Cold Winter Temperatures Research Articles

Isotopic composition on ground ice in Western Yamal (Marre-Sale)

The profile of Quaternary sediments near Marre-Salle polar station, Western Yamal Peninsula, has large bodies of tabular ground ice. This profile is considered strata-typical and critical in understanding of paleogeographic conditions of the Arctic in Pleistocene-Holocene. However, interpretation of the profile is under discussion. It consists of two distinct strata: upper layer of 10–15 m thick represented by continental sediments and lower one with a thickness of more than 100 m represented by marine sediments. Lower layer of saline marine clays has lenses of tabular ground ice (more than 20 m thick), the bases of which are below the sea level. Upper continental layer is characterized by syngenetic ice-wedges of different generations. Samples were collected from ice-wedges and tabular ground ice for chemical and isotope analysis. The results of the analysis allow to reconstruct paleogeographic conditions of the sedimentation and freezing of Quaternary sediments. Heavy stable isotope content and relationship between oxygen and hydrogen isotopes show that the ice bodies in the lower layer were formed in-situ within the ground. In the upper layer, heavier isotope content found in younger ice-wedges relative to the old-generation wedges. Formation of massive syngenetic Upper-Pleistocene ice-wedges occurred in conditions of colder winter temperatures than at present. Syngenetic Holocene wedges were formed after Holocene Optimum under winter conditions similar to present. Younger ice wedges formed smaller polygons, were smaller and often were developing in the locations of the degraded old wedges. Results of the isotope analysis of various types of ground ice near Marre-Sale allow reconstructing changes of marine sedimentation to continental one around Kargino time (MIS 3) and changes in climatic conditions in Arctic in Late Pleistocene and Holocene.

What drives growth of Scots pine in continental Mediterranean climates: Drought, low temperatures or both?

Scots pine forests subjected to continental Mediterranean climates undergo cold winter temperatures and drought stress. Recent climatic trends towards warmer and drier conditions across the Mediterranean Basin might render some of these pine populations more vulnerable to drought-induced growth decline at the Southernmost limit of the species distribution. We investigated how cold winters and dry growing seasons drive the radial growth of Scots pine subject to continental Mediterranean climates by relating growth to climate variables at local (elevational gradient) and regional (latitudinal gradient) scales. Local climate-growth relationships were quantified on different time scales (5-, 10- and 15-days) to evaluate the relative role of elevation and specific site characteristics. A negative water balance driven by high maximum temperatures in June (low-elevation sites) and July (high-elevation sites) was the major constraint on growth, particularly on a 5- to 10-day time scale. Warm nocturnal conditions in January were associated with wider rings at the high-elevation sites. At the regional scale, Scots pine growth mainly responded positively to July precipitation, with a stronger association at lower elevations and higher latitudes. January minimum temperatures showed similar patterns but played a secondary role as a driver of tree growth. The balance between positive and negative effects of summer precipitation and winter temperature on radial growth depends on elevation and latitude, with low-elevation populations being more prone to suffer drought and heat stress; whereas, high-elevation populations may be favoured by warmer winter conditions. This negative impact of summer heat and drought has increased during the past decades. This interaction between climate and site conditions and local adaptations is therefore decisive for the future performance and persistence of Scots pine populations in continental Mediterranean climates. Forecasting changes in the Scots pine range due to climate change should include this site-related information to obtain more realistic predictions, particularly in Mediterranean rear-edge areas.

First records from the Ligurian Sea of the cold water species Okenia aspersa and Doto koenneckeri (Gastropoda: Nudibranchia)

Okenia aspersais a north-eastern Atlantic species, only previously recorded asOkenia quadricornisfrom the Malta Archipelago in the Mediterranean Sea, and in juvenile forms, from Sicily and the Gulf of Naples. A second adult specimen is recorded in the present paper, which was found along the Noli Cape coast, in the western Ligurian Sea (Italy). It was found on pebbles at a depth of 10 m. In the same area, at a depth of 5.5 m, two specimens ofDoto koenneckeriand three of their egg masses were found. This species, also described from Norway and Ireland, was only previously known to occur in the Mediterranean Sea off Spain and France. It is likely that the cold winter temperatures of the Ligurian Sea allowed this species to live and reproduce.

