Devon Island Research Articles

Field testing of visual odometry aided by a sun sensor and inclinometer

AbstractIn this paper, we present a novel approach to planetary rover localization that incorporates sun sensor and inclinometer data directly into a stereo visual odometry pipeline. Utilizing the absolute orientation information provided by the sun sensor and inclinometer significantly reduces the error growth of the visual odometry path estimate. The measurements have very low computation, power, and mass requirements, providing localization improvement at nearly negligible cost. We describe the mathematical formulation of error terms for the stereo camera, sun sensor, and inclinometer measurements, as well as the bundle adjustment framework for determining the maximum likelihood vehicle transformation. Extensive results are presented from experimental trials utilizing data collected during a 10‐km traversal of a Mars analogue site on Devon Island in the Canadian high Arctic. We also illustrate how our approach can be used to reduce the computational burden of visual odometry for planetary exploration missions. © 2012 Wiley Periodicals, Inc.

Over-Winter Oceanographic Profiles in Jones Sound, Canadian Arctic Archipelago, November 1961 – June 1962: Temperature, Salinity, Oxygen, and Nutrients

Vertical profiles of temperature, salinity, dissolved oxygen, and inorganic nutrients (nitrate, phosphate, and silicate) were measured at five depths (2, 10, 25, 50, and 80 m) beneath the ice off the southern shore of Jones Sound, north of Devon Island, through the winter of 1961 – 62. Additional data were collected from the north side of the sound off Grise Fiord, Ellesmere Island, on 13 May 1962 and 12 May 1969. The over-winter data set is used here to characterize the transition of Arctic waters from autumn to late-spring–early summer. Minimum temperatures (< -1.8˚C) and maximum salinities (> 33.2) were reached in late winter and early spring. Oxygen levels declined over the same fall-to-late-spring period and increased markedly in June. Nitrate, phosphate, and silicate concentrations all increased from their lowest values in fall to overall highest values in late spring, after which each nutrient showed evidence of biological uptake. A deep pycnocline, between 50 and 80 m, persisted from November to February, isolating a bottom-water layer that showed evidence of microbially mediated silicate regeneration (silicate concentrations increased, phosphate decreased, and nitrate concentrations were variable). In early spring (19 March to 1 May), nitrate concentrations dropped abruptly at all depths from more than 10 μM to less than 7 μM, apparently in response to the growth of ice algae. Temperature-salinity (T-S) analyses found little evidence of significant water-mass replacements during the study period, but interpretations of coherent variations in nutrient concentrations, as well as observed salinities slightly different from those expected on the basis of ice formation, suggest otherwise. Comparison of results from north of Devon Island with those from sampling off Grise Fiord in May 1962 indicate both higher salinities and lower nutrient concentrations at the latter site; however, data collected at the same site off Grise Fiord in May 1969 showed lower salinities and more variable nutrient concentrations than in 1962.

Effects of Seabird Vectors on the Fate, Partitioning, and Signatures of Contaminants in a High Arctic Ecosystem

Seabirds bioaccumulate contaminants from prey, transport them to their nesting sites, and deposit them in their excreta and carcasses, thereby focusing marine-derived contaminants into remote, terrestrial receptor sites. In the case of organochlorine chemicals transported by northern fulmars (Fulmarus glacialis) to a High Arctic seabird colony on Devon Island, Nunavut, Canada (76°13'N, 89°14'W), this contaminant pathway dominates all others. In freshwater ponds below the nesting cliffs, concentrations of organochlorine contaminants characteristic of fulmar input were 2- to 45-fold higher in sediments and water (depending on seabird input to the particular pond) than in ponds remote from the colony. Air-water fugacity quotients for the ponds decreased with seabird input, indicating that fulmar contaminant input shifts air-water partitioning to increasingly favor volatilization to air. Although contaminant evasion from water was favored, direct evidence of it was not detected in air samples. For PCBs, congener profiles of pond sediments or water became more similar to seabird sources as seabird input increased, and less similar to air profiles. Based on measurements of contaminants in fulmars and other local environmental media, this study presents the first application of fugacities and multivariate source apportionment statistics to resolve seabird biological vectors.

