Cascading hazards of a major Bengal basin earthquake and abrupt avulsion of the Ganges River.

Earthquakes present severe hazards for people and economies and can be primary drivers of landscape change yet their impact to river-channel networks remains poorly known. Here we show evidence for an abrupt earthquake-triggered avulsion of the Ganges River at ~2.5 ka leading to relocation of the mainstem channel belt in the Bengal delta. This is recorded in freshly discovered sedimentary archives of an immense relict channel and a paleo-earthquake of sufficient magnitude to cause major liquefaction and generate large, decimeter-scale sand dikes >180 km from the nearest seismogenic source region. Precise luminescence ages of channel sand, channel fill, and breached and partially liquefied floodplain deposits support coeval timing of the avulsion and earthquake. Evidence for reorganization of the river-channel network in the world's largest delta broadens the risk posed by seismic events in the region and their recognition as geomorphic agents in this and other tectonically active lowlands. The recurrence of comparable earthquake-triggered ground liquefaction and a channel avulsion would be catastrophic for any of the heavily populated, large river basins and deltas along the Himalayan arc (e.g., Indus, Ganges, Brahmaputra, Ayeyarwady). The compounding effects of climate change and human impacts heighten and extend the vulnerability of many lowlands worldwide to such cascading hazards.

Emerging forest-peatland bistability and resilience of European peatland carbon stores.

Northern peatlands store large amounts of carbon. Observations indicate that forests and peatlands in northern biomes can be alternative stable states for a range of landscape settings. Climatic and hydrological changes may reduce the resilience of peatlands and forests, induce persistent shifts between these states, and release the carbon stored in peatlands. Here, we present a dynamic simulation model constrained and validated by a wide set of observations to quantify how feedbacks in water and carbon cycling control resilience of both peatlands and forests in northern landscapes. Our results show that 34% of Europe (area) has a climate that can currently sustain existing rainwater-fed peatlands (raised bogs). However, raised bog initiation and restoration by water conservation measures after the original peat soil has disappeared is only possible in 10% of Europe where the climate allows raised bogs to initiate and outcompete forests. Moreover, in another 10% of Europe, existing raised bogs (concerning ∼20% of the European raised bogs) are already affected by ongoing climate change. Here, forests may overgrow peatlands, which could potentially release in the order of 4% (∼24 Pg carbon) of the European soil organic carbon pool. Our study demonstrates quantitatively that preserving and restoring peatlands requires looking beyond peatland-specific processes and taking into account wider landscape-scale feedbacks with forest ecosystems.

Landscape dynamics revealed by luminescence signals of feldspars from fluvial terraces.

Luminescence signals of quartz and feldspar minerals are widely used to determine the burial age of Quaternary sediments. Although luminescence signals bleach rapidly with sunlight exposure, incomplete bleaching may affect luminescence ages, in particular in fluvial settings where an unbleached remnant signal is commonly encountered in modern alluvium. Here, we use feldspar single-grain post-infrared IR stimulation (pIRIR) dating to show that recent (<11 ka) fluvial terraces of the Rangitikei River (New Zealand) were formed in a context of non-linear incision rate. We relate this pattern to the rapid reinstatement of steady-state incision following the formation of a major, climate-driven, aggradation terrace, causing a phase of accelerated incision. In addition, we show systematic variations in the proportion of unbleached grains in the fluvial sediments over time, mirroring incision rate at the time of deposition. Deposits formed during rapid incision contain fewer bleached grains, which we attribute to large input of unbleached material and limited bleaching opportunities during fluvial transport. This finding demonstrates that the luminescence signals recorded in fluvial terraces not only yield age information, but also inform us on past fluvial transport and ultimately, landscape dynamics.

Spatial early warning signals for impending regime shifts: A practical framework for application in real-world landscapes.

Prediction of ecosystem response to global environmental change is a pressing scientific challenge of major societal relevance. Many ecosystems display nonlinear responses to environmental change, and may even undergo practically irreversible 'regime shifts' that initiate ecosystem collapse. Recently, early warning signals based on spatiotemporal metrics have been proposed for the identification of impending regime shifts. The rapidly increasing availability of remotely sensed data provides excellent opportunities to apply such model-based spatial early warning signals in the real world, to assess ecosystem resilience and identify impending regime shifts induced by global change. Such information would allow land-managers and policy makers to interfere and avoid catastrophic shifts, but also to induce regime shifts that move ecosystems to a desired state. Here, we show that the application of spatial early warning signals in real-world landscapes presents unique and unexpected challenges, and may result in misleading conclusions when employed without careful consideration of the spatial data and processes at hand. We identify key practical and theoretical issues and provide guidelines for applying spatial early warning signals in heterogeneous, real-world landscapes based on literature review and examples from real-world data. Major identified issues include (1) spatial heterogeneity in real-world landscapes may enhance reversibility of regime shifts and boost landscape-level resilience to environmental change (2) ecosystem states are often difficult to define, while these definitions have great impact on spatial early warning signals and (3) spatial environmental variability and socio-economic factors may affect spatial patterns, spatial early warning signals and associated regime shift predictions. We propose a novel framework, shifting from an ecosystem perspective towards a landscape approach. The framework can be used to identify conditions under which resilience assessment with spatial remotely sensed data may be successful, to support well-informed application of spatial early warning signals, and to improve predictions of ecosystem responses to global environmental change.