Optimal Ranking Regime Analysis of Intra- to Multidecadal U.S. Climate Variability. Part I: Temperature*

Abstract The optimal ranking regime (ORR) method was used to identify intradecadal to multidecadal (IMD) time windows containing significant ranking sequences in U.S. climate division temperature data. The simplicity of the ORR procedure’s output—a time series’ most significant nonoverlapping periods of high or low rankings—makes it possible to graphically identify common temporal breakpoints and spatial patterns of IMD variability in the analyses of 102 climate division temperature series. This approach is also applied to annual Atlantic multidecadal oscillation (AMO) and Pacific decadal oscillation (PDO) climate indices, a Northern Hemisphere annual temperature (NHT) series, and divisional annual and seasonal temperature data during 1896–2012. In addition, Pearson correlations are calculated between PDO, AMO, and NHT series and the divisional temperature series. Although PDO phase seems to be an important influence on spring temperatures in the northwestern United States, eastern temperature regimes in annual, winter, summer, and fall temperatures are more coincident with cool and warm phase AMO regimes. Annual AMO values also correlate significantly with summer temperatures along the Eastern Seaboard and fall temperatures in the U.S. Southwest. Given evidence of the abrupt onset of cold winter temperatures in the eastern United States during 1957/58, possible climate mechanisms associated with the cause and duration of the eastern U.S. warming hole period—identified here as a cool temperature regime occurring between the late 1950s and late 1980s—are discussed.

Abiotic and Biotic Factors Influencing Sugar Maple Health: Soils, Topography, Climate, and Defoliation

Sugar maple (Acer saccharum Marsh.), a keystone species of northern hardwood forests, is susceptible to decline, especially on sites low in the soil base cations calcium (Ca) and magnesium (Mg). A common stressor of sugar maple is forest tent caterpillar (FTC; Malacosoma disstria Hübner), an indigenous defoliator. The recent outbreak of FTC (2002–2007) affected 600,000 ha of forest in the northeastern United States and Canada. We assessed the condition of sugar maple trees in 47 North American Maple Project stands in Massachusetts (2006–2007) and Vermont and New York (2007–2008) just after the peak of the FTC outbreak. Mortality was highest in stands with the most crown dieback the previous year (R2 = 0.62, P < 0.001). In addition to drought, cold winter temperatures, and concave microrelief, mortality reflected an interaction of defoliation with soil base cation availability (P = 0.02), with stands defoliated in 2005 that also had low Mg saturation in the A horizon being most likely to suffer high mortality. Sites with above‐average annual sugar maple mortality (>3 or 4%) occurred on soils with low concentrations of Ca (0.31–0.46 cmolc kg−1 in the upper B horizon), Mg (0.06–0.10 cmolc kg−1), and K (0.03–0.05 cmolc kg−1). This work extends the thresholds for these base cations determined by previous research on the Allegheny Plateau to a larger geographic area.

Interspecific hybrid identification of Vitis aestivalis-derived ‘Norton’-based populations using microsatellite markers

The Vitis aestivalis-derived ‘Norton’ is one of the very few commercial red grape varieties that can be grown in regions with high disease pressure and cold temperatures in winter and spring where V. vinifera is difficult to grow. This study began with the objectives of generating interspecific hybrids of Norton and V. vinifera (Cabernet Sauvignon, Pinot Noir, Syrah, and Merlot) in order to combine the disease resistance and cold hardiness characters of V. aestivalis with the excellent wine quality of V. vinifera. Norton grapes were also crossed with the Vitis interspecific hybrid ‘Vignoles’ for the same reason. The true hybrids obtained from all of the crosses were identified using microsatellite markers. A high percentage of hybrids (70–92%) were obtained in all crosses except Norton×Merlot (17%). Results demonstrate the reliability of SSR markers for Norton-based interspecific hybrid identification.

