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We have developed a course-based undergraduate research experience (CURE) that can be carried out in the context of an existing second-semester or upper-level organic laboratory course. In this three-week laboratory module, students synthesize a small library of molecules, test them in a robust biological assay, and design a new compound library on the basis of their results.

Arctic snow and ice cover are vital indicators of climate variability and change, yet while the Arctic shows overall warming and dramatic changes in snow and ice cover, the response of these high-latitude regions to recent climatic change varies regionally. Although previous studies have examined changing snow and ice separately, examining phenology changes across multiple components of the cryosphere together is important for understanding how these components and their response to climate forcing are interconnected. In this work, we examine recent changes in sea ice, lake ice, and snow together at the pan-Arctic scale using the Interactive Multisensor Snow and Ice Mapping System 24 km product from 1997–2019, with a more detailed regional examination from 2004–2019 using the 4 km product. We show overall that for sea ice, trends toward earlier open water (−7.7 d per decade, p) and later final freeze (10.6 d per decade, p) are evident. Trends toward earlier first snow-off (−4.9 d per decade, p), combined with trends toward earlier first snow-on (−2.8 d per decade, p), lead to almost no change in the length of the snow-free season, despite shifting earlier in the year. Sea ice-off, lake ice-off, and snow-off parameters were significantly correlated, with stronger correlations during the snow-off and ice-off season compared to the snow-on and ice-on season. Regionally, the Bering and Chukchi seas show the most pronounced response to warming, with the strongest trends identified toward earlier ice-off and later ice-on. This is consistent with earlier snow-off and lake ice-off and later snow-on and lake ice-on in west and southwest Alaska. In contrast to this, significant clustering between sea ice, lake ice, and snow-on trends in the eastern portion of the North American Arctic shows an earlier return of snow and ice. The marked regional variability in snow and ice phenology across the pan-Arctic highlights the complex relationships between snow and ice, as well as their response to climatic change, and warrants detailed monitoring to understand how different regions of the Arctic are responding to ongoing changes.

The quorum sensing signaling systems in Vibrio bacteria converge to control levels of the master transcription factors LuxR/HapR, a family of highly conserved proteins that regulate gene expression for bacterial behaviors. A compound library screen identified 2-thiophenesulfonamide compounds that specifically inhibit Vibrio campbellii LuxR but do not affect cell growth. We synthesized a panel of 50 thiophenesulfonamide compounds to examine the structure-activity relationship effects on Vibrio quorum sensing. The most potent molecule identified, PTSP (3-phenyl-1-(thiophen-2-ylsulfonyl)-1H-pyrazole), inhibits quorum sensing in multiple strains of Vibrio vulnificus, Vibrio parahaemolyticus, and V. campbellii at nanomolar concentrations. However, thiophenesulfonamide inhibition efficacy varies significantly among Vibrio species: PTSP is most inhibitory against V. vulnificus SmcR, but V. cholerae HapR is completely resistant to all thiophenesulfonamides tested. Reverse genetics experiments show that PTSP efficacy is dictated by amino acid sequence in the putative ligand binding pocket: F75Y and C170F SmcR substitutions are each sufficient to eliminate PTSP inhibition. Further, in silico modeling distinguished the most potent thiophenesulfonamides from less effective derivatives. Our results revealed the previously unknown differences in LuxR/HapR proteins that control quorum sensing in Vibrio species and underscore the potential for developing thiophenesulfonamides as specific quorum sensing-directed treatments for Vibrio infections.

Lake ice supports a range of socio‐economic and cultural activities including transportation and winter recreational actives. The influence of weather patterns on ice‐cover dynamics of temperate lakes requires further understanding for determining how changes in ice composition will impact ice safety and the range of ecosystem services provided by seasonal ice cover. An investigation of lake ice formation and decay for three lakes in Central Ontario, Canada, took place over the course of two winters, 2015–2016 and 2016–2017, through the use of outdoor digital cameras, a Shallow Water Ice Profiler (upward‐looking sonar), and weekly field measurements. Temperature fluctuations across 0°C promoted substantial early season white ice growth, with lesser amounts of black ice forming later in the season. Ice thickening processes observed were mainly through meltwater, or midwinter rain, refreezing on the ice surface. Snow redistribution was limited, with frequent melt events limiting the duration of fresh snow on the ice, leading to a fairly uniform distribution of white ice across the lakes in 2015–2016 (standard deviations week to week ranging from 3 to 5 cm), but with slightly more variability in 2016–2017 when more snow accumulated over the season (5 to 11 cm). White ice dominated the end‐of‐season ice composition for both seasons representing more than 70% of the total ice thickness, which is a stark contrast to Arctic lake ice that is composed mainly of black ice. This research has provided the first detailed lake ice processes and conditions from medium‐sized north‐temperate lakes and provided important information on temperate region lake ice characteristics that will enhance the understanding of the response of temperate lake ice to climate and provide insight on potential changes to more northern ice regimes under continued climate warming.

Vibrio campbellii BB120 (previously classified as Vibrio harveyi) is a fundamental model strain for studying quorum sensing in vibrios. A phylogenetic evaluation of sequenced Vibrio strains in Genbank revealed that BB120 is closely related to the environmental isolate V. campbellii DS40M4. We exploited DS40M4's competence for exogenous DNA uptake to rapidly generate greater than 30 isogenic strains with deletions of genes encoding BB120 quorum-sensing system homologues. Our results show that the quorum-sensing circuit of DS40M4 is distinct from BB120 in three ways: (i) DS40M4 does not produce an acyl homoserine lactone autoinducer but encodes an active orphan LuxN receptor, (ii) the quorum regulatory small RNAs (Qrrs) are not solely regulated by autoinducer signalling through the response regulator LuxO and (iii) the DS40M4 quorum-sensing regulon is much smaller than BB120 (~100 genes vs. ~400 genes, respectively). Using comparative genomics to expand our understanding of quorum-sensing circuit diversity, we observe that conservation of LuxM/LuxN proteins differs widely both between and within Vibrio species. These strains are also phenotypically distinct: DS40M4 exhibits stronger interbacterial cell killing, whereas BB120 forms more robust biofilms and is bioluminescent. These results underscore the need to examine wild isolates for a broader view of bacterial diversity in the marine ecosystem.

