On the variability of the Charnock constant and the functional dependence of the drag coefficient on wind speed

A model for the air–sea interface, based on the coupled pair of similarity relations for “aerodynamically” rough flow in both fluids, is presented, which is applied to fetch-limited and high wind speed conditions which occur, for example, in hurricanes. It is shown that the specification of the maximum 10-m drag coefficient and the 10-m wind speed and the peak wave speed at which it occurs are sufficient to uniquely determine the drag law, which asymptotes at low wind speeds to a Charnock constant similar to that for the fully developed wind wave sea and is almost independent of the peak wave speed at the maximum in drag coefficient. A feature of the drag law is that it is of Charnock form, almost independent of the wave age, consistent with the transfer of momentum to the wave spectrum being due to the smaller rather than the dominant wavelengths. The analysis is also applied to a variable sea state in which either the surface wind or the surface Stokes drift vary, but the peak wave speed is kept constant. The corresponding variability in the Charnock constant is in general accord with observations.     

The restricted buffer capacity of a south Baltic estuary — The oder estuary

In the river Oder high-waters of the river with high nutrient loads and low biological activity mainly occur during winter. Thus, a remarkable portion of the annual load passes the estuary untransformed. During summer high level of biological activity is observed in the whole estuary, but while more than 10 mol/l dissolved inorganic nitrogen (DIN) is found in the Großes Haff, where the theoretical water-residence time is only 1 month, in the western part of the estuary, where the water-residence time is approximately 3 months, all DIN is transformed into organic matter.The transformed nutrients settle partly as biological products, but they are released again in these shallow waters due to biological and physical degradation, and transported into the Baltic Sea.This behaviour may explain why in the sediments of the Oderhaff with a sedimentation rate of 1 mm/year only 1% of the annual nutrient load of the Oder river can be found.     

On the circulation in the East Frisian Wadden Sea: numerical modeling and data analysis

 In this paper we use a combination of numerical modeling and data analysis to gain a better understanding of the major characteristics of the circulation in the East Frisian Wadden Sea. In particular, we concentrate on the asymmetry of the tidal wave and its modulation in the coastal area, which results in a complex pattern of responses to the sea-level forcing from the North Sea. The numerical simulations are based on the 3-D primitive equation General Estuarine Transport Model (GETM) with a horizontal resolution of 200 m and terrain-following vertical coordinates. The model is forced at its open boundaries with sea-level data from an operational model for the German Bight (German Hydrographic Office). The validation data for our model simulations include time series of tidal gauge data and surface currents measured at a pile in the back-barrier basin of the Island Langeoog, as well as several ADCP transects in the Accumer Ee tidal inlet. Circulation and turbulence characteristics are investigated for typical situations driven by spring and neap tides, and the analysis is focused on dominating temporal and spatial patterns. By investigating the response of five back-barrier basins with rather different morphologies to external forcing, an attempt is made to elucidate the dominating physical balances controlling the circulation in the individual sub-basins. It is demonstrated that the friction at the seabed tends to slow down the tidal signal in the shallow water. This leads to the establishment of flood dominance in the shallow sea north of the barrier islands. South of the islands, where the water volume of the channels at low tide is smaller than the tidal prism, the asymmetry of the tidal signal is shifted towards ebb dominance, a feature which is particularly pronounced at spring tide. At the northern open boundary, the tidal wave propagating from west to east generates a sea-level difference of ∼1 m along the boundary, and thereby triggers vigorous alongshore currents. The frictional control in the model is located in the inlets, as well as along the northern boundary. The correlation between velocity and turbulent kinetic energy tends to the establishment of a net southward transport, giving theoretical support to the observed accumulation of sediments on the intertidal flats. Weak turbulence along the northern shores of the barrier islands and the small magnitude of the residual currents there promote accumulation of suspended matter in these areas, although wave action will generally counteract this effect. Received: 29 May 2002 / Accepted: 26 September 2002 Responsible Editor: Jean-Marie Beckers Acknowledgements We are indebted to S. Dick for providing the data from the operational model of BSH and to B. Flemming for the useful discussions. The topography data and Fig. 1 have been prepared in cooperation with F. Meyer. Figure 2 has been prepared by G. Brink-Spalink. We also thank for the comments from an anonymous reviewer which helped to improve our paper.     