Seasonal Abundance of the CtenophoreMnemiopsis leidyiin Relation to Water Temperature and Other Zooplankton in the Thames River Estuary, Connecticut

I examined seasonal patterns in the abundance of the ctenophore Mnemiopsis leidyi (Atlantic Comb Jelly) to determine whether unusually early ctenophore blooms occur outside the range in which they were originally reported (Narragansett Bay, RI) and whether ctenophore abundance is correlated with sea surface temperature (SST) or with declines in zooplankton prey. Sampling was conducted from 23 April to 16 November 2004 in the Thames River Estuary, CT. Adult (≥1 cm) ctenophores first appeared in the estuary on 20 May 2004, with a seasonal peak in mean (± SD) density (9.9 ± 2.5 individuals m-3, n = 7 stations) and biovolume (26.6 ± 9.9 ml m-3, n = 7 stations) on 9 July 2004. Adult Atlantic Comb Jelly abundance was positively correlated with SST, but only during the spring and early summer. Food availability also likely played an important role in ctenophore-population growth early in the year. However, I observed a delay between copepod density and ctenophore biovolume, possibly due to unusually cold winter temperatures that reduced ctenophore survivorship in the months preceding the study. Ctenophore diets in 2004 consisted primarily of copepods. I observed an inverse correlation between ctenophore biovolume and copepod density, but my data suggest that adult Atlantic Comb Jellies consumed only 0.0–2.2% of the copepod standing stock per day. Overall, my results are consistent with the hypothesis that early summer ctenophore blooms occured over a relatively large spatial scale; however, trophic impacts in the Thames River Estuary in 2004 appeared to be relatively low.

A critical season approach to Allen's rule: bill size declines with winter temperature in a cold temperate environment

AbstractAimBill size is positively correlated with average air temperature in several avian taxa. The conventional explanation for this pattern is that the poorly insulated surface area of the bill functions to dissipate excess heat in hot climates or retain heat in cold climates (Allen's rule). We hypothesize that the applicability of Allen's rule depends upon the season of critical thermal stress, which may vary by location and species. We previously found that bill size increases with high summer temperature in song sparrows (Melospiza melodia) of California, supporting the hypothesis that larger bills are an adaptation to release dry heat and minimize evaporative water loss in a hot, dry environment. Song sparrows in eastern North America face a different climatic regime, in which summers are warm but moist, and winters are cold. We predicted that this climate region would select for smaller bills to minimize heat loss.LocationFrom coastal Delaware and Maryland to the Allegheny Plateau of the eastern USA.MethodsWe measured body size and bill morphology of 274 song sparrow individuals across a climatic gradient and geographical gradient. We used linear regression models to test for effects of geographical location and 30‐year means of minimum winter and maximum summer temperatures and annual rainfall on bill size.ResultsBill size was best predicted by, and positively correlated with, cold winter temperatures and distance from the Atlantic coast. Body size did not change substantially with distance from the coast, indicating that the pattern of bill size was not a result of allometry. Coastal birds had bills larger than predicted by a linear effect of minimum temperature.Main conclusionsCollectively, these results support the hypothesis that variation in bill size reflects selection for winter heat retention rather than for summer heat dissipation. Bill size may be shaped by physiological responses to regional climates, and the season of critical thermal stress may vary geographically, even on relatively small spatial scales.

Spatial analysis of targeted surveillance for screw-worm fly (Chrysomya bezziana or Cochliomyia hominivorax) in Australia.

