demonstrate that reconnection in the photosphere and chromosphere is a likely way to supply cool material to a filament, as well as re-organizing the magnetic field configuration, and, hence, is important in the formation of filaments.     

Modes of variability of Southern Hemisphere atmospheric circulation estimated by AGCMs

The seasonal mean variability of the atmospheric circulation is affected by processes with time scales from less than seasonal to interannual or longer. Using monthly mean data from an ensemble of Atmospheric General Circulation Model (AGCM) realisations, the interannual variability of the seasonal mean is separated into intraseasonal, and slowly varying components. For the first time, using a recently developed method, the slowly varying component in multiple AGCM ensembles is further separated into internal and externally forced components. This is done for Southern Hemisphere 500?hPa geopotential height from five AGCMs in the CLIVAR International Climate of the Twentieth Century project for the summer and winter seasons. In both seasons, the intraseasonal and slow modes of variability are qualitatively well reproduced by the models when compared with reanalysis data, with a relative metric finding little overall difference between the models. The Southern Annular Mode (SAM) is by far the dominant mode of slowly varying internal atmospheric variability. Two slow-external modes of variability are related to El Ni?o-Southern Oscillation (ENSO) variability, and a third is the atmospheric response to trends in external forcing. An ENSO-SAM relationship is found in the model slow modes of variability, similar to that found by earlier studies using reanalysis data. There is a greater spread in the representation of model slow-external modes in winter than summer, particularly in the atmospheric response to external forcing trends. This may be attributable to weaker external forcing constraints on SH atmospheric circulation in winter.