Shock-induced changes in density and porosity in shock-metamorphosed crystalline rocks, Haughton impact structure, Canada

Abstract– Shock metamorphism can occur at transient pressures that reach tens of GPa and well over 1000 °C, altering the target material on both megascopic and microscopic scales. This study explores the effects of shock metamorphism on crystalline, quartzofeldspathic basement material from the Haughton impact structure on Devon Island, Arctic Canada. Shock levels were assigned to samples based on petrographic examination of main mineral phases. Conventional shock classification schemes proved to incompletely describe the Haughton samples so a modified shock classification system is presented. Fifty-two crystalline bedrock samples from the clast-rich impact melt rocks in the crater, and one reference site outside of the crater, were classified using this system. The shock levels range from 0 to 7 (according to the new shock stage classification proposed here, i.e., stages 0–IV after the Stoffler classification), indicating shock pressures ranging from 0 to approximately 80 GPa. The second aspect of this study involved measuring bulk physical characteristics of the shocked samples. The bulk density, grain density, and porosity were determined using a water displacement method, a bead displacement method, and a Hepycnometer. Results suggest a nonlinear, negative correlation between density and shock level such that densities of crystalline rocks with original densities of approximately 3 g cm−3 are reduced to <1.0 g cm−3 at high shock levels. The results also show a positive nonlinear correlation between porosity and shock level. These data illustrate the effect of shock on the bulk physical characteristics of crystalline rocks, and has implications for assessing the habitability of shocked rocks.

PCB and organochlorine pesticides in northern fulmars (Fulmarus glacialis) from a High Arctic colony: Chemical exposure, fate, and transfer to predators

Organochlorine contaminant concentrations, associated fugacities, and stable isotopes of nitrogen (δ(15) N) are reported for liver, whole body homogenate, and opportunistically collected samples of prey (amphipods), stomach oils, digestive tract contents, and guano for northern fulmars (Fulmarus glacialis) collected at Cape Vera, Devon Island in the Canadian High Arctic. Liver concentrations of polychlorinated biphenyls (ΣPCB) and ΣDDT were on average 49.9 ± 35.4 ng g(-1) and 29.9 ± 25.2 ng g(-1) wet weight, respectively. Whole body homogenate concentrations of ΣPCB and ΣDDT were 637 ± 293 ng g(-1) and 365 ± 212 ng g(-1) wet weight, respectively. A mass and energy balance showed that whole body contaminant concentrations, which are seldom reported for Arctic seabirds, are critical in determining contaminant exposure and associated risk to predators such as the Arctic fox (Alopex lagopus). Biomagnification in the fulmars is evident, because concentrations and fugacities of contaminants were generally one to three orders of magnitude higher than those of likely prey items. The fate of diet-derived contaminants along the digestive tract is discussed, in particular with respect to stomach oils, which are used to feed chicks and for defensive purposes. The benefits of considering both concentrations and fugacities are demonstrated and provide information on the absorption and distribution of chemicals within the fulmars and contaminant transfer to offspring and predators.

Weathering of Post-Impact Hydrothermal Deposits from the Haughton Impact Structure: Implications for Microbial Colonization and Biosignature Preservation

