The Bunsen gas solubility coefficient of ethylene as a function of temperature and salinity and its importance for nitrogen fixation assays

The acetylene reduction assay is a common method for assessing nitrogen fixation in a variety of marine and freshwater systems. The method measures ethylene, the product of the conversion of the gas acetylene to its reduced form by nitrogenase. Knowledge of the solubility of ethylene in aqueous solution is crucial to the calculation of nitrogen fixation rates and depends on the temperature and salinity of the assay conditions. Despite the increasing interest in marine nitrogen fixation, no gas solubility (Bunsen) coefficients for ethylene in seawater are published to date. Here, we provide a set of equations and present semiempirically derived Bunsen coefficients for ethylene in water (ranging from 0.069 to 0.226) for a range of temperatures and salinities that are relevant for aquatic nitrogen fixation. We apply these data to nitrogen fixation scenarios at different temperatures and salinities and stress the importance of using accurate Bunsen coefficients in nitrogen fixation assays

Meridional circulation in the tropical North Atlantic

A transatlantic CTD/ADCP section nominally located at 11°N was carried out in March 1989. In this paper relative geostrophic velocities are computed from these data via the thermal wind balance, with reference level choices based primarly on water mass distributions. A brief overview of the meridional circulation of the upper waters resulting from these analysis techniques is presented. Schematic circulation patterns of the NADW and AAW are also presented. In both the western and eastern basins these waters are characterized by cyclonic recirculation gyres. A paricularly notable result of the deep western basin analysis is the negligible net flow of middle NADW. Although the horizontal circulation patterns described in this study agree well with results from many previous studies, the meridional overturning cell and net heat flux are considerably lower, while the net freshwater flux is slightly higher than previous estimates. These discrepancies may be attbuted to: (1) differences in methodologies, (2) the increased resolution of this section, and (3) temporal (including decadal, synoptic, and most importantly, seasonal) variability.Funding was provided by the National Science Foundation through Grant Nos. OCE-8716314 and OCE-9101636 and the Office of Naval Research through the American Society for Engineering Education

A data assimilative marine ecosystem model of the central equatorial Pacific: Numerical twin experiments

A five-component, data assimilative marine ecosystem model is developed for the high-nutrient low-chlorophyll region of the central equatorial Pacific (0N, 140W). Identical twin experiments, in which model-generated synthetic \u27data\u27 are assimilated into the model, are employed to determine the feasibility of improving simulation skill by assimilating in situ cruise data (plankton, nutrients and primary production) and remotely-sensed ocean color data. Simple data assimilative schemes such as data insertion or nudging may be insufficient for lower trophic level marine ecosystem models, since they require long time-series of daily to weekly plankton and nutrient data as well as adequate knowledge of the governing ecosystem parameters. In contrast, the variational adjoint technique, which minimizes model-data misfits by optimizing tunable ecosystem parameters, holds much promise for assimilating biological data into marine ecosystem models. Using sampling strategies typical of those employed during the U.S. Joint Global Flux Study (JGOFS) equatorial Pacific process study and the remotely-sensed ocean color data available from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS), parameters that characterize processes such as growth, grazing, mortality, and recycling can be estimated. Simulation skill is improved even if synthetic data associated with 40% random noise are assimilated; however, the presence of biases of 10-20% proves to be more detrimental to the assimilation results. Although increasing the length of the assimilated time series improves simulation skill if random errors are present in the data, simulation skill may deteriorate as more biased data are assimilated. As biological data sets, including in situ, satellite and acoustic sources, continue to grow, data assimilative biological-physical models will play an increasingly crucial role in large interdisciplinary oceanographic observational programs

Medienerziehung in Kindertagesstätten - Nachhaltigkeitsüberlegungen im Anschluss an eine Fortbildungsinitiative

Durch die Einführung und Aktualisierung der Bildungspläne sind Kindertagesstätten seit einigen Jahren vermehrt aufgefordert, medienerzieherisch aktiv zu werden. Auch wenn es inzwischen verschiedene Fortbildungsinitiativen gibt, können aktuelle Studien keine grundlegenden Fortschritte in einer flächendeckenden praktizierten Medienerziehung nachweisen. Im vorliegenden Beitrag wird mit Bezug auf empirische Studien und strukturelle Rahmenbedingungen die aktuelle Situation der Medienerziehung in Deutschland und spezifisch in Nordrhein-Westfalen aufgezeigt. Daran anknüpfend stellen die Autorinnen ein Fortbildungskonzept der medienpädagogischen Initiative Medienkompetenz-Kitas NRW vor, das mittels eines Inhouse-Schulungsansatzes in zwölf Kindertagesstätten in NRW durchgeführt wurde. Im Fokus der Fortbildung standen die Vermittlung technischen Grundlagenwissens und handlungsorientierter Methoden für eine aktive medienpraktische Arbeit sowie die Förderung medienpädagogischen Reflexionswissens. Auf der Grundlage der Evaluation des Projekts und der aktuellen Situation der Medienerziehung werden im Zuge einer angestrebten nachhaltigen Verankerung von Medienerziehung in Kindertagesstätten Implikationen zur Fort- und Ausbildung von Erzieherinnen und Erziehern benannt