Vibrio bacteria are pathogens of fish, shellfish, coral, and humans due to contaminated seafood consumption. Vibrio virulence factors are controlled by the cell-to-cell communication called quorum sensing, thus this signaling system is a promising target for therapeutic design. We screened a compound library and identified nine compounds, including several 2-thiophenesulfonamides, that inhibit the master quorum sensing transcription factor LuxR in Vibrio campbellii but do not affect cell growth. We synthesized a panel of 50 thiophenesulfonamide compounds to examine the structure-activity relationship effects on quorum sensing in vivo. The most potent molecule identified, PTSP (3-phenyl-1-(thiophen-2-ylsulfonyl)-1H-pyrazole), specifically inhibits LuxR homologs in multiple strains of Vibrio vulnificus, Vibrio parahaemolyticus, and V. campbellii with sub-micromolar concentrations. PTSP efficacy is driven by amino acid conservation in the binding pocket, which is accurately predicted using in silico modeling of inhibitors. Our results underscore the potential for developing thiophenesulfonamides as specific quorum sensing-directed treatments for Vibrio infections.

Arctic snow and ice cover are vital indicators of climate variability and change, yet while the Arctic shows overall warming and dramatic changes in snow and ice cover, the response of these high-latitude regions to recent climatic change varies regionally. Although previous studies have examined changing snow and ice separately, examining phenology changes across multiple components of the cryosphere together is important for understanding how these components, and their response to climate forcing, are interconnected. In this work, we examine recent changes in sea ice, lake ice and snow together at the pan-Arctic scale using the Interactive Multisensor Snow and Ice Mapping System 24 km product from 1997–2019, with a more detailed regional examination from 2004–2019 using the 4 km product. We show overall that for sea ice, trends towards earlier open water (−7.7 d decade−1, p −1, p −1, p −1 p&thinsp

Arctic wetlands can occur as isolated patches with areas of 1–10 km2, or they can cover extensive areas in the landscape. Wetlands exert a strong influence on the hydrological cycle as they can both store and release water to streams, other wetlands (ponds) and replenish groundwater reserves. Arctic landscapes are also rich with lakes and their occurrence depends on geology, geomorphic or anthropogenic setting. Like ponds, lake sustainability over time depends on inputs exceeding losses. Hence, their capacity to hold water and the nature of shifting storage capacity especially in light of climate warming (shifts in precipitation/evaporation), or stream/river connectivity, together with growing expansion of mining, oil development are critical issues for northern ecosystems and communities. To survive over time, a wetland or lake needs positive water storage to maintain a high degree of saturation (wetland) or storage capacity (lake). Snow is particularly important, and for Arctic wetlands and lakes, it is the total winter snow accumulation that is of major hydrological consequence. Summer rainfall in most permafrost areas is not high, and often is insufficient to match evaporation rates in lakes. However, the frequency and duration of rainfall can be important for arctic wetlands. Climate warming has been tied to an increase in ground thaw, resulting in both the loss of lakes/ponds and expansion of ponds/lakes depending on permafrost conditions. The timing of ice cover on lakes can affect evaporation, where shallower lakes that experience bed-fast ice during the winter become ice-free sooner in the warm season, which leads to longer open-water seasons and greater amounts of evaporation. Northern lakes have shown shifts towards shorter ice cover duration during the cold seasons, resulting in longer open-water seasons. Lake ice modelling suggests continued shifts towards earlier break-up and later freeze-up may be expected.

Lake ice models can be used to study the latitudinal differences of current and projected changes in ice covered lakes under a changing climate. The Canadian Lake Ice Model (CLIMo) is a one-dimensional freshwater ice cover model that simulates Arctic and sub-Arctic lake ice cover well. Modelling ice cover in temperate regions has presented challenges due to the differences in composition between northern and temperate ice. This study presents a comparison of measured and modelled ice regimes, with a focus on refining CLIMo for temperate regions. The study sites include two temperate region lakes (MacDonald Lake and Clear Lake, Central Ontario) and two High Arctic lakes (Resolute Lake and Small Lake, Nunavut) where climate and ice cover information have been recorded over three seasons. The ice cover simulations were validated with a combination of time lapse imagery, field measurements of snow depth, snow density, ice thickness and albedo data, and historical ice records from the Canadian Ice Database (for Resolute Lake). Simulations of the High Arctic ice cover show good agreement with previous studies for ice-on and ice-off dates (MAE 6 to 8 days). Unadjusted simulations for the temperate region lakes show both an underestimation in ice thickness (~ 4 to 18 cm) and ice-off timing (~ 25 to 30 days). Field measurements were used to adjust the albedo parameterization used in CLIMo, which resulted in improvements to both simulated ice thickness, within 0.1 cm to 10 cm of manual measurements, and ice-off timing, within 1 to 7 days of observations. These findings suggest regionally specific measurements of albedo can improve the accuracy of lake ice simulations. These results further our knowledge regarding of the response of temperate and High Arctic lake ice regimes to climate conditions.

