Convection behind the Humidification of Titan’s Stratosphere

On Titan, methane is responsible for the complex prebiotic chemistry, the global haze, most of the cloud cover, and the rainfall that models the landscape. Its sources are located in liquid reservoirs at and below the surface, and its sink is the photodissociation at high altitude. Titan’s present and past climates strongly depend on the connection between the surface sources and the atmosphere upper layers. Despite its importance, very little information is available on this topic. In this work, we reanalyze two solar occultations made by Cassini before the northern spring equinox. We find a layer rich in methane at 165 km and at 70°S (mixing ratio 1.62% ± 0.1%) and a dryer background stratosphere (1.1%–1.2%). In the absence of local production, this reveals an intrusion of methane transported into the stratosphere by convective circulation. On the other hand, methane transport through the tropopause at a global scale appears quite inhibited. Leaking through the tropopause is an important bottleneck of Titan’s methane cycle at all timescales. As such, it affects the long-term evolution of Titan’s atmosphere and the exchange fluxes with the surface and subsurface reservoirs in a complex way. Global climate models accounting for cloud physics, thermodynamical feedbacks, and convection are needed to understand the methane cycle, and specifically the humidification of the stratosphere, at the present time, and its evolution under changing conditions at a geological timescale.

Prosets: making continued use of fossil fuels compatible with a credible transition to net zero

Interest in carbon offsetting is resurging among companies and institutions, but existing offerings fail to make continued use of fossil fuels compatible with a credible transition to sustainable net zero emissions. A clear definition of what makes an offset net-zero-compliant is needed. We introduce the ‘proset’, a new form of composite offset in which the fraction of carbon allocated to geological-timescale storage options increases progressively, reaching 100% by the target net zero date, generating predictable demand for effectively permanent CO2 storage while making the most of the near-term opportunities provided by nature-based climate solutions, all at an affordable cost to the offset purchaser.

Deep-sea panoramas: Progress and remaining challenges in late Miocene stratigraphy and climate

<p>During the late Miocene, meridional sea surface temperature gradients, deep ocean circulation patterns, and continental configurations evolved to a state similar to modern day. Deep-sea benthic foraminiferal stable oxygen (δ<sup>18</sup>O) and carbon (δ<sup>13</sup>C) isotope stratigraphy remains a fundamental tool for providing accurate chronologies and global correlations, both of which can be used to assess late Miocene climate dynamics. Until recently, late Miocene benthic δ<sup>18</sup>O and δ<sup>13</sup>C stratigraphies remained poorly constrained, due to relatively poor global high-resolution data coverage.</p><p>Here, I present ongoing work that uses high-resolution deep-sea foraminiferal stable isotope records to improve late Miocene (chrono)stratigraphy. Although challenges remain, the coverage of late Miocene benthic δ<sup>18</sup>O and δ<sup>13</sup>C stratigraphies has drastically improved in recent years, with high-resolution records now available across the Atlantic and Pacific Oceans. The recovery of these deep-sea records, including the first astronomically tuned, deep-sea integrated magneto-chemostratigraphy, has also helped to improve the late Miocene geological timescale. Finally, I will briefly touch upon how our understanding of late Miocene climate evolution has improved, based on the high-resolution deep-sea archives that are now available.</p>

Plate tectonics and volatiles: the nanorock connexion

<p>The global geological volatile cycle (H, C, N) plays an important role in the long term self-regulation of the Earth system. However, the complex interaction between its deep, solid Earth component (i.e. crust and mantle), Earth’s fluid envelope (i.e. atmosphere and hydrosphere) and plate tectonic processes is a subject of ongoing debate. Here, we want to draw attention to how the presence of primary, pristine melt (MI) and fluid (FI) inclusions in high grade metamorphic minerals could help constrain the crustal component of the volatile cycle. We review the distribution of pristine MI and FI throughout Earth’s history, from the onset of plate tectonics at ca. 3.0 Ga to the present day. Combined with thermodynamic modelling, our compilation indicates that periods of well-established plate tectonics regimes at 0-1.2 Ga and 1.8-2.0 Ga, might be more prone to the reworking of supracrustal lithologies and the storage of volatiles at lower crustal depths. We then argue that the lower crust might constitute an important, although temporary, volatile storage unit, capable to influence the composition of the surface envelopes through the mean of weathering, crustal thickening, partial melting and crustal assimilation during volcanic activity.</p><p>Such hypothesis has implication beyond the scope of metamorphic petrology as it potentially links geodynamic mechanisms to habitable surface conditions. MI and FI in metamorphic rocks is a rich but still relatively uncharted realm. In the near future, a concerted research effort should aim to find and characterize new instances of pristine inclusions in periods of the Earth’s history currently underrepresented in the inclusion database, e.g. the Boring Billion. The merging of the messages of thousands of minuscule droplets of fluids trapped in the deepest roots of the continental plates will then eventually provide a truly comprehensive portrait of how the Earth’s evolution proceeds through the geological timescale.</p><p> </p>

Granite Landscapes, Geodiversity and Geoheritage—Global Context

Granite geomorphological sceneries are important components of global geoheritage, but international awareness of their significance seems insufficient. Based on existing literature, ten distinctive types of relief are identified, along with several sub-types, and an overview of medium-size and minor landforms characteristic for granite terrains is provided. Collectively, they tell stories about landscape evolution and environmental changes over geological timescale, having also considerable aesthetic values in many cases. Nevertheless, representation of granite landscapes and landforms on the UNESCO World Heritage List and within the UNESCO Global Geopark network is relatively scarce and only a few properties have been awarded World Heritage status in recognition of their scientific value or unique scenery. Much more often, reasons for inscription resided elsewhere, in biodiversity or cultural heritage values, despite very high geomorphological significance. To facilitate future global comparative analysis a framework is proposed that can be used for this purpose.

