Sedimentation rates in the Makarov Basin, central Arctic Ocean: A paleomagnetic and rock magnetic approach

Three long sediment cores from the Makarov Basin have been subjected to detailed paleomagnetic and rock magnetic analyses. Investigated sediments are dominated by normal polarity including short reversal excursions, indicating that most of the sediments are of Brunhes age. In general, the recovered sediments show only low to moderate variability in concentration and grain size of the remanence-carrying minerals. Estimations of relative paleointensity variations yielded a well-documented succession of pronounced lows and highs that could be correlated to published reference curves. However, together with five accelerator mass spectrometry C-14 ages and an incomplete Be-10 record, still two different interpretations of the paleomagnetic data are possible, with long-term sedimentation rates of either 1.3 or 4 cm kyr(-1) However, both models implicate highly variable sedimentation rates of up to 10 cm kyr(-1), and abrupt changes in rock magnetic parameters might even indicate several hiatuses

Signifying “students”, “teachers” and “mathematics”: a reading of a special issue

This paper examines a Special Issue of Educational Studies in Mathematics comprising research reports centred on Peircian semiotics in mathematics education, written by some of the major authors in the area. The paper is targeted at inspecting how subjectivity is understood, or implied, in those reports. It seeks to delineate how the conceptions of subjectivity suggested are defined as a result of their being a function of the domain within which the authors reflexively situate themselves. The paper first considers how such understandings shape concepts of mathematics, students and teachers. It then explores how the research domain is understood by the authors as suggested through their implied positioning in relation to teachers, teacher educators, researchers and other potential readers

Personality in the Cockroach (Diploptera punctate): Evidence for Stability Across Developmental Stages Despite Age Effects on Boldness

Despite a recent surge in the popularity of animal personality studies and their wide-ranging associations with various aspects of behavioural ecology, our understanding of the development of personality over ontogeny remains poorly understood. Stability over time is a central tenet of personality; ecological pressures experienced by an individual at different life stages may, however, vary considerably, which may have a significant effect on behavioural traits. Invertebrates often go through numerous discrete developmental stages and therefore provide a useful model for such research. Here we test for both differential consistency and age effects upon behavioural traits in the gregarious cockroach Diploptera punctata by testing the same behavioural traits in both juveniles and adults. In our sample, we find consistency in boldness, exploration and sociality within adults whilst only boldness was consistent in juveniles. Both boldness and exploration measures, representative of risk-taking behaviour, show significant consistency across discrete juvenile and adult stages. Age effects are, however, apparent in our data; juveniles are significantly bolder than adults, most likely due to differences in the ecological requirements of these life stages. Size also affects risk-taking behaviour since smaller adults are both bolder and more highly explorative. Whilst a behavioural syndrome linking boldness and exploration is evident in nymphs, this disappears by the adult stage, where links between other behavioural traits become apparent. Our results therefore indicate that differential consistency in personality can be maintained across life stages despite age effects on its magnitude, with links between some personality traits changing over ontogeny, demonstrating plasticity in behavioural syndromes

Magnetostratigraphy of Lower Pleistocene Banyoles Palaeolake Carbonate Sediments From Catalonia, Ne Spain - Evidence for Relocation of the Cobb Mountain Sub-chron

The Banyoles palaeolake carbonate sediments cored at Bobila Ordis (hole BO IV, 52.15 m long) carry a weak natural remanent magnetization (mean NRM intensity: 0.59 +/- 0.54 mAm(-1)) of reversed magnetic polarity except for a shea zone of normal polarity close to the top (16.7-14.05 m). The NRM is probably carried by magnetite as well as by greigite (Fe3S4) in some zones. A chronostratigraphic constraint based on the presence of rodent teeth belonging to the Lower Pleistocene, coinciding climatic events, duration of the deposit estimated by cyclostratigraphy as well as sedimentation rates, suggests that the short normal polarity zone can be correlated to the Cobb Mountain sub-chron (1.19 Ma). This event is recorded at the Oxygen Isotope Stage 36/35 transition in marine sediment cores. In core BO IV, the normal polarity zone probably belongs to the end of an interglacial period as indicated by a cool and humid climate inferred from conifer pollen grains. There is thus an apparent time difference between the oxygen isotope and pollen signal, which is tentatively attributed to a significantly larger post-depositional lag in the acquisition of the remanent magnetization in marine sediments relative to the lacustrine sediment in question. The Cobb Mountain sub-chron might therefore have actually occurred at the end of the interglacial isotope stage 35