Controls on late-Holocene drift-sand dynamics: The dominant role of human pressure in the Netherlands.

Holocene drift-sand activity in the northwest European sand belt is commonly directly linked to population pressure (agricultural activity) or to climate change (e.g. storminess). In the Pleistocene sand areas of the Netherlands, small-scale Holocene drift-sand activity began in the Mesolithic, whereas large-scale sand drifting started during the Middle Ages. This last phase not only coincides with the intensification of farming and demographic pressure but also is commonly associated with a colder climate and enhanced storminess. This raises the question to what extent drift-sand activity can be attributed to either human activities or natural forcing factors. In this study, we compare the spatial and temporal patterns of drift-sand occurrence for the four characteristic Pleistocene sand regions in the Netherlands for the period between 1000 BC and AD 1700. To this end, we compiled a new supra-regional overview of drift-sand activity based on age estimates (14C, optically stimulated luminescence (OSL), archaeological and historical ages). The occurrence of sand drifting was then compared in time and space with historical-route networks, relative vegetation openness and climate. Results indicate a constant but low drift-sand activity between 1000 BC and AD 1000, interrupted by a remarkable decrease in activity around the BC/AD transition. It is evident that human pressure on the landscape was most influential on initiating sand drifting: this is supported by more frequent occurrences close to routes and the uninterrupted increase of drift-sand activity from AD 900 onwards, a period of high population density and large-scale deforestation. Once triggered by human activities, this drift-sand development was probably further intensified several centuries later during the cold and stormier 'Little Ice Age' (LIA; AD 1570-1850).

Anatomy of Mississippi Delta growth and its implications for coastal restoration.

The decline of several of the world's largest deltas has spurred interest in expensive coastal restoration projects to make these economically and ecologically vital regions more sustainable. The success of these projects depends, in part, on our understanding of how delta plains evolve over time scales longer than the instrumental record. Building on a new set of optically stimulated luminescence ages, we demonstrate that a large portion (~10,000 km2) of the late Holocene river-dominated Mississippi Delta grew in a radially symmetric fashion for almost a millennium before abandonment. Sediment was dispersed by deltaic distributaries that formed by means of bifurcations at the coeval shoreline and remained active throughout the life span of this landform. Progradation rates (100 to 150 m/year) were surprisingly constant, producing 6 to 8 km2 of new land per year. This shows that robust rates of land building were sustained under preindustrial conditions. However, these rates are several times lower than rates of land loss over the past century, indicating that only a small portion of the Mississippi Delta may be sustainable in a future world with accelerated sea-level rise.

Homo erectus at Trinil on Java used shells for tool production and engraving.

The manufacture of geometric engravings is generally interpreted as indicative of modern cognition and behaviour. Key questions in the debate on the origin of such behaviour are whether this innovation is restricted to Homo sapiens, and whether it has a uniquely African origin. Here we report on a fossil freshwater shell assemblage from the Hauptknochenschicht ('main bone layer') of Trinil (Java, Indonesia), the type locality of Homo erectus discovered by Eugène Dubois in 1891 (refs 2 and 3). In the Dubois collection (in the Naturalis museum, Leiden, The Netherlands) we found evidence for freshwater shellfish consumption by hominins, one unambiguous shell tool, and a shell with a geometric engraving. We dated sediment contained in the shells with (40)Ar/(39)Ar and luminescence dating methods, obtaining a maximum age of 0.54 ± 0.10 million years and a minimum age of 0.43 ± 0.05 million years. This implies that the Trinil Hauptknochenschicht is younger than previously estimated. Together, our data indicate that the engraving was made by Homo erectus, and that it is considerably older than the oldest geometric engravings described so far. Although it is at present not possible to assess the function or meaning of the engraved shell, this discovery suggests that engraving abstract patterns was in the realm of Asian Homo erectus cognition and neuromotor control.