Geochemical evidence of Milankovitch cycles in Atlantic Ocean ferromanganese crusts

Hydrogenetic ferromanganese crusts are considered a faithful record of the isotopic composition of seawater influenced by weathering processes of continental masses. Given their ubiquitous presence in all oceans of the planet at depths of 400–7000 meters, they form one of the most well-distributed and accessible records of water-mass mixing and climate. However, their slow accumulation rate and poor age constraints have to date limited their use to explore 100 ka paleoclimatic phenomena. Here it is shown how the Pb isotope signature and major element content of a Fe-Mn crust from the north-east Atlantic responded to changes in the intensity and geographic extent of monsoonal rainfall over West Africa, as controlled by climatic precession during the Paleocene. The studied high-spatial resolution (4 μm) laser-ablation multi-collector inductively coupled plasma mass spectrometer (LA-MC-ICP-MS) Pb isotope data is a nearly 2 order of magnitude improvement in spatial and temporal resolution compared to micro-drill subsamples. The record demonstrates cyclicity of the 206Pb/204Pb and 208, 207Pb/206Pb ratios at the scale of single Fe-Mn oxide laminae, in conjunction with variations in the Fe/Mn ratio, Al, Si and Ti content. Time-frequency analysis and astronomical tuning of the Pb isotope data demonstrates the imprint of climatic precession (∼20 ka) modulated by eccentricity (∼100 and 405 ka), yielding growth rates of 1.5–3.5 mm/Ma consistent with previous chemostratigraphic age models. In this context, boreal summer at the perihelion causes stronger insolation over West Africa, resulting in more intense and geographically extended monsoonal rainfalls compared to aphelion boreal summer conditions. This, in turn, influences the balance between the weathering endmembers feeding the north-east Atlantic basin. These results provide a new approach for calibrating Fe-Mn crust records to astronomical solutions, and allow their isotopic and chemical archive to be exploited with an improved temporal resolution of 1000–5000 years

Talc-dominated seafloor deposits reveal a new class of hydrothermal system

The Von Damm Vent Field (VDVF) is located on the flanks of the Mid-Cayman Spreading Centre, 13?km west of the axial rift, within a gabbro and peridotite basement. Unlike any other active vent field, hydrothermal precipitates at the VDVF comprise 85–90% by volume of the magnesium silicate mineral, talc. Hydrothermal fluids vent from a 3-m high, 1-m diameter chimney and other orifices at up to 215?°C with low metal concentrations, intermediate pH (5.8) and high concentrations (667?mmol?kg?1) of chloride relative to seawater. Here we show that the VDVF vent fluid is generated by interaction of seawater with a mafic and ultramafic basement which precipitates talc on mixing with seawater. The heat flux at the VDVF is measured at 487±101?MW, comparable to the most powerful magma-driven hydrothermal systems known, and may represent a significant mode of off-axis oceanic crustal cooling not previously recognized or accounted for in global models

Improving confidence in ferromanganese crust age models: a composite geochemical approach

Accurate age models for marine ferromanganese (Fe-Mn) crusts are essential to understand paleoceanographic changes and variations in local environmental factors affecting crust growth rate and their lateral continuity. However, no absolute method exists for dating these deposits beyond the age of 10 Myr, which requires the combination of a number of approaches. Here, we present a composite age model for a 15 cm thick Fe-Mn crust sample obtained by unique core drilling using a remotely operated vehicle at a water depth of 1130 m, on the summit of Tropic Seamount, in the north-east Atlantic. The age model is based on cross-validation of laser-ablation U-Pb dating, Co-chronometry and Os isotopes. These enable robust calibration of the age-depth model using the Bayesian statistical modelling of Markov Chain Monte Carlo (MCMC) simulations. The results show that this Fe-Mn crust commenced growth in the Late Cretaceous between 73 and 77 Ma, and grew at a rate between 1 and 24 mm/Myr, averaging 4 mm/Myr. The phosphatised carbonate substrate, capping Tropic Seamount and underlying most of the Fe-Mn crusts, yields a U-Pb age of 84 ± 4 Myr, and provides the upper age limit for the model. Less radiogenic excursions of 188Os/187Os in the vertical profile through the crust permit the identification of key inflection points in the Os isotope seawater curve at the Eocene-Oligocene and Cretaceous-Paleogene transitions. Growth rates estimated from the empirical Co-chronometer are combined with the age envelope defined by the Os data and used to validate the MCMC simulations. The model identifies five hiatuses that occurred during the Pliocene (2.5 ± 1.9–5.3 ± 1.7 Ma), Early Miocene (16 ± 1–27 ± 2 Ma), Oligocene (29 ± 2–32 ± 1 Ma), Eocene (41 ± 2–52 ± 0.6 Ma), and the Late Paleocene (55 ± 1–59 ± 1.4 Ma). A major phosphatisation event affecting the Fe-Mn core can be dated to the Late Eocene (38 ± 1.2 Ma), which coincides with a recorded change in the global oceanic system, from warm and sluggish circulation to cold and vigorous thermohaline-driven meridional overturn at the onset of Antarctic glaciation

Suburban Neighbourhood Adaptation for a Changing Climate (SNACC) final report

The report presents findings from the Suburban Neighbourhood Adaptation to a Changing Climate (SNACC) project. The project tested the effectiveness, feasibility and acceptability of a range of adaptations to the physical environment (i.e. to homes, gardens, and public spaces) that could be used to both mitigate and adapt to climate change in the UK

The formation of gold-rich seafloor sulfide deposits: Evidence from the Beebe Hydrothermal Vent Field, Cayman Trough

