Comment on “Is there a paleolimnological explanation for ‘walking on water’ in the Sea of Galilee?”

In a recent paper, Nof et al. (J Paleolimnol 35:417–439, 2006) suggest a physical mechanism which could account for the formation of ice on Lake Kinneret (Sea of Galilee) in northern Israel. Based on the sea surface temperature record of sediment cores from the Mediterranean Sea the authors argue that centennial-scale cold events had the potential to trigger local ‘springs ice’ formation on the lake in the past. Here, we demonstrate that a closer inspection of the paleoceanographic record in combination with correlation and regression analyses of meteorological data provides no evidence for such cold events in the lake region during the last 10,000 years. Thus, the formation of ‘springs ice’ on Lake Kinneret was unlikely at least since the beginning of the Neolithic.     

A sediment budget for a cultivated floodplain in tropical North Queensland,Australia

Sugarcane is grown on the floodplains of northern Queensland adjacent to the Great Barrier Reef lagoon. Sediment and nutrient loss from these sugarcane areas is considered a potential threat to coastal and marine ecosystems. To enable sugarcane cultivation, farmers have structured the landscape into different elements, comprising fields, water furrows, ‘headlands’ and drains. In order to apply appropriate management of the landscape and reduce export of sediment, it is important to identify which of these elements act as sediment sources or sinks. In this study erosion and deposition rates were measured for the different landscape elements in a subcatchment of the Herbert River and used to create a sediment budget. Despite large uncertainties, the budget shows that the floodplain area is a net source of sediment. Estimated sediment export varies between 2 and 5 t ha^?1 y^?1. The relative importance of the landscape elements as sediment sources could also be determined. Plant cane is identified as the most important sediment source. Water furrows generate most sediment, but are a less important source of exported sediment due to their low connectivity. Headlands and minor drains act as sediment traps. Copyright © 2007 John Wiley & Sons, Ltd.     

The world''s large lake basins as denudation-accumulation systems and implications for their lifetimes

The mechanical denudation rates of 81 large lake basins (lake area > 500 km²) were determined from long-term river loads and erosion maps. Using the drainage area/lake area ratios the mean sedimentation rates of the lakes were calculated for a porosity of 0.3. The mean sedimentation rates of different lake types vary between 0.1 mm/a (glacial lakes, lowland) and 5.4 mm/a (mostly sag basin lakes). The calculated lifetimes of the lakes are based on the lake volumes and mean sedimentation rates, assuming steady-state conditions and solely clastic material. On average, glacial lakes in highlands and fault-related lakes show the shortest lifetimes (c. 70 ka), glacial lakes in lowlands and rift lakes have the longest lifetimes (c. 1 Ma). Some lakes remain unfilled for very long time spans due to rapid subsidence of their basin floors. The calculated lifetimes are compared with those derived from sediment core studies. Most core studies indicate lower mechanical sedimentation rates than the calculated ones because a major part of the incoming sediment is trapped in deltas. However, a number of lakes (e.g., the Great Lakes of North America) show the opposite tendency which is largely caused by extensive shoreline erosion and resuspension. The lifetimes of large glacial lakes often exceed the duration of interglacials. Hence, their lifetimes are restricted by glaciation and not by sediment infill. Rift lakes persist for long time periods which exceed the calculated lifetimes in some cases. Time-dependent subsidence, basin extension, as well as the impact of climate change are briefly described.     

On the existence of a relation between the Kolmogoroff and von Kármán constants

A model is described, in which the mean vertical wind profile and turbulence spectra at different heights are calculated for a turbulent boundary layer without thermal stratification. The model makes use of Heisenberg's formula for the transfer of turbulent energy and is based on the assumption of a constant shearing stress in that boundary layer. As a result, a logarithmic wind profile follows with 0.39 as the value of von Kármán's constant, which is — in this model — strongly related to the inertial subrange of the turbulent energy spectra and therefore to the Kolmogoroff constant.This paper is based on studies done by the author during a one-year visit to CSIRO Division of Meteorological Physics, Aspendale, Australia, and was presented at the AGARD Specialists Meeting on The Aerodynamics of Atmospheric Shear Flows sponsored by the Fluid Dynamics Panel at Munich, Germany, during 15–17 Sept. 1969.     

Über interne Wellen in der Nähe der Trägheitsperiode

Zusammenfassung Für winderzeugte interne Wellen wird gezeigt, daß bei der Trägheitsperiode in erster Näherung Resonanz eintritt, die in zweiter Näherung in zwei symmetrisch zur Trägheitsperiode liegende Resonanzen zerfällt. Der Effekt wächst mit zunehmender Schichtung und ist außerdem abhängig vom virtuellen Austauschkoeffizienten und der WellenlängeL der internen Wellen. Die Näherung erfolgt in Termen des Verhältnissesd ² H ² (d=Dicke der winderzeugten Grenzschicht,H=Wassertiefe).

---

On internal waves near the inertia period

Summary Wind-generated internal waves are shown to have a resonance at the inertia period to first order of an analytical approximation which, to second order, splits into two resonances lying symmetrically to the inertia period. The effect is large for strong stratification and depends also on the Austausch coefficient and the wave lengthL of the internal waves. The approximation is done in terms ofd ² H ² whered=thickness of the wind-generated boundary layer andH=water depth.

---

Sur les ondes internes près de la période d'inertie

Résumé On montre que pour les ondes internes dues au vent, il se produit en première approximation, à la période d'inertie, une résonance qui, en deuxième approximation, se décompose en deux résonances symétriques par rapport à la période d'inertie. L'effet augmente avec une stratification croissante et dépend en outre du coefficient de turbulence virtuel et de la longueur d'ondeL des ondes internes. L'approximation s'obtient en termes du rapportd ² H ² (d=épaisseur de la couche-limite due au vent,H=profondeur de l'eau).

     

Intensive Zucht von Besatzfischen im Rundtrog

Ohne Zusammenfassung