Drill Sites Research Articles

Design Improvements in Conventional Drilling Machine to Control Thermal Necrosis during Orthopaedic Surgeries

Bone drilling operation is performed to join fractured bone tissues during physical trauma. Natural bone growth and remodelling of fractured bone fragments is possible by immobilisation of affected bone. Immobilisation is achieved by use of screws and plates with drilling facilities. Similarly internal fixation of screws [1] during intramedullary nailing often involves bone drilling. The heat generation model [2] has proved that, generation and accumulation of heat above temperature level of 470c for one minute during drilling is the alarming signal for thermal necrosis which causes irreversible bone damage. To study bone drilling in concern with thermal necrosis, threshold temperature has to be the prime concern and accordingly drilling parameters and specifications are to be selected. In this study, drilling process is conducted on a sheep rib bone. Optimization of drilling parameters such as drilling speed, feed rate and drill specification like drill tool diameter is suggested using Taguchi and ANOVA method. Results indicate drill diameter is most influencing factor contributing 90.71% for heat generation, followed by feed rate 5.69% and drill speed 2.22%. Based on discussions and conclusions a drill machine with attachments of infrared thermometer, speed sensor and camera is designed and fabricated. This machine alarms surgeon when temperature level at drill site increases above 470c, which is a threshold temperature of thermal necrosis.

Antarctic Winds: Pacemaker of Global Warming, Global Cooling, and the Collapse of Civilizations

We report a natural wind cycle, the Antarctic Centennial Wind Oscillation (ACWO), whose properties explain milestones of climate and human civilization, including contemporary global warming. We explored the wind/temperature relationship in Antarctica over the past 226 millennia using dust flux in ice cores from the European Project for Ice Coring in Antarctica (EPICA) Dome C (EDC) drill site as a wind proxy and stable isotopes of hydrogen and oxygen in ice cores from EDC and ten additional Antarctic drill sites as temperature proxies. The ACWO wind cycle is coupled 1:1 with the temperature cycle of the Antarctic Centennial Oscillation (ACO), the paleoclimate precursor of the contemporary Antarctic Oscillation (AAO), at all eleven drill sites over all time periods evaluated. Such tight coupling suggests that ACWO wind cycles force ACO/AAO temperature cycles. The ACWO is modulated in phase with the millennial-scale Antarctic Isotope Maximum (AIM) temperature cycle. Each AIM cycle encompasses several ACWOs that increase in frequency and amplitude to a Wind Terminus, the last and largest ACWO of every AIM cycle. This historic wind pattern, and the heat and gas exchange it forces with the Southern Ocean (SO), explains climate milestones including the Medieval Warm Period and the Little Ice Age. Contemporary global warming is explained by venting of heat and carbon dioxide from the SO forced by the maximal winds of the current positive phase of the ACO/AAO cycle. The largest 20 human civilizations of the past four millennia collapsed during or near the Little Ice Age or its earlier recurrent homologs. The Eddy Cycle of sunspot activity oscillates in phase with the AIM temperature cycle and therefore may force the internal climate cycles documented here. Climate forecasts based on the historic ACWO wind pattern project imminent global cooling and in ~4 centuries a recurrent homolog of the Little Ice Age. Our study provides a theoretically-unified explanation of contemporary global warming and other climate milestones based on natural climate cycles driven by the Sun, confirms a dominant role for climate in shaping human history, invites reconsideration of climate policy, and offers a method to project future climate.

Adaptation of the Winkie Drill for subglacial bedrock sampling

AbstractThe Winkie Drill is an agile, commercially available rock coring system. The U.S. Ice Drilling Program has modified a Winkie Drill for subglacial rock and ice/rock interface coring, as well as drilling and coring access holes through ice. The original gasoline engine was replaced with an electric motor though the two-speed gear reducer and Unipress hand feed system were maintained. Using standard aluminum AW34 drill rod (for 33.5 mm diameter core), the system has a depth capability of 120 m. The drill uses forward fluid circulation in a closed loop system. The drilling fluid is Isopar K, selected for favorable properties in polar environment. When firn or snow is present at the drill site, casing with an inflatable packer can be deployed to contain the drill fluid. The Winkie Drill will operate from sea level to high altitudes and operation results in minimal environmental impact. The drill can be easily and quickly assembled and disassembled in the field by two people. All components can be transported by Twin Otter or helicopter to the field site.