To assess Australia's targeted surveillance to detect an incursion of screw-worm fly (Chrysomya bezziana). A multi-criteria analysis shell was used to combine data on potential pathways of entry, availability of host species and environmental factors affecting survival of screw-worm fly in order to map spatial variation in the relative likelihood of a screw-worm fly incursion into Australia. Australia's current screw-worm fly surveillance activities were reviewed to determine whether they are located in the areas of highest likelihood of an incursion. Under average environmental conditions, an incursion of screw-worm fly in Australia is relatively more likely to occur along the north coast, down the eastern seaboard or in the south-east. Cold winter temperatures would limit the environmental suitability for screw-worm fly survival to the north and north-east coast and adjacent inland areas. Australia's current targeted surveillance conducted by the Northern Australia Quarantine Strategy program of the Australian Department of Agriculture (adult screw-worm fly trapping and myiasis sampling) correlated well with areas considered to have a high relative likelihood of an incursion of screw-worm fly. Adult fly trapping conducted at sea ports was less well correlated. Changes to surveillance at sea ports are proposed to better target areas considered to have a higher relative likelihood of screw-worm fly incursion. These include increasing the trapping intensity along the north and north-east coasts and shifting surveillance activity from the west coast to the south-east.

Towards an energetic landscape: broad‐scale accelerometry in woodland caribou

Energetic balance is a central driver of individual survival and population change, yet estimating energetic costs in free- and wide-ranging animals presents a significant challenge. Animal-borne activity monitors (using accelerometer technology) present a promising method of meeting this challenge and open new avenues for exploring energetics in natural settings. To determine the behaviours and estimated energetic costs associated with a given activity level, three captive reindeer (Rangifer tarandus tarandus) at the Toronto Zoo were fitted with collars and observed for 53 h. Activity patterns were then measured over 13 months for 131 free-ranging woodland caribou (R. t. caribou) spanning 450,000 km(2) in northern Ontario. The captive study revealed a positive but decelerating relationship between activity level and energetic costs inferred from previous behavioural studies. Field-based measures of activity were modelled against individual displacement, vegetation abundance (Normalized Difference Vegetation Index), snow depth and temperature, and the best fit model included all parameters and explained over half of the variation in the data. Individual displacement was positively related to activity levels, suggesting that broad differences in energetic demands are influenced by variation in movement rates. After accounting for displacement, activity was highest at intermediate levels of vegetation abundance, presumably due to foraging behaviour. Snow depth, probably associated with digging for winter forage, moderately increased activity. Activity levels increased significantly at the coldest winter temperatures, suggesting the use of behavioural thermoregulation by caribou. These interpretations of proximate causal factors should be regarded as hypotheses subject to validation under normal field conditions. These results illustrate the landscape characteristics that increase energetic demands for caribou and confirm the great potential for the use of accelerometry in studies of animal energetics.

Cold and warm air temperature spells during the winter and summer seasons and their impact on energy consumption in urban areas

The main objective of this study is to determine and analyze cold and warm air temperature spells in the last 6 years (2007–2012) and reveal their impact on electrical energy consumption in a small-sized city such as Sombor (Serbia) with less than 50,000 inhabitants. Hourly air temperature values and electrical energy consumption data have been used as database for all methods. Warm and cold temperature spells (during heat and cold waves) have had the increasing tendencies in the last 6 years and they reflect on additional electrical energy consumption. Detailed analysis showed that higher energy demands occur during workdays and daytime period. Monitoring of the amount of consumed energy showed a clear relationship during the winter cold temperature spells, when electrical energy demand was higher than 0.3 MW. In summer period, the relationship was weaker and consumption was higher than 0.15 MW only when temperature exceeded 30 °C. A small number of air condition devices in houses and companies and mainly one-store buildings with thick walls, which make a good insulation from the outside air temperatures, are probably the main reasons for the above-mentioned results in summer. This paper introduces a new method to resolve the problem of short-term load forecasting, based on the support vector machines (SVM) technology and particle swarm optimization that has been used to optimize the SVM parameters. Similar-day-based forecast has shown that similar days for training should be filtered also using classifier of temperature period (cooling degree-days or heating degree-days in a row). Forecasting error is smaller compared to solutions where similar days are found only on season and temperature.