The Coral of Plants

The present article has two primary objectives. First, the article provides a historical overview of graphical tools used in the past centuries for summarizing the classification and phylogeny of plants. It is emphasized that each published diagram focuses on only a single or a few aspects of the present and past of plant life on Earth. Therefore, these diagrams are less useful for communicating general knowledge in botanical research and education. Second, the article offers a solution by describing the principles and methods of constructing a lesser- known image type, the coral, whose potential usefulness in phylogenetics was first raised by Charles Darwin. Cladogram topology, phylogenetic classification and nomenclature, diversity of taxonomic groups, geological timescale, paleontological records, and other relevant information on the evolution of Archaeplastida are simultaneously condensed for the first time into the same figure – the Coral of Plants. This image is shown in two differently scaled parts to efficiently visualize as many details as possible, because the evolutionary timescale is much longer, and the extant diversity is much lower for red and green algae than for embryophytes. A fundamental property of coral diagrams, that is their self-similarity, allows for the redrawing of any part of the diagram at smaller scales.

Dynamical mechanism of the poleward intensification of the Southern Hemispheric Westerlies due to sea ice extent change

<p>Paleoclimate data shows a good correlation between the concentration of CO<sub>2</sub> and atmospheric temperature in the geological timescale. Many studies compare the Last Glacial Maximum (LGM) and the Pre-Industrial era (PI), to understand the coupling processes. A popular mechanism explaining this coupling process is a modulation of the ocean circulation and related CO<sub>2</sub> emission over the Southern Ocean due to atmospheric westerly. The atmospheric westerly plays an important role in driving ocean circulation; however, the related processes are not fully understood for the LGM period.</p><p>In this study, we examine physical processes determining the characteristics of the atmospheric westerly focusing on the Southern Ocean. Atmospheric states for LGM and PI are reproduced using a coupled earth system model with different sea ice conditions. A poleward intensification of the Southern Hemispheric Westerlies is observed for the LGM experiment. A comparison to PI shows that the meridional temperature gradient largely determines this intensification, and the enhanced meridional gradient is observed due to decreased heat flux from the subantarctic ocean in the LGM experiment. This result suggests that the Antarctic sea ice is a crucial component for understanding the Southern Hemispheric Westerly.</p>

About this title - Cretaceous Climate Events and Short-Term Sea-Level Changes

Sea-level constitutes a critical planetary boundary for both geological processes and human life. Sea-level fluctuations during major greenhouse phases are still enigmatic and widely discussed in terms of changing climate systems. The geological record of the Cretaceous greenhouse period provides a deep-time view on greenhouse-phase Earth system processes that facilitates a much better understanding of the causes and consequences of global, geologically short-term, sea-level changes. In particular, Cretaceous hothouse periods can serve as a laboratory to better understand a near-future greenhouse Earth. This volume presents high-resolution sea-level records from globally distributed sedimentary archives of the Cretaceous involving a large group of scientists from the International Geoscience Programme IGCP 609. Marine to non-marine sedimentary successions were analysed for revised age constraints, the correlation of global palaeoclimate shifts and sea-level changes, tested for climate-driven cyclicities, and correlated within a high-resolution stratigraphic framework of the Geological Timescale. For hothouse periods, the hypothesis of significant global groundwater-related sea-level change, i.e. aquifer-eustasy as a major process, is reviewed and substantiated.

An introduction to causes and consequences of Cretaceous sea-level changes (IGCP 609)

The International Geoscience Programme Project IGCP 609 addressed correlation, causes and consequences of short-term sea-level fluctuations during the Cretaceous. Processes causing several ka to several Ma (third- to fourth-order) sea-level oscillations during the Cretaceous are so far poorly understood. IGCP 609 proved the existence of sea-level cycles during potential ice sheet-free greenhouse to hothouse climate phases. These sea-level fluctuations were most probably controlled by aquifer-eustasy that is altering land-water storage owing to groundwater aquifer charge and discharge. The project investigated Cretaceous sea-level cycles in detail in order to differentiate and quantify both short- and long-term records based on orbital cyclicity. High-resolution sea-level records were correlated to the geological timescale resulting in a hierarchy of sea-level cycles in the longer Milankovitch band, especially in the 100 ka, 405 ka, 1.2 Ma and 2.4 Ma range. The relation of sea-level highs and lows to palaeoclimate events, palaeoenvironments and biota was also investigated using multiproxy studies. For a hothouse Earth such as the mid-Cretaceous, humid–arid climate cycles controlling groundwater-related sea-level change were evidenced by stable isotope data, correlation to continental lake-level records and humid–arid weathering cycles.