Bias aware Kalman filters: Comparison and improvements

This paper reviews two different approaches that have been proposed to tackle the problems of model bias with the Kalman filter: the use of a colored noise model and the implementation of a separate bias filter. Both filters are implemented with and without feedback of the bias into the model state. The colored noise filter formulation is extended to correct both time correlated and uncorrelated model error components. A more stable version of the separate filter without feedback is presented. The filters are implemented in an ensemble framework using Latin hypercube sampling. The techniques are illustrated on a simple one-dimensional groundwater problem. The results show that the presented filters outperform the standard Kalman filter and that the implementations with bias feedback work in more general conditions than the implementations without feedback.     

Geomorphic evolution of small river–lake‐systems in northeast Germany during the Late Quaternary

This study investigates the post‐glacial development of four small river–lake systems in the Weichselian belt of northern central Europe. The valleys investigated are part of an immature drainage system characterized by frequent and abrupt changes in flow direction and the presence of numerous stagnant‐ice depressions in the valley course. The depressions contain thick sedimentary sequences which provide excellent archives for the reconstruction of the post‐glacial valley development. Study results indicate that the valleys reuse segments of former subglacial meltwater channels. During the Late Pleniglacial these channels carried meltwater streams. Stagnant‐ice melting occurred in stages from the Oldest Dryas to the early Holocene and was often followed by the formation of lakes in the valley course. Flow reversals occurred during the Late‐glacial–Holocene transition and were in response to general base‐level lowering caused by stagnant‐ice melting, headwater erosion and lake overspills. Lacustrine deposition typically started during the early Late‐glacial comprising mainly silicate gyttjas, whereas organic gyttjas and peats accumulated during the Allerød. The Younger Dryas is associated with a marked increase in fluvial and aeolian sedimentation, and lake‐level high stands. This was followed by early Holocene lake‐level low stands and a subsequent stabilization phase with decreasing silicate input and increasing organic lacustrine deposition. In general, dramatic changes in Late Pleniglacial to early Holocene sedimentation suggest that small‐scale catastrophic events played a more important role in triggering geomorphic changes then previously recognized. Infilling continued until peat accumulation and terrestrialization of lake basins became widespread during the mid‐ to late Holocene. Beginning in the late Holocene anthropogenic influences become important mainly involving an increase in sediment supply due to forest clearing and land use, followed by mill stowage, river course correction and anthropogenic lake‐level manipulations. Copyright © 2007 John Wiley & Sons, Ltd.     

Cosmoclimatology: a new theory emerges

Henrik Svensmark draws attention to an overlooked mechanism of climate change: clouds seeded by cosmic rays.     

Southwest Scandinavia, 40–15 kyr BP: palaeogeography and environmental change

Twelve palaeogeographical reconstructions illustrate environmental changes at the southwest rim of the Scandinavian Ice Sheet 40–15 kyr BP. Synchronised land, sea and glacier configurations are based on the lithostratigraphy of tills and intertill sediments. Dating is provided by optically stimulated luminescence and calibrated accelerator mass spectrometry radiocarbon. An interstadial sequence ca. 40–30 kyr BP with boreo‐arctic proglacial fjords and subarctic flora and occasional glaciation in the Baltic was succeeded by a Last Glacial Maximum sequence ca. 30–20 kyr BP, with the closure of fjords and subsequent ice streams in glacial lake basins in Kattegat and the Baltic. Steadily flowing ice from Sweden bordered the Norwegian Channel Ice Stream. A deglaciation sequence ca. 20–15 kyr BP indicates the transgression of arctic waters, retreat of the Swedish ice and advance of Baltic ice streams succeeded by a return to interstadial conditions. When ameliorated ice‐free conditions prevailed in maritime regions, glaciers advanced through the Baltic and when interstadial regimes dominated the Baltic, glaciers expanded off the Norwegian coast. The largest glacier extent was reached in the North Sea around 29 kyr BP, about 22 kyr BP in Denmark and ca. 18 kyr BP in the Baltic. Our model provides new data for future numerical and qualitative landform‐based models. Copyright © 2003 John Wiley & Sons, Ltd.     

The architecture of a sandy braided-meandering river system: an example from the lower triassic Soiling Formation (M. Buntsandstein) in W-Germany

The dominantly sandy fluvial deposits of the Soiling Formation in the Hessian Depression in W-Germany are excellently exposed in abandoned sandstone quarries N of Kassel near Bad Karlshafen und Stadtoldendorf.Detailed mapping of the quarry walls indicates the presence of five architectural elements: (1) lateral accretion deposits; (2) minor cross-cutting channel-fills; (3) major broad channel deposits; (4) laminated sand sheets; and (5) muddy deposits. The vertical and lateral relationships of these elements suggest deposition in a braided-meandering river system. Sinuous parts of the river channels were dominated by point bar deposition at river high stage (element 1), whereas low-stage flow was characterized by a braided stream pattern (element 2). Less sinuous parts of the river channels were characterized by moderate braiding indices (element 3). Proximal overbank areas were dominated by sandy sheet flows (element 4) whereas distal overbank areas received muddy sediments (element 5).

