Paleoclimatic and diagenetic history of the Late Quaternary sediments in a core from the Southeastern Arabian Sea: geochemical and magnetic signals

Geochemical and rock-magnetic investigations were carried out on a sediment core collected from the SE Arabian Sea at 1420 m depth in oxygenated waters below the present-day oxygen minimum zone. The top 250 cm of the core sediments represent the last 35 kaBP. The δ18O values of Globigerinoides ruber are heaviest during the Last Glacial Maximum (LGM) and appear unaffected by low-saline waters transported from the Bay of Bengal by the strong northeast monsoon and West Indian coastal current. The signatures of Bølling-Allerød and Younger Dryas events are distinct in the records of magnetic susceptibility, organic carbon (OC) and δ 18O. Glacial sediments show higher OC, CaCO3, Ba, Mo, U and Cd, while the early-to-late Holocene sediments show increasing concentrations of OC, CaCO3, Ba, Cu, Ni and Zn and decreasing concentrations of Mo, U and Cd. Productivity induced low-oxygenated bottom waters and reducing sedimentary conditions during glaciation, and productivity and oxygenated bottom waters in the Holocene are responsible for their variation. The core exhibits different stages of diagenesis at different sediment intervals. The occurrence of fine-grained, low-coercivity, ferrimagnetic mineral during glacial periods is indicative of its formation in organic-rich, anoxic sediments, which may be analogous to the diagenetic magnetic enhancement known in sapropels of the Mediterranean Sea and Japan Sea. The glacial sediments exhibiting reductive diagenesis with anoxic sedimentary environment in this core correspond to reductive diagenesis and intermittent bioturbation (oxygenation) reported in another core in the vicinity. This suggests that the poorly oxygenated bottom water conditions during glacial times should not be generalized, but are influenced locally by productivity, sedimentation rates and sediment reworking

Helping behaviour during cooperative learning and learning gains

Is helping behaviour (i.e., solicited help and peer tutoring) during cooperative learning (CL) related to subsequent learning gains? And can teachers influence pupils’ helping behaviour? One hundred one 5th grade pupils from multiethnic schools, 10-12 years old, participated in the study. Forty two pupils (31 immigrant) worked in an experimental condition, characterized by the stimulation of solicited high quality help and 59 (24 immigrant) worked in a control condition. It was found that learning gains were predicted positively by pupils’ unsolicited helping behaviour (i.e., peer tutoring) and negatively by solicited help. Furthermore, teachers were able to affect pupils’ low quality solicited help only. Lastly, immigrant pupils used less helping behaviour than local pupils, irrespective of CL setting

Teacher interventions in small group work in secondary mathematics and science lessons

Collaborative problem solving, when students work in pairs or small groups on a curriculum-related task, has become an increasingly common feature of classroom education. This paper reports a study of a topic which has received relatively little attention: how teachers can most usefully intervene when students are working in a group, but have encountered some sort of problem. The data used comes from a large scale interventional study of mathematics and science teaching in secondary schools in south east England, in which interactions between teachers and students were recorded in their usual classrooms. We identify the typical problem situations which lead to teachers’ interventions, and describe the different ways teachers were observed to intervene. We examine the different types of intervention, and consider how effective they are in helping group work proceed in a productive manner. Finally, we offer some conclusions about the practical implications of these findings.This is the final version of the article. It was first available from Taylor & Francis via http://dx.doi.org/10.1080/09500782.2015.112536

Spatial and temporal variations in basal melting at Nivlisen ice shelf, East Antarctica, derived from phase-sensitive radars

