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The Southern Hemisphere has experienced widespread changes to its climate over the instrumental record, with many of these recent changes exceeding ranges associated with natural variability over the last millennia. Decadal oscillations, such as the Interdecadal Pacific Oscillation (IPO), have significantly influenced long-term rainfall patterns across the Southern Hemisphere continents. In recent decades, it has become possible to attribute many aspects of these changes to the Southern Hemisphere climate to human-induced causes. Since the pre-industrial period, temperatures have warmed by ~1–1.5°C over the Southern Hemisphere land masses with anthropogenic greenhouse gas emissions being the primary driver of this warming. Additionally, changes in many extremes, including heat waves and heavy rainfall, have also been observed. The decline in stratospheric ozone over Antarctica from ~1970s to the early 2000s has been implicated in the observed poleward movement of the Southern Hemisphere midlatitude jet and expansion of the tropics during austral summer. Future anthropogenic climate change in the Southern Hemisphere extratropical circulation will be driven by the competing effects of ozone recovery and increasing greenhouse gases. The Southern Ocean – which has an enormous capacity to uptake heat and carbon – is expected to warm at an accelerated rate, with associated consequences for Antarctic sea ice and ice sheet stability.
Sea surface films significantly influence air–sea interaction. While their damping effect on gravity–capillary waves is well recognised, the detailed mechanisms by which surface films alter small-scale wave dynamics – particularly energy dissipation and near-surface flow patterns – remain insufficiently understood. This paper presents experimental observations focusing on small-scale wave profiles and surface-flow dynamics in the presence of surfactants, providing direct experimental evidence of underlying mechanisms such as Marangoni effects. The experiments demonstrate enhanced energy dissipation and significant alterations in near-surface flow caused by surfactants, including the transformation of typical circular motion into elliptical-like trajectories and the emergence of reverse surface drift.
This chapter discusses the major features of intraseasonal (weekly to three-monthly) and interannual (year-to-year) variability in the Southern Hemisphere’s atmospheric circulation and their relationship with large-scale modes of variability such as the Madden–Julian Oscillation, El Niño Southern Oscillation, the Indian Ocean Dipole, and the Southern Annular Mode. The interactions between these modes of variability are also explored. Teleconnections to regional large-scale temperature and precipitation variability in the Southern Hemisphere are summarised. While the focus of this chapter is large-scale drivers and circulation patterns, we also briefly discuss regional processes occurring on interannual timescales (such as subtropical dipole modes) and associated impacts. Finally, a brief summary of observed trends and projected future changes to these modes is presented, as well as current challenges and research gaps.
Spectral analysis of the transport process of turbulence kinetic energy (TKE) in a channel roughened with spanwise-aligned circular-arc ribs is conducted based on direct numerical simulations (DNS). Test cases of varying pitch-to-height ratios ($P/H=3.0$, 5.0 and 7.5) and bulk Reynolds numbers (${\textit{Re}}_b=5600$ and 14 600) are compared. It is observed that the characteristic spanwise wavelength of the energy-containing eddies in the internal shear layer (ISL) increases as the value of $P/H$ increases, but decreases as the Reynolds number increases. In the ISL, the energy transport processes are dominated by turbulent production as the lead source term, but by turbulent diffusion and dissipation as the lead sink terms. It is found that regions with high production and dissipation rates of TKE in the ISL are associated with moderate and small wavelengths, respectively. The TKE production for sustaining moderate- and large-scale motions enhances gradually with an increasing value of $P/H$, while that for sustaining small-scale motions augments as the Reynolds number increases. It is interesting to observe that the interscale-transport term plays a critical role in draining TKE at moderate wavelengths as a sink and carries the drained TKE to small-scale eddies as a source. It is discovered that a higher pitch-to-height ratio leads to shortening of the characteristic spanwise wavelength of the dissipation process but prolongation of those of the production, interscale-transport and turbulent-diffusion processes in the ISL. By contrast, a higher Reynolds number results in reductions in the characteristic spanwise wavelengths of all spectral transport terms.
The emergence of large-scale spatial modulations of turbulent channel flow, as the Reynolds number is decreased, is addressed numerically using the framework of linear stability analysis. Such modulations are known as the precursors of laminar–turbulent patterns found near the onset of relaminarisation. A synthetic two-dimensional base flow is constructed by adding finite-amplitude streaks to the turbulent mean flow. The streak mode is chosen as the leading resolvent mode from linear response theory. In addition, turbulent fluctuations can be taken into account or not by using a simple Cess eddy viscosity model. The linear stability of the base flow is considered by searching for unstable eigenmodes with wavelengths larger than the base flow streaks. As the streak amplitude is increased in the presence of the turbulent closure, the base flow loses its stability to a large-scale modulation below a critical Reynolds-number value. The structure of the corresponding eigenmode, its critical Reynolds number, its critical angle and its wavelengths are all fully consistent with the onset of turbulent modulations from the literature. The existence of a threshold value of the Reynolds number is directly related to the presence of an eddy viscosity, and is justified using an energy budget. The values of the critical streak amplitudes are discussed in relation with those relevant to turbulent flows.