Sedimentary pigments as indicators of cyanobacterial dynamics in a hypereutrophic lake

Lac Saint-Augustin is an urban lake located on the outskirts of Quebec City, one of North America’s oldest cities. Anthropogenic inputs from land clearing, agriculture, highway development and urbanization in the surrounding catchment have resulted in strong impacts on the limnology of the lake throughout the past three centuries. In recent years, this lake has experienced severe eutrophication, including persistent cyanobacterial blooms. In winter 2011, a sediment core was extracted from the deepest area of the lake. A detailed paleopigment analysis was used to assess eutrophication processes in the lake and to determine the timing and appearance of cyanobacterial blooms and their subsequent variability. Extracted chlorophyll a, its degradation products and 11 carotenoid pigments were identified and quantified via reverse-phase high performance liquid chromatography to examine relative changes in the phytoplankton. The results revealed large variations in the phytoplankton community structure of Lac Saint-Augustin over the past 356 years. Chlorophyll a concentrations per unit organic matter (OM) increased significantly from the base of the core to present day, rising more than 15-fold from 18.4 µg (g OM)^?1 at the base of the core to 287 µg (g OM)^?1 in the most recent strata. Biostratigraphical analysis revealed three major periods of enrichment, with episodes of cyanobacterial abundance from the 1890s onwards. The greatest changes occurred in the most recent period (from the 1960s to the present) relative to earlier periods, with pigment increases for all phytoplankton groups. The cyanobacterial pigments canthaxanthin, echinenone and zeaxanthin (also a marker for green algae) showed concentrations in the surface sediments that were significantly above values at the bottom of the core, and these differences were large, even giving consideration to the lesser pigment degradation near the surface. Overall, the results indicate that cyanobacterial blooms are not a recent feature of Lac Saint-Augustin but began to occur soon after catchment modification 150 years ago. The pigment records also imply that cyanobacterial and associated algal populations have risen to unprecedented levels over the last few decades of ongoing development of the Lac Saint-Augustin catchment. This study highlights the utility of multiple pigment analysis of lake sediments for identifying the timing and magnitude of anthropogenic impacts.     

Spatial Pair-Copula Modeling of Grade in Ore Bodies: A Case Study

A real-world mining application of pair-copulas is presented to model the spatial distribution of metal grade in an ore body. Inaccurate estimation of metal grade in an ore reserve can lead to failure of a mining project. Conventional kriged models are the most commonly used models for estimating grade and other spatial variables. However, kriged models use the variogram or covariance function, which produces a single average value to represent the spatial dependence for a given distance. Kriged models also assume linear spatial dependence. In the application, spatial pair-copulas are used to appropriately model the non-linear spatial dependence present in the data. The spatial pair-copula model is adopted over other copula-based spatial models since it is better able to capture complex spatial dependence structures. The performance of the pair-copula model is shown to be favorable compared to a conventional lognormal kriged model.     

Coalification and thermal histories of Tertiary basins in relation to late Alpidic evolution of the Eastern Alps

The thermal histories of Tertiary basins situated around and within the Eastern Alps are examined using coalification data.Waples' method is used to estimate paleogeothermal conditions. The data suggest that the basins' thermal histories are intimately related to late Alpidic geodynamics of the Eastern Alps.Basins situated near the thrust front (Eastern Alpine foredeep, Vienna basin) are characterized by hypothermal histories and low coalification gradients. This is a consequence of relatively thick crust, high paleosedimentation rates in the Alpine foredeep, and Oligocene to Early Miocene stacking of cool sediments along the southern margin of the Eastern Alpine foredeep. Extension in the Vienna basin region is restricted mainly to shallow crustal levels and did not change the thermal pattern beneath the Alpine nappes. Major hyperthermal events of Oligocene age and local coalification maxima in the central Slovenian basin date from magmatic activity along the Periadriatic lineament, caused by Oligocene subduction. In Miocene times subduction migrated eastward and magmatic activity shifted to the northern Slovenian and Styrian basins, resulting in a strong hyperthermal phase of Ottnangian to Lower Badenian age in these basins.Rapid uplift of the Tauern window in the central part of the Eastern Alps, due to buoyancy, is related to E-W directed crustal stretching and resulted in raised heat flow in Miocene times in the Tauern window region, and in relatively high rank in adjacent Tertiary basins (Wagrain, Tamsweg).Present geothermal patterns are controlled primarily by raised heat flow along the south-eastern margin of the Alps, a consequence of thinned crust beneath the Pannonian basin.

