MAPPING SEA CLIFFS ON DOMINICA USING PHOTO MOSAICS

Mapping on islands covered by rain forest presents challenges due to the extremely limited exposure of bedrock. In general, exposures are limited to road cuts, quarries, and sea cliffs. While the first two are easily accessible, the last one provides the most reliable series of exposures for most islands, and generally forms the largest exposures. However, these outcrops are frequently difficult to impossible to reach from land, due to a lack of roads and/or strong surf right to the bases of the cliffs. Therefore, in July 2007, we chartered a boat to circumnavigate the island of Dominica in the Lesser Antilles to map and photograph the sea cliffs all around the island. The results provide modifications to the published geological map of the island and hitherto unknown details on the geology of the Miocene, Pliocene, and Pleistocene-to-Recent volcanic centers. For example, an area previously mapped as part of the oldest sequence on the island (Miocene), has been identified as a megabreccia that is part of the Pleistocene sequence of the Grande Soufriere Hills volcanic center, and is now identified as much more extensive than was known from exposures accessible from land. Detailed stratigraphic sections of selected sequences will be presented to illustrate the effectiveness of this technique

Hydrologic exchange and chemical weathering in a proglacial watershed near Kangerlussuaq, west Greenland

The exchange of proglacial river water with active layer pore water could alter water chemical compositions in glacial outwash plains and oceanic solute fluxes. To evaluate effects of this exchange, we sampled Watson River and adjacent pore water during the 2013 melt season at two sandurs in western Greenland; one in Sandflugtdalen and the other near the confluence with Søndre Strømfjord. We measured temperature, specific conductivity, and head gradients between the river and bank over a week-long period at Sandflugtdalen, as well as sediment hydraulic conductivity and chemical compositions of waters from both sites. Specific conductivity of pore water is four to ten times greater than river water as solutes are concentrated from weathering reactions, cryoconcentration, and evaporation. Pore water compositions are predominantly altered by carbonate dissolution and sulfide mineral oxidation. High concentrations of HCO3 and SO4 result from solute recycling and dissolution of secondary Ca-Mg carbonate/sulfate salts initially formed by near-surface evaporation in the summer and at depth by freeze-in of the active layer and cryoconcentration in the winter. High hydraulic conductivity (10−5 to 10−4 m/s) and diurnal fluctuations of river stage during our study caused exchange of river and pore water immediately adjacent to the river channel, with a net loss of river water to the bank. Pore water \u3e6 m from the river continuously flowed away from the river. Approximately 1–8% of the river discharge through the Sandflugtdalen was lost to the river bank during our 6.75 day study based on calculations using Darcy’s Law. Although not sampled, some of this water should discharge to the river during low river stage early and late in the melt season. Elevated pore water solute concentrations in sandurs and water exchange at diurnal and seasonal frequency should impact fluxes of solutes to the ocean, although understanding the magnitude of this effect will require long-term evaluation throughout the melt season

OCEANIC FLUXES FROM PROGLACIAL AND DEGLACIAL WATERSHEDS IN WESTERN GREENLAND

Weathering in western Greenland occurs in two distinct environments: proglacial watersheds that extend from the margin of the Greenland Ice Sheet (GIS) and derive water from ice melt, and deglacial watersheds that develop on terrains unconnected to the GIS and derive water from annual precipitation. Proglacial and deglacial watersheds currently provide equal amounts of runoff in western Greenland. These watersheds may contribute different solute fluxes to the oceans depending on exposure age, climate, and weathering environment. We test this hypothesis by comparing chemical compositions of streams in four deglacial watersheds (Sisimiut, Nerumaq, Qorlortoq, Kangerlussuaq) and one proglacial watershed (Watson River Akuliarusiarsuup Kuua River; AKR) along a ~160 km transect from the coast to the GIS. Recent work found that weathering reactions in the deglacial watersheds shift from being dominated by carbonate dissolution inland to sulfide oxidation near the coast. Silicate weathering, based on increased Si, Na and K concentrations, is a minor source of solutes to deglacial streams and is less extensive near the GIS than the coast, where older moraines experience greater precipitation. In general, specific conductivity (SpC: 48-301 μS/cm) and pH (7.0-8.2) increase inland as precipitation decreases and fresh mineral surfaces become more common. The AKR, in contrast, has lower average SpC (11.9 uS/cm) and pH (6.86) than the deglacial streams. Low SpC reflects dilution by ice melt and short residence time of water in the subglacial system. Proglacial flow is enriched in Si compared to deglacial flow particularly near headwaters, indicating higher silicate weathering rates in the pro- and sub-glacial systems. Low pH values indicate: 1) equilibration with atmospheric CO2 in the supraglacial system near headwaters, and 2) acid production generated by sulfide oxidation in the hyporheic zone identified by elevated SO4 concentrations. However, Ca, Mg and HCO3 are the dominant ions over the length of the AKR indicating that dissolution of carbonate is the predominant form of weathering. Our results indicate the two types of watersheds provide distinct fluxes of solutes to the oceans that are likely to change as ice sheets retreat and advance with changing climate