SummaryVibrio campbellii BB120 (previously classified as Vibrio harveyi) is a fundamental model strain for studying quorum sensing in vibrios. A phylogenetic evaluation of sequenced Vibrio strains in Genbank revealed that BB120 is closely related to the environmental isolate V. campbellii DS40M4. We exploited DS40M4’s competence for exogenous DNA uptake to rapidly generate >30 isogenic strains with deletions of genes encoding BB120 quorum-sensing system homologs. Our results show that the quorum-sensing circuit of DS40M4 is distinct from BB120 in three ways: 1) DS40M4 does not produce an acyl homoserine lactone autoinducer but encodes an active orphan LuxN receptor, 2) the quorum regulatory small RNAs (Qrrs) are not solely regulated by autoinducer signaling through the response regulator LuxO, and 3) the DS40M4 quorum-sensing regulon is much smaller than BB120 (~100 genes vs ~400 genes, respectively). Using comparative genomics to expand our understanding of quorum-sensing circuit diversity, we observe that conservation of LuxM/LuxN proteins differs widely both between and within Vibrio species. These strains are also phenotypically distinct: DS40M4 exhibits stronger interbacterial cell killing, whereas BB120 forms more robust biofilms and is bioluminescent. These results underscore the need to examine wild isolates for a broader view of bacterial diversity in the marine ecosystem.Originality-Significance StatementWild bacterial isolates yield important information about traits that vary within species. Here, we compare environmental isolate Vibrio campbellii DS40M4 to its close relative, the model strain BB120 that has been a fundamental strain for studying quorum sensing for >30 years. We examine several phenotypes that define this species, including quorum sensing, bioluminescence, and biofilm formation. Importantly, DS40M4 is naturally transformable with exogenous DNA, which allows for the rapid generation of mutants in a laboratory setting. By exploiting natural transformation, we genetically dissected the functions of BB120 quorum-sensing system homologs in the DS40M4 strain, including two-component signaling systems, transcriptional regulators, and small RNAs.

Information on arctic snow covers is relevant for climate and hydrology studies and investigations into the sustainability of both arctic fauna and flora. This study aims to (1) highlight the variability of snow cover at Polar Bear Pass (PBP) at a range of scales: point, local, and regional using both in situ snow cover measurements and remote sensing imagery products; and (2) consider how snow cover at PBP might change in the future. Terrain-based snow surveys documented the end-of-winter snowpacks over several seasons (2008–2010, 2012–2013), and snowmelt was measured daily at typical terrain types. MODIS products (snow cover) were used to document spatial snow cover variability across PBP and Bathurst and Cornwallis Islands. Due to limited data, no significant difference in snow cover duration can be identified at PBP over the period of record. Locally, end-of-winter snow cover does vary across a range of terrain types with snow depths and densities reflecting polar oasis sites. Aspect remains a defining factor in terms of snow cover variability at PBP. Northern areas of the Pass melt earlier. Regionally, PBP tends to melt out earlier than most of Bathurst Island. In the future, we surmise that snowpacks at PBP will be thinner and disappear earlier.

The magnitude and timing of water delivery in two large northern basins are analysed to clarify where runoff is generated and how their rivers acquire comparable regimes (or seasonal rhythms) of flow. These two rivers, the Mackenzie in Canada and the Yenisei in Russia, traverse similar latitudes, physiographic provinces, vegetation zones and climatic regions. Within the basins, mountainous terrain and high-precipitation sections usually yield large runoff, but low runoff comes from the plains, low plateaus and areas of aridity. Winter runoff is commonly low and snowmelt is responsible for annual peak runoff in most parts of these basins, though rainfall is a prominent runoff source in southern Yenisei. Many rivers in the drainage networks display a seasonal pattern that suggests the dominance of snowmelt to produce a spring freshet followed by a general decline in summer that diminishes to winter low flows. Regulation of reservoir outflow greatly distorts the natural flow regime. Yet, along the main river downstream of the reservoirs, the influx of tributary discharge can dilute such human influence. To truly understand how water is produced and transferred in large northern rivers, the spatial and temporal complexity of flow-generation mechanisms and storage effects need to be unravelled.

Paid: Tales of Dongles, Checks, and Other Money Stuff introduces itself as a catalogue for a museum exhibit that never happened. Contributors – drawn from a range of disciplines including archeolog...

Lakes are a prominent geographic feature in northern landscapes and play an important role in understanding regional climate systems. In order to better model changes within climate systems it is important to study lake ice processes. Although the availability of records for lake ice through ground measurements has declined in recent years, the increased use of remote sensing provides an alternative to this. Using a pre-classified snow and ice remote sensing product with a 500 metre resolution, based on images from the Moderate Resolution Imaging Spectroradiometer (MODIS/MOD10A1), and the use of measured and reanalysis temperature data, this study evaluated lake ice phenology dates in connection to recent trends in temperature and 0°C isotherms within Ontario and Manitoba between 2001 and 2014. Temperature trends indicated both regional warming and cooling, with significant cooling observed in Southern Ontario (p < 0.05) and significant warming in Southern Manitoba (p < 0.1) during the fall. Spatial analysis of the trends in the lake ice data showed significant clustering of significant trends in ice on dates (p < 0.01). When analyzing the trends in ice phenology in connection to the trends in temperature, it was found that 70% of lakes experienced a change in the ice on date with the expected change in temperature and 85% of lakes for ice off date. When shifting ice on and ice off dates are investigated in relation to 0°C isotherms, it was seen that 80% of ice on dates and 100% of ice off dates shifted in sync with the isotherm dates. This demonstrates that the ice phenology of lakes in Ontario and Manitoba, Canada is responding to short-term variability in temperature. The MODIS product could be used to investigate ice phenology on a large scale and contribute towards expanding existing records of ice phenology. Establishing long term ice records could be a valuable asset for other research ranging from water balance studies to the response of lake biota under changing climate.

The gut microbiota synthesize hundreds of molecules, many of which influence host physiology. Among the most abundant metabolites are the secondary bile acids deoxycholic acid (DCA) and lithocholic acid (LCA), which accumulate at concentrations of around 500 μM and are known to block the growth of Clostridium difficile1, promote hepatocellular carcinoma2 and modulate host metabolism via the G-protein-coupled receptor TGR5 (ref. 3). More broadly, DCA, LCA and their derivatives are major components of the recirculating pool of bile acids4; the size and composition of this pool are a target of therapies for primary biliary cholangitis and nonalcoholic steatohepatitis. Nonetheless, despite the clear impact of DCA and LCA on host physiology, an incomplete knowledge of their biosynthetic genes and a lack of genetic tools to enable modification of their native microbial producers limit our ability to modulate secondary bile acid levels in the host. Here we complete the pathway to DCA and LCA by assigning and characterizing enzymes for each of the steps in its reductive arm, revealing a strategy in which the A–B rings of the steroid core are transiently converted into an electron acceptor for two reductive steps carried out by Fe–S flavoenzymes. Using anaerobic in vitro reconstitution, we establish that a set of six enzymes is necessary and sufficient for the eight-step conversion of cholic acid to DCA. We then engineer the pathway into Clostridium sporogenes, conferring production of DCA and LCA on a nonproducing commensal and demonstrating that a microbiome-derived pathway can be expressed and controlled heterologously. These data establish a complete pathway to two central components of the bile acid pool. The biosynthetic pathway that produces the secondary bile acids DCA and LCA in human gut microbes has been fully characterized, engineered into another bacterial host, and used to confer DCA production in germ-free mice—an important proof-of-principle for the engineering of gut microbial pathways.