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Zusammenfassung Die Inkohlungsbilder von tertiären Sedimentbecken, die im Bereich der Ostalpen situiert sind, werden hinsichtlich der thermischen Geschichte diskutiert. In einigen Becken erfolgt eine Abschätzung der paläogeothermischen Verhältnisse mit Hilfe derWaples-Methode. Die Inkohlungsbilder der Tertiärbecken belegen eine enge Beziehung zwischen der thermischen Geschichte dieser Becken und der jungalpidischen Geodynamik der Ostalpen.In der Nähe der Überschiebungsfront gelegene Becken (Molassebecken, Wiener Becken) werden durch hypothermische Verhältnisse und geringe Inkohlung charakterisiert. Dies ist eine Folge relativ dicker Kruste, hoher Paläo-Sedimentationsraten in der alpinen Vortiefe und des Übereinanderstapelns kühler Sedimente am Südrand des Molassebeckens während Oligozän und frühem Miozän. Die Extension im Wiener Becken war auf den obersten Krustenabschnitt beschränkt und hat die thermischen Verhältnisse unterhalb der alpinen Decken nicht beeinflußt.Die magmatische Aktivität entlang der Periadriatischen Naht steht in Zusammenhang mit der oligozänen Subduktion und ist für hyperthermische Ereignisse und lokale Inkohlungsmaxima in oligozänen Sedimenten des zentralen Slowenischen Beckens verantwortlich. Im Miozän wanderte die Subduktion ostwärts und die magmatische Aktivität verlagerte sich in das nördliche Slowenische und Steirische Becken. Dadurch wurde in diesen Becken eine starke hyperthermische Phase während Ottnang bis Unterbaden initiiert.Der rasche isostatische Aufstieg des Tauernfensters in den zentralen Ostalpen steht mit miozäner, E-W gerichteter Dehnungstektonik in Zusammenhang. Er ist für erhöhten Wärmefluß im Miozän im Bereich des Tauernfensters und für die relativ hohe Inkohlung des Wagrainer und Tamsweger Beckens verantwortlich.Die heutigen geothermischen Verhältnisse werden vor allem durch erhöhten Wärmefluß am Südostrand der Alpen geprägt. Dieser ist eine Folge der Krustenausdünnung unter dem Pannonischen Becken.

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Résumé La houillification des bassins sédimentaires tertiaires des Alpes orientales est discutée dans la perspective de leur histoire thermique. Les conditions paléogéothermiques sont estimées au moyen de la méthode deWaples. L'étude de la houillification de ces bassins montre une relation étroite entre leur histoire thermique et la géodynamique des Alpes orientales à la fin du Tertiaire.Ces bassins, situés à proximité du front de charriage — il sagit du Bassin molassique et du Bassin viennois —, se caractérisent par leur condition «hypothermique» et leur faible gradient de houillification; cette propriété provient de l'épaississement de la croute terrestre due à une sédimentation rapide en avant des Alpes et à l'empilement tectonique des sédiments froids les uns sur les autres le long de la bordure méridionale du Bassin molassique au cours de l'Oligocène et du Miocène inférieur. L'extension, dans la région du Bassin viennois, s'est limitée à un niveau crustal peu profond et n'a pas influencé la situation thermique dans les nappes alpines.L'activité magmatique le long du linéament périadriatique, due à la subduction oligocène, est contemporaine des événements «hyperthermiques» et des maxima locaux de houillification dans les sédiments oligocènes du bassin central de Slovénie.Pendant le Miocène, la subduction progressa vers l'est et l'activité magmatique se déplaça vers les bassins de Slovénie septentrionale et de Styrie, avec comme conséquence, dans ces bassins, une phase «hyperthermique» marquée à l'Ottnangien et au Badenien inférieur.La montée isostatique rapide de la Fenêtre des Tauern dans la partie centrale des Alpes orientales est en relation avec l'extension tectonique est-ouest au Miocène; elle est responsable d'un flux thermique élevé dans la région de la Fenêtre et d'une houillification relativement importante dans les bassins tertiaires adjacents de Wagrain et de Tamsweg.La géothermie actuelle de la bordure sud-est des Alpes est régie par un flux thermique élevé, conséquence de l'amincissement crustal sous le bassin Pannonique.