Low temperature or GroEL/ES overproduction permits growth of Escherichia coli cells lacking trigger factor and DnaK

AbstractEscherichia coli trigger factor (TF) and DnaK cooperate in the folding of newly synthesized proteins. The combined deletion of the TF-encoding tig gene and the dnaK gene causes protein aggregation and synthetic lethality at 30°C. Here we show that the synthetic lethality of ΔtigΔdnaK52 cells is abrogated either by growth below 30°C or by overproduction of GroEL/GroES. At 23°C ΔtigΔdnaK52 cells were viable and showed only minor protein aggregation. Overproduction of GroEL/GroES, but not of other chaperones, restored growth of ΔtigΔdnaK52 cells at 30°C and suppressed protein aggregation including proteins ≥60 kDa, which normally require TF and DnaK for folding. GroEL/GroES thus influences the folding of proteins previously identified as DnaK/TF substrates

SEASONAL EVOLUTION AND SPATIAL DISTRIBUTION OF WEATHERING IN WESTERN GREENLAND

Through physical weathering, the Greenland Ice Sheet (GIS) produces sediments which are subsequently chemically weathered in three types of watersheds: 1) deglacial watersheds that are physically disconnected from the GIS and drain local precipitation, 2) proglacial watersheds that are hydrologically connected to the GIS, and 3) subglacial watersheds that form beneath the GIS. Chemical weathering in the glacial foreland may be important to atmospheric CO2 drawdown and oceanic fluxes of solutes, yet no holistic study exists that compares solute sources across all types of watersheds and through the melt season. Consequently, we investigated spatiotemporal changes in weathering through the 2013 ablation season from a transect of watersheds spanning the coast to the GIS in western Greenland. We sampled one proglacial (PG) watershed, from which we also assess subglacial (SG) weathering, one inland deglacial (IDG) and one coastal deglacial (CDG) watershed. A simple stoichiometric mass balance quantifies solute sources in each watershed. The principal solute source is trace carbonates in all watersheds; however, IDG has more carbonate (61 vs 36 mol%) and less silicate (3 vs 14 mol%) weathering than CDG. PG has similar carbonate (41 mol%) and silicate weathering (16 mol%) proportions to CDG, despite proximity to IDG. Weathering of biotite decreases from 12 mol% at PG to 3 mol% at CDG along an exposure age gradient, consistent with more radiogenic 87Sr/86Sr in waters at PG (0.73556) than DGC (0.71114). Carbonate weathering decreases and biotite + silicate weathering increases downstream through PG, reflecting increased weathering. Solute sources change little through time or space at IDG, but at PG, silicate weathering increases and carbonate weathering decreases as flow increases through the melt season, consistent with increased contributions of SG waters with long residence times in distributed channels. Thus, the evolution of SG through time and connections between subglacial reservoirs and main flow paths plays an important role in weathering at PG. As the GIS retreats, deglacial watersheds will constitute a greater fraction of the weathering flux and thus increased silicate weathering should alter solute fluxes to the oceans and increase atmospheric CO2 drawdown

Exposure age and climate controls on weathering in deglaciated watersheds of western Greenland

Fine-grained sediments deposited by retreating glaciers weather faster than the global average and this weathering can impact the global carbon cycle and oceanic fluxes of nutrients and radiogenic isotopes. Much work has focused on subglacial and proglacial weathering of continental ice sheets, but little is known about weathering and resulting fluxes from deglacial watersheds, which are disconnected from the ice sheets and discharge only annual precipitation and permafrost melt. We investigate the effects of exposure age and precipitation on weathering intensity in four deglacial watersheds on Greenland that form a transect from the coast near Sisimiut toward the Greenland Ice Sheet (GrIS) near Kangerlussuaq based on evaluations of major ion compositions, Sr isotope ratios, and mineral saturation states of waters and sediments. The transect is underlain by Archean orthogneiss and is characterized by gradients in moraine ages (∼7.5–8.0 ky inland to ∼10 ky at the coast) and water balance (−150 mm/yr inland to +150 mm/yr at the coast). Anion compositions are generally dominated by HCO3, but SO4 becomes increasingly important toward the coast, reflecting a switch from trace carbonate dissolution to sulfide mineral oxidation. Coastal watersheds have a higher proportion of dissolved silica, higher Na/Cl, Si/Ca, and lower Ca/Sr ratios than inland watersheds, indicating an increase in the relative proportion of silicate weathering and an increase in the extent of weathering toward the coast. More extensive weathering near the coast is also apparent in differences in the 87Sr/86Sr ratios of stream water and bedload (Δ87Sr/86Sr), which decreases from 0.017 inland to 0.005 at the coast, and in increased saturation states relative to amorphous SiO2 and quartz. The steep weathering gradient from inland to coastal watersheds reflects enhanced weathering compared to that expected from the 2 to 3 ky difference in exposure age caused by elevated coastal precipitation. The gradient of weathering with exposure age, water budget and distance from the ice sheet indicates that oceanic and atmospheric fluxes will change as continental glaciers retreat, precipitation patterns across the deglacial region readjust, and the relative proportion of deglacial to proglacial runoff increases