Meteorite impacts are among the very few processes common to all planetary bodies with solid surfaces. Among the effects of impact on water-bearing targets is the formation of post-impact hydrothermal systems and associated mineral deposits. The Haughton impact structure (Devon Island, Nunavut, Canada, 75.2 °N, 89.5 °W) hosts a variety of hydrothermal mineral deposits that preserve assemblages of primary hydrothermal minerals commonly associated with secondary oxidative/hydrous weathering products. Hydrothermal mineral deposits at Haughton include intra-breccia calcite-marcasite vugs, small intra-breccia calcite or quartz vugs, intra-breccia gypsum megacryst vugs, hydrothermal pipe structures and associated surface "gossans," banded Fe-oxyhydroxide deposits, and calcite and quartz veins and coatings in shattered target rocks. Of particular importance are sulfide-rich deposits and their associated assemblage of weathering products. Hydrothermal mineral assemblages were characterized structurally, texturally, and geochemically with X-ray diffraction, micro X-ray diffraction, optical and electron microscopy, and inductively coupled plasma atomic emission spectroscopy. Primary sulfides (marcasite and pyrite) are commonly associated with alteration minerals, including jarosite (K,Na,H(3)O)Fe(3)(SO(4))(2)(OH)(6), rozenite FeSO(4)·4(H(2)O), copiapite (Fe,Mg)Fe(4)(SO(4))(6)(OH)(2)·20(H(2)O), fibroferrite Fe(SO(4))(OH)·5(H(2)O), melanterite FeSO(4)·7(H(2)O), szomolnokite FeSO(4)·H(2)O, goethite α-FeO(OH), lepidocrocite γ-FeO(OH) and ferrihydrite Fe(2)O(3)·0.5(H(2)O). These alteration assemblages are consistent with geochemical conditions that were locally very different from the predominantly circumneutral, carbonate-buffered environment at Haughton. Mineral assemblages associated with primary hydrothermal activity, and the weathering products of such deposits, provide constraints on possible microbial activity in the post-impact environment. The initial period of active hydrothermal circulation produced primary mineral assemblages, including Fe sulfides, and was succeeded by a period dominated by oxidation and low-temperature hydration of primary minerals by surface waters. Active hydrothermal circulation can enable the rapid delivery of nutrients to microbes. Nutrient availability following the cessation of hydrothermal circulation is likely more restricted; therefore, the biological importance of chemical energy from hydrothermal mineral deposits increases with time. Weathering of primary hydrothermal deposits and dissolution and reprecipitation of mobile weathering products also create many potential habitats for endolithic microbes. They also provide a mechanism that may preserve biological materials, potentially over geological timescales.

Sun Sensor Navigation for Planetary Rovers: Theory and Field Testing

In this paper, we present an experimental study of sun sensing as a rover navigational aid. Algorithms are outlined to determine rover heading in an absolute reference frame. The sensor suite consists of a sun sensor, inclinometer, and clock (as well as ephemeris data). We describe a technique to determine ground-truth orientation in the field (without using a compass) and present a large number of experimental results (both in Toronto and on Devon Island) showing our ability to determine absolute rover heading to within a few degrees.

Recent melt rates of Canadian arctic ice caps are the highest in four millennia

There has been a rapid acceleration in ice-cap melt rates over the last few decades across the entire Canadian Arctic. Present melt rates exceed the past rates for many millennia. New shallow cores at old sites bring their melt series up-to-date. The melt-percentage series from the Devon Island and Agassiz (Ellesmere Island) ice caps are well correlated with the Devon net mass balance and show a large increase in melt since the middle 1990s. Arctic ice core melt series (latitude range of 67 to 81 N) show the last quarter century has had the highest melt in two millennia and The Holocene-long Agassiz melt record shows that the last 25years has the highest melt in 4200years. The Agassiz melt rates since the middle 1990s resemble those of the early Holocene thermal maximum over 9000years ago.

