Colonization of the Americas, 'Little Ice Age' climate, and bomb-produced carbon: their role in defining the Anthropocene

A recently published analysis by Lewis and Maslin (Lewis SL and Maslin MA (2015) Defining the Anthropocene. Nature 519: 171–180) has identified two new potential horizons for the Holocene−Anthropocene boundary: 1610 (associated with European colonization of the Americas), or 1964 (the peak of the excess radiocarbon signal arising from atom bomb tests). We discuss both of these novel suggestions, and consider that there is insufficient stratigraphic basis for the former, whereas placing the latter at the peak of the signal rather than at its inception does not follow normal stratigraphical practice. Wherever the boundary is eventually placed, it should be optimized to reflect stratigraphical evidence with the least possible ambiguity

Tipping from the Holocene to the Anthropocene: How threatened are major world deltas?

Coastal deltas are landforms that typically offer a wide variety of benefits to society including highly fertile soils for agricultural development, freshwater resources, and rich biodiversity. For these reasons, many deltas are densely populated, are important economic hubs, and have been transformed by human interventions such as agricultural intensification, modification of water and sediment fluxes, as well as urbanization and industrialization. Additionally, deltas are increasingly affected by the consequences of climate change including sea level rise, and by other natural hazards such as cyclones and storm surges. Five examples of major deltas (Rhine-Meuse, Ganges, Indus, Mekong, and Danube) illustrate the force of human interventions in shaping and transforming deltas and in inducing shifts between four different social-ecological system (SES) states: Holocene, modified Holocene, Anthropocene and ‘collapsed’. The three Asian deltas are rapidly changing but whereas SES in the Ganges and Indus deltas are in danger of tipping into a ‘collapsed’ state, SES in the Mekong delta, which is at the crossroads of various development pathways, could increase in resilience in the future. The Rhine-Meuse and Danube delta examples show that highly managed states may allow, under specific conditions, for interventions leading to increasingly resilient systems. However, little is known about the long-term effects of rapid human interventions in deltas. It is therefore critical to increase the knowledge-base related to SES dynamics and to better characterize social tipping points or turning points in order to avoid unacceptable changes

Moderate seismic activity affects contemporary sediment yields

Current models aiming to simulate contemporary sediment yield (SY) implicitly assume that tectonic effects are either irrelevant or are reflected by catchment topography. In this study we analyse the relation between SY and seismic activity, a component of tectonic processes. Results show a spatial correlation between SY and seismic activity expressed as the estimated peak ground acceleration (PGA) with a 10% exceedance probability in 50 years. PGA has a significant impact on the spatial variation of SY, even after correcting for cross-correlations with topography, lithology or other factors that may influence SY. Based on three distinct data sets, we demonstrate that this effect is significant both for small catchments in Europe (0.3-3940 km2) and for large river systems worldwide (1580-6.15×106 km2) and that seismic activity may be even more important for explaining regional variation in SY than land use or many other commonly considered factors (e.g. catchment area, climate). We show that explicitly considering seismic activity may lead to SY-estimates that easily deviate a factor 2 or more compared to estimates that do not consider seismic activity. This is not only the case for highly seismically active regions: also in regions with a weak to moderate seismic regime seismic activity helps explaining regional patterns in SY. We argue that these findings have important implications for a better understanding of SY and its sensitivity to human impacts, as well as for our comprehension of sediment fluxes at longer timescales. © The Author(s) 2014.status: publishe