Pliocene climate change of the Southwest Pacific and the impact of ocean gateways

The transition from the early Pliocene “Warmhouse” towards the present “Icehouse” climate and the role of Gateway dynamics are intensively debated. Both, the constrictions of the Central American Seaway and the Indonesian Gateway affected ocean circulation and climate during the Pliocene epoch. Here, we use combined δ¹⁸O and Mg/Ca ratios of planktonic foraminifera (marine protozoa) from surface and subsurface levels to reconstruct the thermal structure and changes in salinities from the Southwest Pacific Deep Sea Drilling Project (DSDP) Site 590B from 6.5 to 2.5 Ma. Our data suggest a gradual cooling of ~ 2 °C and freshening of the sea surface during ~ 4.6–4 Ma with an increased meridional temperature gradient between the West Pacific Warm Pool and the Southwest Pacific when the closing of the Central American Seaway reached a critical threshold. After ~ 3.5 Ma, the restricted Indonesian Gateway might have amplified the East Australian Current, allowing enhanced heat transport towards the Southwest Pacific with reduced meridional temperature gradients when the global climate gradually cooled. At the same time our data suggest a cooling and freshening of Subantarctic Mode Water (SAMW) or/and an increased northward flow of SAMW towards Site 590B, possibly a first step towards the present Antarctic Frontal System.     

Turbulent characteristics of a shallow convective internal boundary layer

Turbulent characteristics of a 50 to 100 m deep convective internal boundary layer (I.B.L.) have been studied. The data were gathered at a flat coastal site (Näsudden on the island of Gotland, Sweden) during three consecutive days in May 1980 which were characterized by a steady, very stable stratified marine approach flow. The site is situated on a flat area ca. 1500 m from the shoreline. Only daytime runs have been analysed in the present paper. The sensible heat flux at the ground was typically 200 W m^-2 and was found to decrease more or less linearly with height throughout the I.B.L., being slightly negative at greater heights. The momentum flux was also found to decrease with height, but nevertheless shear production of turbulent kinetic energy was found to be large throughout the entire I.B.L. The analysis shows that the turbulent regime has a mixed character. Certain characteristics, such as the rate of growth of the I.B.L., appear to be almost entirely controlled by mechanical turbulence, while others, notably temperature variance and the spectrum of vertical velocity, scale remarkably well with w _* and z _i, in accordance with the results found in fully convective conditions during the experiments at Minnesota and Aschurch. Other turbulent characteristics, such as spectra of the horizontal wind components measured near the top of the I.B.L. tend to adhere to mixed-layer scaling in the high frequency range, exhibiting much increased energy in the lower (reduced) frequency range. Spectra of the velocity components from 10 m are shown to be in general agreement with findings from ‘ideal’, homogeneous sites (Kansas) when properly normalized, although the low frequency part of u- and v-spectra are slightly reduced compared to the case with deep convection.     

Diagnosis of weathering damage on rock-cut monuments in Petra, Jordan

Studies of many years—combining in situ investigation and laboratory analysis—have provided comprehensive information on weathering damage on the rock-cut monuments in the ancient city of Petra in Jordan. These rock-cut monuments represent outstanding world heritage. Many hundred monuments were carved by the Nabataeans from bedrock about 2000 years ago. The awareness of increasing weathering damage on the monuments has resulted in international efforts towards their preservation. The damage diagnosis has addressed the complex mutual relationships between stone types, stone properties, monument exposure regimes, environmental influences, weathering phenomena, development and extent of weathering damage and weathering progression. The rocks were classified lithostratigraphically and petrographically. Results on weathering forms, weathering profiles and weathering products obtained from monument mapping, in situ measurements and laboratory studies revealed a complex diversity of weathering phemomena with respect to type and intensity. Damage categories and damage indices were used to create a reproducible quantitative rating of weathering damage. Detailed results on weathering forms allowed the characterization and quantification of weathering progression including weathering prognoses. Stone properties and states of weathering damage were jointly considered for the rating of the rocks’ susceptibility to weathering. The systematic evaluation of weathering damage and monument exposure regimes can enhance the assessment of weathering factors and processes.     