Historical seabird population dynamics and their effects on Arctic pond ecosystems: a multi-proxy paleolimnological study from Cape Vera, Devon Island, Arctic Canada

Rapid environmental changes occurring in polar regions may pose a signifi cant threat to the ~10 mil- lion seabirds currently inhabiting the Canadian Arctic. However, a paucity of long-term data on seabird population dynamics makes effective management diffi cult. As top predators in the oceanic pelagic foodweb, seabirds provide marine-derived nutrients to freshwater habitats via their guano, causing trophic cascades that may be tracked using paleolimnological techniques. Diatoms (Bacillariophyceae) are the most commonly used bioindicators in paleolim- nological studies and, because they are known to respond sensitively to changes in trophic status, may be effective proxies for tracking changes in seabird population dynamics. Here, we present diatom data obtained from sediment cores in seabird-affected ponds near Cape Vera, Devon Island, High Arctic Canada. We also report on additional sedimentary proxies that can be used to track seabird infl uence, namely stable isotopes of nitrogen (δ 15 N) and

Sleep Stability and Cognitive Function in an Arctic Martian Analogue

Human performance is affected by sleep disruption and sleep deprivation can critically affect mission outcome in both spaceflight and other extreme environments. In this study, the seven-person crew (four men, three women) lived a Martian sol (24.65 h) for 37 d during a long-term stay at the Flashline Mars Arctic Research Station (FMARS) on Devon Island, Canada. Crewmembers underwent cardiopulmonary monitoring for signs of circadian disruption and completed a modified Pittsburgh Sleep Diary to monitor subjective fatigue. Crewmembers underwent cognitive testing to identify the effects, if any, of sleep disruption upon cognitive skill. A Martian sol was implemented for 37 d during the Arctic mission. Each crewmember completed an adapted version of the Pittsburgh Sleep Diary in tandem with electrocardiograph (ECG) cardiopulmonary monitoring of sleep by the Cardiac Adapted Sleep Parameters Electrocardiogram Recorder (CASPER). Crewmembers also underwent cognitive testing during this time period. Sleep diary data indicate improvement in alertness with the onset of the sol (fatigue decreasing from 5.1 to 4.0, alertness increasing from 6.1 to 7.0). Cardiopulmonary data suggest sleep instability, though trends were not statistically significant. Crewmember decision speed time scores improved from pre-Mars to Mars (average improving from 66.5 to 84.0%), though the remainder of cognitive testing results were not significant. While subjective data demonstrate improved sleep and alertness during the sol, objective data demonstrate no significant alteration of sleep patterns. There was no apparent cognitive decline over the course of the mission.

Field testing of a rover guidance, navigation, and control architecture to support a ground-ice prospecting mission to Mars

This paper provides an overview of a rover guidance, navigation, and control (GN&C) architecture being developed to support a ground-ice prospecting mission to Mars. The main contribution of this paper is to detail an integrated field campaign that demonstrates the viability of the key rover GN&C techniques needed to carry out this mission. Tests were conducted on Devon Island in the Canadian High Arctic during the summer of 2009, wherein a large field robot was driven on real polygonal terrain (a landform of interest on Mars). Lessons learned and recommendations for future work are provided.

Spatial Variability of the Dominant Climate Signal in &lt;i&gt;Cassiope tetragona&lt;/i&gt; from Sites in Arctic Canada

&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;Our study investigates the nature of the climate signal in three populations of the Arctic dwarf-shrub &lt;em&gt;Cassiope tetragona &lt;/em&gt;using dendrochronological and stable isotope analysis techniques. We present 15 new &lt;em&gt;C. tetragona &lt;/em&gt;chronologies from three sites (Axel Heiberg, Bathurst, and Devon islands) in the eastern Canadian Arctic, of which three are the first continuous stable carbon isotope ratio (δ¹³C) time series developed for Arctic shrubs. Correlation and multivariate regression analyses revealed that multiple and different climate factors influenced the chronologies within and between the three sites. At the Axel Heiberg Island site, the dominant climatic influences over annual stem elongation were previous year (t-1) and current year (t) summer precipitation, while annual production of flower buds was influenced by (t) winter precipitation and spring temperature. At Bathurst Island, annual production of flower buds responded to (t-1) growing season sunshine hours and winter precipitation and to (t) late growing season temperature and moisture availability. Our analysis of the Axel &lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: black;"&gt;H&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;eiberg and Bathurst Island models revealed the positive influence on δ&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;13&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;C values of (t-1) winter temperature—and on &lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: black;"&gt;B&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;athurst Island only, of (t-1) spring sunshine hours. The combined influence of these parameters on spring moisture availability suggests that the δ&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;13&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;C ratios varied in response to stomatal conductance. At Devon Island, the δ&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;13&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;C values varied in response to (t) and (t-1) spring and summer temperature and spring and fall solar radiation, which in turn influence the rate of photosynthesis. Our study supports the emerging hypothesis that Arctic shrubs are sensitive to climate. &lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: black;"&gt;H&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;owever, strong spatial variation in plant-climate response characterized our sampling sites. &lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: black;"&gt;T&lt;/span&gt;&lt;span style="font-family: 'Times New Roman'; color: #221e1f;"&gt;his variation may be linked to site sensitivity, or regional climate variability due to geographic and topographic differences, or both. &lt;/span&gt;