The Beebe vent field (BVF) in the Cayman Trough has built an auriferous massive sulfide deposit on the ultra-slow spreading mid-Cayman spreading centre. The genesis of auriferous sulfide deposits at mid-ocean ridges is not fully understood, although there is a growing recognition that slow and ultra-slow spreading centres are conducive to gold mineralization. Analysis of hydrothermal precipitates from the BVF indicates that the highest gold contents are present within “beehive diffusers”, which have developed a highly porous pyrrhotite framework. The beehive structure allows vent fluids to effuse slowly, while allowing ingress of seawater to cool the fluid. The prevalence of pyrrhotite in the beehive samples, lack of sulfates, association between pyrrhotite and gold grains, and results of thermodynamic modelling, suggests gold precipitation occurred under highly reduced conditions even during mixing with seawater. In contrast, high temperature chimneys, with a single orifice, maintain high temperatures to the primary vent orifice and much of the gold is lost to seawater. Despite this, both chimney types are relatively gold enriched, which points to a further underlying cause for high gold at the BVF such as interaction of hydrothermal fluids with ultramafic lithologies in the basement. The final gold composition of the deposit is partially controlled by loss of gold during mass-wasting of the material, with gold depletion most prevalent in blocks formed at beehive-type chimneys. The BVF demonstrates that the overall gold content of a massive sulfide deposit is the sum of basement, precipitation, and surface processes

Exploring high temperature responses of photosynthesis and respiration to improve heat tolerance in wheat

High temperatures account for major wheat yield losses annually and, as the climate continues to warm, these losses will probably increase. Both photosynthesis and respiration are the main determinants of carbon balance and growth in wheat, and both are sensitive to high temperature. Wheat is able to acclimate photosynthesis and respiration to high temperature, and thus reduce the negative affects on growth. The capacity to adjust these processes to better suit warmer conditions stands as a potential avenue toward reducing heat-induced yield losses in the future. However, much remains to be learnt about such phenomena. Here, we review what is known of high temperature tolerance in wheat, focusing predominantly on the high temperature responses of photosynthesis and respiration. We also identify the many unknowns that surround this area, particularly with respect to the high temperature response of wheat respiration and the consequences of this for growth and yield. It is concluded that further investigation into the response of photosynthesis and respiration to high temperature could present several methods of improving wheat high temperature tolerance. Extending our knowledge in this area could also lead to more immediate benefits, such as the enhancement of current crop models

Exploring high temperature responses of photosynthesis and respiration to improve heat tolerance in wheat

High temperatures account for major wheat yield losses annually and, as the climate continues to warm, these losses will probably increase. Both photosynthesis and respiration are the main determinants of carbon balance and growth in wheat, and both are sensitive to high temperature. Wheat is able to acclimate photosynthesis and respiration to high temperature, and thus reduce the negative affects on growth. The capacity to adjust these processes to better suit warmer conditions stands as a potential avenue toward reducing heat-induced yield losses in the future. However, much remains to be learnt about such phenomena. Here, we review what is known of high temperature tolerance in wheat, focusing predominantly on the high temperature responses of photosynthesis and respiration. We also identify the many unknowns that surround this area, particularly with respect to the high temperature response of wheat respiration and the consequences of this for growth and yield. It is concluded that further investigation into the response of photosynthesis and respiration to high temperature could present several methods of improving wheat high temperature tolerance. Extending our knowledge in this area could also lead to more immediate benefits, such as the enhancement of current crop models

Geology, sulfide geochemistry and supercritical venting at the Beebe Hydrothermal Vent Field, Cayman Trough

The Beebe Vent Field (BVF) is the world's deepest known hydrothermal system, at 4960m below sea level. Located on the Mid-Cayman Spreading Centre, Caribbean, the BVF hosts high temperature (∼401°C) ‘black smoker' vents that build Cu, Zn and Au-rich sulphide mounds and chimneys. The BVF is highly gold-rich, with Au values up to 93 ppm and an average Au:Ag ratio of 0.15. Gold precipitation is directly associated with diffuse flow through ‘beehive' chimneys. Significant mass-wasting of sulphide material at the BVF, accompanied by changes in metal content, results in metaliferous talus and sediment deposits. Situated on very thin (2-3km thick) oceanic crust, at an ultraslow spreading centre, the hydrothermal system circulates fluids to a depth of ∼1.8km in a basement that is likely to include a mixture of both mafic and ultramafic lithologies. We suggest hydrothermal interaction with chalcophile-bearing sulphides in the mantle rocks, together with precipitation of Au in beehive chimney structures, has resulted in the formation of a Au-rich volcanogenic massive sulphide (VMS) deposit. With its spatial distribution of deposit materials and metal contents, the BVF represents a modern day analogue for basalt hosted, Au-rich VMS systems. This article is protected by copyright. All rights reserved

The problem of assessing problem solving: can comparative judgement help?

This definitive version of this paper is available at Springerlink: http:dx.doi.org/10.1007/s10649-015-9607-1School mathematics examination papers are typically dominated by short, structured items that fail to assess sustained reasoning or problem solving. A contributory factor to this situation is the need for student work to be marked reliably by a large number of markers of varied experience and competence. We report a study that tested an alternative approach to assessment, called comparative judgement, which may represent a superior method for assessing open-ended questions that encourage a range of unpredictable responses. An innovative problem solving examination paper was specially designed by examiners, evaluated by mathematics teachers, and administered to 750 secondary school students of varied mathematical achievement. The students’ work was then assessed by mathematics education experts using comparative judgement as well as a specially designed, resourceintensive marking procedure. We report two main findings from the research. First, the examination paper writers, when freed from the traditional constraint of producing a mark scheme, designed questions that were less structured and more problem-based than is typical in current school mathematics examination papers. Second, the comparative judgement approach to assessing the student work proved successful by our measures of inter-rater reliability and validity. These findings open new avenues for how school mathematics, and indeed other areas of the curriculum, might be assessed in the future