Holocene history of the 79°N ice shelf reconstructed from epishelf lake and uplifted glaciomarine sediments

Nioghalvfjerdsbrae, or 79°N Glacier, is the largest marine-terminating glacier draining the Northeast Greenland Ice Stream (NEGIS). In recent years, its ∼70 km long fringing ice shelf (hereafter referred to as the 79°N ice shelf) has thinned, and a number of small calving events highlight its sensitivity to climate warming. With the continued retreat of the 79°N ice shelf and the potential for accelerated discharge from NEGIS, which drains 16 % of the Greenland Ice Sheet (GrIS), it has become increasingly important to understand the long-term history of the ice shelf in order to put the recent changes into perspective and to judge their long-term significance. Here, we reconstruct the Holocene dynamics of the 79°N ice shelf by combining radiocarbon dating of marine molluscs from isostatically uplifted glaciomarine sediments with a multi-proxy investigation of two sediment cores recovered from Blåsø, a large epishelf lake 2-13 km from the current grounding line of 79°N Glacier. Our reconstructions suggest that the ice shelf retreated between 8.5 and 4.4 kacalBP, which is consistent with previous work charting grounding line and ice shelf retreat to the coast as well as open marine conditions in Nioghalvfjerdsbrae. Ice shelf retreat followed a period of enhanced atmospheric and ocean warming in the Early Holocene. Based on our detailed sedimentological, microfaunal, and biomarker evidence, the ice shelf reformed at Blåsø after 4.4 kacalBP, reaching a thickness similar to present by 4.0 kacalBP. Reformation of the ice shelf coincides with decreasing atmospheric temperatures, the increased dominance of Polar Water, a reduction in Atlantic Water, and (near-)perennial sea-ice cover on the adjacent continental shelf. Along with available climate archives, our data indicate that the 79°N ice shelf is susceptible to collapse at mean atmospheric and ocean temperatures ∼2 °C warmer than present, which could be achieved by the middle of this century under some emission scenarios. Finally, the presence of "marine"markers in the uppermost part of the Blåsø sediment cores could record modern ice shelf thinning, although the significance and precise timing of these changes requires further work

Habitat and forage associations of a naturally colonising insect pollinator, the Tree Bumblebee Bombus hypnorum

Bumblebees (Bombus species) are major pollinators of commercial crops and wildflowers but factors affecting their abundance, including causes of recent population declines, remain unclear. Investigating the ecology of species with expanding ranges provides a potentially powerful means of elucidating these factors. Such species may also bring novel pollination services to their new ranges. We therefore investigated landscape-scale habitat use and foraging preferences of the Tree Bumblebee, B. hypnorum, a recent natural colonist that has rapidly expanded its range in the UK over the past decade. Counts of B. hypnorum and six other Bombus species were made in March-June 2012 within a mixed landscape in south-eastern Norfolk, UK. The extent of different landscape elements around each transect was quantified at three scales (250 m, 500 m and 1500 m). We then identified the landscape elements that best predicted the density of B. hypnorum and other Bombus species. At the best fitting scale (250 m), B. hypnorum density was significantly positively associated with extent of both urban and woodland cover and significantly negatively associated with extent of oilseed rape cover. This combination of landscape predictors was unique to B. hypnorum. Urban and woodland cover were associated with B. hypnorum density at three and two, respectively, of the three scales studied. Relative to other Bombus species, B. hypnorum exhibited a significantly higher foraging preference for two flowering trees, Crataegus monogyna and Prunus spinosa, and significantly lower preferences for Brassica napus, Glechoma hederacea and Lamium album. Our study provides novel, quantitative support for an association of B. hypnorum with urban and woodland landscape elements. Range expansion in B. hypnorum appears to depend, on exploitation of widespread habitats underutilised by native Bombus species, suggesting B. hypnorum will readily co-exist with these species. These findings suggest that management could target bumblebee species with distinctive habitat requirements to help maintain pollination service

Computational models in plant-pathogen interactions: the case of Phytophthora infestans

<p>Abstract</p> <p>Background</p> <p><it>Phytophthora infestans </it>is a devastating oomycete pathogen of potato production worldwide. This review explores the use of computational models for studying the molecular interactions between <it>P. infestans </it>and one of its hosts, <it>Solanum tuberosum</it>.</p> <p>Modeling and conclusion</p> <p>Deterministic logistics models have been widely used to study pathogenicity mechanisms since the early 1950s, and have focused on processes at higher biological resolution levels. In recent years, owing to the availability of high throughput biological data and computational resources, interest in stochastic modeling of plant-pathogen interactions has grown. Stochastic models better reflect the behavior of biological systems. Most modern approaches to plant pathology modeling require molecular kinetics information. Unfortunately, this information is not available for many plant pathogens, including <it>P. infestans</it>. Boolean formalism has compensated for the lack of kinetics; this is especially the case where comparative genomics, protein-protein interactions and differential gene expression are the most common data resources.</p

The evolution of the Patagonian Ice Sheet from 35 ka to the present day (PATICE)

\ua9 2020 The AuthorsWe present PATICE, a GIS database of Patagonian glacial geomorphology and recalibrated chronological data. PATICE includes 58,823 landforms and 1,669 geochronological ages, and extends from 38\ub0S to 55\ub0S in southern South America. We use these data to generate new empirical reconstructions of the Patagonian Ice Sheet (PIS) and subsequent ice masses and ice-dammed palaeolakes at 35 ka, 30 ka, 25 ka, 20 ka, 15 ka, 13 ka (synchronous with the Antarctic Cold Reversal), 10 ka, 5 ka, 0.2 ka and 2011 AD. At 35 ka, the PIS covered of 492.6 x103 km2, had a sea level equivalent of ~1,496 mm, was 350 km wide and 2090 km long, and was grounded on the Pacific continental shelf edge. Outlet glacier lobes remained topographically confined and the largest generated the suites of subglacial streamlined bedforms characteristic of ice streams. The PIS reached its maximum extent by 33 – 28 ka from 38\ub0S to 48\ub0S, and earlier, around 47 ka from 48\ub0S southwards. Net retreat from maximum positions began by 25 ka, with ice-marginal stabilisation then at 21 – 18 ka, which was then followed by rapid, irreversible deglaciation. By 15 ka, the PIS had separated into disparate ice masses, draining into large ice-dammed lakes along the eastern margin, which strongly influenced rates of recession. Glacial readvances or stabilisations occurred at least at 14 – 13 ka, 11 ka, 6 – 5 ka, 2 – 1 ka, and 0.5 – 0.2 ka. We suggest that 20th century glacial recession (% a-1) is occurring faster than at any time documented during the Holocene