Lake ice models are a vital tool for studying the response of ice-covered lakes to changing climates throughout the world. The Canadian Lake Ice Model (CLIMo) is a one-dimensional freshwater ice cover model that simulates Arctic and sub-Arctic lake ice cover well. Modelling ice cover in temperate regions has presented challenges due to the differences in ice composition between northern and temperate region lake ice. This study presents a comparison of measured and modelled ice regimes, with a focus on refining CLIMo for temperate regions. The study sites include two temperate region lakes (MacDonald Lake and Clear Lake, Central Ontario) and two High Arctic lakes (Resolute Lake and Small Lake, Nunavut) where climate and ice cover information have been recorded over three seasons. The ice cover simulations were validated with a combination of time lapse imagery, field measurements of snow depth, snow density, ice thickness and albedo data, and historical ice records from the Canadian Ice Database (for Resolute Lake). Simulations of High Arctic lake ice cover show good agreement with previous studies for ice-on and ice-off dates (MAE 6 to 8 days). Unadjusted simulations for the temperate region lakes show good ice-on timing, but an under-representation of ice thickness, and earlier complete ice-off timing (~3 to 5 weeks). Field measurements were used to adjust the albedo values used in CLIMo, which resulted in improvements to both simulated ice thickness (~3 cm MAE compared to manual measurements), and ice-off timing, within 0 to 7 days (2 days MAE) of observations. These findings suggest regionally specific measurements of albedo can improve the accuracy of lake ice simulations, which further our knowledge of the response of temperate and High Arctic lake ice regimes to climate conditions.

We have developed an organic-chemistry-themed museum exhibit that is appropriate for all ages. The goal of the exhibit is to introduce the general public to the concept of molecular structure by relating structure to scent.

Lake ice is an important component in understanding the local climate as changes in temperature have an impact on the timing of key ice phenology events. In recent years, there has been a decline in the in-situ monitoring of lake ice events in Canada and microwave remote sensing imagery from synthetic aperture radar (SAR) is more widely used due to the high spatial resolution and response of backscatter to the freezing and melting of the ice surface. RADARSAT-2 imagery was used to develop a threshold-based method for determining lake ice events for mid-latitude lakes in Central Ontario from 2008 to 2017. Estimated lake ice phenology events are validated with ground-based observations and are compared against the Moderate Resolution Imaging Spectroradiometer (MODIS band 2). The threshold-based method was found to accurately identify 12 out of 17 freeze events and 13 out of 17 melt events from 2015–2017 when compared to ground-based observations. Mean absolute errors for freeze events ranged from 2.5 to 10.0 days when compared to MODIS imagery while the mean absolute error for water clear of ice (WCI) ranged from 1.5 to 7.1 days. The method is important for the study of mid-latitude lake ice due to its unique success in detecting multiple freeze and melting events throughout the ice season.

Time series of ground-based X- and Ku-band frequency-modulated continuous-wave (FMCW) radar data are used to derive ice thickness for bubbled freshwater lake ice with heterogeneous snow cover under the assumption of interactions in range occurring at the ice–snow and ice–water interface. Once adjusted for the refractive index of ice and slant range, the distance between peak returns agrees with in-situ ice thickness observations. Ice thicknesses are derived from the distance of peak returns in range acquired in the off-nadir incidence angle range 21°–60°. Derived ice thicknesses are compared to in-situ measurements, an upward-looking acoustic sonar (Shallow Water Ice-Profiler (SWIP)), and a one-dimensional thermodynamic lake ice model (Canadian Lake Ice Model (CLIMo)). Median ice thicknesses derived with University of Waterloo X- and Ku-band scatterometers (UW-Scat) agreed well with in-situ measurements ( R 2 = 0.953 and 0.964), SWIP ( R 2 = 0.842 and 0.893), and Canadian Lake Ice Model (CLIMo) simulations using 25% of terrestrial snowpack scenario, respectively. UW-Scat derived ice thicknesses produced root mean square error (RMSE) values of 0.053 and 0.088 m for X- and Ku-band, respectively, relative to in-situ ice thickness measurements. This study is the first FMCW X- and Ku-band off-nadir approach to observe interactions at the snow–ice and ice–water interface to derive ice thickness.

Summary In complex biological systems, small molecules often mediate microbe-microbe and microbe-host interactions. Using a systematic approach, we identified 3,118 small-molecule biosynthetic gene clusters (BGCs) in genomes of human-associated bacteria and studied their representation in 752 metagenomic samples from the NIH Human Microbiome Project. Remarkably, we discovered that BGCs for a class of antibiotics in clinical trials, thiopeptides, are widely distributed in genomes and metagenomes of the human microbiota. We purified and solved the structure of a thiopeptide antibiotic, lactocillin, from a prominent member of the vaginal microbiota. We demonstrate that lactocillin has potent antibacterial activity against a range of Gram-positive vaginal pathogens, and we show that lactocillin and other thiopeptide BGCs are expressed in vivo by analyzing human metatranscriptomic sequencing data. Our findings illustrate the widespread distribution of small-molecule-encoding BGCs in the human microbiome, and they demonstrate the bacterial production of drug-like molecules in humans. PaperClip

