Anthropocene最新文献

The North American prairie-forest border is a major biogeographic boundary ultimately determined by the macroclimate. Climate variability during the Holocene affected the vegetation in this area, but impacts on human paleodemography are unknown. At a regional scale, community structure is partly determined by fire, however the extent to which anthropogenic burning has affected fire regimes over the Holocene is unresolved. This study investigates the interaction between climate variability, vegetation changes, fire regimes, and human population levels in the North American prairie-forest ecotone during the Holocene using information from publically-available paleoenvironmental databases. Biomass burning was associated with moisture and vegetation more than with human population size, suggesting anthropogenic burning did not significantly influence the composition and location of the prairie-forest border. Human population growth rates were impacted by sociocultural developments and environmental changes, with most changes in subsistence strategies occurring during climate regime shifts. The development of the Eastern Agricultural Complex (5.0 – 3.8 ka) and the transition to more mesic conditions after 4.0 ka facilitated long-term population growth. The arrival of maize and the bow-and-arrow at 2.2 and 1.6 ka, respectively, resulted in increased population growth, and after 1 ka, maize agriculture intensification, aided by a warmer climate, accelerated population growth. The collapse of the city of Cahokia is linked to a wider population decline across the Midwest precipitated by the Medieval Warm Period – Little Ice Age transition. Populations across a significant portion of North America were in decline at the time of European colonization. These findings provide evidence against a large-scale early Anthropocene in North America, and illustrate the importance of climate change in influencing human history.

Climate change is expected to put significant pressure on global food production. Although previous work has explored impacts of climate, management, and genetics on food production, additional research is needed to examine the effects of large-scale climate modes at local and regional scales. This study explores the impact of climate variability on rice yield in Mainland Southeast Asia from 1961 to 2017 at three different spatial scales: the whole Mainland Southeast Asia region, country-level (Cambodia, Laos, Myanmar, Thailand, and Vietnam), and province-level for Vietnam. Annual rice yields over this period have nearly tripled with Vietnam experiencing the largest increases. Correlations between annual rice yield anomalies at the regional and country levels and climate data reveal clear influences of tropical climate variability associated with the El Niño-Southern Oscillation and the Pacific Meridional Mode. At the provincial level in Vietnam, many provinces show similar correlation patterns for the spring-summer season of rice (e.g., a co-occurring La Niña and positive phase of the Pacific Meridional Mode in the preceding boreal winter and spring are associated with increased yields in spring-summer rice). However, the late summer-fall season rice yield anomalies show much weaker correlations with tropical climate patterns. Variations across provinces were also noted, particularly between the Red River and Mekong River Deltas. The history of this 56-year period, which included the Vietnam-American War and changes in land management policies, makes it challenging to disentangle the effects of climate variability and social factors on rice yields in these areas. However, these results highlight the importance of using a multidisciplinary and multiscale approach to help inform local and regional decision-making.

Investigating past human-environment interactions provides clues to understand landscape responses to catastrophic events. This study uses a multiproxy approach to reconstruct landscape change over the past 800 years, in an area where slopes and soils were reshaped by the Mont Granier landslide (French Alps) in 1248 CE. Pollen and sediment analyses of an 89-cm sediment core retrieved from Lake St. André, a lake formed by the landslide, were used to reconstruct vegetation recovery and agro-pastoral activities. These analyses of lake sediments were supplemented by studying land-cover changes based on cadastral maps. Aerial photographs provided information about spatial landscape organization from the 18th century onwards. Results showed that significant changes in land-use systems were closely linked to social, political, and economic events. Rapid recolonization by pioneer vegetation communities began just after the landslide. Despite short phases of conflict-induced agricultural decline, agro-pastoral activities diversified from the 16th century onwards, with land use dominated by croplands, vineyards, and grasslands. The extension of arable lands, particularly vineyards, continued until the 19th century. At the beginning of the 20th century, this territory was characterized by an agro-pastoral economy based on mixed family farming. From the 1960 s onwards, cattle grazing ceased, and dairy production was replaced by viticulture.

Changes in the agro-pastoral system after the landslide therefore reflect complex geomorphological, political, social, and economic interactions. This study also demonstrates how a multiproxy approach can decipher landscape evolution and reveal the human-environment interactions behind landscape change.

The planktic foraminifera are an important component of the global carbon cycle, as they sequester the carbon, thus burying it in the sediments for ages. The burial of planktic foraminiferal shells, however, depends on the carbonate chemistry of the deep ocean. A significant fraction of foraminiferal shells dissolves well above the carbonate compensation depth. The foraminiferal lysocline is defined to delineate such zones of planktic foraminiferal dissolution well above the carbonate compensation depth. The dissolution of carbonate above the lysocline, termed supralysoclinal dissolution, has also been reported from highly productive basins. This study demarcates the extent of foraminiferal dissolution in the western Bay of Bengal. We document the distribution of planktic foraminifera and shell fragments in 100 core top samples collected from the coast perpendicular transects at depths ranging from 27 m to 2760 m. We examine the possible reasons for the foraminiferal dissolution by comparing the foraminiferal indices with the ambient bottom water parameters. The absolute abundance of planktic foraminifera is significantly low, both on the continental shelf and below ∼1000 m. The low abundance on the shelf is due to the terrigenous dilution. The fragmentation indices and the ratio between dissolution resistant and dissolution susceptible assemblage, however, confirm a significant increase in the dissolution at depths deeper than 1000 m. The foraminiferal shell dissolution at deeper depths is due to the high pressure, whereas the biogenic respiration-induced calcite under-saturation is responsible for the significant dissolution at a very shallow depth in the western Bay of Bengal, as compared to other parts of the world ocean.

