Global Peak in Atmospheric Radiocarbon Provides a Potential Definition for the Onset of the Anthropocene Epoch in 1965

Anthropogenic activity is now recognised as having profoundly and permanently altered the Earth system, suggesting we have entered a human-dominated geological epoch, the ‘Anthropocene’. To formally define the onset of the Anthropocene, a synchronous global signature within geological-forming materials is required. Here we report a series of precisely-dated tree-ring records from Campbell Island (Southern Ocean) that capture peak atmospheric radiocarbon (14C) resulting from Northern Hemisphere-dominated thermonuclear bomb tests during the 1950s and 1960s. The only alien tree on the island, a Sitka spruce (Picea sitchensis), allows us to seasonally-resolve Southern Hemisphere atmospheric 14C, demonstrating the ‘bomb peak’ in this remote and pristine location occurred in the last-quarter of 1965 (October-December), coincident with the broader changes associated with the post-World War II ‘Great Acceleration’ in industrial capacity and consumption. Our findings provide a precisely-resolved potential Global Stratotype Section and Point (GSSP) or ‘golden spike’, marking the onset of the Anthropocene Epoch

A guideline for sample preparation in modern tree-ring stable isotope research

The comprehensive procedure of wood sample preparation, including tree-ring dissection, cellulose extraction, homogenization and packing for stable isotope analysis, is labour intensive and time consuming. Based on a brief compilation of existing methods, we present a methodological approach from pre-analyses considerations to wood sample preparation, semi-automated chemical extraction of cellulose from tree-ring cross-sections, and tree-ring dissection for stable isotope ratio mass spectrometry: the Cross-Section Extraction and Dissection (CSED) guideline. Following the CSED guideline can considerably increase efficiency of tree-ring stable isotope measurement compared to classical methods We introduce a user-friendly device for cellulose extraction, allowing simultaneous treatment of wood cross-sections of a total length of 180 cm (equivalent to 6 increment cores of 30 cm length) and thickness of 0.6–2.0 mm. After cellulose extraction, tree-ring structures of 10 tree species (coniferous and angiosperm wood) with different wood growth rates and tree-ring boundaries, largely remained well identifiable. Further, we demonstrate that tree rings from cellulose cross-sections can be dissected at annual to intra-seasonal resolution, utilizing simple manual devices as well as sophisticated UV-laser microdissection microscopes in a way that sample homogenization is no longer necessary in most cases. We investigate seasonal precipitation signals in high-resolution intra-annual δ18O cellulose values from African baobab, performed by using UV-laser microdissection microscopes

ENSO flavors in a tree-ring δ¹⁸O record of <i>Tectona grandis</i> from Indonesia

Indonesia's climate is dominated by the equatorial monsoon system, and has been linked to El Niño–Southern Oscillation (ENSO) events that often result in extensive droughts and floods over the Indonesian archipelago. In this study we investigate ENSO-related signals in a tree-ring δ18O record (1900–2007) of Javanese teak. Our results reveal a clear influence of Warm Pool (central Pacific) El Niño events on Javanese tree-ring δ18O, and no clear signal of Cold Tongue (eastern Pacific) El Niño events. These results are consistent with the distinct impacts of the two ENSO flavors on Javanese precipitation, and illustrate the importance of considering ENSO flavors when interpreting palaeoclimate proxy records in the tropics

Tree Rings in the Tropics: Insights into the Ecology and Climate Sensitivity of Tropical Trees

Tree-ring studies provide important contributions to understanding the climate sensitivity of tropical trees and the effects of global change on tropical forests. This chapter reviews recent advances in tropical tree-ring research. In tropical lowlands, tree ring formation is mainly driven by seasonal variation in precipitation or flooding , and not in temperature. Annual ring formation has now been confirmed for 230 tropical tree species across continents and climate zones. Tree-ring studies indicate that lifespans of tropical tree species average c. 200 years and only few species live >500 years; these values are considerably lower than those based on indirect age estimates. Size-age trajectories show large and persistent growth variation among trees of the same species, due to variation in light, water and nutrient availability. Climate-growth analyses suggest that tropical tree growth is moderately sensitive to rainfall (dry years reduce growth) and temperature (hot years reduce growth). Tree-ring studies can assist in evaluating the effects of gradual changes in climatic conditions on tree growth and physiology but this requires that sampling biases are dealt with and ontogenetic changes are disentangled from temporal changes. This remains challenging, but studies have reported increases in intrinsic water use efficiency based on δ13C measurements in tree rings, most likely due to increasing atmospheric CO2. We conclude that tree-ring studies offer important insights to global change effects on tropical trees and will increasingly do so as new techniques become available and research efforts intensify