Substrate characteristics associated with the distribution of the ribbed mussel,Geukensia demissa (Modiolus demissus), on a tidal creek bank in Southern New Jersey

The substrate composition is directly associated with the distribution of the Ribbed Mussel Geukensia demissa (=Modiolus demissus) along tidal-creek banks. Mussels were counted within a 2 dm × 5 dm microplot frame, and soil samples were collected at 5 m intervals for 320 m along Big Sheepshead Creek, near Tuckerton, New Jersey. Organic decomposition, percentage organic matter, and percentages of sand, silt, and clay were determined for each soil sample. Mussels were most frequently found in substrates characterized by low organic decomposition (Von Post >5), high organic matter content, (10–20%), and low sand content (0–20%).     

A complete sea-breeze circulation cell derived from aircraft observations

Using an instrumented aircraft, a complete sea-breeze circulation cell was sampled from its offshore end to the sea-breeze front over land and up to a height of approximately 1000 m AMSL. Many of its typical features can be resolved in detail mainly by cross-sectional analysis. These are: the diverging onshore flow in the lower layers over the sea the convergence over land at the seabreeze front and the connected cross-frontal circulation, a distinct return flow in the upper layers, the propagation of the seaward end of the cell over water, as well as the propagation of the front over land, the baroclinicity as a driving mechanism of the cell and also budget and frontogenesis terms.     

Dispersive behaviors of black drum and red drum: Is otolith Sr:Ca a reliable indicator of salinity history?

We tested the hypothesis that strontium:calcium (Sr:Ca) in otoliths are reflective of environmental salinity experienced by two estuarine fishes during early life. Laboratory and field experiments were performed to examine the effects of salinity and temperature on Sr:Ca in otoliths of black drum (Pogonias cromis) and red drum (Sciaenops ocellatus). Otolith Sr:Ca of juveniles reared at four salinities (5‰, 15‰, 25‰, 35‰) differed significantly forP. cromis while no salinity effect was observed forS. ocellatus. Otolith Sr:Ca of both species were not affected by temperature (23°C and 30°C), suggesting that partitioning of Sr in otoliths of these taxa is constant over the temperature range examined. A field verification trial was conducted forP. cromis and a positive relationship between otolith Sr:Ca and ambient salinity was observed, even though the percent variability explained was modest. A series of Sr:Ca point measurements were taken from the core to the edge of the otoliths of wildP. cromis andS. ocellatus, and otolith Sr:Ca chronologies of both species showed conspicuous declines during the first few months of life. While Sr:Ca chronologies of both species suggest that ingress is associated with a reduction in otolith Sr:Ca, inconsistencies in laboratory and field experiments intimate that Sr uptake in the otolith may be insensitive to salinity and regulated by other factors (aqueous chemistry, ontogenetic shifts in habitat, or physiology). Results from early life history transects of otolith Sr:Ca conform to expected patterns of estuarine ingress-egress during early life and indicate that the approach may be useful for detecting large-scale habitat transitions (marine to estuarine habitats).     

Das Wachstum der Kontinente nach der Zyklustheorie

Ohne Zusammenfassung     

The excretion of heavy metals by the salt marsh cord grass,Spartina alterniflora, and Spartina's role in mercury cycling

Excreted salts and leaves from the Salt Marsh Cordgrass Spartina alterniflora were collected from two different sites. One site, Piles Creek (PC), is near heavily industrialized Linden, New Jersey, USA. The other site, Big Sheepshead Creek (BSC), is located near non-industrialized Tuckerton, New Jersey, USA. PC soil concentrations of mercury were 18·17 ± 7·67 ppm, while BSC soil concentrations were 0·22 ± 0·04 ppm. Spartina leaves from PC contained 0·16 ± 0·07 ppm of mercury, and BSC leaves contained 0·02 ± 0·0 ppm. Laboratory studies showed that S. alterniflora from both sites was capable of excreting mercury. Field collected salts from PC Spartina plants contained 0·11 ± 0·02 ppm of mercury, 2·60 ± 0·52 ppm of cadmium and 11·98 ± 0·94 ppm of zinc. These levels of heavy metals were as much as five- and-a-half times the concentrations of these metals found in ambient sea salts.     