A high latitude hesperornithiform (Aves) from Devon Island: palaeobiogeography and size distribution of North American hesperornithiforms

A new hesperornithiform bird specimen from Devon Island in the Canadian High Arctic is represented by three cervical vertebrae and is assigned to Canadaga arctica. The new specimen is only the second occurrence of C. arctica and corresponds in morphology and size to the type specimen from Bylot Island, also in the High Arctic. This new fossil adds to the record of North American hesperornithiforms, which had a well-documented Arctic presence. Body size comparisons of all North American specimens from the Campanian reveal that the largest known hesperornithiforms were from high latitudes, but otherwise no clear correlation between body size and latitude is apparent. The largest hesperornithiforms (Canadaga arctica and Heperornis regalis) are found at the highest latitudes, while the smallest forms (Baptornis advenus and Parahesperornis alexi) are found at the southern extent of the birds’ range. Coniornis (a medium body-sized genus) is only found in the middle of the range. No size trends are discernable within the genus Hesperornis or within the species H. regalis. The presence of large hesperornithiforms at high latitudes may indicate that either strong seasonal distribution of resources contributed to larger body sizes at higher latitudes, or Campanian thermal gradients along the Western Interior Seaway were significant enough to affect body size for thermoregulatory reasons (sensu Bergmann's rule). The absence of body size trends within mid-latitude Hesperornis specimens suggests that the climatic gradient in the southern portion of the Seaway was not strong enough to force morphological evolutionary responses, or that character displacement, migration and/or other factors affected body size. Sample size and the inherent problems of an incomplete fossil record must also be considered.

Endorhizal Fungi Associated with Vascular Plants on Truelove Lowland, Devon Island, Nunavut, Canadian High Arctic

Truelove Lowland on Devon Island, Nunavut (75°N), has long been investigated for its flora, fauna, and microbiota. Unlike ectomycorrhizae, endomycorrhizal interactions have been described as sparse or absent in this High Arctic environment. To probe this observation, samples of roots and associated soils (55 plants in total) from 10 genera in 9 families were collected during July 2006. Fungi growing within these roots were visualized using our high-sensitivity lactofuchsin epifluorescence method. Fungal colonization within plant roots (collectively, endorhizal fungi) was assessed with our quantitative microintersect method. Of the 3988 intersections assessed at 400× total magnification, only 154 lacked fungi. Most colonization was by septate endophytes (average abundance 66%, range 13–100%), and fine endophytes (average abundance 48%, range 0–100%). Endorhizal morphology in Dryas and Saxifraga roots typically consisted of thin extraradical hyphae that formed a sheath and grew between and within root cortical cells, resembling ericoid or ectendomycorrhizae. Soil in which the Truelove plants had grown, which had been stored at −20 °C, was planted with wheat seeds. After 10 weeks, fungal colonization of these roots was 35–100%. Endorhizal fungi are typically present in roots of plants living on Devon Island tundra.

