47242 research outputs found
Sort by
Post-LGM sedimentation history and deglaciation processes in the southern Gulf of St. Lawrence, Canada
No full textHighlights
• Significant influence of the Bølling-Allerød and Younger Dryas on sedimentation.
• Buried sediment basins and channels filled by late Pleistocene sediments.
• Sedimentation rates >0.4 cm a−1 during deglaciation.
• Erosional truncation possibly related to the Holocene RSL lowstand.
• Marine sedimentation close to the coast of PEI as early as ∼13.6 ka BP.
Abstract
During the last glacial period, continents and surrounding shelves in high latitude regions of the Northern Hemisphere were covered by ice sheets. Their retreat after the Last Glacial Maximum resulted in isostatic adjustments of the previously glaciated landmass and post-glacial changes in relative sea level during the late Pleistocene and Holocene. Many questions, however, remain about the timing and impact of the ice retreat and of short-lived climatic events on continental shelf environments. This study aims to reconstruct the sedimentation and deglaciation processes on the continental shelf of the southern Gulf of St. Lawrence (Canada) over the past 14 ka by investigating changes in the sedimentation patterns and paleo-environments. Using information from sub-bottom profiles, sediment cores, and multibeam bathymetry, this study finds that most of the continental shelf was flooded 13.6 ka ago, as evidenced by the presence of Bølling-Allerød marine sediments at a water depth of ∼50 m and ∼15 km off the modern coastline, which also suggests an earlier retreat of the Laurentide Ice Sheet than suggested by previous studies. We estimate sedimentation rates for the Bølling-Allerød of ∼0.4 cm a−1, which increased up to 1 cm a−1 during the Younger Dryas cooling event, likely associated with increased storm-wave activity and sea ice development caused by deteriorating climatic conditions. The presence of an erosional truncation atop Younger Dryas sediments indicates a late Pleistocene-early Holocene relative sea level fall and associated lowstand. Based on our new data, we established a geological model that highlights sedimentation processes since the Last Glacial Maximum and demonstrate the potential impact of short-lived climatic events on the former ice margin during deglaciation
On the importance of Mongolian cyclones to East Asian dust storms
No full textIn East Asia, dust storms typically occur in spring with adverse impacts on socio-economic activities, loss of life, and climate. Mongolian cyclones that form downstream of the Altai-Sayan Mountain have been known for some time as drivers of spring dust storms in East Asia. The passage of Mongolian cyclones primarily induces dust-emitting winds in the Gobi Desert, leading to dust emissions and favoring the subsequent transport of dust aerosols across Northern China. Herein, the relative contributions of Mongolian cyclones to dust emissions in the Gobi Desert and subsequent dust storm activity in Northern China are assessed from a climatological perspective for the first time in this dissertation. Furthermore, this study provides the first evidence that dust activity in the Taklamakan Desert, which is located in the west of the Gobi Desert, is also supported by Mongolian cyclones. This assessment aims to illustrate the importance of Mongolian cyclones in generating spring dust storms across East Asia
Source location of oceanic transform fault earthquakes constrained by IMS hydrophone triplets in the Indian Ocean
No full textMidwater invertebrates in the deep ocean: Adaptations, interactions and impacts of stressors
No full textThe midwater, or deep open ocean, forms over 90% of the livable space on Earth and houses one of the largest animal communities alive. As such, midwater ecosystems form important links in oceanic food webs and play a crucial role in the regulation of our climate by keeping atmospheric carbon at depth. Yet despite their importance on a global scale, midwater ecosystems remain largely unexplored. My PhD thesis aims to investigate adaptations in midwater invertebrates, including their associations, evolution and responses to human-induced stressors. The focus was on gelatinous organisms and hyperiid amphipods, as both are highly abundant in the midwater and frequently interact. In my first chapter, I investigated the impacts of global warming and deep-sea mining induced sediment plumes on a midwater jellyfish, combining insights gained from physiology, gene expression and changes in associated microbiota. For my second chapter, I studied the interactions of hyperiid amphipods with gelatinous organisms to show how symbiotic behavior drives morphological adaptations in camouflage and eye complexity, using nearly 30 years of remotely operated vehicle observations. For my third chapter, I investigated the compound eyes in a family of closely related hyperiid amphipods (Oxycephalidae) using micro-computed tomography (micro-CT) to map their optics and model their vision. Here, I was able to show how fine-scale visual adaptations can elucidate visual ecology and provide insights into the evolutionary drivers of vision in midwater amphipods. All in all, my PhD emphasizes the importance of combining multiple methods to gain detailed insights into life in the largest, but least studied habitat on Earth
A workflow for estimating injection pressure limits for CO2 storage: A reservoir-geomechanical analysis of a candidate site in the German North Sea sector
No full textHighlights:
• A novel workflow integrates multiphase flow and geomechanical models to determine site-specific CO₂ injection pressure limits.
• Injection rates of up to 1.7 Mt CO₂/year per well are sustainable under reservoir constraints, with higher rates achievable due to a 10 MPa increase in pressure governed by the cap rock’s tensile strength.
• Vertical wells exhibit an injection limit of ∼18 MPa/km, while horizontal configurations extend this to ∼20 MPa/km, highlighting the influence of well geometry on injection strategy design.
• At the investigated storage site, overpressure in the reservoir and cap rock remains compressive over a 100-year period, confirming robust containment and long-term storage integrity.
