Some agri-environment schemes promote the creation and management of a variety of non-crop habitats on farmland in the UK, yet there has been relatively little monitoring to assess how species, ...particularly birds, use these habitats. The present study deals with a declining UK farmland bird species, yellowhammer
Emberiza citrinella, and considers to what extent grass margins of arable fields are used as a foraging habitat when feeding nestlings. Studies were carried out in lowland mixed farmland in southern England.
Grass margins and other non-crop field boundary habitats, such as hedgerows and ditches, were selected relative to cropped areas by yellowhammers. No significant difference was found between use of cut and uncut grass margins. Studies have shown that grass margins support high densities of invertebrates and their provision at the edge of arable fields would benefit yellowhammers during the breeding season both as habitat for prey and as nesting habitat. During the breeding season from May to August, management should create cut and uncut grass margins in close proximity to each other. This could be achieved by cutting only the outer edge of the grass margin, maintaining cover next to the hedgerow. Cut areas would provide easier access to food resources for birds and prevent weed encroachment to the crop, whilst adjacent uncut areas would maintain invertebrate sources and provide nesting cover for yellowhammers.
•We test whether higher-level scheme (HLS) agri-environment affects avian population growth.•Changes in abundance were significantly more positive on HLS in at least one region for six species.•Five ...of six species affected by HLS were associated with field edges.•HLS can benefit priority birds without high levels of ongoing advisory support.
Agri-environment schemes (AES) are the main policy mechanism available to reverse the widespread losses of farmland biodiversity across Europe. Previous examples of AES enhancing the abundance of farmland birds have been restricted to targeted species recovery programmes, often with bespoke habitat management and high levels of advisory support for landowners. Here, we tested whether standard higher-tier AES agreements targeted at multiple species and with lower levels of advisory support than targeted species recovery programmes can enhance the breeding densities of farmland birds. Surveys of breeding birds were undertaken during 2008 and 2011 on 65 farms under higher level stewardship (HLS) and 21 farms lacking AES interventions, in three regions of England. After allowing for any impacts of predator control, changes in density were more positive on HLS farms in at least one region for six priority species. Five of the six species had mixed diets and were predominantly associated with field edges; the other (lapwing) probably responded to the provision of field-centre fallow plots. Changes in bird numbers were not consistently related to the extent of AES habitat provision. This is the first study to demonstrate that standard AES management without substantial ongoing advisory support can increase or maintain the densities of widespread declining species.
Over a period of approximately 7 months, multiple subepithelial spots were noted in one or both corneas of some patients examined 2 to 6 months after laser in situ keratomileusis (LASIK). The lesions ...appeared identical to adenovirus keratitis. The eyes were quiet, had good vision, and no patient had a history of adenoviral keratoconjunctivitis. In all eyes, the lesions resolved spontaneously or with topical steroid eyedrops. All investigations were negative for adenovirus. Corneal laser scanning in vivo confocal microscopy revealed Langerhans cells in the epithelium, which disappeared after the lesions resolved.
Serpentinization of ultramafic rocks during hydrothermal alteration at mid‐ocean ridges profoundly changes the physical, chemical, rheological, and magnetic properties of the oceanic lithosphere. ...There is renewed interest in this process following the discovery of widespread exposures of serpentinized mantle on the seafloor in slow spreading oceans. Unroofing of mantle rocks in these settings is achieved by displacement along oceanic detachment faults, which eventually results in structures known as oceanic core complexes (OCCs). However, we have limited understanding of the mechanisms of serpentinization at the seafloor and in particular their relationship with the evolution of OCCs. Since magnetite is a direct product of serpentinization, the magnetic properties of variably serpentinized peridotites can provide unique insights into these mechanisms and their evolution in the oceanic lithosphere. Here we present new results from an integrated, rock magnetic, paleomagnetic, and petrological study of variably serpentinized peridotites from the first fossil OCC recognized in an ophiolite. Integration with existing data from mid‐ocean ridge‐related abyssal peridotites recovered from several scientific ocean drilling sites yields the first magnetic database from peridotites extending across the complete range (0–100%) of degrees of serpentinization. Variations in a range of magnetic parameters with serpentinization, and associated paleomagnetic data, provide: (i) key constraints on the mechanism(s) of serpentinization at mid‐ocean ridges; (ii) insights on the potential for serpentinized peridotites to contribute to marine magnetic anomalies; and (iii) evidence that leads to a new conceptual model for the evolution of serpentinization and related remanence acquisition at OCCs.