Origin of the rhythmic reddish-brown and greenish-gray sediments in the abyssal South China Sea: Implications for oceanic circulation in the late Miocene

During International Ocean Discovery Program (IODP) Expedition 368, a series of drillings were conducted in the northern South China Sea (SCS). At the abyssal drilling Site 1502 Hole A (3764 m below sea level), successive core sections were recovered from 442 to 497 m below sea floor. These cores were placed into the late Miocene period, and the most remarkable feature of these ~50-m-long cores were the consecutive occurrences of the rhythmic reddish-brown and greenish-gray sediments. Such color transitions during the late Miocene period were not remarkable for the cores at the adjacent shallower IODP 368 Sites 1501 and 1505. In this study, we aimed to determine the origin of these cyclicity-like color transitions at Site 1502 in the abyssal SCS. We conducted experiments dealing with sediment color reflectance, nannofossil, key element content, and clay minerals. We inferred that the in-situ formed amorphous hematite caused the coloration of the reddish sediments, in which ferrum and manganese contents were high and carbonate was not poorly preserved. We suggest that the occurrence of the cyclicity-like color transitions could result from the extent of deep-water ventilation in the abyssal SCS. Such changes in deep-water ventilation were possibly related to an orbital-forced rearrangement of deep oceanic circulation in the Pacific Ocean.

ARSENIC-INDUCED DOWNSHIFT OF RAMAN BAND POSITIONS FOR PYRITE

Abstract Pyrite commonly incorporates a wide range of trace and minor elements, which in turn may modify some of the mineral’s physical and chemical properties. Published band position data for the Raman spectra of pyrite show a wide variation, and the relationship between band position and the trace/minor element incorporation in pyrite is poorly constrained until now. This prompted a case study on pyrite with varying As content from the Shizilishan Sr-(Pb-Zn) deposit, eastern China, combining electron probe microanalysis with Raman spectroscopy. Results show a significant correlation, with a major downshift (~10 cm–1) of the positions of all three Raman bands with increase of As content from below 0.05 to 4.89 wt % in pyrite. This phenomenon is attributed to increased bond lengths and local distortions within an expanded pyrite crystal structure. Results highlight the potential that Raman spectroscopy offers to estimate the contents of trace/minor elements—especially As—in pyrite. Given that substitution of As into pyrite often facilitates co-incorporation of both economically useful (Au) and environmentally significant elements (Hg and Tl), Raman methodology could provide valuable, rapid assessment of pyrite chemistry in both gold deposit exploration and environmental science, although the impact of laser heating and mechanical polishing needs to be avoided or effectively reduced. Raman spectroscopy may also find a valuable future role within semiautomated multispectral analytical platforms that can generate close- to-real-time geologic information on freshly drilled core directly at the drill site or in outcrop.

Underpressure in the northern Barents shelf: Causes and implications for hydrocarbon exploration

The underexplored Barents shelf petroleum province is a globally unique example where naturally occurring underpressure is observed offshore and onshore. In the offshore parts of the northern Barents shelf, minor underpressure (up to 23 bar below hydrostatic pressure) is observed in the fault-bounded Mesozoic reservoirs of the Fingerdjupet subbasin. More severe (50 bar below hydrostatic pressure although irregular, occurrences of underpressure are encountered in the Triassic intervals of the neighboring Greater Hoop area. The abnormal pressures extend to the onshore archipelago of Svalbard, where pressures exceeding 60 bar below hydrostatic were encountered during drilling for a CO2 sequestration project. In Svalbard, reservoir pressures were constantly monitored over 3 yr, providing an insight into the reservoir behavior at unique time scales. The low-permeability (<2 md) reservoir in Svalbard is exposed some 15 km to the north of the drill site. Quantitative analysis with the apparent lack of a regional lateral seal suggests a geologically recent origin of underpressure. Evidence that the underpressure extends into the top seal provides further indication to the likely cause of underpressure. Similar to many global occurrences of underpressure in petroleum provinces, the Barents shelf has undergone severe uplift, most recently caused by deglaciation. Well data, outcrop observations, and isotope data combined with the area’s geological history indicate that glacial loading, unloading, and erosion, potentially with the aid of natural fractures, is the likely dominant underpressure-generating mechanism.

