Bacterioplankton dispersal and biogeochemical function across Alaskan Arctic catchments.

In Arctic catchments, bacterioplankton are dispersed through soils and streams, both of which freeze and thaw/flow in phase, seasonally. To characterize this dispersal and its potential impact on biogeochemistry, we collected bacterioplankton and measured stream physicochemistry during snowmelt and after vegetation senescence across multiple stream orders in alpine, tundra, and tundra-dominated-by-lakes catchments. In all catchments, differences in community composition were associated with seasonal thaw, then attachment status (i.

Superlinear scaling of riverine biogeochemical function with watershed size.

River networks regulate carbon and nutrient exchange between continents, atmosphere, and oceans. However, contributions of riverine processing are poorly constrained at continental scales. Scaling relationships of cumulative biogeochemical function with watershed size (allometric scaling) provide an approach for quantifying the contributions of fluvial networks in the Earth system.

Tundra wildfire triggers sustained lateral nutrient loss in Alaskan Arctic.

Climate change is creating widespread ecosystem disturbance across the permafrost zone, including a rapid increase in the extent and severity of tundra wildfire. The expansion of this previously rare disturbance has unknown consequences for lateral nutrient flux from terrestrial to aquatic environments. Lateral loss of nutrients could reduce carbon uptake and slow recovery of already nutrient-limited tundra ecosystems.

Cavity-enhanced non-destructive detection of atoms for an optical lattice clock.

We demonstrate a new method of cavity-enhanced non-destructive detection of atoms for a strontium optical lattice clock. The detection scheme is shown to be linear in atom number up to at least 2×10 atoms, to reject technical noise sources, to achieve signal to noise ratio close to the photon shot noise limit, to provide spatially uniform atom-cavity coupling, and to minimize inhomogeneous ac Stark shifts. These features enable detection of atoms with minimal perturbation to the atomic state, a critical step towards realizing an ultra-high-stability, quantum-enhanced optical lattice clock.

Revealing biogeochemical signatures of Arctic landscapes with river chemistry.

Riverine fluxes of carbon and inorganic nutrients are increasing in virtually all large permafrost-affected rivers, indicating major shifts in Arctic landscapes. However, it is currently difficult to identify what is causing these changes in nutrient processing and flux because most long-term records of Arctic river chemistry are from small, headwater catchments draining <200 km or from large rivers draining >100,000 km. The interactions of nutrient sources and sinks across these scales are what ultimately control solute flux to the Arctic Ocean.

A pyramid MOT with integrated optical cavities as a cold atom platform for an optical lattice clock.

We realize a two-stage, hexagonal pyramid magneto-optical trap (MOT) with strontium, and demonstrate loading of cold atoms into cavity-enhanced 1D and 2D optical lattice traps, all within a single compact assembly of in-vacuum optics. We show that the device is suitable for high-performance quantum technologies, focusing especially on its intended application as a strontium optical lattice clock. We prepare 2 × 10 spin-polarized atoms of Sr in the optical lattice within 500 ms; we observe a vacuum-limited lifetime of atoms in the lattice of 27 s; and we measure a background DC electric field of 12 V m from stray charges, corresponding to a fractional frequency shift of (-1.

A scalable arbitrary waveform generator for atomic physics experiments based on field-programmable gate array technology.

We present a field-programmable gate array (FPGA) based control system that has been implemented to control a strontium optical lattice clock at the National Physical Laboratory, UK. Bespoke printed circuit boards have been designed and manufactured, including an 8-channel, 16-bit digital to analog converter board with a 2 μs update rate and a 4-channel direct-digital synthesis board clocked at 1 GHz. Each board includes its own FPGA with 28 digital output lines available alongside the specialized analog or radio frequency outputs.

Linking permafrost thaw to shifting biogeochemistry and food web resources in an arctic river.

Rapidly, increasing air temperatures across the Arctic are thawing permafrost and exposing vast quantities of organic carbon, nitrogen, and phosphorus to microbial processing. Shifts in the absolute and relative supplies of these elements will likely alter patterns of ecosystem productivity and change the way carbon and nutrients are delivered from upland areas to surface waters such as rivers and lakes. The ultra-oligotrophic nature of surface waters across the Arctic renders these ecosystems particularly susceptible to changes in productivity and food web dynamics as permafrost thaw alters terrestrial-aquatic linkages.

Effects of long-term nutrient additions on Arctic tundra, stream, and lake ecosystems: beyond NPP.

Primary producers form the base of food webs but also affect other ecosystem characteristics, such as habitat structure, light availability, and microclimate. Here, we examine changes caused by 5-30+ years of nutrient addition and resulting increases in net primary productivity (NPP) in tundra, streams, and lakes in northern Alaska. The Arctic provides an important opportunity to examine how ecosystems characterized by low diversity and low productivity respond to release from nutrient limitation.

An adaptable dual species effusive source and Zeeman slower design demonstrated with Rb and Li.

We present a dual-species effusive source and Zeeman slower designed to produce slow atomic beams of two elements with a large mass difference and with very different oven temperature requirements. We demonstrate this design for the case of (6)Li and (85)Rb and achieve magneto-optical trap (MOT) loading rates equivalent to that reported in prior work on dual species (Rb+Li) Zeeman slowers operating at the same oven temperatures. Key design choices, including thermally separating the effusive sources and using a segmented coil design to enable computer control of the magnetic field profile, ensure that the apparatus can be easily modified to slow other atomic species.

Microbial iron oxidation in the Arctic tundra and its implications for biogeochemical cycling.

The role that neutrophilic iron-oxidizing bacteria play in the Arctic tundra is unknown. This study surveyed chemosynthetic iron-oxidizing communities at the North Slope of Alaska near Toolik Field Station (TFS) at Toolik Lake (lat 68.63, long -149.

Anomalous behavior of dark states in quantum gases of (6)Li.

We create atom-molecule dark states in a degenerate Fermi gas of ^{6}Li in both weakly and strongly interacting regimes using two-photon Raman scattering to couple fermion pairs to bound molecular states in the ground singlet and triplet potential. Near the unitarity point in the BEC-BCS crossover regime, the atom number revival height associated with the dark state abruptly and unexpectedly decreases and remains low for magnetic fields below the Feshbach resonance center at 832.2 G.

Microbial biogeography of arctic streams: exploring influences of lithology and habitat.

Terminal restriction fragment length polymorphism and 16S rRNA gene sequencing were used to explore the community composition of bacterial communities in biofilms on sediments (epipssamon) and rocks (epilithon) in stream reaches that drain watersheds with contrasting lithologies in the Noatak National Preserve, Alaska. Bacterial community composition varied primarily by stream habitat and secondarily by lithology. Positive correlations were detected between bacterial community structure and nutrients, base cations, and dissolved organic carbon.

High-throughput analysis of single hematopoietic stem cell proliferation in microfluidic cell culture arrays.

Heterogeneity in cell populations poses a major obstacle to understanding complex biological processes. Here we present a microfluidic platform containing thousands of nanoliter-scale chambers suitable for live-cell imaging studies of clonal cultures of nonadherent cells with precise control of the conditions, capabilities for in situ immunostaining and recovery of viable cells. We show that this platform mimics conventional cultures in reproducing the responses of various types of primitive mouse hematopoietic cells with retention of their functional properties, as demonstrated by subsequent in vitro and in vivo (transplantation) assays of recovered cells.