Implications of Glacial Melt-Related Processes on the Potential Primary Production of a Microphytobenthic Community in Potter Cove (Antarctica)

The Antarctic Peninsula experiences a fast retreat of glaciers, which results in an increased release of particles and sedimentation and, thus, a decrease in the available photosynthetic active radiation (PAR, 400-700 nm) for benthic primary production. In this study, we investigated how changes in the general sedimentation and shading patterns affect the primary production by benthic microalgae, the microphytobenthos. In order to determine potential net primary production and respiration of the microphytobenthic community, sediment cores from locations exposed to different sedimentation rates and shading were exposed to PAR of 0-70 mu.mol photons m(-2)s(-1). Total oxygen exchange rates and microphytobenthic diatom community structure, density, and biomass were determined. Our study revealed that while the microphytobenthic diatom density and composition remained similar, the net primary production of the microphytobenthos decreased with increasing sedimentation and shading. By comparing our experimental results with in situ measured PAR intensities, we furthermore identified microphytobenthic primary production as an important carbon source within Potter Cove's benthic ecosystem. We propose that the microphytobenthic contribution to the total primary production may drop drastically due to Antarctic glacial retreat and related sedimentation and shading, with yet unknown consequences for the benthic heterotrophic community, its structure, and diversity

Total oxygen fluxes, and diatom density, diatom biomass and diversity of the diatom community in spring 2016 and environmental photosynthetically active radiation from 2015 and 2016 from three stations in Potter Cove, Antarctica

The Antarctic Peninsula experiences a fast retreat of glaciers, which correlates with an increased release of particles and related increased sedimentation and thus, a decrease in the available light for benthic primary production. We investigated how changes in the general sedimentation and shading patterns affect the primary production by benthic microalgae, the microphytobenthos. In order to determine potential net primary production and respiration of the microphytobenthic community, sediment cores from locations exposed to different sedimentation rates and shading were exposed to photosynthetic active radiation (PAR, 400–700 nm) of 0–70 µmol photons m-2 s-1. Total oxygen fluxes and microphytobenthic diatom community structure, density, and biomass were determined. Our study revealed that the net primary production of the microphytobenthos decreased with increasing sedimentation and shading, while the microphytobenthic diatom density and composition remained similar. By comparing our experimental results with in situ measured PAR intensities, we furthermore assessed the microphytobenthic primary production as an important carbon source within Potter Cove's benthic ecosystem. We propose that the microphytobenthic contribution to the total primary production may drop drastically due to Antarctic glacial retreat and correlated sedimentation and shading, with yet unknown consequences for the benthic heterotrophic community, its structure, and diversity

Seaweeds and their communities in polar regions

Polar seaweeds typically begin to grow in late winter-spring, around the time of sea-ice break up. They can grow under very low light enabling distributions to depths of ≥40 m. Moreover, they are physiologically adapted to low temperatures. Intertidal species exhibit a remarkable stress tolerance against freezing, desiccation and salinity changes. Endemism is much greater in the Antarctic compared to the Arctic species. On rocky shores of the Antarctic Peninsula and of Spitsbergen >80% of the bottom can be covered by seaweeds with standing biomass levels ≥20 kg wet wt m-2. Species richness and biomass declines, however, towards higher latitudes. Seaweeds are the dominant organisms in coastal waters and thus play important roles in benthic food webs and are likely to be of particular importance to benthic detrital food chains. Chemical defenses against herbivores are common in Antarctic, but not in Arctic seaweeds. More research is needed especially to study the effects of global climate changes

Prediction and Modeling of Effects on the QTc Interval for Clinical Safety Margin Assessment, Based on Single-Ascending-Dose Study Data with AZD3839

Corrected QT interval (QTc) prolongation in humans is usually predictable based on results from preclinical findings. This study confirms the signal from preclinical cardiac repolarization models (human ether-a-go-go-related gene, guinea pig mono-phasic action potential, and dog telemetry) on the clinical effects on the QTc interval. A thorough QT/QTc study is generally required for bioavailable pharmaceutical compounds to de-termine whether or not a drug shows a QTc effect above a threshold of regulatory interest. However, as demonstrated in this AZD3839 [(S)-1-(2-(difluoromethyl)pyridin-4-yl)-4-fluoro-1-(3-(pyrimidin-5-yl)phenyl)-1H-isoindol-3-amine hemifumarate] single-ascending-dose (SAD) study, high-resolution digital electrocardiogram data, in combination with adequate efficacy biomarker and pharmacokinetic data and nonlinear mixe