Persistent and highly contrasting biological patterns in the southwestern sector of the Atlantic Ocean: relating local circulation to phytoplankton pigment biomass

Primary production in the Southern Ocean (SO) is believed to be mostly iron limited; despite the high macronutrient content of waters transported by the Antarctic Circumpolar Current, the SO is considered a High Nutrient Low Chlorophyll region. However, ocean color imagery shows a variable and patchy environment, where sharp chlorophyll concentration (chl-a) gradients separate highly productive regions, which are found mostly downstream from islands and along coastal shelves, from the less productive ones, where pigment biomass remains low. In the western sector of the Atlantic SO, an intense and long-lasting phytoplankton bloom is found northwest of the Island of South Georgia, while very low chl-a are persistently measured southwest of the Shackleton Transverse Ridge (STR), in the southern Drake Passage. In both cases, local circulation, which is steered by bottom topography, plays a major role in controlling biogeochemistry and thus the distribution and intensity of chl-a. By combining surface drifter trajectories with satellite based measurements of sea surface height and ocean color, we relate local flow regimes to the observed pigment biomass patterns. Basing our analysis on 13 years of SeaWiFS imagery, the intense and long-lasting phytoplankton bloom developing northwest of South Georgia appears to be recurrent in time with little inter-annual variability; furthermore,our results show how the bloom is clearly confined to the area enclosed by the cyclonic circulation flowing along the periphery of the South Georgia Basin (SGB). Here, current velocities appear to gradually decrease towards the center of the basin possibly favoring the accumulation of shelf-derived iron, and thus the growth of phytoplankton cells. Southwest of the STR, the available ocean color time-series highlights an area with very low productivity values, which can be detected yearly and with little inter-annual variability. This region is adjacent to the more productive one found to the northeast of the ridge, above the Ona Basin. The former appears to be related to the intense Shackleton Jet flowing along the ridge, while the latter to the calmer cyclonic circulation located above the Ona Basin; just above the STR lies the area where maximum chl-a gradients can be measured. Absolute dynamic topography values retrieved for the two regions together with surface drifter trajectories, suggest a clear spatial and temporal correspondence between local circulation patterns and those of surface chl-a; furthermore, the AVISO time-series confirms the low inter-annual variability of the two previously described flow patterns. We argue how similarly above the STR and the SGB, the presence of the cyclonic circulation acts as a precondition to the observed higher chl-a. In both cases, nutrient (i.e. iron) rich waters may be entrained in the cyclone, and separated from those lying outside its borders. Similar observations have been made in the Crozet and the Kerguelen regions

Ocean Data View

Ocean Data View (ODV) is a software package for the interactive exploration, analysis and visualization of oceanographic and other geo-referenced profile, time-series, trajectory or sequence data. ODV runs on Windows, macOS, Linux, and UNIX (Solaris, Irix, AIX) systems. ODV data and configuration files are platform-independent and can be exchanged between different systems. ODV can display original data points or gridded fields based on the original data. ODV has two fast weighted-averaging gridding algorithms as well as the advanced DIVA gridding software built-in. Gridded fields can be color-shaded and/or contoured. ODV supports five different map projections and can be used to produce high quality cruise maps. ODV graphics output can be send directly to printers or may be exported to PostScript, gif, png, or jpg files. The resolution of exported graphics files is specified by the user and not limited by the pixel resolution of the screen. ODV is available for download at https://odv.awi.de/

Cascade Reactions to Access Bioactive Scaffolds

In the recent decade there has been a shift in drug development to favor planar, aromatic small molecules with easy synthetic access, despite centuries of research in bioactive natural products, which are often highly rigid, three-dimensional structures like spirocycles. These scaffolds remain underexplored in drug development efforts, predominantly due to the challenges associated with their synthesis, and lack of a general, convergent methodology. To address these challenges, we have designed an O–H Insertion/Conia-ene reaction cascade between homopropargylic alcohols and acceptor/acceptor diazo compounds, which uses dual Rh/Au+ catalytic system. This cascade occurs instantly at room temperature, and has been applied towards the synthesis of substituted tetrahydrofurans when linear diazo compounds are used. Thus far, the cascade accommodates a variety of substituted diazo compounds with carboxylic acids/alcohols to provide functionalized tetrahydrofurans, and g-butyrolactones, with a high degree of regio- and stereo-selectivity. Next, we were able to extend the utility of our O–H Insertion/Conia-ene reaction cascade towards the synthesis of spiroheterocycles by employing cyclic diazo substrates with propargylic alcohols. This convergent approach furnishes an array of spiroheterocycles by employing the same dual Rh/Au+ catalytic system in refluxing dichloromethane. This approach has proven general, and was used to synthesize a substrate scope of twenty-four substrates based on natural product scaffolds, including spirobarbituates, spiromeldrum’s acids, spirooxindoles, and the spirocyclic core of the pseurotin natural products. Lastly, we have extended our X–H Insertion/Conia-ene strategy towards uncommon nucleophiles, for the synthesis of sulfur- and all-carbon spirocycles. When propargylic thiols are employed as substrates with linear diazos, we have found that the S-H insertion reaction proceeds in high yield, and Conia-ene cyclization can be promoted when the reaction is conducted in a stepwise fashion. However, when the reaction is conducted in a single pot, we isolated a new, thiofuranofuran compound, which we expect forms via undesired 5-endo-dig cyclization of the propargylic thiol, followed by cyclopropanation and subsequent ring opening. Additionally, by changing our retrosynthetic approach to an intramolecular disconnection, we were able to synthesize an all-carbon spirocycle through a benzylic C-H Insertion/Conia-ene cascade, by using a catalytic mixture consisting of Rh2(HFB)4, ClAuPPh3, and CuOTf in refluxing dichloromethane. In an orthogonal research effort, we have also developed a metal-free cascade for the synthesis of aromatic heterocycles. This cascade uses precursors synthesized from readily accessible 2’-hydroxy/aminochalcones, and commences with a DBU-mediated intramolecular aldol condensation, which occurs within 90 minutes at room temperature, to generate a 1,3,5-triene. This triene is heated overnight (80 – 120 °C) to promote a 6p-electrocyclization, and oxidative aromatization to generate a new aromatic ring. This cascade has proven general, and has been applied towards the synthesis of benzo[c]coumarins, phenanthradinones, dibenzofurans, and carbazoles, up to a 1-gram scale. The cascade reactions developed throughout the course of this dissertation research provide new retrosynthetic strategies for the formation of natural product cores, which could be used to expand the chemical space in drug discovery