Although a rapid decrease in sea ice due to global warming has improved the navigable potential of the Arctic passages, the extent to which this area will become viable for commercial shipping in the future remains unclear. This study investigated the accessibility of the Northern Sea Route and Northwest Passage under global warming of 2 °C and 3 °C. We applied the Polar Operational Limit Assessment Risk Indexing System to measure navigability by considering the impacts of sea ice and ice resistance of ships. Except for the Parry Channel, surface air temperature is positive in the Seas along two passages in September under 2 ℃ warming. With global warming of 3 °C, the warming area extends northward, and the concentration of sea ice drops below 20%. The thickness of the sea ice is still substantial in the eastern Beaufort Sea and the waters within the Canadian Arctic Archipelago and north of Greenland, both of which can restricting the opening of the Arctic passages. Temperature increases cause sea ice to be younger and are more pronounced in the seas on the European side of the Arctic. The results indicate that changes in sea ice improve the navigability of the Arctic passages. Ships in Polar Class 6 may be unimpeded along two Arctic passages in November from 2 ℃ warming onward, whereas ordinary ships may be capable of passing the Northern Sea Route with global warming of 3 ℃, with maximum potential in September. This study provides an important reference for planning global shipping in the Arctic in the future, even with some uncertainty in the model projections.

Understanding vegetation dynamics is essential to interpret long-term ecological changes under different precipitation regimes and land use scenarios. Northeastern Brazil has been subjected to both climatic and anthropic disturbances in recent centuries. This paper presents a high-resolution record from the SAC18 sediment core, collected in a Cerrado ecotone in the Sete Cidades National Park. Multiproxy analyses based on pollen, charcoal and grain size showed the Cerrado landscape was restructured during dry and wet intervals over a period of 800 years. The beginning of the record was marked by a dry episode, testified by the presence of a drought resistant taxon Curatella (wild cashew tree) and coincided with the Medieval Climate Anomaly (950–1250 CE). Almost no fire activity was observed between 1210 and 1300 CE, linked to reduced human presence during this dry period. A wetter interval began in 1400 CE, with expansion of the palm swamp and the moisture-related tree/herbaceous taxa Myrtaceae and Spathiphyllum, which was synchronous with the Little Ice Age (1400–1700 CE). Reduced burning of biomass and the absence of deforestation at the beginning of the wet interval changed to extensive fires and deforestation after 1650 CE, enabling dating of the arrival of European colonists in the north of Piauí State. Fires stopped after the creation of Sete Cidades National Park in 1961 CE, resulting in the expansion of the Cerrado arboreal cover. This study provides new knowledge about past human occupation of the Northeastern Cerrado, defined by three types of land use practices (indigenous, colonist and protection policy), and underlines the importance of including historical aspects of the landscape in future conservation scenarios.

Tropical peatlands are a globally important carbon store. They host significant biodiversity and provide a range of other important ecosystem services, including food and medicines for local communities. Tropical peatlands are increasingly modified by humans in the rapid and transformative way typical of the “Anthropocene,” with the most significant human—driven changes to date occurring in Southeast Asia. This review synthesizes the dominant changes observed in human interactions with tropical peatlands in the last 200 years, focusing on the tropical lowland peatlands of Southeast Asia. We identify the beginning of transformative anthropogenic processes in these carbon-rich ecosystems, chart the intensification of these processes in the 20th and early 21st centuries, and assess their impacts on key ecosystem services in the present. Where data exist, we compare the tropical peatlands of Central Africa and Amazonia, which have experienced very different scales of disturbance in the recent past. We explore their global importance and how environmental pressures may affect them in the future. Finally, looking to the future, we identify ongoing efforts in peatland conservation, management, restoration, and socio-economic development, as well as areas of fruitful research toward sustainability of tropical peatlands.

Understanding past water management is crucial to address contemporary human-environmental challenges in sub-Saharan Africa, where urban growth is impacting upon water availability and supply. This study integrates soil profiles, high-resolution topographic data, historical sources, and socioecological memory to reconstruct how the ancient urban society at Great Zimbabwe negotiated water security. New evidence shows for the first time that closed depressions known as dhaka pits were used by the inhabitants of Great Zimbabwe for water storage and harvesting for a long time, possibly since the emergence of settlement in the mid-second millennium CE. These pits were part of a landscape-scale water management system that exploited catchment hydrology and groundwater by means of artificial dhaka reservoirs, wells, and springs to secure water for subsistence, farming, ritual and ceremony services. This study highlights the need for precise dating of the construction and functioning period of this water management system at Great Zimbabwe. Understanding past water management in such a water-scarce region is important for reconstructing how the ancient Great Zimbabwe urban society negotiated water security, but also for understanding contemporary human-environmental challenges.

Climate change, land subsidence, and coastal population growth are increasing coastal flood risks and changing land uses. Large-scale levee systems protect many urban areas from flooding, but much less is known about how rural coasts respond to sea level rise and increasing flood risks. This study examined previously unreported, small-scale earthen levees that have been constructed for centuries by individual landowners in rural, low-lying portions of the Chesapeake Bay region in the USA. Analysis of aerial imagery, digital elevation models, and field measurements revealed that levees are constructed from inorganic silt loam sediment consistent with adjacent terrestrial soils. They extend above Highest Astronomical Tide, and are today surrounded by marsh or low-lying terrestrial vegetation. Although preliminary measurements revealed inconsistent effects of levees on soil salinity or soil organic content, the landward side of levees are generally lower in elevation than the seaward side. They are also characterized by less flood tolerant vegetation and shallower organic-rich soils. These results suggest that small-scale levees may have historically impeded wetland development, though their effects today are unclear. This work highlights a historical approach to rural flood defense and suggests that, in some cases, the impacts of small levees are observable long after coastal retreat and levee abandonment. They are therefore part of the evolving human-landscape system for potential management into the future.