Anther meiosis time is related to winter cold temperatures in apricot (Prunus armeniaca L.)

In temperate woody plants, flowering time is adjusted to the environmental temperature, and survival to cold winter temperatures is achieved through dormancy. But also chilling temperatures during dormancy are required for proper flower bud development and flowering. The time the flower bud remains dormant is both genetically and environmentally controlled, and is a major factor determining the adaptation of species and cultivars to particular ecological conditions because chilling requirements vary greatly among genotypes. Recently this adaptation is jeopardised with climate changing conditions. However, little is known on the biological milestones underpinning these events, and when differences in flowering time are established. In this work we evaluate the hypothesis that anther meiosis time is related to winter cold temperatures, and that differences in flowering time are set up by differences in the time when pollen meiosis occurs. For this purpose, anther development has been characterised in five apricot cultivars with different chilling requirements. The work was done over two years with different weather conditions, a cold and a mild winter. The sporogenous tissues differentiated prior to dormancy and remained in this apparently quiescent stage during the winter. Once chilling requirements were fulfilled, meiosis closely followed and was highly correlated to breaking of endodormancy. Meiosis was completed within one week and was followed by a change in the colour of the anthers from green to yellowish, which could be a useful visual indicator to know that breaking of endodormancy had already occurred. The fact that this sequence of events was consistent in all the cultivars, and different climatic years analysed, supports the hypothesis that winter cold temperatures are related to the time of pollen meiosis, which in turn reflects in different flowering times.

144 INFLUENCE OF REPEATED OVUM PICKUP ON BUFFALO WELFARE

The aim of this work was to evaluate the effect of repeated ovum pickup (OPU) on buffalo welfare. The OPU was carried out as previously described (Neglia et al. 2003 Theriogenology 59, 1123–1130) twice per week on 11 buffalo cows at 121 ± 15 days in milk for 2 months (end of October–end of December). Blood samples were collected before the beginning of the trial (time 0), after 1 month (time 1), and after 2 months (time 2) in animals that had undergone OPU and in control animals (n = 10) of the same herd. The following parameters of clinical immunology were evaluated on sera: haemolytic complement (Arya et al. 1992 Vet. Immunol. Immunopathol. 30, 411–418), lysozyme, bactericidal capacity (Amadori et al. 1997 J. Vet. Med. 44, 321–327), and haptoglobin (Phase Haptoglobin Colourimetric Assay kit, Tridelta Development Ltd., Maynooth, County Kildare, Ireland). Data, here reported as means ± s.e.m., were analysed by ANOVA taking into account treatment, time, and the interaction. The number of aspirated follicles and collected oocytes per buffalo per session was 6.6 ± 0.2 and 3.6 ± 0.2, respectively. Interestingly, the OPU treatment did not affect haptoglobin (a reliable marker of acute stress), lysozyme, complement, and bactericidal capacity, whereas the time influenced (P < 0.05) only the complement. In animals that had undergone OPU, no differences among times 0, 1, and 2 in lysozyme (3.9 ± 0.3, 4.0 ± 0.6, and 3.6 ± 0.4 μg mL–1, respectively), bactericidal capacity (92.8 ± 0.8, 92.1 ± 0.8, and 92.2 ± 0.9%, respectively), and haptoglobin (1.8 ± 0.4, 1.4 ± 0.2, and 1.9 ± 0.6 mg mL–1, respectively) were found. Likewise, similar values were recorded at times 0, 1, and 2 in the control group in lysozyme (3.2 ± 0.3, 2.9 ± 0.3, and 3.1 ± 0.8 μg mL–1, respectively), bactericidal capacity (94.2 ± 0.6, 93.0 ± 1.1, and 89.2 ± 3.2%, respectively), and haptoglobin (0.7 ± 0.5, 1.3 ± 0.5, and 1.4 ± 0.4 mg mL–1, respectively). A significant decrease (P < 0.05) of complement (UE/150 mL) in OPU-treated animals was recorded at times 1 (33.6 ± 1.4) and 2 (35.9 ± 2.9) compared to time 0 (67.3 ± 3.3). However, the same pattern was observed in the control (62.8 ± 4.0, 31.3 ± 0.3, and 31.0 ± 0.8, respectively at times 0, 1, and 2; P < 0.05). Therefore, it is not possible to rule out that the decrease was due to other factors, such as the cold winter temperatures incoming, as previously reported. Furthermore, the values recorded at times 1 and 2 fall in the physiological ranges of the species (De Carlo et al. 2011 Joint Annual Meeting, Riccione, Italy). During the whole period of the experiment (and few weeks after), there were neither signs of behavioural modifications nor clinical signs of any disease. Furthermore, there were no differences in average daily milk production between treated and control buffaloes both at the start (9.1 ± 0.8 v. 9.4 ± 0.8) and at the end of the trial (7.6 ± 0.6 v. 6.5 ± 0.7), and all the animals that had undergone OPU conceived within 113.0 ± 25.4 days from the last OPU session. These preliminary results indicate that a regimen of OPU carried out twice per week for 2 months do not affect the welfare of buffaloes.

