1,001 research outputs found

    The Last Cordilleran Ice Sheet in Southern Yukon Territory

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    The Cordilleran Ice Sheet in Yukon radiated from ice-divides in the Selwyn, PeIIy1 Cassiar, and eastern Coast Mountains and was contiguous with a piedmond glacier complex from the St. Elias Mountains. Expansion of glaciers in divide areas could have been underway by 29 ka BP but these did not merge to form the ice sheet until after 24 ka BP. The firn line fell to approximately 1500 m at the climax of McConnell Glaciation. Flow within the ice sheet was more analogous to a complex of merged valley glaciers than to that of extant ice sheets: topographic relief was typically equal to or exceeded ice thickness, and strongly influenced ice flow. Surface gradients on the ice sheet were fractions of a degree. Steeper ice-surface gradients occurred locally along the digitate ice margin. Retreat from the terminal moraine was initially gradual as indicated by recessional moraines within a few tens of kilometres of the terminal moraine. Small magnitude readvances occurred locally. The ice sheet eventually disappeared through regional stagnation and downwasting in response to a rise in the firn line to above the surface of the ice sheet. Regional déglaciation was complete prior to approximately 10 ka BP.L'Inlandsis de la Cordillère a progressé dans le Yukon à partir des lignes de partage des glaces des monts Selwyn, PeIIy et Cassiar et de l'est de la chaîne Côtière; il était contigu à un glacier de piémont complexe en provenance des monts St. Elias. Les glaciers ont pu se développer dans les régions de partage des glaces à partir de 29 ka BP, mais ils ne se sont fusionnés pour former un inlandsis qu'à partir de 24 ka BP. À l'optimum de la Glaciation de McConnell, la ligne de névé s'est abaissée à environ 1500 m. L'écoulement à l'intérieur de l'inlandsis ressemblait davantage à celui d'un complexe de glaciers de vallées coalescents qu'à celui des inlandsis actuels: le relief rejoignait l'épaisseur de glace ou la dépassait et influençait grandement l'écoulement glaciaire. Sur l'inlandsis, les gradients du profil topographique se mesuraient en fractions de degrés, mais le long de la marge digitée, les gradients étaient par endroits plus prononcés. Le retrait à partir de la moraine frontale a au départ été graduel comme l'indiquent les moraines de retrait à quelques dizaines de kilomètres de la moraine frontale. Il y eut localement quelques récurrences mineures. L'inlandsis disparut avec le temps par stagnation à une échelle régionale et fonte en réponse à une hausse de la ligne de névé au-dessus de la surface de l'inlandsis. À l'échelle régionale, la déglaciation était terminée avant 10kaBP environ.Die Kordilleren-Eisdecke in Yukon breitete sich strahlenfôrmig von den Eisscheiden der Seywyn-, Pelley- und Cassiar-Berge und den ôstlichen Kùstenbergen aus und grenzte an einen Vorlandgletscher von den St. Elias-Bergen. Die Ausdehnung der Gletscher in den Eisscheiden-Gebieten kônnte schon um 29 ka v.u.Z. eingesetzt haben; doch sind sie erst nach 24 ka v.u.Z. zu der Eisdecke verschmolzen. Die Firn-Linie sank auf etwa 1500m wâhrend des Hôhepunkts der McConnell-Vereisung. Das Fliessen innerhalb der Eisdecke entsprach mehr einer Einheit verschmolzener Talgletscher als dem der noch vorhandenen Eisdecke: das topographische relief stimmt in beispielhafter Weise mit der Dicke des Eises ùberein, oder ùbertraf dièse und beeinflusste sehr stark die Eisstrômung. Auf der Oberflàche der Eisdecke betrug das Gefàlle nur Bruchteile eines Grads. Steilere Eisoberflàchengefàlle gab es ôrtlich entlang des fingerfôrmigen Eisrands. Der Rùckzug von der Endmoràne geschah anfangs graduell, was aus den einige 10 km von der Endmoràne entfernten Rùckzugsmorànen hervogeht. Ôrtlich gab es einige kleinere Rùckvorstôsse. Die Eisdecke verschwand schliesslich durch régionale Stagnation und Abzehrung infolge eines Anhubs der Firnlinie ùber die Oberflàche der Eisdecke hinaus. Die régionale Enteisung war vor etwa 10 ka v.u.Z. vollendet