Procolophonidae, a clade of stem reptiles, are hypothesized to be some of the first highly specialized herbivores to evolve following the end-Permian mass extinction event. That hypothesis is largely based on qualitative observations of tooth shape, which are highly subjective and not generalizable. Quantitative studies of reptilian tooth shape have employed relatively sophisticated methods to capture tooth complexity, but these approaches often require expensive equipment and software and are time intensive. In this study, we built a predictive model based on extant lizards to quantitatively predict the diets of procolophonids using simple measures of tooth morphology. We use linear discriminant analysis (LDA) to predict dietary ecology from tooth dimensions and phylogenetic MANOVA to test for significant differences in tooth dimensions for different diet categories. We report two key findings: (1) procolophonids are largely predicted as herbivorous but occupy a different area of the LDA space from extant lizards, and (2) simple metrics return similar results as complex methods, but with less confidence. We hypothesize that Triassic flora posed different mechanical and processing challenges from modern plants, which contributed to the unique tooth morphologies of procolophonids and likely other Triassic taxa.
The Quaternary period, which began 2.58 million years ago and continues to the present day, is distinctive for its significant climate variability. Understanding the mechanisms of climate change during this period and the relationship between carbon dioxide levels and temperature are hugely important in improving our ability to develop models to predict future climate change. This book discusses the main methods of empirical climatology and the models used to address different aspects of Quaternary climate dynamics, offering a multidisciplinary view of past and future climate changes. It examines the proposed mechanisms of Quaternary climate variability, including glacial cycles and abrupt climate changes, and their relationship to the intrinsic instability of ocean circulation and ice sheets. Including a final chapter on the Anthropocene, it provides a comprehensive overview of Quaternary and modern climate dynamics for graduate students and researchers working in paleoclimatology and climate change science.
A stratigraphic section made of Quaternary alluvial–lacustrine sediments belonging to the Baza Formation (South Spain) has been logged and studied for paleomagnetism, rock magnetic cyclostratigraphy, and electron spin resonance (ESR) quartz dating. Our results indicate that the section, which is found in the vicinity of a number of paleontological and archaeological localities, falls within the mid-Early Pleistocene (Calabrian), within the Matuyama Chron, and runs to the Jaramillo Subchron, encompassing the Cobb Mountain Subchron. The magnetostratigraphic results combined with rock magnetic cyclostratigraphy and ESR provide solid timelines, which allow gross accumulation rates to be estimated, and revealing an upsection decrease of sedimentation in accordance with the lithological and paleodepositional changes. Our study furnishes new chronologies to better understand the timing of the latest stages of endorheic sedimentation that precedes the capture of the Baza Basin by the Gualdalquivir River in the Middle Pleistocene.
In January 1852, as searches continued for Sir John Franklin’s missing Arctic expedition, large quantities of preserved (that is, canned) meats supplied to the Royal Navy were found putrid and caused concern that the expedition had received similar meats with fatal consequences. Whilst a Parliamentary enquiry concluded correctly that the expedition had received good-quality meats, it neglected the fact that some 5% of all canned meats were condemned on ships due to damage and corrosion. As the Franklin expedition would be no exception, the study applies recent evidence of the expedition’s victualling schedule to estimate the number of cans condemned by the time at Beechey Island when a decision would be made whether enough remained to sustain the mission. It also estimates the vitamin B1 (thiamine) content of the meat because high temperatures during canning would have degraded or destroyed that vitamin, and vitamin C, both being essential to health. Any reduction in general rations would add to the decline in the quality of the diet. The expedition’s unique circumstances of long entrapment without recourse to hunting to supplement such deficiencies, or to escape, would prove fatal regardless of the good quality of the canned provisions.
We present a critical survey on the consistency of uncertainty quantification used in deep learning and highlight partial uncertainty coverage and many inconsistencies. We then provide a comprehensive and statistically consistent framework for uncertainty quantification in deep learning that accounts for all major sources of uncertainty: input data, training and testing data, neural network weights, and machine-learning model imperfections, targeting regression problems. We systematically quantify each source by applying Bayes’ theorem and conditional probability densities and introduce a fast, practical implementation method. We demonstrate its effectiveness on a simple regression problem and a real-world application: predicting cloud autoconversion rates using a neural network trained on aircraft measurements from the Azores and guided by a two-moment bin model of the stochastic collection equation. In this application, uncertainty from the training and testing data dominates, followed by input data, neural network model, and weight variability. Finally, we highlight the practical advantages of this methodology, showing that explicitly modeling training data uncertainty improves robustness to new inputs that fall outside the training data, and enhances model reliability in real-world scenarios.
