40Ar/39Ar ages of the sill complex of the Karoo large igneous province: implications for the Pliensbachian-Toarcian climate change.

Reliable geochronological results gathered so far (n = 76) have considerably constrained the timing of the emplacement of the Karoo large igneous province (LIP). Yet strikingly missing from this dating effortis the huge southern sill complex cropping out in the >0.6 x 10(6) km2 Main Karoo sedimentary basin. We present 16 new 40Ar/39Ar analyses carried out on fresh plagioclase and biotite separates from 15 sill samples collected along a N-S trend in the eastern part of the basin. The results show a large range of plateau and miniplateau ages (176.2 +- 1.3 to 183.8 +- 2.4 Ma), with most dates suggesting a -3 Ma (181-184 Ma) duration for the main sill events. The available age database allows correlation of the Karoo LIP emplacement with the Pliensbachian-Toarcian second-order biotic extinction, the global warming, and the Toarcian anoxic event (provided that adequate calibration between the 40K and 238U decay constant ismade). The mass extinction and the isotopic excursions recorded at the base of the Toarcian appear to be synchronous with both the increase of magma emission of the Karoo LIP and the emplacement of the sills.The CO2 and SO2 derived from both volcanic emissions as well as carbon-rich sedimentary layers intrudedby sills might be the main culprits of the Pliensbachian-Toarcian climate perturbations. We propose that the relatively low eruption rate of the Karoo LIP is one of the main reasons explaining why its impact on thebiosphere is relatively low contrary to, e.g., the CAMP (Triassic-Jurassic) and Siberia (Permo-Triassic) LIPs

Impact of a Dedicated Teaching Attending Experience on a Required Emergency Medicine Clerkship

Introduction: One published strategy for improving educational experiences for medical students in the emergency department (ED) while maintaining patient care has been the implementation of dedicated teaching attending shifts. To leverage the advantages of the ED as an exceptional clinical educational environment and to address the challenges posed by the rapid pace and high volume of the ED, our institution developed a clerkship curriculum that incorporates a dedicated clinical educator role – the teaching attending – to deliver quality bedside teaching experiences for students in a required third-year clerkship. The purpose of this educational innovation was to determine whether a dedicated teaching attending experience on a third-year required emergency medicine (EM) clerkship would improve student-reported clinical teaching evaluations and student-reported satisfaction with the overall quality of the EM clerkship.Methods: Using a five-point Likert-type scale (1 - poor to 5 - excellent), student-reported evaluation ratings and the numbers of graduating students matching into EM were trended for 10 years retrospectively from the inception of the clerkship for the graduating class of 2009 through and including the graduating class of 2019. We used multinomial logistic regression to evaluate whether the presence of a teaching attending during the EM clerkship improved student-reported evaluation ratings for the EM clerkship. We used sample proportion tests to assess the differences between top-box (4 or 5 rating) proportions between years when the teaching attending experience was present and when it was not. Results: For clinical teaching quality, when the teaching attending is present the estimated odds of receiving a rating of 5 is 77.2 times greater (p <0.001) than when the teaching attending is not present and a rating of 4 is 27.5 times greater (p =0.0017). For overall clerkship quality, when the teaching attending is present, the estimated odds of receiving a rating of 5 is 13 times greater (p <0.001) and a rating of 4 is 5.2 times greater (p=0.0086) than when the teaching attending is not present.Conclusion: The use of a dedicated teaching attending shift is a successful educational innovation for improving student self-reported evaluation items in a third-year required EM clerkship

Quantification of recA gene expression as an indicator of repair potential in marine bacterioplankton communities of Antarctica

Marine bacteria in surface waters must cope daily with the damaging effects of exposure to solar radiation (containing both UV-A and UV-B wavelengths), which produces lesions in their DNA. As the stratospheric ozone layer is depleted, these coping mechanisms are likely to play an even more important role in the viability of marine bacterial communities. The recA gene is ubiquitous among eubacteria and is highly conserved both in nucleotide and amino acid sequence. Besides its role in generalized recombination, the gene's translational product, RecA, is the regulator of 'dark repair' activity (DNA-repair mechanisms that do not require visible light as a cofactor). We have taken advantage of this function and used recA gene expression as a barometer of the DNAdamage repair capacity of bacterial assemblages in the Southern Ocean. Studies were conducted in the Gerlache Strait, Antarctica, in the austral springs of 1995 and 1996. Analysis of both recA mRNA and RecA protein extracted from natural communities indicated that the level of expression of this gene varied in a diel fashion, suggesting an increased repair capacity in these organisms. These included an early morning rise in RecA levels followed by a plateau or even a reduction in RecA concentration during the remainder of the day. A much greater increase in RecA was consistently observed after sunset, followed by a constant decrease during the night. Microcosm experiments with a RecA+ Gerlache Strait g-proteobacteria isolate, RM11001, demonstrated a similar diel pattern of expression. These studies demonstrate the usefulness of RecA as a biological indicator of DNA repair capacity in natural bacterial assemblages. They indicate that 'dark repair' of DNA damage is an important coping mechanism for bacteria in the marine environment of Antarctica.Peer reviewedMicrobiology and Molecular Genetic