Snowball Earth, population bottleneck and Prochlorococcus evolution

Prochlorococcus are the most abundant photosynthetic organisms in the modern ocean. A massive DNA loss event occurred in their early evolutionary history, leading to highly reduced genomes in nearly all lineages, as well as enhanced efficiency in both nutrient uptake and light absorption. The environmental landscape that shaped this ancient genome reduction, however, remained unknown. Through careful molecular clock analyses, we established that this Prochlorococcus genome reduction occurred during the Neoproterozoic Snowball Earth climate catastrophe. The lethally low temperature and exceedingly dim light during the Snowball Earth event would have inhibited Prochlorococcus growth and proliferation, and caused severe population bottlenecks. These bottlenecks are recorded as an excess of deleterious mutations accumulated across genomic regions and inherited by descendant lineages. Prochlorococcus adaptation to extreme environmental conditions during Snowball Earth intervals can be inferred by tracing the evolutionary paths of genes that encode key metabolic potential. Key metabolic innovation includes modified lipopolysaccharide structure, strengthened peptidoglycan biosynthesis, the replacement of a sophisticated circadian clock with an hourglass-like mechanism that resets daily for dim light adaption and the adoption of ammonia diffusion as an efficient membrane transporter-independent mode of nitrogen acquisition. In this way, the Neoproterozoic Snowball Earth event may have altered the physiological characters of Prochlorococcus , shaping their ecologically vital role as the most abundant primary producers in the modern oceans.

Transient Response of a Simulated Aeroengine with a Fusing Structure during a Fan-Blade Out Event

A fan-blade out (FBO) event may cause complex vibrations in an aeroengine. A fusing structure protects the structural integrity of the whole aeroengine after an extreme accident, such as a blade-loss event. In this paper, we investigate not only the transient and steady responses of a simulated aeroengine model with a fusing structure after an FBO event but also the changes made to the model because of the fusing structure. Our simulated model of an aeroengine includes two rotors, bearings, and a casing. The results for the dynamic response of the simulated model show that the fusing structure can reduce the steady-state response and the impact load on the support bearings in the rotor system. The rubbing impact between the blades and casing was accounted for. A fast method for calculating the response of fused structures was developed, which may be useful when designing the stiffness of the fusing structure.

Sanctions and international interaction improve cooperationto avert climate change

We report the protocol relative to the experimental project "Sanctions and international interaction improve cooperation to avert climate change",which connected through the internet pairs of laboratories from Kiel and Bonn (Germany) and Moscow and Tomsk (Russia). The connection was realized through Z-Tree. Each research session comprised 24 participants, who were randomly allocated to 4 groups, whose members were three from one laboratory and three from the other. After receiving instructions and passing a comprehension test, participants interacted over ten rounds. Each participant had a fixed allocation of money in each round, which could have been kept for oneself or contributed to a group account. Contributions decreased the probability that everyone suffered a 75% loss in their personal account at the end of the interaction. A random draw determined whether occurrence the loss event occurred, and individual payoffs were paid privately in cash at the end of the session.

Nigeria JV Onshore OHGP Recent Experience: Beyond Flawless Execution

An oil producing swamp field, BX, is located in the coastal region of the western Niger Delta with an average water depth of 15 – 20 ft. The wells in the most recent development drilling campaign were designed as horizontal wells with critical well objective of meeting the target oil production rates with sand control. In order to achieve these goals, the sand control methodology deployed is the Open Hole Gravel Pack (OHGP) pumped through Concentric Annular Pack Screen (CAPS) system. This completion methodology has similar comparisons to the AX field completions where 19 completions were successfully installed between 2016 and 2018. The lessons learnt from the AX campaign were implemented on the BX campaign and this contributed to the campaign's near-flawless completion execution evidenced by the world class operational excellence, very low Non-Productive Times (NPTs) best-in-class production performances with no sand production However, the following opportunities were identified and implemented during the BX campaign focused on either increasing operational efficiency or preventing post-completion productivity impairment:Elimination of slickline required for tubing test operations by incorporating a "RH" catcher sub into the completion designPerforming required analysis and implementing procedural change to ensure that the change from WBM to NAF does not compromise completion performance due to the presence of reactive shales intervals encountered in the lateralDeveloping and implementing an enhanced fluid loss protocol to address the fluid loss event in one of the BX well that prevented the execution of OHGP pumping operation in the well. The implementation of these opportunities contributed significantly to the continued consistent delivery of superior completions performance in the BX field. This paper aims to provide a background to these opportunities and highlights the steps and processes that were applied to ensure their flawless implementation.