Associations between Exposure to Oil and Gas Extraction and Pregnancy-Related Hypertension: A Difference-in-Differences Analysis

Background: An estimated 17.6 million Americans live within 1.6km of an oil or gas drilling site, and this industry is rapidly expanding. Recent evidence suggests that drilling-related exposures are associated with increased blood pressure. No studies have focused on pregnant women, a population that may be highly susceptible to drilling-related air pollution (e.g. truck traffic, gas flaring.) Using a difference-in-differences design, we examine associations between drilling exposures and pregnancy-related hypertension.Methods: We utilized a population-based retrospective term birth cohort (37-42 weeks gestation) between 1996 and 2009 in Texas, where all mothers reside &lt;10km of an active or future drilling site (n=2,598,025). Using full address data, we linked maternal residences at delivery to the coordinates of active oil and gas extraction sites between 1985 and 2019. We evaluated two markers of pregnancy-related hypertension (gestational hypertension, eclampsia) in a difference-in-differences framework. This design first evaluates hypertension risks among pregnant women residing within 0-3km of 1+ site pre-drilling (unexposed) vs. post-drilling (exposed), and then compares those women to a contemporaneous temporal control group residing 3-10km away in a pre-drilling vs. post-drilling context. We use logistic regression models and control for sociodemographic, behavioral, and clinical information.Results: Among pregnant women residing 0-1km of an active drilling site, we find a 7% increased odds of gestational hypertension (95% CI: 1.02, 1.12) and a 28% increased odds of eclampsia (95% CI: 1.03, 1.58). These associations dissipate for residences 1-2 and 2-3km of 1+ drilling site during pregnancy. In restricted models, we find persistent associations among nulliparous women for gestational hypertension (1.15; 95% CI: 1.07, 1.23) and eclampsia (1.64; 95% CI: 1.23, 2.19).Conclusions: Residential location less than 1km from an oil or gas extraction site, which aligns with hypothesized air pollution gradients from drilling sites, is associated with increased odds of gestational hypertension and eclampsia.

Impact of coastal East Antarctic ice rises on surface mass balance: insights from observations and modeling

Abstract. About 20 % of all snow accumulation in Antarctica occurs on the ice shelves. There, ice rises control the spatial surface mass balance (SMB) distribution by inducing snowfall variability and wind erosion due to their topography. Moreover these ice rises buttress the ice flow and represent ideal drilling locations for ice cores. In this study we assess the connection between snowfall variability and wind erosion to provide a better understanding of how ice rises impact SMB variability, how well this is captured in the regional atmospheric climate model RACMO2 and the implications of this SMB variability for ice rises as an ice core drilling site. By combining ground-penetrating radar (GPR) profiles from two ice rises in Dronning Maud Land with ice core dating, we reconstruct spatial and temporal SMB variations from 1983 to 2018 and compare the observed SMB with output from RACMO2 and SnowModel. Our results show snowfall-driven differences of up to 1.5 times higher SMB on the windward side of both ice rises than on the leeward side as well as a local erosion-driven minimum at the ice divide of the ice rises. RACMO2 captures the snowfall-driven differences but overestimates their magnitude, whereas the erosion on the peak can be reproduced by SnowModel with RACMO2 forcing. Observed temporal variability of the average SMBs, retrieved from the GPR data for four time intervals in the 1983–2018 range, are low at the peak of the easternmost ice rise (∼0.06 mw.e.yr-1), while they are higher (∼0.09 mw.e.yr-1) on the windward side of the ice rise. This implies that at the peak of the ice rise, higher snowfall, driven by orographic uplift, is balanced out by local erosion. As a consequence of this, the SMB recovered from the ice core matches the SMB from the GPR at the peak of the ice rise but not at the windward side of the ice rise, suggesting that the SMB signal is damped in the ice core.