    North to south: ecosystem features determine seagrass community response to sea otter foraging

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    We compared sea otter recovery in California (CA) and British Columbia (BC) to determine how key ecosystem properties shape top-down effects in seagrass communities. Potential ecosystem drivers of sea otter foraging in CA and BC seagrass beds that we examined include the role of coastline complexity and environmental stress on sea otter effects. In BC, we found greater species richness across seagrass trophic assemblages. Furthermore, Cancer spp. crabs, an important link in the seagrass trophic cascade observed in CA, was less common. Additionally, the more recent reintroduction of sea otters, more complex coastline, and reduced environmental stress in BC seagrass habitats supported the hypothesis that sea otter foraging pressure is currently reduced in more northern latitudes. In order to manage the ecosystem features that lead to regional differences in top predator effects in seagrass communities, we review our findings, their spatial and temporal constraints, and present a social-ecological framework for future re- search

    Are coastal habitats important nurseries? A meta-analysis

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    Nearshore‐structured habitats—including underwater grasses, mangroves, coral, and other biogenic reefs, marshes, and complex abiotic substrates—have long been postulated to function as important nurseries for juvenile fishes and invertebrates. Here, we review the evolution of the “nursery habitat hypothesis” and use \u3e11,000 comparisons from 160 peer‐reviewed studies to test whether and which structured habitats increase juvenile density, growth, and survival. In general, almost all structured habitats significantly enhanced juvenile density—and in some cases growth and survival—relative to unstructured habitats. Underwater grasses and mangroves also promoted juvenile density and growth beyond what was observed in other structured habitats. These conclusions were robust to variation among studies, although there were significant differences with latitude and among some phyla. Our results confirm the basic nursery function of certain structured habitats, which lends further support to their conservation, restoration, and management at a time when our coastal environments are becoming increasingly impacted. They also reveal a dearth of evidence from many other systems (e.g., kelp forests) and for responses other than density. Although recent studies have advocated for increasingly complex approaches to evaluating nurseries, we recommend a renewed emphasis on more straightforward assessments of juvenile growth, survival, reproduction, and recruitment

    GeneWaltz--A new method for reducing the false positives of gene finding

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    <p>Abstract</p> <p>Background</p> <p>Identifying protein-coding regions in genomic sequences is an essential step in genome analysis. It is well known that the proportion of false positives among genes predicted by current methods is high, especially when the exons are short. These false positives are problematic because they waste time and resources of experimental studies.</p> <p>Methods</p> <p>We developed GeneWaltz, a new filtering method that reduces the risk of false positives in gene finding. GeneWaltz utilizes a codon-to-codon substitution matrix that was constructed by comparing protein-coding regions from orthologous gene pairs between mouse and human genomes. Using this matrix, a scoring scheme was developed; it assigned higher scores to coding regions and lower scores to non-coding regions. The regions with high scores were considered candidate coding regions. One-dimensional Karlin-Altschul statistics was used to test the significance of the coding regions identified by GeneWaltz.</p> <p>Results</p> <p>The proportion of false positives among genes predicted by GENSCAN and Twinscan were high, especially when the exons were short. GeneWaltz significantly reduced the ratio of false positives to all positives predicted by GENSCAN and Twinscan, especially when the exons were short.</p> <p>Conclusions</p> <p>GeneWaltz will be helpful in experimental genomic studies. GeneWaltz binaries and the matrix are available online at <url>http://en.sourceforge.jp/projects/genewaltz/</url>.</p
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