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Zusammenfassung Die überwiegend sandigen fluviatilen Ablagerungen der Solling-Folge in der Hessischen Senke sind sehr gut in ehemaligen Sandsteinbrüchen nördlich von Kassel in der Nähe von Bad Karlshafen und Stadtoldendorf aufgeschlossen.Detaillierte Kartierung der Bruchwände zeigt fünf architektonische Elemente: (1) Ablagerungen mit lateralem Zuwachs; (2) kleine durchschneidende Rinnenfüllungen; (3) Absätze in großen und breiten Kanälen; (4) laminierte Sandschichten und (5) tonige Ablagerungen. Die vertikalen und lateralen Beziehungen dieser Elemente zueinander deuten auf Sedimentation in einem verflochtenen bis mäandrierenden Flussnetz hin. Die stark gekrümmten Teile der Flussrinnen sind bei Hochwasser von Point Bar-Absätzen dominiert (Element 1), während sie bei Niedrigwasser Ströme mit verflochtenem Muster zeigen (Element 2). Die weniger gekrümmten Teile der Flussrinnen sind durch moderate Vernetzungsindizien charakterisiert (Element 3). Proximale Überflutungsbereiche sind von sandigen Schichtflutsedimenten dominiert (Element 4), während auf den distalen Überflutungsebenen tonige Sedimente abgelagert wurden (Element 5).

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Résumé Les dépôts fluviatiles à dominance sableuse de la Soiling Formation (dépression de Hesse, en Allemagne) affleurent de manière exceptionnelle dans des carrières abandonnées près de Bad-Karlshafen et Stadtoldendorf. Une cartographie détaillée des parois des carrières révèle cinq éléments architecturaux: 1) dépôts à croissance latérale; 2) remplissage entrecroisé de chenaux mineurs; 3) dépôts de chenaux majeurs; 4) couches de sable à structure laminée; 5) dépôts argileux. Les relations verticales et latérales de ces éléments suggèrent une sédimentation dans une rivière anastomosée et à méandres. Les parties sinueuses des chenaux étaient le siège d'une sédimentation de »point bar« lors des périodes de hautes eaux (élément 1), tandis que les périodes de basses eaux se traduisent par un type de cours d'eau anastomosé (élément 2). Les parties moins sinueuses des chenaux étaient caractérisées par des indices d'anastomose plus modérés (élément 3). Les domaines proximaux de crue étaient dominés par des influx sableux (élément 4), tandis que les domaines de crue distaux recevaient des sédiments argileux (élément 5).

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- . 5 : 1) ; 2) : 3) ; 4) 5) . . , ( 1), ( 2). ( 3). , , ( 4), - , ( 5).

     

The role of regional information in estimation of extreme point rainfalls

Previous analysis has shown that inclusion of regional information improves at-site estimation of point rainfalls and makes it possible to obtain estimates at non-monitored sites. The basis for this analysis was a partial duration series (PDS) modelling of individual rainfall observations and use of regional prior distributions for the PDS-parameters in a Bayesian estimation procedure. The advantages of this theoretically satisfactory, but also somewhat complicated procedure are evaluated by means of a comparison with simplified procedures. These include modelling based on regional pooling of all point rainfall data into one sample from a common parent distribution and modelling with disregard of either the dependence between stations or the regional heterogeneity. The different models are analysed and compared with respect to the uncertainty of the predicted extreme events.     

Organic petrography and geochemistry of inertinite-rich mudstones, Jakobsstigen Formation, Upper Jurassic, northeast Greenland: Indications of forest fires and variations in relative sea-level

The lower-middle Oxfordian Jakobsstigen Formation, Wollaston Forland, northeast Greenland, consists mainly of stacked coarsening-upward successions of offshore to shoreface heteroliths, sandstone and rare foreshore sandstones. The units are separated by thin, laterally extensive sheets of terrigenous carbonaceous mudstones, which have been subjected to organic petrographic and geochemical studies. The mudstones are thermally immature, with maturities corresponding to R₀ in the range 0.35–0.50%. The mudstones contain very high proportions of allochthonous inertinite, subordinate huminite, char and negligible proportions of liptinite. Inertinite reflectance distributions are markedly bimodal, with maxima at approximately 1.73 and 4.91% R_m. Both pyrolysis yields and solvent extract yields are low. The distributions of n-alkanes are markedly light-end skewed and show a pronounced predominance of even-numbered compounds in the lower carbon number range. Biomarker-distributions feature a dominance of C₂₉-steranes, slight enhancement of extended hopanes and αββ-steranes, low proportion of tricyclic triterpanes and very low hopane/sterane ratios. Sedimentological, organic petrographical and geochemical evidence suggests that the regular alternation between marine and terrestrial depositional environments during deposition of the Jakobsstigen Formation was related to low-amplitude, high-frequency changes in relative sea-level and local climate. The mudstones were deposited during early rise of relative sea-level in shallow, flat-bottomed lakes or lagoons on a broad coastal plain. The lakes acted as traps for fine elastic sediment and for predominantly windborne inertinite, generated by wildfires in the hinterland. High rates of evaporation rendered the lakes mildly saline, hampering their colonization by vegetation other than cyanobacteria and halophilic microorganisms. Similarly, saline porewaters excluded higher plant vegetation from emergent areas. Upon continued rise of the relative sea-level, the lakes were gradually flooded and their deposits became covered by sandy shallow marine sediments. The larger areas covered by shallow marine waters during periods of high relative sea-level led to a more humid local climate and to lower frequency of wildfires. During falling relative sea-level, the marine deposits were eroded and partially removed and the cycle subsequently repeated upon renewed rise in relative sea-level. Hence, minor changes in relative sea-level gave rise to the regular alternation of two vastly different depositional environments, as well as to marked variations in local climate.     