Frontogenesis and cross frontal circulation in a strong summertime cold front

Summary The characteristics of a strong European summertime cold front are investigated using the wealth of synoptic observations, which were analysed by the dynamical initialization scheme of an operational meso-scale model. The study was also extended to forecasted fields.Cross-sections perpendicular to the front, covering a dormain of more than 2000 km in the horizontal and 10 km in the vertical direction, bring out the basic parameters (as potential temperature and the components of the geostrophic and ageostrophic wind vectors), the ageostrophic crossfrontal circulation and all cross-frontal frontogenesis terms.None of the many frontogenesis terms plays a dominant role, there is a concerted action of geostrophic and ageostrophic deformation and shear, of tilting and diabatic sources in producing a rather complex structure of total frontogenesis. The cross-sectional fields of all presented terms strongly underline the fact, that a front is not a line of discontinuity but a rather wide three-dimensional field phenomenon.With 12 Figures     

Intraday radio variability in active galactic nuclei

Rapid flux density variations on timescales of the order of a day or less (Intraday Variability, IDV) in the radio regime are a common phenomenon within the blazar class. Observations with the Effelsberg 100-m telescope of the MPIfR showed that the variations occur not only in total intensity, but also in the polarized intensity and in polarization angle. Here we present an overview of our IDV-observations and discuss briefly some models which may explain the effect.     

The Multi-Scale Structure of the Australian Cool Changes

Summary In Southern Australia summertime deep cold fronts are frequently preceded by a shallow cold frontal line connected to a prefrontal lower tropospheric trough. The advance of this line defines a “cool change” which in many cases causes severe weather events. The goal of this paper is to analyze the multi-scale structure of these cool changes using aircraft observations and synoptic-scale analyses. The aircraft measurements on cross-frontal tracks of horizontal lengths of up to 300 km are performed with an average resolution of 3 to 4 m along the track. Thus a multi-scale analysis from micro-scale events up to the synoptic-scale phenomena can be presented. All flights and thus all meso- and micro-scale analyses are performed over water only. The obviously very different characteristics of the cool change structure elements over land are not investigated. The synoptic analyses for one very typical case show a prefrontal trough as characterized by its position in relation to the main deep cold front, its source region in Western Australia and its extent to the southeast. Fields of strong wind shear, temperature gradients, vertical wind and Q-vectors are displayed. The meso-β-scale x, z-cross-sections derived from two aircraft missions (data of the second one in brackets) show: a shallow cold front with a 160 (60) km wide transition zone in which the near surface potential temperature drops rather steadily by 9 °C (20 °C); a shallow feeder flow topped by a strong inversion with a vertical gradient of potential temperature up to 5 °C/100 m between the top of the feeder flow at 400 (200) m and 1500 (700) m; a cross-frontal circulation expressed by the ageostrophic wind components u _ϕ,subscale and w with a center at 1200 m over the frontal edge of the feeder flow (for one mission only); a strong shear of the along-frontal wind component v _ϕ with a large increase of the negative v _ϕ-values with height, which very well fits to the synoptic-scale view of the wave structure of the geostrophic wind (well-known from the upper level synoptic charts) at different heights; a jet core of this along-frontal wind in the center of the cross-frontal circulation, again for one mission only. A very striking example of a micro-scale event is an approximately 1 km wide head of a frontal squall line. It shows dramatic changes of all meteorological parameters. The event is displayed in a horizontal domain of 4 km with full resolution (∼ 4 m). Derivatives of the measured parameters in the cross-frontal direction add information to the space series of the parameters themselves. Deformation frontogenesis of potential temperature and specific humidity show very large values on the scale resolved here. Fortunately the squall line could be sampled again at the same height, but in a somewhat degenerated state 1? h later. Received September 3, 1999 Revised December 14, 1999