Photobiological Effects on Ice Algae of a Rapid Whole-Fjord Loss of Snow Cover during Spring Growth in Kangerlussuaq, a West Greenland Fjord

Snow cover on sea ice is the most important factor controlling light availability for sea ice algae, but it is predicted by climate models to become more variable and stochastic. Here, we document effects of a sudden, complete loss of the entire snow cover on first-year sea ice at Kangerlussuaq Fjord, West Greenland, due to a natural Föhn wind event that caused a ca. 17 °C air temperature increase over 36 h. We applied Imaging-PAM fluorometry to examine effects of snow cover on algal distribution and photobiology and observed a rapid decrease in algal biomass associated with loss of the skeletal ice crystal layer on the underside of the ice that had supported most of the visible algae. Furthermore, the remaining algae were photobiologically stressed, as seen in a significant decrease in the dark-acclimated fluorescence yield (ΦPSII_max) from 0.55 before snow loss to 0.41 after. However, recovery in the dark suggested that non-photosynthetic quenching was successfully dissipating excess energy in the community and that there was little photodamage. An observed decrease in the photosynthetic efficiency α from 0.22 to 0.16 µmol é m−2 s−1 is therefore likely to be due to photoacclimation and the change in community composition. Centric diatoms and flagellates were the main taxa lost in the snow loss event, whereas the sea ice specialist Nitzschia frigida increased in numbers. These observations are similar to those seen in artificial snow-clearing experiments and consistent with snow clearing being a useful approach for investigating the complex interactions between snow cover, irradiance fluctuations, and ice algal performance.

Predrill Geomechanical Evaluation Helps in Successful Drilling in High Depletion Wells in a Mature Field, Offshore Sarawak, Malaysia

Hydrocarbon-bearing reservoirs in a mature field, offshore Sarawak, Malaysia, contains multiple reservoir cycles interbedded with weak shale and coal formations. Years of production from these reservoirs caused significant pressure depletion, as well as reduced fracture gradient and a narrower drilling mud weight window. An improperly weighted mud may induce wellbore instability in weaker, but normally pressured, formations or mud losses in the heavily depleted reservoirs. Globally, mud losses are considered the most expensive well control operation incidents. Earlier drilling campaigns in ths field encountered numerous wellbore instability incidents; hence, a study was conducted to develop an understanding of the drilling issues and assess the stability of the heavily depleted reservoirs. Collaboration between the drilling and geomechanics teams facilitated better understanding of the stability challenges and helped in mitigating risk related to wellbore instability. A field scale geomechanical model was developed and validated using data from exploration and development wells from different phases of drilling in the study area. The stress path factor (SPF), which determines the reduction in fracture gradient with pore pressure depletion is crucial for defining drilling mud windows, is difficult to constrain in the absence of measured formation fracturing data in virgin and depleted reservoirs. A mud loss event in the depleted zone from a recent drilled well and regional information were used to estimate the range of SPF in the study area. Recorded bottom hole pressures from pressure while drilling (PWD) data suggested that the maximum equivalent circulating density (ECD) recorded was close or within the depleted section. The loss event was associated with reduced fracture gradient due to depletion from its pre-depleted range. This paper describes how geomechanical evaluation with effective well drilling practices and fit for purpose-drilling fluids have helped drilling through depleted reservoirs with ECD management. At the end, it shows a comparison of the predrill wellbore stability mud weight estimates with the actual mud weights used to successfully drill and complete the planned wells.

Reflections on COVID-19, Insurance, Business Interruption, Systemic Risk, and the Future

The COVID-19 pandemic is a major loss event for the insurance industry. This chapter begins with an overview of the pandemic’s most significant insurance implications. Because business interruption has been the most prominently discussed of these impacts, the second part of this chapter takes a closer look at business interruption insurance. This part describes how markets for this coverage are structured in the U.S., and then undertakes a detailed analysis of one of the most common business interruption policy forms, demonstrating that some aspects of this form, insofar as pandemic-caused business interruption is concerned, were not drafted with utmost precision. This part also discusses how disputes over common policy language used in the U.S. have unfolded, both in legislatures and the courts. The chapter concludes with a discussion of the future of insuring the business continuity risk. It explores the limitations of private markets, the role of government, and the need for an overarching strategy for pandemic risk management, within which insurance would play a significant but partial role.