Abstract
Geological carbon capture and storage (CCS) in saline formations is seen as a plausible short-term solution to reduce atmospheric carbon dioxide (CO₂) concentrations and mitigate climate change. Besides storage capacity, largely determined by pore space within a geological trap, the maximum allowable pressure in the storage formation represents a major limitation for geological CO₂ storage. This study, therefore, addresses the hydromechanical aspects of geological CO₂ storage by developing an integrated workflow to determine site-specific injection pressure limits and applying it to a potential storage site in the German North Sea sector. The workflow ensures consistency between reservoir flow and geomechanical models by automatically extracting near-wellbore geomechanical domains from the large-scale model. For a vertical well, the site-specific injection pressure limit is estimated at 17.9 MPa/km, governed by tensile failure in the storage formation. Within the cap rock, the limit increases to 28.6 MPa/km, providing a large margin of safety and enabling higher injection rates. A horizontal well configuration yields a slightly higher limit of 19.7 MPa/km, due to the larger well-reservoir contact area and improved pressure dissipation. The derived pressure limits are subsequently implemented in a large-scale dynamic simulation to verify workflow performance and assess formation integrity. Results indicate that injection rates of approximately 1.7 Mt CO₂ per year per vertical well can be sustained over 30 years, with reservoir overpressure and the corresponding stress states strongly dependent on the hydraulic setting of the reservoir. Importantly, injection-induced stresses and thus the probability of fracture formation decreases rapidly after CO₂ injection ends
Earth System responses to highly ambitious mitigation scenarios : Contributions from forcing and model uncertainties
No full textHuman activities have caused strong alterations to the climate system. International political efforts have attempted to avoid further impacts by limiting global warming levels. In this sense, highly ambitious emissions mitigation scenarios are a desirable future to be aimed for. Despite a clear necessity of reaching such scenarios, uncertainty remains on potential system responses as the importance of carbon forcing decreases. This thesis shows that varying aerosols spatial implementation allows for a considerable surface temperature variability, as well as variability in individual components’, such as land carbon uptake, contributions to the warming or cooling of the system. Triggered feedbacks due to aerosols implementations can have a crucial impact in assessing ambitious mitigation scenarios. Furthermore, the thesis introduces a new framework (FROT: Framework for Radiative cOntributions to Temperature responses), to comprehensively assess the temperature variability for different ambitious mitigation future scenarios, and to account for individual contributions from different climate components. The findings corroborate the need for including forcings and transient responses when assessing climate development. Finally, the thesis focused on techniques to remove carbon dioxide from the atmosphere. It finds that for centennial timescales dissolved ocean oxygen under cabon dioxide removal is unable to return to pre-industrial levels. This response is dependent on the region and depth considered. The findings indicate that apparent oxygen use dominates the simulated oxygen development, especially due to changes in circulation and ventilation. These findings widen the understanding of expected responses and components development under ambitious mitigation scenarios, either by reducing or by clarifying different uncertainties expected in the assessment, analysis and potential real-world outcomes of these scenarios
Qualitative modeling for representing the social-ecological system of the Groix–Belle-île offshore wind farm project
No full textThe increasing numbers of offshore wind farm (OWF) projects question the impacts of such infrastructures on the social-ecological system (SES) in which they are to be constructed. Some answers can be given using qualitative modeling and loop analysis. We used participatory modeling to co-construct a qualitative model of the socio-ecosystem together with stakeholders of the APPEAL project. The goal of the project was to evaluate the potential impacts of the pilot OWF in the Groix-Belle-& icirc;le region. Then, loop analysis was used to study the characteristics of the SES created by the setting-up of an OWF. We focused on the impacts of SES variables on each other by evaluating their effects through direct and indirect pathways. Pleasure boating appeared as one of the SES components prone to suffer from the OWF construction, whereas industrial tourism was likely to benefit from it. This article presents the methodology used to obtain such results, for it to be used in spatial planning or in citizen-science processes
Growth response of Emiliania huxleyi to ocean alkalinity enhancement
No full textThe urgent necessity of reducing greenhouse gas emissions is coupled with a pressing need for widespread implementation of carbon dioxide removal (CDR) techniques to limit the increase in mean global temperature to levels below 2 °C compared to pre-industrial times. One proposed CDR method, Ocean Alkalinity Enhancement (OAE), mimics natural rock weathering processes by introducing suitable minerals into the ocean thereby increasing ocean alkalinity and promoting CO2 chemical absorption. While theoretical studies hold promise for OAE as a climate mitigation strategy, careful consideration of its ecological implications is essential. Indeed, the ecological impacts of enhanced alkalinity on marine organisms remain a subject of investigation as they may lead to changes in species composition. OAE implicates favourable conditions for calcifying organisms by enhancing the saturation state of calcium carbonate and decreasing the energetic costs for calcification. This may affect marine primary production by improving conditions for calcifying phytoplankton, among which coccolithophores play the leading role. They contribute <10 % to the global marine primary production, but are responsible for a large proportion of the marine calcite deposition. While previous research has extensively studied the effects of ocean acidification on coccolithophores, fewer studies have explored the impacts of elevated pH and alkalinity. In this context, we studied the sensitivity of Emiliania huxleyi, the most widespread coccolithophore species, to ocean alkalinity enhancement in a culture experiment. We monitored the species’ growth and calcification response to progressively increasing levels of total alkalinity (TA). Above a change in total alkalinity (ΔTA) of ~ 600 µmol kg-1, as CO2 concentrations decreased, E. huxleyi growth rate diminished, suggesting a threshold CO2 concentration of ~ 100 μatm necessary for optimal growth. The cellular calcite to organic carbon ratio (PIC:POC) remained stable over the total alkalinity range. Due to the decreasing growth rate in response to alkalinity enhancement, total carbonate formation was lower. OAE is rapidly advancing and has already reached the field-testing stage. Hence, our study contributes to the most critical part of investigations required to comprehend potential biological implications before large-scale OAE will be adapted