Sr/Sr isotope fingerprinting of Scottish and Icelandic migratory shorebirds

Biosphere Sr isotope composition data from Iceland and Scotland suggest that terrestrially feeding birds from these two countries will have significantly different ⁸⁷Sr/⁸⁶Sr isotope composition in their tissues. The aim of this study is to test if these differences can be measured within the bone and feather of migratory wading birds, who feed terrestrially as juveniles, thus providing a provenance tool for these birds.     

Geochemistry of mafic dykes in the Antarctic Peninsula continental-margin batholith: a record of arc evolution

Mafic dykes of the Antarctic Peninsula continental-margin arc are compositionally diverse, comprising calc-alkaline (dominant), shoshonite, tholeiite, and OIB-like varieties. Their compositions give information about different mafic magma sources tapped during arc evolution. The compositional groups represent partial melts of at least five distinct mantle sources: a low-ɛNd subduction-modified, garnet-bearing, lithospheric mantle (older calc-alkaline); a high-ɛNd subduction-modified, garnet-bearing, lithospheric mantle (shoshonites); a high-ɛNd subduction-modified, spinel-bearing, asthenospheric mantle (younger calc-alkaline); E-MORB-like spinel-bearing asthenosphere depleted by a previous melting event (tholeiites); and within-plate non-subduction modified, garnet- and spinel-bearing, asthenosphere (OIB-like). Slab-derived fluids, subducted sediment, and arc crust also contributed to the magmas. Consideration of previous work in the light of our new compositional and geochronological data enables presentation of a summary of arc evolution. For most of the Cretaceous and Tertiary, the tectonic regime of the Antarctic Peninsula arc was transtensional, and calc-alkaline magmas intruded. An oceanic spreading centre collided with the trench during the Late Cretaceous and induced tectonic changes which caused tapping of different magma sources. A pulse of shoshonitic, tholeiitic, and OIB-like mafic magmatism resulted. Three ridge-trench collisions are now recognized during the history of the arc, in Mid–Late Jurassic, Late Cretaceous, and Early–Mid Tertiary times. Received: 13 January 1997 / Accepted: 5 December 1997     

Crustal volatile release at Merapi volcano; the 2006 earthquake and eruption events

High‐temperature gas in volcanic island arcs is widely considered to originate predominantly from the mantle wedge and from subducted sediments of the down‐going slab. Over the decade (1994–2005) prior to the 2006 eruption of Merapi volcano, summit fumarole CO₂ gas δ¹³C ratios are relatively constant at ?4.1 ± 0.3‰. In contrast, CO₂ samples taken during the 2006 eruption and after the May 26th 2006 Yogyakarta earthquake (M6.4) show a dramatic increase in carbon isotope ratios to ?2.4 ± 0.2‰. Directly following the earthquake (hypocentre depth 10–15 km), a 3–5‐fold increase in eruptive intensity was observed. The elevated carbon isotope gas data and the mid‐crustal depth of the earthquake source are consistent with crustal volatile components having been added during the 2006 events, most probably by the thick local limestone basement beneath Merapi. This ‘extra’ crustal gas likely played an important role in modifying the 2006 eruptive behaviour at Merapi and it appears that crustal volatiles are able to intensify and maintain eruptions independently of traditional magmatic recharge and fractionation processes.     

Fluid heterogeneities and hornblende stability in interlayered graphitic and nongraphitic schists (Tauern Window,Eastern Alps)

The assemblage hornblende+white mica occurs in graphite-free schists at two localities in the southwest corner of the Tauern Window, Eastern Alps. In interbedded graphitic layers (1 mm to 1 m thick), however, hornblende is typically replaced by pseudomorphs of biotite+plagioclase +epidote±chlorite+staurolite in the presence of white mica. Garnets adjacent to these pseudomorphs have pronounced growth discontinuities near their rims, in contrast to the continuously zoned garnets in nongraphitic layers. These observations imply that reactions of the type hbl+white micagar+bio+plag+epid±chl±staur +H₂O occurred in the graphitic samples, but that hbl+white mica remained stable in graphite-free layers.Calculation of the equilibrium constants for solid phases in five dehydration equilibria at locality 1 indicates thata(H₂O) in the nongraphitic layers was 6 to 11 times greater thana(H₂O) in the graphitic layers. Similar calculations involving six dehydration equilibria at locality 2 show no difference ina(H₂O) between layers at the conditions of final equilibration. Initial differences in fluid composition maintained between the graphitic and nongraphitic layers caused the hbl+white mica reaction to occur at differentP-T conditions in different horizons of the schists.These data indicate that systematic differences in fluid composition were generated during metamorphism of the interlayered graphitic and non-graphitic schists but were subsequently homogenized at locality 2. The heterogeneities could initially have been produced while the rocks were in theP-T field of CO₂-H₂O immiscibility. Development of a penetrative, layer-parallel shear foliation at this time would have prevented subsequent mixing of the fluids across layers after temperatures exceeded the consolute temperature in the CO₂-H₂O system. Late-stage homogenization of fluids at locality 2 is thought to reflect loss of the buffer capacity of the mineral assemblage in response to total consumption of hornblende.     