Accurate simulations of freshwater lake ice are integral for the study of climatic variability in northern environments. Surface albedo, a component often parameterized in lake ice models, has been shown to affect the timing of ice break-up during the melt season. In situ snow and ice albedo measurements were taken over a partially snow-covered freshwater lake near Churchill, Manitoba for the evaluation of the albedo parameterization of the Canadian Lake Ice Model (CLIMo) and the Moderate Resolution Imaging Spectrometer (MODIS) albedo products (MOD10A1/MYD10A1 and MCD43A3). The albedo simulations using CLIMo were performed with and without snow integrated into the model and evaluated against in situ albedo measurements recorded over clear ice, snow ice and snow-covered ice. The simulated snow albedo from CLIMo for the entire ice growth season evaluated against snow albedo observations had a root mean square error of 0.07, a mean absolute error of 0.06, and a mean bias error (MBE) of −0.01. With snow removed from CLIMo, the albedo parameterization overestimated albedo values measured in the field over snow-free clear ice and snow ice with MBE values of 0.13 and 0.10, respectively. These findings suggest that CLIMo's bare ice albedo parameterization needs to be revised to account for albedo differences between ice types. The evaluation of the MODIS albedo products with in situ snow and ice albedo observations and the comparison of these satellite products with CLIMo's albedo parameterization during the melt period, when in situ radiation measurement stations needed to be removed from the lake-ice surface, are addressed in paper Part II (this issue). Copyright © 2014 John Wiley & Sons, Ltd.

There is concern over the fate of surface water bodies at high latitudes as a consequence of rising global temperatures. The goal of this study is to characterize climatic change that has occurred in the northern Hudson Bay Lowlands (HBL), Canada, from 1943 to 2009, to determine if this has resulted in a change to pond surface areas and to predict if changes may continue in the future. Climate change and changes to pond volume and size over the past ∼60 years were examined using a combination of field methods/instrumental records (1943–2009), modeling (1953–2009; 1961–2100), and remote sensing/imagery analyses (1947–2008). Results demonstrate that temperatures are warming and breakup dates are earlier, but this has not significantly increased the duration of the open-water period or pond evaporation rates, which can be highly variable from year to year. Annual precipitation, primarily summer rainfall, has increased, lessening the summer moisture deficit and leading to wetter conditions. The obser...

Air temperature and winter precipitation changes over the last five decades have impacted the timing, duration, and thickness of the ice cover on Arctic lakes as shown by recent studies. In the case of shallow tundra lakes, many of which are less than 3 m deep, warmer climate conditions could result in thinner ice covers and consequently, in a smaller fraction of lakes freezing to their bed in winter. However, these changes have not yet been comprehensively documented. The analysis of a 20 yr time series of European remote sensing satellite ERS-1/2 synthetic aperture radar (SAR) data and a numerical lake ice model were employed to determine the response of ice cover (thickness, freezing to the bed, and phenology) on shallow lakes of the North Slope of Alaska (NSA) to climate conditions over the last six decades. Given the large area covered by these lakes, changes in the regional climate and weather are related to regime shifts in the ice cover of the lakes. Analysis of available SAR data from 1991 to 2011, from a sub-region of the NSA near Barrow, shows a reduction in the fraction of lakes that freeze to the bed in late winter. This finding is in good agreement with the decrease in ice thickness simulated with the Canadian Lake Ice Model (CLIMo), a lower fraction of lakes frozen to the bed corresponding to a thinner ice cover. Observed changes of the ice cover show a trend toward increasing floating ice fractions from 1991 to 2011, with the greatest change occurring in April, when the grounded ice fraction declined by 22% (α = 0.01). Model results indicate a trend toward thinner ice covers by 18–22 cm (no-snow and 53% snow depth scenarios, α = 0.01) during the 1991–2011 period and by 21–38 cm (α = 0.001) from 1950 to 2011. The longer trend analysis (1950–2011) also shows a decrease in the ice cover duration by ~24 days consequent to later freeze-up dates by 5.9 days (α = 0.1) and earlier break-up dates by 17.7–18.6 days (α = 0.001).

Lake surface temperature (LST) and ice phenology were simulated for various points differing in depth on Great Slave Lake and Great Bear Lake, two large lakes located in the Mackenzie River Basin in Canada's Northwest Territories, using the 1-D Freshwater Lake model (FLake) and the Canadian Lake Ice Model (CLIMo) over the 2002–2010 period, forced with data from three weather stations (Yellowknife, Hay River and Deline). LST model results were compared to those derived from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard the Earth Observing System Terra and Aqua satellite platforms. Simulated ice thickness and freeze-up/break-up dates were also compared to in situ observations. Both models showed a good agreement with daily average MODIS LSTs on an annual basis (0.935 ≤ relative index of agreement ≤ 0.984 and 0.94 ≤ mean bias error ≤ 4.83). The absence of consideration of snow on lake ice in FLake was found to have a large impact on estimated ice thicknesses (25 cm thicker on average by the end of winter compared to in situ measurements; 9 cm thicker for CLIMo) and break-up dates (6 d earlier in comparison with in situ measurements; 3 d later for CLIMo). The overall agreement between the two models and MODIS LST products during both the open water and ice seasons was good. Remotely sensed data are a promising data source for assimilation into numerical weather prediction models, as they provide the spatial coverage that is not captured by in situ data. Keywords: lake surface temperature; lake ice; lake modelling; MODIS; Great Slave Lake; Great Bear Lake (Published: 23 March 2012) Citation: Tellus A 2012, 64 , 17614, DOI: 10.3402/tellusa.v64i0.17614

This paper reviews the current state of knowledge pertaining to the interactions of lake ice and climate. Lake ice has been shown to be sensitive to climate variability through observations and modelling, and both long-term and short-term trends have been identified from ice records. Ice phenology trends have typically been associated with variations in air temperatures while ice thickness trends tend to be associated more to changes in snow cover. The role of ice cover in the regional climate is less documented and with longer ice-free seasons possible as a result of changing climate conditions, especially at higher latitudes, the effects of lakes on their surrounding climate (such as increased evaporation, lake-effect snow and thermal moderation of surrounding areas, for example) can be expected to become more prominent. The inclusion of lakes and lake ice in climate modelling is an area of increased attention in recent studies. An important step in improving predictions of ice conditions in models is the assimilation of remote sensing data in areas where in-situ data is lacking, or non-representative of the lake conditions. The ability to accurately represent ice cover on lakes will be an important step in the improvement of global circulation models, regional climate models and numerical weather forecasting.