This study presents the first sponge biodiversity inventory of Los Picos reef in Veracruz, Mexico. Although the Veracruz Reef System is known for its high sponge diversity, several recently discovered submerged reefs – including Los Picos – had remained biologically uncharacterised until this investigation. Our comprehensive inventory documents 37 species, identified at the species level, all belonging to Demospongiae; 15 of which are new records for the Mexican coast, and 13 for the Gulf of Mexico (GoM). Six species are described as new: Psammocinia alcoladoi sp. nov., distinguished by a dermal surface armoured with sand and spongin filaments, lightly fasciculated primary fibres, and non fasciculated secondary with long conules and slender fiber diameters; Hyatella hyattus sp. nov., distinguished by its soft and lobular habitus, and slender fiber diameters; Zyzzya marinagreenae sp. nov., is an open fistula with acanthostrongyles irregularly spined and both, acanthostrongyles and isochelae, smaller in size; Desmapsamma paulumharenae sp. nov., has an encrusting shape with larger spicules than D. anchorata; Phorbas veracruzanus sp. nov., consists of conule-shaped processes on an embedded layer and morphometric differences on spicules; and Timea citlallitzina sp. nov., stands out by the lumpy tips of the oxyaster type. The whole, highlighted by two genera, Psammocinia and Zyzzya, both reported for the first time in the GoM. Samples were obtained by SCUBA surveys at 10–16 m depth, between August and October 2017.
Plastic pollution is an emerging threat to our marine and terrestrial environments. International policy development to mitigate this pollution is currently underway; however, the process is complex. In parallel, local, national and regional initiatives are being developed. The research community is advocating for strong regulations based on robust evidence of the harm and severity of plastic pollution on oceans, land and for humans. However, the research community comprises different disciplines, research traditions and methodological approaches. This heterogeneity is in its core a great advantage, but only when we manage to build on each other where “synthesis” occurs. Currently, there remains a divide between the physical and social sciences, with research predominantly skewed toward the physical sciences, focusing on concentrations, fate and impact of plastic pollution.
In this article, I question the lack of philosophical discussions about the foundation of our research on plastic pollution, our knowledge claims, our views of “clean,” “pristine” and nature itself, as well as of the need for such discussions. I also propose a possible way forward to bridge the gap between disciplines and research traditions, fostering real interdisciplinarity.
We propose a novel multiple-scale spatial marching method for flows with slow streamwise variation. The key idea is to couple the boundary region equations, which govern large-scale flow evolution, with local exact coherent structures that capture the small-scale dynamics. This framework is consistent with high-Reynolds-number asymptotic theory and offers a promising approach to constructing time-periodic finite-amplitude solutions in a broad class of spatially developing shear flows. As a first application, we consider a non-uniformly curved channel flow, assuming that a finite-amplitude travelling-wave solution of plane Poiseuille flow is sustained at the inlet. The method allows for the estimation of momentum transport and highlights the impact of the inlet condition on both the transport properties and the overall flow structure. We then consider a case with gradually decreasing curvature, starting with Dean vortices at the inlet. In this setting, small external oscillatory disturbances can give rise to subcritical self-sustained states that persist even after the curvature vanishes.
In the paper, we consider a two-dimensional free-surface flow past a single point vortex in fluid of infinite depth. The flow moves from left to right with uniform speed $c$ far upstream and is subject to the downward acceleration $g$ of gravity. A point vortex of circulation $\varGamma$ is located at depth $H$. The positive direction of circulation is counterclockwise. The flow is characterised by two dimensionless parameters which are the dimensionless vortex circulation $\gamma =\varGamma /(\textit{cH}\,)$ and the Froude number $ \textit{Fr}=c/\sqrt {gH}$. The goal of the paper is to find the solutions of the solitary wave type with one or several crests on the free surface. These solutions are waveless far downstream and have a vertical line of symmetry. We have established that for a fixed Froude number $ \textit{Fr}\le 0.8$, there exists a finite set of positive $\gamma$ for which the solutions of the solitary wave type occur.
Granular flow down an inclined plane is ubiquitous in geophysical and industrial applications. On rough inclines, the flow exhibits Bagnold’s velocity profile and follows the so-called $\mu (I)$ local rheology. On insufficiently rough or smooth inclines, however, velocity slip occurs at the bottom and a basal layer with strong agitation emerges below the bulk, which is not predicted by the local rheology. Here, we use discrete element method simulations to study detailed dynamics of the basal layer in granular flows down both smooth and rough inclines. We control the roughness via a dimensionless parameter, $R_a$, varied systematically from 0 (flat, frictional plane) to near 1 (very rough plane). Three flow regimes are identified: a slip regime ($R_a \lesssim 0.45$) where a dilated basal layer appears, a no-slip regime ($R_a \gtrsim 0.6$) and an intermediate transition regime. In the slip regime the kinematics profiles (velocity, shear rate and granular temperature) of the basal layer strongly deviate from Bagnold’s profiles. General basal slip laws are developed that express the slip velocity as a function of the local shear rate (or granular temperature), base roughness and slope angle. Moreover, the basal layer thickness is insensitive to flow conditions but depends somewhat on the interparticle coefficient of restitution. Finally, we show that the rheological properties of the basal layer do not follow the $\mu (I)$ rheology, but are captured by Bagnold’s stress scaling and an extended kinetic theory for granular flows. Our findings can help develop more predictive granular flow models in the future.