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1.
Nature ; 514(7524): 616-9, 2014 Oct 30.
Artigo em Inglês | MEDLINE | ID: mdl-25355363

RESUMO

Global climate and the concentration of atmospheric carbon dioxide (CO2) are correlated over recent glacial cycles. The combination of processes responsible for a rise in atmospheric CO2 at the last glacial termination (23,000 to 9,000 years ago), however, remains uncertain. Establishing the timing and rate of CO2 changes in the past provides critical insight into the mechanisms that influence the carbon cycle and helps put present and future anthropogenic emissions in context. Here we present CO2 and methane (CH4) records of the last deglaciation from a new high-accumulation West Antarctic ice core with unprecedented temporal resolution and precise chronology. We show that although low-frequency CO2 variations parallel changes in Antarctic temperature, abrupt CO2 changes occur that have a clear relationship with abrupt climate changes in the Northern Hemisphere. A significant proportion of the direct radiative forcing associated with the rise in atmospheric CO2 occurred in three sudden steps, each of 10 to 15 parts per million. Every step took place in less than two centuries and was followed by no notable change in atmospheric CO2 for about 1,000 to 1,500 years. Slow, millennial-scale ventilation of Southern Ocean CO2-rich, deep-ocean water masses is thought to have been fundamental to the rise in atmospheric CO2 associated with the glacial termination, given the strong covariance of CO2 levels and Antarctic temperatures. Our data establish a contribution from an abrupt, centennial-scale mode of CO2 variability that is not directly related to Antarctic temperature. We suggest that processes operating on centennial timescales, probably involving the Atlantic meridional overturning circulation, seem to be influencing global carbon-cycle dynamics and are at present not widely considered in Earth system models.


Assuntos
Ciclo do Carbono , Regiões Antárticas , Atmosfera/química , Dióxido de Carbono/análise , Efeito Estufa , Groenlândia , História Antiga , Camada de Gelo , Isótopos , Metano/análise , Oceanos e Mares , Água/análise , Água/química
2.
Proc Natl Acad Sci U S A ; 114(38): 10035-10040, 2017 09 19.
Artigo em Inglês | MEDLINE | ID: mdl-28874529

RESUMO

Glacial-state greenhouse gas concentrations and Southern Hemisphere climate conditions persisted until ∼17.7 ka, when a nearly synchronous acceleration in deglaciation was recorded in paleoclimate proxies in large parts of the Southern Hemisphere, with many changes ascribed to a sudden poleward shift in the Southern Hemisphere westerlies and subsequent climate impacts. We used high-resolution chemical measurements in the West Antarctic Ice Sheet Divide, Byrd, and other ice cores to document a unique, ∼192-y series of halogen-rich volcanic eruptions exactly at the start of accelerated deglaciation, with tephra identifying the nearby Mount Takahe volcano as the source. Extensive fallout from these massive eruptions has been found >2,800 km from Mount Takahe. Sulfur isotope anomalies and marked decreases in ice core bromine consistent with increased surface UV radiation indicate that the eruptions led to stratospheric ozone depletion. Rather than a highly improbable coincidence, circulation and climate changes extending from the Antarctic Peninsula to the subtropics-similar to those associated with modern stratospheric ozone depletion over Antarctica-plausibly link the Mount Takahe eruptions to the onset of accelerated Southern Hemisphere deglaciation ∼17.7 ka.

3.
Environ Sci Technol ; 36(1): 7-11, 2002 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-11811493

RESUMO

Impurities trapped in ice sheets and glaciers have the potential to provide detailed, high temporal resolution proxy information on paleo-environments, atmospheric circulation, and environmental pollution through the use of chemical, isotopic, and elemental tracers. We present a novel approach to ice-core chemical analyses in which an ice-core melter is coupled directly with both an inductively coupled plasma mass spectrometer and a traditional continuous flow analysis system. We demonstrate this new approach using replicated measurements of ice-core samples from Summit, Greenland. With this method, it is possible to readily obtain continuous, exactly coregistered concentration records for a large number of elements and chemical species at ppb and ppt levels and at unprecedented depth resolution. Such very-high depth resolution, multiparameter measurements will significantly expand the use of ice-core records for environmental proxies.


Assuntos
Monitoramento Ambiental/métodos , Poluentes Ambientais/análise , Gelo/análise , Espectrometria de Massas/métodos , Sensibilidade e Especificidade
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