Development and Plasticity of murine plasmacytoid dendritic cells

The data presented in this thesis identifies a subpopulation of CCR9- MHC class IIlow BST2+ Siglec H+ plasmacytoid dendritic cells (pDCs) within the bone marrow (BM) pDC population. CCR9- MHC class IIlow BST2+ Siglec H+ pDCs express the essential pDC transcription factor E2-2 and produce high levels of interferon-α (IFN-α) and proinflammatory cytokines upon toll-like receptor 9 (TLR9) stimulation. This phenotypically immature pDC population is an immediate precursor for fully differentiated CCR9+ pDCs in vitro as well as in vivo, but does not harbour a pDC-specific gene rearrangement in the Ig gene locus. CCR9- pDCs retain plasticity to downregulate pDC specific surface molecules and upregulate CD11b and MHC class II, acquiring phenotype and function of CD8α- CD11b+ conventional dendritic cell (cDC) - like cells after conditioning with supernatant derived from colonic epithelial cells or exposure to recombinant granulocyte macrophage colony stimulating factor (GM-CSF) in vitro. Functionally cDC-like cells generated from CCR9- pDCs acquire properties of cDCs such as efficient T cell activation and the production of high levels of proinflammatory cytokines comparable to those of splenic CD8α- DCs. This phenotypic and functional change is also reflected on the level of transcription factor expression by downregulation of E2-2, Spi-b and IRF8 but upregulation of ID2, PU.1 and BATF3. CCR9- pDCs can give rise to fully differentiated CCR9+ pDCs and CD11b+ MHC class IIhigh cDC-like cells locally in the tissue in vivo in the steady state. However the plasticity and lineage commitment of CCR9- pDCs is regulated in a tissue specific manner. In BM and liver CCR9- pDCs primarily give rise to CCR9+ pDCs, whereas in spleen, lymph nodes, lung and small intestine a substantial fraction deviates from the pDC lineage to the cDC lineage. Furthermore, this study shows that GM-CSF is necessary for the appearance of CCR9- pDCs and CCR9+ pDCs in lung and small intestine but is dispensable for the generation of CD11b+ MHC class IIhigh cDCs from CCR9- pDCs in vivo. Moreover, GM-CSF controls the proliferation of CCR9- and CCR9+ pDCs in BM and spleen upon adoptive transfer. In conclusion these results show that CCR9- pDCs are tissue resident precursors of pDCs and cDCs and that the generation of DC subsets is regulated by tissue derived factors, thereby allowing adaptation to local microenvironments. This increases the flexibility of the DC compartment under circumstances of infection or inflammation

Design Simulation for Solar Energy Research and Education

Solar research is primarily conducted in regions with consistent sunlight, severely limiting research opportunities in many areas. Unfortunately, the unreliable weather in Lewisburg, PA, can prove difficult for such testing to be conducted. As such, a solar simulator was developed for educational purposes for the Mechanical Engineering department at Bucknell University. The objective of this work was to first develop a geometric model to evaluate a one sun solar simulator. This was intended to provide a simplified model that could be used without the necessity of expensive software. This model was originally intended to be validated experimentally, but instead was done using a proven ray tracing program, TracePro. Analyses with the geometrical model and TracePro demonstrated the influence the geometrical properties had results, specifically the reflector (aperture) diameter and the rim angle. Subsequently, the two were approaches were consistent with one another for aperture diameters 0.5 m and larger, and for rim angles larger than 45°. The constructed prototype, that is currently untested, was designed from information provided by the geometric model, includes a metal halide lamp with a 9.5 mm arc diameter and parabolic reflector with an aperture diameter of 0.631 meters. The maximum angular divergence from the geometrical model was predicted to be 30 mRadians. The average angular divergence in TraceProof the system was 19.5 mRadians, compared to the sun’s divergence of 9.2 mRadians. Flux mapping in TracePro showed an intensity of 1000 W/m2 over the target plane located 40 meters from the lamp. The error between spectrum of the metal halide lamp and the solar spectrum was 10.9%, which was found by comparing their respective Plank radiation distributions. The project did not satisfy the original goal of matching the angular divergence of sunlight, although the system could still to be used for optical testing. The geometric model indicated performance in this area could be improved by increasing the diameter of the reflector, as well as decreasing the source diameter. Although ray tracing software provides more information to analyze the simulator system, the geometrical model is adequate to provide enough information to design a system