222Rn as Natural Tracer for LNAPL Recovery in a Crude Oil‐Contaminated Aquifer

The objective of this study was to investigate whether ²²²Rn in groundwater can be used as a tracer for light non‐aqueous phase liquid (LNAPL) quantification at a field site treated by dual‐phase LNAPL removal. After the break of a pipeline, 5 ha of soil in the nature reserve Coussouls de Crau in southern France was contaminated by 5100 m³ of crude oil. Part of this oil seeped into the underlying gravel aquifer and formed a floating oil body of about 3.9 ha. The remediation consists of plume management by hydraulic groundwater barriers and LNAPL extraction in the source zone. ²²²Rn measurements were performed in 21 wells in and outside the source zone during 15 months. In uncontaminated groundwater, the radon activity was relatively constant and remained always >11 Bq/L. The variability of radon activity measurements in wells affected by the pump‐and‐skim system was consistent with the measurements in wells that were not impacted by the system. The mean activities in wells in the source zone were, in general, significantly lower than in wells upgradient of the source zone, owing to partitioning of ²²²Rn into the oil phase. The lowest activities were found in zones with high non‐aqueous phase liquid (NAPL) recovery. LNAPL saturations around each recovery well were furthermore calculated during a period of high groundwater level, using a laboratory‐determined crude oil–water partitioning coefficient of 38.5 ± 2.9. This yielded an estimated volume of residual crude oil of 309 ± 93 m³ below the capillary fringe. We find that ²²²Rn is a useful and cheap groundwater tracer for finding zones of good LNAPL recovery in an aquifer treated by dual‐phase LNAPL removal, but that quantification of NAPL saturation using Rn is highly uncertain.     

Artificial light at night: implications for early life stages development in four temperate freshwater fish species

Flora and fauna have both evolved under a natural cycle of light and dark. But especially in urban areas, the night is now increasingly disturbed by artificial light. Many traits and behaviours in fish are triggered by a circadian clock, for example hatching and swim bladder inflation, which predominantly take place at dusk or night. As lighting becomes brighter and extends farther into rural areas, the distinction between day and night becomes increasingly blurred. Therefore, the loss of diurnal trigger by artificial light at night was hypothesized having deleterious effects on these traits and impact fish reproduction. To assess these effects, eggs of four native freshwater fishes, Eurasian perch Perca fluviatilis, roach Rutilus rutilus, bleak Alburnus alburnus and chub Leuciscus cephalus, were incubated under two different light conditions: a photoperiod of 14 h light:10 h darkness (LD) and continuous illumination (LL). The time to hatch and swim bladder inflation was recorded. The species showed inconsistent reactions to the light treatments. In roach and bleak, the time to 50% hatch was longer in LL, whereas continuous lighting had an accelerating effect in chub. Incubation in LL elongated the hatching period in perch and roach and, in perch, the onset of darkness seemed to trigger hatching. The swim bladder inflation was significantly promoted by continuous light in chub and bleak but was not affected in roach. In conclusion, nocturnal artificial illumination could have an effect on hatching and initial swim bladder filling by masking the day–night-change and thereby diminish the trigger effect. However, the reactions were species specific and the increase in variation indicated a lack of diurnal triggering, whilst a general deleterious effect of artificial light at night has not been identified on early life stages.     

On the response of a turbulent coastal buoyant current to wind events: the case of the Western Adriatic Current

This numerical study focuses on the response of the Western Adriatic Current to wind forcing. The turbulent buoyant surface current is induced by the Po river outflow in the Adriatic Sea. Idealized and realistic wind conditions are considered by retaining the complex geomorphology of the middle Adriatic basin. In the absence of wind, the Adriatic Promontories force the current to separate from the coast and induce instabilities. Persistent 7-m s^− 1 downwelling favorable northwesterly winds thicken and narrow the current. Instabilities whose size is ~10 km develop but ultimately vanish, since there is not enough across-shore space to grow. On the contrary, 7-m s^− 1 upwelling favorable southeasterly winds thin and widen the current, and instabilities can grow to form mesoscale (~35 km) features. When realistic winds are considered, the same trends are observed, but the state of the sea set up by previous wind events also plays a crucial role. The turbulent regimes set up by different winds affect mixing and the WAC meridional transport. With downwelling winds, the transport is generally southward and mixing happens mostly between the fresher (S ≤ 38) salinity classes. With upwelling winds, the transport decreases and changes sign, and mixing mainly involves saltier (S > 38) waters. In all cases, mixing is enhanced when a finer 0.5-km horizontal resolution is employed.     

