Clément Poirier

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.

Microbiotic signatures of the Anthropocene in marginal marine and freshwater palaeoenvironments

Abstract The term ‘Anthropocene’ has been proposed to indicate a geological interval characterized by global anthropogenic environmental change. This paper attempts to recognize a method by which the Anthropocene can be defined micropalaeontologically. In order to do this, microfloras and microfaunas (diatoms, macrophytes, dinoflagellate cysts, foraminifera and ostracods) from nearshore waters through to paralic and freshwater aquatic milieux are considered, and biotic variability with an anthropogenic causation identified. Microbiotic change can be related to anthropogenically induced extinctions, pollution-related mutation, environmentally influenced assemblage variability, geochemistry of carapaces/tests, floral change related to lacustrine acidification, faunal and floral correlation to industrial and agricultural signatures and introduction of exotic species via shipping. The influence of humanity on a local scale can be recognized in assemblages as far back as 5000 years BP. However, widespread anthropogenic change took place in Europe and America, particularly in the nineteenth and twentieth centuries, although in Asia (e.g. Japan) it cannot be observed prior to the twentieth century. Profound and global biotic change began in the mid-twentieth century and, if the Anthropocene is to be defined in this way, then the period 1940–1945 might encompass the biotic base of the interval.

Climate control on late Holocene high-energy sedimentation along coasts of the northeastern Atlantic Ocean

Abundant sedimentological and geochronological data gathered on European sandy coasts highlight major phases of increased high-energy sedimentation in the North Atlantic Ocean during the late Holocene. Owing to an inconsistent use of the terminology, it is often difficult to determine whether studies have described storm-built or wave-built deposits. Both deposits can be identified by overall similar coarse-grained sedimentary facies, but may provide contradictory paleoenvironmental interpretations. The aim of this study is to address this issue, by analysing a set of published 14C ages recovered from wave-built sediment bodies of the Pertuis Charentais (France). Integration of 14C data highlights seven coarse-grained sedimentation pulses (CSPs) that reflect a synchronous increase in wave-induced sediment supply occurring around 2650, 2420, 1240, 970, 800, 650 and 450 cal. yr B.P. CSPs can be matched with geochronological data published on other exposed sandy coasts of the western Europe. In first order, CSPs were preserved during phases of decreased storm activity and thus limited coastal erosion in the North Atlantic Ocean from 2700 to 2000 and from 1200 to 600 cal. yr B.P. In second order, CSPs occurred during positive NAO and/or negative EA/WR peaks, which are known from previous studies to induce higher waves and to enhance wave-induced sediment transport in the Pertuis Charentais. Chronological boundaries of CSPs could be used as a diagnostic tool to differentiate storm deposits indicative of sudden, episodic very high-energy sedimentation from wave deposits resulting from the sustained action of above-average westerly winds blowing across the North Atlantic Ocean.