The temporal evolution of the backscatter coefficient, sigma-nought (σ°) from QuikSCAT was evaluated for monitoring ice phenology on Great Bear Lake (66°N, 121°W) and Great Slave Lake (61°40′N, 114°W), Northwest Territories, Canada. Results indicated that σ° from QuikSCAT can be used to detect melt onset, water clear of ice and freeze onset dates on both lakes. An ice phenology algorithm was then developed to assess the spatiotemporal variability on both lakes from QuikSCAT for the period 2000–2006. Results showed that for Great Slave Lake, the average melt onset date occurred on year day (YD) 123, the average water clear of ice date was on YD164, and the average freeze onset date was on YD330. On Great Bear Lake, the average melt onset date occurred on YD139, the average water clear of ice date was YD191, and the average freeze onset date was YD321. Ice cover remained present for at least five weeks longer on Great Bear Lake than on Great Slave Lake and most of the difference can be explained by earlier ice melt on Great Slave Lake. Spatially, on Great Bear Lake, melt onset took place first in the eastern arm, water clear of ice occurred first in southeastern and western arms, and freeze onset appeared first in the northern arm and along the shorelines. On Great Slave Lake, melt onset began first in the central basin and then progressed to the northern and eastern arms later in the season. The central basin of Great Slave Lake cleared earlier than the periphery due to the discharge from the Slave River. Freeze onset on Great Slave Lake occurred first within the east arm, closely followed by the north and west arms, and then finally in the centre of the main basin.

Owing to the scarcity of hydro-climatic data in high latitudes, most hydrological models are validated using only discharge data from the basin outlets. In view of the important contribution of snowmelt to northern river flows, there is a need to evaluate model performance in terms of the ability to simulate the seasonal pattern of change in the basin snow cover. The paucity of ground observations renders satellite information a suitable alternative. The moderate resolution imaging spectroradiometer (MODIS) global snow-cover product provided by the National Snow and Ice Data Center (NSIDC) offers one such tool to validate simulated snow coverage in rugged sub-arctic and boreal terrain. This study examines the usefulness of applying MODIS data to validate the hydrological simulation for two test basins: the Liard (275 000 km2) and the Athabasca (133 000 km2) Basins in Canada. Changing extent of snow cover simulated by the Semi-distributed Land Use-based Runoff Processes (SLURP) macro-hydrologic model was compared with MODIS imagery at four bi-weekly intervals in 2000 and 2001. The simulated patterns of seasonal snow-cover change are consistent with the remotely sensed information, with melt beginning from the lower elevations in the east where less snow was accumulated, to the higher elevations in the west bearing more snow. The overall results show the need and the usefulness of MODIS as a tool for validating snow distribution simulated by the hydrological model in large northern basins. Copyright © 2008 John Wiley & Sons, Ltd.

Shallow lakes, with depths less than ca. 3.5–4 m, are a ubiquitous feature of the Arctic Alaskan Coastal Plain, covering up to 40% of the land surface. With such an extended areal coverage, lakes and their ice regimes represent an important component of the cryosphere. The duration of the ice season has major implications for the regional and local climate, as well as for the physical and biogeochemical processes of the lakes. With day and night observations in all weather conditions, synthetic aperture radar (SAR) sensors provide year-round acquisitions. Monitoring the evolution of radar backscatter (σ°) is useful for detecting the timing of the beginning and end of the ice season. Analysis of the temporal evolution of C-band σ° from Advanced Synthetic Aperture Radar (ASAR) Wide Swath and RADARSAT-2 ScanSAR, with a combined frequency of acquisitions from two to five days, was employed to evaluate the potential of SAR to detect the timing of key lake-ice events. SAR observations from 2005 to 2011 were compared to outputs of the Canadian Lake Ice Model (CLIMo). Model simulations fall within similar ranges with those of the SAR observations, with a mean difference between SAR observations and model simulations of only one day for water-clear-of-ice (WCI) from 2006 to 2010. For freeze onset (FO), larger mean differences were observed. SAR analysis shows that the mean FO date for these shallow coastal lakes is 30 September and the mean WCI date is 5 July. Results reveal that greater variability existed in the mean FO date (up to 26 days) than in that of melt onset (MO) (up to 12 days) and in that of WCI (6 days). Additionally, this study also identifies limitations and provides recommendations for future work using C-band SAR for monitoring the lake- ice phenology of shallow Arctic lakes.

Wetlands in the polar desert environment of the High Arctic provide a special ecological niche for the tundra plants, insects, birds, and animals. Non-tidal patchy wetlands exhibit a hydrologic regime that includes a high water table and extensive flooding in the snowmelt period, followed by a gradual summer drying that is interrupted by rainfall events that raise water levels. These wetlands are also prone to inter-annual variations in wetness. Given sufficient local water supply, they are self-sustaining entities in which soil saturation favors ground ice formation, but the ice-rich permafrost prevents deep percolation while vegetation growth and peat development further insulate the ground. Several processes can alter this balance: a change in drainage can reduce inflow; excessive melting of ground ice leading to thermokarst can modify wetland morphology and flow pattern. On a regional scale, projected climatic warming of the Arctic may extend the thawed season, enhance evaporation, and eliminate the l...