Conformational flexibility within the nascent polypeptide–associated complex enables its interactions with structurally diverse client proteins

As newly synthesized polypeptides emerge from the ribosome, it is crucial that they fold correctly. To prevent premature aggregation, nascent chains interact with chaperones that facilitate folding or prevent misfolding until protein synthesis is complete. Nascent polypeptide–associated complex (NAC) is a ribosome-associated chaperone important for protein homeostasis. However, how NAC binds its substrates remains unclear. Using native electrospray ionization MS (ESI MS), limited proteolysis, NMR and cross-linking, we analysed the conformational properties of NAC from Caenorhabditis elegans and studied its ability to bind proteins in different conformational states. Our results revealed that NAC adopts an array of compact and expanded conformations and binds weakly to client proteins that are unfolded, folded, or intrinsically disordered, suggestive of broad substrate compatibility. Of note, we found that this weak binding retards aggregation of the intrinsically disordered protein α-synuclein both in vitro and in vivo. These findings provide critical insights into the structure and function of NAC. Specifically, they reveal the ability of NAC to exploit its conformational plasticity to bind a repertoire of substrates having unrelated sequences and structures independently of actively translating ribosomes

Impact of anthropogenic disturbance on the chemistry of a small urban pond

Mirror Lake, one of the scenic locations on The Ohio State University\u27s campus, experiences an intense bioturbation event as part of an annual tradition revolving around the rivalry football game against the University of Michigan. This tradition involves thousands of students jumping into the lake over one night in the week leading up to the football game. Water samples were collected from several locations in the lake before, during, and after the Mirror Lake Jump to determine the impact of this event on lake water chemistry. There were significant and systematic increases in the concentrations of Na+, K+, Cl−, total nitrogen, ammonia, and dissolved organic carbon (DOC) associated with the jump, especially in the eastern side of the lake where most of the students entered. Over the 3-h period from 10 p.m. to 1 a.m. on the eastern side of the lake, Na+, K+, and Cl− concentrations increased by about 2–4 ppm, 1.5–3 ppm, and 4–6 ppm, respectively. The total nitrogen concentration increased about five to six fold, from 450–500 ppb to 2300–2800 ppb over the height of the event on the eastern side of the lake. Similar increases were observed for DOC, increasing from 3.6 to 18 ppm. This DOC increase was coincident with a 5‰ shift in δ13C, from a mean of around −28‰ in the early hours of the evening to a maximum of −23‰, implying a large influx of isotopically heavy carbon into the lake. Ammonia concentrations varied substantially from year to year, but always showed a systematic increase in concentration during the event. Smaller changes in major ion and nutrient concentrations were observed in the middle and western side of the lake, where fewer students entered the lake. The changes in concentration and the timing and spatial distribution of these changes are primarily attributed to anthropogenic input from jumpers in the form of bodily fluids (e.g., evaporated sweat, sebum and urine). Over a single night, these anthropogenic event inputs represent roughly 10% of the annual nitrogen budget of the lake, emphasizing the direct impact humans can have on urban water bodies on short time scales

Photon detector system timing performance in the DUNE 35-ton prototype liquid argon time projection chamber

The 35-ton prototype for the Deep Underground Neutrino Experiment far detector was a single-phase liquid argon time projection chamber with an integrated photon detector system, all situated inside a membrane cryostat. The detector took cosmic-ray data for six weeks during the period of February 1, 2016 to March 12, 2016. The performance of the photon detection system was checked with these data. An installed photon detector was demonstrated to measure the arrival times of cosmic-ray muons with a resolution better than 32 ns, limited by the timing of the trigger system. A measurement of the timing resolution using closely-spaced calibration pulses yielded a resolution of 15 ns for pulses at a level of 6 photo-electrons. Scintillation light from cosmic-ray muons was observed to be attenuated with increasing distance with a characteristic length of 155 ± 28 cm