Olenelloid trilobites from Cambrian Series 2 of Devon Island, Nunavut, Arctic Canada

Four species of olenelloid trilobites characterized by advanced or robust genal spines are described from the lower Cambrian Rabbit Point Formation (Cambrian Series 2, Stage 4) of eastern Devon Island, representing the most diverse assemblage of olenelloids yet described from Arctic Canada. New taxa: Bristolia kurtzi n. sp., Paranephrolenellus cowiei n. sp., Siciliolenellus fritzi n. gen. and n. sp.

Taxonomic composition, paleoecology and biostratigraphy of Late Cretaceous diatoms from Devon Island, Nunavut, Canadian High Arctic

Upper Cretaceous sediments of the Kanguk Formation exposed in Eidsbotn and Viks Fiord grabens on Devon Island, Nunavut, Canadian High Arctic, yielded 91 fossil marine diatom species and varieties (including indeterminate taxa), representing 41 genera. Excellent preservation of the assemblages was aided by shallow burial, protection in downfaulted linear grabens, and the presence of abundant volcanic material. Planktonic species and resting spores comprise nearly 70% of the diatom assemblage, and provided abundant food resources for the Late Cretaceous Arctic ecosystem. Deposition of the approximately 225 m-thick stratigraphic sequence was predominantly in a shallow marine neritic setting, with an upward progression to interbedded terrestrial deposits of the Expedition Fiord Formation, reflecting a regression and eventual persistence of terrestrial facies into the Early Cenozoic. The Kanguk Formation is widespread across the Canadian Arctic, and diatom biostratigraphy indicates a Santonian–Campanian age for the sequences reported herein, based on the presence of Gladius antiquus in the lowermost strata and occurrence of Costopyxis antiqua throughout the succession. However, Amblypyrgus sp. A and Archepyrgus sp. aff. A. melosiroides, encountered in the lower part of the succession, are known exclusively from the Lower Cretaceous. This may suggest a slightly older age. New information on shallow shelf diatom assemblages from this study is compared to reports on two other Late Cretacous Arctic diatom assemblages. These three sites represent an environmental transect from shallow to distal shelf settings and into the oceanic realm.

Chironomid assemblages from seabird-affected High Arctic ponds

Seabirds can shunt nutrients and contaminants from marine to terrestrial ecosystems by forming dense breeding colonies and releasing wastes to these sites. A large colony of seabirds at Cape Vera (Devon Island, High Arctic Canada) has resulted in eutrophic conditions and potentially toxic concentrations of sedimentary metals in several freshwater ponds that drain their nesting sites. Here, we investigated the effects of elevated nutrient and sedimentary metal concentrations on the distribution of subfossil chironomids in surface sediments from 21 ponds that span a gradient of seabird influence. Although many ponds registered high nutrient concentrations (e.g., mean TP = 45 μg l −1), eutrophic taxa typical of temperate waters were not common, with most assemblages being dominated by morphotypes of Psectrocladius and Tanytarsina, as well as Corynoneura arctica-type, and Metriocnemus hygropetricus-type. Although the ponds within and outside the area influenced by seabirds contained largely similar taxa, variations did exist in the relative abundances of the different species. Lakewater pH was the only measured environmental variable that explained statistically significant amounts of variation in the chironomid assemblages. Although direct effects of pH on chironomids cannot be ruled out, pH is likely tracking production-related changes driven by limnetic dissolved inorganic carbon dynamics. Sediment cores collected from seabird-affected and seabird-free ponds showed a greater number of chironomid taxa and higher head capsule abundances in the pond receiving seabird inputs. Chironomid assemblages in both cores recorded increased abundances in recent decades, likely in response to warmer conditions and lengthened growing seasons.