Magmatic Processes at the Oman Ophiolite Paleoridge – Perspectives on the Role of Water

AbstractThe Oman ophiolite is regarded as best proxy for accreted oceanic crust from typical fast‐spreading ridge systems on land. However, the Oman ophiolite is influenced by initial subduction zone initiation, and the nature of the details of the subduction zone setting is still under controversial debate. While a first magmatic phase shows features of magmatic accretion very similar to those known from the East Pacific Rise, except that the primary melts were slightly water‐enriched, a second type of magmatism is characterized by an apparent subduction‐zone related imprint, producing rocks like FAB basalts and boninites in the upper crust, as well as cross‐cutting gabbronorites and wehrlites in the deeper crust. In this paper, we apply diverse experimental studies in wet tholeiitic and peridotitic systems performed at lower pressures (100 to 500 MPa) in the experimental lab of the University Hannover, in order to constrain the details of the magmatic processes proceeded at the Oman ophiolite paleoridge during the Cretaceous, with special focus on the influence of water on the phase stabilities and phase relations. The experiments were performed in vertically oriented internally heated pressure vessels (IHPV) (see Berndt et al., 2002; Fig. 1). This facility uses as pressure medium mixtures of Ar and H2 in order to adjust the required fH2 in the vessel, enabling us to control the redox conditions. The fH2 prevailing in the IHPV at high P and T was measured with a Shaw‐membrane made of platinum. The overall variation in fO2 in all experimental series was in the range between ∼FMQ‐1 and ∼FMQ+3.2, thus covering the range of oxygen fugacities prevailing in natural MORB magmas (Bezos and Humler, 2005).For understanding the magmatic processes during the Oman ophiolite paleoridge accretion, transects through the lower (GT1) and middle (GT2) crust have been drilled in the frame of ICDP (International Continental Scientific Drilling Program). Drill sites have been selected in the Wadi Tayin massif, which is known that the influence of magmatic phase 2 characterized by subduction‐related primary melts is minimal. Details and progress obtained in the Oman Drilling Project (OmanDP) can be found here: (https://www.omandrilling.ac.uk/). Regarding the first magmatic phase of the processes at the Oman ophiolite paleoridge, a characteristic observation made during the description of the drilled cores GT1 (lower crust) and GT2 (mid‐curst) was that quite often layers in the layered gabbro series occur which show the presence of clinopyroxene joining olivine instead of plagioclase (under near liquidus conditions). In terms of lithologies this could be interpreted as presence of wehrlitic crystal mushes as early cumulates instead of troctolitic, which are the typical ones for primary magmatism at typical fast‐spreading ridges. This situation could be experimentally simulated by adding a moderate to high water activity to primitive MORB at pressures ≥ 200 MPa, resulting in a shift of the clinopyroxene‐in curve to higher temperatures above the plagioclase‐in curve (Feig et al. 2006; see Fig. 2).Regarding the second, late‐stage magmatic phase, the formation of typical Oman high‐Ca‐boninites could be experimentally simulated by water‐saturated partial melting of Oman harzburgite at 200 MPa and relatively low temperatures between 1100 and 1200°C. Depleted gabbronorites crosscutting layered gabbros of phase 1 magmatism can be regarded as cumulates formed in these boninitic melts. Late wehrlites crosscutting layered gabbro could be produced by accumulation of olivine and clinopyroxene at temperatures between 1040 and 1080°C in a hydrous gabbroic system at pressures &gt; 100 MPa with bulk water content of 2–3 wt%.

Development of mathematical model for prediction of bone drilling temperature

During orthopaedic drilling for screw fixation, if temperature rises above a certain level, thermal damage to bone cells occurs. This damage is in the form of cell death and is permanent in nature. The cell death, termed as thermal necrosis cause slackening of screw fixations. The heat generation studies have proved that if temperature increases to 47 °C and remains the same for one minute, thermal necrosis could occur. So to avoid thermal necrosis controlling and prediction of temperature is necessary. In this research work, mathematical model is developed with the help of multiple regression analysis for prediction of bone drilling temperature with regression analysis an mathematical model is suggested that can predict the temperature at bone drilling site. The data required for the mathematical model is the value of drill speed, feed rate and drill tool diameter. These values are collected by drilling a sheep rib bone. Experimentation is performed with combinations of drill speed, feed rate and drill tool diameter at three levels each, counts to total 27 trials.

