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Article Reference Intense aqueous alteration on C-type asteroids: Perspectives from giant fine-grained micrometeorites
This study explores the petrology of five giant (>400 μm) hydrated fine-grained micrometeorites from the Transantarctic Mountain (TAM) micrometeorite collection. For the first time, the extent and mechanisms of aqueous alteration in unmelted cosmic dust are evaluated and quantified. We use a range of criteria, previously defined for use on hydrated chondrites, including phyllosilicate fraction, matrix geochemistry and micro textures. Collectively, these micrometeorites represent ∼2.22 mm2 of intensely altered hydrated chondritic matrix (with petrologic subtypes of <1.2 in the scheme of Howard et al. (2015)) and reveal a range of alteration styles. Two particles are found to contain pseudomorphic chondrules with thick fine-grained rims, while another micrometeorite contains several aqueously altered CAIs. Their outlines range from well-defined to indistinct, demonstrating that the advanced stages of aqueous alteration progressively remove evidence of coarse-grained components. The remaining two micrometeorites entirely lack coarse-grained components but are similarly altered. Thus, the combined chondrule-to-matrix ratio among these giant micrometeorites is extremely low (6.45 area%), and significantly below the average ratio found in typical CM or CR chondrites (∼20%, Weisberg et al., 2006). Our findings are consistent with previous analyses from smaller Antarctic micrometeorites, which suggest that chondrules (and CAIs) derived from hydrated carbonaceous chondrite parent bodies are underrepresented among the micrometeorite flux, even when considering contributions from coarse-grained micrometeorites. Therefore, to explain the relative paucity of anhydrous material, we propose that the flux of fine-grained micrometeorites is primarily derived from intensely aqueously altered, primitive C-type asteroids, which have lost the majority of their refractory coarse-grained components by replacement with secondary phyllosilicate minerals.
Located in Library / RBINS Staff Publications 2019
Article Reference How the larval traits of six flatfish species impact connectivity
Located in Library / RBINS Staff Publications 2019
Article Reference Digital mapping of coastal boulders – high-resolution data acquisition to infer past and recent transport dynamics
Coastal boulder fields provide clues to long-term frequency-magnitude patterns of coastal flooding events and have the potential to play an important role in coastal hazard assessment. Mapping boulders in the field is time and labour-intensive, and work on intertidal reef platforms, as in the present study, is physically challenging. By addressing coastal scientists not specialized in remote sensing, this contribution reports on the possibilities and limitations of digital applications in boulder mapping in Eastern Samar, Philippines, where recent supertyphoons Haiyan and Hagupit induced high waves, coastal flooding and boulder transport. It is demonstrated how satellite imagery of submetre resolution (Pléiades, WorldView-3) enables efficient analysis of transport vectors and distances of larger boulders, reflecting variation in latitudes of both typhoon tracks and approaching angles of typhoon-generated waves. During the investigated events, boulders with a-axes of up to 8 m were clearly identified to have been shifted for up to 32 m, mostly along the seaward margin of the boulder field. It is, however, hard to keep track of smaller boulders, and the length of a-axes and b-axes including their orientation is often impossible to map with sufficient accuracy. Orthophotographs and digital surface models created through the application of an unmanned aerial vehicle and the ‘Structure from Motion’ technique provide ultrahigh-resolution data, and have the potential to not only improve the results of satellite image analysis, but also from field mapping and may significantly reduce overall time in the field. Orthophotographs permit unequivocal mapping of a- and b-axes including their orientation, while precise values for c-axes can be derived from the respective digital surface models. Volume of boulders is best inferred from boulder-specific Structure from Motion-based three-dimensional models. Battery power, flight speed, and altitude determine the limits of the area covered, while patches shielded by the boulders are difficult to resolve. For some tasks field mapping remains mandatory and cannot be replaced by currently available remote sensing tools: for example, sampling for rock type, density and age dating,recording of lithological separation of boulders from the underlying geological unit and of geomorphic features on a millimetre to decimetre-scale, or documentation of fine-grained sediment transport in between the boulders in supratidal settings. In terms of future events, the digital products presented here will provide a valuable reference to track boulder transport on a centimetre to decimetre-scale and to better understand the hydrodynamics of extreme-wave events on a fringing reef coastline.
Located in Library / RBINS Staff Publications 2019
Article Reference Long-term trends of land use and demography in Greece: a comparative study
This paper offers a comparative study of land use and demographic development in northern and southern Greece from the Neolithic to the Byzantine period. Results from summed probability densities (SPD) of archaeological radiocarbon dates and settlement numbers derived from archaeological site surveys are combined with results from cluster-based analysis of published pollen core assemblages to offer an integrated view of human pressure on the Greek landscape through time. We demonstrate that SPD can be a useful approach to outline differences between regions and a useful complement to archaeological site records, evaluated here especially for the onset of the Neolithic and the Final Neolithic/Early Bronze Age transition. Pollen analysis highlight differences in vegetation between the two subregions but also several parallel changes. The comparison of land cover changes between two sub-regions of Greece further demonstrate the significance of the bioclimatic conditions of core locations and that apparent oppositions between regions may in fact be two sides of the same coin in terms of socio-ecological trajectories. We also assess the balance between anthropogenic and climate related impacts on vegetation and suggest that climatic variability was as an important factor for vegetation regrowth. Finally, our evidence suggest that the impact of humans on land cover is amplified from the Late Bronze Age onwards as more extensive herding and agricultural practices are introduced.
Located in Library / RBINS Staff Publications 2019
Article Reference A little-known German naturalist: Konrad Miller (1844-1933) and his malacological contributions
Located in Library / RBINS Staff Publications 2019
Article Reference More than just a name: Colonel Messager and his correspondents
Located in Library / RBINS Staff Publications 2019
Article Reference A global database for metacommunity ecology: integrating species, traits, environment and space
Located in Library / RBINS Staff Publications 2020
Article Reference Preface : Emerging Trends in Aquatic Ecology III
Located in Library / RBINS Staff Publications 2020
Article Reference Are Cardinium infections causing asexuality in non-marine ostracods?
Located in Library / RBINS Staff Publications 2020
Article Reference The avifauna, conservation and biogeography of the Njesi Highlands in northern Mozambique, with a review of the country’s Afromontane birdlife
Located in Library / RBINS Staff Publications 2020