Thinning rates of ice shelves vary widely around Antarctica, and basal melting is a major component of ice shelf mass loss. In this study, we present records of basal melting at a unique spatial and temporal resolution for East Antarctica, derived from autonomous phase-sensitive radars. These records show spatial and temporal variations of basal melting in 2017 and 2018 at Nivlisen, an ice shelf in central Dronning Maud Land. The annually averaged basal melt rates are in general moderate (∼0.8 m yr−1). Radar profiling of the ice shelf shows variable ice thickness from smooth beds to basal crevasses and channels. The highest basal melt rates (3.9 m yr−1) were observed close to a grounded feature near the ice shelf front. Daily time-varying measurements reveal a seasonal melt signal 4 km from the ice shelf front, at an ice draft of 130 m, where the highest daily basal melt rates occurred in summer (up to 5.6 m yr−1). In comparison with wind, air temperatures, and sea ice cover from reanalysis and satellite data, the seasonality in basal melt rates indicates that summer-warmed ocean surface water was pushed by wind beneath the ice shelf front. We observed a different melt regime 35 km into the ice shelf cavity, at an ice draft of 280 m, with considerably lower basal melt rates (annual average of 0.4 m yr−1) and no seasonality. We conclude that warm deep-ocean water at present has a limited effect on the basal melting of Nivlisen. On the other hand, a warming in surface waters, as a result of diminishing sea ice cover, has the potential to increase basal melting near the ice shelf front. Continuous in situ monitoring of Antarctic ice shelves is needed to understand the complex mechanisms involved in ice shelf–ocean interactions

The dominant role of extreme precipitation events in Antarctic snowfall variability

Antarctic snowfall consists of frequent clear‐sky precipitation and heavier falls from intrusions of maritime airmasses associated with amplified planetary waves. We investigate the importance of different precipitation events using the output of the RACMO2 model. Extreme precipitation events consisting of the largest 10% of daily totals are shown to contribute more than 40% of the total annual precipitation across much of the continent, with some areas receiving in excess of 60% of the total from these events. The greatest contribution of extreme precipitation events to the annual total is in the coastal areas and especially on the ice shelves, with the Amery Ice Shelf receiving 50% of its annual precipitation in less than the 10 days of heaviest precipitation. For the continent as a whole, 70% of the variance of the annual precipitation is explained by variability in precipitation from extreme precipitation events, with this figure rising to over 90% in some areas

INVESTIGATION OF XIAP AND MITOCHONDRIAL APOPTOSIS SIGNALLING DURING LISTERIA MONOCYTOGENES INFECTION OF MACROPHAGES

Apart from its well-established role as an inhibitor of apoptotic caspase proteases, X-Linked Inhibitor of Apoptosis Protein (XIAP) has recently been suggested to play a role in the regulation of mitochondrial outer membrane permeabilization (MOMP) in response to different stresses. XIAP has been shown to translocate to mitochondria alongside Rab5+ and Rab7+ endolysosomes in response to mitochondrial depolarization and intrinsic apoptosis initiation. Mitochondrial translocation of XIAP and endolysosomes impacts Bax-mediated pore formation in the outer mitochondrial membrane and MOMP-related cell death signalling. In addition, XIAP also plays a pro-survival role by activating the NF-κB pathway using its BIR1 domain. However not much is known about the role of mitochondria and MOMP specifically in Listeria monocytogenes infection. To study the potential role of XIAP in macrophages in regulating mitochondrial apoptosis during infection with L. monocytogenes we investigated the bacterial burden, Bax activation, cytochrome c release, P-p65 translocation into the nucleus and Rab5 colocalization with mitochondria at 2, 3, 6 and 24 hours post-infection, in wildtype and XIAP KO THP-1 macrophages. Our results suggest that XIAP plays an important role in promoting the growth and internalisation of the bacteria leading up to 6 hours. In XIAP KO cells, cytochrome c release was increased and Rab5+ endosomes colocalized with mitochondria at earlier time points. The NF-κB pathway did not appear to be significantly activated at these time points. These results give further insights into the role of XIAP in host innate immune responses to intracellular pathogens. Furthermore, we also investigated the potential anti-apoptotic role of LPS on Valinomycin-treated J774 macrophages by quantifying MOMP markers Bax and cytochrome c. LPS is shown to protect the J774 macrophages from MOMP by activating NF-κB which was confirmed by increased P-p65 translocation in LPS pre-treated, Valinomycin-treated cells. Together, our results support that XIAP plays a central role in the mitochondria-related immune response elicited by L. monocytogenes in macrophages