Development of Work-based Vestibule Training E-module For Accident Prevention at Malaysian Oil and Gas Drilling Industries: A Proposed Framework

This article discusses the conceptual action plan and detailed methodology for the identification of potential hazard controls and the development of work integrated E-vestibule training module for safe onshore and offshore oil and gas drilling operation at Malaysian industries. According to the previous studies, there is a sheer industrial need of an effective work integrated vestibule training module for accident prevention at oil and gas drilling sites at Malaysian drilling domains. In this proposed study, 80 drilling crew will be randomly selected for quantitative research phase. Similarly, 03 safety experts will be purposively selected for qualitative research from each drilling domain. Whereas, for the identification of hazard controlling measures What-If analysis and thematic analysis approaches will be adopted. Furthermore, the open source vestibule training module will be developed by using ADDIE based on identified hazard controlling measures. However, the visual studio and MySQL software will use to develop the E-Module for drilling crew safety training. The proposed E-vestibule training module development framework will be used as an effective source for the elimination of life-threatening drilling hazards associated with its activities at oil and gas industries. Similarly, the proposed framework can also be implemented on other work-based learning training designs. Moreover, this proposed safety and health vestibule training module will be the first E- drilling safety module which covers all onshore and offshore drilling operation in Malaysian oil and gas extraction settings.

Modeling shallow self-potential anomalies over electronic conductors

Field measurements of self-potential indicate that anomalies may be divided in a shallow anomaly and a deep anomaly. This paper presents a new understanding of the current flow causing SP-anomalies, and how this can be modeled by using the analogy between magnetic flux density lines and electric current lines. Mathematical models are presented for shallow SP-anomalies. Several older models may be applied for the deep part of the anomaly. The new model is applied for interpretation of an SP-anomaly from the KTB drilling site in Oberpfalz in Germany. The deep part was interpreted using a plate model which has been known for years. The final curves of the measured anomaly and the calculated curves for the shallow part and the deep part of the anomaly are presented.

Healing at implants installed in osteotomies prepared either with a piezoelectric device or drills: an experimental study in dogs.

To compare osseointegration and marginal bone level at implants placed in osteotomies prepared with either conventional drills or a piezoelectric device. Three months after the extraction of all mandibular premolars and first molars, two recipient sites were selected. The osteotomies were randomly prepared with either conventional drills (drill sites) or a piezoelectric device (piezoelectric sites). Implants were installed and a submerged healing was allowed. The animals were euthanized in groups of six after 4 and 8 weeks of healing. Biopsies were obtained for histological preparation. Coronal level of osseointegration (bone level) and bone-to-implant contact percentage (BIC%) were evaluated. After 4 weeks of healing, the bone level was 0.6 ± 0.9 mm for the piezoelectric sites and 1.6 ± 0.7 mm for the drill sites (p = 0.173). After 8 weeks, the respective measures were 0.9 ± 0.3 mm and 1.0 ± 1.1 mm (p = 0.917). After 4 weeks of healing, a new bone apposed onto the implant surface was found at fractions of 54.9 ± 6.7% and 55.1 ± 16.6% for the piezoelectric and the drill sites, respectively (p = 0.674). The respective total bone fractions, including new and old bone, was 64.0 ± 4.8% and 63.4 ± 20.4% (p = 0.917). After 8 weeks, a new bone increased to 67.4 ± 6.7% and 62.9 ± 12.5% for the piezoelectric and the drill sites, respectively (p = 0.463). The respective total bone fractions were 70.4 ± 5.5% and 67.8 ± 12.1% (p = 0.753). The use of a piezoelectric device for implant site preparation is a safe procedure that allows a proper integration since the early periods of healing similar to that observed using conventional drills.