Formation and diagenesis of bedding cycles in uppermost Cretaceous chalks of the Dan Field, Danish North Sea

Metre-scale lithologic cycles, visible in core and on logs from Maastrichtian chalks of the Dan Field, were examined to determine their mechanisms of deposition and relation to hydrocarbon production. The lower parts of cycles consist of porous, cream-coloured, largely non-stylolitic, commonly laminated chalk with limited bioturbation (mainly escape burrows). Cycles are capped by thinner intervals of white to grey, hard, stylolitic chalk with concentrations of bioclastic material, intense burrowing and few preserved primary sedimentary structures. The cycle caps contain nearly twice as much Mg as compared to the more porous parts of cycles and also have slightly larger δ¹⁸O values (?4·1‰ for the caps; ?4·4‰ for porous zones). There is a significant reduction of average cycle thickness, as well as total thickness of the Maastrichtian chalk section, from SW to NE across the Dan Field. The cycle thinning largely results from a reduced thickness of porous chalks from the lower parts of cycles and thus is reflected in lower average porosity and permeability on the NE side of the field. These data indicate that episodic winnowing removed fine-grained constituents from highstanding northeastern areas. Porous cycle bases were deposited at relatively high rates that precluded complete bioturbation; preserved laminae, coupled with escape burrows, reflect episodic sediment influx in areas that flank the seafloor highs. Cycle tops apparently accumulated more slowly (throughout the region, but especially on seafloor highs), perhaps because of reduced productivity of planktic organisms. Slower sedimentation allowed more complete bioturbation and destruction of sedimentary structures, and also led to incipient high-magnesium calcite seafloor cementation (sufficient to yield firmer sediment and enhanced burrow preservation, but not to form true hardgrounds). Thus, the elevated magnesium contents and reduced porosity of the cycle caps reflect very early diagenetic processes that were only partially modified by burial diagenesis. Rates of chalk deposition, as inferred from physical and geochemical evidence, appear to be a significant control on reservoir characteristics in North Sea chalks. The highest average porosities and permeabilities are found in areas with the highest sediment accumulation rates where seafloor diagenesis is minimized. Topographic depressions at the time of sedimentation can thus be expected to have the best production characteristics, and synsedimentary topographic highs should have the thinnest sections and the poorest petrophysical properties.     

Refinement of Phosphorus Determination in Quartz by LA‐ICP‐MS through Defining New Reference Material Values

The aim of this study was to improve the quality of laser ablation inductively coupled plasma‐mass spectrometry (LA‐ICP‐MS) determination of phosphorus in crystalline quartz. Over the last decade, the Geological Survey of Norway has routinely performed trace element determinations on quartz from both operating and potential quartz deposits by LA‐ICP‐MS. The determined phosphorus concentrations were, with but few exceptions, consistently within the range of 10 to 30 μg g^?1, results that seemed to be both too high and too consistent. The multi‐material calibration curve obtained from a suite of reference materials (NIST SRM 610, 612, 614, 1830, BAM No. 1 amorphous SiO₂ glass) did not define a precise regression line. Published phosphorus concentrations for the reference materials are poorly constrained and the observed dispersions along the multi‐material calibration curve suggest that some of the reference values may be inaccurate. Furthermore, the calibration curve did not pass through the origin of the [(cps ³¹P/cps ³⁰Si) · cone. Si] vs. P concentration diagram; thus, in addition to the uncertainties of the literature values of phosphorus, it is difficult to define the calibration curve. Three reference materials (NIST SRM 614, 1830, synthetic quartz KORTH) were sent for phosphorus accelerator implantation, providing an independent and accurate (± 3%) approach for determining phosphorus concentrations in crystalline quartz. The intrinsic phosphorus concentrations of the three implanted samples plus those for NIST SRM 610 and 612 were determined by secondary ion mass spectrometry (SIMS), yielding new phosphorus values for NIST SRM 610, 612, 614 and 1830. Using these new values resulted in a better defined LA‐ICP‐MS calibration curve. However, the source of the ICP‐MS related background could not be defined, such that it must still be empirically corrected for.