Assessing water renewal time scales for marine environments from three-dimensional modelling: a case study for Hervey Bay, Australia

We apply the three-dimensional Coupled Hydrodynamical Ecological model for Regional Shelf Seas (COHERENS) to compute water renewal time scales for Hervey Bay, a large coastal embayment situated off the central eastern coast of Australia. Water renewal time scales are not directly observable but are derived indirectly from computational studies. Improved knowledge of these time scales assists in evaluating the water quality of coastal environments and can be utilised in sustainable marine resource management. Results from simulations with climatological September forcing are presented and compared to cruise data reported by Ribbe (2006). A series of simulations using idealised forcing provides detailed insight into water renewal pathways and regional differences in renewal timescales. We find that more than 85 % of the coastal embayment’s water is fully renewed within about 50-80 days. The eastern and western shallow coastal regions are ventilated more rapidly than the central, deeper part of the domain. The climatological simulation yields temperature and salinity patterns that are consistent with the observed situation and water renewal times scales in the range of those derived from idealised model studies. While the reported simulations involve many simplifications, the global assessment of the renewal time scale is in the range of a previous estimate derived for this coastal embayment from a simpler model and observational data

Sensitivity of middle Miocene climate and regional monsoon to palaeo-altimetry

It is well-known that plate motions and the elevation of mountains belts have played a major role in palaeoclimate evolution. The present day monsoon in southeast Asia and northern Australia is associated with the Tibetan plateau. We investigate how the Miocene Climate Optimum (MCO) developed in response to altimetry changes in Eurasia and South America impacting changes in regional monsoon, wind stress and precipitation. We carried out a number of numerical experiments with alternative paleo-altimetries, using an updated NCAR coupled climate model, CCSM3, and CAM3.1 and CLM3 with slab ocean and ice models, validated with proxies. Our model results explore the sensitivities of regional climate change to plate motions and rising mountain belts as well as sea-level change. Especially, the model simulations ground-truth the monsoon evolution in the southeast Asia, northern Australia and South America

El desarrollo de la autonomía del estudiante en los cursos online universitarios

This paper deals with the question in what ways teachers and course designers can support the development and exertion of learner autonomy among online university students. It advocates that a greater attention to learner autonomy could help more students to complete their course successfully and thus contribute the decrease of the high dropout rates in e-learning. To illustrate this position, the paper defines three principles of scaffolding learner autonomy and discusses them in relation to the specific challenges of e-learning settings. Drawing on relevant literature on course design, as result the paper presents exemplary design aspects that can serve the scaffolding of learner autonomyEste artículo trata sobre el tema de cómo los profesores y los diseñadores de cursos online pueden contribuir al desarrollo de la autonomía del estudiante en el contexto de la enseñanza universitaria online. Defiende que prestar una mayor atención a la autonomía del estudiante en el diseño y desarrollo de cursos online puede contribuir a que más estudiantes finalicen sus estudios con éxito y por tanto al descenso de los elevados índices de abandono que se dan en la enseñanza online. Para ilustrar este posicionamiento, el artículo define tres principios para apoyar social y educativamente (“andamiaje”) la autonomía del alumno y los relaciona con los retos propios de los contextos e-learning. Basándose en una importante revisión bibliográfica sobre diseño de cursos online, el presente estudio finaliza con ejemplos concretos de diseño que pueden servir para apoyar y reforzar la autonomía del estudiante

Identity and function of an essential nitrogen ligand of the nitrogenase cofactor biosynthesis protein NifB.

NifB is a radical S-adenosyl-L-methionine (SAM) enzyme that is essential for nitrogenase cofactor assembly. Previously, a nitrogen ligand was shown to be involved in coupling a pair of [Fe4S4] clusters (designated K1 and K2) concomitant with carbide insertion into an [Fe8S9C] cofactor core (designated L) on NifB. However, the identity and function of this ligand remain elusive. Here, we use combined mutagenesis and pulse electron paramagnetic resonance analyses to establish histidine-43 of Methanosarcina acetivorans NifB (MaNifB) as the nitrogen ligand for K1. Biochemical and continuous wave electron paramagnetic resonance data demonstrate the inability of MaNifB to serve as a source for cofactor maturation upon substitution of histidine-43 with alanine; whereas x-ray absorption spectroscopy/extended x-ray fine structure experiments further suggest formation of an intermediate that lacks the cofactor core arrangement in this MaNifB variant. These results point to dual functions of histidine-43 in structurally assisting the proper coupling between K1 and K2 and concurrently facilitating carbide formation via deprotonation of the initial carbon radical