Analysis of marine controlled source electromagnetic data for the assessment of gas hydrates in the Danube deep-sea fan, Black Sea

Marine controlled source electromagnetic (CSEM) data have been analyzed as part of a larger interdisciplinary field study to reveal the distribution and concentration of gas hydrates and free gas in two working areas (WAs) in the offshore Danube fan in the western Black Sea. The areas are located in the Bulgarian sector in about 1500 m water depth (WA1) and in the Romanian sector in about 650 m water depth (WA2). Both areas are characterized by channel levee systems and wide spread occurrences of multiple bottom simulating reflections (BSRs) suggesting the presence of gas hydrates. Electrical resistivity models have been derived from two-dimensional (2D) inversions of inline CSEM data using a seafloor-towed electric dipole-dipole system. Comparing the resistivity models with coincident reflection seismic profiles reveals insight in the sediment stratigraphy of the gas hydrate stability zone (GHSZ). Gas hydrate and free gas saturation estimates have been derived with a stochastic approach of Archie's relationship considering uncertainties in the input parameters available from drilling with the MeBo-200 seafloor rig in WA2.The resistivity models generally reflect the transition of marine to lacustrine conditions expressed by a sharp decay of pore water salinities in the top 30–40 m below seafloor caused by freshwater phases of the Black Sea due to sea level low stands in the past. In WA1, we derived saturation estimates of 10–20% within a 100 m thick layer at around 50 m depth below the channel which compares well with estimates from seismic P-wave velocities. The layer extends below the western levee with even higher saturations of 20–30%, but high gas hydrate saturations are unlikely within the fine grained, clayey sediment section, and the high resistivities may reflect different lithologies of lower permeability and porosity. The resistive layer terminates below the eastern levee where increasing resistivities at depth towards a stack of multiple BSRs indicate gas hydrate and free gas concentrations in the order of 10% to locally 30%. WA2 is characterized by a major slope failure at the landward edge of the gas hydrate stability field next to the channel. Gas hydrate saturation estimates within the slump area are close to zero within the GHSZ which is in agreement with coring results of the nearby MeBo drill sites. Elevated resistivities below the steeply upward bending BSR lead to saturation estimates less than 10% of free gas that may have accumulated.

Glaciological and Meteorological Conditions at the Chinese Taishan Station, East Antarctica

The glacio-meteorological characteristics of Princess Elizabeth Land in East Antarctica are poorly known due to a lack of measurement. This is problematic given the importance of this area for understanding ice sheet dynamics and climate change. We present a comprehensive approach (including field surveys, reanalysis data, remote sensing, and ice flow models) to investigate the glaciological and meteorological conditions in the vicinity of the new Chinese Taishan Station (73.864°S, 76.974°E) in Princess Elizabeth Land. We collected the datasets of satellite-derived ice surface velocities, surface mass balance, and wind field; mapped the ice thickness and internal layers around the Taishan Station site; and constructed profiles of the surface snow temperature and snow density. Also, we used transient thermodynamical 1-D vertical models to simulate the age of ice and the basal temperature with surface meteorological data and subglacial topography as boundary conditions. These investigations showed that Taishan Station is subject to a relatively high wind velocity, low temperatures (about -36 °C), and simple ice flow. The well-behaved internal layer stratigraphy implies that the ice flow of Taishan Station has been relatively stable, possibly for a long time. The fact that the internal layers are conformal with bed topography, there is a relatively higher basal ice age from ice modelling, and that the site lies over a bed depression filled with ice 1900 m thick, suggests that Taishan Station may be a good location for obtaining undisturbed old ice at depth. The combination of glacio-meteorological parameters suggests that Taishan Station is a potential drill site for the Chinese Antarctic Research Expedition (CHINARE) and an ideal logistical support location for proposed scientific field activities in the East Antarctic ice sheet (e.g. Dome A, Grove Mountains, and Princess Elizabeth Land).

The relationship between organoclastic sulfate reduction and carbonate precipitation/dissolution in marine sediments

Pore fluid sulfate, calcium and magnesium concentrations in ocean drilling sites 981–984, 925–929 and 803–807 are modeled to estimate the rates of sulfate reduction and carbonate precipitation/dissolution. These sites represent scenarios where the sulfate reduction rate is high, moderate, and low. Results show that the rate of carbonate precipitation decreases with decreasing sulfate reduction rate. When sulfate reduction rate is sufficiently low carbonate minerals dissolve. Sulfate reduction produces H+ and bicarbonate which compete in driving carbonate minerals to dissolve or precipitate. The results suggest that the carbonate reactions are mainly driven by the produced H+ when sulfate reduction rate is low, and by the produced bicarbonate when the sulfate reduction rate is high.