Observations of ammonia, nitric acid, and fine particles in a rural gas production region

Continuous measurements of the atmospheric trace gases ammonia (NH3) and nitric acid (HNO3) and of fine particle (PM2.5) ammonium (NH4+), nitrate (NO3−) and sulfate (SO42−) were conducted using a denuder/filter system from December 2006 to December 2011 at Boulder, Wyoming, a region of active gas production. The average five year concentrations of NH3, HNO3, NH4+, NO3− and SO42− were 0.17, 0.19, 0.26, 0.32, and 0.48 μg m−3, respectively. Significant seasonal patterns were observed. The concentration of NH3 was higher in the summer than in other seasons, consistent with increased NH3 emissions and a shift in the ammonium nitrate (NH4NO3) equilibrium toward the gas phase at higher temperatures. High HNO3 concentrations were observed both in the summer and the winter. Elevated wintertime HNO3 production appeared to be due to active local photochemistry in a shallow boundary layer over a reflective, snow-covered surface. PM2.5 NH4+ and SO42− concentrations peaked in summer while NO3− concentrations peaked in winter. Cold winter temperatures drive the NH3–HNO3–NH4NO3 equilibrium toward particulate NH4NO3. A lack of NH3, however, frequently results in substantial residual gas phase HNO3 even under cold winter conditions.

Wine Grape Cultivar Performance in the Four Corners Region of New Mexico in 2010–12

Commercial wine grape (Vitis sp.) production in northwestern New Mexico and the greater Four Corners region is now supported by four wineries. The challenges of growing grape vines in northwestern New Mexico include cold winter temperatures and killing spring frosts exacerbated by a semiarid climate and elevations exceeding 1700 m. Nineteen nongrafted European wine grape (Vitis vinifera) and interspecific hybrid wine grape cultivars were planted in 2007 and evaluated between 2010 and 2012. Among European wine grape cultivars, Agria, Malbec, Sangiovese, Viognier, Müller-Thurgau, and Sauvignon Blanc performed poorly or failed altogether. Interspecific hybrid cultivars Baco Noir, Kozma 55, Leon Millot, Chardonel, Seyval Blanc, Siegfried, Traminette, Valvin Muscat, and Vidal Blanc showed greater adaptability to a high-elevation intermountain western U.S. site, yielding on greater than 71% of their vines in each year (except Kozma 55 which only produced on 38% of its vines in 2012 due to severe spring frost damage). We speculate that fruit-bearing shoots on these vines arose from latent buds that survived when primary buds were killed from spring frost events. Once vines were established, grape berry sugar and pH appeared to be within acceptable ranges (3-year mean above 21% soluble solids and juice pH of 3.2), suggesting regional potential to produce favorable wines within acceptable commercial wine grape production ranges. Selection of sites without considerable frost risk and other mesoclimate variances is critical when considering vineyard establishment at high-elevation locations.