Cooling and Warming of Climate of the Earth’s Northern Hemisphere (On the Basis of Fluctuations of the Oxygen Isotope Δ18O and Dendrological Data)

Abstract Content fluctuations of the oxygen isotope δ18O in the Devon Island ice core during the last 100 000 years are a measure of climate fluctuations in the Northern Hemisphere. The course of content of the oxygen isotope δ18O and the sums of solar radiation reaching the upper edge of the atmosphere are characterized by approximate minima and maxima (by positive correlation). This proves that, during the last hundred thousand years, climate fluctuations (cooling and warming) in the Northern Hemisphere were conditioned by long-term changes of the orbit and altitude of the Earth’s axis. Climate fluctuation forecasts for the Northern Hemisphere were developed for the next 40 000 years on the basis of the established periods of change of the oxygen isotope δ18O and the known solar radiation periodicity. Climate changes in Europe during the last 25000 years were presented together with a forecast for 1000 years (according to organic substances in deposits and radiation) as well as climate changes in Europe in the period from -500 years BP to 2100 AD (according to δ18O and pine tree-rings). It showed that climate changes depended on the concentration of planet mass in relation to the ecliptic plane (from the gravitational impact of planets on the Sun). Concentration courses of planet mass in the Solar System and climate fluctuations in the Northern Hemisphere were compared. Of interest are examples of synchronic fluctuations, i.e. dispersal of planet mass in the Solar System, the widths of pine and spruce tree rings and air temperatures in Europe.

Unusual assemblages of Late Cretaceous silicoflagellates from the Canadian Archipelago

Devon and Ellef Ringnes islands in the Canadian Arctic Archipelago contain well-preserved Santonian through early Campanian silicoflagellates. These occur in three unusual assemblages, which comprise three biostratigraphic zones. The oldest, the Vallacerta tumidula Partial Range Zone of Santonian age, contains an extremely variable microflora that includes species of the poorly-known genus Variramus, two new species of Cornua, and a new genus Umpiocha. The Schulzyocha ruppelii Range Zone of early Campanian age includes several species of the new genus Schulzyocha, reflecting quadrate silicoflagellate skeletal morphologies that lack a basal structure. The youngest assemblage includes the poorly-known species Cornua trifurcata, the nominative taxon of the C. trifurcata Partial Range Zone (proposed by McCartney et al., in press c; emended herein), which allows a correlation with a silicoflagellate-bearing sequence from the Horton River area, Northwest Territories of Canada. This report presents information on 24 silicoflagellate taxa, proposes 2 new genera, Schulzyocha and Umpiocha, and describes 13 new species and 1 new combination. All of these new taxa disappear by the top of the Campanian Cornua trifurcata Partial Range Zone. These assemblages reveal a new history of silicoflagellate evolution prior to the late Campanian, the period from which most of our prior knowledge about Cretaceous silicoflagellates was derived. The assemblages show progressive change from skeletons with highly variable morphologies to more stable silicoflagellate skeletal geometry. Two important Corbisema species, C. apiculata and C. archangelskiana, appear to be derived from separate lines within Cornua in the latest Santonian and early Campanian. The important Cretaceous genus Lyramula makes its first appearance at the beginning of the Campanian.

BLOCHIA AND NIKOLAEVIA: NEW CRETACEOUS DIATOM GENERA RELATED TO STELLARIMA HASLE & SIMS

Two new genera of fossil diatoms, Blochia gen. nov. and Nikolaevia gen. nov., are proposed from Kanguk Formation (Upper Cretaceous) outcrops on Devon Island, Canadian Arctic margin. Both genera display morphological features suggesting a relationship with Stellarima Hasle & Sims. Nikolaevia is unusual in having an external opening of the rimoportula in the form of an arcuate canal. Blochia is a genus of large diatoms that are ornamented with spines, and bear a centrally positioned rimoportula with a prominent external tube. Inferred vegetative and resting stages are presented for Nikolaevia symbolica sp. nov., while Blochia magna sp. nov. is considered a resting spore. Observations summarized in the present paper further document the diversity of the Stellarimaceae in one of the oldest available fossil localities providing well-preserved material.