Key Points
Magnetic properties of variably serpentinized peridotite are investigated
Abyssal peridotites are unlikely to contribute to marine magnetic anomalies
A new conceptual model for serpentinization at OCCs is proposed
The repeated proximity of West Antarctic Ice Sheet (WAIS) ice to the eastern Ross Sea continental shelf break during past ice age cycles has been inferred to directly influence sedimentary processes ...occurring on the continental slope, such as turbidity current and debris flow activity; thus, the records of these processes can be used to study the past history of the WAIS. Ross Sea slope sediments may additionally provide an archive on the history and interplay of density-driven or geostrophic oceanic bottom currents with ice-sheet-driven depositional mechanisms. We investigate the upper 121 m of Hole U1525A, collected during International Ocean Discovery Program (IODP) Expedition 374 in 2018. Hole U1525A is located on the southwestern external levee of the Hillary Canyon (Ross Sea, Antarctica) and the depositional lobe of the nearby trough-mouth fan. Using core descriptions, grain size analysis, and physical properties datasets, we develop a lithofacies scheme that allows construction of a detailed depositional model and environmental history of past ice sheet-ocean interactions at the eastern Ross Sea continental shelf break/slope since ~2.4 Ma. The earliest Pleistocene interval (~2.4- ~ 1.4 Ma) represents a hemipelagic environment dominated by ice-rafting and reworking/deposition by relatively persistent bottom current activity. Finely interlaminated silty muds with ice-rafted debris (IRD) layers are interpreted as contourites. Between ~1.4 and ~0.8 Ma, geostrophic bottom current activity was weaker and turbiditic processes more common, likely related to the increased proximity of grounded ice at the shelf edge. Silty, normally-graded laminations with sharp bases may be the result of flow-stripped turbidity currents overbanking the canyon levee during periods when ice was grounded at or proximal to the shelf edge. A sandy, IRD- and foraminifera-bearing interval dated to ~1.18 Ma potentially reflects warmer oceanographic conditions and a period of stronger Antarctic Slope Current flow. This may have enhanced upwelling of warm Circumpolar Deep Water onto the shelf, leading to large-scale glacial retreat at that time. The thickest interval of turbidite interlamination was deposited after ~1 Ma, following the onset of the Mid-Pleistocene Transition, interpreted as a time when most ice sheets grew and glacial periods were longer and more extreme. Sedimentation after ~0.8 Ma was dominated by glacigenic debris flow deposition, as the trough mouth fan that dominates the eastern Ross Sea continental slope prograded and expanded over the site. These findings will help to improve estimations of WAIS ice extent in future Ross Sea shelf-based modelling studies, and provide a basis for more detailed analysis of the inception and growth of the WAIS under distinct oceanographic conditions.
•A detailed analysis of Pleistocene sediments from IODP Expedition 374 Site U1525•Three main intervals of deposition between: 2.4 Ma–1.4 Ma, 1.4 Ma–0.8 Ma and < 0.8 Ma•Depositional context for the Hillary Canyon and the Ross Sea trough-mouth fan•Sandy, foraminifera-bearing interval at ~1.18 Ma suggests ice sheet collapse•Ice grounded at shelf edge more often after 1 Ma, TMF prograded over Site U1525
Three-quarters of the oceanic crust formed at fast-spreading ridges is composed of plutonic rocks whose mineral assemblages, textures and compositions record the history of melt transport and ...crystallization between the mantle and the sea floor. Despite the importance of these rocks, sampling them in situ is extremely challenging owing to the overlying dykes and lavas. This means that models for understanding the formation of the lower crust are based largely on geophysical studies and ancient analogues (ophiolites) that did not form at typical mid-ocean ridges. Here we describe cored intervals of primitive, modally layered gabbroic rocks from the lower plutonic crust formed at a fast-spreading ridge, sampled by the Integrated Ocean Drilling Program at the Hess Deep rift. Centimetre-scale, modally layered rocks, some of which have a strong layering-parallel foliation, confirm a long-held belief that such rocks are a key constituent of the lower oceanic crust formed at fast-spreading ridges. Geochemical analysis of these primitive lower plutonic rocks--in combination with previous geochemical data for shallow-level plutonic rocks, sheeted dykes and lavas--provides the most completely constrained estimate of the bulk composition of fast-spreading oceanic crust so far. Simple crystallization models using this bulk crustal composition as the parental melt accurately predict the bulk composition of both the lavas and the plutonic rocks. However, the recovered plutonic rocks show early crystallization of orthopyroxene, which is not predicted by current models of melt extraction from the mantle and mid-ocean-ridge basalt differentiation. The simplest explanation of this observation is that compositionally diverse melts are extracted from the mantle and partly crystallize before mixing to produce the more homogeneous magmas that erupt.