In 2013, the vast majority of the monitored climate variables reported here maintained trends established in recent decades. ENSO was in a neutral state during the entire year, remaining mostly on the cool side of neutral with modest impacts on regional weather patterns around the world. This follows several years dominated by the effects of either La Niña or El Niño events. According to several independent analyses, 2013 was again among the 10 warmest years on record at the global scale, both at the Earths surface and through the troposphere. Some regions in the Southern Hemisphere had record or near-record high temperatures for the year. Australia observed its hottest year on record, while Argentina and New Zealand reported their second and third hottest years, respectively. In Antarctica, Amundsen-Scott South Pole Station reported its highest annual temperature since records began in 1957. At the opposite pole, the Arctic observed its seventh warmest year since records began in the early 20th century. At 20-m depth, record high temperatures were measured at some permafrost stations on the North Slope of Alaska and in the Brooks Range. In the Northern Hemisphere extratropics, anomalous meridional atmospheric circulation occurred throughout much of the year, leading to marked regional extremes of both temperature and precipitation. Cold temperature anomalies during winter across Eurasia were followed by warm spring temperature anomalies, which were linked to a new record low Eurasian snow cover extent in May. Minimum sea ice extent in the Arctic was the sixth lowest since satellite observations began in 1979. Including 2013, all seven lowest extents on record have occurred in the past seven years. Antarctica, on the other hand, had above-average sea ice extent throughout 2013, with 116 days of new daily high extent records, including a new daily maximum sea ice area of 19.57 million km2 reached on 1 October. ENSO-neutral conditions in the eastern central Pacific Ocean and a negative Pacific decadal oscillation pattern in the North Pacific had the largest impacts on the global sea surface temperature in 2013. The North Pacific reached a historic high temperature in 2013 and on balance the globally-averaged sea surface temperature was among the 10 highest on record. Overall, the salt content in nearsurface ocean waters increased while in intermediate waters it decreased. Global mean sea level continued to rise during 2013, on pace with a trend of 3.2 mm yr-1 over the past two decades. A portion of this trend (0.5 mm yr-1) has been attributed to natural variability associated with the Pacific decadal oscillation as well as to ongoing contributions from the melting of glaciers and ice sheets and ocean warming. Global tropical cyclone frequency during 2013 was slightly above average with a total of 94 storms, although the North Atlantic Basin had its quietest hurricane season since 1994. In the Western North Pacific Basin, Super Typhoon Haiyan, the deadliest tropical cyclone of 2013, had 1-minute sustained winds estimated to be 170 kt (87.5 m s-1) on 7 November, the highest wind speed ever assigned to a tropical cyclone. High storm surge was also associated with Haiyan as it made landfall over the central Philippines, an area where sea level is currently at historic highs, increasing by 200 mm since 1970. In the atmosphere, carbon dioxide, methane, and nitrous oxide all continued to increase in 2013. As in previous years, each of these major greenhouse gases once again reached historic high concentrations. In the Arctic, carbon dioxide and methane increased at the same rate as the global increase. These increases are likely due to export from lower latitudes rather than a consequence of increases in Arctic sources, such as thawing permafrost. At Mauna Loa, Hawaii, for the first time since measurements began in 1958, the daily average mixing ratio of carbon dioxide exceeded 400 ppm on 9 May. The state of these variables, along with dozens of others, and the 2013 climate conditions of regions around the world are discussed in further detail in this 24th edition of the State of the Climate series. © 2014, American Meteorological Society. All rights reserved.

Lake ice was simulated for the province of Quebec, Canada, for both contemporary and future climate conditions using a one-dimensional thermodynamic ice model. The model was forced with NARR data (32 km) and both the daily IMS product (4 km) and the MODIS snow product (500 m) were assessed for their utility at determining lake ice phenology at the subgrid cell level (based on the 32 km NARR grid). Both products were useful for detecting ice-off; however, the MODIS product was advantageous for detecting ice-on, mainly due to the finer resolution and resulting spatial detail. The subgrid cell variability in ice-on/off dates was typically less than 2% of the mean, although it ranged up to 10% for some grid cells. The simulations were found to be within the satellite-detected subgrid cell variability: 62% of the time for ice-off and 80% of the time for ice-on. Forcing the model with future climate scenarios from the Canadian Regional Climate Model predicts the regional ice cover durations will decrease by up to 50 days from the current 1981–2010 means to the 2041–2070 means and decrease from 15 to nearly 100 days shorter from the current means to the 2071–2100 means.

Lakes comprise a large portion of the surface cover in northern North America, forming an important part of the cryosphere. The timing of lake ice phenological events (e.g. break-up/freeze-up) is a useful indicator of climate variability and change, which is of particular relevance in environmentally sensitive areas such as the North American Arctic. Further alterations to the present day ice regime could result in major ecosystem changes, such as species shifts and the disappearance of perennial ice cover. The Canadian Lake Ice Model (CLIMo) was used to simulate lake ice phenology across the North American Arctic from 1961–2100 using two climate scenarios produced by the Canadian Regional Climate Model (CRCM). Results from the 1961–1990 time period were validated using 15 locations across the Canadian Arctic, with both in situ ice cover observations from the Canadian Ice Database as well as additional ice cover simulations using nearby weather station data. Projected changes to the ice cover using the 30-year mean data between 1961–1990 and 2041–2070 suggest a shift in break-up and freeze-up dates for most areas ranging from 10–25 days earlier (break-up) and 0–15 days later (freeze-up). The resulting ice cover durations show mainly a 10–25 day reduction for the shallower lakes (3 and 10 m) and 10–30 day reduction for the deeper lakes (30 m). More extreme reductions of up to 60 days (excluding the loss of perennial ice cover) were shown in the coastal regions compared to the interior continental areas. The mean maximum ice thickness was shown to decrease by 10–60 cm with no snow cover and 5–50 cm with snow cover on the ice. Snow ice was also shown to increase through most of the study area with the exception of the Alaskan coastal areas.

Circadian changes in cardiovascular function during the progression of diabetes mellitus in the diabetes prone rat (BBDP) (n=8) were studied. Age-matched diabetes-resistant rats (BBDR) served as controls. BP was recorded via telemetry in contiguous 4 hr time periods over 24 hours starting with 12 midnight to 4 am as period zero (P0). Prior to onset of diabetes BP was high at P0, peaked at P2, and then fell again at P3; BP and heart rate (HR) then increased gradually at P4 and leveled off at P5, thereby exhibiting a bipodal rhythm. These patterns changed during long-term diabetes. The cross-correlation coefficient of BP and HR was not significantly different across groups at onset, but it fell significantly at 9 months of duration of diabetes (BBDP: 0.39 ± 0.06; BBDR: 0.65 ± 0.03;P<.05). These results show that changes in circadian cardiovascular rhythms in diabetes mellitus became significant at the late stage of the disease.