The contribution of cold winter temperatures to the 2003 alewife population collapse in Lake Huron

The Lake Huron ecosystem has recently undergone dramatic changes. As part of those changes, the once highly abundant non-native alewife Alosa pseudoharengus population crashed in 2003 and has yet to recover. The purpose of this study was to evaluate whether temperature played a role in the population crash, because historically alewife have been subject to die-off events in response to cold temperatures in other lakes. Long-term climate data (1973–2009) showed that the winter of 2002–2003 exhibited the largest drop in degree days relative to the previous year, had the most extensive average March ice coverage, and was among the coldest years on record. However, since 2003, winter temperatures have not been overly cold, and air temperature has shown an increasing trend. Also, the relationship between temperature and alewife abundance between 1975 and 2006 was non-significant. Therefore, although we found evidence that cold winter temperatures contributed to the abrupt decline of alewife in 2003, they could not explain why the population failed to recover as it had after previous cold winters. Historically, Chinook salmon abundance contributed to long-term trends in alewife abundance, however, we found predation by Chinook to play a lesser role on the 2003 alewife collapse. In the absence of direct estimates of food availability, analyses of alewife length data suggest that a declining prey base altered the ecosystem conditions for alewife, possibly contributing to their collapse and lack of recovery.

Seed Burial Physical Environment Explains Departures from Regional Hydrothermal Model of Giant Ragweed (Ambrosia trifida) Seedling Emergence in U.S. Midwest

Robust predictions of weed seedling emergence from the soil seedbank are needed to aid weed management. A common seed accession (Illinois) of giant ragweed was buried in replicate experimental gardens over 18 site years in Illinois, Michigan, Kansas, Nebraska, Ohio, and South Dakota to examine the importance of site and climate variability by year on seedling emergence. In a nonlinear mixed-effects modeling approach, we used a flexible sigmoidal function (Weibull) to model giant ragweed cumulative seedling emergence in relation to hydrothermal time accumulated in each site-year. An iterative search method across a range of base temperature (Tb) and base and ceiling soil matric potentials (ψband ψc) for accumulation of hydrothermal time identified optima (Tb= 4.4 C, ψb= −2,500 kPa, ψc= 0 kPa) that resulted in a parsimonious regional model. Deviations between the fits for individual site-years and the fixed effects regional model were characterized by a negative relationship between random effects for the shape parameterlrc(natural log of the rate constant, indicating the speed at which emergence progressed) and thermal time (base 10 C) during the seed burial period October through March (r= −0.51, P = 0.03). One possible implication of this result is that cold winter temperatures are required to break dormancy in giant ragweed seeds. By taking advantage of advances in statistical computing approaches, development of robust regional models now is possible for explaining arable weed seedling emergence progress across wide regions.

Simulated Arctic atmospheric feedbacks associated with late summer sea ice anomalies

The coupled regional climate model HIRHAM‐NAOSIM is used to investigate feedbacks between September sea ice anomalies in the Arctic and atmospheric conditions in autumn and the subsequent winter. A six‐member ensemble of simulations spanning the period 1949–2008 is analyzed. The results show that negative Arctic sea ice anomalies are associated with increased heat and moisture fluxes, decreased static stability, increased lower tropospheric moisture, and modified baroclinicity, synoptic activity, and atmospheric large‐scale circulation. The circulation changes in the following winter display meridionalized flow but are not fully characteristic of a negative Arctic Oscillation pattern, though they do support cold winter temperatures in northern Eurasia. Internally generated climate variability causes significant uncertainty in the simulated circulation changes due to sea ice‐atmosphere interactions. The simulated atmospheric feedback patterns depend strongly on the position and strength of the regional sea ice anomalies and on the analyzed time period. The strongest atmospheric feedbacks are related to sea ice anomalies in the Beaufort Sea. This work suggests that there are complex feedback mechanisms that support a statistical link between reduced September sea ice and Arctic winter circulation. However, the feedbacks depend on regional and decadal variations in the coupled atmosphere‐ocean‐sea ice system.