To learn more about magnetic properties of the lower ocean crust and its contributions to marine magnetic anomalies, gabbro samples were collected from International Ocean Discovery Program Hole ...U1473A at Atlantis Bank on the Southwest Indian Ridge. Detailed magnetic property work links certain magnetic behaviors and domain states to specific magnetic mineral populations. Measurements on whole rocks and mineral separates included magnetic hysteresis, first‐order reversal curves, low‐temperature remanence measurements, thermomagnetic analysis, and magnetic force microscopy. Characteristics of the thermomagnetic data indicate that the upper ~500 m of the hole has undergone hydrothermal alteration. The thermomagnetic and natural remanent magnetization data are consistent with earlier observations from Hole 735B that show remanence arises from low‐Ti magnetite and that natural remanent magnetizations are up to 25 A m−1 in evolved Fe‐Ti oxide gabbros, but are mostly <1 A m−1. Magnetite is present in at least three forms. Primary magnetite is associated with coarse‐grained oxides that are more frequent in the upper part of the hole. This magnetic population is linked to dominantly “pseudo‐single‐domain” behavior that arises from fine‐scale lamellar intergrowths within the large oxides. Deeper in the hole the magnetic signal is more commonly dominated by an interacting single‐domain assemblage most likely found along crystal discontinuities in olivine and/or pyroxene. A third contribution is from noninteracting single‐domain inclusions within plagioclase. Because the concentration of the highly magnetic, oxide‐rich gabbros is greatest toward the surface, the signal from coarse oxides will likely dominate the near‐bottom magnetic anomaly signal at Atlantis Bank.
Plain Language Summary
Critical evidence documenting Earth's evolution has been provided by measuring the magnetic field generated by a magnetized ocean crust. Most of this field comes from the uppermost crust produced by seafloor volcanic eruptions. However, sometimes important contributions come from the lower crust that is not commonly exposed on the seafloor. To better understand these lower crustal contributions, rock samples were collected via ocean drilling at Atlantis Bank in the Indian Ocean. Previous magnetic work on this type of rock has mostly been limited to measurements that provide an average of all magnetic minerals present. In this study, we perform more detailed analyses and are able to link certain magnetic behaviors with specific populations of the magnetic mineral magnetite. In one form, magnetite is present in relatively large (tens of microns) oxide minerals with fine‐scale compositional variations. Magnetite is also present as tiny particles enclosed within other minerals (plagioclase and pyroxene and/or olivine). Because rock layers containing the large oxides are relatively close to the seafloor at Atlantis Bank, and because they contain a large quantity of magnetite, they will contribute most strongly to any magnetic field measurements made close to the seafloor.
Key Points
Magnetite in Atlantis Bank gabbros is present as single‐domain inclusions in silicate minerals and as intergrowths in coarse oxides
Fine‐scale lamellar intergrowths in the coarse oxides give rise to pseudo‐single‐domain‐like behavior and likely dominates near‐bottom anomalies
Thermomagnetic data are consistent with high‐temperature hydrothermal alteration in the uppermost 200–500 m
New palaeomagnetic data from the Late Cretaceous, Neotethyan Troodos ophiolite and related units in SW Cyprus provide compelling evidence that transform tectonism is recorded outside the main outcrop ...of the fossil Southern Troodos Transform Fault Zone (STTFZ). High-level intrusive and extrusive sequences were sampled along the SW margin of the Troodos massif and in ophiolitic slivers preserved along arcuate fault lineaments further to the south and west. These units show cross-cutting relationships with corresponding differences in remanent magnetisation directions, characteristic of syn-magmatic rotation in an active transform setting. Net tectonic rotation analyses allow decomposition of the total rotation at these sites into early and late components. Early transform-related rotations are consistently clockwise, in agreement with all other studies of rotations associated with the STTFZ further to the east. Late rotations and the net rotations derived at localities where cross-cutting relationships were not present are regarded as composite in origin. The composite rotation axes closely relate to the orientation of observed regional structures. In these circumstances, additional constraints are used to attempt geologically viable interpretations. The overall distribution of transform-related rotations (steeply and shallowly plunging rotation axes) and spreading axis-related rotations (sub-horizontal rotation axes) is comparable with that along the STTFZ and adjacent parts of the Troodos massif. This is most readily explained by simple along-strike extension of the primary spreading axis and transform fabrics into SW Cyprus, with minor late disruption by high-angle dextral shear zones and neotectonic graben systems.
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