Changes in biogeographic distribution patterns of southern mid-to high latitude planktonic foraminifera during the Late Cretaceous hot to cool greenhouse climate transition

The biogeographic distribution of planktonic foraminifera from southern mid-to high latitudes region are discussed to identify links between species distribution patterns and the changes in Late Cretaceous climate. We present relative abundance data for planktonic foraminifera spanning from the hot greenhouse climate of the Turonian to the cooler greenhouse of the Maastrichtian based on study of Ocean Drilling Program (ODP) holes 690C (Maud Rise), 700B (Northeast Georgia Rise), 1138A (Kerguelen Plateau) and 762C (Exmouth Plateau). These drill sites were located between 47° and 65°S paleolatitude in the southern South Atlantic and southern Indian Ocean where there is a good record of changes in vertical gradients and sea surface temperatures (SSTs) and shifts are well expressed due to amplification of global climatic variations in the circum-Antarctic region.The stratigraphic distribution of planktonic foraminiferal marker species that consistently occur at all sites enables construction of a new biozonation scheme that is applicable to the southern mid-to high latitude region. Quantitative data from planktonic foraminifera are used to examine variation in assemblage composition, permitting interpretation of changes in the patterns of surface water stratification. In addition, temporal biogeographic patterns are documented from the stratigraphic record of endemic species of the Southern Ocean and of species displaying poleward or equatorward migration.Results indicate that the broadest latitudinal expansion of the Tethyan tropical climatic belt coincided with the highest paleotemperatures of the Turonian–Santonian. The onset of significant sea surface temperature cooling in the late Santonian–early Campanian led to a progressive increase in the latitudinal temperature gradient and greater biogeographic differentiation among planktonic foraminiferal assemblages. These trends resulted in the establishment of a Transitional Bioprovince with Tethyan and Austral affinities in the southern latitudes that persisted through the Campanian and Maastrichtian and the development of a well-defined Austral Bioprovince that is observed by the early Maastrichtian at paleolatitudes south of 60°S.

Moisture Source Tagging Confirming the Polar Amplification Effect in Amplifying the Temperature-δ18O Temporal Slope Since the LGM

Stable water isotopologues in paleoclimate archives ( δ 18 O ) have been widely used as an indicator to derive past climate variations. The modern observed spatial δ 18 O -temperature relation in the middle and high latitudes has been used to infer the paleotemperatures changes from ice core data. However, various studies have shown that the spatial slope is larger than the temporal slope at the drill site by a factor of 2. Physically, the different spatial and temporal slope has been suggested to result from the amplified local surface air temperature cooling in the polar region at Last Glacial Maximum (LGM), according to the slope ratio equation derived in our previous study. To explicitly confirm the “polar amplification” effect in understanding the differences between temporal and spatial isotope–temperature relations, here we use the same isotope-enabled atmospheric general circulation model with a moisture-tracing module embedded to quantitatively estimate the contributions of different sources to the precipitated heavy oxygen isotopes in the middle and high latitudes. Our results show that the major sources of δ 18 O in precipitation over middle and high latitudes are from oceans where the sea surface temperature cooling at Last Glacial Maximum (LGM) is less than −2 ° C , while the local moisture sources with a higher cooling can be also relevant for polar regions, such as north Greenland. Additionally, the neglect of the strengthened local inversion layer strength at LGM could be the main cause for the overestimated source temperature cooling by the slope ratio equation, especially for the polar regions in the Northern Hemisphere.

A 15-million-year-long record of phenotypic evolution in the heavily calcified coccolithophore &amp;lt;i&amp;gt;Helicosphaera&amp;lt;/i&amp;gt; and its biogeochemical implications

