Progress in Physical Geography: Earth and Environment

The Arctic is thought to be an area where we can expect to see the first and strongest signs of global-scale climate variability and change. We have already begun to see a reduction in: (1) the aerial extent of sea ice at about 3% per decade and (2) ice thickness at about 40%. At the current rate of reduction we can expect a seasonally ice-free Arctic by midway through this century given the current changes in thermodynamic processes controlling sea-ice freeze-up and decay. Many of the factors governing the thermodynamic processes of sea ice are strongly tied to the presence and geophysical state of snow on sea ice, yet snow on sea ice remains poorly studied. In this review, we provide a summary of the current state of knowledge pertaining to the geophysical, thermodynamic and dielectric properties of snow on sea ice. We first give a detailed description of snow thermophysical properties such as thermal conductivity, diffusivity and specific heat and how snow geophysical/electrical properties and the seasonal surface energy balance affect them. We also review the different microwave emission and scattering mechanisms associated with snow-covered first-year sea ice. Finally, we discuss the annual evolution of the Arctic system through snow thermodynamic (heat/mass transfer, metamorphism) and aeolian processes, with linkages to microwave remote sensing that have yet to be defined from an annual perspective in the Arctic.

Research in tsunami geoscience has accelerated markedly ever since the tragedy of the Indian Ocean tsunami of Boxing Day 2004. Yet, for many decades and centuries, scholars have been describing a multiplicity of tsunami events. Thus the Royal Society devoted a whole volume to the effects of the Great Lisbon earthquake and tsunami of November AD 1755 while in the early nineteenth century Charles Darwin was describing the great tsunami at Valdivia, Chile, in his account of the Voyage of the Beagle. Today, research in tsunami geoscience is still finding its feet. Thus, whereas there has been a wealth of publications on the reconstruction of Late Quaternary and Holocene tsunamis, the literature describing evidence for tsunamis in the geological record are rare. In this paper, we describe how our understanding of tsunamis has changed over time and we try also to identify areas of tsunami geoscience worthy of future study.

Over recent decades several modern geoinformatic height-finding methods have emerged, including global positioning system (GPS), interferometric radar, and airborne laser scanner (ALS) or lidar. In conjunction with the conventional survey and photogrammetric method, they have found wide applications that demand varying levels of accuracy. In this paper, the principles of each method are briefly summarized. The discussion then concentrates on the accuracy level achievable with each method. The factors that affect the accuracy, wherever possible, are comprehensively evaluated. This review has revealed that the highest accuracy achievable is still with the levelling method, followed by the photogrammetric method. This situation is likely to change in light of real-time kinematic GPS coupled with ALS. In contrast to the imaging methods that are suited to obtain highly accurate, fine-resolution digital elevation models (DEMs) at a local scale, GPS is the most efficient at obtaining heights at spots or along lines accurately. ALS is the only method applicable to acquisition of subsurface heights in vegetated areas. These airborne methods are complementary to their space-borne counterparts, such as Shuttle Radar Topographic Mapping and Shuttle Laser Altimeter, both being ideal in obtaining DEMs at the regional and global scales. The synergistic use of GPS with lidar offers the best hope in obtaining cm-level accuracies essential for monitoring ground subsidence and tectonic uplift. Height measurements accurate to subcentimetres needed for national levelling surveys are possible only after the tropospheric path delay is externally calibrated using Raman lidar data during GPS data analysis.

Along with the major water erosion process, large amounts of soil nutrient can be transported to water bodies that may degrade the erosion sites and result in water pollution problems in the nutrient-receiving water bodies. Because of the far-reaching ecological and environmental impacts of the nutrient transport processes during water erosion, much research has been done on this topic. The progress of this research topic is reviewed from the perspective of nutrient sources, covering triggers, carriers and forms of nutrient transport, and the factors regulating nutrient transport. Although much progress has been made, challenges still lie ahead. A multidisciplinary and integrative approach, therefore, needs to be taken to resolve the theoretical, methodological and practical problems in water erosion and nutrient transport research. More specifically, the interactions between landscape pattern and nutrient transport processes and spatiotemporal scale and scaling are the two central themes of consideration in methodological integration. It is also important to respect the dynamic and stochastic nature of nutrient transport which is closely related to rainfall-runoff events. The human dimension, formerly a relative weak point in research, needs to be strengthened to gain understanding and a more informed practical control over soil and nutrient loss and conservation.