Micromorphological analysis of poly‐phase deformation associated with the transport and emplacement of glaciotectonic rafts at West Runton,north Norfolk,UK

The ability of glaciers to detach and transport bedrock as glaciotectonic rafts is widely observed throughout Quaternary sections. However, the glaciological, hydrological and geological parameters controlling rafting are currently poorly constrained. There is a lack of structural and sedimentary evidence concerning rafting, and therefore the processes driving raft detachment, transport and emplacement are poorly understood. This paper contributes to our understanding by presenting a macro‐ and microstructural study of deformation associated with a chalk raft at West Runton, north Norfolk. Detailed thin‐section analysis reveals several discrete micro‐fabric orientations, representing poly‐phase deformation occurring during raft transport and emplacement. A four‐stage conceptual model for raft transport and emplacement is proposed, with deformation being partitioned into the relatively weaker Happisburgh Till member, the latter forming the host to the raft. Stage 1 is the main transport phase of the chalk raft, and was dominated by easterly (down‐ice) directed ductile shearing. During Stage 2 a narrow ductile shear zone within the Happisburgh Till member propagated upwards through the base of the raft, leading to the detachment of an elongate block of chalk. Attenuated lenses of diamicton in this shear zone possess kinematics recording an easterly directed sense of shear. As deformation progressed, during Stage 3, the detached block impinged on the ‘high‐strain’ zone wrapping the base of the raft, influencing the style of deformation partitioning and leading to localized, up‐ice‐directed kinematics. Stage 4 represents the final stages of raft emplacement, when the detachment zone at the base of the raft began to ‘lock‐up’. These results demonstrate the relative importance of the hydrological controls associated with raft transport and emplacement underneath an actively advancing glacier. Furthermore, the model represents an example of how micromorphological analysis can reveal detailed poly‐phase deformation histories in deformed glacial sediments.     

'Contracted out': some implications of the casualization of academic labour in geography

This paper presents the initial findings of a survey of geographers working on fixed-term or other temporary contracts (FTCs), with particular reference to their characteristics, achievements and employment conditions. The results suggest that job satisfaction among contract geographers is related to career stage, and that structural features of the academic labour market combine to restrict many highly qualified academic staff to FTCs for longer than may be appropriate. This phenomenon is highly gendered, with women over-represented among the more junior ranks of contract staff and men dominating the senior ranks. Prolonged employment on FTCs can result in negative effects on the health, welfare and personal finances of many contract staff, and also on staff morale and productivity. The paper concludes that underlying structural inequalities in the academic labour market need to be addressed.     

Local physiographic controls on the responses of Arctic lakes to climate warming in Sirmilik National Park,Nunavut, Canada

Twenty high Arctic lakes and ponds were sampled for water chemistry and modern diatom assemblages in two distinct physiographic sectors of Sirmilik National Park, Nunavut, Canada. Sites on southwestern Bylot Island were warmer, more alkaline, less dilute, and had higher concentrations of nutrients, DOC and Chl-a (mesotrophic to oligo-mesotrophic), whereas sites on Qorbignaluk Headland on northern Baffin Island were deeper, very dilute, mostly oligotrophic and had lower pH. Diatom assemblages differed markedly between these two regions as a consequence of limnological differences between them. Paleolimnological records, spanning > 200 years and dated by ²¹⁰Pb activity, were produced from each region to compare biological responses to recent warming inferred from glaciological studies on Bylot Island and regional syntheses for the Arctic. Diatom assemblages began to change around AD 1900 at both sites. At Qorbignaluk Headland, marked shifts in diatom community composition occurred during the twentieth century, with large increases in the abundance of planktonic diatoms. At Bylot Island, diatom community changes began around the same time, and involved modest decreases in planktonic diatoms and increases in inferred specific conductance, likely because of a decrease in the areal extent of the small lake as a response to warming. The study confirms that responses of freshwater ecosystems to climate warming vary depending on local physiographic factors.     

Oxygen isotope analysis of diatom silica and authigenic calcite from Lake Pinarbasi, Turkey

There is increasing interest in the ¹⁸O/¹⁶O ratio of diatom silica, particularly for lakes where carbonates are absent. Here we compare the ¹⁸O/¹⁶O ratios preserved in diatom silica and authigenic calcite from an open, spring-fed, freshwater lake core from Turkey which spans marine oxygen isotope stage 3. The two sets of isotope data show contrasting trends in spite of their mutual dependence on the water ¹⁸O/¹⁶O ratio and lake-water temperature. The most likely explanation for this divergence is difference in seasonality of biological productivity mediated by the strongly continental climate of the Anatolian plateau. Diatom silica and authigenic calcite are precipitated from solutes in the lake-water at different times of the year. Diatom productivity follows a well-defined seasonal cycle, peaking first and most importantly in the spring and then in the autumn. The precipitation of calcite follows productivity by all forms of photosynthetic organisms that deplete CO₂ but in most lakes this occurs during the summer months. The ¹⁸O_calcite curve shows mean summer temperature maxima at ca. 30–35 and ca. 58 ka BP while the intervening data represent a period of relatively cool summers. The ¹⁸O_diatom curve shows bipolar results (15–20 and 29–33), which suggests that at least two discrete sources or processes contributed to the oxygen composition of the diatoms but probably involved a dilution mechanism to shift the isotopic values. The most likely source of depleted water is from snow entering the lake during the spring thaw. We infer that many authigenic calcite curves from regions with markedly seasonal climates may be temporally limited to a few summer months and that diatom silica provides complementary data on seasonally-specific water isotopic composition rather than a substitute for analyses based on carbonate.     

The market(able) place of school geography scholarship, 2007–2016

This report analyses a decade of geography scholarship student entry and achievement data (n = 10,205) to reveal patterns and trends of high‐achieving school students. The study is an exploratory analysis, the aim of which is to describe where the greatest scholarship success has occurred, as well as attendant demographic characteristics of New Zealand's most capable geography students and their schools. Emerging from the regions is a localised story of students from an extremely narrow number of schools achieving disproportionate scholarship success. This raises questions in the wider geography teaching community about the possibility of a broader constituency achieving scholarship awards.