Magmatic evolution of the South Shetland Islands,Antarctica, and implications for continental crust formation

Lavas from the South Shetland Islands volcanic arc (northern Antarctic Peninsula) have been investigated in order to determine the age, petrogenesis and compositional evolution of a long-lived volcanic arc constructed on 32-km-thick crust, a thickness comparable with average continental crust. New ⁴⁰Ar–³⁹Ar ages for the volcanism range between 135 and 47 Ma and, together with published younger ages, confirm a broad geographical trend of decreasing ages for the volcanism from southwest to northeast. The migration pattern breaks down in Palaeogene time, with Eocene magmatism present on both Livingston and King George islands, which may be due to a change in both subduction direction and velocity after c. 60 Ma. The lavas range from tholeiitic to calc-alkaline, but there is no systematic change with age or geographic location. The compositions of lavas from the north-eastern islands indicate magma generation in a depleted mantle wedge with relatively low Sr and high Nd isotopic compositions and low U/Nb, Th/Nd and Ba/Nb ratios that was metasomatized by hydrous fluids from subducted basaltic oceanic crust. Lavas from the south-western islands show an additional sedimentary influence most likely due to fluid release from subducted sediments into the mantle wedge. Although magmatic activity in the South Shetland arc extended over c. 100 m.y., there is no evolution towards more enriched or evolved magmas with time. Few South Shetland arc lavas are sufficiently enriched with incompatible elements to provide a potential protolith for the generation of average continental crust. We conclude that even long-established subduction zones with magmatic systems founded on relatively thick crust do not necessarily form continental crustal building blocks. They probably represent only the juvenile stages of continental crust formation, and additional re-working, for example during subsequent arc-continental margin collision, is required before they can evolve into average continental crust.     

A nonlinear PDE formulation for offshore vessel pipeline installation

In this paper a nonlinear dynamic PDE formulation for a pipe string suspended from a pipelay vessel to the seabed in a pipelay operation is developed. This model extends a three-dimensional beam model capable of undergoing finite extension, shearing, twist and bending, to apply for marine applications by adding the effects of restoring forces, hydrodynamic drag and seabed interaction. The model is validated against the natural catenary equation and the FEM code RIFLEX. The model is extended to include the pipelay vessel dynamics by applying a potential theory formulation of a surface vessel, suited for dynamic positioning and low speed maneuvering, as a boundary condition for the PDE. This system is found to be input-output passive and stable. Pipeline installation applications where the presented model is suited are e.g., analysis and simulation of the installation operation, operability analysis, hardware-in-the-loop (HIL) testing for vessel control systems, and automation of the pipelay operation.     

Geochemistry and Rb–Sr geochronology of a ductile shear zone in the Orlica-Śnieżnik dome (West Sudetes, Poland)

Amphibolite-facies orthogneisses of the Orlica-vnie™nik dome in the West Sudetes (Poland) show a local continuous transition from weakly deformed augen gneisses to finely laminated mylonites. Field evidence indicates that ductile shearing developed pre- or syntectonically to a migmatization event. Bulk-rock compositions of variably deformed samples yield no indications for deformation- and/or fluid-enhanced element mobility and redistribution. ⁸⁷Rb-⁸⁶Sr geochronology (biotite, phengite, whole rock) places time constraints on the deformation process and the post-orogenic cooling history. Phengite- and biotite-whole-rock pairs yield Rb-Sr ages of 340 to 334 Ma and 335 to 294 Ma, respectively, independent of the degree of deformation. The weighted mean of phengite-whole-rock pairs indicates an age of 337.4DŽ.3 Ma. Combining most of the biotite-whole-rock data yields a weighted mean age of 328.6dž.4 Ma. Because of their different closure temperatures for the Rb-Sr system, these differences are interpreted to date cooling after a thermal event. Direct dating of the deformation is not possible, but the cooling history record defines a minimum age for the development of ductile shearing and the last migmatization event. These time constraints provide evidence for the initiation of crustal collapse during or immediately following peak metamorphic conditions. The results of this study further document the importance of Variscan metamorphism in the Orlica-vnie™nik dome.