Recent evidence points to warmer and wetter conditions for Arctic regions. It is not clear how High Arctic environments, in particular extensive wetlands, will respond to these rapid changes. Sustainability studies of wetland complexes will require accurate mapping of water bodies (lakes, ponds, streams) over time. This information is critical to obtain reliable estimates of water inputs (e.g., snowmelt), outputs (e.g., evaporation), and storage, and to assess environmental change (e.g., pond desiccation, expansion, or both). Numerous tools and techniques are available to provide this information, though each approach has its benefits and limitations. In this study, we systematically explore the differences and similarities inherent in three different techniques used to delineate lakes and small ponds at an extensive wetland area near Creswell Bay, Somerset Island, Nunavut (72°43' N, 94°15' W). The mapping techniques compared are satellite mapping (extraction from a satellite-based land cover map), black-and-white aerial photography, and a topographic map sheet. Results indicate that while all three techniques could delineate large lake boundaries and their positions successfully, they differed in the number of ponds they delineated, as well as their boundaries and positions. A misrepresentation of water bodies can hinder hydrologic studies of Arctic water resources, and the results of this study emphasize the need to apply appropriate mapping techniques at different scales. The three mapping techniques are based on data from three different dates over several decades, so the different results also may indicate short- and long-term environmental change.

In contrast to talk in more central parts of the city, and even in domestic space, interactions surrounding roadside grocery shops in Thanjavur, Tamil Nadu entail a body of possible overhearers that is both limited and indefinite. Drawing on conversations recorded in roadside shops, I describe interactions in which the characterization of these spaces as principally concerned with routine provisioning allowed responsibility for participation in potentially disreputable talk to be plausibly denied. I suggest that petty traders seek to classify interactions surrounding shops as unremarkable because doing so supports the validity of commercial transactions. At the same time, customers exploit talk in grocery shops, and similar provisioning spaces, as a means by which to engage with a public while remaining “backstage”.

SummaryAlthough biosynthetic gene clusters (BGCs) have been discovered for hundreds of bacterial metabolites, our knowledge of their diversity remains limited. Here, we used a novel algorithm to systematically identify BGCs in the extensive extant microbial sequencing data. Network analysis of the predicted BGCs revealed large gene cluster families, the vast majority uncharacterized. We experimentally characterized the most prominent family, consisting of two subfamilies of hundreds of BGCs distributed throughout the Proteobacteria; their products are aryl polyenes, lipids with an aryl head group conjugated to a polyene tail. We identified a distant relationship to a third subfamily of aryl polyene BGCs, and together the three subfamilies represent the largest known family of biosynthetic gene clusters, with more than 1,000 members. Although these clusters are widely divergent in sequence, their small molecule products are remarkably conserved, indicating for the first time the important roles these compounds play in Gram-negative cell biology.

During the International Polar Year (IPY), comprehensive observational research programs were undertaken to increase our understanding of the Canadian polar cryosphere response to a changing climate. Cryospheric components considered were snow, permafrost, sea ice, freshwater ice, glaciers and ice shelves. Enhancement of conventional observing systems and retrieval algorithms for satellite measurements facilitated development of a snapshot of current cryospheric conditions, providing a baseline against which future change can be assessed. Key findings include: 1. surface air temperatures across the Canadian Arctic exhibit a warming trend in all seasons over the past 40 years. A consistent pan-cryospheric response to these warming temperatures is evident through the analysis of multi-decadal datasets; 2. in recent years (including the IPY period) a higher rate of change was observed compared to previous decades including warming permafrost, reduction in snow cover extent and duration, reduction in summer sea ice extent, increased mass loss from glaciers, and thinning and break-up of the remaining Canadian ice shelves. These changes illustrate both a reduction in the spatial extent and mass of the cryosphere and an increase in the temporal persistence of melt related parameters. The observed changes in the cryosphere have important implications for human activity including the close ties of northerners to the land, access to northern regions for natural resource development, and the integrity of northern infrastructure. © 2012 UKCrown: Environment Canada; © Her Majesty the Queen in Right of Canada.

We present an evaluation of the Interactive Multisensor Snow and Ice Mapping System (IMS) for monitoring northern hemisphere sea ice phenology. Analysts utilize a variety of datasets to manually derive the daily extent of snow, ice, water and land, available at both 24 and 4 km. The 4 km IMS product was assessed for 2004–2008 against several previously established melt/freeze algorithms using Scatterometer Image Reconstruction (SIR) SeaWinds/QuikSCAT (QuikSCAT) backscatter (σ°), Advanced Microwave Scanning Radiometer for the Earth Observing System (AMSR-E) brightness temperature (T B ) measurements, data from the Special Sensor Microwave/Image data (SSM/I) and sea ice concentrations derived from DMSP Special Sensor Microwave/Imager–Special Sensor Microwave Imager Sounder (SSMI–SSMIS) data (NASATeam dataset). The resolution possible with the 4 km IMS product allows for better spatial representation of sea ice along the coastlines, the ice edges and in the narrow channels of the Canadian Arctic Archipelago as compared to the microwave products. IMS detects open water earlier and freeze onset later than the automated microwave products, and also allows for the detection of opening, and the subsequent closing, of leads that the other datasets are unable to detect. Using RADARSAT-1 imagery for evaluation, IMS is shown to outperform the other datasets for the timing and extent of the first open water detection. IMS identified between 17 and 53% greater open water coverage than the other datasets in the narrow channels of the Northwest Passage (Barrow Strait). In order to further the use of IMS for sea ice applications, we derived two new spatial datasets using the full record of IMS data (4 km: 2004–present, 24 km: 1997–present): melt duration to open water (duration from melt onset detected with SSM/I passive microwave until open water detected by IMS) and first year ice cover duration (duration from freeze onset until open water, both detected by IMS).