Widespread reforestation before European influence on Amazonia

An estimated 90-95% of indigenous people in Amazonia died following European Contact. This population collapse is postulated to have caused decreases in atmospheric CO2 concentrations at c. 1610 CE, as a result of a wave of land abandonment in the wake of disease, slavery and warfare, whereby the attendant reversion to forest significantly increased terrestrial carbon sequestration. Based on 39 Amazonian fossil pollen records, we show that there was no synchronous reforestation event associated with such an atmospheric CO2 response following European arrival in Amazonia. Instead, we find that, at most sites, land abandonment and forest regrowth began c. 300 - 600 years before European arrival. Pre-European pandemics, social strife or environmental change may have contributed to these early site abandonments and ecological shifts

Terrestrial biosphere changes over the last 120 kyr

A new global synthesis and biomization of long (> 40 kyr) pollen-data records is presented and used with simulations from the HadCM3 and FAMOUS climate models and the BIOME4 vegetation model to analyse the dynamics of the global terrestrial biosphere and carbon storage over the last glacial–interglacial cycle. Simulated biome distributions using BIOME4 driven by HadCM3 and FAMOUS at the global scale over time generally agree well with those inferred from pollen data. Global average areas of grassland and dry shrubland, desert, and tundra biomes show large-scale increases during the Last Glacial Maximum, between ca. 64 and 74 ka BP and cool substages of Marine Isotope Stage 5, at the expense of the tropical forest, warm-temperate forest, and temperate forest biomes. These changes are reflected in BIOME4 simulations of global net primary productivity, showing good agreement between the two models. Such changes are likely to affect terrestrial carbon storage, which in turn influences the stable carbon isotopic composition of seawater as terrestrial carbon is depleted in 13C

A Progressively Wetter Early through Middle Holocene Climate in the Eastern Lowlands of Guatemala

Climate records from Central America and the Caribbean region reveal considerable spatiotemporal complexity in precipitation variability, with multiple hypotheses explaining the likely ocean-atmosphere processes influencing precipitation in the region. Here we report on findings from a 760-cm long sediment core from Lake Izabal, eastern Guatemala that affords insight on regional hydroclimate change over the last ∼9,500 years. We utilized a radiocarbon-based age-depth model integrated with lithological, XRF elemental abundances, and principal component analyses to infer changes in erosion/precipitation, lake productivity, and lake water chemistry. Abundance of elements commonly associated with terrigenous sources increase from the early to the latest mid-Holocene, from ca. 9,500 to ca. 4,800 calibrated years before present (cal yr BP), suggesting a progressive increase in erosion/precipitation. This is followed by relatively stable and high erosion/precipitation conditions until ca. 1,200 cal yr BP, with an abrupt decrease in erosion/precipitation ∼1,200 years ago. Comparison of the Izabal record with other paleoclimate records from Central America and the Caribbean region indicates substantial heterogeneity in hydroclimate, even across relatively short distances, likely due to a combination of topographic complexity and the combined influences of Atlantic and Pacific basin ocean-atmosphere dynamics. Our results suggest that the progressive increase in boreal autumn insolation throughout the middle and late Holocene may have driven an increase in Caribbean sea-surface temperatures (SST) during the late wet season, leading to increased moisture availability through enhanced evaporation and greater precipitation amounts associated with zonal convergence and orographic uplift along the eastern coast of Central America. However, other nearby records demonstrate hydroclimate changes that are at least partially at odds with the Izabal record, indicating that the modern SST relationships with atmospheric circulation, including Intertropical Convergence Zone dynamics, and precipitation alone cannot be used as a framework for explaining hydroclimate variability across Central America during the Holocene

Human disturbance amplifies Amazonian El Niño-Southern Oscillation signal

The long-term interaction between human activity and climate is subject to increasing scrutiny. Humans homogenize landscapes through deforestation, agriculture, and burning and thereby might reduce the capacity of landscapes to provide archives of climate change. Alternatively, land-use change might overwhelm natural buffering and amplify latent climate signals, rendering them detectable. Here we examine a sub-annually resolved sedimentary record from Lake Sauce in the western Amazonian lowlands that spans 6900 years. Finely-laminated sediments were deposited from ca. 5000 years ago until the present, and human activity in the watershed was revealed through the presence of charcoal and maize agriculture. The laminations, analyzed for color content and bandwidth, showed distinctive changes that were coupled to more frequent occurrence of fossil maize pollen. As agricultural activity intensified ca. 2200 cal. BP, the 2- to 8-year periodicity characteristic of El Niño-Southern Oscillation became evident in the record. These agricultural activities appeared to have amplified an existing, but subtle climatic signal that was previously absorbed by natural vegetation. When agricultural activity slowed, or land use around Lake Sauce changed at ca. 800 cal. BP, the signal of El Niño-Southern Oscillation (ENSO) activity became erratic

Central American climate and microrefugia: A view from the last interglacial

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