Abstract. The biogeochemical impact of coccolithophores is defined not only by their overall abundance in the oceans but also by wide ranges in physiological traits such as cell size, degree of calcification and carbon production rates between different species. Species' sensitivity to environmental forcing has been suggested to relate to their cellular PIC : POC (particulate inorganic carbon : particulate organic carbon) ratio and other physiological constraints. Understanding both the short-term and longer-term adaptive strategies of different coccolithophore lineages, and how these in turn shape the biogeochemical role of the group, is therefore crucial for modeling the ongoing changes in the global carbon cycle. Here we present data on the phenotypic evolution of a large and heavily calcified genus Helicosphaera (order Zygodiscales) over the past 15 million years (Myr), at two deep-sea drill sites in the tropical Indian Ocean and temperate South Atlantic. The modern species Helicosphaera carteri, which displays ecophysiological adaptations in modern strains, was used to benchmark the use of its coccolith morphology as a physiological proxy in the fossil record. Our results show that, on the single-genotype level, coccolith morphology has no correlation with growth rates, cell size or PIC and POC production rates in H. carteri. However, significant correlations of coccolith morphometric parameters with cell size and physiological rates do emerge once multiple genotypes or closely related lineages are pooled together. Using this insight, we interpret the phenotypic evolution in Helicosphaera as a global, resource-limitation-driven selection for smaller cells, which appears to be a common adaptive trait among different coccolithophore lineages, from the warm and high-CO2 world of the middle Miocene to the cooler and low-CO2 conditions of the Pleistocene. However, despite a significant decrease in mean coccolith size and cell size, Helicosphaera kept a relatively stable PIC : POC ratio (as inferred from the coccolith aspect ratio) and thus highly conservative biogeochemical output on the cellular level. We argue that this supports its status as an obligate calcifier, like other large and heavily calcified genera such as Calcidiscus and Coccolithus, and that other adaptive strategies, beyond size adaptation, must support the persistent, albeit less abundant, occurrence of these taxa. This is in stark contrast with the ancestral lineage of Emiliania and Gephyrocapsa, which not only decreased in mean size but also displayed much higher phenotypic plasticity in their degree of calcification while becoming globally more dominant in plankton communities.

Large Drill Holes Are Still Present in the Long Term After Arthroscopic Bankart Repair With Absorbable Tacks: An 18-Year Randomized Prospective Study

Background: Studies have demonstrated the development of an osseous reaction at the drill sites of anchors after arthroscopic shoulder surgery. Purpose: To investigate the drill-hole size at 18 years after arthroscopic Bankart repair using either fast polygluconate acid (PGA) or slow polylevolactic acid (PLLA) absorbable tacks and to compare the functional outcomes and development of osteoarthritis. Study design: Randomized controlled trial; Level of evidence, 2. Methods: 40 patients with unidirectional anterior shoulder instability, treated with arthroscopic Bankart repair, were randomized into the PGA group (n = 20) or the PLLA group (n = 20). Plain radiographs of both shoulders, as well as computed tomography (CT) images of the operated shoulder, were used to evaluate the drill-hole size, volume, and degenerative changes. Functional outcomes were assessed by use of the Rowe score, Constant score, and Western Ontario Shoulder Instability (WOSI) index. Results: Of the 40 patients, 32 patients returned for the follow-up (15 PGA and 17 PLLA). No significant differences were found in the population characteristics between the study groups. The mean follow-up time was 18 years for both groups. No significant differences were seen in range of motion, strength in abduction, or Constant, Rowe, and WOSI scores between the groups. Recurrence rate was 33% in the PGA group and 6% in the PLLA group during the follow-up period (P = .07). The drill-hole appearance on plain radiographs (invisible/hardly visible/visible/cystic) was 11/2/2/0 and 6/5/5/1 for the PGA and PLLA groups, respectively (P = .036). The mean ± SD drill-hole volume as estimated on CT images was 89 ± 94 and 184 ± 158 mm3 in the PGA and PLLA groups, respectively (P = .051). Degenerative changes (normal/minor/moderate/severe) on plain radiographs were 7/4/4/0 and 3/8/5/1 for the PGA and PLLA groups, respectively (P = .21), and on CT images were 5/7/3/0 and 2/6/6/3 for the PGA and PLLA groups, respectively (P = .030). Conclusion: This long-term follow-up study demonstrated that the PLLA group had significantly more visible drill holes than the PGA group on plain radiographs. However, this difference was not evident on CT imaging, with both groups having several visible cystic drill holes and a substantial drill-hole volume defect. No significant differences were found between the study groups in terms of clinical outcomes.