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Syn- and post-collisional heat flow in the Cenozoic Eastern Alps

The heat flow evolution of a continental collisional zone is exemplified by the Eastern Alps. Heat flow maps for the syn-collision (Oligocene), syn-extrusion (Early/Middle Miocene), and post-extrusion (Late Miocene, Recent) stages are presented, and are discussed in relation to the orogenic evolution. Continental collision during Paleogene time was characterized by extremely low heat flow (<40 mW/m²) along the orogenetic front, and very high heat flow (>150 mW/m²) a few hundred kilometers south of it. The former was a result of crustal thickening and of thermal blanketing due to rapid sedimentation and nappe stacking. The latter was caused by slab break-off and magmatic activity. The Early/Middle Miocene syn-extrusion stage was characterized by rapid exhumation of metamorphic core complexes (Tauern and Rechnitz Windows), and by magmatic activity (Styrian Basin). Both mechanisms caused extremely high heat flow (>200 mW/m²). In contrast, the orogenetic front remained cold. Thereafter, magmatic activity ended and uplift rates decreased. Thus, Late Miocene heat flow is characterized by low to moderately high values. Heat flow values >75 mW/m² were restricted to the transition zone of the Pannonian Basin characterized by thinned crust, and to the Tauern Window area. Recent temperature data indicate a subtle post-Miocene increase in heat flow.     

History of scoria-cone eruptions on the eastern shoulder of the Kenya–Tanzania Rift revealed in the 250-ka sediment record of Lake Chala near Mount Kilimanjaro

Reconstructions of the timing and frequency of past eruptions are important to assess the propensity for future volcanic activity, yet in volcanic areas such as the East African Rift only piecemeal eruption histories exist. Understanding the volcanic history of scoria-cone fields, where eruptions are often infrequent and deposits strongly weathered, is particularly challenging. Here we reconstruct a history of volcanism from scoria cones situated along the eastern shoulders of the Kenya–Tanzania Rift, using a sequence of tephra (volcanic ash) layers preserved in the ~250-ka sediment record of Lake Chala near Mount Kilimanjaro. Seven visible and two non-visible (crypto-) tephra layers in the Lake Chala sequence are attributed to activity from the Mt Kilimanjaro (northern Tanzania) and the Chyulu Hills (southern Kenya) volcanic fields, on the basis of their glass chemistry, textural characteristics and known eruption chronology. The Lake Chala record of eruptions from scoria cones in the Chyulu Hills volcanic field confirms geological and historical evidence of its recent activity, and provides first-order age estimates for seven previously unknown eruptions. Long and well-resolved sedimentary records such as that of Lake Chala have significant potential for resolving regional eruption chronologies spanning hundreds of thousands of years.     

Trophic modeling of the Northern Humboldt Current Ecosystem, Part II: Elucidating ecosystem dynamics from 1995 to 2004 with a focus on the impact of ENSO

The Northern Humboldt Current Ecosystem is one of the most productive in the world in terms of fish production. Its location near to the equator permits strong upwelling under relatively low winds, thus creating optimal conditions for the development of plankton communities. These communities ultimately support abundant populations of grazing fish such as the Peruvian anchoveta, Engraulis ringens. The ecosystem is also subject to strong inter-annual environmental variability associated with the El Niño Southern Oscillation (ENSO), which has major effects on nutrient structure, primary production, and higher trophic levels. Here our objective is to model the contributions of several external drivers (i.e. reconstructed phytoplankton changes, fish immigration, and fishing rate) and internal control mechanisms (i.e. predator-prey) to ecosystem dynamics over an ENSO cycle. Steady-state models and time-series data from the Instituto del Mar del Perú (IMARPE) from 1995 to 2004 provide the base data for simulations conducted with the program Ecopath with Ecosim. In simulations all three external drivers contribute to ecosystem dynamics. Changes in phytoplankton quantity and composition (i.e. contribution of diatoms and dino- and silicoflagellates), as affected by upwelling intensity, were important in dynamics of the El Niño of 1997–98 and the subsequent 3 years. The expansion and immigration of mesopelagic fish populations during El Niño was important for dynamics in following years. Fishing rate changes were the most important of the three external drivers tested, helping to explain observed dynamics throughout the modeled period, and particularly during the post-El Niño period. Internal control settings show a mix of predator–prey control settings; however a “wasp-waist” control of the ecosystem by small pelagic fish is not supported.