The riddle of the sands: how population dynamics explains causes of high bivalve mortality

Summary Large‐scale bivalve mortalities in estuarine and coastal habitats are a major environmental and economic concern. They may have obvious causes such as extremely cold winter temperatures, but in the absence of an apparent chain of cause and effect, a rigorous, objective approach is needed to define a probable set of factors responsible for such mortalities. This study interrogates recurrent mortalities of the cockle Cerastoderma edule L. in the Burry Inlet (South Wales, UK), where the causes of the observed die‐offs were obscure. Spatial and temporal patterns in cockle population dynamics were analysed to determine whether mortalities were episodic or continuous, and related to cockle density. Laboratory survival experiments complemented the field studies to indicate the fitness of the cockles. The population dynamics of other species were studied to test for environmental disturbances affecting the entire benthic community. High cockle mortalities occurred throughout the estuary in a specific cohort, namely 1‐year‐old cockles after their first winter. The mortalities did not appear to be episodic, but happened over the spring to early summer months. Cockle densities played a minor role in the decline. The laboratory experiments showed that cockles from the Burry Inlet had higher survival rates than those collected from other areas at early life stages (0‐year class). However, by the time they reached the end of their first year (1‐year class), their survival rates declined significantly. Results suggested a physiological weakness in the cohort after the first winter. Other benthic species did not suffer unusual mortalities. Synthesis and applications. We emphasize that (i) interrogating patterns in population dynamics allows us to limit the number of likely causes of high bivalve mortality and generate more specific hypotheses; (ii) extending studies to other benthic species indicates the likelihood of environmental problems that affect the entire ecosystem; (iii) joined‐up field and laboratory studies suggested that probable causes of cockle mortality were primarily species‐, or even cohort‐specific, biological factors; and (iv) well‐designed monitoring systems will indicate the population dynamics of the target species on spatio‐temporal scales suitable for assessing shifts in the populations, such as unexpected extirpation.

Evaluation of Near-Surface Parameters in the Two Versions of the Atmospheric Model in CESM1 using Flux Station Observations

Abstract This paper describes the performance of the Community Atmosphere Model (CAM) versions 4 and 5 in simulating near-surface parameters. CAM is the atmospheric component of the Community Earth System Model (CESM). Most of the parameterizations in the two versions are substantially different, and that is also true for the boundary layer scheme: CAM4 employs a nonlocal K-profile scheme, whereas CAM5 uses a turbulent kinetic energy (TKE) scheme. The evaluation focuses on the diurnal cycle and global observational and reanalysis datasets are used together with multiyear observations from 35 flux tower sites, providing high-frequency measurements in a range of different climate zones. It is found that both model versions capture the timing of the diurnal cycle but considerably overestimate the diurnal amplitude of net radiation, temperature, wind, and turbulent heat fluxes. The seasonal temperature range at mid- and high latitudes is also overestimated with too warm summer temperatures and too cold winter temperatures. The diagnosed boundary layer is deeper in CAM5 over ocean in regions with low-level marine clouds as a result of the turbulence generated by cloud-top cooling. Elsewhere, the boundary layer is in general shallower in CAM5. The two model versions differ substantially in their representation of near-surface wind speeds over land. The low-level wind speed in CAM5 is about half as strong as in CAM4, and the difference is even larger in areas where the subgrid-scale terrain is significant. The reason is the turbulent mountain stress parameterization, only applied in CAM5, which acts to increase the surface stress and thereby reduce the wind speed.